@article{boebinger_yilmaz_ghosh_misra_mathis_kalinin_jesse_gogotsi_van duin_unocic_2024, title={Direct Fabrication of Atomically Defined Pores in MXenes Using Feedback‐Driven STEM}, volume={5}, ISSN={2366-9608 2366-9608}, url={http://dx.doi.org/10.1002/smtd.202400203}, DOI={10.1002/smtd.202400203}, abstractNote={Abstract Controlled fabrication of nanopores in 2D materials offer the means to create robust membranes needed for ion transport and nanofiltration. Techniques for creating nanopores have relied upon either plasma etching or direct irradiation; however, aberration‐corrected scanning transmission electron microscopy (STEM) offers the advantage of combining a sub‐Å sized electron beam for atomic manipulation along with atomic resolution imaging. Here, a method for automated nanopore fabrication is utilized with real‐time atomic visualization to enhance the mechanistic understanding of beam‐induced transformations. Additionally, an electron beam simulation technique, Electron‐Beam Simulator (E‐BeamSim) is developed to observe the atomic movements and interactions resulting from electron beam irradiation. Using the MXene Ti 3 C 2 T x , the influence of temperature on nanopore fabrication is explored by tracking atomic transformations and find that at room temperature the electron beam irradiation induces random displacement and results in titanium pileups at the nanopore edge, which is confirmed by E‐BeamSim. At elevated temperatures, after removal of the surface functional groups and with the increased mobility of atoms results in atomic transformations that lead to the selective removal of atoms layer by layer. This work can lead to the development of defect engineering techniques within functionalized MXene layers and other 2D materials.}, journal={Small Methods}, publisher={Wiley}, author={Boebinger, Matthew G. and Yilmaz, Dundar E. and Ghosh, Ayana and Misra, Sudhajit and Mathis, Tyler S. and Kalinin, Sergei V. and Jesse, Stephen and Gogotsi, Yury and van Duin, Adri C. T. and Unocic, Raymond R.}, year={2024}, month={May} }
@article{yang_yuwono_whittaker_ibáñez_wang_kim_borisevich_chua_prada_wang_et al._2024, title={Double Hydroxide Nanocatalysts for Urea Electrooxidation Engineered toward Environmentally Benign Products}, volume={7}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.202403187}, DOI={10.1002/adma.202403187}, abstractNote={Recent advancements in the electrochemical urea oxidation reaction (UOR) present promising avenues for wastewater remediation and energy recovery. Despite progress toward optimized efficiency, hurdles persist in steering oxidation products away from environmentally unfriendly products, mostly due to a lack of understanding of structure-selectivity relationships. In this study, the UOR performance of Ni and Cu double hydroxides, which show marked differences in their reactivity and selectivity is evaluated. CuCo hydroxides predominantly produce N}, journal={Advanced Materials}, publisher={Wiley}, author={Yang, Yuwei and Yuwono, Jodie A and Whittaker, Todd and Ibáñez, Marc Manyé and Wang, Bingliang and Kim, Changmin and Borisevich, Albina Y and Chua, Stephanie and Prada, Jhair Pena and Wang, Xichu and et al.}, year={2024}, month={Jul} }
@article{wittman_sacci_unocic_zawodzinski_2024, title={In Situ Liquid Electron Microscope Cells Strongly Attenuate Electrochemical Behavior}, volume={171}, ISSN={["1945-7111"]}, DOI={10.1149/1945-7111/ad963a}, abstractNote={In situ electrochemical Scanning Transmission Electron Microscopy (ec-S/TEM) probes the dynamics of electrochemical processes in real time and at high spatial resolution. This method utilizes microfabricated electrochemical cells, with enclosed dimensions of 800 μm wide, 800 μm long, and 1–2 μm tall, with electron-transparent silicon nitride windows. Working, counter, and reference electrodes in the configuration studied are deposited Pt with a planar surface area of about 1 μm 2 and a height of 50 nm. The cell confines the electrolyte within a 1 μm tall channel, and the microfabricated electrodes have a non-standard geometry, are coplanar, and are not front-facing. As such, standard assumptions of electrochemical experiments do not apply. COMSOL modeling was used to compare and contrast differences in electrochemical behavior between conventional experimental setups and the in situ ec-S/TEM cells. Cell height strongly affected voltammogram measurements: peak magnitudes and shifts correlate directly to cell height. Reactant concentration above the electrode quickly decreases during deposition, leading to a planar diffusion-dominated regime. The concentration gradient prioritizes particle growth along the thin edges of the electrode and not on the planar part of the electrode. Experiments done in the ec-S/TEM ex situ of a TEM verify the model’s accuracy.}, number={12}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Wittman, Reed M. and Sacci, Robert L. and Unocic, Raymond R. and Zawodzinski, Thomas A.}, year={2024}, month={Dec} }
@article{liang_wu_misra_dun_husmann_prenger_urban_presser_unocic_jiang_et al._2024, title={Nitrogen‐Doped Graphene‐Like Carbon Intercalated MXene Heterostructure Electrodes for Enhanced Sodium‐ and Lithium‐Ion Storage}, volume={6}, ISSN={2198-3844 2198-3844}, url={http://dx.doi.org/10.1002/advs.202402708}, DOI={10.1002/advs.202402708}, abstractNote={Abstract MXene is investigated as an electrode material for different energy storage systems due to layered structures and metal‐like electrical conductivity. Experimental results show MXenes possess excellent cycling performance as anode materials, especially at large current densities. However, the reversible capacity is relatively low, which is a significant barrier to meeting the demands of industrial applications. This work synthesizes N‐doped graphene‐like carbon (NGC) intercalated Ti 3 C 2 T x (NGC‐Ti 3 C 2 T x ) van der Waals heterostructure by an in situ method. The as‐prepared NGC‐Ti 3 C 2 T x van der Waals heterostructure is employed as sodium‐ion and lithium‐ion battery electrodes. For sodium‐ion batteries, a reversible specific capacity of 305 mAh g −1 is achieved at a specific current of 20 mA g −1 , 2.3 times higher than that of Ti 3 C 2 T x . For lithium‐ion batteries, a reversible capacity of 400 mAh g −1 at a specific current of 20 mA g −1 is 1.5 times higher than that of Ti 3 C 2 T x . Both sodium‐ion and lithium‐ion batteries made from NGC‐Ti 3 C 2 T x shows high cycling stability. The theoretical calculations also verify the remarkable improvement in battery capacity within the NGC‐Ti 3 C 2 O 2 system, attributed to the additional adsorption of working ions at the edge states of NGC. This work offers an innovative way to synthesize a new van der Waals heterostructure and provides a new route to improve the electrochemical performance significantly.}, journal={Advanced Science}, publisher={Wiley}, author={Liang, Kun and Wu, Tao and Misra, Sudhajit and Dun, Chaochao and Husmann, Samantha and Prenger, Kaitlyn and Urban, Jeffrey J. and Presser, Volker and Unocic, Raymond R. and Jiang, De‐en and et al.}, year={2024}, month={Jun} }
@article{lasseter_gellerup_ghosh_yun_vasudevan_unocic_olunloyo_retterer_xiao_randolph_et al._2024, title={Selected Area Manipulation of MoS2 via Focused Electron Beam-Induced Etching for Nanoscale Device Editing}, volume={16}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/acsami.3c17182}, DOI={10.1021/acsami.3c17182}, abstractNote={We demonstrate direct-write patterning of single and multilayer MoS}, number={7}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Lasseter, John and Gellerup, Spencer and Ghosh, Sujoy and Yun, Seok Joon and Vasudevan, Rama and Unocic, Raymond R. and Olunloyo, Olugbenga and Retterer, Scott T. and Xiao, Kai and Randolph, Steven J. and et al.}, year={2024}, month={Feb}, pages={9144–9154} }
@article{smeaton_abellan_spurgeon_unocic_jungjohann_2024, title={Tutorial on In Situ and Operando (Scanning) Transmission Electron Microscopy for Analysis of Nanoscale Structure–Property Relationships}, url={https://doi.org/10.1021/acsnano.4c09256}, DOI={10.1021/acsnano.4c09256}, abstractNote={In situ and}, journal={ACS Nano}, author={Smeaton, Michelle A. and Abellan, Patricia and Spurgeon, Steven R. and Unocic, Raymond R. and Jungjohann, Katherine L.}, year={2024}, month={Dec} }
@article{harutyunyan_li_wyss_yanev_li_wu_sun_unocic_stage_strasbourg_et al._2024, title={Width-Dependent Growth of Atomically Thin Quantum Nanoribbons}, url={https://doi.org/10.21203/rs.3.rs-4419911/v1}, DOI={10.21203/rs.3.rs-4419911/v1}, abstractNote={
Abstract Nanoribbons (NRs) of atomic layer transition metal dichalcogenides (TMDs) can boost the rapidly emerging field of quantum materials owing to their width-dependent phases and electronic properties. However, the controllable downscaling of width by direct growth and the underlying mechanism remain elusive. Here, we demonstrate the vapor-liquid-solid growth of single crystal of single layer NRs of a series of TMDs (MeX2: Me=Mo, W; X=S, Se) under chalcogen vapor atmosphere, seeded by pre-deposited and respective transition metal-alloyed nanoparticles that also control the NR width. We found linear dependence of growth rate on supersaturation, known as a criterion for continues growth mechanism, which decreases with decreasing of NR width driven by the Gibbs-Thomson effect. The NRs show width-dependent photoluminescence and strain-induced quantum emission signatures with up to ~90% purity of single photons. We propose the path and underlying mechanism for width-controllable growth of TMD NRs for applications in quantum optoelectronics.}, author={Harutyunyan, Avetik and Li, Xufan and Wyss, Samuel and Yanev, Emanuil and Li, Qing-Jie and Wu, Shuang and Sun, Yongwen and Unocic, Raymond and Stage, Joseph and Strasbourg, Matthew and et al.}, year={2024}, month={May} }
@article{li_wyss_yanev_li_wu_sun_unocic_stage_strasbourg_sassi_et al._2024, title={Width-dependent continuous growth of atomically thin quantum nanoribbons from nanoalloy seeds in chalcogen vapor}, volume={15}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-024-54413-9}, abstractNote={Nanoribbons (NRs) of atomic layer transition metal dichalcogenides (TMDs) can boost the rapidly emerging field of quantum materials owing to their width-dependent phases and electronic properties. However, the controllable downscaling of width by direct growth and the underlying mechanism remain elusive. Here, we demonstrate the vapor-liquid-solid growth of single crystal of single layer NRs of a series of TMDs (MeX2: Me = Mo, W; X = S, Se) under chalcogen vapor atmosphere, seeded by pre-deposited and respective transition metal-alloyed nanoparticles that also control the NR width. We find linear dependence of growth rate on supersaturation, known as a criterion for continues growth mechanism, which decreases with decreasing of NR width driven by the Gibbs-Thomson effect. The NRs show width-dependent photoluminescence and strain-induced quantum emission signatures with up to ≈ 90% purity of single photons. We propose the path and underlying mechanism for width-controllable growth of TMD NRs for applications in quantum optoelectronics. Size control in quantum materials by direct growth is still difficult to achieve. Here, the authors present the width-dependent growth of single-layer nanoribbons of transition metal dichalcogenides from nanoalloy seeds, achieving strain-induced quantum emission with a purity of up to 90 % for single photons.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Li, Xufan and Wyss, Samuel and Yanev, Emanuil and Li, Qing-Jie and Wu, Shuang and Sun, Yongwen and Unocic, Raymond R. and Stage, Joseph and Strasbourg, Matthew and Sassi, Lucas M. and et al.}, year={2024}, month={Nov} }
@article{vlassiouk_smirnov_puretzky_olunloyo_geohegan_dyck_lupini_unocic_meyer_xiao_et al._2023, title={Armor for Steel: Facile Synthesis of Hexagonal Boron Nitride Films on Various Substrates}, volume={11}, ISSN={2196-7350 2196-7350}, url={http://dx.doi.org/10.1002/admi.202300704}, DOI={10.1002/admi.202300704}, abstractNote={Abstract While hexagonal boron nitride (hBN) has been widely used as a buffer or encapsulation layer for emerging electronic devices, interest in utilizing it for large‐area chemical barrier coating has somewhat faded. A chemical vapor deposition process is reported here for the conformal growth of hBN on large surfaces of various alloys and steels, regardless of their complex shapes. In contrast to the previously reported very limited protection by hBN against corrosion and oxidation, protection of steels against 10% HCl and oxidation resistance at 850 °C in air is demonstrated. Furthermore, an order of magnitude reduction in the friction coefficient of the hBN coated steels is shown. The growth mechanism is revealed in experiments on thin metal films, where the tunable growth of single‐crystal hBN with a selected number of layers is demonstrated. The key distinction of the process is the use of N 2 gas, which gets activated exclusively on the catalyst's surface and eliminates adverse gas‐phase reactions. This rate‐limiting step allowed independent control of activated nitrogen along with boron coming from a solid source (like elemental boron). Using abundant and benign precursors, this approach can be readily adopted for large‐scale hBN synthesis in applications where cost, production volume, and process safety are essential.}, number={1}, journal={Advanced Materials Interfaces}, publisher={Wiley}, author={Vlassiouk, Ivan and Smirnov, Sergei and Puretzky, Alexander and Olunloyo, Olugbenga and Geohegan, David B. and Dyck, Ondrej and Lupini, Andrew R. and Unocic, Raymond R. and Meyer, Harry M., III and Xiao, Kai and et al.}, year={2023}, month={Oct} }
@article{weber_starchenko_yuan_anovitz_ievlev_unocic_borisevich_boebinger_stack_2023, title={Armoring of MgO by a Passivation Layer Impedes Direct Air Capture of CO2}, volume={57}, ISSN={0013-936X 1520-5851}, url={http://dx.doi.org/10.1021/acs.est.3c04690}, DOI={10.1021/acs.est.3c04690}, abstractNote={It has been proposed to use magnesium oxide (MgO) to separate carbon dioxide directly from the atmosphere at the gigaton level. We show experimental results on MgO single crystals reacting with the atmosphere for longer (decades) and shorter (days to months) periods with the goal of gauging reaction rates. Here, we find a substantial slowdown of an initially fast reaction as a result of mineral armoring by reaction products (surface passivation). In short-term experiments, we observe fast hydroxylation, carbonation, and formation of amorphous hydrated magnesium carbonate at early stages, leading to the formation of crystalline hydrated Mg carbonates. The preferential location of Mg carbonates along the atomic steps on the crystal surface of MgO indicates the importance of the reactive site density for carbonation kinetics. The analysis of 27-year-old single-crystal MgO samples demonstrates that the thickness of the reacted layer is limited to ∼1.5 μm on average, which is thinner than expected and indicates surface passivation. Thus, if MgO is to be employed for direct air capture of CO2, surface passivation must be circumvented.}, number={40}, journal={Environmental Science & Technology}, publisher={American Chemical Society (ACS)}, author={Weber, Juliane and Starchenko, Vitalii and Yuan, Ke and Anovitz, Lawrence M. and Ievlev, Anton V. and Unocic, Raymond R. and Borisevich, Albina Y. and Boebinger, Matthew G. and Stack, Andrew G.}, year={2023}, month={Sep}, pages={14929–14937} }
@article{thompson_liu_leshchev_hoffman_hong_bare_unocic_stavitski_xin_karim_2023, title={CO Oxidation on Ir1/TiO2: Resolving Ligand Dynamics and Elementary Reaction Steps}, volume={13}, ISSN={2155-5435 2155-5435}, url={http://dx.doi.org/10.1021/acscatal.3c01433}, DOI={10.1021/acscatal.3c01433}, abstractNote={Identifying the rate-controlling steps and the evolution of the ligand environment throughout the catalytic cycle on supported single-atom catalysts is crucial to bridge the gap between heterogeneous and homogeneous catalysis. Here we identified the rate-controlling elementary steps for CO oxidation on TiO2-supported Ir single atoms and isolated the corresponding intermediate Ir complexes. Kinetic measurements, operando spectroscopy, and quantum-chemical calculations indicate that the reaction mechanism has two kinetically relevant steps, CO adsorption/oxidation and O2 dissociation. By varying the reaction conditions, three Ir1 complexes (states) along the reaction cycle were isolated and identified using in situ spectroscopy. Furthermore, we show that all the intermediate Ir1 states share a common CO ligand that does not turn over. This study provides atomic level details on the active, intermediate complexes and reaction cycle of supported single-metal-atom catalysts, thereby offering future possibilities to control the ligand environment and reactivity.}, number={12}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Thompson, Coogan B. and Liu, Liping and Leshchev, Denis S. and Hoffman, Adam S. and Hong, Jiyun and Bare, Simon R. and Unocic, Raymond R. and Stavitski, Eli and Xin, Hongliang and Karim, Ayman M.}, year={2023}, month={May}, pages={7802–7811} }
@article{yang_lie_unocic_yuwono_klingenhof_merzdorf_buchheister_kroschel_walker_gallington_et al._2023, title={Defect‐Promoted Ni‐Based Layer Double Hydroxides with Enhanced Deprotonation Capability for Efficient Biomass Electrooxidation}, volume={35}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.202305573}, DOI={10.1002/adma.202305573}, abstractNote={Ni-based hydroxides are promising electrocatalysts for biomass oxidation reactions, supplanting the oxygen evolution reaction (OER) due to lower overpotentials while producing value-added chemicals. The identification and subsequent engineering of their catalytically active sites are essential to facilitate these anodic reactions. Herein, the proportional relationship between catalysts' deprotonation propensity and Faradic efficiency of 5-hydroxymethylfurfural (5-HMF)-to-2,5 furandicarboxylic acid (FDCA, FEFDCA ) is revealed by thorough density functional theory (DFT) simulations and atomic-scale characterizations, including in situ synchrotron diffraction and spectroscopy methods. The deprotonation capability of ultrathin layer-double hydroxides (UT-LDHs) is regulated by tuning the covalency of metal (M)-oxygen (O) motifs through defect site engineering and selection of M3+ co-chemistry. NiMn UT-LDHs show an ultrahigh FEFDCA of 99% at 1.37 V versus reversible hydrogen electrode (RHE) and retain a high FEFDCA of 92.7% in the OER-operating window at 1.52 V, about 2× that of NiFe UT-LDHs (49.5%) at 1.52 V. Ni-O and Mn-O motifs function as dual active sites for HMF electrooxidation, where the continuous deprotonation of Mn-OH sites plays a dominant role in achieving high selectivity while suppressing OER at high potentials. The results showcase a universal concept of modulating competing anodic reactions in aqueous biomass electrolysis by electronically engineering the deprotonation behavior of metal hydroxides, anticipated to be translatable across various biomass substrates.}, number={48}, journal={Advanced Materials}, publisher={Wiley}, author={Yang, Yuwei and Lie, William Hadinata and Unocic, Raymond R and Yuwono, Jodie A and Klingenhof, Malte and Merzdorf, Thomas and Buchheister, Paul Wolfgang and Kroschel, Matthias and Walker, Anne and Gallington, Leighanne C. and et al.}, year={2023}, month={Oct} }
@article{unocic_stach_2023, title={Gas-phase electron microscopy for materials research}, volume={48}, ISSN={0883-7694 1938-1425}, url={http://dx.doi.org/10.1557/s43577-023-00588-3}, DOI={10.1557/s43577-023-00588-3}, abstractNote={Abstract Detailed studies of interfacial gas-phase chemical reactions are important for understanding factors that control materials synthesis and environmental conditions that govern materials performance and degradation. Out of the many materials characterization methods that are available for interpreting gas–solid reaction processes, in situ and operando transmission electron microscopy (TEM) is perhaps the most versatile, multimodal materials characterization technique. It has successfully been utilized to study interfacial gas–solid interactions under a wide range of environmental conditions, such as gas composition, humidity, pressure, and temperature. This stems from decades of R&D that permit controlled gas delivery and the ability to maintain a gaseous environment directly within the TEM column itself or through specialized side-entry gas-cell holders. Combined with capabilities for real-time, high spatial resolution imaging, electron diffraction and spectroscopy, dynamic structural and chemical changes can be investigated to determine fundamental reaction mechanisms and kinetics that occur at site-specific interfaces. This issue of MRS Bulletin covers research in this field ranging from technique development to the utilization of gas-phase microscopy methods that have been used to develop an improved understanding of multilength-scaled processes incurred during materials synthesis, catalytic reactions, and environmental exposure effects on materials properties. Graphical abstract}, number={8}, journal={MRS Bulletin}, publisher={Springer Science and Business Media LLC}, author={Unocic, Raymond R. and Stach, Eric A.}, year={2023}, month={Aug}, pages={828–832} }
@article{ghimire_ulaganathan_tempez_ilchenko_unocic_heske_miakota_xiang_chaigneau_booth_et al._2023, title={Molybdenum Disulfide Nanoribbons with Enhanced Edge Nonlinear Response and Photoresponsivity}, volume={35}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.202302469}, DOI={10.1002/adma.202302469}, abstractNote={MoS2 nanoribbons have attracted increased interest due to their properties, which can be tailored by tuning their dimensions. Herein, the growth of MoS2 nanoribbons and triangular crystals formed by the reaction between films of MoOx (2x Sites in Zeolite}, volume={12}, ISSN={2155-5435 2155-5435}, url={http://dx.doi.org/10.1021/acscatal.2c00230}, DOI={10.1021/acscatal.2c00230}, abstractNote={The conventional reforming produces H2 with stoichiometric amounts of CO and CO2 from hydrocarbons. Here, we show that COx-free H2 can be produced from ammonia-assisted reforming (ammoreforming) of natural gas liquids (CnH2n+2 + nNH3 = nHCN + (2n + 1) H2, n = 2 or 3) at the same conditions as the steam reforming. Such a process co-produces HCN, which can be easily separated from H2 and used as value-added chemicals or for NH3 recycling through hydrolysis. The ammoreforming of ethane and propane was realized over the Re-modified HZSM-5 zeolite rather than the traditional Pt-based catalyst for the BMA process (methane ammoreforming). The specific activity of the Re/HZSM-5 catalysts at 650 °C is up to 1 molH2/gRe/min (or 180 min–1) during ethane ammoreforming. The catalyst is highly coke resistant and shows only slight deactivation with a time-on-stream up to 20 h. Characterization of the fresh and used catalysts by X-ray absorption and Raman spectroscopies suggested that the isolated ReOx site grafted by AlO4– tetrahedral in the zeolite framework is responsible for the outstanding catalytic activity and coke resistibility.}, number={5}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Fadaeerayeni, Siavash and Yu, Xinbin and Sarnello, Erik and Bao, Zhenghong and Jiang, Xiao and Unocic, Raymond R. and Fang, Lingzhe and Wu, Zili and Li, Tao and Xiang, Yizhi}, year={2022}, month={Feb}, pages={3165–3172} }
@misc{hattar_unocic_2022, title={Applications of Liquid Cell-TEM in Corrosion Research}, ISBN={9783030891008 9783030891015}, url={http://dx.doi.org/10.1007/978-3-030-89101-5_6}, DOI={10.1007/978-3-030-89101-5_6}, journal={Recent Developments in Analytical Techniques for Corrosion Research}, publisher={Springer International Publishing}, author={Hattar, Khalid and Unocic, Raymond R.}, year={2022}, pages={121–150} }
@article{zhou_fuentes-cabrera_singh_unocic_carrillo_xiao_li_li_2022, title={Atomic Edge-Guided Polyethylene Crystallization on Monolayer Two-Dimensional Materials}, volume={55}, ISSN={0024-9297 1520-5835}, url={http://dx.doi.org/10.1021/acs.macromol.1c01978}, DOI={10.1021/acs.macromol.1c01978}, abstractNote={Here, we combine an advanced synthesis of two-dimensional (2D) materials (MoSe2) having well-defined atomic edge configurations with ab initio and atomistic molecular dynamics (MD) simulations to study how atomic edges interact with polyethylene (HDPE) chains in a dilute solution assembly process. Our results reveal that Mo-terminated zigzag (Mo-ZZ) edges act as preferred nucleation sites and strongly interact with HDPE chains. The HDPE chains align in parallel with the Mo-ZZ edges and form arrays of lamellae that are perpendicular to the edges. Interestingly, atomic edge configurations are observed to dramatically change such interactions. The crystallization discrepancy at different edges was demonstrated on the same piece of MoSe2 with different types of edges. The ab initio and MD simulations between n-alkane (n = 5 and 25), a segment of HDPE, and MoSe2 suggest that the atomic structures of MoSe2 can affect their interactions with n-alkane chains. Following the Mo-ZZ edge preferred nucleation principle, controlled long-range alignment of HDPE lamellae can be realized by creating multilayer MoSe2 with parallel atomic steps. This research opens a pathway toward an atomic level understanding of polymer–2D nanomaterial interactions. It also bridges the gap between atomic-level and long-range mesoscopic structures and introduces a novel strategy for long-range structural control.}, number={2}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Zhou, Dong and Fuentes-Cabrera, Miguel and Singh, Akash and Unocic, Raymond R. and Carrillo, Jan Michael Y. and Xiao, Kai and Li, Yumeng and Li, Bo}, year={2022}, month={Jan}, pages={559–567} }
@article{ahmadi_lee_patel_unocic_shamsaei_mahjouri‐samani_2022, title={Dry Printing and Additive Nanomanufacturing of Flexible Hybrid Electronics and Sensors}, volume={9}, ISSN={2196-7350 2196-7350}, url={http://dx.doi.org/10.1002/admi.202102569}, DOI={10.1002/admi.202102569}, abstractNote={Abstract The growing demand for flexible and wearable hybrid electronics has triggered the need for advanced manufacturing techniques with versatile printing capabilities. Complex ink formulations, use of surfactants/contaminants, limited source materials, and the need for high‐temperature heat treatments for sintering are major issues facing the current inkjet and aerosol printing methods. Here, the nanomanufacturing of flexible hybrid electronics (FHE) by dry printing silver and indium tin oxide on flexible substrates using a novel laser‐based additive nanomanufacturing process is reported. The electrical resistance of the printed lines is tailored during the print process by tuning the geometry and structure of the printed samples. Different FHE designs are fabricated and tested to check the performance of the devices. Mechanical reliability tests including cycling, bending, and stretching confirm the expected performance of the printed samples under different strain levels. This transformative liquid‐free process allows the on‐demand formation and in situ laser crystallization of nanoparticles for printing pure materials for future flexible and wearable electronics and sensors.}, number={12}, journal={Advanced Materials Interfaces}, publisher={Wiley}, author={Ahmadi, Zabihollah and Lee, Seungjong and Patel, Aarsh and Unocic, Raymond R. and Shamsaei, Nima and Mahjouri‐Samani, Masoud}, year={2022}, month={Feb} }
@article{thapaliya_misra_yang_jafta_meyer_bagri_unocic_bridges_dai_2022, title={Enhancing Cycling Stability and Capacity Retention of NMC811 Cathodes by Reengineering Interfaces via Electrochemical Fluorination}, volume={9}, ISSN={2196-7350 2196-7350}, url={http://dx.doi.org/10.1002/admi.202200035}, DOI={10.1002/admi.202200035}, abstractNote={Abstract High‐capacity cathodes (LiNi 0.8 Mn 0.1 Co 0.1 O 2 ) that can boost the energy density of lithium‐ion batteries are promising candidates for vehicle electrification. However, several factors specific to high energy density materials entailing electrode reactions inhibit their application. Fluorination has shown a promising ability to combat the detrimental electrochemical performances of cathode materials, however, it remains difficult to achieve the desired functionality. Herein, a novel electrochemical fluorination (ECF) that demonstrates a promising electrochemical performance enhancement via stabilization of the cathode–electrolyte‐interphase (CEI) by forming conformal LiF is proposed. Besides LiF surface layer formation, ECF reduces the degree of fluorination‐induced Ni/Li disordering and enhances the layered structural stability as probed by X‐ray diffraction. Because of the robust CEI, ECF‐NMC811 cathodes deliver 203.0 mAh g −1 first discharge capacity at the current rate of C /10, with ≈98% capacity retention up to 100 cycles. Similarly, it delivers ≈180 mAh g −1 capacity at a 1 C rate with 86.4% capacity retention up to 200 cycles with average coulombic efficiency of > 99.5%. Comprehensive characterization with a multitude of probes reveals that ECF enhances the cycling stability of the electrode without altering bulk structure and morphology.}, number={18}, journal={Advanced Materials Interfaces}, publisher={Wiley}, author={Thapaliya, Bishnu P. and Misra, Sudhajit and Yang, Shi‐ze and Jafta, Charl J. and Meyer, Harry M., III and Bagri, Prashant and Unocic, Raymond R. and Bridges, Craig A. and Dai, Sheng}, year={2022}, month={Feb} }
@article{jorgensen_santodonato_littrell_kuo_lee_unocic_liaw_gilbert_debeer-schmitt_2022, title={In-Situ Study of Microstructure Evolution of Spinodal Decomposition in an Al-Rich High-Entropy Alloy}, volume={9}, ISSN={2296-8016}, url={http://dx.doi.org/10.3389/fmats.2022.827333}, DOI={10.3389/fmats.2022.827333}, abstractNote={High-entropy alloys (HEAs) are materials which leverage the entropy of mixing to motivate the formation of single-phase solid solutions, even of immiscible elements. While these materials are well-recognized for their application to structural engineering, there is increasing interest in the use of HEAs for functional applications such as memory storage and energy devices. The current work investigates the HEA Al 1.3 CoCrCuFeNi, which has been previously shown to be single-phase at high temperatures, but undergoes phase separation at lower temperatures, transforming the structural and the functional properties. This phase separation is investigated at high temperatures with in-situ small angle neutron scattering (SANS) and scanning transmission electron microscopy (EDS). These techniques show that increasing the temperature up to 800°C, the microstructure of the HEA adiabatically disorders and abruptly homogenizes near 700°C, which is consistent with spinodal decomposition. Overall, the microstructural evolution proceeds mainly by the atomistic redistribution of the constituent elements within simple crystal lattices, producing coherent phase mixtures.}, journal={Frontiers in Materials}, publisher={Frontiers Media SA}, author={Jorgensen, Cameron S. and Santodonato, Louis J. and Littrell, Kenneth C. and Kuo, Chih Hsiang and Lee, Chanho and Unocic, Raymond R. and Liaw, Peter K. and Gilbert, Dustin A. and DeBeer-Schmitt, Lisa M.}, year={2022}, month={Mar} }
@article{azam_boebinger_jaiswal_unocic_fathi-hafshejani_mahjouri-samani_2022, title={Laser-Assisted Synthesis of Monolayer 2D MoSe2 Crystals with Tunable Vacancy Concentrations: Implications for Gas and Biosensing}, volume={5}, ISSN={2574-0970 2574-0970}, url={http://dx.doi.org/10.1021/acsanm.2c01458}, DOI={10.1021/acsanm.2c01458}, abstractNote={Tuning the structural and electronic properties of atomically thin two-dimensional (2D) materials via defect and vacancy engineering is the key to enabling their potential use in various applications, including electronics, energy, and sensing devices. Vacancies are, for instance, becoming highly promising for the enhanced interaction of gases and biomolecules with 2D materials in energy and sensing applications. However, the deterministic generation of desirable vacancies with tunable concentrations remains a challenge in 2D materials due to the limitations in the current growth methods, such as the complex reaction chemistries and gas flow dynamics. Therefore, engineering defects and vacancies in 2D materials have been mainly limited to destructive top-down processes such as heating, ion bombardments, and laser postprocessing. Here, we introduce a single-step bottom-up synthesis approach for the growth of monolayer MoSe2 crystals with tunable vacancy concentrations. This method utilizes the spatiotemporal properties and adjustable power densities of the lasers to control the vaporization dynamics of the stoichiometric MoSe2 powders. Such a mechanism in the vaporization allows us to grow tunable stoichiometry monolayer MoSe2–x crystals on the substrates. The localized and time-controlled (250 ms to 2 s) vaporization of the MoSe2 powder by a CO2 laser enables the formation of monolayer crystals with controlled vacancy concentrations ranging from ∼1 to 20%. The effects of laser power, laser irradiation time, and background pressure on the tuning range and subsequent properties of the crystals are investigated and quantified using Raman and photoluminescence spectroscopy, scanning transmission electron microscopy (STEM), and time-correlated single-photon counting (TCSPC). This bottom-up synthesis is a promising approach that allows the deterministic vacancy tuning for future electronics and, in particular, gas and biosensing applications without the need for further postprocessing and potential structural disruption of the crystals.}, number={7}, journal={ACS Applied Nano Materials}, publisher={American Chemical Society (ACS)}, author={Azam, Nurul and Boebinger, Matthew G. and Jaiswal, Suman and Unocic, Raymond R. and Fathi-Hafshejani, Parvin and Mahjouri-Samani, Masoud}, year={2022}, month={Jun}, pages={9129–9139} }
@article{whitcomb_sviripa_schapowal_mamedov_unocic_paolucci_davis_2022, title={Mechanistic Insights on the Low-Temperature Oxidation of CO Catalyzed by Isolated Co Ions in N-Doped Carbon}, volume={12}, ISSN={2155-5435 2155-5435}, url={http://dx.doi.org/10.1021/acscatal.2c04380}, DOI={10.1021/acscatal.2c04380}, abstractNote={Isolated cobalt ions on nitrogen-doped carbon (Co–N–C) catalyze CO oxidation at temperatures as low as 196 K, but the active site and mechanism for this reaction remain elusive. In this work, steady-state CO oxidation around 273 K over Co–N–C revealed nearly first-order behavior in both CO and O2 as well as a negative apparent activation energy. Isotopic transient analysis of the reaction confirmed a rapid turnover frequency and low surface coverage of adsorbed intermediates leading to CO2 (<10% of the Co). Results from kinetics experiments combined with quantum chemical calculations and molecular dynamics simulations are consistent with a reaction path involving weak adsorption of CO onto Co ions followed by a low barrier for the CO-assisted activation of weakly adsorbed O2. This proposed mechanism for dioxygen activation does not involve a redox cycle with the transition-metal ion and may be important in other low-temperature catalytic reactions involving O2.}, number={24}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Whitcomb, Colby A. and Sviripa, Anna and Schapowal, Michael I. and Mamedov, Konstantin and Unocic, Raymond R. and Paolucci, Christopher and Davis, Robert J.}, year={2022}, month={Dec}, pages={15529–15540} }
@article{roccapriore_boebinger_dyck_ghosh_unocic_kalinin_ziatdinov_2022, title={Probing Electron Beam Induced Transformations on a Single-Defect Level via Automated Scanning Transmission Electron Microscopy}, volume={16}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.2c07451}, DOI={10.1021/acsnano.2c07451}, abstractNote={A robust approach for real-time analysis of the scanning transmission electron microscopy (STEM) data streams, based on ensemble learning and iterative training (ELIT) of deep convolutional neural networks, is implemented on an operational microscope, enabling the exploration of the dynamics of specific atomic configurations under electron beam irradiation via an automated experiment in STEM. Combined with beam control, this approach allows studying beam effects on selected atomic groups and chemical bonds in a fully automated mode. Here, we demonstrate atomically precise engineering of single vacancy lines in transition metal dichalcogenides and the creation and identification of topological defects in graphene. The ELIT-based approach facilitates direct on-the-fly analysis of the STEM data and engenders real-time feedback schemes for probing electron beam chemistry, atomic manipulation, and atom by atom assembly.}, number={10}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Roccapriore, Kevin M. and Boebinger, Matthew G. and Dyck, Ondrej and Ghosh, Ayana and Unocic, Raymond R. and Kalinin, Sergei V. and Ziatdinov, Maxim}, year={2022}, month={Oct}, pages={17116–17127} }
@article{subhash_unocic_gallington_wright_cheong_tilley_bedford_2022, title={Resolving Atomic-Scale Structure and Chemical Coordination in High Entropy Alloy Electrocatalysts for Structure-Function Relationship Elucidation}, url={https://doi.org/10.21203/rs.3.rs-2155469/v1}, DOI={10.21203/rs.3.rs-2155469/v1}, abstractNote={Abstract The wide range of potential surface configurations in high entropy alloy nanocatalysts (HEAs) offer substantial degrees of freedom to tune their catalytic properties. This complexity in possible atomic arrangements, however, presents a significant challenge in resolving active structural motifs, preventing the establishment of structure-function relationships for rational catalyst optimization. Herein, we present a methodology for creating sub 5 nm HEAs using an aqueous-based peptide-directed route. Using a combination of synchrotron scattering and spectroscopy techniques, HEA structure models are constructed from stochastic modelling of experimental datasets and showcase a clear peptide-induced influence on atomic-structure and chemical miscibility. Analysis of our models allow for the construction of structure-function correlations applied to electrochemical methanol oxidation reactions, revealing the complex interactions between multiple metals that lead to improved catalytic properties. Our results showcase a viable strategy for elucidating structure-function relationship in HEAs, prospectively providing a pathway for future materials design.}, author={Subhash, Bijil and Unocic, Raymond and Gallington, Leighanne and Wright, Joshua and Cheong, Soshan and Tilley, Richard and Bedford, Nicholas}, year={2022}, month={Nov} }
@article{sutter_komsa_puretzky_unocic_sutter_2022, title={Stacking Fault Induced Symmetry Breaking in van der Waals Nanowires}, volume={16}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.2c09172}, DOI={10.1021/acsnano.2c09172}, abstractNote={While traditional ferroelectrics are based on polar crystals in bulk or thin film form, two-dimensional and layered materials can support mechanisms for symmetry breaking between centrosymmetric building blocks, e.g., by creating low-symmetry interfaces in van der Waals stacks. Here, we introduce an approach toward symmetry breaking in van der Waals crystals that relies on the spontaneous incorporation of stacking faults in a nonpolar bulk layer sequence. The concept is realized in nanowires consisting of Se-rich group IV monochalcogenide (GeSe1-xSx) alloys, obtained by vapor-liquid-solid growth. The single crystalline wires adopt a layered structure in which the nonpolar A-B bulk stacking along the nanowire axis is interrupted by single-layer stacking faults with local A-A' stacking. Density functional theory explains this behavior by a reduced stacking fault formation energy in GeSe (or Se-rich GeSe1-xSx alloys). Computations demonstrate that, similar to monochalcogenide monolayers, the inserted A-layers should show a spontaneous electric polarization with a switching barrier consistent with a Curie temperature above room temperature. Second-harmonic generation signals are consistent with a variable density of stacking faults along the wires. Our results point to possible routes for designing ferroelectrics via the layer stacking in van der Waals crystals.}, number={12}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Sutter, Eli and Komsa, Hannu-Pekka and Puretzky, Alexander A. and Unocic, Raymond R. and Sutter, Peter}, year={2022}, month={Nov}, pages={21199–21207} }
@article{sharma_kannan_li_anderson_rashid_collins_poplawsky_unocic_2021, title={A Mechanism for Carbon Depletion at Bondline of High-Frequency Electric-Resistance-Welded X70 Pipeline Steel}, volume={52}, ISSN={1073-5623 1543-1940}, url={http://dx.doi.org/10.1007/s11661-021-06339-w}, DOI={10.1007/s11661-021-06339-w}, number={9}, journal={Metallurgical and Materials Transactions A}, publisher={Springer Science and Business Media LLC}, author={Sharma, Nitin Kumar and Kannan, Rangasayee and Li, Leijun and Anderson, Neil and Rashid, Muhammad and Collins, Laurie and Poplawsky, Jonathan D. and Unocic, Raymond}, year={2021}, month={Jun}, pages={3788–3798} }
@article{ahmadi_lee_unocic_shamsaei_mahjouri‐samani_2021, title={Additive Nanomanufacturing of Multifunctional Materials and Patterned Structures: A Novel Laser‐Based Dry Printing Process}, volume={6}, ISSN={2365-709X 2365-709X}, url={http://dx.doi.org/10.1002/admt.202001260}, DOI={10.1002/admt.202001260}, abstractNote={Abstract Direct printing of functional materials, structures, and devices on various platforms such as flexible to rigid substrates is of interest for applications ranging from electronics to energy and sensing to biomedical devices. Current additive manufacturing (AM) and printing processes are either limited by the available sources of functional materials or require to be in the form of precisely designed inks. Here, a novel laser‐based additive nanomanufacturing (ANM) system capable of in situ and on‐demand generations of nanoparticles that can serve as nanoscale building blocks for real‐time sintering and dry printing a variety of multifunctional materials and patterns at atmospheric pressure and room temperature is reported. The ability to print different functional materials on various rigid and flexible platforms is shown. This nonequilibrium process involves pulsed laser ablation of targets and in situ formation of pure amorphous nanoparticles’ stream that are guided through a nozzle onto the surface of the substrate, where they are sintered/crystallized in real‐time. Further, the process–structure relationship of the printed materials from nanoscale to microscale is shown. This new ANM concept opens up an opportunity for printing advanced functional materials and devices on rigid and flexible substrates that can be employed both on the earth and in space.}, number={5}, journal={Advanced Materials Technologies}, publisher={Wiley}, author={Ahmadi, Zabihollah and Lee, Seungjong and Unocic, Raymond R. and Shamsaei, Nima and Mahjouri‐Samani, Masoud}, year={2021}, month={Mar} }
@article{vogt_meirer_monai_groeneveld_ferri_van santen_nachtegaal_unocic_frenkel_weckhuysen_2021, title={Dynamic restructuring of supported metal nanoparticles and its implications for structure insensitive catalysis}, volume={12}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-021-27474-3}, DOI={10.1038/s41467-021-27474-3}, abstractNote={Some fundamental concepts of catalysis are not fully explained but are of paramount importance for the development of improved catalysts. An example is the concept of structure insensitive reactions, where surface-normalized activity does not change with catalyst metal particle size. Here we explore this concept and its relation to surface reconstruction on a set of silica-supported Ni metal nanoparticles (mean particle sizes 1-6 nm) by spectroscopically discerning a structure sensitive (CO2 hydrogenation) from a structure insensitive (ethene hydrogenation) reaction. Using state-of-the-art techniques, inter alia in-situ STEM, and quick-X-ray absorption spectroscopy with sub-second time resolution, we have observed particle-size-dependent effects like restructuring which increases with increasing particle size, and faster restructuring for larger particle sizes during ethene hydrogenation while for CO2 no such restructuring effects were observed. Furthermore, a degree of restructuring is irreversible, and we also show that the rate of carbon diffusion on, and into nanoparticles increases with particle size. We finally show that these particle size-dependent effects induced by ethene hydrogenation, can make a structure sensitive reaction (CO2 hydrogenation), structure insensitive. We thus postulate that structure insensitive reactions are actually apparently structure insensitive, which changes our fundamental understanding of the empirical observation of structure insensitivity.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Vogt, Charlotte and Meirer, Florian and Monai, Matteo and Groeneveld, Esther and Ferri, Davide and van Santen, Rutger A. and Nachtegaal, Maarten and Unocic, Raymond R. and Frenkel, Anatoly I. and Weckhuysen, Bert M.}, year={2021}, month={Dec} }
@article{rimal_schmidt_hijazi_feldman_liu_skoropata_lapano_brahlek_mukherjee_unocic_et al._2021, title={Effective reduction of
PdCoO
thin films via hydrogenation and sign tunable anomalous Hall effect}, volume={5}, ISSN={2475-9953}, url={http://dx.doi.org/10.1103/physrevmaterials.5.l052001}, DOI={10.1103/physrevmaterials.5.l052001}, abstractNote={PdCoO2 , belonging to a family of triangular oxides called delafossite, is one of the most conducting oxides. Its in-plane conductivity is comparable to those of the best metals, and exhibits hydrodynamic electronic transport with extremely long mean free path at cryogenic temperatures. Nonetheless, it is nonmagnetic despite the presence of the cobalt ion. Here, we show that a mild hydrogenation process reduces PdCoO2 thin films to an atomically-mixed alloy of PdCo with strong out-of-plane ferromagnetism and sign-tunable anomalous Hall effect. Considering that many other compounds remain little affected under a similar hydrogenation condition, this discovery may provide a route to creating novel spintronic heterostructures combining strong ferromagnetism, involving oxides and other functional materials.}, number={5}, journal={Physical Review Materials}, publisher={American Physical Society (APS)}, author={Rimal, Gaurab and Schmidt, Caleb and Hijazi, Hussein and Feldman, Leonard C. and Liu, Yiting and Skoropata, Elizabeth and Lapano, Jason and Brahlek, Matthew and Mukherjee, Debangshu and Unocic, Raymond R. and et al.}, year={2021}, month={May} }
@article{liang_matsumoto_zhao_osti_popov_thapaliya_fleischmann_misra_prenger_tyagi_et al._2021, title={Engineering the Interlayer Spacing by Pre‐Intercalation for High Performance Supercapacitor MXene Electrodes in Room Temperature Ionic Liquid}, volume={31}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.202104007}, DOI={10.1002/adfm.202104007}, abstractNote={Abstract MXenes exhibit excellent capacitance at high scan rates in sulfuric acid aqueous electrolytes, but the narrow potential window of aqueous electrolytes limits the energy density. Organic electrolytes and room‐temperature ionic liquids (RTILs) can provide higher potential windows, leading to higher energy density. The large cation size of RTIL hinders its intercalation in‐between the layers of MXene limiting the specific capacitance in comparison to aqueous electrolytes. In this work, different chain lengths alkylammonium (AA) cations are intercalated into Ti 3 C 2 T x , producing variation of MXene interlayer spacings ( d ‐spacing). AA‐cation‐intercalated Ti 3 C 2 T x (AA‐Ti 3 C 2 ), exhibits higher specific capacitances, and cycling stabilities than pristine Ti 3 C 2 T x in 1 m 1‐ethly‐3‐methylimidazolium bis‐(trifluoromethylsulfonyl)‐imide (EMIMTFSI) in acetonitrile and neat EMIMTFSI RTIL electrolytes. Pre‐intercalated MXene with an interlayer spacing of ≈2.2 nm, can deliver a large specific capacitance of 257 F g −1 (1428 mF cm −2 and 492 F cm −3 ) in neat EMIMTFSI electrolyte leading to high energy density. Quasi elastic neutron scattering and electrochemical impedance spectroscopy are used to study the dynamics of confined RTIL in pre‐intercalated MXene. Molecular dynamics simulations suggest significant differences in the structures of RTIL ions and AA cations inside the Ti 3 C 2 T x interlayer, providing insights into the differences in the observed electrochemical behavior.}, number={33}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Liang, Kun and Matsumoto, Ray A. and Zhao, Wei and Osti, Naresh C. and Popov, Ivan and Thapaliya, Bishnu P. and Fleischmann, Simon and Misra, Sudhajit and Prenger, Kaitlyn and Tyagi, Madhusudan and et al.}, year={2021}, month={Jun} }
@article{liu_li_soto_li_unocic_balbuena_harutyunyan_hone_esposito_2021, title={Enhancing Hydrogen Evolution Activity of Monolayer Molybdenum Disulfide via a Molecular Proton Mediator}, volume={11}, ISSN={2155-5435 2155-5435}, url={http://dx.doi.org/10.1021/acscatal.1c03016}, DOI={10.1021/acscatal.1c03016}, abstractNote={The configuration and local environment of active sites in transition metal dichalcogenides can significantly alter their electrocatalytic activity toward the hydrogen evolution reaction (HER). Herein, we demonstrate that the HER activity of monolayer MoS2 electrocatalysts can be enhanced through the modulation of active sites by introducing a molecular mediator that alters the coverage of adsorbed protons. Sodium dodecyl sulfate (SDS) promotes the intrinsic HER activity of both terrace-based sulfur vacancies (VS) and edge sites during HER operation in an acidic environment, leading to increases in the turnover frequency (TOF) of both sites by up to 5 orders of magnitude. Simulations indicate that SDS facilitates proton adsorption by catching protons from hydronium ions and releasing them to VS, which reduces the energy barrier by creating a stair-case-like free energy profile. Our results highlight the ability to tailor the activity of electrocatalysts by synergistically combining proton transfer mediators with engineered active sites.}, number={19}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Liu, Xiangye and Li, Baichang and Soto, Fernando A. and Li, Xufan and Unocic, Raymond R. and Balbuena, Perla B. and Harutyunyan, Avetik R. and Hone, James and Esposito, Daniel V.}, year={2021}, month={Sep}, pages={12159–12169} }
@article{bertoldo_unocic_lin_sang_puretzky_yu_miakota_rouleau_schou_thygesen_et al._2021, title={Intrinsic Defects in MoS2 Grown by Pulsed Laser Deposition: From Monolayers to Bilayers}, volume={15}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.0c08835}, DOI={10.1021/acsnano.0c08835}, abstractNote={Pulsed laser deposition (PLD) can be considered a powerful method for the growth of two-dimensional (2D) transition-metal dichalcogenides (TMDs) into van der Waals heterostructures. However, despite significant progress, the defects in 2D TMDs grown by PLD remain largely unknown and yet to be explored. Here, we combine atomic resolution images and first-principles calculations to reveal the atomic structure of defects, grains, and grain boundaries in mono- and bilayer MoS2 grown by PLD. We find that sulfur vacancies and MoS antisites are the predominant point defects in 2D MoS2. We predict that the aforementioned point defects are thermodynamically favorable under a Mo-rich/S-poor environment. The MoS2 monolayers are polycrystalline and feature nanometer size grains connected by a high density of grain boundaries. In particular, the coalescence of nanometer grains results in the formation of 180° mirror twin boundaries consisting of distinct 4- and 8-membered rings. We show that PLD synthesis of bilayer MoS2 results in various structural symmetries, including AA′ and AB, but also turbostratic with characteristic moiré patterns. Moreover, we report on the experimental demonstration of an electron beam-driven transition between the AB and AA′ stacking orientations in bilayer MoS2. These results provide a detailed insight into the atomic structure of monolayer MoS2 and the role of the grain boundaries on the growth of bilayer MoS2, which has importance for future applications in optoelectronics.}, number={2}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Bertoldo, Fabian and Unocic, Raymond R. and Lin, Yu-Chuan and Sang, Xiahan and Puretzky, Alexander A. and Yu, Yiling and Miakota, Denys and Rouleau, Christopher M. and Schou, Jørgen and Thygesen, Kristian S. and et al.}, year={2021}, month={Feb}, pages={2858–2868} }
@article{sutter_unocic_idrobo_sutter_2021, title={Multilayer Lateral Heterostructures of Van Der Waals Crystals with Sharp, Carrier–Transparent Interfaces}, volume={9}, ISSN={2198-3844 2198-3844}, url={http://dx.doi.org/10.1002/advs.202103830}, DOI={10.1002/advs.202103830}, abstractNote={Research on engineered materials that integrate different 2D crystals has largely focused on two prototypical heterostructures: Vertical van der Waals stacks and lateral heterostructures of covalently stitched monolayers. Extending lateral integration to few layer or even multilayer van der Waals crystals could enable architectures that combine the superior light absorption and photonic properties of thicker crystals with close proximity to interfaces and efficient carrier separation within the layers, potentially benefiting applications such as photovoltaics. Here, the realization of multilayer heterstructures of the van der Waals semiconductors SnS and GeS with lateral interfaces spanning up to several hundred individual layers is demonstrated. Structural and chemical imaging identifies {110} interfaces that are perpendicular to the (001) layer plane and are laterally localized and sharp on a 10 nm scale across the entire thickness. Cathodoluminescence spectroscopy provides evidence for a facile transfer of electron-hole pairs across the lateral interfaces, indicating covalent stitching with high electronic quality and a low density of recombination centers.}, number={3}, journal={Advanced Science}, publisher={Wiley}, author={Sutter, Eli and Unocic, Raymond R. and Idrobo, Juan‐Carlos and Sutter, Peter}, year={2021}, month={Nov} }
@article{cochell_unocic_graña-otero_martin_2021, title={Nanoscale oxidation behavior of carbon fibers revealed with in situ gas cell STEM}, volume={199}, ISSN={1359-6462}, url={http://dx.doi.org/10.1016/j.scriptamat.2021.113820}, DOI={10.1016/j.scriptamat.2021.113820}, journal={Scripta Materialia}, publisher={Elsevier BV}, author={Cochell, Thomas J. and Unocic, Raymond R. and Graña-Otero, José and Martin, Alexandre}, year={2021}, month={Jul}, pages={113820} }
@article{li_li_lei_bets_sang_okogbue_liu_unocic_yakobson_hone_et al._2021, title={Nickel particle–enabled width-controlled growth of bilayer molybdenum disulfide nanoribbons}, volume={7}, ISSN={2375-2548}, url={http://dx.doi.org/10.1126/sciadv.abk1892}, DOI={10.1126/sciadv.abk1892}, abstractNote={Nickel nanoparticles drive the width of bilayer nanoribbons down to 8 nm, enabling quantum transport at high temperatures.}, number={50}, journal={Science Advances}, publisher={American Association for the Advancement of Science (AAAS)}, author={Li, Xufan and Li, Baichang and Lei, Jincheng and Bets, Ksenia V. and Sang, Xiahan and Okogbue, Emmanuel and Liu, Yang and Unocic, Raymond R. and Yakobson, Boris I. and Hone, James and et al.}, year={2021}, month={Dec} }
@article{unocic_hensley_walden_bigelow_griffin_habas_unocic_allard_2021, title={Performing In Situ Closed-Cell Gas Reactions in the Transmission Electron Microscope}, volume={7}, ISSN={1940-087X}, url={http://dx.doi.org/10.3791/62174-v}, DOI={10.3791/62174-v}, abstractNote={Gas reactions studied by in situ electron microscopy can be used to capture the real-time morphological and microchemical transformations of materials at length scales down to the atomic level. In situ closed-cell gas reaction (CCGR) studies performed using (scanning) transmission electron microscopy (STEM) can separate and identify localized dynamic reactions, which are extremely challenging to capture using other characterization techniques. For these experiments, we used a CCGR holder that utilizes microelectromechanical systems (MEMS)-based heating microchips (hereafter referred to as "E-chips"). The experimental protocol described here details the method for performing in situ gas reactions in dry and wet gases in an aberration-corrected STEM. This method finds relevance in many different materials systems, such as catalysis and high-temperature oxidation of structural materials at atmospheric pressure and in the presence of various gases with or without water vapor. Here, several sample preparation methods are described for various material form factors. During the reaction, mass spectra obtained with a residual gas analyzer (RGA) system with and without water vapor further validates gas exposure conditions during reactions. Integrating an RGA with an in situ CCGR-STEM system can, therefore, provide critical insight to correlate gas composition with the dynamic surface evolution of materials during reactions. In situ/operando studies using this approach allow for detailed investigation of the fundamental reaction mechanisms and kinetics that occur at specific environmental conditions (time, temperature, gas, pressure), in real-time, and at high spatial resolution.}, number={173}, journal={Journal of Visualized Experiments}, publisher={MyJove Corporation}, author={Unocic, Kinga A. and Hensley, Dale K. and Walden, Franklin S. and Bigelow, Wilbur C. and Griffin, Michael B. and Habas, Susan E. and Unocic, Raymond R. and Allard, Lawrence F.}, year={2021}, month={Jul} }
@article{albrahim_thompson_leshchev_shrotri_unocic_hong_hoffman_meloni_runnebaum_bare_et al._2021, title={Reduction and Agglomeration of Supported Metal Clusters Induced by High-Flux X-ray Absorption Spectroscopy Measurements}, volume={125}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/acs.jpcc.1c01823}, DOI={10.1021/acs.jpcc.1c01823}, abstractNote={Supported metal clusters are widely used in catalysis for many important reactions. To understand the catalytic properties, in situ/operando characterization techniques, such as X-ray absorption spectroscopy (XAS), provide essential details of the size, shape, and chemical composition of the cluster and the nature of the active sites. New-generation synchrotrons combined with focusing beamlines provide high-flux-density X-rays for improved detection sensitivity as well as higher time and spatial resolution. Understanding the effects of a high-flux-density X-ray beam on the catalyst during the actual measurement, whether XAS or another synchrotron-based technique, is crucial. This is especially important for in situ and operando studies where both the high flux density and reaction conditions can affect the catalyst structure. In this work, we investigated the effect of the flux density on rhodium clusters supported on Al2O3 at two different beamlines: National Synchrotron Light Source II beamline 08-ID and Stanford Synchrotron Radiation Light Source (SSRL) beamline 4-1. We show that the higher flux density at beamline 08-ID causes the reduction of the highly dispersed RhOx/Al2O3 catalyst, even at room temperature. Additionally, exposure to the higher flux density X-rays at beamline 08-ID during in situ reduction results in significant agglomeration of the Rh clusters. The final size of the Rh nanoparticles reduced at 310 °C is equivalent to that of particles formed after the reduction at 600–650 °C in the absence of the beam. Significant beam-induced reduction and agglomeration is also shown for Ni supported on beta zeolite during in situ reduction at an intermediate-flux-density beamline 9-3 at SSRL, indicating that beam-induced changes in heterogeneous catalysts could be common at intermediate- and high-flux-density beamlines. We provide precautions and recommendations for detecting and minimizing beam damage during in situ/operando XAS measurements.}, number={20}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Albrahim, Malik and Thompson, Coogan and Leshchev, Denis and Shrotri, Abhijit and Unocic, Raymond R. and Hong, Jiyun and Hoffman, Adam S. and Meloni, Michael J. and Runnebaum, Ron C. and Bare, Simon R. and et al.}, year={2021}, month={May}, pages={11048–11057} }
@article{wang_zhang_nguyen_sang_liu_yu_ko_unocic_puretzky_rouleau_et al._2021, title={Selective Antisite Defect Formation in WS2 Monolayers via Reactive Growth on Dilute W‐Au Alloy Substrates}, volume={34}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.202106674}, DOI={10.1002/adma.202106674}, abstractNote={Defects are ubiquitous in 2D materials and can affect the structure and properties of the materials and also introduce new functionalities. Methods to adjust the structure and density of defects during bottom-up synthesis are required to control the growth of 2D materials with tailored optical and electronic properties. Here, the authors present an Au-assisted chemical vapor deposition approach to selectively form SW and S2W antisite defects, whereby one or two sulfur atoms substitute for a tungsten atom in WS2 monolayers. Guided by first-principles calculations, they describe a new method that can maintain tungsten-poor growth conditions relative to sulfur via the low solubility of W atoms in a gold/W alloy, thereby significantly reducing the formation energy of the antisite defects during the growth of WS2 . The atomic structure and composition of the antisite defects are unambiguously identified by Z-contrast scanning transmission electron microscopy and electron energy-loss spectroscopy, and their total concentration is statistically determined, with levels up to ≈5.0%. Scanning tunneling microscopy/spectroscopy measurements and first-principles calculations further verified these antisite defects and revealed the localized defect states in the bandgap of WS2 monolayers. This bottom-up synthesis method to form antisite defects should apply in the synthesis of other 2D materials.}, number={3}, journal={Advanced Materials}, publisher={Wiley}, author={Wang, Kai and Zhang, Lizhi and Nguyen, Giang D. and Sang, Xiahan and Liu, Chenze and Yu, Yiling and Ko, Wonhee and Unocic, Raymond R. and Puretzky, Alexander A. and Rouleau, Christopher M. and et al.}, year={2021}, month={Nov} }
@article{chen_unocic_hoffman_hong_braga_bao_bare_szanyi_2021, title={Unlocking the Catalytic Potential of TiO2-Supported Pt Single Atoms for the Reverse Water–Gas Shift Reaction by Altering Their Chemical Environment}, volume={1}, ISSN={2691-3704 2691-3704}, url={http://dx.doi.org/10.1021/jacsau.1c00111}, DOI={10.1021/jacsau.1c00111}, abstractNote={Single-atom catalysts (SACs) often exhibit dynamic responses to the reaction and pretreatment environment that affect their activity. The lack of understanding of these behaviors hinders the development of effective, stable SACs, and makes their investigations rather difficult. Here we report a reduction–oxidation cycle that induces nearly 5-fold activity enhancement on Pt/TiO2 SACs for the reverse water–gas shift (rWGS) reaction. We combine microscopy (STEM) and spectroscopy (XAS and IR) studies with kinetic measurements, to convincingly show that the low activity on the fresh SAC is a result of limited accessibility of Pt single atoms (Pt1) due to high Pt–O coordination. The reduction step mobilizes Pt1, forming small, amorphous, and unstable Pt aggregates. The reoxidation step redisperses Pt into Pt1, but in a new, less O-coordinated chemical environment that makes the single metal atoms more accessible and, consequently, more active. After the cycle, the SAC exhibits superior rWGS activity to nonatomically dispersed Pt/TiO2. During the rWGS, the activated Pt1 experience slow deactivation, but can be reactivated by mild oxidation. This work demonstrates a clear picture of how the structural evolution of Pt/TiO2 SACs leads to ultimate catalytic efficiency, offering desired understanding on the rarely explored dynamic chemical environment of supported single metal atoms and its catalytic consequences.}, number={7}, journal={JACS Au}, publisher={American Chemical Society (ACS)}, author={Chen, Linxiao and Unocic, Raymond R. and Hoffman, Adam S. and Hong, Jiyun and Braga, Adriano H. and Bao, Zhenghong and Bare, Simon R. and Szanyi, Janos}, year={2021}, month={Jun}, pages={977–986} }
@article{cui_hu_unocic_van tendeloo_sang_2021, title={Atomic defects, functional groups and properties in MXenes}, volume={32}, ISSN={1001-8417}, url={http://dx.doi.org/10.1016/j.cclet.2020.04.024}, DOI={10.1016/j.cclet.2020.04.024}, number={1}, journal={Chinese Chemical Letters}, publisher={Elsevier BV}, author={Cui, Wenjun and Hu, Zhi-Yi and Unocic, Raymond R. and Van Tendeloo, Gustaaf and Sang, Xiahan}, year={2021}, month={Jan}, pages={339–344} }
@article{dyck_ziatdinov_lingerfelt_unocic_hudak_lupini_jesse_kalinin_2020, title={Author Correction: Atom-by-atom fabrication with electron beams}, url={https://doi.org/10.1038/s41578-020-0188-y}, DOI={10.1038/s41578-020-0188-y}, journal={Nature Reviews Materials}, author={Dyck, Ondrej and Ziatdinov, Maxim and Lingerfelt, David B. and Unocic, Raymond R. and Hudak, Bethany M. and Lupini, Andrew R. and Jesse, Stephen and Kalinin, Sergei V.}, year={2020}, month={Feb} }
@article{guo_mahurin_unocic_luo_dai_2020, title={Broadening the Gas Separation Utility of Monolayer Nanoporous Graphene Membranes by an Ionic Liquid Gating}, volume={20}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/acs.nanolett.0c02860}, DOI={10.1021/acs.nanolett.0c02860}, abstractNote={Ultrathin two-dimensional (2D) monolayer atomic crystal materials offer great potential for extending the field of novel separation technology due to their infinitesimal thickness and mechanical strength. One difficult and ongoing challenge is to perforate the 2D monolayer material with subnanometer pores with atomic precision for sieving similarly sized molecules. Here, we demonstrate the exceptional separation performance of ionic liquid (IL)/graphene hybrid membranes for challenging separation of CO2 and N2. Notably, the ultrathin ILs afford dynamic tuning of the size and chemical affinity of nanopores while preserving the high permeance of the monolayer nanoporous graphene membranes. The hybrid membrane yields a high CO2 permeance of 4000 GPU and an outstanding CO2/N2 selectivity up to 32. This rational hybrid design provides a universal direction for broadening gas separation capability of atomically thin nanoporous membranes.}, number={11}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Guo, Wei and Mahurin, Shannon M. and Unocic, Raymond R. and Luo, Huimin and Dai, Sheng}, year={2020}, month={Oct}, pages={7995–8000} }
@article{misra_aguiar_gardner_sang_unocic_munshi_sampath_ferekides_scarpulla_2020, title={Cadmium Selective Etching in CdTe Solar Cells Produces Detrimental Narrow-Gap Te in Grain Boundaries}, volume={3}, ISSN={2574-0962 2574-0962}, url={http://dx.doi.org/10.1021/acsaem.9b02224}, DOI={10.1021/acsaem.9b02224}, abstractNote={Recent advances in design and processing technology have made possible commercialization of polycrystalline (px)-CdTe as a photovoltaic absorber. Grain boundaries (GBs) are the most prominent structural defects in these devices and undergo significant changes during device fabrication. However, the effects of device fabrication processes on these GBs are not entirely understood. Prevailing models of GBs in thin-film photovoltaics consider individual GBs to have homogeneous properties in their area. Here, using an aberration-corrected scanning transmission electron microscope (STEM)-based low-loss and core-loss electron energy-loss spectroscopy (EELS), we show that back-surface etching of CdTe leads to inhomogeneity within individual grain boundaries. We observe that etching the back surface leads to the conversion of a region of GBs from CdTe to an elemental Te, which has an only 0.33 eV band gap, as deep as 1 μm from the back surface. The presence of elemental Te in GBs this deep into the absorber layer will increase recombination in the absorber layer and limit the extractable open-circuit voltage, thus reducing device efficiency. However, additive methods for back contact formation such as deposition of Te, ZnTe, or other materials preserve the CdTe stoichiometry of the GBs. Thus, especially for the next generations of CdTe-based cells having longer minority carrier diffusion length and/or thinner absorber layers, additive back contacting methods are superior.}, number={2}, journal={ACS Applied Energy Materials}, publisher={American Chemical Society (ACS)}, author={Misra, Sudhajit and Aguiar, Jeffery A. and Gardner, Sophia and Sang, Xiahan and Unocic, Raymond R. and Munshi, Amit and Sampath, Walajabad S. and Ferekides, Chris S. and Scarpulla, Michael A.}, year={2020}, month={Jan}, pages={1749–1758} }
@article{gamler_leonardi_sang_koczkur_unocic_engel_skrabalak_2020, title={Effect of lattice mismatch and shell thickness on strain in core@shell nanocrystals}, volume={2}, ISSN={2516-0230}, url={http://dx.doi.org/10.1039/d0na00061b}, DOI={10.1039/D0NA00061B}, abstractNote={Bimetallic nanocrystals with a core@shell architecture are versatile, multifunctional particles. The lattice mismatch between core and shell regions induces strain, affecting the electronic properties of the shell metal, which is important for applications in catalysis. Here, we analyze this strain in core@shell nanocubes as a function of lattice mismatch and shell thickness. Coupling geometric phase analysis from atomic resolution scanning transmission electron microscopy images with molecular dynamics simulations reveals lattice relaxation in the shell within only a few monolayers and an overexpansion in the axial direction. Interestingly, many works report core@shell metal nanocatalysts with optimum performance at greater shell thicknesses. Our findings suggest that not strain alone but secondary factors, such as structural defects or structural changes in operando, may account for observed enhancements in some strain-engineered nanocatalysts; e.g., Rh@Pt nanocubes for formic acid electrooxidation.}, number={3}, journal={Nanoscale Advances}, publisher={Royal Society of Chemistry (RSC)}, author={Gamler, Jocelyn T. L. and Leonardi, Alberto and Sang, Xiahan and Koczkur, Kallum M. and Unocic, Raymond R. and Engel, Michael and Skrabalak, Sara E.}, year={2020}, pages={1105–1114} }
@article{zhou_lang_yoo_unocic_wu_li_2020, title={Fluid-Guided CVD Growth for Large-Scale Monolayer Two-Dimensional Materials}, volume={12}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/acsami.0c04125}, DOI={10.1021/acsami.0c04125}, abstractNote={Atmospheric pressure chemical vapor deposition (APCVD) has been used extensively for synthesizing two-dimensional (2D) materials, due to its low cost and promise for high-quality monolayer crystal synthesis. However, the understanding of the reaction mechanism and the key parameters affecting the APCVD processes is still in its embryonic stage. Hence, the scalability of the APCVD method in achieving large scale continuous film remains very poor. Here, we use MoSe2 as a model system and present a fluid guided growth strategy for understanding and controlling the growth of 2D materials. Through the integration of experiment and computational fluid dynamics (CFD) analysis in the full-reactor scale, we identified three key parameters: precursor mixing, fluid velocity and shear stress, which play a critical role in the APCVD process. By modifying the geometry of the growth setup, to enhance precursor mixing and decrease nearby velocity shear rate and adjusting flow direction, we have successfully obtained inch-scale monolayer MoSe2. This unprecedented success of achieving scalable 2D materials through fluidic design lays the foundation for designing new CVD systems to achieve the scalable synthesis of nanomaterials.}, number={23}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Zhou, Dong and Lang, Ji and Yoo, Nicholas and Unocic, Raymond R. and Wu, Qianhong and Li, Bo}, year={2020}, month={May}, pages={26342–26349} }
@article{hernández-escobar_unocic_kawasaki_boehlert_2020, title={High-pressure torsion processing of Zn–3Mg alloy and its hybrid counterpart: A comparative study}, volume={831}, ISSN={0925-8388}, url={http://dx.doi.org/10.1016/j.jallcom.2020.154891}, DOI={10.1016/j.jallcom.2020.154891}, journal={Journal of Alloys and Compounds}, publisher={Elsevier BV}, author={Hernández-Escobar, David and Unocic, Raymond R. and Kawasaki, Megumi and Boehlert, Carl J.}, year={2020}, month={Aug}, pages={154891} }
@article{unocic_jungjohann_mehdi_browning_wang_2020, title={In situ electrochemical scanning/transmission electron microscopy of electrode–electrolyte interfaces}, volume={45}, ISSN={0883-7694 1938-1425}, url={http://dx.doi.org/10.1557/mrs.2020.226}, DOI={10.1557/mrs.2020.226}, number={9}, journal={MRS Bulletin}, publisher={Springer Science and Business Media LLC}, author={Unocic, Raymond R. and Jungjohann, Katherine L. and Mehdi, B. Layla and Browning, Nigel D. and Wang, Chongmin}, year={2020}, month={Sep}, pages={738–745} }
@article{mukherjee_gamler_skrabalak_unocic_2020, title={Lattice Strain Measurement of Core@Shell Electrocatalysts with 4D Scanning Transmission Electron Microscopy Nanobeam Electron Diffraction}, volume={10}, ISSN={2155-5435 2155-5435}, url={http://dx.doi.org/10.1021/acscatal.0c00224}, DOI={10.1021/acscatal.0c00224}, abstractNote={Strain engineering enables the direct modification of the atomic bonding and is currently an active area of research aimed at improving the electrocatalytic activity. However, directly measuring the lattice strain of individual catalyst nanoparticles is challenging, especially at the scale of a single unit cell. Here, we quantitatively map the strain present in rhodium@platinum (core@shell) nanocube electrocatalysts using conventional aberration-corrected scanning transmission electron microscopy (STEM) and the recently developed technique of 4D-STEM nanobeam electron diffraction. We demonstrate that 4D-STEM combined with data pre-conditioning allows for quantitative lattice strain mapping with sub-picometer precision without the influence of scan distortions. When combined with multivariate curve resolution, 4D-STEM allows us to distinguish the nanocube core from the shell and to quantify the unit cell size as a function of distance from the core-shell interface. Our results demonstrate that 4D-STEM has significant precision and accuracy advantages in strain metrology of catalyst materials compared to aberration-corrected STEM imaging and is beneficial for extracting information about the evolution of strain in catalyst nanoparticles.}, number={10}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Mukherjee, Debangshu and Gamler, Jocelyn T. L. and Skrabalak, Sara E. and Unocic, Raymond R.}, year={2020}, month={Apr}, pages={5529–5541} }
@article{zhu_poplawsky_li_unocic_bland_taylor_locke_marquis_frankel_2020, title={Localized corrosion at nm-scale hardening precipitates in Al-Cu-Li alloys}, volume={189}, ISSN={1359-6454}, url={http://dx.doi.org/10.1016/j.actamat.2020.03.006}, DOI={10.1016/j.actamat.2020.03.006}, journal={Acta Materialia}, publisher={Elsevier BV}, author={Zhu, Yakun and Poplawsky, Jonathan D. and Li, Sirui and Unocic, Raymond R. and Bland, Leslie G. and Taylor, Christopher D. and Locke, Jenifer S. and Marquis, Emmanuelle A. and Frankel, Gerald S.}, year={2020}, month={May}, pages={204–213} }
@article{hu_fung_sang_unocic_ganesh_2020, title={Predicting synthesizable multi-functional edge reconstructions in two-dimensional transition metal dichalcogenides}, volume={6}, ISSN={2057-3960}, url={http://dx.doi.org/10.1038/s41524-020-0327-4}, DOI={10.1038/s41524-020-0327-4}, abstractNote={Abstract Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted tremendous interest as functional materials due to their exceptionally diverse and tunable properties, especially in their edges. In addition to the conventional armchair and zigzag edges common to hexagonal 2D materials, more complex edge reconstructions can be realized through careful control over the synthesis conditions. However, the whole family of synthesizable, reconstructed edges remains poorly studied. Here, we develop a computational approach integrating ensemble-generation, force-relaxation, and electronic-structure calculations to systematically and efficiently discover additional reconstructed edges and screen their functional properties. Using MoS 2 as a model system, we screened hundreds of edge-reconstruction to discover over 160 reconstructed edges to be more stable than the conventional ones. More excitingly, we discovered nine new synthesizable reconstructred edges with record thermodynamic stability, in addition to successfully reproducing three recently synthesized edges. We also find our predicted reconstructed edges to have multi-functional properties—they show near optimal hydrogen evolution activity over the conventional edges, ideal for catalyzing hydrogen-evolution reaction (HER) and also exhibit half-metallicity with a broad variation in magnetic moments, making them uniquely suitable for nanospintronic applications. Our work reveals the existence of a wide family of synthesizable, reconstructed edges in 2D TMDCs and opens a new materials-by-design paradigm of ‘intrinsic’ edge engineering multifunctionality in 2D materials.}, number={1}, journal={npj Computational Materials}, publisher={Springer Science and Business Media LLC}, author={Hu, Guoxiang and Fung, Victor and Sang, Xiahan and Unocic, Raymond R. and Ganesh, P.}, year={2020}, month={May} }
@article{jiang_bridges_unocic_pitike_cooper_zhang_lin_page_2020, title={Probing the Local Site Disorder and Distortion in Pyrochlore High-Entropy Oxides}, volume={143}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/jacs.0c10739}, DOI={10.1021/jacs.0c10739}, abstractNote={High-entropy oxides (HEOs) have attracted great interest in diverse fields because of their inherent opportunities to tailor and combine materials functionalities. The control of local order/disorder in the class is by extension a grand challenge toward realizing their vast potential. Here we report the first examples of pyrochlore HEOs with five M-site cations, for Nd2M2O7, in which the local structure has been investigated by neutron diffraction and pair distribution function (PDF) analysis. The average structure of the pyrochlores is found to be orthorhombic Imma, in agreement with radius-ratio rules governing the structural archetype. The computed PDFs from density functional theory relaxed special quasirandom structure models are compared with real space PDFs in this work to evaluate M-site order/disorder. Reverse Monte Carlo combined with ab initio molecular dynamics and Metropolis Monte Carlo simulations demonstrates that Nd2(Ta0.2Sc0.2Sn0.2Hf0.2Zr0.2)2O7 is synthesized with its M-site local to nanoscale order highly randomized/disordered, while Nd2(Ti0.2Nb0.2Sn0.2Hf0.2Zr0.2)2O7+x exhibits a strong distortion of the TiO6 octahedron and small degree of Ti chemical short-range order (SRO) on the subnanometer scale. Calculations suggest that this may be intrinsic, energetically favored SRO rather than due to sample processing. These results offer an important demonstration that the engineered variation of participating ions in HEOs, even among those with very similar radii, provides richly diverse opportunities to control local order/disorder motifs—and therefore materials properties for future designs. This work also hints at the exquisite level of detail that may be needed in computational and experimental data analysis to guide structure–property tuning in the emerging HEO materials class.}, number={11}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Jiang, Bo and Bridges, Craig A. and Unocic, Raymond R. and Pitike, Krishna Chaitanya and Cooper, Valentino R. and Zhang, Yuanpeng and Lin, De-Ye and Page, Katharine}, year={2020}, month={Dec}, pages={4193–4204} }
@article{zhou_chen_sterbinsky_mukherjee_unocic_tait_2020, title={Pt-Ligand single-atom catalysts: tuning activity by oxide support defect density}, volume={10}, ISSN={2044-4753 2044-4761}, url={http://dx.doi.org/10.1039/c9cy02594d}, DOI={10.1039/C9CY02594D}, abstractNote={Metal–ligand coordination stabilizes single atom Pt on pristine and defective TiO2 supports to impact local coordination and catalytic hydrosilylation activity.}, number={10}, journal={Catalysis Science & Technology}, publisher={Royal Society of Chemistry (RSC)}, author={Zhou, Xuemei and Chen, Linxiao and Sterbinsky, George E. and Mukherjee, Debangshu and Unocic, Raymond R. and Tait, Steven L.}, year={2020}, pages={3353–3365} }
@article{boebinger_yarema_yarema_unocic_unocic_wood_mcdowell_2020, title={Spontaneous and reversible hollowing of alloy anode nanocrystals for stable battery cycling}, volume={15}, ISSN={1748-3387 1748-3395}, url={http://dx.doi.org/10.1038/s41565-020-0690-9}, DOI={10.1038/s41565-020-0690-9}, number={6}, journal={Nature Nanotechnology}, publisher={Springer Science and Business Media LLC}, author={Boebinger, Matthew G. and Yarema, Olesya and Yarema, Maksym and Unocic, Kinga A. and Unocic, Raymond R. and Wood, Vanessa and McDowell, Matthew T.}, year={2020}, month={Jun}, pages={475–481} }
@article{li_dyck_unocic_ievlev_jesse_kalinin_2020, title={Statistical learning of governing equations of dynamics from in-situ electron microscopy imaging data}, volume={195}, ISSN={0264-1275}, url={http://dx.doi.org/10.1016/j.matdes.2020.108973}, DOI={10.1016/j.matdes.2020.108973}, abstractNote={Recent developments in (scanning) transmission electron microscopy (S)TEM have enabled in-situ investigations of nanoscale transformations. However, understanding the physical and chemical process defining matter transformations via the analysis of large-scale in-situ (S)TEM imaging data remains challenging. Here, we experimentally investigated a reaction-convection-diffusion model to track spatial-temporal patterns in (S)TEM videos of Pt nanoparticle formation and graphene contamination. Model parameters are pursued by statistical model selection algorithms that balance descriptive capability and model parsimony to aid interpretability and suppress overfitting. Besides conventional bottom-up analysis from individual entities, the integrated mathematical model based on partial differential equations (PDE) utilizing pixel level information provides complementary system status that may serve as a feedback for optimizing experiment setting.}, journal={Materials & Design}, publisher={Elsevier BV}, author={Li, Xin and Dyck, Ondrej and Unocic, Raymond R. and Ievlev, Anton V. and Jesse, Stephen and Kalinin, Sergei V.}, year={2020}, month={Oct}, pages={108973} }
@article{li_kahn_chen_sang_lei_passarello_oyedele_zakhidov_chen_chen_et al._2020, title={Surfactant-Mediated Growth and Patterning of Atomically Thin Transition Metal Dichalcogenides}, volume={14}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.0c00132}, DOI={10.1021/acsnano.0c00132}, abstractNote={The role of additives in facilitating the growth of conventional semiconducting thin films is well-established. Apparently, their presence is also decisive in the growth of two-dimensional transition metal dichalcogenides (TMDs), yet their role remains ambiguous. In this work, we show that the use of sodium bromide enables synthesis of TMD monolayers via a surfactant-mediated growth mechanism, without introducing liquefaction of metal oxide precursors. We discovered that sodium ions provided by sodium bromide chemically passivate edges of growing molybdenum disulfide crystals, relaxing in-plane strains to suppress 3D islanding and promote monolayer growth. To exploit this growth model, molybdenum disulfide monolayers were directly grown into desired patterns using predeposited sodium bromide as a removable template. The surfactant-mediated growth not only extends the families of metal oxide precursors but also offers a way for lithography-free patterning of TMD monolayers on various surfaces to facilitate fabrication of atomically thin electronic devices.}, number={6}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Li, Xufan and Kahn, Ethan and Chen, Gugang and Sang, Xiahan and Lei, Jincheng and Passarello, Donata and Oyedele, Akinola D. and Zakhidov, Dante and Chen, Kai-Wen and Chen, Yu-Xun and et al.}, year={2020}, month={Apr}, pages={6570–6581} }
@article{gamler_leonardi_ashberry_daanen_losovyj_unocic_engel_skrabalak_2019, title={Achieving Highly Durable Random Alloy Nanocatalysts through Intermetallic Cores}, volume={13}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.8b08007}, DOI={10.1021/acsnano.8b08007}, abstractNote={Pt catalysts are widely studied for the oxygen reduction reaction, but their cost and susceptibility to poisoning limit their use. A strategy to address both problems is to incorporate a second transition metal to form a bimetallic alloy; however, the durability of such catalysts can be hampered by leaching of non-noble metal components. Here, we show that random alloyed surfaces can be stabilized to achieve high durability by depositing the alloyed phase on top of intermetallic seeds using a model system with PdCu cores and PtCu shells. Specifically, random alloyed PtCu shells were deposited on PdCu seeds that were either the atomically random face-centered cubic phase (FCC A1, Fm3m) or the atomically ordered CsCl-like phase (B2, Pm3m). Precise control over crystallite size, particle shape, and composition allowed for comparison of these two core@shell PdCu@PtCu catalysts and the effects of the core phase on electrocatalytic durability. Indeed, the nanocatalyst with the intermetallic core saw only an 18% decrease in activity after stability testing (and minimal Cu leaching), whereas the nanocatalyst with the random alloy core saw a 58% decrease (and greater Cu leaching). The origin of this enhanced durability was probed by classical molecular dynamics simulations of model catalysts, with good agreement between model and experiment. Although many random alloy and intermetallic nanocatalysts have been evaluated, this study directly compares random alloy and intermetallic cores for electrocatalysis with the enhanced durability achieved with the intermetallic cores likely general to other core@shell nanocatalysts.}, number={4}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Gamler, Jocelyn T. L. and Leonardi, Alberto and Ashberry, Hannah M. and Daanen, Nicholas N. and Losovyj, Yaroslav and Unocic, Raymond R. and Engel, Michael and Skrabalak, Sara E.}, year={2019}, month={Apr}, pages={4008–4017} }
@article{dyck_ziatdinov_lingerfelt_unocic_hudak_lupini_jesse_kalinin_2019, title={Atom-by-atom fabrication with electron beams}, volume={4}, ISSN={2058-8437}, url={http://dx.doi.org/10.1038/s41578-019-0118-z}, DOI={10.1038/s41578-019-0118-z}, number={7}, journal={Nature Reviews Materials}, publisher={Springer Science and Business Media LLC}, author={Dyck, Ondrej and Ziatdinov, Maxim and Lingerfelt, David B. and Unocic, Raymond R. and Hudak, Bethany M. and Lupini, Andrew R. and Jesse, Stephen and Kalinin, Sergei V.}, year={2019}, month={Jun}, pages={497–507} }
@article{sang_li_puretzky_geohegan_xiao_unocic_2019, title={Atomic Insight into Thermolysis‐Driven Growth of 2D MoS2}, volume={29}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.201902149}, DOI={10.1002/adfm.201902149}, abstractNote={Abstract Understanding and controlling the transformations of transition metal dichalcogenides (TMDs) from amorphous precursors into two‐dimensional (2D) materials is important for guiding synthesis, directing fabrication, and tailoring functional properties. Here, the combined effects of thermal energy and electron beam irradiation are explored on the structural evolution of 2D MoS 2 flakes through the thermal decomposition of a (NH 4 ) 2 MoS 4 precursor inside an ultrahigh vacuum (10 −9 Torr) scanning transmission electron microscope (STEM). The influence of reaction temperature, growth substrate, and the initial precursor morphology on the resulting 2D MoS 2 flake morphology, edge structures, and point defects are explored. Although thermal decomposition occurs extremely fast at elevated temperatures and is difficult to capture using current STEM techniques, electron beam irradiation can induce local transformations at lower temperatures, enabling direct observation and interpretation of critical growth steps including oriented attachment and transition from single‐ to multilayer structures at atomic resolution. An increase in the number of layers of the MoS 2 flakes from island growth is investigated using electron beam irradiation. These findings provide insight into the growth mechanisms and factors that control the synthesis of few‐layer MoS 2 flakes through thermolysis and toward the prospect of atomically precise control and growth of 2D TMDs.}, number={52}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Sang, Xiahan and Li, Xufan and Puretzky, Alexander A. and Geohegan, David B. and Xiao, Kai and Unocic, Raymond R.}, year={2019}, month={May} }
@article{gamler_ashberry_sang_unocic_skrabalak_2019, title={Building Random Alloy Surfaces from Intermetallic Seeds: A General Route to Strain-Engineered Electrocatalysts with High Durability}, volume={2}, ISSN={2574-0970 2574-0970}, url={http://dx.doi.org/10.1021/acsanm.9b00901}, DOI={10.1021/acsanm.9b00901}, abstractNote={Pt-based catalysts are common in fuel cells but suffer from high cost and poor durability. To overcome these limitations, earth-abundant metals are often incorporated with Pt in core@shell architectures or through alloy formation. Here, the concepts of a core@shell architecture, alloyed surfaces, and high-durability intermetallics are integrated into one nanostructure platform using seed-mediated co-reduction (SMCR). Specifically, random alloy PtM (where M = Ni, Co, Cu, or Fe) shells are deposited on intermetallic PdCu B2 seeds. Control of shell thickness and Pt:M ratios is also demonstrated, providing a general route to strain-engineered alloyed surfaces. The performance of these nanocatalysts was evaluated for the oxygen reduction reaction (ORR) as a function of shell thickness and shell composition, where PtCu and PtNi shells showed a 230% and 270% activity increase, respectively, compared to the Pt reference. This evaluation is coupled with Tafel plot analysis which shows significant changes in the Tafel slopes, which indicate a shift in the rate-limiting step when a core@shell architecture is incorporated. Significantly, this work demonstrates the versatility of SMCR as a facile way to integrate a core@shell architecture, alloyed surfaces, and high-durability intermetallics within one platform.}, number={7}, journal={ACS Applied Nano Materials}, publisher={American Chemical Society (ACS)}, author={Gamler, Jocelyn T. L. and Ashberry, Hannah M. and Sang, Xiahan and Unocic, Raymond R. and Skrabalak, Sara E.}, year={2019}, month={Jun}, pages={4538–4546} }
@article{stricker_ke_wainright_unocic_savinell_2019, title={Current Density Distribution in Electrochemical Cells with Small Cell Heights and Coplanar Thin Electrodes as Used in ec-S/TEM Cell Geometries}, volume={166}, ISSN={0013-4651 1945-7111}, url={http://dx.doi.org/10.1149/2.0211904jes}, DOI={10.1149/2.0211904jes}, abstractNote={The electrochemical engineering aspects of high aspect ratio cells, such as those used in in situ electrochemical scanning transmission microscopy (ec-S/TEM) were examined, focusing on aspects that could cause non-uniform current distribution. Having a uniform current distribution across the working electrode is important for any spectroelectrochemical technique in order to provide accurate electrochemical information as well as structural electrolyte-electrode interface information. An analytical model was developed to determine current density distribution and a Wagner number was derived for a small cell height with coplanar electrodes. The main assumptions of this analysis are: 1) mass transport effects are negligible, 2) a uniform potential distribution in the direction of the cell height due to their small size, and 3) the working electrode potential is constant across its length. With our analysis, the assumptions were found to be reasonable. In addition, the effect of the conductivity and thickness of the thin film electrode and its potential effect on current density distribution have been analyzed. Now, with this work, high aspect ratio cells with a small cell heights and coplanar thin electrodes can be analyzed to determine their current density distribution.}, number={4}, journal={Journal of The Electrochemical Society}, publisher={The Electrochemical Society}, author={Stricker, Elizabeth A. and Ke, Xinyou and Wainright, Jesse S. and Unocic, Raymond R. and Savinell, Robert F.}, year={2019}, pages={H126–H134} }
@article{aguiar_gong_unocic_tasdizen_miller_2019, title={Decoding crystallography from high-resolution electron imaging and diffraction datasets with deep learning}, volume={5}, ISSN={2375-2548}, url={http://dx.doi.org/10.1126/sciadv.aaw1949}, DOI={10.1126/sciadv.aaw1949}, abstractNote={While machine learning has been making enormous strides in many technical areas, it is still massively underused in transmission electron microscopy. To address this, a convolutional neural network model was developed for reliable classification of crystal structures from small numbers of electron images and diffraction patterns with no preferred orientation. Diffraction data containing 571,340 individual crystals divided among seven families, 32 genera, and 230 space groups were used to train the network. Despite the highly imbalanced dataset, the network narrows down the space groups to the top two with over 70% confidence in the worst case and up to 95% in the common cases. As examples, we benchmarked against alloys to two-dimensional materials to cross-validate our deep-learning model against high-resolution transmission electron images and diffraction patterns. We present this result both as a research tool and deep-learning application for diffraction analysis.}, number={10}, journal={Science Advances}, publisher={American Association for the Advancement of Science (AAAS)}, author={Aguiar, J. A. and Gong, M. L. and Unocic, R. R. and Tasdizen, T. and Miller, B. D.}, year={2019}, month={Oct} }
@article{oyedele_yang_feng_haglund_gu_puretzky_briggs_rouleau_chisholm_unocic_et al._2019, title={Defect-Mediated Phase Transformation in Anisotropic Two-Dimensional PdSe2 Crystals for Seamless Electrical Contacts}, volume={141}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/jacs.9b02593}, DOI={10.1021/jacs.9b02593}, abstractNote={The failure to achieve stable Ohmic contacts in two-dimensional material devices currently limits their promised performance and integration. Here we demonstrate that a phase transformation in a region of a layered semiconductor, PdSe2, can form a contiguous metallic Pd17Se15 phase, leading to the formation of seamless Ohmic contacts for field-effect transistors. This phase transition is driven by defects created by exposure to an argon plasma. Cross-sectional scanning transmission electron microscopy is combined with theoretical calculations to elucidate how plasma-induced Se vacancies mediate the phase transformation. The resulting Pd17Se15 phase is stable and shares the same native chemical bonds with the original PdSe2 phase, thereby forming an atomically sharp Pd17Se15/PdSe2 interface. These Pd17Se15 contacts exhibit a low contact resistance of ∼0.75 kΩ μm and Schottky barrier height of ∼3.3 meV, enabling nearly a 20-fold increase of carrier mobility in PdSe2 transistors compared to that of traditional Ti/Au contacts. This finding opens new possibilities in the development of better electrical contacts for practical applications of 2D materials.}, number={22}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Oyedele, Akinola D. and Yang, Shize and Feng, Tianli and Haglund, Amanda V. and Gu, Yiyi and Puretzky, Alexander A. and Briggs, Dayrl and Rouleau, Christopher M. and Chisholm, Matthew F. and Unocic, Raymond R. and et al.}, year={2019}, month={May}, pages={8928–8936} }
@article{ashberry_gamler_unocic_skrabalak_2019, title={Disorder-to-Order Transition Mediated by Size Refocusing: A Route toward Monodisperse Intermetallic Nanoparticles}, volume={19}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/acs.nanolett.9b02610}, DOI={10.1021/acs.nanolett.9b02610}, abstractNote={Intermetallic nanoparticles are remarkable due to their often enhanced catalytic, magnetic, and optical properties, which arise from their ordered crystal structures and high structural stability. Typical syntheses of intermetallic nanoparticles include thermal annealing of the disordered counterpart in atmosphere (or vacuum) or colloidal syntheses, where the phase transformation is achieved in solution. Although both methods can produce intermetallic nanoparticles, there is difficulty in achieving monodisperse nanoparticles, which is critical to exploiting their properties for various applications. Here, we show that overgrowth on random alloy AuCu nanoparticles mediated by size refocusing yields monodisperse intermetallic AuCu nanoparticles. Size refocusing has been used in syntheses of semiconductor and upconverting nanocrystals to achieve monodisperse samples, but now we demonstrate size refocusing as a mechanism to achieve the disorder-to-order phase transformation in multimetallic nanoparticles. The phase transformation was monitored by time evolution experiments, where analysis of reaction aliquots with transmission electron microscopy and powder X-ray diffraction revealed the generation and dissolution of small nanoparticles coupled with an increase in the average size of the nanoparticles and conversion to the ordered phase. This demonstration advances the understanding of intermetallic nanoparticle formation in colloidal syntheses, which can expedite the development of electrocatalysts and magnetic storage materials.}, number={9}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Ashberry, Hannah M. and Gamler, Jocelyn T. L. and Unocic, Raymond R. and Skrabalak, Sara E.}, year={2019}, month={Aug}, pages={6418–6423} }
@inbook{sang_naguib_alhabeb_unocic_2019, title={Effect of Synthesis Methods on the Structure and Defects of Two-Dimensional MXenes}, ISBN={9783030190255 9783030190262}, url={http://dx.doi.org/10.1007/978-3-030-19026-2_7}, DOI={10.1007/978-3-030-19026-2_7}, booktitle={2D Metal Carbides and Nitrides (MXenes)}, publisher={Springer International Publishing}, author={Sang, Xiahan and Naguib, Michael and Alhabeb, Mohamed and Unocic, Raymond R.}, year={2019}, pages={111–123} }
@article{hernández-escobar_marcus_han_unocic_kawasaki_boehlert_2020, title={Effect of post-deformation annealing on the microstructure and micro-mechanical behavior of Zn–Mg hybrids processed by High-Pressure Torsion}, volume={771}, ISSN={0921-5093}, url={http://dx.doi.org/10.1016/j.msea.2019.138578}, DOI={10.1016/j.msea.2019.138578}, journal={Materials Science and Engineering: A}, publisher={Elsevier BV}, author={Hernández-Escobar, David and Marcus, Joshua and Han, Jae-Kyung and Unocic, Raymond R. and Kawasaki, Megumi and Boehlert, Carl J.}, year={2020}, month={Jan}, pages={138578} }
@article{brahlek_rimal_ok_mukherjee_mazza_lu_lee_ward_unocic_eres_et al._2019, title={Growth of metallic delafossite
PdCo
by molecular beam epitaxy}, volume={3}, ISSN={2475-9953}, url={http://dx.doi.org/10.1103/physrevmaterials.3.093401}, DOI={10.1103/physrevmaterials.3.093401}, abstractNote={The Pd, and Pt based ABO2 delafossites are a unique class of layered, triangular oxides with 2D electronic structure and a large conductivity that rivals the noble metals. Here, we report successful growth of the metallic delafossite PdCoO2 by molecular beam epitaxy (MBE). The key challenge is controlling the oxidation of Pd in the MBE environment where phase-segregation is driven by the reduction of PdCoO2 to cobalt oxide and metallic palladium. This is overcome by combining low temperature (300 {\deg}C) atomic layer-by-layer MBE growth in the presence of reactive atomic oxygen with a post-growth high-temperature anneal. Thickness dependence (5-265 nm) reveals that in the thin regime (<75 nm), the resistivity scales inversely with thickness, likely dominated by surface scattering; for thicker films the resistivity approaches the values reported for the best bulk-crystals at room temperature, but the low temperature resistivity is limited by structural twins. This work shows that the combination of MBE growth and a post-growth anneal provides a route to creating high quality films in this interesting family of layered, triangular oxides.}, number={9}, journal={Physical Review Materials}, publisher={American Physical Society (APS)}, author={Brahlek, Matthew and Rimal, Gaurab and Ok, Jong Mok and Mukherjee, Debangshu and Mazza, Alessandro R. and Lu, Qiyang and Lee, Ho Nyung and Ward, T. Zac and Unocic, Raymond R. and Eres, Gyula and et al.}, year={2019}, month={Sep} }
@article{gutiérrez-kolar_baggetto_sang_shin_yurkiv_mashayek_veith_shahbazian-yassar_unocic_2019, title={Interpreting Electrochemical and Chemical Sodiation Mechanisms and Kinetics in Tin Antimony Battery Anodes Using in Situ Transmission Electron Microscopy and Computational Methods}, volume={2}, ISSN={2574-0962 2574-0962}, url={http://dx.doi.org/10.1021/acsaem.9b00310}, DOI={10.1021/acsaem.9b00310}, abstractNote={Intermetallic compounds such as SnSb are promising anode materials for sodium ion batteries; however, their nanoscale sodiation mechanisms are not well understood. Here, we used a combination of in situ transmission electron microscopy (TEM), first-principles electronic structure calculations, computational thermodynamic modeling, and phase-field simulations to reveal the sodiation mechanisms and to quantify microstructural effects contributing to the underlying reaction kinetics in SnSb electrodes. During in situ sodiation experiments, the nanocrystalline SnSb thin films underwent a rapid amorphous phase transformation upon sodiation, as determined by in situ TEM and electron diffraction experiments. The Na+ diffusion coefficients were measured with and without an external electrical bias, and the data showed that an applied potential increased Na+ diffusion by an order of magnitude compared to solid-state diffusion. Furthermore, there was a distinct decrease in sodium diffusion upon the formation of the amorphous phase that resulted from a change in the local structure and grain boundaries. To further understand how the Na+ transport mechanism correlated with the changes observed in the SnSb thin films, phase-field modeling was used, which considered sodium diffusion within the grain boundaries together with their evolution and stress–strain state. These findings enhance our understanding of sodiation mechanisms within intermetallic anode materials for sodium ion battery applications.}, number={5}, journal={ACS Applied Energy Materials}, publisher={American Chemical Society (ACS)}, author={Gutiérrez-Kolar, Jacob S. and Baggetto, Loïc and Sang, Xiahan and Shin, Dongwon and Yurkiv, Vitaliy and Mashayek, Farzad and Veith, Gabriel M. and Shahbazian-Yassar, Reza and Unocic, Raymond R.}, year={2019}, month={Apr}, pages={3578–3586} }
@article{key_zhu_rouleau_unocic_xie_kacher_2020, title={Investigating local oxidation processes in Fe thin films in a water vapor environment by in situ liquid cell TEM}, volume={209}, ISSN={0304-3991}, url={http://dx.doi.org/10.1016/j.ultramic.2019.112842}, DOI={10.1016/j.ultramic.2019.112842}, journal={Ultramicroscopy}, publisher={Elsevier BV}, author={Key, Jordan W. and Zhu, Shixiang and Rouleau, Christopher M. and Unocic, Raymond R. and Xie, Yao and Kacher, Josh}, year={2020}, month={Feb}, pages={112842} }
@article{li_zhang_puretzky_yoshimura_sang_cui_li_liang_ghosh_zhao_et al._2019, title={Isotope-Engineering the Thermal Conductivity of Two-Dimensional MoS2}, volume={1}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.8b09448}, DOI={10.1021/acsnano.8b09448}, abstractNote={Isotopes represent a degree of freedom that might be exploited to tune the physical properties of materials while preserving their chemical behaviors. Here, we demonstrate that the thermal properties of two-dimensional (2D) transition-metal dichalcogenides can be tailored through isotope engineering. Monolayer crystals of MoS2 were synthesized with isotopically pure 100Mo and 92Mo by chemical vapor deposition employing isotopically enriched molybdenum oxide precursors. The in-plane thermal conductivity of the 100MoS2 monolayers, measured using a non-destructive, optothermal Raman technique, is found to be enhanced by ∼50% compared with the MoS2 synthesized using mixed Mo isotopes from naturally occurring molybdenum oxide. The boost of thermal conductivity in isotopically pure MoS2 monolayers is attributed to the combined effects of reduced isotopic disorder and a reduction in defect-related scattering, consistent with observed stronger photoluminescence and longer exciton lifetime. These results shed light on the fundamentals of 2D nanoscale thermal transport important for the optimization of 2D electronic devices.}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Li, Xufan and Zhang, Jingjie and Puretzky, Alexander A. and Yoshimura, Anthony and Sang, Xiahan and Cui, Qiannan and Li, Yuanyuan and Liang, Liangbo and Ghosh, Avik W. and Zhao, Hui and et al.}, year={2019}, month={Jan} }
@article{chen_lin_zhang_jie_mullins_sang_yang_jafta_bridges_hu_et al._2019, title={Mechanochemical Synthesis of High Entropy Oxide Materials under Ambient Conditions: Dispersion of Catalysts via Entropy Maximization}, volume={1}, ISSN={2639-4979 2639-4979}, url={http://dx.doi.org/10.1021/acsmaterialslett.9b00064}, DOI={10.1021/acsmaterialslett.9b00064}, abstractNote={The solid-solution metal oxide (NiMgCuZnCo)O is the first known high-entropy (HE) metal oxide synthesized, forming a poster child of the emerging high-entropy oxide materials, which is derived from high-temperature synthesis methodologies (>900 °C). In this work, we report the mechanochemical synthesis of this known HE metal oxide (NiMgCuZnCo)O under ambient conditions. The advantage of this approach was further demonstrated by the introduction of up to 5 wt % noble metal into (NiMgCuZnCo)O, as single atoms or nanoclusters, which showed good stability at high temperature and produced a high catalytic activity in the hydrogenation of atmospheric CO2 to CO. The latter work demonstrated the unique advantage of using HE materials to disperse catalysis centers.}, number={1}, journal={ACS Materials Letters}, publisher={American Chemical Society (ACS)}, author={Chen, Hao and Lin, Wenwen and Zhang, Zihao and Jie, Kecheng and Mullins, David R. and Sang, Xiahan and Yang, Shi-Ze and Jafta, Charl J. and Bridges, Craig A. and Hu, Xiaobing and et al.}, year={2019}, month={May}, pages={83–88} }
@article{zeng_chen_zhang_li_mendes_sang_luo_ming_fu_du_et al._2019, title={Molecular Scaffold Growth of Two-Dimensional, Strong Interlayer-Bonding-Layered Materials}, volume={1}, ISSN={2096-5745}, url={http://dx.doi.org/10.31635/ccschem.019.20180003}, DOI={10.31635/ccschem.019.20180003}, abstractNote={Open AccessCCS ChemistryRESEARCH ARTICLE1 Apr 2019Molecular Scaffold Growth of Two-Dimensional, Strong Interlayer-Bonding-Layered Materials Mengqi Zeng†, Yunxu Chen†, Enze Zhang, Jiaxu Li, Rafael G. Mendes, Xiahan Sang, Shulin Luo, Wenmei Ming, Yuhao Fu, Mao-Hua Du, Lijun Zhang, David S. Parker, Raymond R. Unocic, Kai Xiao, Chenglai Wang, Tao Zhang, Yao Xiao, Mark H. Rümmeli, Faxian Xiu and Lei Fu Mengqi Zeng† College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 (China) , Yunxu Chen† College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 (China) , Enze Zhang State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433 (China) , Jiaxu Li College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 (China) , Rafael G. Mendes IFW Dresden, P.O. Box 270116, Dresden 01069 (Germany) , Xiahan Sang Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States) , Shulin Luo State Key Laboratory of Superhard Materials, Key Laboratory of Automobile Materials of MOE, and College of Materials Science and Engineering, Jilin University, Changchun 130012 (China) , Wenmei Ming Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States) , Yuhao Fu State Key Laboratory of Superhard Materials, Key Laboratory of Automobile Materials of MOE, and College of Materials Science and Engineering, Jilin University, Changchun 130012 (China) , Mao-Hua Du Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States) , Lijun Zhang State Key Laboratory of Superhard Materials, Key Laboratory of Automobile Materials of MOE, and College of Materials Science and Engineering, Jilin University, Changchun 130012 (China) , David S. Parker Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States) , Raymond R. Unocic Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States) , Kai Xiao Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States) , Chenglai Wang College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 (China) , Tao Zhang College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 (China) , Yao Xiao College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 (China) , Mark H. Rümmeli IFW Dresden, P.O. Box 270116, Dresden 01069 (Germany) Soochow Institute for Energy and Materials Innovation, College of Physics, Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology & Suzhou Key Laboratory for Advanced Carbon Materials and Wearable Energy Technologies, Soochow University, Suzhou 215006 (China) Centre of Polymer and Carbon Materials, Polish Academy of Sciences, Zabrze 41-819 (Poland) , Faxian Xiu State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433 (China) and Lei Fu *Corresponding author: E-mail Address: [email protected] College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 (China) https://doi.org/10.31635/ccschem.019.20180003 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Currently, most two-dimensional (2D) materials that are of interest to emergent applications have focused on van der Waals–layered materials (VLMs) because of the ease with which the layers can be separated (e.g., graphene). Strong interlayer-bonding-layered materials (SLMs) in general have not been thoroughly explored, and one of the most critical present issues is the huge challenge of their preparation, although their physicochemical property transformation should be richer than VLMs and deserves greater attention. MAX phases are a classical kind of SLM. However, limited to the strong interlayer bonding, their corresponding 2D counterparts have never been obtained, nor has there been investigation of their fundamental properties in the 2D limitation. Here, the authors develop a controllable bottom-up synthesis strategy for obtaining 2D SLMs single crystal through the design of a molecular scaffold with Mo2GaC, which is a typical kind of MAX phase, as an example. The superconducting transitions of Mo2GaC at the 2D limit are clearly inherited from the bulk, which is consistent with Berezinskii–Kosterlitz–Thouless behavior. The authors believe that their molecular scaffold strategy will allow the fabrication of other high-quality 2D SLMs single crystals, which will further expand the family of 2D materials and promote their future application. Download figure Download PowerPoint Introduction Graphene provided humankind the first exposure to materials with a two-dimensional (2D) extended structure and transformed the landscape of condensed-matter physics.1–3 In the past 10 years, graphene analogues, such as hexagonal boron nitride, transition metal dichalcogenides, and black phosphorus, have been continually investigated and have brought about various unique transport properties.4–8 These 2D films are all van der Waals–layered materials (VLMs), where the bonding within a layer is covalent whereas the interlayer bonding occurs through weak noncovalent (van der Waals) interactions, thus allowing individual layers to be easily separated and to be thinned to atomic thickness. Meanwhile, there exists another kind of layered materials where their interlayer bonding belongs to strong interaction, such as covalent bonding. We call them strong interlayer-bonding-layered materials (SLMs). At first glance, they will be prohibited from existing as an atomic layer. Exfoliation strategies that are applicable for producing few layer or even monolayer VLMs are ineffective for obtaining 2D SLMs, while their direct synthesis usually leads to bulk material formation. Considering that 2D-layered materials with stronger interlayer coupling exhibit higher sensitivity to layer number,9,10 the transformation of SLMs to 2D systems should be more exciting and deserves an in-depth investigation because the surficial unsaturated dangling bonds will lead to the enhanced surface states or surface relaxation or reconstruction11,12 and even improved performance.13–15 Providing the establishment of a controllable strategy for fabricating SLMs is found, the discovery of such materials in the 2D limit will certainly redefine the landscape of 2D-layered materials in general. MAX phases (Mn+1AXn; M is the transition metal, A is the p-block element, and X is the C or N) are typical SLMs.16–18 The layered structure and the mixed metallic-covalent nature of the M–X bonds, which are exceptionally strong, together with M–A bonds allow MAX phases to exhibit many excellent properties.19,20 MAX phases combine the property of metal and ceramic, such as being electrically and thermally conductive, exceptionally damage tolerant, lightweight, and able to maintain strength at high temperature.16,21–23 This provides a broad array of applications of this material family, such as magnetism transport24 and new optoelectronic devices,25 as well as ohmic contacts for semiconductor electronics26 and as a heterogeneous catalyst for dehydrogenation of alkanes27 in harsh high-temperature environments. Some MAX phases also display self-healing behavior28 and reversible deformation.29 However, the metallic or covalent bonds between the layers in the MAX phases are too strong to be broken by shear or any similar mechanical means,20,30 which is a great barrier to realize their two-dimensionalization. The top-down chemical exfoliating or etching methods can only produce its derivatives, MXenes.31 The bottom-up synthesis also has not realized the fabrication of 2D MAX phase single crystals with high quality.18,26,27,32–36 Thus far, the fabrication of 2D MAX phase single crystals has never been achieved, which significantly hampers the further exploitation of their fundamental properties and the promotion of their application in the 2D limit. Here, we present a precise bottom-up synthesis strategy for obtaining 2D ultrathin SLM single crystals via the design of a molecular scaffold. We took Mo2GaC, a typical kind of MAX phase, as an example. We preset a precise molecular scaffold—an ultrathin crystalline Ga2O3 layer—to achieve a confined chemical reaction. Based on a designed molecular scaffold, the chemical reaction will occur at the scaffold during a chemical vapor deposition (CVD) process. For the first time, we obtained Mo2GaC single crystals with a thickness comparable to that of the unit cell, and these flakes showed very high quality as indicated by transmission electron microscopy (TEM) structural investigations. In addition, the superconducting transport properties of the ultrathin Mo2GaC-layered single crystal in the 2D limit were clearly observed, such as Berezinskii–Kosterlitz–Thouless (BKT) behavior and strong anisotropy with magnetic field orientation. What's more, our as-obtained 2D Mo2GaC is the first CVD-grown high-quality superconducting single crystal with strong interlayer interaction, which will offer an ideal platform for the exploration of the unprecedented physical properties, such as localization of electrons or Cooper pairs, transition–temperature oscillations caused by quantum size effects, excess conductivity originating from superconducting fluctuations, and quantum phase transitions at zero temperature.37 We believe such a design through the use of a scaffold will allow the fabrication of other high-quality 2D SLM single crystals, which will further expand the family of 2D materials and promote their future application. Molecular scaffold growth of 2D, strong interlayer-bonding Mo2GaC single crystal We design a precise molecular scaffold, an ultrathin Ga2O3 layer, to construct the Mo2GaC crystals, as shown in Figure 1. The design of the molecular scaffold is the key. Main group III metals, such as gallium (Ga), naturally form a thin surface metal oxide layer on contact with oxygen in the atmosphere, which creates a physical barrier to corrosion or further oxidation in most environments. Ga is an active metal with an ultralow melting point and tends to be oxidized easily with time under ambient atmospheric conditions.38 The oxidized layer of Ga is initially one-unit-cell thick and reaches a saturation state, leading to the formation of an intimate self-passivated oxidation layer. The thickness of the oxidation layer is just a few nanometers and does not increase over time.39,40 At temperatures above 300°C, the as-formed amorphous or poorly crystallized oxide layer at room temperature is transformed into a crystalline β-Ga2O3 layer as a molecular scaffold to build the Mo2GaC crystals with unit cell thickness (). The existence of the ultrathin Ga2O3 layer on the metallic Ga surface is identified by an X-ray photoelectron spectroscopy (XPS) depth analysis. The Ga 3p signal attributed to the formation of Ga2O3 could only be detected on the surface and disappeared after a ∼150 s Ar-ion sputtering to remove the superficial metal oxide (). With such an ultrathin Ga2O3 layer serving as the molecular scaffold and with methane (CH4) as the carbon source, large-area ultrathin Mo2GaC crystals embedded in the Ga2O3 molecular scaffold were obtained at 1000°C. The high temperature allows the Ga underneath the ultrathin Ga2O3 layer to stay in a liquid state, and a Mo–Ga alloy forms simultaneously, ensuring decomposition of the CH4. Subsequently, some Mo atoms diffuse from the Ga–Mo liquid alloy bulk to the surface of the liquid Ga, which react with the ultrathin Ga2O3 film and adsorbed C atoms (from decomposed CH4) to form Mo2GaC crystals, as shown in the schematic diagram (Figure 1). Figure 1 | Schematic of the growth of 2D, strong interlayer-bonding Mo2GaC single crystals via the design of molecular scaffold. Download figure Download PowerPoint The ultrathin crystalline Ga2O3 layer acts as a molecular scaffold to enable the bottom-up synthesis of 2D Mo2GaC single crystals. Traditional synthesis requires Mo and C powders to react with liquid Ga over a period of up to 4 weeks,41 which is inefficient. To confirm the important role of the Ga2O3 molecular scaffold in the growth of Mo2GaC, contrast experiments were conducted. It was found that Mo2GaC would not form without the Ga2O3 layer (). Accurate Auger electronic spectroscopy (AES) further helps to confirm the as-proposed growth process. When not reacting with the Mo and C atoms, the Ga2O3 film remains well preserved (). We ascribe this to its compactness and passivation nature. The compactness of the atomically thin Ga2O3 molecular scaffold not only allows an extremely low amount of Mo diffusing across the defect site to be involved in the reaction, but also ensures an effective reaction to form the high-quality 2D Mo2GaC crystals with few defects and high phase purity. Because the as-formed Mo2GaC crystals are highly related to the Ga2O3 molecular scaffold, the thickness of Mo2GaC crystals can be tuned by adjusting the thickness of the Ga2O3 layer. The Ga2O3 layers with different thickness are obtained by altering the duration of preoxidization of the liquid Ga. We conducted the preoxidization process at a temperature of 50°C for different durations and subsequently performed the growth process under the same conditions. The thickness of the oxide layer was identified by detecting the signal of O1s peak using an XPS depth analysis (). The statistics of the relationship between etching duration and the peroxidation duration is also given in the supplementary information (). When the preoxidization duration was increased to 10 min, the Ga2O3 layer stopped growing, verifying the self-passivation behavior of Ga. The relationship between the thickness of the as-derived Mo2GaC and the peroxidation duration also demonstrated the self-passivating growth behavior (). The as-grown crystals were initially examined using a scanning electron microscopy (SEM) as shown in Figure 2a. Large-scale distributed Mo2GaC crystals with lateral sizes of over 10 μm can be successfully obtained from our designed molecular scaffold synthesis approach. Figure 2b shows the typical circular shape of the Mo2GaC crystals due to the growth happening on an isotropic liquid growth substrate.42 Figure 2c shows the corresponding atomic force microscope (AFM) image. The thickness of the flake is around 2.2 nm, which is consistent with the value of the Mo2GaC unit cell. In addition, XPS spectra of the as-synthesized Mo2GaC crystals that were transferred onto 300 nm SiO2/Si were collected to confirm the chemical composition of the as-obtained ultrathin crystal. Figure 2d shows a typical XPS spectrum of the Mo 3d edge, which exhibits the primary spin-orbital components 3d5/2 and 3d3/2 located at 227.9 and 231.1 eV, respectively. The Ga 3p3/2 and 3p1/2 components show dominant peaks at the binding energies of 104.0 and 107.1 eV, respectively (Figure 2e). Ga2O3 is also indicated by shoulder peaks at the high binding energy side of the Ga 3p1/2 peak, which we attribute to an unreacted ultrathin Ga2O3 molecular scaffold. The characteristic carbide carbon peak from a Mo2GaC crystal is observed at 283.3 eV, as shown in Figure 2f. A C 1s peak at 284.8 eV is also observed, which probably originates from carbon adsorbates from the atmosphere. All these peaks are in accordance with the literature.43,44 In addition, the AES mapping further confirms the uniform elemental distribution from an individual Mo2GaC (). Figure 2 | Large-area 2D, strong interlayer-bonding Mo2GaC crystals fabricated by design from a molecular scaffold via CVD growth. (a) A low-magnification SEM image of the Mo2GaC crystals distributed on Ga–Mo substrates. (b) A high-magnification SEM image of a typical circular Mo2GaC crystal. (c) A typical AFM image of the ultrathin Mo2GaC crystal. The thickness of the flake is 2.2 nm. (d–f) XPS spectra for ultrathin Mo2GaC crystal of Mo 3d peaks, Ga 3p peaks, and C 1s peaks, respectively. Download figure Download PowerPoint Characterization of 2D, strong interlayer-bonding Mo2GaC single crystals High-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), energy-dispersive spectrometry (EDS), and electron diffraction were used to evaluate the quality and crystal structure of these ultrathin Mo2GaC crystals. Figure 3a shows a low-magnification TEM image of a Mo2GaC crystal. We recorded the selected area electron diffraction (SAED) pattern and convergent beam electron diffraction (CBED) pattern. The inset in Figure 3a shows the SAED pattern and the derived in-plane lattice parameters of the crystal, a and b are equal and their value is about 2.97 Å. The lattice parameter c is derived from the CBED pattern (Figure 3b) and its value is 13.18 Å, according to the equation, r2 + (λ−1 − c−1)2 = λ−2, where λ = 0.00197 nm is the electron wavelength in a 300 kV TEM, and r = 27.78 nm−1 is the radius of the first-order Laue ring. These lattice parameters are consistent with those of a hexagonal Mo2GaC crystal. The EDS spectrum extracted from the crystal indicates that the crystal was composed of Mo, Ga, and C with an atomic ratio of ∼2∶1∶1, as seen in Figure 3c. Figure 3 | The atomic structure of 2D, strong interlayer-bonding Mo2GaC crystals. (a) A low-magnification HAADF-STEM image of a Mo2GaC single crystal. (b) CBED pattern of the Mo2GaC crystal in (a), showing the radius of the first-order Laue ring of 27.78 nm−1. (c) A typical EDS spectrum collected from the Mo2GaC crystal. (d) An atomic resolution HAADF-STEM image of the Mo2GaC crystal acquired along the c axis. (e) The atomic structure simulation of Mo2GaC crystal along the c axis. (f) Comparison between line profiles extracted from experimental (solid green line) and simulated (brown dashed line) images. (g) A HAADF-STEM atomic resolution image of the cross-section of the ultrathin Mo2GaC crystal. The inset shows the SAED pattern. (h) Magnified HAADF-STEM atomic image shows the cross-sectional structure of the lamella. The inset corresponds to the atomic structure models indicating the aligning positions of the Ga, Mo, and C atoms in the stacking sequence. (i) Schematic of the unit cell of a Mo2GaC crystal. Download figure Download PowerPoint The aberration-corrected atomic resolution, high-angle, annular dark-field STEM (HAADF-STEM) image further reveals the atomic structure of the 2D, strong interlayer-bonding Mo2GaC single crystal. Mo2GaC is a typical superconducting MAX phase with two formula units per unit cell.45 In this compound, the hexagonal close-packed lattice is formed by six Mo atoms. The C and Mo atoms form an orthorhombic structure [Mo6C], with C atoms located at the octahedral sites surrounded by six Mo atoms. It is worth noting that the contrast between Ga and Mo sites is not obvious because there are always two Mo atoms overlapping with one Ga atom, which makes the intensity of six atoms around C atoms similar in intensity within the STEM image. C atoms are not visible due to their low element number compared with surrounded heavier atoms of Ga and Mo in the crystal. Here, the simulated Mo2GaC structure is consistent with the experimental results. It is assumed that the electron beam irradiates the crystal from the Ga atom side, as shown in Figure 3f. Details of the image simulation are shown in the supplementary information (). The line scanning profiles taken directly from the experimental (solid green line) and simulated (brown dashed line) images are in good agreement. In addition, the near close-packed Mo atoms are interleaved with a single layer of pure Ga element. Figure 3g shows a high-magnification HAADF-STEM atomically resolved cross-section view of the flakes. The inset shows the SAED pattern from the cross-section of the Mo2GaC lamella. The lattice parameters a and c are calculated to be 2.97 and 13.18 Å, respectively, which is consistent with the analysis described previously. The STEM image in Figure 3h acquired at a higher magnification clearly shows the sequential ordering of the close-packed layers, which agrees well with the simulated structure shown in Figure 3h. To validate the single crystal structure, a series of SAED patterns were acquired from different sample regions, and all of them showed the same sixfold symmetry with a consistent orientation (). Moreover, EDS mapping shows C–K, Mo–L, and Ga–L signals, indicating that the crystal is comprised of uniformly distributed C, Mo, and Ga (). Superconductivity of 2D, strong interlayer-bonding Mo2GaC single crystals The high-quality ultrathin Mo2GaC crystals provide an ideal system to probe the intrinsic transport properties in the 2D limit. In this work, a four terminal device was fabricated based on a Mo2GaC single crystal with a thickness of 12.4 nm for superconducting property measurements, as shown in . The collected normalized resistance versus temperature R/R-N(T) curve in the superconducting transition regime is shown in Figure 4a. The resistance displays a decline at 4.06 K and decreases to zero at 3.1 K. This provides convincing evidence for the existence of superconductivity. The transport properties of Mo2GaC single crystals with different thicknesses are also exhibited. When the thickness is down to 11.2 or 8.9 nm, the superconductive transitions can still be observed and the corresponding transition temperatures (Tc) are 2.75 and 2.33 K, respectively. Figure 4 | 2D superconducting characteristics of the 2D strong interlayer-bonding Mo2GaC crystal. (a) R(T), normalized to the normal state resistance at T = 10 K, of Mo2GaC crystals with different thickness. (b) Upper critical field Hc2 versus temperature for a magnetic field applied perpendicular to the sample plane and parallel to the plane. The dashed lines correspond to the theoretical curves based on the 2D GL theory. (c) Upper critical field Hc2 as a function of magnetic field angle θ. The dashed line is a fit to the data following the Tinkham formula for a 2D superconductor. The inset shows the arrangement of the experimental configuration and the definition of the magnetic field direction θ. (d) Voltage–current characteristics at different temperatures on a logarithmic scale. The dashed blue line indicates the ohmic behavior expected at high temperature. The solid blue line corresponds to the V/I3 behavior expected at the BKT transition. (e) Temperature dependence of the exponent α deduced from the power-law behavior, V ∝ Iα. As indicated by the red dashed line, α approaches 3 at T = 2.93 K. (f) Temperature dependence of the resistance. The blue line is a fit to the data based on the BKT transition, yielding TBKT of 2.87 K. Download figure Download PowerPoint To clarify why the superconducting Tc decreases with the thickness, first principles calculations of electron–phonon coupling for the ultrathin film and the bulk phases have been conducted according to the Allen–Dynes formula,46 which is modified from BCS theory.47 Based on the experimentally observed Mo-terminated surface of the thin Mo2GaC single crystal, an ultrathin film with a minimal thickness represented by a seven atomic-layer MoCMo–Ga–MoCMo slab model was studied and compared with the bulk phase. According to the calculations, Tc will decrease with the thickness of the Mo2GaC due to the weaker electron–phonon coupling in the slab, which can be attributed to the Ga deficiency and structural relaxation within the slab. The slab is Ga deficient compared with the bulk because it is terminated by Mo2C at both the front and the back surfaces. Compared with the strong Mo–C bonds, Ga is weakly bonded to the adjacent Mo2C layers. As such, the Ga-related phonons are soft. The reduction in Ga-related soft phonons in the Ga-deficient Mo-terminated slab contributes strongly to the reduction of the electron–phonon coupling and the Tc in the slab. Further analyses of the structures of the bulk and the slab reveal that the Mo–C bond length on the surfaces of the slab (2.08 Å) is shorter than that in the bulk (2.12 Å) as a result of the relaxation of the surfaces and the in-plane crystal lattice. From the SAED patterns (the inset of Figure 3a,g), we can derive the in-plane lattice constant to be 2.97 Å, which is close to the calculated value (3.03 Å) corresponding to the 2D Mo2GaC. This leads to stronger Mo-related phonons, which contribute to the weaker electron–phonon coupling in the slab. The Ga deficiency and the enhanced Mo–C bonding on the surface of the slab and their influence on the electron–phonon coupling should become less significant with increasing film thickness. The detailed calculations are shown in . The foregoing analysis also suggests that it should be possible to raise the superconducting Tc substantially by terminating the structure with a Ga end layer, which would induce soft Ga-related phonons and thereby more Eliashberg spectral weight at low energy, raising the electron–phonon coupling constant λ. Temperature-dependent resistance under different magnetic fields with the direction perpendicular to the crystal surface was also probed. As shown in , the transition temperature would drop as the applied magnetic field increases and the superconducting transition region broadens. When the magnetic field increases to 0.5 T, the superconducting transition behavior disappears. To reveal the dimensionality of the intrinsic superconductivity in our crystals, the relationship between the superconducting transition and the angle of the applied magnetic field on the crystals is further investigated.48 We recorded the upper critical field for superconductivity (Hc2) at selected angles (θ) at 1.9 K for a 12.4 nm thick Mo2GaC crystal, where θ is the angle between the crystal plane and the applied magnetic field, as indicated in the inset of Figure 4c. As shown in , the superconductivity transition shifts to higher fields with a decreasing angle. When the rotated magnetic field direction is parallel to the sample plane (θ = 0°), Hc2 is obviously enhanced, from which the existence of strong anisotropy is confirmed.48,49 Furthermore, the Ginzburg–Landau (GL) coherence length (ξGL) and effective superconducting thickness (dSC) of the Mo2GaC crystals can be used to analyze the character of the 2D superconductor. They can be derived from the temperature-dependent upper critical fields in the directions perpendicular (Hc2,⊥) and parallel to the plane. The superconducting critical transition field in the perpendicular direction or in the parallel direction under different temperatures (Hc2) (which is defined as the field at which the resistance drops to 10% of the normal state value just above the onset) is extracted from the magnetic-field–dependent resistance characteristics at different temperatures (). The corresponding temperature-dependent upper critical field (Hc2[T]) values are provided in Figure 4b. For the perpendicular magnetic field condition, Hc2,⊥ a linear dependence to T is observed, which is in accordance with the standard linearized GL theory for 2D superconductors50 H c 2 , ⊥ ( T ) = Φ 0 2 π ξ GL ( 0 ) 2 ( 1 − T T c ) where Φ0 is the magnetic flux quantum and ξGL(0) is the GL in-plane coherence length at a temperature of 0 K. The value of ξGL(0) is calculated to be 18.0 ± 0.3 nm from the fitted curve of Hc2,⊥(T), whereas for the parallel field condition, the temperature-dependent Hc2,∥ relationship fits the following formula H c 2 , ∥ ( T ) = Φ 0 12 2 π ξ GL ( 0 ) d SC ( 1 − T T c ) 1 / 2 where dSC is the effective superconducting thickness. The value of dSC is extracted to be 12.4 ± 0.1 nm from the analysis and fittings of (T) curve. Notably, this value is in excellent agreement with the measured thickness of our test sample. The value of dSC is smaller than that of ξGL(0), demonstrating good agreement with 2D superconducting behavior. Moreover, the function relationship between Hc2 and θ at a temperature of 1.9 K is described in Figure 4c. When the applied field is parallel to the crystal surface, the upper critical field exhibits a maximum. Careful fitting of the Hc2(θ) data is consistent with the Tinkham formula,50 namely, | H c 2 ( θ ) sin θ H c 2 , ⊥ | + ( H c 2 ( θ ) cos θ}, number={1}, journal={CCS Chemistry}, publisher={Chinese Chemical Society}, author={Zeng, Mengqi and Chen, Yunxu and Zhang, Enze and Li, Jiaxu and Mendes, Rafael G. and Sang, Xiahan and Luo, Shulin and Ming, Wenmei and Fu, Yuhao and Du, Mao-Hua and et al.}, year={2019}, month={Apr}, pages={117–127} }
@article{nandi_sang_hoglund_unocic_molodov_howe_2019, title={Nanoscale mapping of the electron density at Al grain boundaries and correlation with grain-boundary energy}, volume={3}, ISSN={2475-9953}, url={http://dx.doi.org/10.1103/physrevmaterials.3.053805}, DOI={10.1103/physrevmaterials.3.053805}, abstractNote={Grain-boundary (GB) structures and energies are often calculated and have revealed correlations between the GB energy and change in electron density at the GB. In this work, the plasmon peak in valence electron energy-loss spectroscopy (VEELS) was used to determine the variation in electron density across four well-characterized GBs in Al, spanning a range of known GB energies. The results show that the plasmon energy is lower at the GB than in the adjacent grains due to a decrease in electron density, and the GB energy increases proportional to the density decrease. The decrease in electron density also extends further into adjacent grains with increasing GB energy, extending beyond the geometric changes, or physical width, revealed by electron microscopy. Plasmon damping also increases with increasing GB energy, indicative of increasing disruption of the electron density with increasing GB energy. These results demonstrate that VEELS can be a valuable tool for detecting small electron density changes at GBs, and this change clearly influences, and is correlated to, the GB energy.}, number={5}, journal={Physical Review Materials}, publisher={American Physical Society (APS)}, author={Nandi, Proloy and Sang, Xiahan and Hoglund, Eric R. and Unocic, Raymond R. and Molodov, Dmitri A. and Howe, James M.}, year={2019}, month={May} }
@article{hu_fung_sang_unocic_ganesh_2019, title={Superior electrocatalytic hydrogen evolution at engineered non-stoichiometric two-dimensional transition metal dichalcogenide edges}, volume={7}, ISSN={2050-7488 2050-7496}, url={http://dx.doi.org/10.1039/c9ta05546k}, DOI={10.1039/C9TA05546K}, abstractNote={Compared with the stoichiometric edges (ZZSe and ZZMo), there is a wider family of synthesizable non-stoichiometric MoSe2edges, where the degree of non-stoichiometry can be tuned to potentially achieve optimal HER activity.}, number={31}, journal={Journal of Materials Chemistry A}, publisher={Royal Society of Chemistry (RSC)}, author={Hu, Guoxiang and Fung, Victor and Sang, Xiahan and Unocic, Raymond R. and Ganesh, P.}, year={2019}, pages={18357–18364} }
@article{phillip_ruther_sang_wang_unocic_westover_daniel_veith_2019, title={Synthesis of Ni-Rich Thin-Film Cathode as Model System for Lithium Ion Batteries}, volume={2}, ISSN={2574-0962 2574-0962}, url={http://dx.doi.org/10.1021/acsaem.8b01982}, DOI={10.1021/acsaem.8b01982}, abstractNote={We demonstrate a process to prepare model electrodes of the Ni-rich layered compound LiNi0.6Mn0.2Co0.2O2. These thin-film cathodes are compared with the composite materials to demonstrate the system is a viable platform for isolating interfacial phenomena between the electrolyte and active material without the influence of binders and conductive additives. The appropriate choice of heterolayers was found to influence the preferential orientation of the (101) and (104) planes relative to the (003) plane of the layered R-3m crystal structure, enhancing Li+ diffusion and improving electrochemical performance. The addition of a Co interlayer between the Pt current collecting layer and alumina substrate increased the (101) and (104) texturing of the 500 nm Ni-rich film and allowed cells to deliver greater than 50% of their theoretical capacity. This work provides an architecture for isolating complex mechanisms of active materials that suffer from surface reconstruction and degradation in electrochemical cells.}, number={2}, journal={ACS Applied Energy Materials}, publisher={American Chemical Society (ACS)}, author={Phillip, Nathan D. and Ruther, Rose E. and Sang, Xiahan and Wang, Yongqiang and Unocic, Raymond R. and Westover, Andrew S. and Daniel, Claus and Veith, Gabriel M.}, year={2019}, month={Jan}, pages={1405–1412} }
@article{xie_kammert_kaylor_zheng_choi_pham_sang_stavitski_attenkofer_unocic_et al._2018, title={Atomically Dispersed Co and Cu on N-Doped Carbon for Reactions Involving C–H Activation}, volume={8}, ISSN={2155-5435 2155-5435}, url={http://dx.doi.org/10.1021/acscatal.8b00141}, DOI={10.1021/acscatal.8b00141}, abstractNote={Atomically dispersed Co(II) cations coordinated to nitrogen in a carbon matrix (Co-N-C) catalyze oxidative dehydrogenation of benzyl alcohol in water with a specific activity approaching that of supported Pt nanoparticles. Whereas Cu(II) cations in N-doped carbon also catalyze the reaction, they are about an order of magnitude less active compared with Co(II) cations. Results from X-ray absorption spectroscopy suggest that oxygen is also bound to N-coordinated Co(II) sites but that it can be partially removed by H2 treatments at 523–750 K. The N-coordinated Co(II) sites remained cationic in H2 up to 750 K, and these stable sites were demonstrated to be active for propane dehydrogenation. In situ characterization of Cu(II) in N-doped carbon revealed that reduction of the metal in H2 started at about 473 K, indicating a much lower thermal stability of Cu(II) in H2 relative to Co(II). The demonstrated high catalytic activity and thermal stability of Co-N-C in reducing environments suggests that this material may have broad utility in a variety of catalytic transformations.}, number={5}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Xie, Jiahan and Kammert, James D. and Kaylor, Nicholas and Zheng, Jonathan W. and Choi, Eunjin and Pham, Hien N. and Sang, Xiahan and Stavitski, Eli and Attenkofer, Klaus and Unocic, Raymond R. and et al.}, year={2018}, month={Mar}, pages={3875–3884} }
@article{boebinger_yeh_xu_miles_wang_papakyriakou_lewis_kondekar_cortes_hwang_et al._2018, title={Avoiding Fracture in a Conversion Battery Material through Reaction with Larger Ions}, volume={2}, ISSN={2542-4351}, url={http://dx.doi.org/10.1016/j.joule.2018.05.015}, DOI={10.1016/j.joule.2018.05.015}, number={9}, journal={Joule}, publisher={Elsevier BV}, author={Boebinger, Matthew G. and Yeh, David and Xu, Michael and Miles, B. Casey and Wang, Baolin and Papakyriakou, Marc and Lewis, John A. and Kondekar, Neha P. and Cortes, Francisco Javier Quintero and Hwang, Sooyeon and et al.}, year={2018}, month={Sep}, pages={1783–1799} }
@article{vlassiouk_stehle_pudasaini_unocic_rack_baddorf_ivanov_lavrik_list_gupta_et al._2018, title={Evolutionary selection growth of two-dimensional materials on polycrystalline substrates}, volume={17}, ISSN={1476-1122 1476-4660}, url={http://dx.doi.org/10.1038/s41563-018-0019-3}, DOI={10.1038/s41563-018-0019-3}, number={4}, journal={Nature Materials}, publisher={Springer Science and Business Media LLC}, author={Vlassiouk, Ivan V. and Stehle, Yijing and Pudasaini, Pushpa Raj and Unocic, Raymond R. and Rack, Philip D. and Baddorf, Arthur P. and Ivanov, Ilia N. and Lavrik, Nickolay V. and List, Frederick and Gupta, Nitant and et al.}, year={2018}, month={Mar}, pages={318–322} }
@article{sang_xie_yilmaz_lotfi_alhabeb_ostadhossein_anasori_sun_li_xiao_et al._2018, title={In situ atomistic insight into the growth mechanisms of single layer 2D transition metal carbides}, volume={9}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-018-04610-0}, DOI={10.1038/s41467-018-04610-0}, abstractNote={Developing strategies for atomic-scale controlled synthesis of new two-dimensional (2D) functional materials will directly impact their applications. Here, using in situ aberration-corrected scanning transmission electron microscopy, we obtain direct insight into the homoepitaxial Frank-van der Merwe atomic layer growth mechanism of TiC single adlayers synthesized on surfaces of Ti3C2 MXene substrates with the substrate being the source material. Activated by thermal exposure and electron-beam irradiation, hexagonal TiC single adlayers form on defunctionalized surfaces of Ti3C2 MXene at temperatures above 500 °C, generating new 2D materials Ti4C3 and Ti5C4. The growth mechanism for a single TiC adlayer and the energies that govern atom migration and diffusion are elucidated by comprehensive density functional theory and force-bias Monte Carlo/molecular dynamics simulations. This work could lead to the development of bottom-up synthesis methods using substrates terminated with similar hexagonal-metal surfaces, for controllable synthesis of larger-scale and higher quality single-layer transition metal carbides.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Sang, Xiahan and Xie, Yu and Yilmaz, Dundar E. and Lotfi, Roghayyeh and Alhabeb, Mohamed and Ostadhossein, Alireza and Anasori, Babak and Sun, Weiwei and Li, Xufan and Xiao, Kai and et al.}, year={2018}, month={Jun} }
@article{sang_li_zhao_dong_rouleau_geohegan_ding_xiao_unocic_2018, title={In situ edge engineering in two-dimensional transition metal dichalcogenides}, volume={9}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-018-04435-x}, DOI={10.1038/s41467-018-04435-x}, abstractNote={Exerting synthetic control over the edge structure and chemistry of two-dimensional (2D) materials is of critical importance to direct the magnetic, optical, electrical, and catalytic properties for specific applications. Here, we directly image the edge evolution of pores in Mo}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Sang, Xiahan and Li, Xufan and Zhao, Wen and Dong, Jichen and Rouleau, Christopher M. and Geohegan, David B. and Ding, Feng and Xiao, Kai and Unocic, Raymond R.}, year={2018}, month={May} }
@article{ding_balachandran_sang_guo_veith_bridges_rouleau_poplawsky_bassiri-gharb_ganesh_et al._2018, title={Influence of Nonstoichiometry on Proton Conductivity in Thin-Film Yttrium-Doped Barium Zirconate}, volume={10}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/acsami.7b16900}, DOI={10.1021/acsami.7b16900}, abstractNote={Proton-conducting perovskites have been widely studied because of their potential application as solid electrolytes in intermediate temperature solid oxide fuel cells. Structural and chemical heterogeneities can develop during synthesis, device fabrication, or service, which can profoundly affect proton transport. Here, we use time-resolved Kelvin probe force microscopy, scanning transmission electron microscopy, atom probe tomography, and density functional theory calculations to intentionally introduce Ba-deficient planar and spherical defects and link the resultant atomic structure with proton transport behavior in both stoichiometric and nonstoichiometric epitaxial, yttrium-doped barium zirconate thin films. The defects were intentionally induced through high-temperature annealing treatment, while maintaining the epitaxial single crystalline structure of the films, with an overall relaxation in the atomic structure. The annealed samples showed smaller magnitudes of local lattice distortions because of the formation of proton polarons, thereby leading to decreased proton-trapping effect. This resulted in a decrease in the activation energy for proton transport, leading to faster proton transport.}, number={5}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Ding, Jilai and Balachandran, Janakiraman and Sang, Xiahan and Guo, Wei and Veith, Gabriel M. and Bridges, Craig A. and Rouleau, Christopher M. and Poplawsky, Jonathan D. and Bassiri-Gharb, Nazanin and Ganesh, Panchapakesan and et al.}, year={2018}, month={Jan}, pages={4816–4823} }
@article{jin_sang_unocic_kinch_liu_hu_liu_dai_2018, title={Mechanochemical‐Assisted Synthesis of High‐Entropy Metal Nitride via a Soft Urea Strategy}, volume={30}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.201707512}, DOI={10.1002/adma.201707512}, abstractNote={Crystalline high-entropy ceramics (CHC), a new class of solids that contain five or more elemental species, have attracted increasing interest because of their unique structure and potential applications. Up to now, only a couple of CHCs (e.g., high-entropy metal oxides and diborides) have been successfully synthesized. Here, a new strategy for preparing high-entropy metal nitride (HEMN-1) is proposed via a soft urea method assisted by mechanochemical synthesis. The as-prepared HEMN-1 possesses five highly dispersed metal components, including V, Cr, Nb, Mo, Zr, and simultaneously exhibits an interesting cubic crystal structure of metal nitrides. By taking advantage of these unique features, HEMN-1 can function as a promising candidate for supercapacitor applications. A specific capacitance of 78 F g-1 is achieved at a scan rate of 100 mV s-1 in 1 m KOH. In addition, such a facile synthetic strategy can be further extended to the fabrication of other types of HEMNs, paving the way for the synthesis of HEMNs with attractive properties for task-specific applications.}, number={23}, journal={Advanced Materials}, publisher={Wiley}, author={Jin, Tian and Sang, Xiahan and Unocic, Raymond R. and Kinch, Richard T. and Liu, Xiaofei and Hu, Jun and Liu, Honglai and Dai, Sheng}, year={2018}, month={Apr} }
@article{kim_ievlev_jakowski_vlassiouk_sang_brown_dyck_unocic_kalinin_belianinov_et al._2018, title={Multi-purposed Ar gas cluster ion beam processing for graphene engineering}, volume={131}, ISSN={0008-6223}, url={http://dx.doi.org/10.1016/j.carbon.2018.01.098}, DOI={10.1016/j.carbon.2018.01.098}, journal={Carbon}, publisher={Elsevier BV}, author={Kim, Songkil and Ievlev, Anton V. and Jakowski, Jacek and Vlassiouk, Ivan V. and Sang, Xiahan and Brown, Chance and Dyck, Ondrej and Unocic, Raymond R. and Kalinin, Sergei V. and Belianinov, Alex and et al.}, year={2018}, month={May}, pages={142–148} }
@article{santodonato_liaw_unocic_bei_morris_2018, title={Predictive multiphase evolution in Al-containing high-entropy alloys}, volume={9}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-018-06757-2}, DOI={10.1038/s41467-018-06757-2}, abstractNote={The ability to predict and understand phases in high-entropy alloys (HEAs) is still being debated, and primarily true predictive capabilities derive from the known thermodynamics of materials. The present work demonstrates that prior work using high-throughput first-principles calculations may be further utilized to provide direct insight into the temperature- and composition-dependent phase evolution in HEAs, particularly Al-containing HEAs with a strengthening multiphase microstructure. Using a simple model with parameters derived from first-principles calculations, we reproduce the major features associated with Al-containing phases, demonstrating a generalizable approach for exploring potential phase evolution where little experimental data exists. Neutron scattering, in situ microscopy, and calorimetry measurements suggest that our high-throughput Monte Carlo technique captures both qualitative and quantitative features for both intermetallic phase formation and microstructure evolution at lower temperatures. This study provides a simple approach to guide HEA development, including ordered multi-phase HEAs, which may prove valuable for structural applications.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Santodonato, L. J. and Liaw, P. K. and Unocic, R. R. and Bei, H. and Morris, J. R.}, year={2018}, month={Oct} }
@article{kammert_xie_godfrey_unocic_stavitski_attenkofer_sankar_davis_2018, title={Reduction of Propionic Acid over a Pd-Promoted ReOx/SiO2 Catalyst Probed by X-ray Absorption Spectroscopy and Transient Kinetic Analysis}, volume={6}, ISSN={2168-0485 2168-0485}, url={http://dx.doi.org/10.1021/acssuschemeng.8b02820}, DOI={10.1021/acssuschemeng.8b02820}, abstractNote={A Pd-promoted Re/SiO2 catalyst was prepared by sequential impregnation and compared to monometallic Pd/SiO2 and Re/SiO2. All samples were characterized by electron microscopy, H2 and CO chemisorption, H2 temperature-programmed reduction, and in situ X-ray absorption spectroscopy at the Re LIII and Pd K-edges. The samples were also tested in the reduction of propionic acid to 1-propanol and propionaldehyde at 433 K in 0.1–0.2 MPa H2. Whereas monometallic Pd was inactive for carboxylic acid reduction, monometallic Re catalyzed aldehyde formation but only after high-temperature prereduction that produced metallic Re. When Pd was present with Re in a bimetallic catalyst, Pd facilitated the reduction of Re in H2 to ∼+4 oxidation state at modest temperatures, producing an active catalyst for the conversion of propionic acid to 1-propanol. Under the conditions of this study, the orders of reaction in propionic acid and H2 were approximately zero and one, respectively. Transient kinetic analysis of the carboxylic acid reduction to alcohols revealed that at least 50% of the Re in the bimetallic catalyst participated in the catalytic reaction. The Pd is proposed to enhance the catalytic activity of the bimetallic catalyst by spilling over hydrogen that can partially reduce Re and react with surface intermediates.}, number={9}, journal={ACS Sustainable Chemistry & Engineering}, publisher={American Chemical Society (ACS)}, author={Kammert, James D. and Xie, Jiahan and Godfrey, Ian J. and Unocic, Raymond R. and Stavitski, Eli and Attenkofer, Klaus and Sankar, Gopinathan and Davis, Robert J.}, year={2018}, month={Jul}, pages={12353–12366} }
@article{idrobo_lupini_feng_unocic_walden_gardiner_lovejoy_dellby_pantelides_krivanek_2018, title={Temperature Measurement by a Nanoscale Electron Probe Using Energy Gain and Loss Spectroscopy}, volume={120}, ISSN={0031-9007 1079-7114}, url={http://dx.doi.org/10.1103/physrevlett.120.095901}, DOI={10.1103/physrevlett.120.095901}, abstractNote={Heat dissipation in integrated nanoscale devices is a major issue that requires the development of nanoscale temperature probes. Here, we report the implementation of a method that combines electron energy gain and loss spectroscopy to provide a direct measurement of the local temperature in the nanoenvironment. Loss and gain peaks corresponding to an optical-phonon mode in boron nitride were measured from room temperature to $\ensuremath{\sim}1600\text{ }\text{ }\mathrm{K}$. Both loss and gain peaks exhibit a shift towards lower energies as the sample is heated up. First-principles calculations of the temperature-induced phonon frequency shifts provide insights into the origin of this effect and confirm the experimental data. The experiments and theory presented here open the doors to the study of anharmonic effects in materials by directly probing phonons in the electron microscope.}, number={9}, journal={Physical Review Letters}, publisher={American Physical Society (APS)}, author={Idrobo, Juan Carlos and Lupini, Andrew R. and Feng, Tianli and Unocic, Raymond R. and Walden, Franklin S. and Gardiner, Daniel S. and Lovejoy, Tracy C. and Dellby, Niklas and Pantelides, Sokrates T. and Krivanek, Ondrej L.}, year={2018}, month={Mar} }
@article{ding_balachandran_sang_guo_anchell_veith_bridges_cheng_rouleau_poplawsky_et al._2018, title={The Influence of Local Distortions on Proton Mobility in Acceptor Doped Perovskites}, volume={30}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/acs.chemmater.8b00502}, DOI={10.1021/acs.chemmater.8b00502}, abstractNote={Optimizing proton conduction in solids remains the most promising solution for achieving intermediate temperature (∼750–1000 K) solid oxide fuel cell devices, and enabling selective membranes for H2 separation. Proton conduction, a thermally activated process, exhibits its highest rates in yttrium (Y) acceptor doped BaZrO3 at an optimal doping level of 20% Y. The presence of extended defects such as grain boundaries has typically generated a wide variability in reported conductivity values. This has hindered a fundamental mechanistic understanding of how (acceptor) doping levels correlate with the activation energy of protons to produce an optimal doping level for fast proton transport. While isolated dopants have been suggested as the primary source of proton trapping, our results indicate that it is the local dopant-density that matters. Here, we show that increasing the local dopant density promotes localized lattice distortions in the presence of point defects such as oxygen-vacancies or proton interstitials. An increasing distortion amplitude traps the point defects more strongly in the form of polarons, forming defect-clusters at higher concentrations. This leads to a monotonic increase in the activation energy (and hence a decrease in proton mobility) as observed in our measurements. The optimum doping level can now be explained as a competition between increasing proton concentration with doping levels and increasing activation energy due to defect-clusters formed by defect-polarons. Based on our findings, we demonstrate how to improve proton conductivity in doped BaZrO3, by inhibiting this dopant-lattice polaronic interaction. This approach should be generally applicable for ionic conduction in perovskite oxides such as oxygen-ion conduction in solid-oxide fuel cells and alkali-ion conduction in solid-state batteries where carriers might get trapped as defect-polarons.}, number={15}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Ding, Jilai and Balachandran, Janakiraman and Sang, Xiahan and Guo, Wei and Anchell, Jonathan S. and Veith, Gabriel M. and Bridges, Craig A. and Cheng, Yongqiang and Rouleau, Christopher M. and Poplawsky, Jonathan D. and et al.}, year={2018}, month={Jun}, pages={4919–4925} }
@article{lewis_winkler_sang_pudasaini_stanford_plank_unocic_fowlkes_rack_2017, title={3D Nanoprinting via laser-assisted electron beam induced deposition: growth kinetics, enhanced purity, and electrical resistivity}, volume={8}, ISSN={2190-4286}, url={http://dx.doi.org/10.3762/bjnano.8.83}, DOI={10.3762/bjnano.8.83}, abstractNote={We investigate the growth, purity, grain structure/morphology, and electrical resistivity of 3D platinum nanowires synthesized via electron beam induced deposition with and without an in situ pulsed laser assist process which photothermally couples to the growing Pt-C deposits. Notably, we demonstrate: 1) higher platinum concentration and a coalescence of the otherwise Pt-C nanogranular material, 2) a slight enhancement in the deposit resolution and 3) a 100-fold improvement in the conductivity of suspended nanowires grown with the in situ photothermal assist process, while retaining a high degree of shape fidelity.}, journal={Beilstein Journal of Nanotechnology}, publisher={Beilstein Institut}, author={Lewis, Brett B and Winkler, Robert and Sang, Xiahan and Pudasaini, Pushpa R and Stanford, Michael G and Plank, Harald and Unocic, Raymond R and Fowlkes, Jason D and Rack, Philip D}, year={2017}, month={Apr}, pages={801–812} }
@article{han_choksi_milligan_majumdar_manto_cui_sang_unocic_zemlyanov_wang_et al._2017, title={A Discovery of Strong Metal–Support Bonding in Nanoengineered Au–Fe3O4 Dumbbell-like Nanoparticles by in Situ Transmission Electron Microscopy}, volume={17}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/acs.nanolett.7b00827}, DOI={10.1021/acs.nanolett.7b00827}, abstractNote={The strength of metal-support bonding in heterogeneous catalysts determines their thermal stability, therefore, a tremendous amount of effort has been expended to understand metal-support interactions. Herein, we report the discovery of an anomalous "strong metal-support bonding" between gold nanoparticles and "nano-engineered" Fe3O4 substrates by in situ microscopy. During in situ vacuum annealing of Au-Fe3O4 dumbbell-like nanoparticles, synthesized by the epitaxial growth of nano-Fe3O4 on Au nanoparticles, the gold nanoparticles transform into the gold thin films and wet the surface of nano-Fe3O4, as the surface reduction of nano-Fe3O4 proceeds. This phenomenon results from a unique coupling of the size-and shape-dependent high surface reducibility of nano-Fe3O4 and the extremely strong adhesion between Au and the reduced Fe3O4. This strong metal-support bonding reveals the significance of controlling the metal oxide support size and morphology for optimizing metal-support bonding and ultimately for the development of improved catalysts and functional nanostructures.}, number={8}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Han, Chang Wan and Choksi, Tej and Milligan, Cory and Majumdar, Paulami and Manto, Michael and Cui, Yanran and Sang, Xiahan and Unocic, Raymond R. and Zemlyanov, Dmitry and Wang, Chao and et al.}, year={2017}, month={Jul}, pages={4576–4582} }
@article{thompson_dyatkin_wang_turner_sang_unocic_iacovella_gogotsi_van duin_cummings_2017, title={An Atomistic Carbide-Derived Carbon Model Generated Using ReaxFF-Based Quenched Molecular Dynamics}, volume={3}, ISSN={2311-5629}, url={http://dx.doi.org/10.3390/c3040032}, DOI={10.3390/c3040032}, abstractNote={We report a novel atomistic model of carbide-derived carbons (CDCs), which are nanoporous carbons with high specific surface areas, synthesis-dependent degrees of graphitization, and well-ordered, tunable porosities. These properties make CDCs viable substrates in several energy-relevant applications, such as gas storage media, electrochemical capacitors, and catalytic supports. These materials are heterogenous, non-ideal structures and include several important parameters that govern their performance. Therefore, a realistic model of the CDC structure is needed in order to study these systems and their nanoscale and macroscale properties with molecular simulation. We report the use of the ReaxFF reactive force field in a quenched molecular dynamics routine to generate atomistic CDC models. The pair distribution function, pore size distribution, and adsorptive properties of this model are reported and corroborated with experimental data. Simulations demonstrate that compressing the system after quenching changes the pore size distribution to better match the experimental target. Ring size distributions of this model demonstrate the prevalence of non-hexagonal carbon rings in CDCs. These effects may contrast the properties of CDCs against those of activated carbons with similar pore size distributions and explain higher energy densities of CDC-based supercapacitors.}, number={4}, journal={C}, publisher={MDPI AG}, author={Thompson, Matthew and Dyatkin, Boris and Wang, Hsiu-Wen and Turner, C. and Sang, Xiahan and Unocic, Raymond and Iacovella, Christopher and Gogotsi, Yury and Van Duin, Adri and Cummings, Peter}, year={2017}, month={Oct}, pages={32} }
@article{stehle_sang_unocic_voylov_jackson_smirnov_vlassiouk_2017, title={Anisotropic Etching of Hexagonal Boron Nitride and Graphene: Question of Edge Terminations}, volume={17}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/acs.nanolett.7b02841}, DOI={10.1021/acs.nanolett.7b02841}, abstractNote={Chemical vapor deposition (CVD) has been established as the most effective way to grow large area two-dimensional materials. Direct study of the etching process can reveal subtleties of this competing with the growth reaction and thus provide the necessary details of the overall growth mechanism. Here we investigate hydrogen-induced etching of hBN and graphene and compare the results with the classical kinetic Wulff construction model. Formation of the anisotropically etched holes in the center of hBN and graphene single crystals was observed along with the changes in the crystals' circumference. We show that the edges of triangular holes in hBN crystals formed at regular etching conditions are parallel to B-terminated zigzags, opposite to the N-terminated zigzag edges of hBN triangular crystals. The morphology of the etched hBN holes is affected by a disbalance of the B/N ratio upon etching and can be shifted toward the anticipated from the Wulff model N-terminated zigzag by etching in a nitrogen buffer gas instead of a typical argon. For graphene, etched hexagonal holes are terminated by zigzag, while the crystal circumference is gradually changing from a pure zigzag to a slanted angle resulting in dodecagons.}, number={12}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Stehle, Yijing Y. and Sang, Xiahan and Unocic, Raymond R. and Voylov, Dmitry and Jackson, Roderick K. and Smirnov, Sergei and Vlassiouk, Ivan}, year={2017}, month={Nov}, pages={7306–7314} }
@article{ievlev_jakowski_burch_iberi_hysmith_joy_sumpter_belianinov_unocic_ovchinnikova_2017, title={Building with ions: towards direct write of platinum nanostructures using in situ liquid cell helium ion microscopy}, volume={9}, ISSN={2040-3364 2040-3372}, url={http://dx.doi.org/10.1039/c7nr04417h}, DOI={10.1039/C7NR04417H}, abstractNote={Direct write with liquid precursor using an helium ion beam, allows fabrication of nanostructures with sub-15 nm resolution and high chemical purity.}, number={35}, journal={Nanoscale}, publisher={Royal Society of Chemistry (RSC)}, author={Ievlev, Anton V. and Jakowski, Jacek and Burch, Matthew J. and Iberi, Vighter and Hysmith, Holland and Joy, David C. and Sumpter, Bobby G. and Belianinov, Alex and Unocic, Raymond R. and Ovchinnikova, Olga S.}, year={2017}, pages={12949–12956} }
@article{yurkiv_gutiérrez-kolar_unocic_ramsubramanian_shahbazian-yassar_mashayek_2017, title={Competitive Ion Diffusion within Grain Boundary and Grain Interiors in Polycrystalline Electrodes with the Inclusion of Stress Field}, volume={164}, ISSN={0013-4651 1945-7111}, url={http://dx.doi.org/10.1149/2.0121713jes}, DOI={10.1149/2.0121713jes}, abstractNote={Herein, we present a phase-field model (PFM) representing ions diffusion/intercalation into polycrystalline battery electrodes and its coupling to mechanics equations. Electrochemical free energy functions, considering ions diffusion within the grains and the grain boundary (GB), along with the elastic stress field associated with ions intercalation, are considered. The phase-field GB model is used to generate thin film grain structures and subsequently to study their evolution during the ions diffusion. The partial differential equations, representing ions concentration progress and the GB evolution, are solved computationally using the finite element method. In order to validate and to demonstrate capabilities of the model, we use examples of SnSb thin film sodiation. The results showed that the generated stress upon Na diffusion tends to slow down diffusion kinetics. In order to assess the effects of various model parameters on the sodium diffusion and the GB evolution, a sensitivity analysis was performed by calculating the sodiation rate. The present paper, in addition to the development of the coupled grain boundary to concentration field phase-field model, provides new insights concerning the influences of Na diffusion on the SnSb thin film performance.}, number={12}, journal={Journal of The Electrochemical Society}, publisher={The Electrochemical Society}, author={Yurkiv, Vitaliy and Gutiérrez-Kolar, Jacob S. and Unocic, Raymond R. and Ramsubramanian, Ajaykrishna and Shahbazian-Yassar, Reza and Mashayek, Farzad}, year={2017}, pages={A2830–A2839} }
@article{xu_chen_zeng_xue_chen_sang_xiao_zhang_unocic_xiao_et al._2017, title={Crystal‐Field Tuning of Photoluminescence in Two‐Dimensional Materials with Embedded Lanthanide Ions}, volume={130}, ISSN={0044-8249 1521-3757}, url={http://dx.doi.org/10.1002/ange.201711071}, DOI={10.1002/ange.201711071}, abstractNote={Abstract Lanthanide (Ln) group elements have been attracting considerable attention owing to the distinct optical properties. The crystal‐field surroundings of Ln ions in the host materials can determine their energy level splitting, which is of vital importance to tailor their optical properties. 2D MoS 2 single crystals were utilized as the host material to embed Eu 3+ and energy‐level splitting was achieved for tuning its photoluminescence (PL). The high anisotropy of the 2D host materials makes them distort the degenerate orbitals of the Ln ions more efficiently than the symmetrical bulk host materials. A significant red‐shift of the PL peak for Eu 3+ was observed. The strategy for tailoring the energy level splitting of Ln ions by the highly designable 2D material crystal field provides a new method to extend their optical properties.}, number={3}, journal={Angewandte Chemie}, publisher={Wiley}, author={Xu, Ding and Chen, Weiyin and Zeng, Mengqi and Xue, Haifeng and Chen, Yunxu and Sang, Xiahan and Xiao, Yao and Zhang, Tao and Unocic, Raymond R. and Xiao, Kai and et al.}, year={2017}, month={Dec}, pages={763–767} }
@article{ziatdinov_dyck_maksov_li_sang_xiao_unocic_vasudevan_jesse_kalinin_2017, title={Deep Learning of Atomically Resolved Scanning Transmission Electron Microscopy Images: Chemical Identification and Tracking Local Transformations}, volume={11}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.7b07504}, DOI={10.1021/acsnano.7b07504}, abstractNote={Recent advances in scanning transmission electron and scanning probe microscopies have opened exciting opportunities in probing the materials structural parameters and various functional properties in real space with angstrom-level precision. This progress has been accompanied by an exponential increase in the size and quality of data sets produced by microscopic and spectroscopic experimental techniques. These developments necessitate adequate methods for extracting relevant physical and chemical information from the large data sets, for which a priori information on the structures of various atomic configurations and lattice defects is limited or absent. Here we demonstrate an application of deep neural networks to extract information from atomically resolved images including location of the atomic species and type of defects. We develop a "weakly supervised" approach that uses information on the coordinates of all atomic species in the image, extracted via a deep neural network, to identify a rich variety of defects that are not part of an initial training set. We further apply our approach to interpret complex atomic and defect transformation, including switching between different coordination of silicon dopants in graphene as a function of time, formation of peculiar silicon dimer with mixed 3-fold and 4-fold coordination, and the motion of molecular "rotor". This deep learning-based approach resembles logic of a human operator, but can be scaled leading to significant shift in the way of extracting and analyzing information from raw experimental data.}, number={12}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Ziatdinov, Maxim and Dyck, Ondrej and Maksov, Artem and Li, Xufan and Sang, Xiahan and Xiao, Kai and Unocic, Raymond R. and Vasudevan, Rama and Jesse, Stephen and Kalinin, Sergei V.}, year={2017}, month={Dec}, pages={12742–12752} }
@article{zhao_liu_chen_zhu_belianinov_ovchinnikova_unocic_burch_kim_hao_et al._2017, title={Engineering the thermal conductivity along an individual silicon nanowire by selective helium ion irradiation}, volume={8}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/ncomms15919}, DOI={10.1038/ncomms15919}, abstractNote={Abstract The ability to engineer the thermal conductivity of materials allows us to control the flow of heat and derive novel functionalities such as thermal rectification, thermal switching and thermal cloaking. While this could be achieved by making use of composites and metamaterials at bulk length-scales, engineering the thermal conductivity at micro- and nano-scale dimensions is considerably more challenging. In this work, we show that the local thermal conductivity along a single Si nanowire can be tuned to a desired value (between crystalline and amorphous limits) with high spatial resolution through selective helium ion irradiation with a well-controlled dose. The underlying mechanism is understood through molecular dynamics simulations and quantitative phonon-defect scattering rate analysis, where the behaviour of thermal conductivity with dose is attributed to the accumulation and agglomeration of scattering centres at lower doses. Beyond a threshold dose, a crystalline-amorphous transition was observed.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Zhao, Yunshan and Liu, Dan and Chen, Jie and Zhu, Liyan and Belianinov, Alex and Ovchinnikova, Olga S. and Unocic, Raymond R. and Burch, Matthew J. and Kim, Songkil and Hao, Hanfang and et al.}, year={2017}, month={Jun} }
@article{yang_brown_huang_collins_sang_unocic_jesse_kalinin_belianinov_jakowski_et al._2017, title={Enhancing Ion Migration in Grain Boundaries of Hybrid Organic–Inorganic Perovskites by Chlorine}, volume={27}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.201700749}, DOI={10.1002/adfm.201700749}, abstractNote={Ionicity plays an important role in determining material properties, as well as optoelectronic performance of organometallic trihalide perovskites (OTPs). Ion migration in OTP films has recently been under intensive investigation by various scanning probe microscopy (SPM) techniques. However, controversial findings regarding the role of grain boundaries (GBs) associated with ion migration are often encountered, likely as a result of feedback errors and topographic effects common in to SPM. In this work, electron microscopy and spectroscopy (scanning transmission electron microscopy/electron energy loss spectroscopy) are combined with a novel, open‐loop, band‐excitation, (contact) Kelvin probe force microscopy (BE‐KPFM and BE‐cKPFM), in conjunction with ab initio molecular dynamics simulations to examine the ion behavior in the GBs of CH 3 NH 3 PbI 3 perovskite films. This combination of diverse techniques provides a deeper understanding of the differences between ion migration within GBs and interior grains in OTP films. This work demonstrates that ion migration can be significantly enhanced by introducing additional mobile Cl − ions into GBs. The enhancement of ion migration may serve as the first step toward the development of high‐performance electrically and optically tunable memristors and synaptic devices.}, number={26}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Yang, Bin and Brown, Chance C. and Huang, Jingsong and Collins, Liam and Sang, Xiahan and Unocic, Raymond R. and Jesse, Stephen and Kalinin, Sergei V. and Belianinov, Alex and Jakowski, Jacek and et al.}, year={2017}, month={May} }
@article{wang_sang_gamler_chen_unocic_skrabalak_2017, title={Facet-Dependent Deposition of Highly Strained Alloyed Shells on Intermetallic Nanoparticles for Enhanced Electrocatalysis}, volume={17}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/acs.nanolett.7b02239}, DOI={10.1021/acs.nanolett.7b02239}, abstractNote={Surface strains can enhance the performance of platinum-based core@shell electrocatalysts for the oxygen reduction reaction (ORR). Bimetallic core@shell nanoparticles (NPs) are widely studied nanocatalysts but often have limited lattice mismatch and surface compositions; investigations of core@shell NPs with greater compositional complexity and lattice misfit are in their infancy. Here, a new class of multimetallic NPs composed of intermetallic cores and random alloy shells is reported. Specifically, face-centered cubic Pt–Cu random alloy shells were deposited on PdCu B2 intermetallic seeds in a facet-dependent manner, giving rise to faceted core@shell NPs with highly strained surfaces. High-resolution transmission electron microscopy revealed orientation-dependent surface strains, where the compressive strains were greater on Pt–Cu {200} than {111} facets. These core@shell NPs provide higher specific area and mass activities for the ORR when compared to conventional Pt–Cu NPs. Moreover, these intermetallic@random alloy NPs displayed high endurance, undergoing 10,000 cycles with only a slight decay in activity and no apparent structural changes.}, number={9}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Wang, Chenyu and Sang, Xiahan and Gamler, Jocelyn T. L. and Chen, Dennis P. and Unocic, Raymond R. and Skrabalak, Sara E.}, year={2017}, month={Aug}, pages={5526–5532} }
@article{canepa_sneed_sun_unocic_mølhave_2018, title={Influence of Cetyltrimethylammonium Bromide on Gold Nanocrystal Formation Studied by In Situ Liquid Cell Scanning Transmission Electron Microscopy}, volume={122}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/acs.jpcc.7b06383}, DOI={10.1021/acs.jpcc.7b06383}, abstractNote={The synthesis of monodisperse size- and shape-controlled Au nanocrystals is often achieved with cetyltrimethylammonium bromide (CTAB) surfactant; however, its role in the growth of such tailored nanostructures is not well understood. To elucidate the formation mechanism(s) and evolution of the morphology of Au nanocrystals in the early growth stage, we present an in situ liquid-cell scanning transmission electron microscopy (STEM) investigation using electron beam-induced radiolytic species as the reductant. The resulting particle shape at a low beam dose rate is shown to be strongly influenced by the surfactant; the Au nanocrystal growth rate is suppressed by increasing the CTAB concentration. At a low CTAB concentration, the nanoparticles (NPs) follow a reaction-limited growth mechanism, while at high a CTAB concentration the NPs follow a diffusion-limited mechanism, as described by the Lifshitz–Slyozov–Wagner (LSW) model. Moreover, we investigate the temporal evolution of specific NP geometries. The amount of Au reduced by the electron beam outside the irradiated area is quantified to better interpret the nanocrystal growth kinetics, as well as to further develop an understanding of electron beam interactions with nanomaterials toward improving the interpretation of in situ measurements.}, number={4}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Canepa, Silvia A. and Sneed, Brian T. and Sun, Hongyu and Unocic, Raymond R. and Mølhave, Kristian}, year={2018}, month={Jan}, pages={2350–2357} }
@article{muckley_naguib_wang_vlcek_osti_sacci_sang_unocic_xie_tyagi_et al._2017, title={Multimodality of Structural, Electrical, and Gravimetric Responses of Intercalated MXenes to Water}, volume={11}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.7b05264}, DOI={10.1021/acsnano.7b05264}, abstractNote={Understanding of structural, electrical, and gravimetric peculiarities of water vapor interaction with ion-intercalated MXenes led to design of a multimodal humidity sensor. Neutron scattering coupled to molecular dynamics and ab initio calculations showed that a small amount of hydration results in a significant increase in the spacing between MXene layers in the presence of K and Mg intercalants between the layers. Films of K- and Mg-intercalated MXenes exhibited relative humidity (RH) detection thresholds of ∼0.8% RH and showed monotonic RH response in the 0–85% RH range. We found that MXene gravimetric response to water is 10 times faster than their electrical response, suggesting that H2O-induced swelling/contraction of channels between MXene sheets results in trapping of H2O molecules that act as charge-depleting dopants. The results demonstrate the use of MXenes as humidity sensors and infer potential impact of water on structural and electrical performance of MXene-based devices.}, number={11}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Muckley, Eric S. and Naguib, Michael and Wang, Hsiu-Wen and Vlcek, Lukas and Osti, Naresh C. and Sacci, Robert L. and Sang, Xiahan and Unocic, Raymond R. and Xie, Yu and Tyagi, Madhusudan and et al.}, year={2017}, month={Oct}, pages={11118–11126} }
@article{unocic_shin_unocic_allard_2017, title={NiAl Oxidation Reaction Processes Studied In Situ Using MEMS-Based Closed-Cell Gas Reaction Transmission Electron Microscopy}, volume={88}, ISSN={0030-770X 1573-4889}, url={http://dx.doi.org/10.1007/s11085-016-9676-2}, DOI={10.1007/s11085-016-9676-2}, number={3-4}, journal={Oxidation of Metals}, publisher={Springer Science and Business Media LLC}, author={Unocic, Kinga A. and Shin, Dongwon and Unocic, Raymond R. and Allard, Lawrence F.}, year={2017}, month={Feb}, pages={495–508} }
@article{sang_lupini_ding_kalinin_jesse_unocic_2017, title={Precision controlled atomic resolution scanning transmission electron microscopy using spiral scan pathways}, volume={7}, ISSN={2045-2322}, url={http://dx.doi.org/10.1038/srep43585}, DOI={10.1038/srep43585}, abstractNote={Abstract Atomic-resolution imaging in an aberration-corrected scanning transmission electron microscope (STEM) can enable direct correlation between atomic structure and materials functionality. The fast and precise control of the STEM probe is, however, challenging because the true beam location deviates from the assigned location depending on the properties of the deflectors. To reduce these deviations, i . e . image distortions, we use spiral scanning paths, allowing precise control of a sub-Å sized electron probe within an aberration-corrected STEM. Although spiral scanning avoids the sudden changes in the beam location (fly-back distortion) present in conventional raster scans, it is not distortion-free. “Archimedean” spirals, with a constant angular frequency within each scan, are used to determine the characteristic response at different frequencies. We then show that such characteristic functions can be used to correct image distortions present in more complicated constant linear velocity spirals, where the frequency varies within each scan. Through the combined application of constant linear velocity scanning and beam path corrections, spiral scan images are shown to exhibit less scan distortion than conventional raster scan images. The methodology presented here will be useful for in situ STEM imaging at higher temporal resolution and for imaging beam sensitive materials.}, number={1}, journal={Scientific Reports}, publisher={Springer Science and Business Media LLC}, author={Sang, Xiahan and Lupini, Andrew R. and Ding, Jilai and Kalinin, Sergei V. and Jesse, Stephen and Unocic, Raymond R.}, year={2017}, month={Mar} }
@article{jarvis_wang_varela_unocic_manthiram_ferreira_2017, title={Surface Reconstruction in Li-Rich Layered Oxides of Li-Ion Batteries}, volume={29}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/acs.chemmater.7b00120}, DOI={10.1021/acs.chemmater.7b00120}, abstractNote={The performance characteristics of lithium-ion battery cathode materials are governed by the surface structure and chemistry. Synthesis is known to affect the structure of these materials; however, a full understanding of the effects of the surface structure is not well understood. Here, we explore the atomic scale structure of lithium-layered oxides prepared with two different thermal treatments. We show that, under certain thermal treatments, the surface perpendicular to the transition-metal layers is enriched in nickel, which results in Ni occupying the lithium layer of the layered oxide structure. Under both thermal treatments, this surface also shows a reduction of Mn, with some of the reduced Mn occupying sites in the lithium layer. The surface parallel to the transition-metal layers under both treatments shows significant Mn reduction, oxygen loss, and reduced Mn in the lithium layer. The Mn reduction and surface reconstruction are the result of unstable surface terminations and are intrinsic to layered oxides. Synthesis can be tuned to eliminate Ni enrichment at the surface; however, it cannot be tailored to eliminate Mn reduction and surface reconstruction.}, number={18}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Jarvis, Karalee and Wang, Chih-Chieh and Varela, Maria and Unocic, Raymond R. and Manthiram, Arumugam and Ferreira, Paulo J.}, year={2017}, month={Sep}, pages={7668–7674} }
@article{li_wan_veith_unocic_paranthaman_dai_sun_2017, title={A Novel Electrolyte Salt Additive for Lithium‐Ion Batteries with Voltages Greater than 4.7 V}, volume={7}, ISSN={1614-6832 1614-6840}, url={http://dx.doi.org/10.1002/aenm.201601397}, DOI={10.1002/aenm.201601397}, abstractNote={Lithium bis(2-methyl-2-fluoromalonato)borate (LiBMFMB), as an additive for LiNi0.5Mn1.5O4, exhibits improved efficiencies and cycling stability. Cyclic voltammograms indicate the cells with additive form good solid-electrolyte interphases (SEIs) during the first cycle, whereas no additive cell needs more cycles to form a functional SEI. X-ray photoelectron spectroscopy reveals LiBMFMB could reduce the decomposition of LiPF6 salt and solvents, resulting in thinner SEI. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={4}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Li, Yunchao and Wan, Shun and Veith, Gabriel M. and Unocic, Raymond R. and Paranthaman, Mariappan Parans and Dai, Sheng and Sun, Xiao‐Guang}, year={2017}, month={Feb} }
@misc{unocic_more_2016, title={Application of Electrochemical Liquid Cells for Electrical Energy Storage and Conversion Studies}, url={http://dx.doi.org/10.1017/9781316337455.012}, DOI={10.1017/9781316337455.012}, abstractNote={A summary is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.}, journal={Liquid Cell Electron Microscopy}, publisher={Cambridge University Press}, author={Unocic, Raymond R. and More, Karren L.}, year={2016}, month={Dec}, pages={237–257} }
@article{sang_xie_lin_alhabeb_van aken_gogotsi_kent_xiao_unocic_2016, title={Atomic Defects in Monolayer Titanium Carbide (Ti3C2Tx) MXene}, volume={10}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.6b05240}, DOI={10.1021/acsnano.6b05240}, abstractNote={The 2D transition metal carbides or nitrides, or MXenes, are emerging as a group of materials showing great promise in lithium ion batteries and supercapacitors. Until now, characterization and properties of single-layer MXenes have been scarcely reported. Here, using scanning transmission electron microscopy, we determined the atomic structure of freestanding monolayer Ti3C2Tx flakes prepared via the minimally intensive layer delamination method and characterized different point defects that are prevalent in the monolayer flakes. We determine that the Ti vacancy concentration can be controlled by the etchant concentration during preparation. Density function theory-based calculations confirm the defect structures and predict that the defects can influence the surface morphology and termination groups, but do not strongly influence the metallic conductivity. Using devices fabricated from single- and few-layer Ti3C2Tx MXene flakes, the effect of the number of layers in the flake on conductivity has been demonstrated.}, number={10}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Sang, Xiahan and Xie, Yu and Lin, Ming-Wei and Alhabeb, Mohamed and Van Aken, Katherine L. and Gogotsi, Yury and Kent, Paul R. C. and Xiao, Kai and Unocic, Raymond R.}, year={2016}, month={Sep}, pages={9193–9200} }
@article{yoon_rahnamoun_swett_iberi_cullen_vlassiouk_belianinov_jesse_sang_ovchinnikova_et al._2016, title={Atomistic-Scale Simulations of Defect Formation in Graphene under Noble Gas Ion Irradiation}, volume={10}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.6b03036}, DOI={10.1021/acsnano.6b03036}, abstractNote={Despite the frequent use of noble gas ion irradiation of graphene, the atomistic-scale details, including the effects of dose, energy, and ion bombardment species on defect formation, and the associated dynamic processes involved in the irradiations and subsequent relaxation have not yet been thoroughly studied. Here, we simulated the irradiation of graphene with noble gas ions and the subsequent effects of annealing. Lattice defects, including nanopores, were generated after the annealing of the irradiated graphene, which was the result of structural relaxation that allowed the vacancy-type defects to coalesce into a larger defect. Larger nanopores were generated by irradiation with a series of heavier noble gas ions, due to a larger collision cross section that led to more detrimental effects in the graphene, and by a higher ion dose that increased the chance of displacing the carbon atoms from graphene. Overall trends in the evolution of defects with respect to a dose, as well as the defect characteristics, were in good agreement with experimental results. Additionally, the statistics in the defect types generated by different irradiating ions suggested that the most frequently observed defect types were Stone-Thrower-Wales (STW) defects for He+ irradiation and monovacancy (MV) defects for all other ion irradiations.}, number={9}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Yoon, Kichul and Rahnamoun, Ali and Swett, Jacob L. and Iberi, Vighter and Cullen, David A. and Vlassiouk, Ivan V. and Belianinov, Alex and Jesse, Stephen and Sang, Xiahan and Ovchinnikova, Olga S. and et al.}, year={2016}, month={Aug}, pages={8376–8384} }
@article{smith_unocic_deutchman_mills_2016, title={Creep deformation mechanism mapping in nickel base disk superalloys}, volume={33}, ISSN={0960-3409 1878-6413}, url={http://dx.doi.org/10.1080/09603409.2016.1180858}, DOI={10.1080/09603409.2016.1180858}, abstractNote={The creep deformation mechanisms at intermediate temperature in ME3, a modern Ni-based disk superalloy, were investigated using diffraction contrast imaging. Both conventional transmission electron microscopy (TEM) and scanning TEM were utilised. Distinctly different deformation mechanisms become operative during creep at temperatures between 677–815 °C and at stresses ranging from 274 to 724 MPa. Both polycrystalline and single-crystal creep tests were conducted. The single-crystal tests provide new insight into grain orientation effects on creep response and deformation mechanisms. Creep at lower temperatures (≤760°C) resulted in the thermally activated shearing modes such as microtwinning, stacking fault ribbons and isolated superlattice extrinsic stacking faults. In contrast, these faulting modes occurred much less frequently during creep at 815°C under lower applied stresses. Instead, the principal deformation mode was dislocation climb bypass. In addition to the difference in creep behaviour and creep deformation mechanisms as a function of stress and temperature, it was also observed that microstructural evolution occurs during creep at 760°C and above, where the secondary γ′ coarsened and the tertiary γ′ precipitates dissolved. Based on this work, a creep deformation mechanism map is proposed, emphasising the influence of stress and temperature on the underlying creep mechanisms.}, number={4-5}, journal={Materials at High Temperatures}, publisher={Informa UK Limited}, author={Smith, Timothy M. and Unocic, Raymond R. and Deutchman, Hallee and Mills, Michael J.}, year={2016}, month={May}, pages={372–383} }
@article{unocic_lupini_borisevich_cullen_kalinin_jesse_2016, title={Direct-write liquid phase transformations with a scanning transmission electron microscope}, volume={8}, ISSN={2040-3364 2040-3372}, url={http://dx.doi.org/10.1039/c6nr04994j}, DOI={10.1039/c6nr04994j}, abstractNote={The highly energetic electron beam (e-beam) in a scanning transmission electron microscope (STEM) can induce local changes in the state of matter, ranging from knock-on and atomic movement, to amorphization/crystallization, and to localized chemical/electrochemical reactions. To date, fundamental studies of e-beam induced phenomena and practical applications have been limited by conventional STEM e-beam rastering modes that allow only for uniform e-beam exposures. Here, an automated liquid phase nanolithography method has been developed that enables the direct writing of nanometer scaled features within microfabricated liquid cells. An external e-beam control system, connected to the scan coils of an aberration-corrected STEM, is used to precisely control the position, dwell time, and scan rate of a sub-nanometer STEM probe. Site-specific locations in a sealed liquid cell containing an aqueous solution of H2PdCl4 are irradiated to deposit palladium nanocrystals onto silicon nitride membranes in a highly controlled manner. The threshold electron dose required for the radiolytic deposition of metallic palladium has been determined, the influence of electron dose on the nanolithographically patterned feature size and morphology is explored, and a feedback-controlled monitoring method for active control of the nanofabricated structures through STEM detector signal monitoring is proposed. This approach enables fundamental studies of electron beam induced interactions with matter in liquid cells and opens new pathways to fabricate nanostructures with tailored architectures and chemistries via shape-controlled nanolithographic patterning from liquid-phase precursors.}, number={34}, journal={Nanoscale}, publisher={Royal Society of Chemistry (RSC)}, author={Unocic, Raymond R. and Lupini, Andrew R. and Borisevich, Albina Y. and Cullen, David A. and Kalinin, Sergei V. and Jesse, Stephen}, year={2016}, pages={15581–15588} }
@article{jesse_borisevich_fowlkes_lupini_rack_unocic_sumpter_kalinin_belianinov_ovchinnikova_2016, title={Directing Matter: Toward Atomic-Scale 3D Nanofabrication}, volume={10}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.6b02489}, DOI={10.1021/acsnano.6b02489}, abstractNote={Enabling memristive, neuromorphic, and quantum-based computing as well as efficient mainstream energy storage and conversion technologies requires the next generation of materials customized at the atomic scale. This requires full control of atomic arrangement and bonding in three dimensions. The last two decades witnessed substantial industrial, academic, and government research efforts directed toward this goal through various lithographies and scanning-probe-based methods. These technologies emphasize 2D surface structures, with some limited 3D capability. Recently, a range of focused electron- and ion-based methods have demonstrated compelling alternative pathways to achieving atomically precise manufacturing of 3D structures in solids, liquids, and at interfaces. Electron and ion microscopies offer a platform that can simultaneously observe dynamic and static structures at the nano- and atomic scales and also induce structural rearrangements and chemical transformation. The addition of predictive modeling or rapid image analytics and feedback enables guiding these in a controlled manner. Here, we review the recent results that used focused electron and ion beams to create free-standing nanoscale 3D structures, radiolysis, and the fabrication potential with liquid precursors, epitaxial crystallization of amorphous oxides with atomic layer precision, as well as visualization and control of individual dopant motion within a 3D crystal lattice. These works lay the foundation for approaches to directing nanoscale level architectures and offer a potential roadmap to full 3D atomic control in materials. In this paper, we lay out the gaps that currently constrain the processing range of these platforms, reflect on indirect requirements, such as the integration of large-scale data analysis with theory, and discuss future prospects of these technologies.}, number={6}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Jesse, Stephen and Borisevich, Albina Y. and Fowlkes, Jason D. and Lupini, Andrew R. and Rack, Philip D. and Unocic, Raymond R. and Sumpter, Bobby G. and Kalinin, Sergei V. and Belianinov, Alex and Ovchinnikova, Olga S.}, year={2016}, month={May}, pages={5600–5618} }
@article{boebinger_xu_ma_chen_unocic_mcdowell_2017, title={Distinct nanoscale reaction pathways in a sulfide material for sodium and lithium batteries}, volume={5}, ISSN={2050-7488 2050-7496}, url={http://dx.doi.org/10.1039/c6ta09195d}, DOI={10.1039/c6ta09195d}, abstractNote={Copper sulfide is found to exhibit excellent cycle life in Na-ion batteries, and multiscale in situ techniques (TEM and X-ray diffraction) are used to reveal unique aspects of the electrochemical reaction of sodium with this material.}, number={23}, journal={Journal of Materials Chemistry A}, publisher={Royal Society of Chemistry (RSC)}, author={Boebinger, Matthew G. and Xu, Michael and Ma, Xuetian and Chen, Hailong and Unocic, Raymond R. and McDowell, Matthew T.}, year={2017}, pages={11701–11709} }
@article{sang_lupini_unocic_chi_borisevich_kalinin_endeve_archibald_jesse_2016, title={Dynamic scan control in STEM: spiral scans}, volume={2}, ISSN={2198-0926}, url={http://dx.doi.org/10.1186/s40679-016-0020-3}, DOI={10.1186/s40679-016-0020-3}, abstractNote={Abstract Scanning transmission electron microscopy (STEM) has emerged as one of the foremost techniques to analyze materials at atomic resolution. However, two practical difficulties inherent to STEM imaging are: radiation damage imparted by the electron beam, which can potentially damage or otherwise modify the specimen and slow-scan image acquisition, which limits the ability to capture dynamic changes at high temporal resolution. Furthermore, due in part to scan flyback corrections, typical raster scan methods result in an uneven distribution of dose across the scanned area. A method to allow extremely fast scanning with a uniform residence time would enable imaging at low electron doses, ameliorating radiation damage and at the same time permitting image acquisition at higher frame-rates while maintaining atomic resolution. The practical complication is that rastering the STEM probe at higher speeds causes significant image distortions. Non-square scan patterns provide a solution to this dilemma and can be tailored for low dose imaging conditions. Here, we develop a method for imaging with alternative scan patterns and investigate their performance at very high scan speeds. A general analysis for spiral scanning is presented here for the following spiral scan functions: Archimedean, Fermat, and constant linear velocity spirals, which were tested for STEM imaging. The quality of spiral scan STEM images is generally comparable with STEM images from conventional raster scans, and the dose uniformity can be improved.}, number={1}, journal={Advanced Structural and Chemical Imaging}, publisher={Springer Science and Business Media LLC}, author={Sang, Xiahan and Lupini, Andrew R. and Unocic, Raymond R. and Chi, Miaofang and Borisevich, Albina Y. and Kalinin, Sergei V. and Endeve, Eirik and Archibald, Richard K. and Jesse, Stephen}, year={2016}, month={Jun} }
@article{baturina_lu_xu_purdy_dyatkin_sang_unocic_brintlinger_gogotsi_2017, title={Effect of nanostructured carbon support on copper electrocatalytic activity toward CO2 electroreduction to hydrocarbon fuels}, volume={288}, ISSN={0920-5861}, url={http://dx.doi.org/10.1016/j.cattod.2016.11.001}, DOI={10.1016/j.cattod.2016.11.001}, journal={Catalysis Today}, publisher={Elsevier BV}, author={Baturina, Olga and Lu, Qin and Xu, Feng and Purdy, Andrew and Dyatkin, Boris and Sang, Xiahan and Unocic, Raymond and Brintlinger, Todd and Gogotsi, Yury}, year={2017}, month={Jun}, pages={2–10} }
@article{black_zhu_zhang_unocic_guo_okatan_dai_cummings_kalinin_feng_et al._2016, title={Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy}, volume={6}, ISSN={2045-2322}, url={http://dx.doi.org/10.1038/srep32389}, DOI={10.1038/srep32389}, abstractNote={AbstractAtomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.}, number={1}, journal={Scientific Reports}, publisher={Springer Science and Business Media LLC}, author={Black, Jennifer M. and Zhu, Mengyang and Zhang, Pengfei and Unocic, Raymond R. and Guo, Daqiang and Okatan, M. Baris and Dai, Sheng and Cummings, Peter T. and Kalinin, Sergei V. and Feng, Guang and et al.}, year={2016}, month={Sep} }
@article{formo_potterf_yang_unocic_leonard_pawel_2016, title={How a Nanostructure’s Shape Affects its Lifetime in the Environment: Comparing a Silver Nanocube to a Nanoparticle When Dispersed in Aqueous Media}, volume={50}, ISSN={0013-936X 1520-5851}, url={http://dx.doi.org/10.1021/acs.est.6b01172}, DOI={10.1021/acs.est.6b01172}, abstractNote={Herein, we detail how the morphology of a nanomaterial affects its environmental lifetime in aquatic ecosystems. In particular, we focus on the cube and particle nanostructures of Ag and age them in various aquatic mediums including synthetic hard water, pond water, and seawater. Our results show that in the synthetic hard water and pond water cases, there was little difference in the rate of morphological changes as determined by UV–vis spectroscopy. However, when these samples were analyzed with transmission electron microscopy, radically different mechanisms in the loss of their original nanostructures were observed. Specifically, for the nanocube we observed that the corners of the cubes had become more rounded, whereas the aged nanoparticles formed large aggregates. Most interestingly, when the seawater samples were analyzed, the nanocubes showed a substantially higher stability in maintaining the nano length scale in comparison to nanoparticles overtime. Moreover, high-resolution transmission electron microscopy analysis allowed us to determine that Ag+ ions diffused away from both the edge and from the faces of the cube, whereas the nanoparticle rapidly aggregated under the harsh seawater conditions.}, number={13}, journal={Environmental Science & Technology}, publisher={American Chemical Society (ACS)}, author={Formo, Eric V. and Potterf, Caroline B. and Yang, Miaoxin and Unocic, Raymond R. and Leonard, Donovan N. and Pawel, Michelle}, year={2016}, month={Jun}, pages={7082–7089} }
@article{economy_mara_schoeppner_schultz_unocic_kennedy_2016, title={Identifying Deformation and Strain Hardening Behaviors of Nanoscale Metallic Multilayers Through Nano-wear Testing}, volume={47}, ISSN={1073-5623 1543-1940}, url={http://dx.doi.org/10.1007/s11661-015-3284-7}, DOI={10.1007/s11661-015-3284-7}, number={3}, journal={Metallurgical and Materials Transactions A}, publisher={Springer Science and Business Media LLC}, author={Economy, D. Ross and Mara, N. A. and Schoeppner, R. L. and Schultz, B. M. and Unocic, R. R. and Kennedy, M. S.}, year={2016}, month={Jan}, pages={1083–1095} }
@article{weiner_chen_unocic_skrabalak_2016, title={Impact of Membrane‐Induced Particle Immobilization on Seeded Growth Monitored by In Situ Liquid Scanning Transmission Electron Microscopy}, volume={12}, ISSN={1613-6810 1613-6829}, url={http://dx.doi.org/10.1002/smll.201502974}, DOI={10.1002/smll.201502974}, abstractNote={In situ liquid cell scanning transmission electron microscopy probes seeded growth in real time. The growth of Pd on Au nanocubes is monitored as a model system to compare growth within a liquid cell and traditional colloidal synthesis. Different growth patterns are observed due to seed immobilization and the highly reducing environment within the liquid cell.}, number={20}, journal={Small}, publisher={Wiley}, author={Weiner, Rebecca G. and Chen, Dennis P. and Unocic, Raymond R. and Skrabalak, Sara E.}, year={2016}, month={Apr}, pages={2701–2706} }
@article{xie_huang_yin_pham_unocic_datye_davis_2016, title={Influence of Dioxygen on the Promotional Effect of Bi during Pt-Catalyzed Oxidation of 1,6-Hexanediol}, volume={6}, ISSN={2155-5435 2155-5435}, url={http://dx.doi.org/10.1021/acscatal.6b00972}, DOI={10.1021/acscatal.6b00972}, abstractNote={A series of carbon-supported, Bi-promoted Pt catalysts with various Bi/Pt atomic ratios was prepared by selectively depositing Bi on Pt nanoparticles. The catalysts were evaluated for 1,6-hexanediol oxidation activity in aqueous solvent under different dioxygen pressures. The rate of diol oxidation on the basis of Pt loading over a Bi-promoted catalyst was 3 times faster than that of an unpromoted Pt catalyst under 0.02 MPa of O2, whereas the unpromoted catalyst was more active than the promoted catalyst under 1 MPa of O2. After liquid-phase catalyst pretreatment and 1,6-hexanediol oxidation, migration of Bi on the carbon support was observed. The reaction order in O2 was 0 over Bi-promoted Pt/C in comparison to 0.75 over unpromoted Pt/C in the range of 0.02–0.2 MPa of O2. Under low O2 pressure, rate measurements in D2O instead of H2O solvent revealed a moderate kinetic isotope effect (rateH2O/rateD2O) on 1,6-hexanediol oxidation over Pt/C (KIE = 1.4), whereas a negligible effect was observed on Bi-Pt/C (KIE = 0.9), indicating that the promotional effect of Bi could be related to the formation of surface hydroxyl groups from the reaction of dioxygen and water. No significant change in product distribution or catalyst stability was observed with Bi promotion, regardless of the dioxygen pressure.}, number={7}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Xie, Jiahan and Huang, Benjamin and Yin, Kehua and Pham, Hien N. and Unocic, Raymond R. and Datye, Abhaya K. and Davis, Robert J.}, year={2016}, month={Jun}, pages={4206–4217} }
@article{rubio_gunduz_groven_sippel_han_unocic_ortalan_son_2017, title={Microexplosions and ignition dynamics in engineered aluminum/polymer fuel particles}, volume={176}, ISSN={0010-2180}, url={http://dx.doi.org/10.1016/j.combustflame.2016.10.008}, DOI={10.1016/j.combustflame.2016.10.008}, journal={Combustion and Flame}, publisher={Elsevier BV}, author={Rubio, Mario A. and Gunduz, I. Emre and Groven, Lori J. and Sippel, Travis R. and Han, Chang Wan and Unocic, Raymond R. and Ortalan, Volkan and Son, Steven F.}, year={2017}, month={Feb}, pages={162–171} }
@article{xie_yin_serov_artyushkova_pham_sang_unocic_atanassov_datye_davis_2017, title={Selective Aerobic Oxidation of Alcohols over Atomically‐Dispersed Non‐Precious Metal Catalysts}, volume={10}, ISSN={1864-5631 1864-564X}, url={http://dx.doi.org/10.1002/cssc.201601364}, DOI={10.1002/cssc.201601364}, abstractNote={Abstract Catalytic oxidation of alcohols often requires the presence of expensive transition metals. Herein, it is shown that earth‐abundant Fe atoms dispersed throughout a nitrogen‐containing carbon matrix catalyze the oxidation of benzyl alcohol and 5‐hydroxymethylfurfural by O 2 in the aqueous phase. The activity of the catalyst can be regenerated by a mild treatment in H 2 . An observed kinetic isotope effect indicates that β‐H elimination from the alcohol is the kinetically relevant step in the mechanism, which can be accelerated by substituting Fe with Cu. Dispersed Cr, Co, and Ni also convert alcohols, demonstrating the general utility of metal–nitrogen–carbon materials for alcohol oxidation catalysis. Oxidation of aliphatic alcohols is substantially slower than that of aromatic alcohols, but addition of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy as a co‐catalyst with Fe can significantly improve the reaction rate.}, number={2}, journal={ChemSusChem}, publisher={Wiley}, author={Xie, Jiahan and Yin, Kehua and Serov, Alexey and Artyushkova, Kateryna and Pham, Hien N. and Sang, Xiahan and Unocic, Raymond R. and Atanassov, Plamen and Datye, Abhaya K. and Davis, Robert J.}, year={2017}, month={Jan}, pages={359–362} }
@article{wang_chen_sang_unocic_skrabalak_2016, title={Size-Dependent Disorder–Order Transformation in the Synthesis of Monodisperse Intermetallic PdCu Nanocatalysts}, volume={10}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/acsnano.6b02669}, DOI={10.1021/acsnano.6b02669}, abstractNote={The high performance of Pd-based intermetallic nanocatalysts has the potential to replace Pt-containing catalysts for fuel-cell reactions. Conventionally, intermetallic particles are obtained through the annealing of nanoparticles of a random alloy distribution. However, this method inevitably leads to sintering of the nanoparticles and generates polydisperse samples. Here, monodisperse PdCu nanoparticles with the ordered B2 phase were synthesized by seed-mediated co-reduction using PdCu nanoparticle seeds with a random alloy distribution (A1 phase). A time-evolution study suggests that the particles must overcome a size-dependent activation barrier for the ordering process to occur. Characterization of the as-prepared PdCu B2 nanoparticles by electron microscopy techniques revealed surface segregation of Pd as a thin shell over the PdCu core. The ordered nanoparticles exhibit superior activity and durability for the oxygen reduction reaction in comparison with PdCu A1 nanoparticles. This seed-mediated co-reduction strategy produced monodisperse nanoparticles ideally suited for structure–activity studies. Moreover, the study of their growth mechanism provides insights into the size dependence of disorder–order transformations of bimetallic alloys at the nanoscale, which should enable the design of synthetic strategies toward other intermetallic systems.}, number={6}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Wang, Chenyu and Chen, Dennis P. and Sang, Xiahan and Unocic, Raymond R. and Skrabalak, Sara E.}, year={2016}, month={May}, pages={6345–6353} }
@article{li_puretzky_sang_kc_tian_ceballos_mahjouri‐samani_wang_unocic_zhao_et al._2017, title={Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe2}, volume={27}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.201603850}, DOI={10.1002/adfm.201603850}, abstractNote={Defects formed during chemical vapor deposition (CVD) of two‐dimensional (2D) transition metal dichalcogenides (TMDs) currently limit their quality and optoelectronic properties. Effective synthesis and processing strategies to suppress defects and enhance the quality of 2D TMDs are urgently needed to enable next generation optoelectronic devices. In this work, isoelectronic doping is presented as a new strategy to form stable alloys and suppress defects and enhance photoluminescence (PL) in CVD‐grown TMD monolayers. The isoelectronic substitution of W atoms for Mo atoms in CVD‐grown monolayers of Mo 1– x W x Se 2 (0 < x < 0.18) is shown to effectively suppress Se vacancy concentration by 50% compared to those found in pristine MoSe 2 monolayers, resulting in a decrease in defect‐mediated nonradiative recombination, ≈10 times more intense PL, and an increase in the carrier lifetime by a factor of 3. Theoretical predictions reveal that isoelectronic W alloying to form Mo 1– x W x Se 2 monolayers raises the energy of deep level defects in MoSe 2 to enable faster quenching, which is confirmed by low temperature (4–125 K) PL from defect‐related localized states. Isoelectronic substitution therefore appears to be a promising synthetic method to control the heterogeneity of 2D TMDs to realize the scalable production of high performance optoelectronic and electronic devices.}, number={19}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Li, Xufan and Puretzky, Alexander A. and Sang, Xiahan and Kc, Santosh and Tian, Mengkun and Ceballos, Frank and Mahjouri‐Samani, Masoud and Wang, Kai and Unocic, Raymond R. and Zhao, Hui and et al.}, year={2017}, month={May}, pages={1603850} }
@article{john_atkinson_roy_unocic_papandrew_zawodzinski_2016, title={The Effect of Carbonate and pH on Hydrogen Oxidation and Oxygen Reduction on Pt-Based Electrocatalysts in Alkaline Media}, volume={163}, ISSN={0013-4651 1945-7111}, url={http://dx.doi.org/10.1149/2.1071603jes}, DOI={10.1149/2.1071603jes}, abstractNote={We investigated the performance of several carbon-supported RuxPty electrocatalysts for their alkaline hydrogen oxidation and oxygen reduction performance in the presence of carbonate and compared their performance with monometallic, carbon-supported Pt. Our results indicate a strong dependence of HOR upon pH for the monometallic Pt catalysts (22 mV/pH) and a weak dependence upon pH for the Ru-containing electrocatalysts (3.7, 2.5, and 4.7 mV/pH on Ru0.2Pt0.8, Ru0.4Pt0.6, and Ru0.8Pt0.2, respectively). These results are consistent with our previous findings that illustrate a change in rds from electron transfer (on monometallic Pt) to dissociative hydrogen adsorption (on RuxPty catalysts). Analysis of the kinetic currents to determine the rate-determining step via Tafel slope analysis provides additional data supporting this conclusion. There is no difference in the performance at comparable pH values in the presence or absence of carbonate on monometallic Pt indicating that water/hydroxide is the primary proton acceptor for alkaline HOR in 0.1 M KOH aqueous electrolyte. Finally, we observe no pH or carbonate dependence for the ORR on monometallic Pt.}, number={3}, journal={Journal of The Electrochemical Society}, publisher={The Electrochemical Society}, author={John, Samuel St. and Atkinson, Robert W., III and Roy, Asa and Unocic, Raymond R. and Papandrew, Alexander B. and Zawodzinski, Thomas A., Jr.}, year={2016}, pages={F291–F295} }
@article{achtyl_unocic_xu_cai_raju_zhang_sacci_vlassiouk_fulvio_ganesh_et al._2015, title={Aqueous proton transfer across single-layer graphene}, volume={6}, DOI={10.1038/ncomms7539}, abstractNote={Proton transfer across single layer graphene is associated with large computed energy barriers and is therefore thought to be unfavorable at room temperature unless nanoscale holes or dopants are introduced, or a potential bias is applied. Here, we subject single layer graphene supported on fused silica to cycles of high and low pH and show that protons transfer reversibly from the aqueous phase through the graphene to the other side where they undergo acid-base chemistry with the silica hydroxyl groups. After ruling out diffusion through macroscopic pinholes, the protons are found to transfer through rare, naturally occurring atomic defects. Computer simulations reveal low energy barriers of 0.68 to 0.75 eV for aqueous proton transfer across hydroxyl-terminated atomic defects that participate in a Grotthuss-type relay, while pyrylium-like ether terminations shut down proton exchange. Unfavorable energy barriers to helium and hydrogen transfer indicate the transfer process is selective for aqueous protons.}, journal={Nat Comms}, publisher={Nature Publishing Group}, author={Achtyl, Jennifer L. and Unocic, Raymond R. and Xu, Lijun and Cai, Yu and Raju, Muralikrishna and Zhang, Weiwei and Sacci, Robert L. and Vlassiouk, Ivan V. and Fulvio, Pasquale F. and Ganesh, Panchapakesan and et al.}, year={2015}, month={Mar}, pages={6539} }
@article{jesse_he_lupini_leonard_oxley_ovchinnikov_unocic_tselev_fuentes-cabrera_sumpter_et al._2015, title={Atomic-Level Sculpting of Crystalline Oxides: Toward Bulk Nanofabrication with Single Atomic Plane Precision}, volume={11}, DOI={10.1002/smll.201502048}, abstractNote={The atomic‐level sculpting of 3D crystalline oxide nanostructures from metastable amorphous films in a scanning transmission electron microscope (STEM) is demonstrated. Strontium titanate nanostructures grow epitaxially from the crystalline substrate following the beam path. This method can be used for fabricating crystalline structures as small as 1–2 nm and the process can be observed in situ with atomic resolution. The fabrication of arbitrary shape structures via control of the position and scan speed of the electron beam is further demonstrated. Combined with broad availability of the atomic resolved electron microscopy platforms, these observations suggest the feasibility of large scale implementation of bulk atomic‐level fabrication as a new enabling tool of nanoscience and technology, providing a bottom‐up, atomic‐level complement to 3D printing.}, number={44}, journal={Small}, publisher={Wiley-Blackwell}, author={Jesse, Stephen and He, Qian and Lupini, Andrew R. and Leonard, Donovan N. and Oxley, Mark P. and Ovchinnikov, Oleg and Unocic, Raymond R. and Tselev, Alexander and Fuentes-Cabrera, Miguel and Sumpter, Bobby G. and et al.}, year={2015}, month={Oct}, pages={5895–5900} }
@article{naguib_unocic_armstrong_nanda_2015, title={Large-scale delamination of multi-layers transition metal carbides and carbonitrides “MXenes”}, volume={44}, DOI={10.1039/c5dt01247c}, abstractNote={Herein we report on a general approach to delaminate multi-layered MXenes using an organic base to induce swelling that in turn weakens the bonds between the MX layers. Simple agitation or mild sonication of the swollen MXene in water resulted in the large-scale delamination of the MXene layers. The delamination method is demonstrated for vanadium carbide and titanium carbonitride MXenes.}, number={20}, journal={Dalton Trans.}, publisher={Royal Society of Chemistry (RSC)}, author={Naguib, Michael and Unocic, Raymond R. and Armstrong, Beth L. and Nanda, Jagjit}, year={2015}, pages={9353–9358} }
@article{binder_toops_unocic_parks_dai_2015, title={Low-Temperature CO Oxidation over a Ternary Oxide Catalyst with High Resistance to Hydrocarbon Inhibition}, volume={127}, DOI={10.1002/ange.201506093}, abstractNote={Abstract Platinum group metal (PGM) catalysts are the current standard for control of pollutants in automotive exhaust streams. Aside from their high cost, PGM catalysts struggle with CO oxidation at low temperatures (<200 °C) due to inhibition by hydrocarbons in exhaust streams. Here we present a ternary mixed oxide catalyst composed of copper oxide, cobalt oxide, and ceria (dubbed CCC) that outperforms synthesized and commercial PGM catalysts for CO oxidation in simulated exhaust streams while showing no signs of inhibition by propene. Diffuse reflectance IR (DRIFTS) and light‐off data both indicate low interaction between propene and the CO oxidation active site on this catalyst, and a separation of adsorption sites is proposed as the cause of this inhibition resistance. This catalyst shows great potential as a low‐cost component for low temperature exhaust streams that are expected to be a characteristic of future automotive systems.}, number={45}, journal={Angew. Chem.}, publisher={Wiley-Blackwell}, author={Binder, Andrew J. and Toops, Todd J. and Unocic, Raymond R. and Parks, James E. and Dai, Sheng}, year={2015}, month={Sep}, pages={13461–13465} }
@article{kercher_kolopus_carroll_unocic_kirklin_wolverton_stooksbury_boatner_dudney_2015, title={Mixed Polyanion Glass Cathodes: Glass-State Conversion Reactions}, volume={163}, ISSN={0013-4651 1945-7111}, url={http://dx.doi.org/10.1149/2.0381602jes}, DOI={10.1149/2.0381602jes}, abstractNote={Mixed polyanion glasses can undergo glass-state conversion (GSC) reactions to provide an alternate class of high-capacity cathode materials. GSC reactions have been demonstrated in phosphate/vanadate glasses with Ag, Co, Cu, Fe, and Ni cations. These mixed polyanion glasses provided high capacity and good high power performance, but suffer from moderate voltages, large voltage hysteresis, and significant capacity fade with cycling. Details of the GSC reaction have been revealed by X-ray absorption spectroscopy, electron microscopy, and energy dispersive X-ray spectroscopy of ex situ cathodes at key states of charge. Using the Open Quantum Materials Database (OQMD), a computational thermodynamic model has been developed to predict the near-equilibrium voltages of glass-state conversion reactions in mixed polyanion glasses.}, number={2}, journal={Journal of The Electrochemical Society}, publisher={The Electrochemical Society}, author={Kercher, A. K. and Kolopus, J. A. and Carroll, K. J. and Unocic, R. R. and Kirklin, S. and Wolverton, C. and Stooksbury, S. L. and Boatner, L. A. and Dudney, N. J.}, year={2015}, month={Nov}, pages={A131–A137} }
@article{sacci_black_balke_dudney_more_unocic_2015, title={Nanoscale Imaging of Fundamental Li Battery Chemistry: Solid-Electrolyte Interphase Formation and Preferential Growth of Lithium Metal Nanoclusters}, volume={15}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl5048626}, DOI={10.1021/nl5048626}, abstractNote={The performance characteristics of Li-ion batteries are intrinsically linked to evolving nanoscale interfacial electrochemical reactions. To probe the mechanisms of solid electrolyte interphase (SEI) formation and to track Li nucleation and growth mechanisms from a standard organic battery electrolyte (LiPF6 in EC:DMC), we used in situ electrochemical scanning transmission electron microscopy (ec-S/TEM) to perform controlled electrochemical potential sweep measurements while simultaneously imaging site-specific structures resulting from electrochemical reactions. A combined quantitative electrochemical measurement and STEM imaging approach is used to demonstrate that chemically sensitive annular dark field STEM imaging can be used to estimate the density of the evolving SEI and to identify Li-containing phases formed in the liquid cell. We report that the SEI is approximately twice as dense as the electrolyte as determined from imaging and electron scattering theory. We also observe site-specific locations where Li nucleates and grows on the surface and edge of the glassy carbon electrode. Lastly, this report demonstrates the investigative power of quantitative nanoscale imaging combined with electrochemical measurements for studying fluid-solid interfaces and their evolving chemistries.}, number={3}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Sacci, Robert L. and Black, Jennifer M. and Balke, Nina and Dudney, Nancy J. and More, Karren L. and Unocic, Raymond R.}, year={2015}, month={Feb}, pages={2011–2018} }
@article{jesse_he_lupini_leonard_oxley_ovchinnikov_unocic_tselev_fuentes-cabrera_sumpter_et al._2015, title={Patterning: Atomic-Level Sculpting of Crystalline Oxides: Toward Bulk Nanofabrication with Single Atomic Plane Precision (Small 44/2015)}, volume={11}, DOI={10.1002/smll.201570264}, abstractNote={On page 5895, Q. He, A. Y. Borisevich, and co-workers describe how an aberration-corrected e-beam in a scanning transmission electron microscope can be used to crystallize amorphous complex oxides with atomic plane precision. Using this control system, epitaxial growth of SrTiO3 is achieved to pattern text onto a 90 × 25 nm area, as shown in the image. Each feature shown is about 20 unit cells (about 8 nm) wide.}, number={44}, journal={Small}, publisher={Wiley-Blackwell}, author={Jesse, Stephen and He, Qian and Lupini, Andrew R. and Leonard, Donovan N. and Oxley, Mark P. and Ovchinnikov, Oleg and Unocic, Raymond R. and Tselev, Alexander and Fuentes-Cabrera, Miguel and Sumpter, Bobby G. and et al.}, year={2015}, month={Nov}, pages={5854–5854} }
@article{john_atkinson_unocic_unocic_zawodzinski_papandrew_2015, title={Platinum and Palladium Overlayers Dramatically Enhance the Activity of Ruthenium Nanotubes for Alkaline Hydrogen Oxidation}, volume={5}, DOI={10.1021/acscatal.5b01432}, abstractNote={Templated vapor synthesis and thermal annealing were used to synthesize unsupported metallic Ru nanotubes with Pt or Pd overlayers. By controlling the elemental composition and thickness of these overlayers, we obtain nanostructures with very high alkaline hydrogen oxidation activity. Nanotubes with a nominal atomic composition of Ru0.90Pt0.10 display a surface-specific activity (2.4 mA/cm2) that is 35 times greater than that of pure Ru nanotubes at a 50 mV overpotential and ∼2.5 times greater than that of pure Pt nanotubes (0.98 mA/cm2). The surface-segregated structure also confers dramatically increased Pt utilization efficiency. We find a platinum-mass-specific activity of 1240 A/gPt for the optimized nanotube versus 280 A/gPt for carbon-supported Pt nanoparticles and 109 A/gPt for monometallic Pt nanotubes. We attribute the enhancement of both area- and platinum-mass-specific activity to the atomic-scale homeomorphism of the nanotube form factor with adlayer-modified polycrystals. In this case, subsurface ligand and bifunctional effects previously observed on segregated, adlayer-modified polycrystals are translated to nanoscale catalysts.}, number={11}, journal={ACS Catal.}, publisher={American Chemical Society (ACS)}, author={John, Samuel St. and Atkinson, Robert W. and Unocic, Kinga A. and Unocic, Raymond R. and Zawodzinski, Thomas A. and Papandrew, Alexander B.}, year={2015}, month={Nov}, pages={7015–7023} }
@article{unocic_baggetto_veith_aguiar_unocic_sacci_dudney_more_2015, title={Probing battery chemistry with liquid cell electron energy loss spectroscopy}, volume={51}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/c5cc07180a}, DOI={10.1039/c5cc07180a}, abstractNote={We demonstrate the ability to apply electron energy loss spectroscopy (EELS) to follow the chemistry and oxidation states of LiMn2O4 and Li4Ti5O12 battery electrodes within a battery solvent. This is significant as the use and importance of in situ electrochemical cells coupled with a scanning/transmission electron microscope (S/TEM) has expanded and been applied to follow changes in battery chemistry during electrochemical cycling. We discuss experimental parameters that influence measurement sensitivity and provide a framework to apply this important analytical method to future in situ electrochemical studies.}, number={91}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Unocic, Raymond R. and Baggetto, Loïc and Veith, Gabriel M. and Aguiar, Jeffery A. and Unocic, Kinga A. and Sacci, Robert L. and Dudney, Nancy J. and More, Karren L.}, year={2015}, pages={16377–16380} }
@article{ievlev_jesse_cochell_unocic_protopopescu_kalinin_2015, title={Quantitative Description of Crystal Nucleation and Growth from in Situ Liquid Scanning Transmission Electron Microscopy}, volume={9}, DOI={10.1021/acsnano.5b03720}, abstractNote={Recent advances in liquid cell (scanning) transmission electron microscopy (S)TEM has enabled in situ nanoscale investigations of controlled nanocrystal growth mechanisms. Here, we experimentally and quantitatively investigated the nucleation and growth mechanisms of Pt nanostructures from an aqueous solution of K2PtCl6. Averaged statistical, network, and local approaches have been used for the data analysis and the description of both collective particles dynamics and local growth features. In particular, interaction between neighboring particles has been revealed and attributed to reduction of the platinum concentration in the vicinity of the particle boundary. The local approach for solving the inverse problem showed that particles dynamics can be simulated by a stationary diffusional model. The obtained results are important for understanding nanocrystal formation and growth processes and for optimization of synthesis conditions.}, number={12}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Ievlev, Anton V. and Jesse, Stephen and Cochell, Thomas J. and Unocic, Raymond R. and Protopopescu, Vladimir A. and Kalinin, Sergei V.}, year={2015}, pages={11784–11791} }
@article{papandrew_atkinson_unocic_zawodzinski_2015, title={Ruthenium as a CO-tolerant hydrogen oxidation catalyst for solid acid fuel cells}, volume={3}, DOI={10.1039/c4ta06451h}, abstractNote={In solid acid fuel cells operating at 250 °C, Ru catalysts are more tolerant to CO than Pt.}, number={7}, journal={J. Mater. Chem. A}, publisher={Royal Society of Chemistry (RSC)}, author={Papandrew, Alexander B. and Atkinson, Robert W., III and Unocic, Raymond R. and Zawodzinski, Thomas A.}, year={2015}, pages={3984–3987} }
@article{john_atkinson_unocic_zawodzinski_papandrew_2015, title={Ruthenium-Alloy Electrocatalysts with Tunable Hydrogen Oxidation Kinetics in Alkaline Electrolyte}, volume={119}, DOI={10.1021/acs.jpcc.5b03284}, abstractNote={High-surface-area ruthenium-based RuxMy (M = Pt or Pd) alloy catalysts supported on carbon black were synthesized to investigate the hydrogen oxidation reaction (HOR) in alkaline electrolytes. The exchange current density for hydrogen oxidation on a Pt-rich Ru0.20Pt0.80 catalyst is 1.42 mA/cm2, nearly 3 times that of Pt (0.490 mA/cm2). Furthermore, RuxPty alloy surfaces in 0.1 M KOH yield a Tafel slope of ∼30 mV/dec, in contrast with the ∼125 mV/dec Tafel slope observed for supported Pt, signifying that hydrogen dissociative adsorption is rate-limiting rather than charge-transfer processes. Ru alloying with Pd does not result in modified kinetics. We attribute these disparate results to the interplay of bifunctional and ligand effects. The dependence of the rate-determining step on the choice of alloy element allows for tuning catalyst activity and suggests not only that a low-cost, alkaline anode catalyst is possible but also that it is tantalizingly close to reality.}, number={24}, journal={J. Phys. Chem. C}, publisher={American Chemical Society (ACS)}, author={John, Samuel St. and Atkinson, Robert W. and Unocic, Raymond R. and Zawodzinski, Thomas A. and Papandrew, Alexander B.}, year={2015}, month={Jun}, pages={13481–13487} }
@article{atkinson_st. john_dyck_unocic_unocic_burke_cisco_rice_zawodzinski_papandrew_2015, title={Supportless, Bismuth-Modified Palladium Nanotubes with Improved Activity and Stability for Formic Acid Oxidation}, volume={5}, ISSN={2155-5435 2155-5435}, url={http://dx.doi.org/10.1021/acscatal.5b01239}, DOI={10.1021/acscatal.5b01239}, abstractNote={Palladium nanotubes (PdNTs) were synthesized by templated vapor deposition and investigated for formic acid electrooxidation. Annealed PdNTs are 2.4 times more active (2.19 mA/cm2) than commercial carbon-supported palladium (0.91 mA/cm2) at 0.3 V vs RHE. Bismuth modification improved nanotube performance over 4 times (3.75 mA/cm2) vs Pd/C and nearly 2 times vs unmodified PdNTs. A surface Bi coverage of 80% results in optimal site-specific activity by drastically reducing surface-poisoning CO generation during formic acid electrooxidation. The Bi-modified PdNTs are exceptionally stable, maintaining 2 times the area-normalized current density as Pd/C after 24 h at 0.2 V vs RHE. We attribute the enhanced activity and stability of the nanotube catalysts to the presence of highly coordinated surfaces, mimicking a flat polycrystal while retaining high surface area geometry.}, number={9}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Atkinson, Robert W., III and St. John, Samuel and Dyck, Ondrej and Unocic, Kinga A. and Unocic, Raymond R. and Burke, Colten S. and Cisco, Joshua W. and Rice, Cynthia A. and Zawodzinski, Thomas A., Jr. and Papandrew, Alexander B.}, year={2015}, month={Aug}, pages={5154–5163} }
@article{stehle_meyer_unocic_kidder_polizos_datskos_jackson_smirnov_vlassiouk_2015, title={Synthesis of Hexagonal Boron Nitride Monolayer: Control of Nucleation and Crystal Morphology}, volume={27}, DOI={10.1021/acs.chemmater.5b03607}, abstractNote={Monolayer hexagonal boron nitride (hBN) attracts significant attention due to the potential to be used as a complementary two-dimensional dielectric in fabrication of functional 2D heterostructures. Here we investigate the growth stages of the hBN single crystals and show that hBN crystals change their shape from triangular to truncated triangular and further to hexagonal depending on copper substrate distance from the precursor. We suggest that the observed hBN crystal shape variation is affected by the ratio of boron to nitrogen active species concentrations on the copper surface inside the CVD reactor. Strong temperature dependence reveals the activation energies for the hBN nucleation process of ∼5 eV and crystal growth of ∼3.5 eV. We also show that the resulting h-BN film morphology is strongly affected by the heating method of borazane precursor and the buffer gas. Elucidation of these details facilitated synthesis of high quality large area monolayer hexagonal boron nitride by atmospheric pressure chemical vapor deposition on copper using borazane as a precursor.}, number={23}, journal={Chem. Mater.}, publisher={American Chemical Society (ACS)}, author={Stehle, Yijing and Meyer, Harry M. and Unocic, Raymond R. and Kidder, Michelle and Polizos, Georgios and Datskos, Panos G. and Jackson, Roderick and Smirnov, Sergei N. and Vlassiouk, Ivan V.}, year={2015}, pages={8041–8047} }
@article{atkinson_unocic_unocic_veith_zawodzinski_papandrew_2015, title={Vapor Synthesis and Thermal Modification of Supportless Platinum–Ruthenium Nanotubes and Application as Methanol Electrooxidation Catalysts}, volume={7}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am508228b}, DOI={10.1021/am508228b}, abstractNote={Metallic, mixed-phase, and alloyed bimetallic Pt-Ru nanotubes were synthesized by a novel route based on the sublimation of metal acetylacetonate precursors and their subsequent vapor deposition within anodic alumina templates. Nanotube architectures were tuned by thermal annealing treatments. As-synthesized nanotubes are composed of nanoparticulate, metallic platinum and hydrous ruthenium oxide whose respective thicknesses depend on the sample chemical composition. The Pt-decorated, hydrous Ru oxide nanotubes may be thermally annealed to promote a series of chemical and physical changes to the nanotube structures, including alloy formation, crystallite growth, and morphological evolution. Annealed Pt-Ru alloy nanotubes and their as-synthesized analogs demonstrate relatively high specific activities for the oxidation of methanol. As-synthesized, mixed-phase Pt-Ru nanotubes (0.39 mA/cm(2)) and metallic alloyed Pt64Ru36NTs (0.33 mA/cm(2)) have considerably higher area-normalized activities than PtRu black (0.22 mA/cm(2)) at 0.65 V vs RHE.}, number={19}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Atkinson, Robert W., III and Unocic, Raymond R. and Unocic, Kinga A. and Veith, Gabriel M. and Zawodzinski, Thomas A., Jr. and Papandrew, Alexander B.}, year={2015}, month={May}, pages={10115–10124} }
@article{surwade_smirnov_vlassiouk_unocic_veith_dai_mahurin_2015, title={Water desalination using nanoporous single-layer graphene}, volume={10}, DOI={10.1038/nnano.2015.37}, number={5}, journal={Nature Nanotech}, publisher={Nature Publishing Group}, author={Surwade, Sumedh P. and Smirnov, Sergei N. and Vlassiouk, Ivan V. and Unocic, Raymond R. and Veith, Gabriel M. and Dai, Sheng and Mahurin, Shannon M.}, year={2015}, month={Mar}, pages={459–464} }
@article{sun_liao_baggetto_guo_unocic_veith_dai_2014, title={Bis(fluoromalonato)borate (BFMB) anion based ionic liquid as an additive for lithium-ion battery electrolytes}, volume={2}, DOI={10.1039/c3ta14943a}, abstractNote={New ionic liquid BDMIm·BFMB is synthesized and used as an additive (5 wt%) in 1.0 M LiPF6/PC electrolyte to support reversible charge/discharge in graphite half-cell.}, number={20}, journal={J. Mater. Chem. A}, publisher={Royal Society of Chemistry (RSC)}, author={Sun, Xiao-Guang and Liao, Chen and Baggetto, Loïc and Guo, Bingkun and Unocic, Raymond R. and Veith, Gabriel M. and Dai, Sheng}, year={2014}, pages={7606} }
@article{hayes_unocic_nasrollahzadeh_2014, title={Creep Deformation of Allvac 718Plus}, volume={46}, ISSN={1073-5623 1543-1940}, url={http://dx.doi.org/10.1007/s11661-014-2564-y}, DOI={10.1007/s11661-014-2564-y}, number={1}, journal={Metallurgical and Materials Transactions A}, publisher={Springer Science and Business Media LLC}, author={Hayes, Robert W. and Unocic, Raymond R. and Nasrollahzadeh, Maryam}, year={2014}, month={Nov}, pages={218–228} }
@article{unocic_sun_sacci_adamczyk_alsem_dai_dudney_more_2014, title={Direct Visualization of Solid Electrolyte Interphase Formation in Lithium-Ion Batteries with In Situ Electrochemical Transmission Electron Microscopy}, volume={20}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/s1431927614012744}, DOI={10.1017/s1431927614012744}, abstractNote={Abstract Complex, electrochemically driven transport processes form the basis of electrochemical energy storage devices. The direct imaging of electrochemical processes at high spatial resolution and within their native liquid electrolyte would significantly enhance our understanding of device functionality, but has remained elusive. In this work we use a recently developed liquid cell for in situ electrochemical transmission electron microscopy to obtain insight into the electrolyte decomposition mechanisms and kinetics in lithium-ion (Li-ion) batteries by characterizing the dynamics of solid electrolyte interphase (SEI) formation and evolution. Here we are able to visualize the detailed structure of the SEI that forms locally at the electrode/electrolyte interface during lithium intercalation into natural graphite from an organic Li-ion battery electrolyte. We quantify the SEI growth kinetics and observe the dynamic self-healing nature of the SEI with changes in cell potential.}, number={4}, journal={Microscopy and Microanalysis}, publisher={Oxford University Press (OUP)}, author={Unocic, Raymond R. and Sun, Xiao-Guang and Sacci, Robert L. and Adamczyk, Leslie A. and Alsem, Daan Hein and Dai, Sheng and Dudney, Nancy J. and More, Karren L.}, year={2014}, month={Jul}, pages={1029–1037} }
@article{veith_baggetto_sacci_unocic_tenhaeff_browning_2014, title={Direct measurement of the chemical reactivity of silicon electrodes with LiPF6-based battery electrolytes}, volume={50}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/c3cc49269a}, DOI={10.1039/c3cc49269a}, abstractNote={We report the first direct measurement of the extent of the spontaneous non-electrochemically driven reaction between a lithium ion battery electrode surface (Si) and a liquid electrolyte (1.2 M LiPF6-3 : 7 wt% ethylene carbonate : dimethyl carbonate). This layer is estimated to be 35 Å thick with a SLD of ∼ 4 × 10(-6) Å(-2) and likely originates from the consumption of the silicon surface.}, number={23}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Veith, Gabriel M. and Baggetto, Loïc and Sacci, Robert L. and Unocic, Raymond R. and Tenhaeff, Wyatt E. and Browning, James F.}, year={2014}, pages={3081} }
@article{schultz_unocic_desjardins_kennedy_2014, title={Formation of a Metallic Amorphous Layer During the Sliding Wear of Ti/TiN Nanolaminates}, volume={55}, ISSN={1023-8883 1573-2711}, url={http://dx.doi.org/10.1007/s11249-014-0350-z}, DOI={10.1007/s11249-014-0350-z}, number={2}, journal={Tribology Letters}, publisher={Springer Science and Business Media LLC}, author={Schultz, Bradley M. and Unocic, Raymond R. and DesJardins, John D. and Kennedy, Marian S.}, year={2014}, month={May}, pages={219–226} }
@article{borisevich_chi_unocic_2014, title={Functional Electron Microscopy for Electrochemistry Research: From the Atomic to Micro Scale}, volume={23}, DOI={10.1149/2.F07142if}, abstractNote={In this article, we present the possibilities that STEM and electron energy loss spectroscopy (EELS) offer in terms of probing fundamental aspects of electrochemical systems by combining electron microscopy with in situ control of local electrochemical potentials by tuning the atmosphere, by biasing, or using a liquid environment. Some recent advances in electron microscopy based studies of electrochemical processes in solids and at solid-liquid and solid-gas interfaces are summarized. STEM/EELS directly probes a broad range of parameters related to the electrochemical state of the system, including local atomic configurations, bond length and angle and valence states and orbital populations of atoms on the individual column level. The challenge in the development of these techniques is twofold. The first one is the continued need for increase in resolution, both spatial (for imaging) and energy (for spectroscopy). The second challenge is related to electrochemical aspects, and consequently to the necessity to control and probe the local electrochemical potentials and ionic flows in the active region under investigation. This necessitates development of stable electrochemical cells that can support high-resolution studies, while at the same time being able to control global potential and allow local interrogation.}, number={2}, journal={The Electrochemical Society-Interface}, author={Borisevich, A.Y. and Chi, M. and Unocic, R.R.}, year={2014}, pages={61–67} }
@article{sacci_dudney_more_unocic_2014, title={In operando Transmission Electron Microscopy Imaging of SEI Formation and Structure in Li-Ion and Li-Metal Batteries}, volume={20}, DOI={10.1017/s1431927614009428}, abstractNote={An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.}, number={S3}, journal={Microsc Microanal}, publisher={Cambridge University Press (CUP)}, author={Sacci, Robert L. and Dudney, Nancy J. and More, Karren L. and Unocic, Raymond R.}, year={2014}, month={Aug}, pages={1538–1539} }
@article{mehdi_gu_parent_xu_nasybulin_chen_unocic_xu_welch_abellan_et al._2014, title={In-Situ Electrochemical Transmission Electron Microscopy for Battery Research}, volume={20}, DOI={10.1017/s1431927614000488}, abstractNote={The recent development of in-situ liquid stages for (scanning) transmission electron microscopes now makes it possible for us to study the details of electrochemical processes under operando conditions. As electrochemical processes are complex, care must be taken to calibrate the system before any in-situ/operando observations. In addition, as the electron beam can cause effects that look similar to electrochemical processes at the electrolyte/electrode interface, an understanding of the role of the electron beam in modifying the operando observations must also be understood. In this paper we describe the design, assembly, and operation of an in-situ electrochemical cell, paying particular attention to the method for controlling and quantifying the experimental parameters. The use of this system is then demonstrated for the lithiation/delithiation of silicon nanowires.}, number={02}, journal={Microsc Microanal}, publisher={Cambridge University Press (CUP)}, author={Mehdi, B. Layla and Gu, Meng and Parent, Lucas R. and Xu, Wu and Nasybulin, Eduard N. and Chen, Xilin and Unocic, Raymond R. and Xu, Pinghong and Welch, David A. and Abellan, Patricia and et al.}, year={2014}, month={Apr}, pages={484–492} }
@article{unocic_allard_coffey_more_unocic_2014, title={Novel Method for Precision Controlled Heating of TEM Thin Sections to Study Reaction Processes}, volume={20}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/s1431927614009878}, DOI={10.1017/s1431927614009878}, abstractNote={An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.}, number={S3}, journal={Microscopy and Microanalysis}, publisher={Oxford University Press (OUP)}, author={Unocic, Kinga A. and Allard, Lawrence F. and Coffey, Dorothy W. and More, Karren L. and Unocic, Raymond R.}, year={2014}, month={Aug}, pages={1628–1629} }
@article{baggetto_carroll_hah_johnson_mullins_unocic_johnson_meng_veith_2014, title={Probing the Mechanism of Sodium Ion Insertion into Copper Antimony Cu 2 Sb Anodes}, volume={118}, DOI={10.1021/jp501032d}, abstractNote={We report experimental studies to understand the reaction mechanism of the intermetallic anode Cu2Sb with Na and demonstrate that it is capable of retaining about 250 mAh g–1 over 200 cycles when using fluoroethylene carbonate additive. X-ray diffraction data indicate during the first discharge the reaction leads to the formation of crystalline Na3Sb via an intermediate amorphous phase. Upon desodiation the Na3Sb reverts to an amorphous phase, which then recrystallizes into Cu2Sb at full charge, indicating a high degree of structural reversibility. The structure after charging to 1 V is different from that of Cu2Sb, as indicated by X-ray absorption spectroscopy and 121Sb Mössbauer spectroscopy, and is due to the formation of an amorphous Na–Cu–Sb phase. At full discharge, an isomer shift of −8.10 mm s–1 is measured, which is close to that of a Na3Sb reference powder (−7.95 mm s–1) and in agreement with the formation of Na3Sb domains. During charge, the isomer shift at 1 V (−9.29 mm s–1) is closer to that of the pristine material (−9.67 mm s–1), but the lower value is consistent with the lack of full desodiation, as expected from the potential profile and the XAS data.}, number={15}, journal={J. Phys. Chem. C}, publisher={American Chemical Society (ACS)}, author={Baggetto, Loïc and Carroll, Kyler J. and Hah, Hien-Yoong and Johnson, Charles E. and Mullins, David R. and Unocic, Raymond R. and Johnson, Jacqueline A. and Meng, Ying Shirley and Veith, Gabriel M.}, year={2014}, month={Apr}, pages={7856–7864} }
@article{unocic_sacci_brown_veith_dudney_more_walden_gardiner_damiano_nackashi_2014, title={Quantitative Electrochemical Measurements Using In Situ ec-S/TEM Devices}, volume={20}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/s1431927614000166}, DOI={10.1017/s1431927614000166}, abstractNote={Abstract Insight into dynamic electrochemical processes can be obtained with in situ electrochemical-scanning/transmission electron microscopy (ec-S/TEM), a technique that utilizes microfluidic electrochemical cells to characterize electrochemical processes with S/TEM imaging, diffraction, or spectroscopy. The microfluidic electrochemical cell is composed of microfabricated devices with glassy carbon and platinum microband electrodes in a three-electrode cell configuration. To establish the validity of this method for quantitative in situ electrochemistry research, cyclic voltammetry (CV), choronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) were performed using a standard one electron transfer redox couple [Fe(CN) 6 ] 3−/4− -based electrolyte. Established relationships of the electrode geometry and microfluidic conditions were fitted with CV and chronoamperometic measurements of analyte diffusion coefficients and were found to agree with well-accepted values that are on the order of 10 −5 cm 2 /s. Influence of the electron beam on electrochemical measurements was found to be negligible during CV scans where the current profile varied only within a few nA with the electron beam on and off, which is well within the hysteresis between multiple CV scans. The combination of experimental results provides a validation that quantitative electrochemistry experiments can be performed with these small-scale microfluidic electrochemical cells provided that accurate geometrical electrode configurations, diffusion boundary layers, and microfluidic conditions are accounted for.}, number={2}, journal={Microscopy and Microanalysis}, publisher={Oxford University Press (OUP)}, author={Unocic, Raymond R. and Sacci, Robert L. and Brown, Gilbert M. and Veith, Gabriel M. and Dudney, Nancy J. and More, Karren L. and Walden, Franklin S., II and Gardiner, Daniel S. and Damiano, John and Nackashi, David P.}, year={2014}, month={Mar}, pages={452–461} }
@article{zhou_nanda_martha_unocic_meyer_sahoo_miskiewicz_albrecht_2014, title={Role of Surface Functionality in the Electrochemical Performance of Silicon Nanowire Anodes for Rechargeable Lithium Batteries}, volume={6}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am500855a}, DOI={10.1021/am500855a}, abstractNote={We report the synthesis of silicon nanowires using the supercritical-fluid-liquid-solid growth method from two silicon precursors, monophenylsilane and trisilane. The nanowires were synthesized at least on a gram scale at a pilot scale facility, and various surface modification methods were developed to optimize the electrochemical performance. The observed electrochemical performance of the silicon nanowires was clearly dependent on the origination of the surface functional group, either from the residual precursor or from surface modifications. On the basis of detailed electron microscopy, X-ray photoelectron spectroscopy, and confocal Raman spectroscopy studies, we analyzed the surface chemical reactivity of the silicon nanowires with respect to their electrochemical performance in terms of their capacity retention over continuous charge-discharge cycles.}, number={10}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Zhou, Hui and Nanda, Jagjit and Martha, Surendra K. and Unocic, Raymond R. and Meyer, Harry M., III and Sahoo, Yudhisthira and Miskiewicz, Pawel and Albrecht, Thomas F.}, year={2014}, month={Apr}, pages={7607–7614} }
@article{baggetto_carroll_unocic_bridges_meng_veith_2014, title={Sodium Manganese Oxide Thin Films as Cathodes for Na-Ion Batteries}, volume={58}, DOI={10.1149/05812.0047ecst}, abstractNote={This paper presents the fabrication and characterization of sodium manganese oxide cathode thin films for rechargeable Na-ion batteries. Layered oxide compounds of nominal compositions Na 0.6 MnO 2 and Na 1.0 MnO 2 have been prepared by radio frequency magnetron sputtering and post-annealing at high temperatures under various conditions. The Na 0.6 MnO 2 thin films possess either a hexagonal or orthorhombic structure while the Na 1.0 MnO 2 films crystallize in a monoclinic structure, as shown by X-ray diffraction and X-ray absorption spectroscopy results. The potential profiles of the film cathodes are characterized by features similar to those measured for the powders and exhibit reversible storage capacities in the range of 50-60 mAh cm -2 mm -1 , which correspond to about 120-140 mAh g -1 , and are maintained over 80 cycles.}, number={12}, journal={ECS Transactions}, publisher={The Electrochemical Society}, author={Baggetto, L. and Carroll, K. J. and Unocic, R. R. and Bridges, C. A. and Meng, Y. S. and Veith, G. M.}, year={2014}, month={Feb}, pages={47–57} }
@article{unocic_sacci_veith_dudney_more_2014, title={Tuning Electrodeposition Parameters for Tailored Nanoparticle Size, Shape, and Morphology: An In Situ ec-STEM Investigation}, volume={20}, DOI={10.1017/s143192761400926x}, abstractNote={An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.}, number={S3}, journal={Microsc Microanal}, publisher={Cambridge University Press (CUP)}, author={Unocic, Raymond R. and Sacci, Robert L. and Veith, Gabriel M. and Dudney, Nancy J. and More, Karren L.}, year={2014}, month={Aug}, pages={1506–1507} }
@article{xiao_liu_baggetto_veith_more_unocic_2014, title={Unraveling manganese dissolution/deposition mechanisms on the negative electrode in lithium ion batteries}, volume={16}, ISSN={1463-9076 1463-9084}, url={http://dx.doi.org/10.1039/c4cp00833b}, DOI={10.1039/c4cp00833b}, abstractNote={The structure, chemistry, and spatial distribution of Mn-bearing nanoparticles dissolved from the Li1.05Mn2O4 cathode during accelerated electrochemical cycling tests at 55 °C and deposited within the solid electrolyte interphase (SEI) are directly characterized through HRTEM imaging and XPS. Here we use air protection and vacuum transfer systems to transport cycled electrodes for imaging and analytical characterization. From HRTEM imaging, we find that a band of individual metallic Mn nanoparticles forms locally at the SEI/graphite interface while the internal and outermost layer of the SEI contains a mixture of LiF and MnF2 nanoparticles, which is confirmed with XPS. Based on our experimental findings we propose a new interpretation of how Mn is reduced from the cathode and how metallic Mn and Mn-bearing nanoparticles form within the SEI during electrochemical cycling.}, number={22}, journal={Physical Chemistry Chemical Physics}, publisher={Royal Society of Chemistry (RSC)}, author={Xiao, Xingcheng and Liu, Zhongyi and Baggetto, Loïc and Veith, Gabriel M. and More, Karren L. and Unocic, Raymond R.}, year={2014}, pages={10398} }
@article{baggetto_ganesh_meisner_unocic_jumas_bridges_veith_2013, title={Characterization of sodium ion electrochemical reaction with tin anodes: Experiment and theory}, volume={234}, DOI={10.1016/j.jpowsour.2013.01.083}, journal={Journal of Power Sources}, publisher={Elsevier BV}, author={Baggetto, Loïc and Ganesh, P. and Meisner, Roberta P. and Unocic, Raymond R. and Jumas, Jean-Claude and Bridges, Craig A. and Veith, Gabriel M.}, year={2013}, month={Jul}, pages={48–59} }
@article{bridges_harrison_unocic_idrobo_paranthaman_manthiram_2013, title={Defect chemistry of phospho-olivine nanoparticles synthesized by a microwave-assisted solvothermal process}, volume={205}, DOI={10.1016/j.jssc.2013.07.011}, journal={Journal of Solid State Chemistry}, publisher={Elsevier BV}, author={Bridges, Craig A. and Harrison, Katharine L. and Unocic, Raymond R. and Idrobo, Juan-Carlos and Paranthaman, M. Parans and Manthiram, Arumugam}, year={2013}, month={Sep}, pages={197–204} }
@article{gu_parent_mehdi_unocic_mcdowell_sacci_xu_connell_xu_abellan_et al._2013, title={Demonstration of an Electrochemical Liquid Cell for Operando Transmission Electron Microscopy Observation of the Lithiation/Delithiation Behavior of Si Nanowire Battery Anodes}, volume={13}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl403402q}, DOI={10.1021/nl403402q}, abstractNote={Over the past few years, in situ transmission electron microscopy (TEM) studies of lithium ion batteries using an open-cell configuration have helped us to gain fundamental insights into the structural and chemical evolution of the electrode materials in real time. In the standard open-cell configuration, the electrolyte is either solid lithium oxide or an ionic liquid, which is point-contacted with the electrode. This cell design is inherently different from a real battery, where liquid electrolyte forms conformal contact with electrode materials. The knowledge learnt from open cells can deviate significantly from the real battery, calling for operando TEM technique with conformal liquid electrolyte contact. In this paper, we developed an operando TEM electrochemical liquid cell to meet this need, providing the configuration of a real battery and in a relevant liquid electrolyte. To demonstrate this novel technique, we studied the lithiation/delithiation behavior of single Si nanowires. Some of lithiation/delithation behaviors of Si obtained using the liquid cell are consistent with the results from the open-cell studies. However, we also discovered new insights different from the open cell configuration—the dynamics of the electrolyte and, potentially, a future quantitative characterization of the solid electrolyte interphase layer formation and structural and chemical evolution.}, number={12}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Gu, Meng and Parent, Lucas R. and Mehdi, B. Layla and Unocic, Raymond R. and McDowell, Matthew T. and Sacci, Robert L. and Xu, Wu and Connell, Justin Grant and Xu, Pinghong and Abellan, Patricia and et al.}, year={2013}, month={Nov}, pages={6106–6112} }
@article{sacci_dudney_more_parent_arslan_browning_unocic_2014, title={Direct visualization of initial SEI morphology and growth kinetics during lithium deposition by in situ electrochemical transmission electron microscopy}, volume={50}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/c3cc49029g}, DOI={10.1039/c3cc49029g}, abstractNote={Deposition of Li is a major safety concern existing in Li-ion secondary batteries. Here we perform the first in situ high spatial resolution measurement coupled with real-time quantitative electrochemistry to characterize SEI formation on gold using a standard battery electrolyte. We demonstrate that a dendritic SEI forms prior to Li deposition and that it remains on the surface after Li electrodissolution.}, number={17}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Sacci, Robert L. and Dudney, Nancy J. and More, Karren L. and Parent, Lucas R. and Arslan, Ilke and Browning, Nigel D. and Unocic, Raymond R.}, year={2014}, pages={2104} }
@article{browning_baggetto_unocic_dudney_veith_2013, title={Gas evolution from cathode materials: A pathway to solvent decomposition concomitant to SEI formation}, volume={239}, DOI={10.1016/j.jpowsour.2013.03.118}, journal={Journal of Power Sources}, publisher={Elsevier BV}, author={Browning, Katie L. and Baggetto, Loïc and Unocic, Raymond R. and Dudney, Nancy J. and Veith, Gabriel M.}, year={2013}, month={Oct}, pages={341–346} }
@article{bi_paranthaman_guo_unocic_meyer_bridges_sun_dai_2014, title={High performance Cr, N-codoped mesoporous TiO2 microspheres for lithium-ion batteries}, volume={2}, DOI={10.1039/c3ta14535b}, abstractNote={We develop a simple hydrothermal process followed by post-nitridation treatment for the synthesis of chromium, nitrogen-codoped titanium oxide, which exhibits a remarkable charge–discharge capacity at a rate of 5 C and shows an excellent stability for over 300 cycles as an anode material for lithium ion batteries.}, number={6}, journal={Journal of Materials Chemistry A}, publisher={Royal Society of Chemistry (RSC)}, author={Bi, Z. and Paranthaman, M.P. and Guo, B. and Unocic, R.R. and Meyer, H.M., III and Bridges, C.A. and Sun, Xiao-Guang and Dai, Sheng}, year={2014}, pages={1818–1824} }
@article{arruda_lawton_kumar_unocic_kravchenko_zawodzinski_jesse_kalinin_balke_2013, title={In Situ Formation of Micron-Scale Li-Metal Anodes with High Cyclability}, volume={3}, ISSN={2162-8726 2162-8734}, url={http://dx.doi.org/10.1149/2.003401eel}, DOI={10.1149/2.003401eel}, abstractNote={Scanning probe microscopy methods have been used to electrodeposit and cycle micron-scale Li anodes deposited electrochemically under nanofabricated Au current collectors. An average Li volume of 5 × 108 nm3 was deposited and cycled with 100% coulombic efficiency for ∼160 cycles. Integrated charge/discharge values agree with before/after topography, as well as in situ dilatometry, suggesting this is a reliable method to study solid-state electrochemical processes. In this work we illustrate the possibility to deposit highly cyclable nanometer thick Li electrodes by mature SPM and nanofab techniques which can pave the way for inexpensive nanoscale battery arrays.}, number={1}, journal={ECS Electrochemistry Letters}, publisher={The Electrochemical Society}, author={Arruda, T. M. and Lawton, J. S. and Kumar, A. and Unocic, R. R. and Kravchenko, I. I. and Zawodzinski, T. A. and Jesse, S. and Kalinin, S. V. and Balke, N.}, year={2013}, month={Nov}, pages={A4–A7} }
@article{yoon_bridges_unocic_paranthaman_2013, title={Mesoporous TiO2 spheres with a nitridated conducting layer for lithium-ion batteries}, volume={48}, ISSN={0022-2461 1573-4803}, url={http://dx.doi.org/10.1007/s10853-012-7098-3}, DOI={10.1007/s10853-012-7098-3}, number={15}, journal={Journal of Materials Science}, publisher={Springer Science and Business Media LLC}, author={Yoon, Sukeun and Bridges, Craig A. and Unocic, Raymond R. and Paranthaman, M. Parans}, year={2013}, month={May}, pages={5125–5131} }
@article{baggetto_allcorn_unocic_manthiram_veith_2013, title={Mo3Sb7 as a very fast anode material for lithium-ion and sodium-ion batteries}, volume={1}, ISSN={2050-7488 2050-7496}, url={http://dx.doi.org/10.1039/c3ta12040f}, DOI={10.1039/c3ta12040f}, abstractNote={Mo3Sb7 thin films prepared by magnetron sputtering are evaluated as an anode material for Li-ion and Na-ion batteries. The as deposited films are amorphous and composed of small agglomerated domains with an overall Sb/Mo ratio of 2.34 that is almost identical to the ratio measured for the starting powder and the expected nominal ratio of 2.33. When cycled with Li and Na, the films show large storage capacities of around 430 and 330 mA h g−1, respectively, with good capacity retention. In addition, micron thick films retain large capacities of about 310 and 280 mA h g−1 at very high rates of 100 and 30 C-rate currents for Li and Na, respectively. The XRD study of the changes in the structure of the electrode material reveals that Li3Sb forms at full discharge whereas the electrode at full charge is amorphous. For the reaction with Na, the electrode material remains amorphous. Analysis of the surface chemistry characterized by XPS suggests the formation of an inorganic layer (LiF, LixPOyFz) covered by organic products (carbonates, esters, ethers) in the case of Li and the formation of an organic layer only (carbonates) in the case of Na. The electrode surface is visible at full charge for Na, thereby indicating that the Solid Electrolyte Interphase (SEI) layer is thinner when cycling with Na compared to that with Li. Overall, the results highlight the very good potential of Mo3Sb7 as an anode for Li- and Na-ion batteries.}, number={37}, journal={Journal of Materials Chemistry A}, publisher={Royal Society of Chemistry (RSC)}, author={Baggetto, Loïc and Allcorn, Eric and Unocic, Raymond R. and Manthiram, Arumugam and Veith, Gabriel M.}, year={2013}, pages={11163} }
@article{martha_nanda_kim_unocic_pannala_dudney_2013, title={Solid electrolyte coated high voltage layered–layered lithium-rich composite cathode: Li1.2Mn0.525Ni0.175Co0.1O2}, volume={1}, ISSN={2050-7488 2050-7496}, url={http://dx.doi.org/10.1039/c3ta10586e}, DOI={10.1039/c3ta10586e}, abstractNote={The electrochemical rate performance and capacity retention of the "layered–layered" lithium rich Li1.2Mn0.525Ni0.175Co0.1O2 (Li-rich NMC) material are significantly improved by a nanometer layer coating of a lithium conducting solid electrolyte, lithium phosphorus oxynitride (LiPON). The LiPON layer is deposited on the Li-rich NMC particles by the RF-magnetron sputtering method. The presence of the LiPON layer provides interfacial stability under high current (rate) and voltage cycling conditions and thereby improves the capacity retention over cycle life compared to pristine or uncoated Li-rich NMC. Specifically, the LiPON coated Li-rich NMC composite electrode showed stable reversible capacities of >275 mAh g−1 when cycled to 4.9 V for more than 300 cycles, and showed at least threefold improvements in the rate performance compared to the uncoated electrode compositions. Increasing the LiPON layer thickness beyond a few nanometers leads to capacity fade due to increasing electronic resistance. Detailed microstructural and electrochemical impedance spectroscopy studies are undertaken to characterize and understand the role of LiPON in improving the interfacial stability and electrochemical activity at the interface.}, number={18}, journal={Journal of Materials Chemistry A}, publisher={Royal Society of Chemistry (RSC)}, author={Martha, Surendra K. and Nanda, Jagjit and Kim, Yoongu and Unocic, Raymond R. and Pannala, Sreekanth and Dudney, Nancy J.}, year={2013}, pages={5587} }
@article{qiao_brown_adcock_veith_bauer_payzant_unocic_dai_2012, title={A Topotactic Synthetic Methodology for Highly Fluorine-Doped Mesoporous Metal Oxides}, volume={124}, DOI={10.1002/ange.201107812}, abstractNote={F-Taktik: Hoch fluordotierte mesoporöse Metalloxide (bis 40 Atom-%) wurden ausgehend von mesoporösen Metalloxiden durch topotaktische Fluorierung mit Fluor hergestellt. Die Oberflächen, Porengröße und -volumen sowie die Konzentration der Fluoratome dieser Materialien ließen sich durch Variation der Fluorierungszeit und -temperatur über einen breiten Bereich einstellen. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={12}, journal={Angew. Chem.}, publisher={Wiley-Blackwell}, author={Qiao, Zhen-an and Brown, Suree S. and Adcock, Jamie and Veith, Gabriel M. and Bauer, J. Chris and Payzant, E. Andrew and Unocic, Raymond R. and Dai, Sheng}, year={2012}, month={Feb}, pages={2942–2947} }
@article{qiao_brown_adcock_veith_bauer_payzant_unocic_dai_2012, title={A Topotactic Synthetic Methodology for Highly Fluorine‐Doped Mesoporous Metal Oxides}, volume={51}, ISSN={1433-7851 1521-3773}, url={http://dx.doi.org/10.1002/anie.201107812}, DOI={10.1002/anie.201107812}, number={12}, journal={Angewandte Chemie International Edition}, publisher={Wiley}, author={Qiao, Zhen‐an and Brown, Suree S. and Adcock, Jamie and Veith, Gabriel M. and Bauer, J. Chris and Payzant, E. Andrew and Unocic, Raymond R. and Dai, Sheng}, year={2012}, month={Feb}, pages={2888–2893} }
@article{yoon_liao_sun_bridges_unocic_nanda_dai_paranthaman_2012, title={Conductive surface modification of LiFePO4 with nitrogen-doped carbon layers for lithium-ion batteries}, volume={22}, ISSN={0959-9428 1364-5501}, url={http://dx.doi.org/10.1039/c2jm15325d}, DOI={10.1039/c2jm15325d}, abstractNote={The surface of rod-like LiFePO4 modified with a conductive nitrogen-doped carbon layer has been prepared using hydrothermal processing followed by post-annealing in the presence of an ionic liquid. The conductive surface modified rod-like LiFePO4 exhibits good capacity retention and high rate capability as the nitrogen-doped carbon layer improves conductivity and prevents aggregation of the rods during cycling.}, number={11}, journal={Journal of Materials Chemistry}, publisher={Royal Society of Chemistry (RSC)}, author={Yoon, Sukeun and Liao, Chen and Sun, Xiao-Guang and Bridges, Craig A. and Unocic, Raymond R. and Nanda, Jagjit and Dai, Sheng and Paranthaman, M. Parans}, year={2012}, pages={4611} }
@article{unocic_baggetto_unocic_veith_dudney_more_2012, title={Coupling EELS/EFTEM Imaging with Environmental Fluid Cell Microscopy}, volume={18}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/s1431927612007374}, DOI={10.1017/s1431927612007374}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.}, number={S2}, journal={Microscopy and Microanalysis}, publisher={Oxford University Press (OUP)}, author={Unocic, R.R. and Baggetto, L. and Unocic, K.A. and Veith, G.M. and Dudney, N.J. and More, K.L.}, year={2012}, month={Jul}, pages={1104–1105} }
@article{baggetto_unocic_dudney_veith_2012, title={Fabrication and characterization of Li–Mn–Ni–O sputtered thin film high voltage cathodes for Li-ion batteries}, volume={211}, DOI={10.1016/j.jpowsour.2012.03.076}, journal={Journal of Power Sources}, publisher={Elsevier BV}, author={Baggetto, Loïc and Unocic, Raymond R. and Dudney, Nancy J. and Veith, Gabriel M.}, year={2012}, month={Aug}, pages={108–118} }
@article{li_martha_unocic_luo_dai_qu_2012, title={High cyclability of ionic liquid-produced TiO2 nanotube arrays as an anode material for lithium-ion batteries}, volume={218}, DOI={10.1016/j.jpowsour.2012.06.096}, journal={Journal of Power Sources}, publisher={Elsevier BV}, author={Li, Huaqing and Martha, Surendra K. and Unocic, Raymond R. and Luo, Huimin and Dai, Sheng and Qu, Jun}, year={2012}, month={Nov}, pages={88–92} }
@article{alsem_salmon_unocic_veith_more_2012, title={In-situ liquid and gas transmission electron microscopy of nano-scale materials}, volume={18}, DOI={10.1017/s1431927612007647}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.}, number={S2}, journal={Microsc Microanal}, publisher={Cambridge University Press (CUP)}, author={Alsem, D. and Salmon, N.J. and Unocic, R.R. and Veith, G.M. and More, K.L.}, year={2012}, month={Jul}, pages={1158–1159} }
@article{phillips_unocic_mills_2013, title={Low cycle fatigue of a polycrystalline Ni-based superalloy: Deformation substructure analysis}, volume={57}, ISSN={0142-1123}, url={http://dx.doi.org/10.1016/j.ijfatigue.2012.11.008}, DOI={10.1016/j.ijfatigue.2012.11.008}, journal={International Journal of Fatigue}, publisher={Elsevier BV}, author={Phillips, P.J. and Unocic, R.R. and Mills, M.J.}, year={2013}, month={Dec}, pages={50–57} }
@misc{unocic_unocic_pint_lipschutz_2011, title={Characterization of Pre- and Post-Service Grain Boundary Phases in a Cast Austenitic Steel}, url={http://dx.doi.org/10.1115/gt2011-46710}, DOI={10.1115/gt2011-46710}, abstractNote={Austenitic steel castings are currently being used in components for industrial gas turbine engines. Service experience has indicated a degradation of mechanical properties with extended exposures at elevated temperature. The purpose of this study was to characterize the grain boundary phases that develop during the casting processes as a likely explanation for the observed performance. In order to isolate these precipitates, a variety of electron microscopy characterization techniques were used to characterize their composition after various heat treatments and service exposure. In the baseline, as-cast and annealed condition, a discontinuous network of grain boundary metal carbides was observed. These precipitates coarsened during short-term annealing at 649°C and a denuded zone formed in the adjacent matrix. When the 38,600 h service-exposed material was analyzed, the grain boundaries were highly decorated with a more continuous film of grain boundary carbides as well as voids attributed to creep cavitation. In addition to carbides, acicular AlN precipitates were identified on the grain boundaries of the casting examined after service exposure.}, journal={Volume 4: Cycle Innovations; Fans and Blowers; Industrial and Cogeneration; Manufacturing Materials and Metallurgy; Marine; Oil and Gas Applications}, publisher={ASMEDC}, author={Unocic, Raymond R. and Unocic, Kinga A. and Pint, Bruce A. and Lipschutz, Mark D.}, year={2011}, month={Jan}, pages={755–760} }
@article{unocic_zhou_kovarik_shen_wang_mills_2011, title={Dislocation decorrelation and relationship to deformation microtwins during creep of a γ′ precipitate strengthened Ni-based superalloy}, volume={59}, DOI={10.1016/j.actamat.2011.07.069}, number={19}, journal={Acta Materialia}, publisher={Elsevier BV}, author={Unocic, R.R. and Zhou, N. and Kovarik, L. and Shen, C. and Wang, Y. and Mills, M.J.}, year={2011}, month={Nov}, pages={7325–7339} }
@article{liu_mahurin_li_unocic_idrobo_gao_pennycook_dai_2011, title={Dopamine as a Carbon Source: The Controlled Synthesis of Hollow Carbon Spheres and Yolk-Structured Carbon Nanocomposites}, volume={123}, DOI={10.1002/ange.201102070}, abstractNote={C-Schalen: Eine einfache Synthese mit Dopamin als Kohlenstoffquelle liefert hohle Kohlenstoffkugeln und Au@Kohlenstoff-Nanokomposite mit Ei-artiger Struktur (siehe Bild). Die Einheitlichkeit der Dopaminbeschichtungen und ihre hohe Kohlenstoffausbeute hat Produkte mit hoher struktureller Integrität zur Folge. Die Au@C-Nanokomposite sind katalytisch aktiv. Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={30}, journal={Angew. Chem.}, publisher={Wiley-Blackwell}, author={Liu, Rui and Mahurin, Shannon M. and Li, Chen and Unocic, Raymond R. and Idrobo, Juan C. and Gao, Hongjun and Pennycook, Stephen J. and Dai, Sheng}, year={2011}, month={Jun}, pages={6931–6934} }
@article{liu_mahurin_li_unocic_idrobo_gao_pennycook_dai_2011, title={Dopamine as a Carbon Source: The Controlled Synthesis of Hollow Carbon Spheres and Yolk‐Structured Carbon Nanocomposites}, volume={50}, ISSN={1433-7851 1521-3773}, url={http://dx.doi.org/10.1002/anie.201102070}, DOI={10.1002/anie.201102070}, abstractNote={C shells: A facile and versatile synthesis using dopamine as a carbon source gives hollow carbon spheres and yolk–shell Au@Carbon nanocomposites (see pictures). The uniform nature of dopamine coatings and their high carbon yield endow the products with high structural integrity. The Au@C nanocomposites are catalytically active.}, number={30}, journal={Angewandte Chemie International Edition}, publisher={Wiley}, author={Liu, Rui and Mahurin, Shannon M. and Li, Chen and Unocic, Raymond R. and Idrobo, Juan C. and Gao, Hongjun and Pennycook, Stephen J. and Dai, Sheng}, year={2011}, month={Jun}, pages={6799–6802} }
@article{mylavarapu_sun_christensen_unocic_glosup_patterson_2012, title={Fabrication and design aspects of high-temperature compact diffusion bonded heat exchangers}, volume={249}, DOI={10.1016/j.nucengdes.2011.08.043}, journal={Nuclear Engineering and Design}, publisher={Elsevier BV}, author={Mylavarapu, Sai K. and Sun, Xiaodong and Christensen, Richard N. and Unocic, Raymond R. and Glosup, Richard E. and Patterson, Mike W.}, year={2012}, month={Aug}, pages={49–56} }
@article{kim_veith_nanda_unocic_chi_dudney_2011, title={High voltage stability of LiCoO2 particles with a nano-scale Lipon coating}, volume={56}, ISSN={0013-4686}, url={http://dx.doi.org/10.1016/j.electacta.2011.03.070}, DOI={10.1016/j.electacta.2011.03.070}, number={19}, journal={Electrochimica Acta}, publisher={Elsevier BV}, author={Kim, Yoongu and Veith, Gabriel M. and Nanda, Jagjit and Unocic, Raymond R. and Chi, Miaofang and Dudney, Nancy J.}, year={2011}, month={Jul}, pages={6573–6580} }
@article{unocic_adamczyk_dudney_alsem_salmon_more_2011, title={In-situ TEM Characterization of Electrochemical Processes in Energy Storage Systems}, volume={17}, DOI={10.1017/s1431927611008695}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.}, number={S2}, journal={Microsc Microanal}, publisher={Cambridge University Press (CUP)}, author={Unocic, R and Adamczyk, L and Dudney, N and Alsem, D and Salmon, N and More, K}, year={2011}, month={Jul}, pages={1564–1565} }
@article{chan‐thaw_villa_veith_kailasam_adamczyk_unocic_prati_thomas_2011, title={Influence of Periodic Nitrogen Functionality on the Selective Oxidation of Alcohols}, volume={7}, ISSN={1861-4728 1861-471X}, url={http://dx.doi.org/10.1002/asia.201100565}, DOI={10.1002/asia.201100565}, abstractNote={Abstract An enhancement in catalytic alcohol oxidation activity is attributed to the presence of nitrogen heteroatoms on the external surface of a support material. The same Pd particles (3.1–3.2 nm) were supported on polymeric carbon–nitrogen supports and used as catalysts to selectively oxidize benzyl alcohol. The polymeric carbon–nitrogen materials include covalent triazine frameworks (CTF) and carbon nitride (C 3 N 4 ) materials with nitrogen content varying from 9 to 58 atomic percent. With comparable metal exposure, estimated by X‐ray photoelectron spectroscopy, the activity of these catalysts correlates with the concentration of nitrogen species on the surface. Because the catalysts showed comparable acidic/basic properties, this enhancement cannot be ascribed to the Lewis basicity but most probably to the nature of N‐containing groups that govern the adsorption sites of the Pd nanoparticles.}, number={2}, journal={Chemistry – An Asian Journal}, publisher={Wiley}, author={Chan‐Thaw, Carine E. and Villa, Alberto and Veith, Gabriel M. and Kailasam, Kamalakannan and Adamczyk, Leslie A. and Unocic, Raymond R. and Prati, Laura and Thomas, Arne}, year={2011}, month={Dec}, pages={387–393} }
@article{liu_bi_sun_unocic_paranthaman_dai_brown_2011, title={Mesoporous TiO2–B Microspheres with Superior Rate Performance for Lithium Ion Batteries}, volume={23}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.201100599}, DOI={10.1002/adma.201100599}, abstractNote={Mesoporous TiO2–B microspheres with a favorable material architecture are designed and synthesized for highpower lithium ion batteries. This material, which combines the advantages of fast lithium transport with a pseudocapacitive mechanism, adequate electrode-electrolyte contact, and compact particle packing in the electrode layer, shows superior high-rate charge–discharge capability and long-time cyclability for lithium ion batteries. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={30}, journal={Advanced Materials}, publisher={Wiley}, author={Liu, Hansan and Bi, Zhonghe and Sun, Xiao‐Guang and Unocic, Raymond R. and Paranthaman, M. Parans and Dai, Sheng and Brown, Gilbert M.}, year={2011}, month={Jul}, pages={3450–3454} }
@article{rathmell_unocic_howe_wiley_2011, title={TEM and In-situ Liquid Cell Characterization of Copper Nanowire Growth Mechanisms}, volume={17}, DOI={10.1017/s1431927611003187}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.}, number={S2}, journal={Microsc Microanal}, publisher={Cambridge University Press (CUP)}, author={Rathmell, A and Unocic, R and Howe, J and Wiley, B}, year={2011}, month={Jul}, pages={462–463} }
@article{unocic_unocic_hayes_daehn_mills_2012, title={A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus}, DOI={10.1002/9781118495223.ch47}, abstractNote={This chapter contains sections titled: Introduction Materials and Experimental Procedure Results and Discussion Conclusions Acknowledgements}, journal={Superalloy 718 and Derivatives}, publisher={Wiley-Blackwell}, author={Unocic, Raymond R. and Unocic, Kinga A. and Hayes, Robert W. and Daehn, Glenn S. and Mills, Michael J.}, year={2012}, month={Aug}, pages={607–615} }
@article{grassman_brenner_gonzalez_carlin_unocic_dehoff_mills_ringel_2010, title={Characterization of Metamorphic GaAsP/Si Materials and Devices for Photovoltaic Applications}, volume={57}, DOI={10.1109/ted.2010.2082310}, abstractNote={GaAs y P 1- y anion-sublattice compositionally graded buffers and device structures were grown directly on Si(100) substrates by way of a high-quality GaP integration layer, yielding GaAsP target layers having band gaps of photovoltaic interest (1.65-1.8 eV), free of antiphase domains/borders, stacking faults, and microtwins. GaAs y P 1- y growths on both Si and GaP substrates were compared via high-resolution X-ray diffractometry of the metamorphic buffers and deep-level transient spectroscopy (DLTS) of p + -n diodes that are lattice matched to the final buffer layer. Structural analysis indicates highly efficient epitaxial relaxation throughout the entire growth structure for both types of samples and suggests no significant difference in physical behavior between the two types of samples. DLTS measurements performed on GaAsP diodes fabricated on both Si and GaP substrates reveal the existence of identical sets of traps residing in the n-type GaAsP layers in both types of samples: a single majority carrier (electron) trap, which is located at EC - 0.18 eV, and a single minority carrier (hole) trap, which is located at EV + 0.71 eV. Prototype 1.75-eV GaAsP solar cell test devices grown on GaAs y P 1- y /Si buffers show good preliminary performance characteristics and offer great promise for future high-efficiency III-V photovoltaics integrated with Si substrates and devices.}, number={12}, journal={IEEE Trans. Electron Devices}, publisher={Institute of Electrical & Electronics Engineers (IEEE)}, author={Grassman, Tyler J. and Brenner, Mark R. and Gonzalez, Maria and Carlin, Andrew M. and Unocic, Raymond R. and Dehoff, Ryan R. and Mills, Michael J. and Ringel, Steven A.}, year={2010}, pages={3361–3369} }
@article{wang_fulvio_baker_veith_unocic_mahurin_chi_dai_2010, title={Direct exfoliation of natural graphite into micrometre size few layers graphene sheets using ionic liquids}, volume={46}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/c0cc00799d}, DOI={10.1039/c0cc00799d}, abstractNote={Stable high-concentration suspensions (up to 0.95 mg mL(-1)) of non-oxidized few layer graphene (FLG), five or less sheets, with micrometre-long edges were obtained via direct exfoliation of natural graphite flakes in ionic liquids, such as 1-butyl-3-methyl-imidazolium bis(trifluoro-methane-sulfonyl)imide ([Bmim]-[Tf(2)N]), by tip ultrasonication.}, number={25}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Wang, Xiqing and Fulvio, Pasquale F. and Baker, Gary A. and Veith, Gabriel M. and Unocic, Raymond R. and Mahurin, Shannon M. and Chi, Miaofang and Dai, Sheng}, year={2010}, pages={4487} }
@article{unocic_unocic_pint_hayes_2012, title={Effect of Microstucture and Environment on the High-Temperature Oxidation Behavior of Alloy 718Plus}, DOI={10.1002/9781118495223.ch74}, abstractNote={This chapter contains sections titled: Introduction Experimental Procedure Results Discussion Conclusions Acknowledgements}, journal={Superalloy 718 and Derivatives}, publisher={Wiley-Blackwell}, author={Unocic, Kinga A. and Unocic, Raymond R. and Pint, Bruce A. and Hayes, Robert W.}, year={2012}, month={Aug}, pages={977–991} }
@article{phillips_unocic_kovarik_mourer_wei_mills_2010, title={Low cycle fatigue of a Ni-based superalloy: Non-planar deformation}, volume={62}, DOI={10.1016/j.scriptamat.2010.01.044}, number={10}, journal={Scripta Materialia}, publisher={Elsevier BV}, author={Phillips, Patrick J. and Unocic, Raymond R. and Kovarik, L. and Mourer, David and Wei, Dan and Mills, Michael J.}, year={2010}, month={May}, pages={790–793} }
@article{phillips_kovarik_unocic_wei_mourer_mills_2010, title={The Importance of High-Resolution Scanning Transmission Electron Microscopy For Fine-Scale Dislocation Analysis}, volume={16}, DOI={10.1017/s1431927610060575}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.}, number={S2}, journal={Microsc Microanal}, publisher={Cambridge University Press (CUP)}, author={Phillips, PJ and Kovarik, L and Unocic, RR and Wei, D and Mourer, D and Mills, MJ}, year={2010}, month={Jul}, pages={1798–1799} }
@article{grassman_brenner_rajagopalan_unocic_dehoff_mills_fraser_ringel_2009, title={Control and elimination of nucleation-related defects in GaP/Si(001) heteroepitaxy}, volume={94}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3154548}, DOI={10.1063/1.3154548}, abstractNote={GaP films were grown on offcut Si(001) substrates using migration enhanced epitaxy nucleation followed by molecular beam epitaxy, with the intent of controlling and eliminating the formation of heterovalent (III-V/IV) nucleation-related defects—antiphase domains, stacking faults, and microtwins. Analysis of these films via reflection high-energy electron diffraction, atomic force microscopy, and both cross-sectional and plan-view transmission electron microscopies indicate high-quality GaP layers on Si that portend a virtual GaP substrate technology, in which the aforementioned extended defects are simultaneously eliminated. The only prevalent remaining defects are the expected misfit dislocations due to the GaP–Si lattice mismatch.}, number={23}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Grassman, T. J. and Brenner, M. R. and Rajagopalan, S. and Unocic, R. and Dehoff, R. and Mills, M. and Fraser, H. and Ringel, S. A.}, year={2009}, month={Jun} }
@article{sandhage_allan_dickerson_gaddis_shian_weatherspoon_cai_ahmad_haluska_snyder_et al._2014, title={Merging Biological Self-Assembly with Synthetic Chemical Tailoring: The Potential for 3-D Genetically Engineered Micro/Nano-Devices (3-D GEMS)}, DOI={10.1002/9780470588260.ch12}, abstractNote={This chapter discusses several approaches that can be used to change the compositions of diatom frustules or other bioclastic structures into a wide variety of non-natural chemistries without loss of the bioassembled 3-D morphology. These processes are referred to collectively as bioclastic and Shape-preserving/norganic Conversion (BaSIC). By merging the attractive self-assembly characteristics of nature with the chemical versatility of synthetic processing, BaSIC processes may be used to mass produce nanostructured microdevices with complex 3-D shapes and tailored chemistries. Ongoing advances in the genetic engineering of biomineralizing microorganisms may yield nanoparticle structures with tailored 3-D shapes. Such genetic advances may then be coupled with the BaSIC manufacturing paradigm to yield 3-D Genetically Engineered micro/nano-devices (3-D GEMs).}, journal={Progress in Nanotechnology}, publisher={Wiley-Blackwell}, author={Sandhage, Kenneth H. and Allan, Shawn M. and Dickerson, Matthew B. and Gaddis, Christopher S. and Shian, Samuel and Weatherspoon, Michael R. and Cai, Ye and Ahmad, Gul and Haluska, Michael S. and Snyder, Robert L. and et al.}, year={2014}, month={Aug}, pages={85–94} }
@article{kovarik_unocic_li_sarosi_shen_wang_mills_2009, title={Microtwinning and other shearing mechanisms at intermediate temperatures in Ni-based superalloys}, volume={54}, DOI={10.1016/j.pmatsci.2009.03.010}, number={6}, journal={Progress in Materials Science}, publisher={Elsevier BV}, author={Kovarik, L. and Unocic, R.R. and Li, Ju and Sarosi, P. and Shen, C. and Wang, Y. and Mills, M.J.}, year={2009}, month={Aug}, pages={839–873} }
@article{kovarik_unocic_li_mills_2009, title={The intermediate temperature deformation of Ni-based superalloys: Importance of reordering}, volume={61}, DOI={10.1007/s11837-009-0026-6}, number={2}, journal={JOM}, publisher={Springer Science \mathplus Business Media}, author={Kovarik, L. and Unocic, R. R. and Li, J. and Mills, M. J.}, year={2009}, month={Feb}, pages={42–48} }
@inproceedings{grassman_brenner_carlin_rajagopalan_unocic_dehoff_mills_fraser_ringel_2009, title={Toward metamorphic multijunction GaAsP/Si photovoltaics grown on optimized GaP/Si virtual substrates using anion-graded GaAsyP1-y buffers}, DOI={10.1109/pvsc.2009.5411489}, abstractNote={Using migration enhanced epitaxy nucleation followed by molecular beam epitaxy bulk growth on pristine, intentionally offcut Si(001) substrates, we have produced high-quality GaP/Si virtual substrates, successfully demonstrating full control and elimination of heterovalent nucleation-related defects (antiphase domains, stacking faults, and microtwins). These virtual substrates provide a pathway to direct integration of III-V photovoltaic materials and devices on Si substrates. Prototype GaAsP solar cell test devices grown on anion-sublattice step-graded GaAs y P 1-y buffers on early-stage GaP/Si substrates show good preliminary performance characteristics and offer great promise for future devices integrated with the newly-developed defect-free GaP/Si virtual substrates.}, booktitle={2009 34th IEEE Photovoltaic Specialists Conference (PVSC)}, publisher={Institute of Electrical & Electronics Engineers (IEEE)}, author={Grassman, T. J. and Brenner, M. R. and Carlin, A. M. and Rajagopalan, S. and Unocic, R. and Dehoff, R. and Mills, M. and Fraser, H. and Ringel, S. A.}, year={2009}, month={Jun} }
@inproceedings{unocic_kovarik_shen_sarosi_wang_li_ghosh_mills_2008, title={Deformation Mechanisms in Ni-Base Disk Superalloys at Higher Temperatures}, url={http://dx.doi.org/10.7449/2008/superalloys_2008_377_385}, DOI={10.7449/2008/superalloys_2008_377_385}, abstractNote={This paper presents results from a research initiative aimed at investigating high temperature creep deformation mechanisms in Ni-base superalloys through a combination of creep experiments, TEM deformation mechanism characterization, and state of the art modeling techniques.The effect of microstructure on dictating creep rate controlling deformation mechanisms was revealed for specimens with a bimodal size distribution that possessed different secondary size, tertiary volume fraction, and channel width spacing.It was found that the less creep resistant microstructure was the one with a greater secondary size, wider channel width, and higher volume fraction of tertiary .Deformation in this microstructure commences by way of a/2<110> dislocations that are concentrated in the matrix at lower strains, which then transition to a SISF precipitate shearing mode at larger strains.The more creep resistant microstructure possessed a finer channel width spacing, which promoted a/2<110> dislocation dissociation into a/6<112> Shockley partials at lower strains and microtwinning at higher strains.Dislocation precipitate interaction was further explored using microscopic phase field modeling, which was able to capture key microstructural aspects that can favor dislocation dissociation and decorrelation since this appears to be a precursor to the microtwinning deformation mode.New viable diffusion pathways associated with the reordering processes in microtwinning have been explored at the atomistic level.All of the above activities have shed light onto the complex nature of creep deformation mechanisms at higher temperatures.}, booktitle={Superalloys 2008 (Eleventh International Symposium)}, publisher={TMS}, author={Unocic, R.R. and Kovarik, L. and Shen, C. and Sarosi, P.M. and Wang, Y. and Li, J. and Ghosh, S. and Mills, M.J.}, year={2008}, pages={377–385} }
@article{kovarik_unocic_li_mills_2008, title={HAADF Imaging and MD Simulations of Microtwining Partial Dislocations in Nickel Based Superalloy Rene 104,}, volume={14}, DOI={10.1017/s1431927608087114}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008}, number={S2}, journal={Microsc Microanal}, publisher={Cambridge University Press (CUP)}, author={Kovarik, L and Unocic, RR and Li, J and Mills, MJ}, year={2008}, month={Aug}, pages={938–939} }
@article{kovarik_viswanathan_unocic_sarosi_mills_2007, title={HRTEM and STEM HAADF Study of Microtwining During Creep Deformation in Nickel Based Superalloy Rene 104}, volume={13}, DOI={10.1017/s1431927607076817}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007}, number={S02}, journal={MAM}, publisher={Cambridge University Press (CUP)}, author={Kovarik, L and Viswanathan, G and Unocic, R and Sarosi, PM and Mills, M}, year={2007}, month={Aug} }
@misc{sandhage_allan_dickerson_ernst_gaddis_shian_weatherspoon_ahmad_cai_haluska_et al._2007, title={Inorganic Preforms of Biological Origin: Shape‐Preserving Reactive Conversion of Biosilica Microshells (Diatoms)}, ISBN={9783527316410 9783527619443}, url={http://dx.doi.org/10.1002/9783527619443.ch37}, DOI={10.1002/9783527619443.ch37}, journal={Handbook of Biomineralization}, publisher={Wiley}, author={Sandhage, Kenneth H. and Allan, Shawn M. and Dickerson, Matthew B. and Ernst, Eric M. and Gaddis, Christopher S. and Shian, Samuel and Weatherspoon, Michael R. and Ahmad, Gul and Cai, Ye and Haluska, Michael S. and et al.}, year={2007}, month={May}, pages={234–253} }
@article{unocic_viswanathan_sarosi_karthikeyan_li_mills_2008, title={Mechanisms of creep deformation in polycrystalline Ni-base disk superalloys}, volume={483-484}, DOI={10.1016/j.msea.2006.08.148}, journal={Materials Science and Engineering: A}, publisher={Elsevier BV}, author={Unocic, R.R. and Viswanathan, G.B. and Sarosi, P.M. and Karthikeyan, S. and Li, J. and Mills, M.J.}, year={2008}, month={Jun}, pages={25–32} }
@article{unocic_kovarik_sarosi_mills_2007, title={Structural and Chemical Analysis of Stacking Faults in the gamma-phase of a Creep Deformed Ni-Base Superalloy}, volume={13}, DOI={10.1017/s1431927607077458}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007}, number={S02}, journal={MAM}, publisher={Cambridge University Press (CUP)}, author={Unocic, R and Kovarik, L and Sarosi, PM and Mills, M}, year={2007}, month={Aug} }
@article{viswanathan_karthikeyan_sarosi_unocic_mills_2006, title={Microtwinning during intermediate temperature creep of polycrystalline Ni-based superalloys: mechanisms and modelling}, volume={86}, DOI={10.1080/14786430600767750}, abstractNote={Abstract Deformation mechanisms, operative during intermediate temperature creep of Ni-based polycrystalline superalloys, are poorly understood. The creep deformation substructure has been characterized in Renè 88DT following rapid cooling from the super-solvus temperature, yielding a fine γ′-precipitate microstructure. After creep to modest strain levels (up to 0.5% strain) at 650°C and an applied tensile stress of 838 MPa, microtwinning is found to be the predominant deformation mode. This surprising result has been confirmed using diffraction contrast and high-resolution transmission electron microscopy. Microtwinning occurs via the sequential movement of identical 1/6[11–2] Shockley partials on successive (111) planes. This mechanism necessitates reordering within the γ′ precipitates in the wake of the twinning partials, so that the L12 structure can be restored. A quantitative model for creep rate has been derived on the basis that the reordering process is rate-limiting. The model is in reasonable agreement with experimental data. The results are also discussed in relation to previous studies under similar deformation conditions. Acknowledgements Support for this work has been provided by the DARPA Accelerated Insertion of Materials (AIM) Program under contract F33615-00-C-5215 and by the Air Force Office of Scientific Research, for model development, through the MEANS-2 theme grant # FA9550-05-1-0135.}, number={29-31}, journal={Philosophical Magazine}, publisher={Informa UK Limited}, author={Viswanathan, G. B. and Karthikeyan, S. and Sarosi, P. M. and Unocic, R. R. and Mills, M. J.}, year={2006}, month={Oct}, pages={4823–4840} }
@article{sarosi_viswanathan_demania_unocic_mills_2005, title={Imaging and Characterization of the Microstructure and Creep Deformation Mechanisms of Commercial Nickel-based Superalloys}, volume={11}, DOI={10.1017/s1431927605509267}, abstractNote={Extract HTML view is not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button. Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005}, number={S02}, journal={MAM}, publisher={Cambridge University Press (CUP)}, author={Sarosi, P M and Viswanathan, G B and Demania, W and Unocic, R and Mills, M J}, year={2005}, month={Aug} }
@article{sandhage_allan_dickerson_gaddis_shian_weatherspoon_cai_ahmad_haluska_snyder_et al._2005, title={Merging Biological Self‐Assembly with Synthetic Chemical Tailoring: The Potential for 3‐D Genetically Engineered Micro/Nano‐Devices (3‐D GEMS)}, volume={2}, ISSN={1546-542X 1744-7402}, url={http://dx.doi.org/10.1111/j.1744-7402.2005.02035.x}, DOI={10.1111/j.1744-7402.2005.02035.x}, abstractNote={Appreciable global efforts are underway to develop processes for fabricating three‐dimensional (3‐D) nanostructured assemblies for advanced devices. Widespread commercialization of such devices will require: (i) precise 3‐D fabrication of chemically tailored structures on a fine scale and (ii) mass production of such structures on a large scale. These often‐conflicting demands can be addressed with a revolutionary new paradigm that couples biological self‐assembly with synthetic chemistry: B ioclastic a nd S hape‐preserving I norganic C onversion (BaSIC). Nature provides numerous examples of microorganisms that assemble biominerals into intricate 3‐D structures. Among the most spectacular of these microorganisms are diatoms (unicellular algae). Each of the tens of thousands of diatom species assembles silica nanoparticles into a microshell with a distinct 3‐D shape and pattern of fine (nanoscale) features. The repeated doubling associated with biological reproduction enables enormous numbers of such 3‐D microshells to be generated (e.g., only 40 reproduction cycles can yield >1 trillion 3‐D replicas!). Such genetic precision and massive parallelism are highly attractive for device manufacturing. However, the natural chemistries assembled by diatoms (and other microorganisms) are rather limited. With BaSIC processes, biogenic assemblies can be converted into a wide variety of new functional chemistries, while preserving the 3‐D morphologies. Ongoing advances in genetic engineering promise to yield microorganisms tailored to assemble nanoparticle structures with device‐specific shapes. Large‐scale culturing of such genetically tailored microorganisms, coupled with shape‐preserving chemical conversion (via BaSIC processes), would then provide low‐cost 3‐D G enetically E ngineered M icro/nano‐devices (3‐D GEMs).}, number={4}, journal={International Journal of Applied Ceramic Technology}, publisher={Wiley}, author={Sandhage, Kenneth H. and Allan, Shawn M. and Dickerson, Matthew B. and Gaddis, Christopher S. and Shian, Samuel and Weatherspoon, Michael R. and Cai, Ye and Ahmad, Gul and Haluska, Michael S. and Snyder, Robert L. and et al.}, year={2005}, month={Jul}, pages={317–326} }
@article{karthikeyan_unocic_sarosi_viswanathan_whitis_mills_2006, title={Modeling microtwinning during creep in Ni-based superalloys}, volume={54}, DOI={10.1016/j.scriptamat.2005.11.049}, number={6}, journal={Scripta Materialia}, publisher={Elsevier BV}, author={Karthikeyan, S. and Unocic, R.R. and Sarosi, P.M. and Viswanathan, G.B. and Whitis, D.D. and Mills, M.J.}, year={2006}, month={Mar}, pages={1157–1162} }
@article{unocic_sarosi_viswanathan_mills_whitis_2005, title={The Creep Deformation Mechanisms of Nickel Base Superalloy René 104}, volume={11}, DOI={10.1017/s1431927605510031}, abstractNote={Journal Article The Creep Deformation Mechanisms of Nickel Base Superalloy René 104 Get access R R Unocic, R R Unocic Ohio State University, Ohio Search for other works by this author on: Oxford Academic Google Scholar P M Sarosi, P M Sarosi Ohio State University, Ohio Search for other works by this author on: Oxford Academic Google Scholar G B Viswanathan, G B Viswanathan Ohio State University, Ohio Search for other works by this author on: Oxford Academic Google Scholar M J Mills, M J Mills Ohio State University, Ohio Search for other works by this author on: Oxford Academic Google Scholar D A Whitis D A Whitis General Electric Aircraft Engines, Cincinnati, Ohio Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 11, Issue S02, 1 August 2005, Pages 1874–1875, https://doi.org/10.1017/S1431927605510031 Published: 01 August 2005}, number={S02}, journal={MAM}, publisher={Cambridge University Press (CUP)}, author={Unocic, R R and Sarosi, P M and Viswanathan, G B and Mills, M J and Whitis, D A}, year={2005}, month={Aug} }
@article{unocic_zalar_sarosi_cai_sandhage_2004, title={Anatase assemblies from algae: coupling biological self-assembly of 3-D nanoparticle structures with synthetic reaction chemistry}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/b400599f}, DOI={10.1039/b400599f}, abstractNote={The shape-preserving conversion of biologically self-assembled 3-D nanoparticle structures (SiO2-based diatom frustules) into a new nanocrystalline material (anatase TiO2) via a halide gas/solid displacement reaction route is demonstrated.}, number={7}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Unocic, Raymond R. and Zalar, Frank M. and Sarosi, Peter M. and Cai, Ye and Sandhage, Kenneth H.}, year={2004}, pages={796} }
@article{unocic_dupont_2004, title={Process efficiency measurements in the laser engineered net shaping process}, volume={35}, ISSN={1073-5615 1543-1916}, url={http://dx.doi.org/10.1007/s11663-004-0104-7}, DOI={10.1007/s11663-004-0104-7}, number={1}, journal={Metallurgical and Materials Transactions B}, publisher={Springer Science and Business Media LLC}, author={Unocic, R. R. and DuPont, J. N.}, year={2004}, month={Feb}, pages={143–152} }
@article{unocic_dupont_2003, title={Composition control in the direct laser-deposition process}, volume={34}, ISSN={1073-5615 1543-1916}, url={http://dx.doi.org/10.1007/s11663-003-0070-5}, DOI={10.1007/s11663-003-0070-5}, number={4}, journal={Metallurgical and Materials Transactions B}, publisher={Springer Science and Business Media LLC}, author={Unocic, R. R. and DuPont, J. N.}, year={2003}, month={Aug}, pages={439–445} }
@article{dickerson_unocic_guerra_timberlake_sandhage_2000, title={The fabrication of dense carbide/refractory metal composites of near net shape at modest temperatures by the PRIMA-DCP process}, volume={115}, journal={Ceramics Transactions}, author={Dickerson, M.B. and Unocic, R.R. and Guerra, K.T. and Timberlake, M.J. and Sandhage, K.H.}, year={2000}, pages={25–31} }