@article{su_yu_cao_zhang_2023, title={Correlative spectroscopic investigations of the mechanisms of inhomogeneity in CVD-grown monolayer WS<sub>2</sub>}, ISSN={["2199-4501"]}, DOI={10.1007/s40843-023-2616-x}, abstractNote={Chemical vapor deposition (CVD) has been proved to be the most useful method to produce two-dimensional (2D) materials, including tungsten disulfide (WS2). However, the existence of inhomogeneity of strain, doping, and defects in the CVD-grown WS2 monolayers may significantly influence the optical and electronic properties of the materials, thus affecting their device applications. In this work, we systematically characterized the inhomogeneity of strain, doping, and nonradiative defect centers in mesoscopic-size, triangular-shape monolayer WS2 grown by CVD on sapphire substrate by using spatially resolved micro-Raman and photoluminescence (PL) spectroscopy. We performed correlative analyses on the variations of the pertinent spectral parameters (i.e., peak position, intensity, and full width at half maximum) of Raman and PL signatures in two physical scales: (1) the complete-data-set level, including the data of the whole sample, and (2) the sub-data-set level for individual special regions (e.g., apexes, edges, center) that exhibit distinctly different strain, doping, and defect states. This study reveals and explains the inhomogeneous strain, doping, and defects across the WS2 monolayer. Additionally, we find the inhomogeneity substantially diminishes when a mesoscopic-size triangle structure expands into a continuous film. Our work demonstrates that the correlative analyses, supported with physics insights, can offer comprehensive understanding on the underlying mechanisms of the inhomogeneity and guidance for optimizing the growth process and device processing of 2D materials.}, journal={SCIENCE CHINA-MATERIALS}, author={Su, Liqin and Yu, Yifei and Cao, Linyou and Zhang, Yong}, year={2023}, month={Sep} }
 @article{cheng_backman_zhang_abuzaid_li_yu_cao_davydov_luisier_richter_et al._2023, title={Distinct Contact Scaling Effects in MoS2 Transistors Revealed with Asymmetrical Contact Measurements}, ISSN={["1521-4095"]}, DOI={10.1002/adma.202210916}, abstractNote={Abstract}, journal={ADVANCED MATERIALS}, author={Cheng, Zhihui and Backman, Jonathan and Zhang, Huairuo and Abuzaid, Hattan and Li, Guoqing and Yu, Yifei and Cao, Linyou and Davydov, Albert V. and Luisier, Mathieu and Richter, Curt A. and et al.}, year={2023}, month={Apr} }
 @article{yu_li_xu_hu_liu_cao_2023, title={Phase Diagram of High-Temperature Electron-Hole Quantum Droplet in Two-Dimensional Semiconductors}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.3c01365}, abstractNote={Quantum liquids, systems exhibiting effects of quantum mechanics and quantum statistics at macroscopic levels, represent one of the most exciting research frontiers of modern physical science and engineering. Notable examples include Bose-Einstein condensation (BEC), superconductivity, quantum entanglement, and a quantum liquid. However, quantum liquids are usually only stable at cryogenic temperatures, significantly limiting fundamental studies and device development. Here we demonstrate the formation of stable electron-hole liquid (EHL) with the quantum statistic nature at temperatures as high as 700 K in monolayer MoS2 and elucidate that the high-temperature EHL exists as droplets in sizes of around 100-160 nm. We also develop a thermodynamic model of high-temperature EHL and, based on the model, compile an exciton phase diagram, revealing that the ionized photocarrier drives the gas-liquid transition, which is subsequently validated with experimental results. The high-temperature EHL provides a model system to enable opportunities for studies in the pursuit of other high-temperature quantum liquids. The results can also allow for the development of quantum liquid devices with practical applications in quantum information processing, optoelectronics, and optical interconnections.}, journal={ACS NANO}, author={Yu, Yiling and Li, Guoqing and Xu, Yan and Hu, Chong and Liu, Xiaoze and Cao, Linyou}, year={2023}, month={Aug} }
 @article{aslan_yule_yu_lee_heinz_cao_brongersma_2022, title={Excitons in strained and suspended monolayer WSe2}, volume={9}, ISSN={["2053-1583"]}, DOI={10.1088/2053-1583/ac2d15}, abstractNote={Abstract}, number={1}, journal={2D MATERIALS}, author={Aslan, Burak and Yule, Colin and Yu, Yifei and Lee, Yan Joe and Heinz, Tony F. and Cao, Linyou and Brongersma, Mark L.}, year={2022}, month={Jan} }
 @article{abuzaid_cheng_li_cao_franklin_2021, title={Unanticipated Polarity Shift in Edge-Contacted Tungsten-Based 2D Transition Metal Dichalcogenide Transistors}, volume={42}, ISSN={["1558-0563"]}, DOI={10.1109/LED.2021.3106286}, abstractNote={Creating metal edge contacts in transition metal dichalcogenide (TMD) transistors is a promising path to advance transistor miniaturization for future technology nodes. Current experimental demonstrations nearly exclusively focus on MoS2 as the channel material. Here, we create edge-contacted WSe2 and WS2 transistors using a convergent Ar+ ion beam source integrated within an e-beam evaporator chamber for in-situ processing. An unanticipated polarity shift was observed compared to top-contact behavior for Ti-WS2 devices, which displayed p-type conduction. Meanwhile, three distinct metal contact materials yielded comparable p-branch-dominant performance on WSe2. Transmission electron microscope (TEM) imaging with energy dispersive spectroscopy (EDS) analysis indicated the existence of a residual layer of W (and chalcogen atoms to a lesser extent) beneath the metal contacts, even though the substrate was over-etched. The images presented a physically pure edge interface. This intriguing etching effect could carry significant implications for the design of tungsten-based, edge-contacted TMD transistors.}, number={10}, journal={IEEE ELECTRON DEVICE LETTERS}, author={Abuzaid, Hattan and Cheng, Zhihui and Li, Guoqing and Cao, Linyou and Franklin, Aaron D.}, year={2021}, month={Oct}, pages={1563–1566} }
 @article{lau_xia_cao_2020, title={Emergent quantum materials}, volume={45}, ISSN={["1938-1425"]}, DOI={10.1557/mrs.2020.125}, abstractNote={Abstract}, number={5}, journal={MRS BULLETIN}, author={Lau, Chun Ning and Xia, Fengnian and Cao, Linyou}, year={2020}, month={May}, pages={340–347} }
 @article{li_chen_li_zhang_yang_liu_cao_2020, title={Engineering Substrate Interaction To Improve Hydrogen Evolution Catalysis of Monolayer MoS2 Films beyond Pt}, volume={14}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.9b07324}, abstractNote={MoS2 holds great promise as a cost-effective alternative to Pt for catalyzing the hydrogen evolution reaction (HER) of water, but its catalytic efficiency reported is still worse than Pt , the best HER catalyst but too rare and expensive for mass production of hydrogen. We report a strategy to enable the catalytic activity of monolayer MoS2 films even better than that of Pt via engineering the interaction of the monolayer with supporting substrates. The monolayer films were grown with CVD processes and controlled to have optimal density (7-10%) of sulfur vacancies. We find out that the catalytic activity of MoS2 can be affected by substrates in two ways: forming an interfacial tunneling barrier with MoS2 and modifying the chemical nature of MoS2 via charge transfer (proximity doping). Following this understanding, we enable excellent catalytic activities at the monolayer MoS2 films by using substrates that can provide n-doping to MoS2 and forms low interfacial tunneling barriers with MoS2, such as Ti. The catalytic performance may be further boosted to be even better than Pt by crumpling the films on flexible substrates, as the Tafel slope of the film is substantially lowered with the presence of crumpling-induced compressive strain. The monolayer MoS2 films show remarkable stability without any degradation in catalytic performance after being continuously tested for over two months.}, number={2}, journal={ACS NANO}, author={Li, Guoqing and Chen, Zehua and Li, Yifan and Zhang, Du and Yang, Weitao and Liu, Yuanyue and Cao, Linyou}, year={2020}, month={Feb}, pages={1707–1714} }
 @article{ong_zhang_zhang_cao_2020, title={Gate-tunable cross-plane heat dissipation in single-layer transition metal dichalcogenides}, volume={2}, ISSN={["2643-1564"]}, DOI={10.1103/PhysRevResearch.2.033470}, abstractNote={Efficient heat dissipation to the substrate is crucial for optimal device performance in nanoelectronics. We develop a theory of electronic thermal boundary conductance (TBC) mediated by remote phonon scattering for the single-layer transition metal dichalcogenide (TMD) semiconductors MoS$_{2}$ and WS$_{2}$, and model their electronic TBC with different dielectric substrates (SiO$_{2}$, HfO$_{2}$ and Al$_{2}$O$_{3}$). Our results indicate that the electronic TBC is strongly dependent on the electron density, suggesting that it can be modulated by the gate electrode in field-effect transistors, and this effect is most pronounced with Al$_{2}$O$_{3}$. Our work paves the way for the design of novel thermal devices with gate-tunable cross-plane heat-dissipative properties.}, number={3}, journal={PHYSICAL REVIEW RESEARCH}, author={Ong, Zhun-Yong and Zhang, Gang and Zhang, Yong-Wei and Cao, Linyou}, year={2020}, month={Sep} }
 @article{yu_yu_li_puretzky_geohegan_cao_2020, title={Giant enhancement of exciton diffusivity in two-dimensional semiconductors}, volume={6}, ISSN={["2375-2548"]}, DOI={10.1126/sciadv.abb4823}, abstractNote={The exciton diffusivity of 2D semiconductors can be improved by 15-fold with trapped charges that can screen exciton scattering.}, number={51}, journal={SCIENCE ADVANCES}, author={Yu, Yiling and Yu, Yifei and Li, Guoqing and Puretzky, Alexander A. and Geohegan, David B. and Cao, Linyou}, year={2020}, month={Dec} }
 @article{yu_minhaj_huang_yu_cao_2020, title={In-Plane and Interfacial Thermal Conduction of Two-Dimensional Transition-Metal Dichalcogenides}, volume={13}, ISSN={["2331-7019"]}, DOI={10.1103/PhysRevApplied.13.034059}, abstractNote={We elucidate the dependence of the in-plane and interfacial thermal conduction of two-dimensional (2D) transition-metal dichalcogenide (TMDC) materials (including ${\mathrm{Mo}\mathrm{S}}_{2}$, ${\mathrm{WS}}_{2}$, and ${\mathrm{W}\mathrm{Se}}_{2}$) on the materials' physical features, such as size, layer number, composition, and substrates. The in-plane thermal conductivity k is measured at suspended 2D TMDC materials and the interfacial thermal conductance g is measured at materials supported on substrates, both through Raman thermometry techniques. The thermal conductivity k increases with the radius R of the suspended area following a logarithmic scaling as k\ensuremath{\sim}log(R). k also shows a substantial decrease from monolayer to bilayer, but only changes slightly with a further increase in the layer number. In contrast, the interfacial thermal conductance g has a negligible dependence on the layer number, but g increases with the strength of the interaction between 2D TMDC materials and the substrate, substantially varying among different substrates. The result is consistent with theoretical predictions and clarifies much inconsistence in the literature. This work provides useful guidance for thermal management in 2D TMDC materials and devices.}, number={3}, journal={PHYSICAL REVIEW APPLIED}, author={Yu, Yifei and Minhaj, Tamzid and Huang, Lujun and Yu, Yiling and Cao, Linyou}, year={2020}, month={Mar} }
 @article{datta_chae_bhatt_tadayon_li_yu_park_park_cao_basov_et al._2020, title={Low-loss composite photonic platform based on 2D semiconductor monolayers}, volume={14}, ISSN={["1749-4893"]}, DOI={10.1038/s41566-020-0590-4}, abstractNote={Two dimensional materials such as graphene and transition metal dichalcogenides (TMDs) are promising for optical modulation, detection, and light emission since their material properties can be tuned on-demand via electrostatic doping. The optical properties of TMDs have been shown to change drastically with doping in the wavelength range near the excitonic resonances. However, little is known about the effect of doping on the optical properties of TMDs away from these resonances, where the material is transparent and therefore could be leveraged in photonic circuits. Here, we probe the electro-optic response of monolayer TMDs at near infrared (NIR) wavelengths (i.e. deep in the transparency regime), by integrating them on silicon nitride (SiN) photonic structures to induce strong light$-$matter interaction with the monolayer. We dope the monolayer to carrier densities of ($7.2 \pm 0.8$) $\times$ $10^{13} \textrm{cm}^{-2}$, by electrically gating the TMD using an ionic liquid. We show strong electro-refractive response in monolayer tungsten disulphide (WS$_2$) at NIR wavelengths by measuring a large change in the real part of refractive index $\Delta$n = $0.53$, with only a minimal change in the imaginary part $\Delta$k = $0.004$. The doping induced phase change ($\Delta$n), compared to the induced absorption ($\Delta$k) measured for WS$_2$ ($\Delta$n/$\Delta$k $\sim 125$), a key metric for photonics, is an order of magnitude higher than the $\Delta$n/$\Delta$k for bulk materials like silicon ($\Delta$n/$\Delta$k $\sim 10$), making it ideal for various photonic applications. We further utilize this strong tunable effect to demonstrate an electrostatically gated SiN-WS$_2$ phase modulator using a WS$_2$-HfO$_2$ (Hafnia)-ITO (Indium Tin Oxide) capacitive configuration, that achieves a phase modulation efficiency (V$_\pi$L) of 0.8 V $\cdot$ cm with a RC limited bandwidth of 0.3 GHz.}, number={4}, journal={NATURE PHOTONICS}, author={Datta, Ipshita and Chae, Sang Hoon and Bhatt, Gaurang R. and Tadayon, Mohammad Amin and Li, Baichang and Yu, Yiling and Park, Chibeom and Park, Jiwoong and Cao, Linyou and Basov, D. N. and et al.}, year={2020}, month={Apr}, pages={256-+} }
 @article{dong_fu_cao_amoah_gundogdu_li_so_2020, title={Multi-mode Organic Light-Emitting Diode to Suppress the Viewing Angle Dependence}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.0c05825}, abstractNote={A typical top emitting OLED has a strong microcavity effect because of the two reflective electrodes. The cavity effect causes a serious color shift with the viewing angles and restricts the organic layer thickness. To overcome these drawbacks, we designed a multi-mode OLED structure having dual-dielectric spacer layers, which extend the cavity length by more than 10 times. This design completely eliminates the intrinsic cavity effect caused by the top and bottom boundaries respectively and provides freedom for the organic layer thickness. We demonstrate these effects in a white multi-mode OLED using a white emitter, which shows a negligible angular chromaticity shift of 0.006 from 0° to 70° and a Lambertian emission profile. The simple design and the perfect angular color profiles make the multi-mode OLED structure promising in large-area displays and solid-state lighting applications.}, number={28}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Dong, Chen and Fu, Xiangyu and Cao, Linyu and Amoah, Stephen and Gundogdu, Kenan and Li, Jian and So, Franky}, year={2020}, month={Jul}, pages={31667–31676} }
 @article{cheng_abuzaid_yu_zhang_li_noyce_williams_lin_doherty_tao_et al._2019, title={Convergent ion beam alteration of 2D materials and metal-2D interfaces}, volume={6}, ISSN={["2053-1583"]}, DOI={10.1088/2053-1583/ab1764}, abstractNote={Tailoring the properties of two-dimensional (2D) crystals is important for both understanding the material behavior and exploring new functionality. Here we demonstrate the alteration of MoS2 and metal-MoS2 interfaces using a convergent ion beam. Different beam energies, from 60 eV to 600 eV, are shown to have distinct effects on the optical and electrical properties of MoS2. Defects and deformations created across different layers were investigated, revealing an unanticipated improvement in the Raman peak intensity of multilayer MoS2 when exposed to a 60 eV Ar+ ion beam, and attenuation of the MoS2 Raman peaks with a 200 eV ion beam. Using cross-sectional scanning transmission electron microscopy (STEM), alteration of the crystal structure after a 600 eV ion beam bombardment was observed, including generated defects and voids in the crystal. We show that the 60 eV ion beam yields improvement in the metal-MoS2 interface by decreasing the contact resistance from 17.5 kΩ · µm to 6 kΩ · µm at a carrier concentration of n2D  =  5.4  ×  1012 cm−2. These results advance the use of low-energy ion beams to modify 2D materials and interfaces for tuning and improving performance in applications of sensors, transistors, optoelectronics, and so forth.}, number={3}, journal={2D MATERIALS}, author={Cheng, Zhihui and Abuzaid, Hattan and Yu, Yifei and Zhang, Fan and Li, Yanlong and Noyce, Steven G. and Williams, Nicholas X. and Lin, Yuh-Chen and Doherty, James L. and Tao, Chenggang and et al.}, year={2019}, month={Jul} }
 @article{bataller_younts_rustagi_yu_ardekani_kemper_cao_gundogdu_2019, title={Dense Electron–Hole Plasma Formation and Ultralong Charge Lifetime in Monolayer MoS2 via Material Tuning}, volume={19}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/acs.nanolett.8b04408}, DOI={10.1021/acs.nanolett.8b04408}, abstractNote={Many-body interactions in photoexcited semiconductors can bring about strongly interacting electronic states, culminating in the fully ionized matter of electron-hole plasma (EHP) and electron-hole liquid (EHL). These exotic phases exhibit unique electronic properties, such as metallic conductivity and metastable high photoexcitation density, which can be the basis for future transformative applications. However, the cryogenic condition required for its formation has limited the study of dense plasma phases to a purely academic pursuit in a restricted parameter space. This paradigm can potentially change with the recent experimental observation of these phases in atomically thin MoS2 and MoTe2 at room temperature. A fundamental understanding of EHP and EHL dynamics is critical for developing novel applications on this versatile layered platform. In this work, we studied the formation and dissipation of EHP in monolayer MoS2. Unlike previous results in bulk semiconductors, our results reveal that electromechanical material changes in monolayer MoS2 during photoexcitation play a significant role in dense EHP formation. Within the free-standing geometry, photoexcitation is accompanied by an unconstrained thermal expansion, resulting in a direct-to-indirect gap electronic transition at a critical lattice spacing and fluence. This dramatic altering of the material's energetic landscape extends carrier lifetimes by 2 orders of magnitude and allows the density required for EHP formation. The result is a stable dense plasma state that is sustained with modest optical photoexcitation. Our findings pave the way for novel applications based on dense plasma states in two-dimensional semiconductors.}, number={2}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Bataller, Alexander W. and Younts, Robert A. and Rustagi, Avinash and Yu, Yiling and Ardekani, Hossein and Kemper, Alexander and Cao, Linyou and Gundogdu, Kenan}, year={2019}, month={Jan}, pages={1104–1111} }
 @article{cheng_yu_singh_price_noyce_lin_cao_franklin_2019, title={Immunity to Contact Scaling in MoS2 Transistors Using in Situ Edge Contacts}, volume={19}, ISSN={["1530-6992"]}, DOI={10.1021/acs.nanolett.9b01355}, abstractNote={Atomically thin two-dimensional (2D) materials are promising candidates for sub-10 nm transistor channels due to their ultrathin body thickness, which results in strong electrostatic gate control. Properly scaling a transistor technology requires reducing both the channel length (distance from source to drain) and the contact length (distance that source and drain interface with semiconducting channel). Contact length scaling remains an unresolved epidemic for transistor scaling, affecting devices from all semiconductors-silicon to 2D materials. Here, we show that clean edge contacts to 2D MoS2 can provide immunity to the contact-scaling problem, with performance that is independent of contact length down to the 20 nm regime. Using a directional ion beam, in situ edge contacts of various metal-MoS2 interfaces are studied. Characterization of the intricate edge interface using cross-sectional electron microscopy reveals distinct morphological effects on the MoS2 depending on its thickness-from monolayer to few-layer films. The in situ edge contacts also exhibit an order of magnitude higher performance compared to the best-reported ex situ metal edge contacts. Our work provides experimental evidence for a solution to contact scaling in transistors, using 2D materials with clean edge contact interfaces, opening a new way of designing devices with 2D materials.}, number={8}, journal={NANO LETTERS}, author={Cheng, Zhihui and Yu, Yifei and Singh, Shreya and Price, Katherine and Noyce, Steven G. and Lin, Yuh-Chen and Cao, Linyou and Franklin, Aaron D.}, year={2019}, month={Aug}, pages={5077–5085} }
 @article{ma_guzelturk_li_cao_shen_lindenberg_heinz_2019, title={Recording interfacial currents on the subnanometer length and femtosecond time scale by terahertz emission}, volume={5}, ISSN={["2375-2548"]}, DOI={10.1126/sciadv.aau0073}, abstractNote={Electromagnetic radiation emitted by electrons allows their ultrafast motion to be probed on the atomic length scale.}, number={2}, journal={SCIENCE ADVANCES}, author={Ma, Eric Yue and Guzelturk, Burak and Li, Guoqing and Cao, Linyou and Shen, Zhi-Xun and Lindenberg, Aaron M. and Heinz, Tony F.}, year={2019}, month={Feb} }
 @article{yu_bataller_younts_yu_li_puretzky_geohegan_gundogdu_cao_2019, title={Room-Temperature Electron-Hole Liquid in Monolayer MoS2}, volume={13}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.9b04124}, abstractNote={Excitons in semiconductors are usually non-interacting and behave like an ideal gas, but may condense to a strongly-correlated liquid-like state, i.e. electron-hole liquid (EHL), at high density and appropriate temperature. EHL is a macroscopic quantum state with exotic properties and represents the ultimate attainable charge excitation density in steady states. It bears great promise for a variety of fields such as ultrahigh-power photonics and quantum science and technology. However, the condensation of gas-like excitons to EHL has often been restricted to cryogenic temperatures, which significantly limits the prospect of EHL for use in practical applications. Herein we demonstrate the formation of EHL at room temperature in monolayer MoS2 by taking advantage of the monolayer's extraordinarily strong exciton binding energy. This work demonstrates the potential for the liquid-like state of charge excitations to be a useful platform for the studies of macroscopic quantum phenomena and the development of optoelectronic devices.}, number={9}, journal={ACS NANO}, author={Yu, Yiling and Bataller, Alexander W. and Younts, Robert and Yu, Yifei and Li, Guoqing and Puretzky, Alexander A. and Geohegan, David B. and Gundogdu, Kenan and Cao, Linyou}, year={2019}, month={Sep}, pages={10351–10358} }
 @article{su_bradley_yu_yu_cao_zhao_zhang_2019, title={Surface-enhanced Raman scattering of monolayer transition metal dichalcogenides on Ag nanorod arrays}, volume={44}, ISSN={["1539-4794"]}, DOI={10.1364/OL.44.005493}, abstractNote={In this work, we studied surface-enhanced Raman scattering (SERS) of MS2 (M=Mo, W) monolayers that were transferred onto Ag nanorod arrays. Compared to the suspended monolayers, the Raman intensity of monolayers on an Ag nanorod substrate was strongly enhanced for both in-plane and out-of-plane vibration modes: up to 8 (5) for E2g and 20 (23) for A1g in MoS2 (WS2). This finding reveals a promising SERS substrate for achieving uniform and strong enhancement for two-dimensional materials in the applications of optical detecting and sensing.}, number={22}, journal={OPTICS LETTERS}, author={Su, Liqin and Bradley, Layne and Yu, Yiling and Yu, Yifei and Cao, Linyou and Zhao, Yiping and Zhang, Yong}, year={2019}, month={Nov}, pages={5493–5496} }
 @article{lavini_calo_gao_albisetti_li_cao_li_cao_aruta_riedo_2018, title={Friction and work function oscillatory behavior for an even and odd number of layers in polycrystalline MoS2}, volume={10}, ISSN={["2040-3372"]}, DOI={10.1039/c8nr00238j}, abstractNote={We report on a new oscillatory behavior of nanoscopic friction in continuous polycrystalline MoS2films for an odd and even number of atomic layers, related to the different in-plane polarization of crystalline grains and different capability of absorbing charged molecules.}, number={17}, journal={NANOSCALE}, author={Lavini, Francesco and Calo, Annalisa and Gao, Yang and Albisetti, Edoardo and Li, Tai-De and Cao, Tengfei and Li, Guoqing and Cao, Linyou and Aruta, Carmela and Riedo, Elisa}, year={2018}, month={May}, pages={8304–8312} }
 @article{li_zhang_yu_huang_yang_cao_2017, title={Activating MoS2 for pH-Universal Hydrogen Evolution Catalysis}, volume={139}, ISSN={["1520-5126"]}, DOI={10.1021/jacs.7b07450}, abstractNote={MoS2 presents a promising catalyst for the hydrogen evolution reaction (HER) in water splitting, but its worse catalytic performance in neutral and alkaline media than in acidic environment may be problematic for practical application. This is because the other half reaction of water splitting, i.e., oxygen evolution reaction, often needs to be implemented in alkaline environment. Here we demonstrate a universal strategy that may be used to significantly improve the HER catalysis of MoS2 in all kinds of environments from acidic to alkaline, proton intercalation. Protons may be enabled to intercalate between monolayer MoS2 and underlying substrates or in the interlayer space of thicker MoS2 by two processes: electrochemically polarizing MoS2 at negative potentials (vs RHE) in acidic media or immersing MoS2 into certain acid solutions like TFSI. The improvement in catalytic performance is due to the activity enhancement of the active sites in MoS2 by the intercalated protons, which might be related with the effect of the intercalated protons on electrical conductance and the adsorption energy of hydrogen atoms. The enhancement in catalytic activity by the intercalated proton is very stable even in neutral and alkaline electrolytes.}, number={45}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Li, Guoqing and Zhang, Du and Yu, Yifei and Huang, Shengyang and Yang, Weitao and Cao, Linyou}, year={2017}, month={Nov}, pages={16194–16200} }
 @article{mannebach_nyby_ernst_zhou_tolsma_li_sher_tung_zhou_zhang_et al._2017, title={Dynamic Optical Tuning of Interlayer Interactions in the Transition Metal Dichalcogenides}, volume={17}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/acs.nanolett.7b03955}, DOI={10.1021/acs.nanolett.7b03955}, abstractNote={Modulation of weak interlayer interactions between quasi-two-dimensional atomic planes in the transition metal dichalcogenides (TMDCs) provides avenues for tuning their functional properties. Here we show that above-gap optical excitation in the TMDCs leads to an unexpected large-amplitude, ultrafast compressive force between the two-dimensional layers, as probed by in situ measurements of the atomic layer spacing at femtosecond time resolution. We show that this compressive response arises from a dynamic modulation of the interlayer van der Waals interaction and that this represents the dominant light-induced stress at low excitation densities. A simple analytic model predicts the magnitude and carrier density dependence of the measured strains. This work establishes a new method for dynamic, nonequilibrium tuning of correlation-driven dispersive interactions and of the optomechanical functionality of TMDC quasi-two-dimensional materials.}, number={12}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Mannebach, Ehren M. and Nyby, Clara and Ernst, Friederike and Zhou, Yao and Tolsma, John and Li, Yao and Sher, Meng-Ju and Tung, I-Cheng and Zhou, Hua and Zhang, Qi and et al.}, year={2017}, month={Nov}, pages={7761–7766} }
 @article{yu_li_huang_barrette_cai_yu_gundogdu_zhang_cao_2017, title={Enhancing Multifunctionalities of Transition-Metal Dichalcogenide Monolayers via Cation Intercalation}, volume={11}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/ACSNANO.7B04880}, DOI={10.1021/acsnano.7b04880}, abstractNote={We have demonstrated that multiple functionalities of transition-metal dichalcogenide (TMDC) monolayers may be substantially improved by the intercalation of small cations (H+ or Li+) between the monolayers and underlying substrates. The functionalities include photoluminescence (PL) efficiency and catalytic activity. The improvement in PL efficiency may be up to orders of magnitude and can be mainly ascribed to two effects of the intercalated cations: p-doping to the monolayers and reducing the influence of substrates, but more studies are necessary to better understand the mechanism for the improvement in the catalytic functionality. The cation intercalation may be achieved by simply immersing substrate-supported monolayers into the solution of certain acids or salts. It is more difficult to intercalate under the monolayers interacting with substrates stronger, such as as-grown monolayers or the monolayers on 2D material substrates. This result presents a versatile strategy to simultaneously optimize multiple functionalities of TMDC monolayers.}, number={9}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Yu, Yifei and Li, Guoqing and Huang, Lujun and Barrette, Andrew and Cai, Yong-Qing and Yu, Yiling and Gundogdu, Kenan and Zhang, Yong-Wei and Cao, Linyou}, year={2017}, month={Sep}, pages={9390–9396} }
 @article{yu_yu_huang_peng_xiong_cao_2017, title={Giant Gating Tunability of Optical Refractive Index in Transition Metal Dichalcogenide Monolayers}, volume={17}, ISSN={["1530-6992"]}, DOI={10.1021/acs.nanolett.7b00768}, abstractNote={We report that the refractive index of transition metal dichacolgenide (TMDC) monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by >60% in the imaginary part and >20% in the real part around exciton resonances using complementary metal-oxide-semiconductor (CMOS) compatible electrical gating. This giant tunablility is rooted in the dominance of excitonic effects in the refractive index of the monolayers and the strong susceptibility of the excitons to the influence of injected charge carriers. The tunability mainly results from the effects of injected charge carriers to broaden the spectral width of excitonic interband transitions and to facilitate the interconversion of neutral and charged excitons. The other effects of the injected charge carriers, such as renormalizing bandgap and changing exciton binding energy, only play negligible roles. We also demonstrate that the atomically thin monolayers, when combined with photonic structures, can enable the efficiencies of optical absorption (reflection) tuned from 40% (60%) to 80% (20%) due to the giant tunability of the refractive index. This work may pave the way toward the development of field-effect photonics in which the optical functionality can be controlled with CMOS circuits.}, number={6}, journal={NANO LETTERS}, author={Yu, Yiling and Yu, Yifei and Huang, Lujun and Peng, Haowei and Xiong, Liwei and Cao, Linyou}, year={2017}, month={Jun}, pages={3613–3618} }
 @article{su_yu_cao_zhang_2017, title={In Situ Monitoring of the Thermal-Annealing Effect in a Monolayer of MoS2}, volume={7}, ISSN={["2331-7019"]}, DOI={10.1103/physrevapplied.7.034009}, abstractNote={We perform in situ two-cycle thermal-annealing studies for a transferred CVD-grown monolayer MoS2 on a SiO2=Si substrate, using spatially resolved micro-Raman and photoluminescence spectroscopy. The evolution in film morphology and film-substrate bonding is continuously monitored by Raman spectroscopy. After the thermal cycling and being annealed at 305 °C twice, the film morphology and filmsubstrate bonding are significantly modified, which together with the removal of polymer residues causes major changes in the strain and doping distribution over the film, and thus the optical properties. Before annealing, the strain associated with ripples in the transferred film dominates the spatial distributions of the photoluminescence peak position and intensity over the film; after annealing, the variation in film-substrate bonding, affecting both strain and doping, becomes the leading factor. This work reveals that the filmsubstrate bonding, and thus the strain and doping, is nonstationary under thermal stress, which is important for understanding the substrate effects on the optical and transport properties of the 2D material and their impact on device applications.}, number={3}, journal={PHYSICAL REVIEW APPLIED}, author={Su, Liqin and Yu, Yifei and Cao, Linyou and Zhang, Yong}, year={2017}, month={Mar} }
 @article{li_zhang_qiao_yu_peterson_zafar_kumar_curtarolo_hunte_shannon_et al._2016, title={All The Catalytic Active Sites of MoS2 for Hydrogen Evolution}, volume={138}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/jacs.6b05940}, DOI={10.1021/jacs.6b05940}, abstractNote={MoS2 presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS2, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. The intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated to be 7.5 s-1 (65-75 mV/dec), 3.2 s-1 (65-85 mV/dec), and 0.1 s-1 (120-160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7-10%, and the number of sulfur vacancies in high crystalline quality MoS2 is higher than that in low crystalline quality MoS2, which may be related with the proximity of different local crystalline structures to the vacancies.}, number={51}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Li, Guoqing and Zhang, Du and Qiao, Qiao and Yu, Yifei and Peterson, David and Zafar, Abdullah and Kumar, Raj and Curtarolo, Stefano and Hunte, Frank and Shannon, Steve and et al.}, year={2016}, month={Dec}, pages={16632–16638} }
 @article{huang_li_gurarslan_yu_kirste_guo_zhao_collazo_sitar_parsons_et al._2016, title={Atomically Thin MoS2 Narrowband and Broadband Light Superabsorbers}, volume={10}, ISSN={["1936-086X"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000381959100030&KeyUID=WOS:000381959100030}, DOI={10.1021/acsnano.6b02195}, abstractNote={We present a combined theoretical and experimental effort to enable strong light absorption (>70%) in atomically thin MoS2 films (≤4 layers) for either narrowband incidence with arbitrarily prespecified wavelengths or broadband incidence like solar radiation. This is achieved by integrating the films with resonant photonic structures that are deterministically designed using a unique reverse design approach based on leaky mode coupling. The design starts with identifying the properties of leaky modes necessary for the targeted strong absorption, followed by searching for the geometrical features of nanostructures to support the desired modes. This process is very intuitive and only involves a minimal amount of computation, thanks to the straightforward correlations between optical functionality and leaky modes as well as between leaky modes and the geometrical feature of nanostructures. The result may provide useful guidance for the development of high-performance atomic-scale photonic devices, such as solar cells, modulators, photodetectors, and photocatalysts.}, number={8}, journal={ACS NANO}, author={Huang, Lujun and Li, Guoqing and Gurarslan, Alper and Yu, Yiling and Kirste, Ronny and Guo, Wei and Zhao, Junjie and Collazo, Ramon and Sitar, Zlatko and Parsons, Gregory N. and et al.}, year={2016}, month={Aug}, pages={7493–7499} }
 @article{chen_li_lu_zhu_jiang_hu_cao_zhang_2016, title={Chemical vapor deposited MoS2/electrospun carbon nanofiber composite as anode material for high-performance sodium-ion batteries}, volume={222}, ISSN={["1873-3859"]}, url={https://publons.com/publon/26924666/}, DOI={10.1016/j.electacta.2016.11.170}, abstractNote={Due to its high theoretical capacity and unique layered structure, MoS2 has attracted attention as a sodium-ion battery anode material. However, the electrochemical performance of MoS2 based anodes is hindered by their low intrinsic conductivity and large volume change during cycling. In this report, nano-sized MoS2 sheets are synthesized using a scalable chemical vapor deposition method on the surface of electrospun carbon nanofibers (CNFs). The morphology of the resultant MoS2@CNFs is investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction, while their electrochemical performance is studied using cyclic voltammetry and galvanostatic charge-discharge. The results demonstrate that a strong interconnection between MoS2 nanosheets and CNFs is formed and the conductive network of CNFs is beneficial for the sodium ion kinetics. When investigated as an anode for sodium-ion batteries, a high reversible capacity of 380 mA h g−1 is obtained after 50 cycles with good cycling stability. In particular, MoS2@CNFs can deliver a capacity of 198 mA h g−1 under a high current density of 1 A g−1 after 500 cycles, indicating their great potential as anode material for long-life sodium-ion batteries.}, journal={ELECTROCHIMICA ACTA}, publisher={Elsevier BV}, author={Chen, Chen and Li, Guoqing and Lu, Yao and Zhu, Jiadeng and Jiang, Mengjin and Hu, Yi and Cao, Linyou and Zhang, Xiangwu}, year={2016}, month={Dec}, pages={1751–1760} }
 @article{yu_yu_xu_cai_su_zhang_zhang_gundogdu_cao_2016, title={Engineering Substrate Interactions for High Luminescence Efficiency of Transition-Metal Dichalcogenide Monolayers}, volume={26}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201600418}, abstractNote={It is demonstrated that the luminescence efficiency of monolayers composed of MoS2, WS2, and WSe2 is significantly limited by the substrate and can be improved by orders of magnitude through substrate engineering. The substrate affects the efficiency mainly through doping the monolayers and facilitating defect‐assisted nonradiative exciton recombinations, while the other substrate effects including straining and dielectric screening play minor roles. The doping may come from the substrate and substrate‐borne water moisture, the latter of which is much stronger than the former for MoS2 and WS2 but negligible for WSe2. Using proper substrates such as mica or hexagonal boron nitride can substantially mitigate the doping effect. The defect‐assisted recombination depends on the interaction between the defect in the monolayer and the substrate. Suspended monolayers, in which the substrate effects are eliminated, may have efficiency up to 40% at room temperatures. The result provides useful guidance for the rational design of atomic‐scale light emission devices.}, number={26}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Yu, Yifei and Yu, Yiling and Xu, Chao and Cai, Yong-Qing and Su, Liqin and Zhang, Yong and Zhang, Yong-Wei and Gundogdu, Kenan and Cao, Linyou}, year={2016}, month={Jul}, pages={4733–4739} }
 @inproceedings{cao_2016, title={Extreme manipulation of light-matter interactions in 2D TMDC materials}, DOI={10.1109/piers.2016.7735444}, abstractNote={Two-dimensional (2D) transition metal dichalcogenide (TMDC) materials have the potential to open up a new age of atomic-scale photonics. However, much fundamental of the light-matter interaction of these materials has generally remained to be elusive. The optical response of the materials is very weak due to the atomically thin dimension, which stands as a huge challenge for the device development. Here we present our recent results on the light-matter interaction of 2D TMDC. We have demonstrated that excitonic effects dominate the light-matter interaction of the TMDC materials with layer number less than 5-7. The light absorption of atomically thin TMDC materials (<; 4 layers) can be dramatically improved up to > 75% for narrowband or broadband incidence like solar radiation. Additionally, we have demonstrated that the light-matter interaction of 2D TMDC materials can be substantially tuned in electrical ways.}, booktitle={2016 Progress in Electromagnetics Research Symposium (PIERS)}, author={Cao, L. Y.}, year={2016}, pages={3844–3844} }
 @article{yu_yu_xu_barrette_gundogdu_cao_2016, title={Fundamental limits of exciton-exciton annihilation for light emission in transition metal dichalcogenide monolayers}, volume={93}, DOI={10.1103/physrevb.93.201111}, abstractNote={We quantitatively evaluate the exciton-exciton annihilation (EEA) and its effect on light emission properties in monolayer TMDC materials, including WS2, MoS2, and WSe2. The EEA rate is found to be 0.3 cm2/s and 0.1 cm2/s for suspended WS2 and MoS2 monolayers, respectively, and subject to the influence from substrates, being 0.1 cm2/s and 0.05 cm2/s for the supported WS2 and MoS2 on sapphire substrates. It can substantially affect the luminescence efficiency of suspended monolayers even at an exciton concentration as low as 109 cm-2, but plays a milder role for supported monolayers due to the effect of the substrate. However, regardless the presence of substrates or not, the lasing threshold of the monolayer is always predominantly determined by the EEA, which is estimated to be 12-18 MW/cm2 if using 532 nm as the pumping wavelength.}, number={20}, journal={Physical Review B}, author={Yu, Y. L. and Yu, Y. F. and Xu, C. and Barrette, A. and gundogdu and Cao, L. Y.}, year={2016} }
 @article{mills_yu_chen_huang_cao_tao_2016, title={Ripples near edge terminals in MoS2 few layers and pyramid nanostructures}, volume={108}, ISSN={["1077-3118"]}, DOI={10.1063/1.4942088}, abstractNote={Atomically thin transition-metal dichalcogenides are of great interest due to their intriguing physical properties and potential applications. Here, we report our findings from scanning tunneling microscopy and spectroscopy investigations on molybdenum disulfide (MoS2) mono- to few-layers and pyramid nanostructures synthesized through chemical vapor deposition. On the few-layered MoS2 nanoplatelets grown on gallium nitride (GaN) and pyramid nanostructures on highly oriented pyrolytic graphite, we observed an intriguing curved region near the edge terminals. The measured band gap on these curved regions is 1.96 ± 0.10 eV, consistent with the value of the direct band gap in MoS2 monolayers. The curved features near the edge terminals and the associated electronic properties may contribute to the catalytic behaviors of MoS2 nanostructures and have potential applications in future electronic devices and energy-related products based on MoS2 nanostructures.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Mills, Adam and Yu, Yifei and Chen, Chuanhui and Huang, Bevin and Cao, Linyou and Tao, Chenggang}, year={2016}, month={Feb} }
 @article{gurarslan_jiao_li_li_yu_gao_riedo_xu_cao_2016, title={Van der Waals Force Isolation of Monolayer MoS2}, volume={28}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201601581}, abstractNote={Monolayer MoS2 can effectively screen the vdW interaction of underlying substrates with external systems by >90% because of the substantial increase in the separation between the substrate and external systems due to the presence of the monolayer. This substantial screening of vdW interactions by MoS2 monolayer is different from what reported at graphene.}, number={45}, journal={ADVANCED MATERIALS}, author={Gurarslan, Alper and Jiao, Shuping and Li, Tai-De and Li, Guoqing and Yu, Yiling and Gao, Yang and Riedo, Elisa and Xu, Zhiping and Cao, Linyou}, year={2016}, month={Dec}, pages={10055–10060} }
 @article{lin_huang_yu_he_cao_2015, title={Deterministic phase engineering for optical Fano resonances with arbitrary lineshape and frequencies}, volume={23}, ISSN={["1094-4087"]}, DOI={10.1364/oe.23.019154}, abstractNote={We present an approach of deterministic phase engineering that can enable the rational design of optical Fano resonances with arbitrarily pre-specified lineshapes. Unlike all the approaches previously used to design optical Fano resonances, which fall short of designing the resonances with arbitrary lineshapes because of the lack of information for the optical phases involved, we develop our approach by capitalizing on unambiguous knowledge for the phase of optical modes. Optical Fano resonances arise from the interference of photons interacting with two optical modes with substantially different quality factors. We find that the phase difference of the two modes involved in optical Fano resonances is determined by the eigenfrequency difference of the modes. This allows us to deterministically engineer the phase by tuning the eigenfrequency, which may be very straightforward. We use dielectric grating structures as an example to illustrate the notion of deterministic engineering for the design of optical Fano resonances with arbitrarily pre-specified symmetry, linewidth, and wavelengths.}, number={15}, journal={OPTICS EXPRESS}, author={Lin, Jiao and Huang, Lujun and Yu, Yiling and He, Sailing and Cao, Linyou}, year={2015}, month={Jul}, pages={19154–19165} }
 @article{mannebach_li_duerloo_nyby_zalden_vecchione_ernst_reid_chase_shen_et al._2015, title={Dynamic Structural Response and Deformations of Monolayer MoS2 Visualized by Femtosecond Electron Diffraction}, volume={15}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/ACS.NANOLETT.5B02805}, DOI={10.1021/ACS.NANOLETT.5B02805}, abstractNote={Two-dimensional materials are subject to intrinsic and dynamic rippling that modulates their optoelectronic and electromechanical properties. Here, we directly visualize the dynamics of these processes within monolayer transition metal dichalcogenide MoS2 using femtosecond electron scattering techniques as a real-time probe with atomic-scale resolution. We show that optical excitation induces large-amplitude in-plane displacements and ultrafast wrinkling of the monolayer on nanometer length-scales, developing on picosecond time-scales. These deformations are associated with several percent peak strains that are fully reversible over tens of millions of cycles. Direct measurements of electron-phonon coupling times and the subsequent interfacial thermal heat flow between the monolayer and substrate are also obtained. These measurements, coupled with first-principles modeling, provide a new understanding of the dynamic structural processes that underlie the functionality of two-dimensional materials and open up new opportunities for ultrafast strain engineering using all-optical methods.}, number={10}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Mannebach, Ehren M. and Li, Renkai and Duerloo, Karel-Alexander and Nyby, Clara and Zalden, Peter and Vecchione, Theodore and Ernst, Friederike and Reid, Alexander Hume and Chase, Tyler and Shen, Xiaozhe and et al.}, year={2015}, month={Sep}, pages={6889–6895} }
 @article{su_yu_cao_zhang_2015, title={Effects of substrate type and material-substrate bonding on high-temperature behavior of monolayer WS2}, volume={8}, ISSN={["1998-0000"]}, DOI={10.1007/s12274-015-0775-1}, number={8}, journal={NANO RESEARCH}, author={Su, Liqin and Yu, Yifei and Cao, Linyou and Zhang, Yong}, year={2015}, month={Aug}, pages={2686–2697} }
 @article{li_yu_huang_nielsen_goddard_li_cao_2015, title={Engineering the Composition and Crystallinity of Molybdenum Sulfide for High-Performance Electrocatalytic Hydrogen Evolution}, volume={5}, ISSN={["2155-5435"]}, DOI={10.1021/cs501635v}, abstractNote={The key challenge for the development of high-performance molybdenum sulfide HER catalysts lies in the limited fundamental understanding for the correlation between the catalytic activities and physical features of the materials. Here we have demonstrated an unambiguous correlation between the catalytic performance and the composition/crystallinity of molybdenum sulfide. The results indicate that the crystallinity plays an overwhelming role in determining the catalytic performance, while the composition does not matter much. The crystallinity can affect the three figures of merit of the catalytic performance (Tafel slope, turnover frequency (TOF), and stability) in opposite directions. Generally, the materials with low crystalline quality may provide low Tafel slopes (∼40 mV/dec), while highly crystalline molybdenum sulfide shows higher TOFs (by 2 orders of magnitude) and better stability. DFT calculations suggest that the terminal disulfur complex S22–, which may exist in MoS3 and also likely MoS2 of low...}, number={1}, journal={ACS CATALYSIS}, author={Li, Yanpeng and Yu, Yifei and Huang, Yufeng and Nielsen, Robert A. and Goddard, William A., III and Li, Yao and Cao, Linyou}, year={2015}, month={Jan}, pages={448–455} }
 @article{yu_yu_cai_li_gurarslan_peelaers_aspnes_walle_nguyen_zhang_et al._2015, title={Exciton-dominated Dielectric Function of Atomically Thin MoS2 Films}, volume={5}, ISSN={["2045-2322"]}, DOI={10.1038/srep16996}, abstractNote={Abstract}, journal={SCIENTIFIC REPORTS}, author={Yu, Yiling and Yu, Yifei and Cai, Yongqing and Li, Wei and Gurarslan, Alper and Peelaers, Hartwin and Aspnes, David E. and Walle, Chris G. and Nguyen, Nhan V. and Zhang, Yong-Wei and et al.}, year={2015}, month={Nov} }
 @article{cao_2015, title={Two-dimensional transition-metal dichalcogenide materials: Toward an age of atomic-scale photonics}, volume={40}, ISSN={["1938-1425"]}, DOI={10.1557/mrs.2015.144}, abstractNote={Abstract}, number={7}, journal={MRS BULLETIN}, author={Cao, Linyou}, year={2015}, month={Jul}, pages={592–599} }
 @article{su_zhang_yu_cao_2014, title={Dependence of coupling of quasi 2-D MoS2 with substrates on substrate types, probed by temperature dependent Raman scattering}, volume={6}, ISSN={["2040-3372"]}, DOI={10.1039/c3nr06462j}, abstractNote={The coupling of quasi 2-D MoS2 with substrates on different substrate types has been studied and probed by temperature dependent Raman scattering.}, number={9}, journal={NANOSCALE}, author={Su, Liqin and Zhang, Yong and Yu, Yifei and Cao, Linyou}, year={2014}, pages={4920–4927} }
 @article{yu_hu_su_huang_liu_jin_purezky_geohegan_kim_zhang_et al._2014, title={Equally Efficient Interlayer Exciton Relaxation and Improved Absorption in Epitaxial and Nonepitaxial MoS2/WS2 Heterostructures}, volume={15}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl5038177}, DOI={10.1021/nl5038177}, abstractNote={Semiconductor heterostructures provide a powerful platform to engineer the dynamics of excitons for fundamental and applied interests. However, the functionality of conventional semiconductor heterostructures is often limited by inefficient charge transfer across interfaces due to the interfacial imperfection caused by lattice mismatch. Here we demonstrate that MoS(2)/WS(2) heterostructures consisting of monolayer MoS(2) and WS(2) stacked in the vertical direction can enable equally efficient interlayer exciton relaxation regardless the epitaxy and orientation of the stacking. This is manifested by a similar 2 orders of magnitude decrease of photoluminescence intensity in both epitaxial and nonepitaxial MoS(2)/WS(2) heterostructures. Both heterostructures also show similarly improved absorption beyond the simple superimposition of the absorptions of monolayer MoS(2) and WS(2). Our result indicates that 2D heterostructures bear significant implications for the development of photonic devices, in particular those requesting efficient exciton separation and strong light absorption, such as solar cells, photodetectors, modulators, and photocatalysts. It also suggests that the simple stacking of dissimilar 2D materials with random orientations is a viable strategy to fabricate complex functional 2D heterostructures, which would show similar optical functionality as the counterpart with perfect epitaxy.}, number={1}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Yu, Yifei and Hu, Shi and Su, Liqin and Huang, Lujun and Liu, Yi and Jin, Zhenghe and Purezky, Alexander A. and Geohegan, David B. and Kim, Ki Wook and Zhang, Yong and et al.}, year={2014}, month={Dec}, pages={486–491} }
 @article{mai_semenov_barrette_yu_jin_cao_kim_gundogdu_2014, title={Exciton valley relaxation in a single layer ofWS2measured by ultrafast spectroscopy}, volume={90}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.90.041414}, DOI={10.1103/physrevb.90.041414}, abstractNote={We measured the lifetime of optically created valley polarization in single layer WS2 using transient absorption spectroscopy. The electron valley relaxation is very short (< 1ps). However the hole valley lifetime is at least two orders of magnitude longer and exhibits a temperature dependence that cannot be explained by single carrier spin/valley relaxation mechanisms. Our theoretical analysis suggests that a collective contribution of two potential processes may explain the valley relaxation in single layer WS2. One process involves direct scattering of excitons from K to K' valleys with a spin flip-flop interaction. The other mechanism involves scattering through spin degenerate Gamma valley. This second process is thermally activated with an Arrhenius behavior due to the energy barrier between Gamma and K valleys.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Mai, Cong and Semenov, Yuriy G. and Barrette, Andrew and Yu, Yifei and Jin, Zhenghe and Cao, Linyou and Kim, Ki Wook and Gundogdu, Kenan}, year={2014}, month={Jul} }
 @article{yu_huang_li_steinmann_yang_cao_2014, title={Layer-Dependent Electrocatalysis of MoS2 for Hydrogen Evolution}, volume={14}, ISSN={["1530-6992"]}, DOI={10.1021/nl403620g}, abstractNote={The quantitative correlation of the catalytic activity with the microscopic structure of heterogeneous catalysts is a major challenge for the field of catalysis science. It requests synergistic capabilities to tailor the structure with atomic scale precision and to control the catalytic reaction to proceed through well-defined pathways. Here we leverage on the controlled growth of MoS2 atomically thin films to demonstrate that the catalytic activity of MoS2 for the hydrogen evolution reaction decreases by a factor of ∼ 4.47 for the addition of every one more layer. Similar layer dependence is also found in edge-riched MoS2 pyramid platelets. This layer-dependent electrocatalysis can be correlated to the hopping of electrons in the vertical direction of MoS2 layers over an interlayer potential barrier. Our experimental results suggest the potential barrier to be 0.119 V, consistent with theoretical calculations. Different from the conventional wisdom, which states that the number of edge sites is important, our results suggest that increasing the hopping efficiency of electrons in the vertical direction is a key for the development of high-efficiency two-dimensional material catalysts.}, number={2}, journal={NANO LETTERS}, author={Yu, Yifei and Huang, Sheng-Yang and Li, Yanpeng and Steinmann, Stephan N. and Yang, Weitao and Cao, Linyou}, year={2014}, month={Feb}, pages={553–558} }
 @article{yu_cao_2014, title={Leaky mode engineering: A general design principle for dielectric optical antenna solar absorbers}, volume={314}, ISSN={0030-4018}, url={http://dx.doi.org/10.1016/j.optcom.2013.10.051}, DOI={10.1016/j.optcom.2013.10.051}, abstractNote={We present a general principle for the rational design of dielectric optical antennas with optimal solar absorption enhancement: leaky mode engineering. This builds upon our previous study that demonstrates the solar absorption of a material with a given volume only dependent on the density and the radiative loss of leaky modes of the material. Here we systematically examine the correlation among the modal properties (density and radiative loss) of leaky modes, physical features, and solar absorption of dielectric antenna structures. Our analysis clearly points out the general guidelines for the design of dielectric optical antennas with optimal solar absorption enhancement: (a) using 0D structures; (b) the shape does not matter much; (c) heterostructuring with non-absorbing materials is a promising strategy; and (d) the design of a large-scale nanostructure array can use the solar absorption of single nanostructures as a reasonable reference.}, journal={Optics Communications}, publisher={Elsevier BV}, author={Yu, Yiling and Cao, Linyou}, year={2014}, month={Mar}, pages={79–85} }
 @article{yu_huang_cao_2014, title={Semiconductor Solar Superabsorbers}, volume={4}, ISSN={["2045-2322"]}, DOI={10.1038/srep04107}, abstractNote={Understanding the maximal enhancement of solar absorption in semiconductor materials by light trapping promises the development of affordable solar cells. However, the conventional Lambertian limit is only valid for idealized material systems with weak absorption and cannot hold for the typical semiconductor materials used in solar cells due to the substantial absorption of these materials. Herein we theoretically demonstrate the maximal solar absorption enhancement for semiconductor materials and elucidate the general design principle for light trapping structures to approach the theoretical maximum. By following the principles, we design a practical light trapping structure that can enable an ultrathin layer of semiconductor materials, for instance, 10 nm thick a-Si, absorb > 90% sunlight above the bandgap. The design has active materials with one order of magnitude less volume than any of the existing solar light trapping designs in literature. This work points towards the development of ultimate solar light trapping techniques.}, journal={SCIENTIFIC REPORTS}, author={Yu, Yiling and Huang, Lujun and Cao, Linyou}, year={2014}, month={Feb} }
 @article{fu_li_dirican_chen_lu_zhu_li_cao_bradford_zhang_et al._2014, title={Sulfur gradient-distributed CNF composite: a self-inhibiting cathode for binder-free lithium-sulfur batteries}, volume={50}, ISSN={["1364-548X"]}, url={https://publons.com/publon/26924687/}, DOI={10.1039/c4cc04970e}, abstractNote={A novel sulfur gradient cathode was developed with a high specific capacity and improved cycling stability for Li–S batteries.}, number={71}, journal={CHEMICAL COMMUNICATIONS}, publisher={Royal Society of Chemistry (RSC)}, author={Fu, Kun and Li, Yanpeng and Dirican, Mahmut and Chen, Chen and Lu, Yao and Zhu, Jiadeng and Li, Yao and Cao, Linyou and Bradford, Philip D. and Zhang, Xiangwu and et al.}, year={2014}, pages={10277–10280} }
 @article{gurarslan_yu_su_yu_suarez_yao_zhu_ozturk_zhang_cao_2014, title={Surface-Energy-Assisted Perfect Transfer of Centimeter-Scale Mono layer and Few-Layer MoS2 Films onto Arbitrary Substrates}, volume={8}, ISSN={["1936-086X"]}, DOI={10.1021/nn5057673}, abstractNote={The transfer of synthesized 2D MoS2 films is important for fundamental and applied research. However, it is problematic to translate the well-established transfer processes for graphene to MoS2 due to different growth mechanisms and surface properties. Here we demonstrate a surface-energy-assisted process that can perfectly transfer centimeter-scale monolayer and few-layer MoS2 films from original growth substrates onto arbitrary substrates with no observable wrinkles, cracks, and polymer residues. The unique strategies used in this process include leveraging the penetration of water between hydrophobic MoS2 films and hydrophilic growth substrates to lift off the films and dry transferring the film after the lift off. This is in stark contrast with the previous transfer process for synthesized MoS2 films, which explores the etching of the growth substrate by hot base solutions to lift off the films. Our transfer process can effectively eliminate the mechanical force caused by bubble generations, the attacks from chemical etchants, and the capillary force induced when transferring the film outside solutions as in the previous transfer process, which consists of the major causes for the previous unsatisfactory transfer. Our transfer process also benefits from using polystyrene (PS), instead of poly(methyl methacrylate) (PMMA) that was widely used previously, as the carrier polymer. PS can form more intimate interaction with MoS2 films than PMMA and is important for maintaining the integrity of the film during the transfer process. This surface-energy-assisted approach can be generally applied to the transfer of other 2D materials, such as WS2.}, number={11}, journal={ACS NANO}, author={Gurarslan, Alper and Yu, Yifei and Su, Liqin and Yu, Yiling and Suarez, Francisco and Yao, Shanshan and Zhu, Yong and Ozturk, Mehmet and Zhang, Yong and Cao, Linyou}, year={2014}, month={Nov}, pages={11522–11528} }
 @article{mannebach_duerloo_pellouchoud_sher_nah_kuo_yu_marshall_cao_reed_et al._2014, title={Ultrafast Electronic and Structural Response of Monolayer MoS2 under Intense Photoexcitation Conditions}, volume={8}, ISSN={["1936-086X"]}, DOI={10.1021/nn5044542}, abstractNote={We report on the dynamical response of single layer transition metal dichalcogenide MoS2 to intense above-bandgap photoexcitation using the nonlinear-optical second order susceptibility as a direct probe of the electronic and structural dynamics. Excitation conditions corresponding to the order of one electron-hole pair per unit cell generate unexpected increases in the second harmonic from monolayer films, occurring on few picosecond time-scales. These large amplitude changes recover on tens of picosecond time-scales and are reversible at megahertz repetition rates with no photoinduced change in lattice symmetry observed despite the extreme excitation conditions.}, number={10}, journal={ACS NANO}, author={Mannebach, Ehren M. and Duerloo, Karel-Alexander N. and Pellouchoud, Lenson A. and Sher, Meng-Ju and Nah, Sanghee and Kuo, Yi-Hong and Yu, Yifei and Marshall, Ann F. and Cao, Linyou and Reed, Evan J. and et al.}, year={2014}, month={Oct}, pages={10734–10742} }
 @article{yu_li_liu_su_zhang_cao_2013, title={Controlled Scalable Synthesis of Uniform, High-Quality Monolayer and Few-layer MoS2 Films}, volume={3}, ISSN={["2045-2322"]}, DOI={10.1038/srep01866}, abstractNote={Two dimensional (2D) materials with a monolayer of atoms represent an ultimate control of material dimension in the vertical direction. Molybdenum sulfide (MoS2) monolayers, with a direct bandgap of 1.8 eV, offer an unprecedented prospect of miniaturizing semiconductor science and technology down to a truly atomic scale. Recent studies have indeed demonstrated the promise of 2D MoS2 in fields including field effect transistors, low power switches, optoelectronics, and spintronics. However, device development with 2D MoS2 has been delayed by the lack of capabilities to produce large-area, uniform, and high-quality MoS2 monolayers. Here we present a self-limiting approach that can grow high quality monolayer and few-layer MoS2 films over an area of centimeters with unprecedented uniformity and controllability. This approach is compatible with the standard fabrication process in semiconductor industry. It paves the way for the development of practical devices with 2D MoS2 and opens up new avenues for fundamental research.}, journal={SCIENTIFIC REPORTS}, author={Yu, Yifei and Li, Chun and Liu, Yi and Su, Liqin and Zhang, Yong and Cao, Linyou}, year={2013}, month={May} }
 @article{li_yu_chi_cao_2013, title={Epitaxial nanosheet-nanowire heterostructures}, volume={13}, ISSN={["1530-6984"]}, DOI={10.1021/nl303876a}, abstractNote={We demonstrate synthesis of a new type of heterostructures that comprise two-dimensional (2D) nanosheets (NSs) epitaxially grown at one-dimensional (1D) nanowires (NWs). The synthesis involves materials with a graphite-like layered structure in which covalently bonded layers are held by weak van der Waals forces. GeS was used as a prototype material in this work. The synthesis also involves a seeded-growth process, where GeS NWs are grown first as seeds followed by a seeded growth of NSs at the pre-grown NWs. We observe that exposing the pre-grown NWs to air prior to the seeded growth is critical for the formation of NSs to yield NS-NW heterostructures. Our experimental results suggest that this might be due to a mild oxidation at the NW surface caused by the air exposure, which could subsequently facilitate the nucleation of NSs at the NWs. It also suggests that the surface oxidation needs to be controlled in a proper range in order to achieve optimized NS growths. We believe that this synthetic strategy may generally apply to the growth of NS-NW heterostructures of other layered chalcogenide materials. NS-NW heterostructures provide capabilities to monolithically integrate the functionality of 1D NWs and 2D NSs into a 3D space. It holds great potential in applications that request complex nanomaterials with multiple functionality, high surface area, and efficient charge transport, such as energy storage, chemical sensing, solar energy conversion, and 3D electric and photonic devices.}, number={3}, journal={Nano letters}, author={Li, Chun and Yu, Yifei and Chi, Miaofang and Cao, Linyou}, year={2013}, month={Mar}, pages={948–953} }
 @article{huang_yu_cao_2013, title={General Modal Properties of Optical Resonances in Subwavelength Nonspherical Dielectric Structures}, volume={13}, ISSN={["1530-6992"]}, DOI={10.1021/nl401150j}, abstractNote={Subwavelength dielectric structures offer an attractive low-loss alternative to plasmonic materials for the development of resonant optics functionalities such as metamaterials and optical antennas. Nonspherical-like rectangular dielectric structures are of the most interest from the standpoint of device development due to fabrication convenience. However, no intuitive fundamental understanding of the optical resonance in nonspherical dielectric structures is available, which has substantially delayed the development of dielectric resonant optics devices. Here, we elucidate the general fundamentals of the optical resonance in nonspherical subwavelength dielectric structures with different shapes (rectangular or triangular) and dimensionalities (1D nanowires or 0D nanoparticles). We demonstrate that the optical properties of nonspherical dielectric structures are dictated by the eigenvalue of the structure's leaky modes. Leaky modes are defined as optical modes with propagating waves outside the structure. We also elucidate the dependence of the modal eigenvalue on physical features of the structure. The eigenvalue shows scale invariance with respect to the size of the structure, weak dependence on the refractive index, but linear dependence on the size ratio of different sides of the structure. We propose a modified Fabry-Perot model to account for the linear dependence. The knowledge of leaky modes, including the role in optical responses and the dependence on physical features, can serve as a powerful guide for the rational design of devices with desired optical resonances. It may open up a pathway to design devices with functionality that has not been explored due to the lack of intuitive understanding, for instance, imaging devices able to sense incident angle or superabsorbing photodetectors.}, number={8}, journal={NANO LETTERS}, author={Huang, Lujun and Yu, Yiling and Cao, Linyou}, year={2013}, month={Aug}, pages={3559–3565} }
 @article{mai_barrette_yu_semenov_kim_cao_gundogdu_2013, title={Many-Body Effects in Valleytronics: Direct Measurement of Valley Lifetimes in Single-Layer MoS2}, volume={14}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl403742j}, DOI={10.1021/nl403742j}, abstractNote={Single layer MoS2 is an ideal material for the emerging field of "valleytronics" in which charge carrier momentum can be finely controlled by optical excitation. This system is also known to exhibit strong many-body interactions as observed by tightly bound excitons and trions. Here we report direct measurements of valley relaxation dynamics in single layer MoS2, by using ultrafast transient absorption spectroscopy. Our results show that strong Coulomb interactions significantly impact valley population dynamics. Initial excitation by circularly polarized light creates electron-hole pairs within the K-valley. These excitons coherently couple to dark intervalley excitonic states, which facilitate fast electron valley depolarization. Hole valley relaxation is delayed up to about 10 ps due to nondegeneracy of the valence band spin states. Intervalley biexciton formation reveals the hole valley relaxation dynamics. We observe that biexcitons form with more than an order of magnitude larger binding energy compared to conventional semiconductors. These measurements provide significant insight into valley specific processes in 2D semiconductors. Hence they could be used to suggest routes to design semiconducting materials that enable control of valley polarization.}, number={1}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Mai, Cong and Barrette, Andrew and Yu, Yifei and Semenov, Yuriy G. and Kim, Ki Wook and Cao, Linyou and Gundogdu, Kenan}, year={2013}, month={Dec}, pages={202–206} }
 @article{butler_hollen_cao_cui_gupta_gutiérrez_heinz_hong_huang_ismach_et al._2013, title={Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene}, volume={7}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/NN400280C}, DOI={10.1021/NN400280C}, abstractNote={Graphene's success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in field-effect transistors, spin- and valley-tronics, thermoelectrics, and topological insulators, among many other applications.}, number={4}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Butler, Sheneve Z. and Hollen, Shawna M. and Cao, Linyou and Cui, Yi and Gupta, Jay A. and Gutiérrez, Humberto R. and Heinz, Tony F. and Hong, Seung Sae and Huang, Jiaxing and Ismach, Ariel F. and et al.}, year={2013}, month={Mar}, pages={2898–2926} }
 @misc{butler_hollen_cao_cui_gupta_gutierrez_heinz_hong_huang_ismach_et al._2013, title={Progress, challenges, and opportunities in two-dimensional materials beyond graphene}, volume={7}, number={4}, journal={ACS Nano}, author={Butler, S. Z. and Hollen, S. M. and Cao, L. Y. and Cui, Y. and Gupta, J. A. and Gutierrez, H. R. and Heinz, T. F. and Hong, S. S. and Huang, J. X. and Ismach, A. F. and et al.}, year={2013}, pages={2898–2926} }
 @article{fan_huang_cao_brongersma_2013, title={Redesigning Photodetector Electrodes as an Optical Antenna}, volume={13}, ISSN={["1530-6992"]}, DOI={10.1021/nl303535s}, abstractNote={At the nanoscale, semiconductor and metallic structures naturally exhibit strong, tunable optical resonances that can be utilized to enhance light-matter interaction and to dramatically increase the performance of chipscale photonic elements. Here, we demonstrate that the metallic leads used to extract current from a Ge nanowire (NW) photodetector can be redesigned to serve as optical antennas capable of concentrating light in the NW. The NW itself can also be made optically resonant and an overall performance optimization involves a careful tuning of both resonances. We show that such a procedure can result in broadband absorption enhancements of up to a factor 1.7 at a target wavelength of 660 nm and an ability to control the detector's polarization-dependent response. The results of this study demonstrate the critical importance of performing a joint optimization of the electrical and optical properties of the metallic and semiconductor building blocks in optoelectronic devices with nanoscale components.}, number={2}, journal={NANO LETTERS}, author={Fan, Pengyu and Huang, Kevin C. Y. and Cao, Linyou and Brongersma, Mark L.}, year={2013}, month={Feb}, pages={392–396} }
 @article{huang_yu_li_cao_2013, title={Substrate Mediation in Vapor Deposition Growth of Layered Chalcogenide Nanoplates: A Case Study of SnSe2}, volume={117}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/jp400274a}, DOI={10.1021/jp400274a}, abstractNote={The two-dimensional (2D) nanostructure of layered chalcogenide materials (LCMs) is very interesting, but to make it a useful material platform necessiates the development of sophisticated synthetic control. We present the synthesis of single-crystalline SnSe2 nanoplates by a noncatalytic vapor deposition process and demonstrate that the growth is subject to strong influences from substrates. The effect of substrates is evidenced by a temperature-dependent morphological difference in the nanoplates grown on mica and silicon substrates. At a growth temperature of 280 °C, the diameter of the nanoplates grown on mica is larger than those grown on silicon by a ratio of 6.2. This ratio substantially decreases to be unity (1.04) at a higher temperature of 420 °C. Additionally, different from the nanoplates grown on silicon, which always show a well-defined hexagonal shape, the nanoplates grown on mica exhibit an irregular shape at low temperature and can gradually evolve into the hexagonal shape with increasing ...}, number={12}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Huang, Liang and Yu, Yifei and Li, Chun and Cao, Linyou}, year={2013}, month={Mar}, pages={6469–6475} }
 @article{yu_cao_2013, title={The phase shift of light scattering at sub-wavelength dielectric structures}, volume={21}, ISSN={["1094-4087"]}, DOI={10.1364/oe.21.005957}, abstractNote={We present a new theoretical analysis for the light scattering at sub-wavelength dielectric structures. This analysis can provide new intuitive insights into the phase shift of the scattered light that cannot be obtained from the existing approaches. Unlike the traditional analytical (e.g. Mie formalism) and numerical (e.g. FDTD) approaches, which simulate light scattering by rigorously matching electromagnetic fields at boundaries, we consider sub-wavelength dielectric structures as leaky resonators and evaluate the light scattering as a coupling process between incident light and leaky modes of the structure. Our analysis indicates that the light scattering is fundamentally dictated by the eigenvalue of the leaky modes. It indicates that the upper limit for the scattering efficiency of a cylindrical cylinder in free space is 4n, where n is the refractive index. It also indicates that the phase shift of the forward scattered light at dielectric structures can only cover half of the phase space [0, 2π], but backward scattering can provide a full phase coverage.}, number={5}, journal={OPTICS EXPRESS}, author={Yu, Yiling and Cao, Linyou}, year={2013}, month={Mar}, pages={5957–5967} }
 @article{fan_chettiar_cao_afshinmanesh_engheta_brongersma_2012, title={An invisible metal–semiconductor photodetector}, volume={6}, ISSN={1749-4885 1749-4893}, url={http://dx.doi.org/10.1038/nphoton.2012.108}, DOI={10.1038/nphoton.2012.108}, number={6}, journal={Nature Photonics}, publisher={Springer Nature}, author={Fan, Pengyu and Chettiar, Uday K. and Cao, Linyou and Afshinmanesh, Farzaneh and Engheta, Nader and Brongersma, Mark L.}, year={2012}, month={May}, pages={380–385} }
 @article{yu_cao_2012, title={Coupled leaky mode theory for light absorption in 2D, 1D, and 0D semiconductor nanostructures}, volume={20}, ISSN={1094-4087}, url={http://dx.doi.org/10.1364/oe.20.013847}, DOI={10.1364/oe.20.013847}, abstractNote={We present an intuitive, simple theoretical model, coupled leaky mode theory (CLMT), to analyze the light absorption of 2D, 1D, and 0D semiconductor nanostructures. This model correlates the light absorption of nanostructures to the optical coupling between incident light and leaky modes of the nanostructure. Unlike conventional methods such as Mie theory that requests specific physical features of nanostructures to evaluate the absorption, the CLMT model provides an unprecedented capability to analyze the absorption using eigen values of the leaky modes. Because the eigenvalue shows very mild dependence on the physical features of nanostructures, we can generally apply one set of eigenvalues calculated using a real, constant refractive index to calculations for the absorption of various nanostructures with different sizes, different materials, and wavelength-dependent complex refractive index. This CLMT model is general, simple, yet reasonably accurate, and offers new intuitive physical insights that the light absorption of nanostructures is governed by the coupling efficiency between incident light and leaky modes of the structure.}, number={13}, journal={Optics Express}, publisher={The Optical Society}, author={Yu, Yiling and Cao, Linyou}, year={2012}, month={Jun}, pages={13847} }
 @article{yu_ferry_alivisatos_cao_2012, title={Dielectric Core-Shell Optical Antennas for Strong Solar Absorption Enhancement}, volume={12}, ISSN={["1530-6992"]}, DOI={10.1021/nl301435r}, abstractNote={We demonstrate a new light trapping technique that exploits dielectric core-shell optical antennas to strongly enhance solar absorption. This approach can allow the thickness of active materials in solar cells lowered by almost 1 order of magnitude without scarifying solar absorption capability. For example, it can enable a 70 nm thick hydrogenated amorphous silicon (a-Si:H) thin film to absorb 90% of incident solar radiation above the bandgap, which would otherwise require a thickness of 400 nm in typical antireflective coated thin films. This strong enhancement arises from a controlled optical antenna effect in patterned core-shell nanostructures that consist of absorbing semiconductors and nonabsorbing dielectric materials. This core-shell optical antenna benefits from a multiplication of enhancements contributed by leaky mode resonances (LMRs) in the semiconductor part and antireflection effects in the dielectric part. We investigate the fundamental mechanism for this enhancement multiplication and demonstrate that the size ratio of the semiconductor and the dielectric parts in the core-shell structure is key for optimizing the enhancement. By enabling strong solar absorption enhancement, this approach holds promise for cost reduction and efficiency improvement of solar conversion devices, including solar cells and solar-to-fuel systems. It can generally apply to a wide range of inorganic and organic active materials. This dielectric core-shell antenna can also find applications in other photonic devices such as photodetectors, sensors, and solid-state lighting diodes.}, number={7}, journal={NANO LETTERS}, author={Yu, Yiling and Ferry, Vivian E. and Alivisatos, A. Paul and Cao, Linyou}, year={2012}, month={Jul}, pages={3674–3681} }
 @article{li_huang_snigdha_yu_cao_2012, title={Role of Boundary Layer Diffusion in Vapor Deposition Growth of Chalcogenide Nanosheets: The Case of GeS}, volume={6}, ISSN={["1936-086X"]}, DOI={10.1021/nn303745e}, abstractNote={We report a synthesis of single-crystalline two-dimensional GeS nanosheets using vapor deposition processes and show that the growth behavior of the nanosheet is substantially different from those of other nanomaterials and thin films grown by vapor depositions. The nanosheet growth is subject to strong influences of the diffusion of source materials through the boundary layer of gas flows. This boundary layer diffusion is found to be the rate-determining step of the growth under typical experimental conditions, evidenced by a substantial dependence of the nanosheet's size on diffusion fluxes. We also find that high-quality GeS nanosheets can grow only in the diffusion-limited regime, as the crystalline quality substantially deteriorates when the rate-determining step is changed away from the boundary layer diffusion. We establish a simple model to analyze the diffusion dynamics in experiments. Our analysis uncovers an intuitive correlation of diffusion flux with the partial pressure of source materials, the flow rate of carrier gas, and the total pressure in the synthetic setup. The observed significant role of boundary layer diffusions in the growth is unique for nanosheets. It may be correlated with the high growth rate of GeS nanosheets, ~3-5 μm/min, which is 1 order of magnitude higher than other nanomaterials (such as nanowires) and thin films. This fundamental understanding of the effect of boundary layer diffusions may generally apply to other chalcogenide nanosheets that can grow rapidly. It can provide useful guidance for the development of general paradigms to control the synthesis of nanosheets.}, number={10}, journal={ACS NANO}, author={Li, Chun and Huang, Liang and Snigdha, Gayatri Pongur and Yu, Yifei and Cao, Linyou}, year={2012}, month={Oct}, pages={8868–8877} }
 @article{cao_fan_brongersma_2011, title={Optical Coupling of Deep-Subwavelength Semiconductor Nanowires}, volume={11}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl1040429}, DOI={10.1021/nl1040429}, abstractNote={Systems of coupled resonators manifest a myriad of exciting fundamental physical phenomena. Analogous to the synthesis of molecules from single atoms, the construction of photonic molecules from stand-alone optical resonators represents a powerful strategy to realize novel functionalities. The coupling of high quality factor (Q) dielectric and semiconductor microresonators is by now well-understood and chipscale applications are abound. The coupling behavior of low-Q nanometallic structures has also been exploited to realize high-performance plasmonic devices and metamaterials. Although dense arrays of semiconductor nanoparticles and nanowires (NWs) find increasing use in optoelectronic devices, their photonic coupling has remained largely unexplored. These high refractive index nano-objects can serve as low-Q optical antennas that can effectively receive and broadcast light. We demonstrate that the broad band antenna response of a pair of NWs can be tuned significantly by engineering their optical coupling and develop an intuitive coupled-mode theory to explain our observations.}, number={4}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Fan, Pengyu and Brongersma, Mark L.}, year={2011}, month={Apr}, pages={1463–1468} }
 @article{cao_park_fan_clemens_brongersma_2010, title={Resonant Germanium Nanoantenna Photodetectors}, volume={10}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl9037278}, DOI={10.1021/nl9037278}, abstractNote={On-chip optical interconnection is considered as a substitute for conventional electrical interconnects as microelectronic circuitry continues to shrink in size. Central to this effort is the development of ultracompact, silicon-compatible, and functional optoelectronic devices. Photodetectors play a key role as interfaces between photonics and electronics but are plagued by a fundamental efficiency-speed trade-off. Moreover, engineering of desired wavelength and polarization sensitivities typically requires construction of space-consuming components. Here, we demonstrate how to overcome these limitations in a nanoscale metal-semiconductor-metal germanium photodetector for the optical communications band. The detector capitalizes on antenna effects to dramatically enhance the photoresponse (>25-fold) and to enable wavelength and polarization selectivity. The electrical design featuring asymmetric metallic contacts also enables ultralow dark currents (approximately 20 pA), low power consumption, and high-speed operation (>100 GHz). The presented high-performance photodetection scheme represents a significant step toward realizing integrated on-chip communication and manifests a new paradigm for developing miniaturized optoelectronics components.}, number={4}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Park, Joon-Shik and Fan, Pengyu and Clemens, Bruce and Brongersma, Mark L.}, year={2010}, month={Apr}, pages={1229–1233} }
 @article{cao_fan_vasudev_white_yu_cai_schuller_fan_brongersma_2010, title={Semiconductor Nanowire Optical Antenna Solar Absorbers}, volume={10}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl9036627}, DOI={10.1021/nl9036627}, abstractNote={Photovoltaic (PV) cells can serve as a virtually unlimited clean source of energy by converting sunlight into electrical power. Their importance is reflected in the tireless efforts that have been devoted to improving the electrical and structural properties of PV materials. More recently, photon management (PM) has emerged as a powerful additional means to boost energy conversion efficiencies. Here, we demonstrate an entirely new PM strategy that capitalizes on strong broad band optical antenna effects in one-dimensional semiconductor nanostructures to dramatically enhance absorption of sunlight. We show that the absorption of sunlight in Si nanowires (Si NWs) can be significantly enhanced over the bulk. The NW's optical properties also naturally give rise to an improved angular response. We propose that by patterning the silicon layer in a thin film PV cell into an array of NWs, one can boost the absorption for solar radiation by 25% while utilizing less than half of the semiconductor material (250% increase in the light absorption per unit volume of material). These results significantly advance our understanding of the way sunlight is absorbed by one-dimensional semiconductor nanostructures and provide a clear, intuitive guidance for the design of efficient NW solar cells. The presented approach is universal to any semiconductor and a wide range of nanostructures; as such, it provides a new PV platform technology.}, number={2}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Fan, Pengyu and Vasudev, Alok P. and White, Justin S. and Yu, Zongfu and Cai, Wenshan and Schuller, Jon A. and Fan, Shanhui and Brongersma, Mark L.}, year={2010}, month={Feb}, pages={439–445} }
 @article{xiang_zardo_cao_garma_heiß_morante_arbiol_brongersma_fontcuberta i morral_2010, title={Spatially resolved Raman spectroscopy on indium-catalyzed core–shell germanium nanowires: size effects}, volume={21}, ISSN={0957-4484 1361-6528}, url={http://dx.doi.org/10.1088/0957-4484/21/10/105703}, DOI={10.1088/0957-4484/21/10/105703}, abstractNote={The structure of indium-catalyzed germanium nanowires is investigated by atomic force microscopy, scanning confocal Raman spectroscopy and transmission electron microscopy. The nanowires are formed by a crystalline core and an amorphous shell. We find that the diameter of the crystalline core varies along the nanowire, down to few nanometers. Phonon confinement effects are observed in the regions where the crystalline region is the thinnest. The results are consistent with the thermally insulating behavior of the core–shell nanowires.}, number={10}, journal={Nanotechnology}, publisher={IOP Publishing}, author={Xiang, Y and Zardo, I and Cao, L Y and Garma, T and Heiß, M and Morante, J R and Arbiol, J and Brongersma, M L and Fontcuberta i Morral, A}, year={2010}, month={Feb}, pages={105703} }
 @article{cao_fan_barnard_brown_brongersma_2010, title={Tuning the Color of Silicon Nanostructures}, volume={10}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl1013794}, DOI={10.1021/nl1013794}, abstractNote={Empowering silicon (Si) with optical functions constitutes a very important challenge in photonics. The scalable fabrication capabilities for this earth-abundant, environmentally friendly material are unmatched in sophistication and can be unleashed to realize a plethora of high-performance photonic functionalities that find application in information, bio-, display, camouflage, ornamental, and energy technologies. Nanofashioning represents a general strategy to turn Si into a useful optical material and Si structures have already been engineered to enable light emission, optical cloaking, waveguiding, nonlinear optics, enhanced light absorption, and sensing. Here, we demonstrate that a wide spectrum of colors can be generated by harnessing the strong resonant light scattering properties of Si nanostructures under white light illumination. The ability to engineer such colors in a predetermined fashion through a choice of the structure size, dielectric environment, and illumination conditions opens up entirely new applications of Si and puts this material in a new light.}, number={7}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Fan, Pengyu and Barnard, Edward S. and Brown, Ana M. and Brongersma, Mark L.}, year={2010}, month={Jul}, pages={2649–2654} }
 @article{cao_white_park_schuller_clemens_brongersma_2009, title={Engineering light absorption in semiconductor nanowire devices}, volume={8}, ISSN={1476-1122 1476-4660}, url={http://dx.doi.org/10.1038/nmat2477}, DOI={10.1038/nmat2477}, abstractNote={The use of quantum and photon confinement has enabled a true revolution in the development of high-performance semiconductor materials and devices. Harnessing these powerful physical effects relies on an ability to design and fashion structures at length scales comparable to the wavelength of electrons (approximately 1 nm) or photons (approximately 1 microm). Unfortunately, many practical optoelectronic devices exhibit intermediate sizes where resonant enhancement effects seem to be insignificant. Here, we show that leaky-mode resonances, which can gently confine light within subwavelength, high-refractive-index semiconductor nanostructures, are ideally suited to enhance and spectrally engineer light absorption in this important size regime. This is illustrated with a series of individual germanium nanowire photodetectors. This notion, together with the ever-increasing control over nanostructure synthesis opens up tremendous opportunities for the realization of a wide range of high-performance, nanowire-based optoelectronic devices, including solar cells, photodetectors, optical modulators and light sources.}, number={8}, journal={Nature Materials}, publisher={Springer Science and Business Media LLC}, author={Cao, Linyou and White, Justin S. and Park, Joon-Shik and Schuller, Jon A. and Clemens, Bruce M. and Brongersma, Mark L.}, year={2009}, month={Jul}, pages={643–647} }
 @article{xiang_cao_conesa-boj_estrade_arbiol_peiro_heiß_zardo_morante_brongersma_et al._2009, title={Single crystalline and core–shell indium-catalyzed germanium nanowires—a systematic thermal CVD growth study}, volume={20}, ISSN={0957-4484 1361-6528}, url={http://dx.doi.org/10.1088/0957-4484/20/24/245608}, DOI={10.1088/0957-4484/20/24/245608}, abstractNote={Germanium nanowires were synthesized using thermal chemical vapor deposition (CVD) and indium as a catalyst. The process parameter space for successful growth was studied. By optimizing the growth temperature and gas pressure, high aspect ratio germanium nanowires have been obtained. Scanning electron microscopy investigations indicate that the final diameter of the nanowires is strongly influenced by the growth temperature and the germane partial pressure. High resolution transmission electron microscopy reveals that nanowires grow either as high quality single crystalline, or with a high quality single-crystalline core and a concentric amorphous shell. The occurrence of these two morphologies is found to only depend on the wire diameter. Chemical analysis of the nanowire tip indicates the presence of indium, validating its role as a catalyst. Raman spectroscopy measurements reveal a higher incidence of core–shell structures for nanowires synthesized at 30 Torr and indicate the presence of tensile strain. These results are important towards obtaining high quality germanium nanowires without the use of gold as a catalyst, which is known to degrade the wires’ electrical and optical properties.}, number={24}, journal={Nanotechnology}, publisher={IOP Publishing}, author={Xiang, Ying and Cao, Linyou and Conesa-Boj, Sonia and Estrade, Sonia and Arbiol, Jordi and Peiro, Francesca and Heiß, Martin and Zardo, I and Morante, Joan R and Brongersma, Mark L and et al.}, year={2009}, month={May}, pages={245608} }
 @article{xiang_cao_arbiol_brongersma_fontcuberta i morral_2009, title={Synthesis parameter space of bismuth catalyzed germanium nanowires}, volume={94}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3116625}, DOI={10.1063/1.3116625}, abstractNote={The synthesis parameter space of bismuth catalyzed germanium nanowires by chemical vapor deposition is determined. The process window for high aspect ratio nanowires is found to be extremely narrow. The optimal conditions are found to be 300 °C and 150 Torr gas pressure. For lower temperatures, the solubility of Ge in Bi is too low for the nucleation of Ge nanowires to occur. For higher temperatures, small Bi droplets tend to evaporate leading to an extreme reduction in the nanowire density. The extremely low process temperature makes Bi a good candidate for its growth on low cost and low thermal budget substrates such as plastics.}, number={16}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Xiang, Ying and Cao, Linyou and Arbiol, Jordi and Brongersma, Mark L. and Fontcuberta i Morral, Anna}, year={2009}, month={Apr}, pages={163101} }
 @article{cao_brongersma_2009, title={Ultrafast developments}, volume={3}, ISSN={1749-4885 1749-4893}, url={http://dx.doi.org/10.1038/nphoton.2008.259}, DOI={10.1038/nphoton.2008.259}, number={1}, journal={Nature Photonics}, publisher={Springer Science and Business Media LLC}, author={Cao, L. and Brongersma, Mark L.}, year={2009}, month={Jan}, pages={12–13} }
 @article{cao_garipcan_gallo_nonnenmann_nabet_spanier_2008, title={Excitation of Local Field Enhancement on Silicon Nanowires}, volume={8}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl0729983}, DOI={10.1021/nl0729983}, abstractNote={The interaction between light and reduced-dimensionality silicon attracts significant interest due to the possibilities of designing nanoscaled optical devices, highly cost-efficient solar cells, and ultracompact optoelectronic systems that are integrated with standard microelectronic technology. We demonstrate that Si nanowires (SiNWs) possessing metal-nanocluster coatings support a multiplicatively enhanced near-field light-matter interaction. Raman scattering from chemisorbed probing molecules provides a quantitative measure of the strength of this enhanced coupling. An enhancement factor of 2 orders of magnitude larger than that for the surface plasmon resonance alone (without the SiNWs) along with the attractive properties of SiNWs, including synthetic controllability of shape, indicates that these nanostructures may be an attractive and versatile material platform for the design of nanoscaled optical and optoelectronic circuits.}, number={2}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Garipcan, Bora and Gallo, Eric M. and Nonnenmann, Stephen S. and Nabet, Bahram and Spanier, Jonathan E.}, year={2008}, month={Feb}, pages={601–605} }
 @article{cao_laim_valenzuela_nabet_spanier_2007, title={On the Raman scattering from semiconducting nanowires}, volume={38}, ISSN={0377-0486 1097-4555}, url={http://dx.doi.org/10.1002/jrs.1730}, DOI={10.1002/jrs.1730}, abstractNote={Abstract}, number={6}, journal={Journal of Raman Spectroscopy}, publisher={Wiley}, author={Cao, L. and Laim, L. and Valenzuela, P. D. and Nabet, B. and Spanier, J. E.}, year={2007}, pages={697–703} }
 @article{cao_barsic_guichard_brongersma_2007, title={Plasmon-Assisted Local Temperature Control to Pattern Individual Semiconductor Nanowires and Carbon Nanotubes}, volume={7}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl0722370}, DOI={10.1021/nl0722370}, abstractNote={We demonstrate a new versatile strategy to rapidly heat and cool subdiffraction-limited volumes of material with a focused light beam. The local temperature rise is obtained by exploiting the unique optical properties of metallic nanostructures that facilitate efficient light-to-heat conversion through the excitation of surface plasmons (collective electron oscillations). By locally heating nanoscale metallic catalysts, growth of semiconductor nanowires and carbon nanotubes can be initiated and controlled at arbitrarily prespecified locations and down to the single nanostructure level in a room-temperature chamber. This local heating strategy can be orders of magnitude (>10(5)) more energy efficient than conventional chemical vapor deposition (CVD) tools in which an entire chamber/substrate is heated. For these reasons, it has great potential for use in process- and energy-efficient assembly of nanowires into complementary metal-oxide-semiconductor (CMOS) compatible device architectures. In general, the high degree of spatial and temporal control over nanoscale thermal environments afforded by this method inspires new pathways for manipulating a range of important thermally stimulated processes and the development of novel photothermal devices.}, number={11}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Barsic, David N. and Guichard, Alex R. and Brongersma, Mark L.}, year={2007}, month={Nov}, pages={3523–3527} }
 @article{cao_zhu_liu_2006, title={Formation mechanism of nonspherical gold nanoparticles during seeding growth: Roles of anion adsorption and reduction rate}, volume={293}, ISSN={0021-9797}, url={http://dx.doi.org/10.1016/j.jcis.2005.06.012}, DOI={10.1016/j.jcis.2005.06.012}, abstractNote={A small section of nonspherical particles can be observed in the further growth of spherical gold colloids exposed to a mixture of NH2OH and HAuCl4. The concentration ratio of [NH2OH]:[HAuCl4] is critical for the formation of nonspherical particles as higher ratios produce lower yields and smaller of such particles. These concentrations also affect the reaction kinetics; the reaction rate increases with [NH2OH], while independent of [HAuCl4], which we believe is due to the specific adsorption of AuCl−4 onto gold surface. These nonspherical particles come from the preferential growth of {111} facets as indicated by their TEM images and electron diffraction patterns. We propose this preferential growth is ascribed to the preferential adsorption of AuCl−4 on {111} facets, and some competition which determines the yield of nonspherical particles exists between the AuCl−4 adsorption and the AuCl−4 reduction, faster reduction counteracting the effect of this preferential adsorption and thus suppressing nonspherical particle. This result probably provides some guidance to develop a shape-controlled synthesis of gold particles without any additives.}, number={1}, journal={Journal of Colloid and Interface Science}, publisher={Elsevier BV}, author={Cao, Linyou and Zhu, Tao and Liu, Zhongfan}, year={2006}, month={Jan}, pages={69–76} }
 @article{cao_garipcan_atchison_ni_nabet_spanier_2006, title={Instability and Transport of Metal Catalyst in the Growth of Tapered Silicon Nanowires}, volume={6}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl060533r}, DOI={10.1021/nl060533r}, abstractNote={During metal-catalyzed growth of tapered silicon nanowires, or silicon nanocones (SiNCs), Au-Si eutectic particles are seen to undergo significant and reproducible reductions in their diameters. The reductions are accompanied by the transfer of eutectic droplet mass to adjacent, initially metal catalyst-free substrates, producing secondary nucleation and growth of SiNCs. Remarkably, the catalyst particle diameters on the SiNCs grown on the adjacent substrates are strongly correlated with those on the SiNCs grown on the initially Au-nanoparticle-coated substrate. These post-growth nanoparticle sizes depend on temperature and are found to be independent of the initial nanoparticle sizes. Our modeling and analysis indicates that the size reduction and mass transfer could be explained by electrostatic charge-induced dissociation of the droplet. The reduction in size enables the controlled growth of SiNCs with tip sharpnesses approaching the atomic scale, indicating that metal-catalyst nanoparticles can play an even more dynamic role than previously thought, and suggesting additional modes of control of shape, and of nucleation and growth location.}, number={9}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Garipcan, Bora and Atchison, Jennifer S. and Ni, Chaoying and Nabet, Bahram and Spanier, Jonathan E.}, year={2006}, month={Sep}, pages={1852–1857} }
 @article{cao_laim_ni_nabet_spanier_2005, title={Diamond-Hexagonal Semiconductor Nanocones with Controllable Apex Angle}, volume={127}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja0544814}, DOI={10.1021/ja0544814}, abstractNote={We report on the synthesis of nanostructured and crystalline tapered Si and Ge polyhedra via metal-catalyzed chemical vapor deposition. These Si and Ge nanocones (SiNCs, GeNCs) possess tips with near-atomic sharpness, micron-scaled bases, hexagonal cross-sections, and controllable apex angles. High-resolution transmission electron microscopy, selected-area electron diffraction and Raman scattering spectroscopy and analysis indicate that the SiNCs are of the diamond-hexagonal Si(IV) phase.}, number={40}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Laim, Lee and Ni, Chaoying and Nabet, Bahram and Spanier, Jonathan E.}, year={2005}, month={Oct}, pages={13782–13783} }
 @article{cao_chai_li_shen_wu_2005, title={Efficient self-assembly of transition metal oxide nanoclusters on silicon substrates}, volume={492}, ISSN={0040-6090}, url={http://dx.doi.org/10.1016/j.tsf.2005.06.022}, DOI={10.1016/j.tsf.2005.06.022}, abstractNote={Self-assembled monolayers (SAMs) of nanoclusters (< 10 nm) on silicon wafer have been prepared via simply immersing the substrate into a FeCl3/HCl solution. The clusters are hydrous iron oxide resulting from the hydrolysis of FeCl3, and their deposition is driven by the electrostatic attraction between the clusters and the substrate, the surface groups of which are oppositely charged at suitable pH value. HCl is used to enhance the repulsive force among the clusters and cause them uniformly distributed; in this regard, it can be replaced by KCl, NH4Cl, or NH2·HCl. This result provides a general guidance to prepare self-assemblies of transition metal oxide nanoclusters onto silicon substrates and others with appropriate hydroxyl (–OH) groups.}, number={1-2}, journal={Thin Solid Films}, publisher={Elsevier BV}, author={Cao, Linyou and Chai, Yang and Li, Pingjian and Shen, Zhiyong and Wu, Jinlei}, year={2005}, month={Dec}, pages={13–18} }
 @article{cao_diao_tong_zhu_liu_2005, title={Surface-Enhanced Raman Scattering ofp-Aminothiophenol on a Au(core)/Cu(shell) Nanoparticle Assembly}, volume={6}, ISSN={1439-4235 1439-7641}, url={http://dx.doi.org/10.1002/cphc.200400254}, DOI={10.1002/cphc.200400254}, abstractNote={Abstract}, number={5}, journal={ChemPhysChem}, publisher={Wiley}, author={Cao, Linyou and Diao, Peng and Tong, Lianming and Zhu, Tao and Liu, Zhongfan}, year={2005}, month={May}, pages={913–918} }
 @article{cao_tong_diao_zhu_liu_2004, title={Kinetically Controlled Pt Deposition onto Self-Assembled Au Colloids:  Preparation of Au (Core)−Pt (Shell) Nanoparticle Assemblies}, volume={16}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/cm0348491}, DOI={10.1021/cm0348491}, abstractNote={Assemblies of Au (core)−Pt (shell) nanoparticles were prepared by chemical deposition of Pt metal onto colloidal Au particles that self-assembled onto substrates, since PtCl62- may be reduced to Pt(0) by the mild reducing agent NH2OH in the presence of gold nanoparticles. It is shown that the Pt deposition is isotropic and uniform on each particle via the combination of scanning electron microscopy and atomic force microscopy analysis. And the linear dependence of the particle size on the deposition time suggests that the deposition procedure is kinetically controlled. What is more, the kinetics of this Pt deposition onto Au nanoparticles is analyzed, which further reveals that the growth rate of the core−shell nanoparticles depends on the concentration of PtCl62-, the molar mass and density of Pt metal, and a constant related to the surface reaction.}, number={17}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Tong, Lianming and Diao, Peng and Zhu, Tao and Liu, Zhongfan}, year={2004}, month={Aug}, pages={3239–3245} }
 @article{cao_diao_zhu_liu_2004, title={Uniform Electrochemical Deposition of Copper onto Self-Assembled Gold Nanoparticles}, volume={108}, ISSN={1520-6106 1520-5207}, url={http://dx.doi.org/10.1021/jp036688u}, DOI={10.1021/jp036688u}, abstractNote={Assemblies of gold(core)/copper(shell) nanoparticles could be prepared through the electrochemical deposition of copper metal onto self-assembled gold colloids that are immobilized via an organic film onto conductive substrates. In principle, the deposition on each particle is required to be independent of those on other particles, to develop monodispersed core−shell particles. From a simplified model, we derive formulas for the criteria to ensure the deposition independence, demonstrating the required experimental conditions of particle size, assembly density, and the ratio of the surface concentration to the bulk concentration of depositing species. In the electrolyte of 1.0 mM CuSO4/0.10 M Na2SO4, we then manage to realize the experimental conditions lying in the independent region through applying a potential of −0.030 V(vs SCE) onto self-assembled gold particles 13 ± 1.0 nm in size, with a density of 350 μm-2. The resulting core−shell nanoparticles show high monodispersity, especially at a relatively...}, number={11}, journal={The Journal of Physical Chemistry B}, publisher={American Chemical Society (ACS)}, author={Cao, Linyou and Diao, Peng and Zhu, Tao and Liu, Zhongfan}, year={2004}, month={Mar}, pages={3535–3539} }