Atomically resolved phase coexistence in VO2 thin films
Masoud Ahmadi, Atul Atul, Sytze de Graaf, Ewout van der Veer, Ansgar Meise, Amir Hossein Tavabi, Marc Heggen, Rafal E. Dunin-Borkowski, Majid Ahmadi, Bart J. Kooi
Concurrent structural and electronic transformations in VO2 thin films are of twofold importance: enabling fine-tuning of the emergent electrical properties in functional devices, yet creating an intricate interfacial domain structure of transitional phases. Despite the importance of understanding the structure of VO2 thin films, a detailed real space atomic structure analysis in which also the oxygen atomic columns are resolved is lacking. Moreover, intermediate atomic structures have remained elusive due to the lack of robust atomically resolved quantitative analysis. Here, we directly resolve both V and O atomic columns and discover the presence of the strain-stabilized intermediate monoclinic (M2) phase nanolayers (less than 2 nm thick) in epitaxially grown VO2 films on a TiO2 (001) substrate, where the dominant part of VO2 undergoes a transition from the tetragonal (rutile) phase to the monoclinic M1 phase. We unfold the crucial role of imaging the spatial configurations of the oxygen anions (in addition to V cations) utilizing atomic-resolution electron microscopy. Our approach sets a direct pathway to unravel the structural transitions in wide range of correlated oxides, offering substantial implications for e.g. optoelectronics and ferroelectrics.
Atomically-resolved mappings of the indium composition in InGaN/GaN multi-quantum wellstructures have been obtained by quantifying the contrast in HAADF-STEM. The quantificationprocedure presented here does not rely on computation-intensive simulations, but rather uses EDXmeasurements to calibrate the HAADF-STEM contrast. The histogram of indium compositionsobtained from the mapping provides unique insights into the growth of InGaN: the transitionfrom GaN to InGaN and vice versa occurs in discreet increments of composition; each incrementcorresponds to one monolayer of the interface, indicatin…
Rock-salt lead selenide nanocrystals can be used as building blocks for large scale square superlattices via two-dimensional assembly of nanocrystals at a liquid-air interface followed by oriented attachment. Here we report measurements of the local density of states of an atomically coherent superlattice with square geometry made from PbSe nanocrystals. Controlled annealing of the sample permits the imaging of a clean structure and to reproducibly probe the band gap and the valence hole and conduction electron states. The measured band gap and peak positions are compared to the results of opt…
The physics of ferroelectric domain walls is explored using the Bayesian inference analysis of atomically resolved STEM data. We demonstrate that domain wall profile shapes are ultimately sensitive to the nature of the order parameter in the material, including the functional form of Ginzburg-Landau-Devonshire expansion, and numerical value of the corresponding parameters. The preexisting materials knowledge naturally folds in the Bayesian framework in the form of prior distributions, with the different order parameters forming competing (or hierarchical) models. Here, we explore the physics o…
Order and randomness in dopant distributions: exploring the thermodynamics of solid solutions from atomically resolved imaging
作为掺杂剂浓度的函数的结构-性质关系的探索通常基于固溶体的平均场论。然而，这些理论在半导体中很好地工作，在具有强相关性的材料中往往会失败，无论是在电子行为还是化学分离方面。在这些情况下，原子排列的细节通常不会被探索和分析。材料的生成物理和化学的知识可以解决这个问题，因为可以生成作为原子级结构的随机表示的缺陷配置库，或者可以导出介观热力学模型的参数。为了获得这些信息，以改进预测，我们使用原子分辨的显微图像，可视化系统内复杂的结构相关性，并将其转化为结构形成的统计力学模型的数据。鉴于材料加工历史的微观方面存在显著的不确定性，以及可用图像的数量有限，我们将模型优化技术与统计假设检验的原则相结合。我们证明了从一系列的原子分辨扫描透射电子显微镜图像的Mo $_x$ Re $_{1-x}$ S $_2$在不同比例的Mo/Re化学计量的数据上的方法，为此，我们提出了一个有效的相互作用模型，然后用于生成原子配置，并在一系列的浓度和形成温度进行可测试的预测。
The development of high-resolution imaging methods such as electron and scanning probe microscopy and atomic probe tomography have provided a wealth of information on structure and functionalities of solids. The availability of this data in turn necessitates development of approaches to derive quantitative physical information, much like the development of scattering methods in the early XX century which have given one of the most powerful tools in condensed matter physics arsenal. Here, we argue that this transition requires adapting classical macroscopic definitions, that can in turn enable …
The emergence of transition metal dichalcogenides (TMD) as crystalline atomically thin semiconductors has created a tremendous amount of scientific and technological interest. Many novel device concepts have been proposed and realized (1-3). Nonetheless, progress in k-space investigations of ground/excited state electronic structures has been slow due to the challenge to create large scale, laterally homogeneous samples. Taking advantage of recent advancements in chemical vapor deposition, here we create a wafer-size MoS2 monolayer with well-aligned lateral orientation for advanced electron sp…
Atom probe tomography (APT) helps elucidate the link between the nanoscale chemical variations and physical properties, but it has limited structural resolution. Field ion microscopy (FIM), a predecessor technique to APT, is capable of attaining atomic resolution along certain sets of crystallographic planes albeit at the expense of elemental identification. We demonstrate how two commercially-available atom probe instruments, one with a straight flight path and one fitted with a reflectron-lens, can be used to acquire time-of-flight mass spectrometry data concomitant with a FIM experiment. We…
Composition-Driven Phase Evolution in Sm-Doped BiFeO3 via Latent-Field Reconstruction of Atomically Resolved STEM Data
University of Tennessee（田纳西大学）；Oak Ridge National Laboratory（橡树岭国家实验室）；National Academy of Sciences of Ukraine（乌克兰国家科学院）；Frantsevich Institute for Problems of Materials Science（弗兰采维奇材料科学问题研究所）；University of Maryland（马里兰大学）
The emergence of two-dimensional crystals has revolutionized modern solid-state physics. From a fundamental point of view, the enhancement of charge carrier correlations has sparked enormous research activities in the transport- and quantum optics communities. One of the most intriguing effects, in this regard, is the bosonic condensation and spontaneous coherence of many-particle complexes. Here, we find compelling evidence of bosonic condensation of exciton-polaritons emerging from an atomically thin crystal of MoSe2 embedded in a dielectric microcavity under optical pumping. The formation o…
Atomically resolved intrinsic superconducting gap in (La,Pr)3Ni2O7 films
Southern University of Science and Technology（南方科技大学）；Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area（粤港澳大湾区量子科学中心）；Shanghai Jiao Tong University（上海交通大学）；Tsinghua University（清华大学）
Atomic structures and adatom geometries of surfaces encode information about the thermodynamics and kinetics of the processes that lead to their formation, and which can be captured by a generative physical model. Here we develop a workflow based on a machine learning-based analysis of scanning tunneling microscopy images to reconstruct the atomic and adatom positions, and a Bayesian optimization procedure to minimize statistical distance between the chosen physical models and experimental observations. We optimize the parameters of a 2- and 3-parameter Ising model describing surface ordering …
Interfaces of dye molecules and two-dimensional transition metal dichalcogenides (TMDCs) combine strong molecular dipole excitations with high carrier mobilities in semiconductors. Förster type energy transfer is one key mechanism for the coupling between both constituents. We report microscopic calculations of a spectrally resolved Förster induced transition rate from dye molecules to a TMDC layer. Our approach is based on microscopic Bloch equations which are solved self-consistently together with Maxwells equations. This approach allows to incorporate the dielectric environment of a TMDC se…
Aurivillius ferroelectric $Bi_2WO_6$ (BWO) encompasses a broad range of functionalities, including robust fatigue-free ferroelectricity, high photocatalytic activity, and ionic conductivity. Despite these promising characteristics, an in-depth study on the growth of BWO thin films and ferroelectric characterization, especially at the atomic scale, is still lacking. Here, we report pulsed laser deposition (PLD) of BWO thin films on (001) $SrTiO_3$ substrates and characterization of ferroelectricity using the scanning transmission electron microscopy (STEM) and piezoresponse force microscopy (PF…
Atomically Resolved Acoustic Dynamics Coupled with Magnetic Order in a van der Waals Antiferromagnet
Materials Science Division, Argonne National Laboratory（阿贡国家实验室材料科学部）；Department of Physics, University of Washington（华盛顿大学物理系）；Center for Ultrafast Phase Transformation, Department of Physics, Sogang University（西江大学物理系超快相变中心）；Department of Materials Science and Engineering, University of Washington（华盛顿大学材料科学与工程系）；Pohang Accelerator Laboratory, POSTECH（韩国科学技术院浦项加速器实验室）；Institute for Condensed Matter and Complex Systems, School of Physics and Astronomy, The University of Edinburgh（爱丁堡大学物理与天文学学院凝聚态与复杂系统研究所）；Donostia International Physics Center（圣塞巴斯蒂安国际物理中心）；Department of Physics, Cambridge, Massachusetts Institute of Technology（麻省理工学院物理系）；Departments of Physics and Applied Physics, Stanford University（斯坦福大学物理与应用物理系）
Ferroelectricity in Atomically Thin Metallic TaNiTe$_5$ with Ultrahigh Carrier Density
State Key Laboratory of Micro-nano Engineering Science, Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院微纳工程科学国家重点实验室人工结构与量子控制教育部重点实验室）；School of Physical Science and Technology, Ningbo University（宁波大学物理科学与技术学院）；School of Physics, Zhejiang University of Technology（浙江工业大学物理学院）；Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交通大学李政道研究所）；Collaborative Innovation Center of Advanced Microstructures（先进微结构协同创新中心）
Atomically precise triple-step staircase on a vicinal silicon surface: Is it Si(5 5 7), Si(7 7 10) or Si(8 8 11)?
Osipyan Institute of Solid State Physics Russian Academy of Sciences（俄罗斯科学院奥西皮扬固体物理研究所）；Institute for Physics of Microstructures Russian Academy of Sciences（俄罗斯科学院微结构物理研究所）；Center for Advanced Mesoscience and Nanotechnology, Moscow Institute of Physics and Technology（莫斯科物理技术学院先进介观与纳米技术中心）；Lobachevsky State University of Nizhny Novgorod（下诺夫哥罗德罗巴切夫斯基国立大学）；National Research University Higher School of Economics (HSE University)（国立研究高等经济学院）
Evolution of topological phases in atomically thin WTe2 films
Tsung-Dao Lee Institute, School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院淞江研究院）；Institute of Atomic and Molecular Sciences, Academia Sinica（中央研究院原子与分子科学研究所）
Analyzing atomically resolved images is a time-consuming process requiring solid experience and substantial human intervention. In addition, the acquired images contain a large amount of information such as crystal structure, presence and distribution of defects, and formation of domains, which need to be resolved to understand a material's surface structure. Therefore, machine learning techniques have been applied in scanning probe and electron microscopies during the last years, aiming for automatized and efficient image analysis. This work introduces a free and open source tool (AiSurf: Aut…
Atomically thin semiconductors made from transition metal dichalcogenides (TMDs) are model systems for investigations of strong light-matter interactions and applications in nanophotonics, opto-electronics and valley-tronics. However, the photoluminescence spectra of TMD monolayers display a large number of features that are particularly challenging to decipher. On a practical level, monochromatic TMD-based emitters would be beneficial for low-dimensional devices but this challenge is yet to be resolved. Here, we show that graphene, directly stacked onto TMD monolayers enables single and narro…
Coexistence of Surface Ferromagnetism and Gapless Topological State in MnBi$_2$Te$_4$
表面磁性及其与电子结构的相关性对于理解内禀磁性拓扑绝缘体MnBi $_2$ Te $_4$的无带隙拓扑表面态是至关重要的。在这里，使用静态和时间分辨角分辨光电子能谱（ARPES），我们发现了一个显着的ARPES强度变化与间隙开放的拉什巴样导带。与模型模拟的比较强烈地表明，解理MnBi $_2$ Te $_4$的表面磁性与其体相状态相同。表面铁磁性和无带隙TSS的共存揭示了MnBi $_2$ Te $_4$的新的复杂性，这可能是负责剥离的MnBi $_2$ Te $_4$的低量子反常霍尔温度。
Coexistence of Two Sharp-Mode Couplings and Their Unusual Momentum Dependence in the Superconducting State of Bi2Sr2CaCu2O8+d Superconductor Revealed by Laser-Based Angle-Resolved Photoemission
Nanospot Angle-Resolved Photoemission Study of Bernal-Stacked Bilayer Graphene on Hexagonal Boron Nitride: Band Structure and Local Variation of Lattice Alignment
