Bismuth telluride have regained significant attention as a prototype of topological insulator. Thin films of high quality have been investigated as a basic platform for novel spintronic devices. Low mobility of bismuth and high desorption coefficient of telluride compose a scenario where growth parameters have drastic effects on structural and electronic properties of the films. Recently [J. Phys. Chem. C 2019, 123, 24818-24825], a detailed investigation has been performed on the dynamics of defects in epitaxial films of this material, revealing the impact of film/substrate lattice misfit on the films' lateral coherence. Very small lattice misfit (<0.05%) are expected to have no influence on quality of epitaxial system with atomic layers weakly bonded to each other by van der Waals forces, contrarily to what was observed. In this work, we investigate the correlation between lattice misfit and size and morphology of the film crystalline domains. Three-dimensional reciprocal-space maps of film Bragg reflections obtained with synchrotron X-rays are used to visualize the spatial conformation of the crystallographic domains through film thickness, while atomic force microscopy images provide direct information of the domains morphology at the film surface.
Epitaxial films of bismuth telluride topological insulators have received increasing attention due to potential applications in spintronic and quantum computation. One of the most important properties of epitaxial films is the presence of interface defects due to lateral lattice mismatch since electrically active defects can drastically compromise device performance. By describing hybrid reflections in hexagonal bismuth telluride films on cubic substrates, in-plane lattice mismatches were characterized with accuracy at least 20 times better than using other X-ray diffraction methods, providing…
Topological insulator surface properties are strongly correlated to structural properties, requiring high-resolution techniques capable of probing both surface and bulk structures at once. In this work, high flux of synchrotron source, recursive equations for fast X-ray dynamical diffraction simulation, and genetic algorithm for data fitting are combined to reveal the detailed structure of bismuth telluride epitaxic films with thickness ranging from 8 to 168 nm. It includes stacking sequences, thickness and composition of layers in model structures, interface coherence, surface termination and…
In the supporting information file for article Dynamics of Defects in van der Waals Epitaxy of Bismuth Telluride Topological Insulators(J. Phys. Chem. C 2019, 123, 24818-24825, doi: 10.1021/acs.jpcc.9b05377), several topics on X-ray diffraction analysis of thin films were developed or revisited. A simple equation to determine lateral lattice coherence lengths in thin films stands as the main development (section S4 - Lateral lattice coherence length in thin films), while X-ray dynamical diffraction simulation in monochromator crystals stands as an interesting overview on how the ratio between …
First-principles approach is demonstrated to calculate the work function of Bi2Te3. The reference potential and the vacuum energy levels are extracted from the Bi2Te3 (0001) surface structure using the reference potential method based on the density functional theory. The one-shot GOWO many-body perturbation theory is used to place the bulk band edge energies with respect to the reference level and the vacuum energy. At last, the work function of 5.301 - 5.131 eV is predicted for Bi2Te3 (0001) surface and compared to various elements.
Tetradymite-structured chalcogenides such as bismuth telluride Bi_{2}Te_{3} are of significant interest for thermoelectric energy conversion and as topological insulators. Dislocations play a critical role during synthesis and processing of such materials and can strongly affect their functional properties. The dislocations between quintuple layers present special interest since their core structure is controlled by the van der Waals interactions between the layers. In this work, using atomic-resolution electron microscopy, we resolve the basal dislocation core structure in Bi_{2}Te_{3}, quant…
Energetics and diffusion of gold in bismuth telluride
我们将电子显微镜和能量色散谱实验与\textit{ab-initio}模型相结合，研究了Au在Bi $_2$ Te $_3$中的溶解度和扩散。我们发现，热退火的Au膜的结果在Bi $_2$ Te $_3$中的Au浓度高于先前报道的溶解度极限。Au扩散到Bi $_2$ Te $_3$中的时间尺度也比预期的大得多。为了解释我们的观察，我们计算缺陷形成能和扩散势垒内DFT。我们确定了与先前观察到的低溶解度和（快速）各向异性扩散一致的间隙机制。然而，较低的形成能量的替代缺陷表明，他们可能是活跃的，在我们的实验中，并解释观察到的高浓度。
Decreasing thermal conductivity of a thermoelectric material is always a prerequisite for its potential application. Using first-principle calculations, we examine the magnetism induced change in lattice thermal transport in bismuth telluride. The source of magnetic moment, Cr in the doped system, weakly magnetizes the coordinated Te atoms to make the latter's phonon softer than that in the pure compound. Though the transition metal dopants do not participate directly in the heat conduction process, the anharmonicity induced by them favor in reducing the lattice thermal conductivity. Large anh…
We use a magnetothermal resistance method to measure the lattice thermal conductivity of a single crystal of Bi$_2$Te$_3$ from 5 to 60 K. We apply a large transverse magnetic field to suppress the electronic thermal conduction while measuring thermal conductivity and electrical resistivity. The lattice thermal conductivity is then calculated by extrapolating the thermal conductivity versus electrical conductivity curve to a zero electrical conductivity value. Our results show that the measured phonon thermal conductivity follows the $e^{(Δ_{min}/T)}$ temperature dependence and the Lorenz ratio…
Tunneling behavior of bismuth telluride nanoplates in electrical transport
我们研究了溶液化学合成法生长的碲化铋（Bi 2 Te 3）纳米片的电输运性质。由Bi 2 Te 3纳米片组成的器件是通过将溶液滴在结构化的金片上后进行表面处理制成的，并且电阻的温度依赖性显示出非金属行为。在我们的实验结果和基于简单哈密顿量的表面电导的理论计算中，都观察到了I-V中的对称隧穿行为，其中不包括载流子-载流子相互作用。在这里，我们提出了两个设备：一个显示对称，另一个显示两步隧穿行为。后者可以理解为无序。
Pressure-induced transitions from ordered intermetallic phases to substitutional alloys to semi-ordered phases were studied in a series of bismuth tellurides. Using angle-dispersive x-ray diffraction, the compounds Bi4Te5, BiTe, and Bi2Te were observed to form alloys with the disordered body-centered cubic (bcc) crystal structure upon compression to above 14--19 GPa at room temperature. The BiTe and Bi2Te alloys and the previously discovered high-pressure alloys of Bi2Te3 and Bi4Te3 were all found to show atomic ordering after gentle annealing at very moderate temperatures of ~100°C. Upon anne…
Morphology of the interlayer van der Waals surface and differential tunneling conductance in p-Bi2-xSbxTe3-ySey solid solutions were studied by scanning tunneling microscopy and spectroscopy in dependence on compositions. Topological characteristics of the Dirac fermion surface states were determined. It is shown that the thermoelectric power factor and the material parameter enhance with the shift of the Dirac point to the top of the valence band with increasing of atomic substitution in these thermoelectrics. Correlation between topological characteristics, power factor and material paramete…
We report the growth of self-assembled Bi2Se3 quantum dots (QDs) by molecular beam epitaxy on GaAs substrates using the droplet epitaxy technique. The QD formation occurs after anneal of Bismuth droplets under Selenium flux. Characterization by atomic force microscopy, scanning electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy and X-ray reflectance spectroscopy is presented. The quantum dots are crystalline, with hexagonal shape, and have average dimensions of 12 nm height (12 quintuple layers) and 46 nm width, and a density of $8.5 \cdot 10^9 cm^{-2}$. T…
We adopted and extended an efficient Grüneisen formalism to study the phonon anharmonicity and linear thermal expansion coefficients (TECs) of trigonal bismuth selenide (Bi$_2$Se$_3$) and antimony telluride (Sb$_2$Te$_3$). Anharmonicity of the systems is studied via extensive calculation of Grüneisen parameters that exploit symmetry-preserving deformations. Consistent with experimental findings, a large anisotropy between the TECs in the $a$ and $c$ directions is found. The larger anharmonicity inherent in Sb$_2$Te$_3$, as compared to Bi$_2$Se$_3$ is offset by the volumetric effect, resulting …
In topological n-type thermoelectrics based on $Bi_{2}Te_{3}$ with atomic substitutions Bi $\rightarrow$ In, Te $\rightarrow$ Se, S, the morphology and the surface states of Dirac fermions on the interlayer (0001) surface of van der Waals were studied by scanning tunneling microscopy and spectroscopy (STM/STS) techniques. By the STM method, the dark and light spots on the surface were found, which intensities depend on the composition and thermoelectric properties of solid solutions. The observed surface morphology features in the solid solutions are explained by distortions of surface electro…
铋硫属化物Bi $_2$ Se $_3$和Bi $_2$ Te $_3$是半导体，其可以是热电材料（TE）和拓扑绝缘体（TI）。由这些材料中的空位、杂质或掺杂剂引起的晶格缺陷是重要的，因为它们在TE应用中提供了载流子并损害了这些材料作为TI的性能。我们提出了第一个固态核磁共振（NMR）研究的$^{77}$硒和$^{125}$碲核磁共振共振在多晶粉末的铋$_2$硒$_3$和铋$_2$碲$_3$，分别。自旋-晶格（$T_1$）弛豫由至多两个指数来建模。在这个模型的框架内，NMR测量是敏感的，这些材料内的原生缺陷的分布。一种成分对应于化学计量分数，绝缘体具有非常长的$T_1$，而另一种成分归因于具有高缺陷含量的样品分数，其具有由与传导载流子的相互作用产生的短$T_1$。碲化铋中不存在非常长的$T_1$表明整个样品中存在缺陷。对于硒化铋，缺陷区域分离成域。我们还发现一个实质性的差异，在短$T_1$组件$^{125}$ Te核（76毫秒）和$^{77}$硒（0.63秒），尽管这些材料具有几乎相同的晶格结构，化学和物理性质。的NMR位移和Korringa定律的调查表明，在硫属化物网站的导带电子的耦合是更强的碲化物。结果与碲化物中$p$带电子的较强自旋轨道耦合（SOC）一致。如果给定材料的大多数参数保持相等，这种类型的实验可以提供工程TI材料中SOC的有用探针。
Since 2017, epitaxial graphene has been the base material for the US national standard for resistance. A future avenue of research within electrical metrology is to remove the need for strong magnetic fields, as is currently the case for devices exhibiting the quantum Hall effect. The quantum Hall effect is just one of many research endeavours that revolve around recent quantum physical phenomena like composite fermions, charge density waves, and topological properties [1-2]. New materials, like magnetically doped topological insulators (MTIs), offer access to the quantum anomalous Hall effect…
Decoding Thermal Stability: In situ Insights into Phase Controlled Phosphine-free Colloidal Bi-Te Nanosheets
University of Rostock（罗斯托克大学）；Pidstryhach Institute for applied problems of mechanics and mathematics of NAS of Ukraine（乌克兰国家科学院普季里哈赫应用力学与数学研究所）；Center for Interdisciplinary Electron Microscopy (ELMI-MV), Department “Life, Light & Matter”, University of Rostock（罗斯托克大学生·光·物质学院跨学科电子显微镜中心）
Hole-doped perovskite bismuthates such as Ba$_{1-x}$K$_x$BiO$_3$ and Sr$_{1-x}$K$_x$BiO$_3$ are well-known bismuth-based oxide high-transition-temperature superconductors. Reported thin bismuthate films show relatively low quality, likely due to their large lattice mismatch with the substrate and a low sticking coefficient of Bi at high temperatures. Here, we report the successful epitaxial thin film growth of the parent compound strontium bismuthate SrBiO$_3$ on SrO-terminated SrTiO$_3$ (001) substrates by molecular beam epitaxy. Two different growth methods, high-temperature co-deposition or…
The discovery of topological insulators (TIs) and their unique electronic properties has motivated research into a variety of applications, including quantum computing. It has been proposed that TI surface states will be energetically discretized in a quantum dot nanoparticle. These discretized states could then be used as basis states for a qubit that is more resistant to decoherence. In this work, prototypical TI Bi2Se3 nanoparticles are grown on GaAs (001) using the droplet epitaxy technique, and we demonstrate the control of nanoparticle height, area, and density by changing the duration o…
We have grown thulium tellurides (TmTe2, TmTe3) thin layers (less than four layers) on graphene/SiC (0001) by molecular beam epitaxy. The charge density waves (CDWs) and lattice superstructures (LSs) are investigated by scanning tunneling microscopy. Clear CDW patterns in real space are observed on surface of metallic TmTe3. Two CDWs are with wave vectors 0.29c* and 0.31a* respectively. LSs with various periods are unveiled on the surface of TmTe2 and TmTe3. The electronic structures of these films are semiconducting. These results show that superstructures in rare earth tellurides can have tw…
We investigate magnetic anisotropy and magnetization reversal mechanism in chromium telluride thin films grown by molecular beam epitaxy. We report existence of strong perpendicular anisotropy in these thin films, along with a relatively strong second order anisotropy contribution. The angular variation of the switching field observed from the magnetoresistance measurement is explained quantitatively using a one-dimensional defect model. The model reveals the relative roles of nucleation and pinning in the magnetization reversal, depending on the applied field orientation. Micromagnetic simula…
Here we study the kinetics of liquefaction and solidification of thin bismuth films grown on the insulating substrate by the pulsed laser deposited (PLD) and molecular beam epitaxy (MBE) and investigated by in situ electron and X-ray diffraction. By PLD, we can grow films similar to those obtained using MBE, studied by ex-situ AFM, KPFM, XRR, and XRD. The liquefaction-solidification transition is monitored in real-time by RHEED and synchrotron XRD, resulting in a dewetting phenomenon and the formation of spherical droplets which size depends on the initial film thickness. Studying this phase t…
Dilute bismuth (Bi) III-V alloys have recently attracted great attention, due to their properties of band-gap reduction and spin-orbit splitting. The incorporation of Bi into antimonide based III-V semiconductors is very attractive for the development of new optoelectronic devices working in the mid-infrared range (2-5 $μ$m). However, due to its large size, Bi does not readily incorporate into III-V alloys and the epitaxy of III-V dilute bismides is thus very challenging. This book chapter presents the most recent developments in the epitaxy and characterization of GaSbBi alloys and heterostru…
We implement the molecular beam epitaxy method to embed the black-phosphorus-like bismuth nanosheets into the bulk ferromagnet Cr$_2$Te$_3$. As a typical surfactant, bismuth lowers the surface tensions and mediates the layer-by-layer growth of Cr$_2$Te$_3$. Meanwhile, the bismuth atoms precipitate into black-phosphorus-like nanosheets with the lateral size of several tens of nanometers. In Cr$_2$Te$_3$ embedded with Bi-nanosheets, we observe simultaneously a large topological Hall effect together with the magnetic susceptibility plateau and magnetoresistivity anomaly. As a control experiment, …
Te NMR studies were carried out for the bismuth telluride topological insulator in a wide range from room temperature down to 12.5 K. The measurements were made on a Bruker Avance 400 pulse spectrometer. The NMR spectra were collected for the mortar and pestle powder sample and for single crystalline stacks with orientations c parallel and perpendicular to field. The activation energy responsible for thermal activation. The spectra for the stack with c parallel to field showed some particular behavior below 91 K.
As the focus of applied research in topological insulators (TI) evolves, the need to synthesize large-area TI films for practical device applications takes center stage. However, constructing scalable and adaptable processes for high-quality TI compounds remains a challenge. To this end, a versatile van der Waals epitaxy (vdWE) process for custom-feature Bismuth Telluro-Sulfide TI growth and fabrication is presented, achieved through selective-area fluorination and modification of surface free-energy on mica. The TI features grow epitaxially in large single-crystal trigonal domains, exhibiting…
Topological insulator (TI) materials are exciting candidates for integration into next-generation memory and logic devices because of their potential for efficient, low-energy-consumption switching of magnetization. Specifically, the family of bismuth chalcogenides offers efficient spin-to-charge conversion because of its large spin-orbit coupling and spin-momentum locking of surface states. However, a major obstacle to realizing the promise of TIs is the thin-film materials' quality, which lags behind that of epitaxially grown semiconductors. In contrast to the latter systems, the Bi-chalcoge…
Pentagonal nanowires from topological crystalline insulators: a platform for intrinsic core-shell nanowires and higher-order topology
International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所磁顶国际研究中心）；Institute for Advanced Study, Shenzhen University（深圳大学高等研究院）；Consiglio Nazionale delle Ricerche (CNR-SPIN), Unitá di Ricerca presso Terzi c/o Universitá “G. D’Annunzio”（意大利国家研究委员会（CNR-SPIN）第泽齐研究单元/阿布鲁佐大学）
