@misc{moradifar_liu_shi_thurston_utzat_driel_lindenberg_dionne_2023, title={Accelerating Quantum Materials Development with Advances in Transmission Electron Microscopy}, volume={123}, ISSN={["1520-6890"]}, url={https://doi.org/10.1021/acs.chemrev.2c00917}, DOI={10.1021/acs.chemrev.2c00917}, abstractNote={Quantum materials are driving a technology revolution in sensing, communication, and computing, while simultaneously testing many core theories of the past century. Materials such as topological insulators, complex oxides, superconductors, quantum dots, color center-hosting semiconductors, and other types of strongly correlated materials can exhibit exotic properties such as edge conductivity, multiferroicity, magnetoresistance, superconductivity, single photon emission, and optical-spin locking. These emergent properties arise and depend strongly on the material's detailed atomic-scale structure, including atomic defects, dopants, and lattice stacking. In this review, we describe how progress in the field of electron microscopy (EM), including in situ and in operando EM, can accelerate advances in quantum materials and quantum excitations. We begin by describing fundamental EM principles and operation modes. We then discuss various EM methods such as (i) EM spectroscopies, including electron energy loss spectroscopy (EELS), cathodoluminescence (CL), and electron energy gain spectroscopy (EEGS); (ii) four-dimensional scanning transmission electron microscopy (4D-STEM); (iii) dynamic and ultrafast EM (UEM); (iv) complementary ultrafast spectroscopies (UED, XFEL); and (v) atomic electron tomography (AET). We describe how these methods could inform structure-function relations in quantum materials down to the picometer scale and femtosecond time resolution, and how they enable precision positioning of atomic defects and high-resolution manipulation of quantum materials. For each method, we also describe existing limitations to solve open quantum mechanical questions, and how they might be addressed to accelerate progress. Among numerous notable results, our review highlights how EM is enabling identification of the 3D structure of quantum defects; measuring reversible and metastable dynamics of quantum excitations; mapping exciton states and single photon emission; measuring nanoscale thermal transport and coupled excitation dynamics; and measuring the internal electric field and charge density distribution of quantum heterointerfaces- all at the quantum materials' intrinsic atomic and near atomic-length scale. We conclude by describing open challenges for the future, including achieving stable sample holders for ultralow temperature (below 10K) atomic-scale spatial resolution, stable spectrometers that enable meV energy resolution, and high-resolution, dynamic mapping of magnetic and spin fields. With atomic manipulation and ultrafast characterization enabled by EM, quantum materials will be poised to integrate into many of the sustainable and energy-efficient technologies needed for the 21st century.}, number={3}, journal={CHEMICAL REVIEWS}, author={Moradifar, Parivash and Liu, Yin and Shi, Jiaojian and Thurston, Matti Lawton Siukola and Utzat, Hendrik and Driel, Tim B. and Lindenberg, Aaron M. and Dionne, Jennifer A.}, year={2023}, month={Dec}, pages={12757–12794} }
 @article{liu_lau_cheng_johnson_li_simmerman_karni_hu_liu_brongersma_et al._2023, title={Controlling Valley-Specific Light Emission from Monolayer MoS2 with Achiral Dielectric Metasurfaces}, url={https://doi.org/10.1021/acs.nanolett.3c01630}, DOI={10.1021/acs.nanolett.3c01630}, abstractNote={Excitons in two-dimensional transition metal dichalcogenides have a valley degree of freedom that can be optically manipulated for quantum information processing. Here, we integrate MoS2 monolayers with achiral silicon disk array metasurfaces to enhance and control valley-specific absorption and emission. Through the coupling to the metasurface electric and magnetic Mie modes, the intensity and lifetime of the emission of neutral excitons, trions, and defect bound excitons can be enhanced and shortened, respectively, while the spectral shape can be modified. Additionally, the degree of polarization (DOP) of exciton and trion emission from the valley can be symmetrically enhanced at 100 K. The DOP increase is attributed to both the metasurface-enhanced chiral absorption of light and the metasurface-enhanced exciton emission from the Purcell effect. Combining Si-compatible photonic design with large-scale 2D materials integration, our work makes an important step toward on-chip valleytronic applications approaching room-temperature operation.}, journal={Nano Letters}, author={Liu, Yin and Lau, Sze Cheung and Cheng, Wen-Hui and Johnson, Amalya and Li, Qitong and Simmerman, Emma and Karni, Ouri and Hu, Jack and Liu, Fang and Brongersma, Mark L. and et al.}, year={2023}, month={Jul} }
 @article{xu_crust_harbola_arras_patel_prosandeev_cao_shao_behera_caretta_et al._2023, title={Size-Induced Ferroelectricity in Antiferroelectric Oxide Membranes}, volume={3}, ISSN={["1521-4095"]}, url={http://dx.doi.org/10.1002/adma.202210562}, DOI={10.1002/adma.202210562}, abstractNote={Abstract}, journal={ADVANCED MATERIALS}, publisher={Wiley}, author={Xu, Ruijuan and Crust, Kevin J. and Harbola, Varun and Arras, Remi and Patel, Kinnary Y. and Prosandeev, Sergey and Cao, Hui and Shao, Yu-Tsun and Behera, Piush and Caretta, Lucas and et al.}, year={2023}, month={Mar} }
 @article{wu_fang_zhu_song_liu_su_pan_gao_wang_yan_et al._2022, title={Controllable Edge Epitaxy of Helical GeSe/GeS Heterostructures}, url={https://doi.org/10.1021/acs.nanolett.2c00395}, DOI={10.1021/acs.nanolett.2c00395}, abstractNote={Emerging twistronics based on van der Waals (vdWs) materials has attracted great interest in condensed matter physics. Recently, more neoteric three-dimensional (3D) architectures with interlayer twist are realized in germanium sulfide (GeS) crystals. Here, we further demonstrate a convenient way for tailoring the twist rate of helical GeS crystals via tuning of the growth temperature. Under higher growth temperatures, the twist angles between successive nanoplates of the GeS mesowires (MWs) are statistically smaller, which can be understood by the dynamics of the catalyst during the growth. Moreover, we fabricate self-assembled helical heterostructures by introducing germanium selenide (GeSe) onto helical GeS crystals via edge epitaxy. Besides the helical architecture, the moiré superlattices at the twisted interfaces are also inherited. Compared with GeS MWs, helical GeSe/GeS heterostructures exhibit improved electrical conductivity and photoresponse. These results manifest new opportunities in future electronics and optoelectronics by harnessing 3D twistronics based on vdWs materials.}, journal={Nano Letters}, author={Wu, Qi and Fang, Zixuan and Zhu, Yuelei and Song, Haizeng and Liu, Yin and Su, Xin and Pan, Danfeng and Gao, Yuan and Wang, Peng and Yan, Shancheng and et al.}, year={2022}, month={Jul} }
 @article{zhou_li_liao_lin_song_liu_yang_yan_lai_liu_et al._2021, title={Topotactic Growth of Free-Standing Two-Dimensional Perovskite Niobates with Low Symmetry Phase}, volume={21}, url={https://doi.org/10.1021/acs.nanolett.1c00918}, DOI={10.1021/acs.nanolett.1c00918}, abstractNote={Here, we report a novel topotactic method to grow 2D free-standing perovskite using KNbO3 (KN) as a model system. Perovskite KN with monoclinic phase, distorted by as large as ∼6 degrees compared with orthorhombic KN, is obtained from 2D KNbO2 after oxygen-assisted annealing at relatively low temperature (530 °C). Piezoresponse force microscopy (PFM) measurements confirm that the 2D KN sheets show strong spontaneous polarization (Ps) along [101̅]pc direction and a weak in-plane polarization, which is consistent with theoretical predictions. Thickness-dependent stripe domains, with increased surface displacement and PFM phase changes, are observed along the monoclinic tilt direction, indicating the preserved strain in KN induces the variation of nanoscale ferroelectric properties. 2D perovskite KN with low symmetry phase stable at room temperature will provide new opportunities in the exploration of nanoscale information storage devices and better understanding of ferroelectric/ferroelastic phenomena in 2D perovskite oxides.}, number={11}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Zhou, Fei and Li, Yang and Liao, Xingqi and Lin, Shuren and Song, Haizeng and Liu, Yin and Yang, Fuyi and Yan, Shancheng and Lai, Zhonghong and Liu, Yong and et al.}, year={2021}, month={Jun}, pages={4700–4707} }
 @article{chen_luo_liu_song_dong_wu_cao_yang_n'diaye_shafer_et al._2021, title={Tunable room-temperature ferromagnetism in Co-doped two-dimensional van der Waals ZnO}, volume={12}, DOI={10.1038/s41467-021-24247-w}, abstractNote={Abstract}, journal={Nature communications}, author={Chen, R. and Luo, F. and Liu, Y. and Song, Y. and Dong, Y. and Wu, S. and Cao, J. and Yang, F. and N'Diaye, A. and Shafer, P. and et al.}, year={2021}, pages={3952} }
 @article{fang_liu_gee_lin_koyama_so_luo_chen_tang_yao_2020, title={Chemically Modulating the Twist Rate of Helical van der Waals Crystals}, volume={32}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85078237276&partnerID=MN8TOARS}, DOI={10.1021/acs.chemmater.9b03779}, abstractNote={Twisted van der Waals (vdW) materials with a controllable twist are of great interest because the twist offers new opportunities to modify the optoelectronic properties of the materials, giving ris...}, number={1}, journal={Chemistry of Materials}, author={Fang, Z. and Liu, Y. and Gee, S. and Lin, S. and Koyama, S. and So, C. and Luo, F. and Chen, R. and Tang, B. and Yao, J.}, year={2020}, pages={299–307} }
 @article{chen_cao_gee_liu_yao_2020, title={Growth and Properties of Dislocated Two-dimensional Layered Materials}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85094928962&partnerID=MN8TOARS}, DOI={10.1557/adv.2020.334}, abstractNote={Two-dimensional (2D) layered materials hosting dislocations have attracted considerable research attention in recent years. In particular, screw dislocations can result in a spiral topology and an interlayer twist in the layered materials, significantly impacting the stacking order and symmetry of the layers. Moreover, the dislocations with large strain and heavily distorted atomic registry can result in a local modification of the structures around the dislocation. The dislocations thus provide a useful route to engineering optical, electrical, thermal, mechanical and catalytic properties of the 2D layered materials, which show great potential to bring new functionalities. This article presents a comprehensive review of the experimental and theoretical progress on the growth and properties of the dislocated 2D layered materials. It also offers an outlook on the future works in this promising research field.}, journal={MRS Advances}, author={Chen, R. and Cao, J. and Gee, S. and Liu, Y. and Yao, J.}, year={2020} }
 @article{zhou_yan_yang_liao_lin_liao_lou_liu_gong_tom_et al._2020, title={Solution-Based Synthesis of Layered Two-Dimensional Oxides as Broadband Emitters}, volume={14}, url={https://doi.org/10.1021/acsnano.0c06164}, DOI={10.1021/acsnano.0c06164}, abstractNote={Preparing transition-metal oxides in their two-dimensional (2D) form is the key to exploring their unrevealed low-dimensional properties, such as the p-type transparent superconductivity, topological Mott insulator state, existence of the condensed 2D electron/hole gas, and strain-tunable catalysis. However, existing approaches suffer from the specific constraint techniques and precursors that limit their product types. Here, we report a solution-based method to directly synthesize KNbO2 in 2D by an out-of-the-pot growth process at low temperature, which is observed directly in real time. The developed method can also be applied to other 2D ternary oxide syntheses, including CsNbO2 and composited NaxK1-xNbO2, and it can be extended to the preparation of self-assembled nanofilms. In addition, We demonstrate the emission of broadband photoluminescence (PL, λ ∼ 350-800 nm) from as-synthesized single-crystal 2D KNbO2 sheets down to a single unit cell thickness. The ultra-broadband emission is ascribed to the self-trapped excitation state (STEs) from the in-phase distortion of the NbO6 octahedrons in 2D NbO2- layers. Beyond the broader luminescent range and the robust material thermal stability of niobates, the absence of sample size restrictions and the large aspect ratio of the 2D oxide sheets will provide opportunities in miniaturizing and advancing 2D-materials integrated optoelectronic devices.}, number={11}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Zhou, Fei and Yan, Shancheng and Yang, Fuyi and Liao, Xingqi and Lin, Shuren and Liao, Mingqing and Lou, Shuai and Liu, Yin and Gong, Zilun and Tom, Kyle. B. and et al.}, year={2020}, month={Nov}, pages={15544–15551} }
 @article{lin_fang_hou_hsu_so_yeoh_li_liu_chan_chueh_et al._2020, title={Tunable valleytronics with symmetry-retaining high polarization degree in SnS<inf>x</inf>Se<inf>1-x</inf> model system}, volume={116}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85079363202&partnerID=MN8TOARS}, DOI={10.1063/1.5128717}, abstractNote={SnS has recently been shown to possess unique valleytronic capability with a large polarization degree, where non-degenerate valleys can be accessed using linearly polarized light, bestowed upon by the unique anisotropy and wavefunction symmetry. It is thus of utmost importance to demonstrate the extension of such effects for the IV–VI system in general, thereby elucidating the generality and tunability of such valleytronics. We show the highly tunable valleytronics via gradual compositional control of the tin(II) sulfo-selenide (SnSxSe1−x) alloy system with excellent retainment of symmetry-determined selection rules. We show the presence of both ΓY and ΓX valleys in all alloy compositions via selectivity in absorption and emission of linearly polarized light by optical reflection (R)/transmission (T) and photoluminescence measurements and tuned the bandgaps of the valleys within a range of 1.28 eV–1.05 eV and 1.48 eV–1.24 eV, respectively. This simultaneous tuning of non-degenerate valleys agrees well with theoretical calculations. We then fitted the bandgap values in compositional space, obtaining bowing parameters as a useful database. We further demonstrated the feasibility of using IV–VI valleytronics systems in general by elucidating the retainment of strong polarization degrees of as high as 91% across all compositions. The generalization of such purely symmetry-dependent valleytronics also opens up opportunities for the discovery of more multi-functional materials.}, number={6}, journal={Applied Physics Letters}, author={Lin, S. and Fang, Z. and Hou, T. and Hsu, T.W. and So, C.H. and Yeoh, C. and Li, R. and Liu, Y. and Chan, E.M. and Chueh, Y.-L. and et al.}, year={2020} }
 @article{liu_wang_kim_sun_yang_fang_tamura_zhang_song_wen_et al._2019, title={Helical van der Waals crystals with discretized Eshelby twist}, volume={570}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85067472294&partnerID=MN8TOARS}, DOI={10.1038/s41586-019-1308-y}, abstractNote={The ability to manipulate the twisting topology of van der Waals structures offers a new degree of freedom through which to tailor their electrical and optical properties. The twist angle strongly affects the electronic states, excitons and phonons of the twisted structures through interlayer coupling, giving rise to exotic optical, electric and spintronic behaviours1-5. In twisted bilayer graphene, at certain twist angles, long-range periodicity associated with moiré patterns introduces flat electronic bands and highly localized electronic states, resulting in Mott insulating behaviour and superconductivity3,4. Theoretical studies suggest that these twist-induced phenomena are common to layered materials such as transition-metal dichalcogenides and black phosphorus6,7. Twisted van der Waals structures are usually created using a transfer-stacking method, but this method cannot be used for materials with relatively strong interlayer binding. Facile bottom-up growth methods could provide an alternative means to create twisted van der Waals structures. Here we demonstrate that the Eshelby twist, which is associated with a screw dislocation (a chiral topological defect), can drive the formation of such structures on scales ranging from the nanoscale to the mesoscale. In the synthesis, axial screw dislocations are first introduced into nanowires growing along the stacking direction, yielding van der Waals nanostructures with continuous twisting in which the total twist rates are defined by the radii of the nanowires. Further radial growth of those twisted nanowires that are attached to the substrate leads to an increase in elastic energy, as the total twist rate is fixed by the substrate. The stored elastic energy can be reduced by accommodating the fixed twist rate in a series of discrete jumps. This yields mesoscale twisting structures consisting of a helical assembly of nanoplates demarcated by atomically sharp interfaces with a range of twist angles. We further show that the twisting topology can be tailored by controlling the radial size of the structure.}, number={7761}, journal={Nature}, author={Liu, Y. and Wang, J. and Kim, S. and Sun, H. and Yang, F. and Fang, Z. and Tamura, N. and Zhang, R. and Song, X. and Wen, J. and et al.}, year={2019}, pages={358–362} }
 @inproceedings{liu_wang_kim_sun_yang_fang_tamura_zhang_song_wen_et al._2019, title={Helical van der Waals crystals with discretized twist}, booktitle={2019 MRS Fall meeting}, author={Liu, Y. and Wang, J. and Kim, S. and Sun, H. and Yang, F. and Fang, Z. and Tamura, N. and Zhang, R. and Song, X. and Wen, J. and et al.}, year={2019} }
 @article{tom_lin_wan_wang_ahlm_n’diaye_bustillo_huang_liu_lou_et al._2018, title={Solution-based, template-assisted realization of large-scale graphitic ZnO}, volume={12}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85050146304&partnerID=MN8TOARS}, DOI={10.1021/acsnano.8b03835}, abstractNote={With a honeycomb single-atomic-layer structure similar to those of graphene and hexagonal boron nitride (hBN), the graphitic phase of ZnO (gZnO) have been predicted to offer many advantages for engineering, including high-temperature stability in ambient conditions and great potential in heterostructure applications. However, there is little experimental data about this hexagonal phase due to the difficulty of synthesizing large-area gZnO for characterization and applications. In this work, we demonstrate a solution-based approach to realize gZnO nanoflakes with thicknesses down to a monolayer and sizes up to 20 μm. X-ray photoelectron spectroscopy, X-ray absorption near-edge spectroscopy, photoluminescence, atomic force microscopy, and electron microscopy characterizations are conducted on synthesized gZnO samples. Measurements show significant changes to the electronic band structure compared to its bulk phase, including an increase of the band gap to 4.8 eV. The gZnO nanosheets also exhibit excellent stability at temperatures as high as 800 °C in ambient environment. This wide band gap layered material provides us with a platform for harsh environment electronic devices, deep ultraviolet optical applications, and a practical alternative for hBN. Our synthesis method may also be applied to achieve other types of 2D oxides.}, number={8}, journal={ACS Nano}, author={Tom, K.B. and Lin, S. and Wan, L.F. and Wang, J. and Ahlm, N. and N’Diaye, A.T. and Bustillo, K. and Huang, J. and Liu, Y. and Lou, S. and et al.}, year={2018}, pages={7554–7561} }
 @article{lou_liu_yang_lin_zhang_deng_wang_tom_zhou_ding_et al._2018, title={Three-dimensional Architecture Enabled by Strained Two-dimensional Material Heterojunction}, volume={18}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85043780230&partnerID=MN8TOARS}, DOI={10.1021/acs.nanolett.7b05074}, abstractNote={Engineering the structure of materials endows them with novel physical properties across a wide range of length scales. With high in-plane stiffness and strength, but low flexural rigidity, two-dimensional (2D) materials are excellent building blocks for nanostructure engineering. They can be easily bent and folded to build three-dimensional (3D) architectures. Taking advantage of the large lattice mismatch between the constituents, we demonstrate a 3D heterogeneous architecture combining a basal Bi2Se3 nanoplate and wavelike Bi2Te3 edges buckling up and down forming periodic ripples. Unlike 2D heterostructures directly grown on substrates, the solution-based synthesis allows the heterostructures to be free from substrate influence during the formation process. The balance between bending and in-plane strain energies gives rise to controllable rippling of the material. Our experimental results show clear evidence that the wavelengths and amplitudes of the ripples are dependent on both the widths and thicknesses of the rippled material, matching well with continuum mechanics analysis. The rippled Bi2Se3/Bi2Te3 heterojunction broadens the horizon for the application of 2D materials heterojunction and the design and fabrication of 3D architectures based on them, which could provide a platform to enable nanoscale structure generation and associated photonic/electronic properties manipulation for optoelectronic and electromechanic applications.}, number={3}, journal={Nano Letters}, author={Lou, S. and Liu, Y. and Yang, F. and Lin, S. and Zhang, R. and Deng, Y. and Wang, M. and Tom, K.B. and Zhou, F. and Ding, H. and et al.}, year={2018}, pages={1819–1825} }
 @article{zhu_qian_liu_xu_liu_chen_zhou_liu_qiu_2017, title={A volumetric full-color display realized by frequency upconversion of a transparent composite incorporating dispersed nonlinear optical crystals}, volume={9}, DOI={10.1038/am.2017.89}, abstractNote={Popular three-dimensional (3D) TV or film media primarily relies on misleading our visual system by presenting our two eyes with spatially offset two-dimensional (2D) images. In comparison, volumetric displays generate moving objects in three physical dimensions with unlimited viewing angles. In a static volumetric display, voxels instead of pixels are usually addressed by luminescence, scattering or deflection. Although various prototype volumetric display technologies have been developed, the generation of full-color moving objects remains a challenge. Herein, we demonstrate the generation of voxels by frequency upconversion based on second-harmonic generation (SHG) in nonlinear optical crystals that are dispersed in solid-state composite materials that serve as a transparent solid display. Notably, voxels that radiate all colors with near-monochromatic color purity can be created by pumping at different near-infrared wavelengths and thus enable a simple solution to realize a full-color display. A computer-controlled scanner allows the generation of moving 3D objects that are viewable from any direction in a prototype device at a 25 × 25 × 25 mm3 scale, and larger displays that are based on the colloidal dispersion of SHG crystals are envisioned. Our methodology may have important implications for the application of the transparent crystal-in-glass composites in both 3D and 2D display technologies. Creating colorful three-dimensional pixels, or voxels, in panes of transparent composites can bring true depth perception to imaging devices. Xiaofeng Liu from Zhejiang University, China, and co-workers have demonstrated this approach with barium–titanium–silicate (BTS) glasses that contain a uniform distribution of small crystallites. When stimulated by a femtosecond pulse laser, the BTS crystals double the photon frequency, enabling localized red, blue or green glowing voxels to be generated through small tweaks in the laser wavelength. The team constructed a one-inch, see-through cube out of the BTS glass ceramic and used a computer-controlled arrangement of mirrors and mechanical scanners to manipulate the laser. This proof-of-concept device mixed the red, blue, and green voxels to produce full-color, moving 3D images viewable at any angle without the need for clunky goggles. A full-color, solid-state, volumetric display based on second harmonic generation in a transparent glass-ceramic (GC) containing second-order optical nonlinear crystals is described. The device uses infrared femtosecond laser beams that focus inside the GC to address red, green and blue voxels. Three-dimensional images are drawn by scanning the point of focus of the lasers inside of the material. The prototype device is demonstrated using conventional focusing optics and mechanical scanners, and the image is bright enough to be seen in ambient room lighting conditions.}, journal={NPG Asia Materials}, author={Zhu, B. and Qian, B. and Liu, Y. and Xu, C. and Liu, C. and Chen, Q. and Zhou, J. and Liu, X. and Qiu, J.}, year={2017}, pages={e394} }
 @article{liu_tom_zhang_lou_liu_yao_2017, title={Alloying effect on bright-dark exciton states in ternary monolayer Mo <inf>x</inf> W<inf>1-x</inf>Se<inf>2</inf>}, volume={19}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85026795980&partnerID=MN8TOARS}, DOI={10.1088/1367-2630/aa6d39}, abstractNote={Binary transition metal dichalcogenides (TMDCs) in the class MX2 (M = Mo, W; X = S, Se) have been widely investigated for potential applications in optoelectronics and nanoelectronics. Recently, alloy-based monolayers of TMDCs have provided a stable and versatile technique to tune the physical properties and optimize them for potential applications. Here, we present experimental evidence for the existence of an intermediate alloy state between the MoSe2-like and the WSe2-like behavior of the neutral exciton (X0) using temperature-dependent photoluminescence (PL) of the monolayer MoxW1–xSe2 alloy. The existence of a maximum PL intensity around 120 K can be explained by the competition between the thermally activated bright states and the non-radiative quenching of the bright states. Moreover, we also measured localized exciton (XB) PL peak in the alloy and the observed behavior agrees well with a model previously proposed for the 3D case, which indicates the theory also applies to 2D systems. Our results not only shed light on bright–dark states and localized exciton physics of 2D semiconductors, but also offer a new route toward the control of the bright–dark transition and tailoring optical properties of 2D semiconductors through defect engineering.}, number={7}, journal={New Journal of Physics}, author={Liu, Y. and Tom, K. and Zhang, X. and Lou, S. and Liu, Y. and Yao, J.}, year={2017} }
 @article{liu_2015, title={Three-dimensional visualization of carbon networks in nanocomposites}, volume={26}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84944345501&partnerID=MN8TOARS}, DOI={10.1088/0957-4484/26/44/442501}, abstractNote={The exceptional mechanical and physical properties of carbon nanotubes have triggered the development of nanotube-based composite materials, but critical challenges exist to understanding the effect of the dispersion and alignment of nanotubes on the overall mechanical and electrical behavior of the composite. Addressing these fundamental questions requires a proper characterization tool that enables characterization of complex three-dimensional nanotube structures on the nanometer and micrometer scale. Mahdavi et al (2015 Nanotechnology 26 385704) develop a novel approach to visualize complex nanotube structures on a multiscale using data from neutron scattering. Thorough structural information generated by the approach lays the foundation to access structure–property relationships in nanotube nanocomposites and opens up new possibilities in numerical prediction of various properties of nanocomposites.}, number={44}, journal={Nanotechnology}, author={Liu, Y.}, year={2015} }
 @article{liu_dillon_2014, title={Environmental Electron Microscopy: Electron Beam Effects in Electrochemistry}, volume={20}, DOI={10.1017/s1431927614009817}, abstractNote={Liquid containing environmental cell based TEM has, in recent years, become a powerful tool for studying dynamic systems at nanometer length scales.[1-7] Such cells typically confine several hundred nanometers of liquid between two electron transparent windows. These cells can be integrated with electrodes for electrochemical testing, and have been implemented to study processes including electro-deposition, electrolysis, and electrochemical batteries.[2-6] When performing in-situ electrochemical studies, particular caution is required to avoid spurious effects introduced by the electron beam. The electron beam is known to produce free radicals, induce reactions, generate bubbles, and affect the local potential.[3,8] Fortunately, many artifacts can be suppressed by reducing the electron beam flux and dose below certain threshold values.[8] To mitigate electron beam effects, in-situ studies are often performed under low does conditions. A common method for validating the approach is to demonstrate that the system does not respond to the electron beam alone at doses and fluxes larger than those used for the experiment. However, such approaches can not negate the possibility of synergistic effects that may arise due to electrochemically imposed potential and concentration gradients.}, number={S3}, journal={Microscopy and Microanalysis}, author={Liu, Y. and Dillon, S.J.}, year={2014}, month={Aug}, pages={1616–1617} }
 @article{tai_liu_dillon_2014, title={In Situ Cryogenic Transmission Electron Microscopy for Characterizing the Evolution of Solidifying Water Ice in Colloidal Systems}, volume={20}, DOI={10.1017/s1431927613014128}, abstractNote={Abstract}, number={2}, journal={Microscopy and Microanalysis}, author={Tai, K. and Liu, Y. and Dillon, S.J.}, year={2014}, month={Apr}, pages={330–337} }
 @article{liu_dillon_2014, title={In situ observation of electrolytic H2 evolution adjacent to gold cathodes}, volume={50}, DOI={10.1039/c3cc46737f}, abstractNote={The early stages of gas evolution during electrolytic hydrogen production on Au electrodes are characterized by in situ transmission electron microscopy.}, number={14}, journal={Chemical Communications}, author={Liu, Y. and Dillon, S.J.}, year={2014}, pages={1761–1763} }
 @article{liu_tai_dillon_2013, title={Growth kinetics and morphological evolution of ZnO precipitated from solution}, volume={25}, DOI={10.1021/cm303522z}, abstractNote={This work characterizes the nucleation and growth kinetics of zinc oxide (ZnO) precipitated from aqueous hexamethylenetetramine (HMTA) zinc nitrate (Zn(NO3)2) solutions observed by in situ and ex situ transmission electron microscopy. Quantitative comparisons between in situ beam-induced precipitation, in situ thermally activated precipitation, ex situ thermally activated precipitation, and ex situ electrochemistry provide insights into the rate limiting mechanism and the chemistry governing the reactions. All experiments indicate that isotropic ZnO precipitates directly from solution. These particles begin to aggregate and grow anisotropically shortly after nucleation. The conversion to anisotropic growth does not rely on coalescence despite the fact that the two are often observed to occur in concert. The results indicate that the reaction pathway for in situ beam-induced growth more closely mimics ex situ electrochemistry than ex situ chemistry. In situ and ex situ thermally activated growth processes ...}, number={15}, journal={Chemistry of Materials}, author={Liu, Y. and Tai, K. and Dillon, S.J.}, year={2013}, month={Jul}, pages={2927–2933} }
 @inproceedings{liu_dillon_2013, title={In situ TEM investigation of ZnO precipitation from solution}, booktitle={Hard Material Seminar}, author={Liu, Y. and Dillon, S.J.}, year={2013}, month={Jan} }
 @article{noh_liu_sun_dillon_2012, title={Challenges associated with in-situ TEM in environmental systems: The case of silver in aqueous solutions}, volume={116}, DOI={10.1016/j.ultramic.2012.03.012}, abstractNote={This work characterizes the effects of an electron beam on inducing microstructural evolution in Ag during environmental transmission electron microscopy. Two different processes, dissolution of Ag and deposition of Ag under the beam, were observed under different experimental conditions. The former primarily results from ionization induced by the primary beam and the latter primarily results from reduction of Ag+ ions in solution by secondary electrons generated in the substrate. The relative rates vary with the activity of silver in solution and beam current density. A simple model based on chemical kinetics describes the general response of the system as a function of beam current density and solution composition.}, journal={Ultramicroscopy}, author={Noh, K.W. and Liu, Y. and Sun, L. and Dillon, S.J.}, year={2012}, month={May}, pages={34–38} }
 @article{liu_chen_noh_dillon_2012, title={Electron beam induced deposition of silicon nanostructures from a liquid phase precursor}, volume={23}, DOI={10.1088/0957-4484/23/38/385302}, abstractNote={This work demonstrates electron beam induced deposition of silicon from a SiCl4 liquid precursor in a transmission electron microscope and a scanning electron microscope. Silicon nanodots of tunable size are reproducibly grown in controlled geometries. The volume of these features increases linearly with deposition time. The results indicate that secondary electrons generated at the substrate surface serve as the primary source of silicon reduction. However, at high current densities the influence of the primary electrons is observed to retard growth. The results demonstrate a new approach to fabricating silicon nanostructures and provide fundamental insights into the mechanism for liquid phase electron beam induced deposition.}, number={38}, journal={Nanotechnology}, author={Liu, Y. and Chen, X. and Noh, K.W. and Dillon, S.J.}, year={2012}, pages={385302} }
 @article{dillon_liu_2012, title={In-Situ TEM in Complex Environments: Photocatalysis}, volume={18}, DOI={10.1017/S1431927612007210}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.}, number={S2}, journal={Microscopy and Microanalysis}, author={Dillon, S.J. and Liu, Y.}, year={2012}, month={Jul}, pages={1072–1073} }
 @article{wang_sakakura_liu_qiu_shimostuma_hirao_miura_2011, title={Modification of long range order in germanate glass by ultra fast laser}, volume={511}, DOI={10.1016/j.cplett.2011.06.063}, abstractNote={A novel order–disorder phase transition in glasses via ultra fast laser irradiation is first time reported. The Raman spectra of modified region is highly dependent on the polarization of probe beam, indicating the bond orientation at the outer structure of modified region is no longer isotropic and a long-range-order is induced which could be analogue with liquid crystals. The ordered glass phase is not expected from inorganic materials and further investigation is needed.}, number={4-6}, journal={Chemical Physics Letters}, author={Wang, X. and Sakakura, M. and Liu, Y. and Qiu, J. and Shimostuma, Y. and Hirao, K. and Miura, K.}, year={2011}, month={Aug}, pages={266–269} }
 @article{tan_lin_liu_teng_zhuang_zhu_zhao_qiu_ye_zhu_et al._2011, title={Synthesis of nanocrystalline cubic zirconia using femtosecond laser ablation}, volume={13}, DOI={10.1007/s11051-010-0110-4}, journal={Journal of Nanoparticle Research}, author={Tan, D. and Lin, G. and Liu, Y. and Teng, Y. and Zhuang, Y. and Zhu, B. and Zhao, Q. and Qiu, J. and Ye, S. and Zhu, B. and et al.}, year={2011}, pages={1183–1190} }
 @article{teng_qian_jiang_liu_luo_ye_zhou_zhu_zeng_qiu_2010, title={Light and heat driven precipitation of copper nanoparticles inside Cu2+-doped borate glasses}, volume={485}, DOI={10.1016/j.cplett.2009.12.010}, abstractNote={We report on highly localized precipitation of copper nanoparticles in borate glasses by irradiation with femtosecond laser pulses. The area in the vicinity of the laser focal point of an 800 nm femtosecond laser inside the glass sample became red due to the precipitation of copper nanoparticles after the femtosecond laser irradiation. The precipitation of copper nanoparticles was confirmed by transmission electron microscopy images, electron energy-loss spectra and absorption spectra. The average power of the femtosecond laser and the irradiation time are two important factors related to the formation of the precipitates. The mechanism of the precipitation of copper nanoparticles is discussed.}, number={1-3}, journal={Chemical Physics Letters}, author={Teng, Y. and Qian, B. and Jiang, N. and Liu, Y. and Luo, F. and Ye, S. and Zhou, J. and Zhu, B. and Zeng, H. and Qiu, J.}, year={2010}, month={Jan}, pages={91–94} }
 @inproceedings{liu_qiu_2010, title={Modification of glasses using a high repetition rate femtosecond laser}, booktitle={US-China Winter School on New Functionalities in Glass -an International Symposium on Functional Glasses}, author={Liu, Y. and Qiu, J.}, year={2010}, month={Jan} }
 @article{yang_liu_ye_qiu_2010, title={Purple-to-yellow tunable luminescence of Ce3+ doped yttrium–silicon–oxide–nitride phosphors}, volume={451}, DOI={10.1016/j.cplett.2007.12.004}, abstractNote={Phosphors of Ce3+ doped yttrium–silicon–oxide–nitride system (Ce–YSON) were synthesized by carbothermal reduction and nitridation. Their crystal structure changes gradually from pure oxide Y2Si2O7 to nitride YSi3N5 state with an increase in dosage of Si3N4 and carbon powder. Y2Si2O7:0.02Ce3+ has shown bluish purple emission, maximum at 408 nm with 340 nm excitation wavelength. YSi3N5:0.02Ce3+ has shown yellow emission, maximum at 552 nm wavelength with 374 nm excitation. The absorption of Ce–YSON increases and extends from 400 to 600 nm with nitrogen content increment. With 400 nm excitation wavelength, Ce–YSON has shown purple–blue–cyan–yellow tunable luminescence with increasing nitridation degree.}, number={4-6}, journal={Chemical Physics Letters}, author={Yang, H. and Liu, Y. and Ye, S. and Qiu, J.}, year={2010}, month={Jan}, pages={218–221} }
 @article{liu_shimizu_wang_zhu_sakakura_shimotsuma_qiu_miura_hirao_2009, title={Confocal Raman imaging of femtosecond laser induced microstructures in germanate glasses}, volume={477}, DOI={10.1016/j.cplett.2009.06.092}, abstractNote={Localized microstructures were induced in a germanate glass by irradiation with a focused 800 nm, 250 kHz femtosecond laser pulses. Compared with unirradiated glass, an increase in intensity and a frequency shift of the Raman scattering bands have been observed in a ring-shaped region inside the laser-modified structure. After annealing the sample near the glass transition temperature, the ring-shaped contrast due to enhanced Raman scattering faded away. We propose that the increase in Raman scattering band intensity may be due to local compression of the glass induced by the femtosecond laser pulses irradiation.}, number={1-3}, journal={Chemical Physics Letters}, author={Liu, Y. and Shimizu, M. and Wang, X. and Zhu, B. and Sakakura, M. and Shimotsuma, Y. and Qiu, J. and Miura, K. and Hirao, K.}, year={2009}, month={Jul}, pages={122–125} }
 @article{ye_zhu_liu_teng_lin_lakshminarayana_fan_qiu_2009, title={Conversion of near-ultraviolet radiation into visible and infrared emissions through energy transfer in Yb2O3 doped SrO-TiO2-SiO2 glasses}, volume={105}, DOI={10.1063/1.3097381}, abstractNote={We demonstrated the conversion of near-ultraviolet radiation of 250–350 nm into visible emission of 450–600 nm and near-infrared emission of 970–1100 nm in the Yb2O3 doped transparent 40SrO-20TiO2-40SiO2 glasses. The observed broad visible emission band centered at 510 nm is associated with silicon-oxygen-related defects in the glassy matrix, and the near-infrared emission originated from the Yb3+ F25/2→F27/2 transition is due to the energy transfer from silicon-oxygen-related defects to Yb3+. The energy transfer process was studied by both the steady state spectra and the time-resolved spectra of Yb3+ at 15 K. The temperature dependent energy transfer rate was calculated. The Yb2O3 concentration dependent energy transfer efficiency has also been evaluated, and the maximum value is 56% for 12 mol % Yb2O3 doped glass.}, journal={Journal of Applied Physics}, author={Ye, S. and Zhu, B. and Liu, Y. and Teng, Y. and Lin, G. and Lakshminarayana, G. and Fan, X. and Qiu, J.}, year={2009}, pages={063508} }
 @article{liu_zhu_dai_qiao_ye_teng_guo_ma_fan_qiu_2009, title={Femtosecond laser writing of Er3+ doped CaF2 crystalline patterns in glass}, volume={34}, DOI={10.1364/ol.34.003433}, abstractNote={We report on the use of 800 nm, 250 kHz femtosecond laser pulses to precipitate Er(3+)-doped CaF(2) crystals inside oxyfluoride glass, which was confirmed with x-ray diffraction analysis. Confocal upconversion luminescence spectra show that the precipitated crystals have greatly enhanced upconversion luminescence intensity in comparison with unmodified glass. We demonstrate the possibility of three-dimensional optical data storage in the glass by the use of the confocal upconversion luminescence imaging.}, number={21}, journal={Optics Letters}, author={Liu, Y. and Zhu, B. and Dai, Y. and Qiao, X. and Ye, S. and Teng, Y. and Guo, Q. and Ma, H. and Fan, X. and Qiu, J.}, year={2009}, pages={3433–3435} }
 @article{zhu_liu_ye_qian_lin_dai_ma_qiu_2009, title={Greatly enhanced effect of silver on femtosecond laser-induced precipitation of nonlinear optical crystals in glasses}, volume={34}, DOI={10.1364/ol.34.001666}, abstractNote={We report greatly enhanced femtosecond laser-induced precipitation of nonlinear optical crystals in glasses owing to the addition of silver. Ba(2)TiSi(2)O(8) (BTS) crystals were space-selectively precipitated inside a Ag(+)-doped BaO-TiO(2)-SiO(2) glass by using a focused femtosecond laser with 800 nm, 250 kHz, and 150 fs. The laser induced crystals were confirmed by micro-Raman spectra to be BTS phases. The irradiation time for crystallization in Ag(+)-doped BaO-TiO(2)-SiO(2) glasses was much shorter than that in undoped BaO-TiO(2)-SiO(2) glasses under the same irradiation conditions. The mechanism responsible for the observed phenomenon is discussed.}, number={11}, journal={Optics Letters}, author={Zhu, B. and Liu, Y. and Ye, S. and Qian, B. and Lin, G. and Dai, Y. and Ma, H. and Qiu, J.}, year={2009}, pages={1666–1668} }
 @article{liu_shimizu_zhu_dai_qian_qiu_shimotsuma_miura_hirao_2009, title={Micromodification of element distribution in glass using femtosecond laser irradiation}, volume={34}, DOI={10.1364/ol.34.000136}, abstractNote={We report micromodification of Eu element distribution in a silicate glass with femtosecond laser irradiation. Elemental analysis shows that the content of Eu decreased at the focal point and increased in a ring-shaped region around the focal point, which indicates migration of Eu ions has been induced by the femtosecond laser irradiation. Confocal fluorescence spectra demonstrate that the fluorescence intensity of Eu(3+) ions increased by 20% in the laser-induced, Eu-enriched, ring-shaped region compared with that for nonirradiated glass. The mechanism for the laser induced change in fluorescence properties of Eu(3+) has been investigated.}, number={2}, journal={Optics Letters}, author={Liu, Y. and Shimizu, M. and Zhu, B. and Dai, Y. and Qian, B. and Qiu, J. and Shimotsuma, Y. and Miura, K. and Hirao, K.}, year={2009}, pages={136–138} }
 @article{dezhi_teng_liu_yixi_jianrong_2009, title={Preparation of Zirconia Nanoparticles by Pulsed Laser Ablation in Liquid}, volume={38}, DOI={10.1246/cl.2009.1102}, abstractNote={Abstract}, number={11}, journal={Chemistry Letters}, author={Dezhi, T. and Teng, T. and Liu, Y. and Yixi, Z. and Jianrong, Q.}, year={2009}, pages={1102–1103} }
 @article{lakeshiminarayana_yang_ye_liu_qiu_2008, title={Co-operative downconversion luminescence in Tm3+/Yb3+ : SiO2–Al2O3–LiF–GdF3 glasses}, volume={41}, DOI={10.1088/0022-3727/41/17/175111}, abstractNote={Oxyfluoride aluminosilicate glasses in the composition of 50SiO2–20Al2O3–20LiF–10GdF3–0.5TmF3–xYbF3 (x = 0, 1.0, 2.5, 5, 7.5, 10, 15, 20, 25 and 30 mol%) have been prepared to study their thermal and optical properties. From the differential thermal analysis measurements, glass transition temperatures and onset crystallization temperatures have been evaluated and from them glass stability factors were calculated. Glass stabilities decreased gradually with fluoride content increment in all the studied glasses. The photoluminescence and decay measurements have also been carried out for all these glasses. In these glasses, an efficient near infrared quantum cutting with optimal quantum efficiency approaching 187% has been demonstrated, by exploring the co-operative downconversion mechanism from Tm3+ to Yb3+, with 467 nm (Tm3+ : 3H6 → 1G4) excitation wavelength. These glasses are promising materials to achieve high efficiency silicon based solar cells by means of downconversion in the visible part of the solar spectrum.}, number={17}, journal={Journal of Physics D: Applied Physics}, author={Lakeshiminarayana, G. and Yang, H. and Ye, S. and Liu, Y. and Qiu, J.}, year={2008}, pages={175111} }
 @article{lakshminarayana_yang._ye._liu._qiu_2008, title={Cooperative downconversion luminescence in Pr3+/Yb3+:SiO2–Al2O3–BaF2–GdF3 glasses}, volume={23}, DOI={10.1557/jmr.2008.0372}, abstractNote={Oxyfluoride aluminosilicate glasses with compositions of 50SiO2–20Al2O3–20BaF2–10GdF3–0.5PrF3–xYbF3(x = 0, 1.0, 2.5, 5, 7.5, 10, 15, 20, 25, and 30 mol%) have been prepared to study their thermal and optical properties. From the differential thermal analysis (DTA) measurement, glass-transition temperatures and onset crystallization temperatures have been evaluated and from them, glass-stability factors against crystallization were calculated. Glass stabilities were decreased gradually with fluoride content increment in all the studied glasses. The photoluminescence and decay measurements have also been carried out for these glasses. In these glasses, an efficient near-infrared (NIR) quantum cutting with optimal quantum efficiency approaching 160% have been demonstrated, by exploring the cooperative downconversion mechanism from Pr3+ to Yb3+ with 481 nm (3P0 → 3H4) excitation wave length. These glasses are promising materials to achieve high-efficiency silicon-base solar cells by means of downconversion in the visible part of the solar spectrum.}, journal={Journal of Materials Research}, author={Lakshminarayana, G. and Yang., H. and Ye., S. and Liu., Y. and Qiu, J.}, year={2008}, pages={3090–3095} }
 @article{liu_zhu_wang_dai_ma_lakshminarayana_qiu_2008, title={Femtosecond laser direct writing of crystalline TiO2 patterns in glass}, volume={93}, DOI={10.1007/s00340-008-3166-4}, journal={Applied Physics. B: Lasers and Optics}, author={Liu, Y. and Zhu, B. and Wang, L. and Dai, Y. and Ma, H. and Lakshminarayana, G. and Qiu, J.}, year={2008}, pages={613–617} }
 @article{liu_zhu_wang_qiu_dai_ma_2008, title={Femtosecond laser induced coordination transformation and migration of ions in sodium borate glasses}, volume={92}, DOI={10.1063/1.2903710}, abstractNote={We report on the coordination transformation of B3+ ions and migration of Na+ and O2− ions in sodium borate glasses, induced by 250kHz, 800nm femtosecond laser irradiation. Micro-Raman spectra show that the ratio of the integrated intensity of the two peaks at 806 and 774cm−1 decreases at first and then increases with increasing distance from the center of the laser modified zone. Electron dispersive x-ray spectra show that a portion of Na+ and O2− ions migrate from the vicinity of focal point after the femtosecond laser irradiation. A possible mechanism is proposed to explain the observed phenomena.}, journal={Applied Physics Letters}, author={Liu, Y. and Zhu, B. and Wang, L. and Qiu, J. and Dai, Y. and Ma, H.}, year={2008}, pages={121113} }