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 electronic states originated by atomic substitutions, influence of doping impurity, and formation of structural defects. Fast Fourier transform (FFT) of the morphology STM images of the (0001) surface were used to obtain the interference patterns of the quasiparticles excitation caused by surface electrons scattering by defects. The Dirac point energy and its fluctuations, peak energies of surface defects, the positions of the valence and conduction band edges, and the energy gap were determined from an analysis of tunneling spectra. A correlation between the parameters of surface states of Dirac fermions and thermoelectric properties was found. Thus, a contribution of the fermions surface states increases with rise of the surface concentration in solid solutions with high power factor, and the largest concentration value was observed in the $Bi_{1.98}In_{0.02}Te_{2.85}Se_{0.15}$ composition. The dependences of Fermi energy on the wave vector for different solid solutions are described by a set of Dirac cone sections, which are close within the limits of the fluctuations of the Dirac point energy that explained by weak changes of the Fermi velocity in the compositions at studied atomic substitutions in the bismuth telluride sublattices.
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…
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 …
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 t…
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…
One-dimensional tellurides Ta4SiTe4 and Nb4SiTe4 were found to show high thermoelectric performance below room temperature. This study reported the synthesis and thermoelectric properties of whisker crystals of Ta4SiTe4-Nb4SiTe4 solid solutions and Mo- or Ti-doped (Ta0.5Nb0.5)4SiTe4. Thermoelectric power of the solid solutions systematically increased with increasing Ta content, while their electrical resistivity was unexpectedly small. Mo- and Ti-doped (Ta0.5Nb0.5)4SiTe4 showed n- and p-type thermoelectric properties with large power factors exceeding 40 microW cm-1 K-2, respectively. The fac…
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。
Anharmonic phonon effects on linear thermal expansion of trigonal bismuth selenide and antimony telluride crystals
采用并扩展了一种有效的Grüneisen方法，研究了三方结构硒化铋（Bi $_2$ Se $_3$）和碲化锑（Sb $_2$ Te $_3$）的声子非谐性和线性热膨胀系数（TEC）.系统的非谐性进行了研究，通过广泛的计算Grüneisen参数，利用保序变形。与实验结果相一致，在$a$和$c$方向的TEC之间存在较大的各向异性。Sb $_2$ Te $_3$中固有的较大非谐性与Bi $_2$ Se $_3$相比被体积效应抵消，导致它们的线性TEC具有可比的温度依赖性。从我们的第一性原理数据推导出的德拜温度也非常符合现有的表中的值。这项工作中开发的高效方法首次应用于研究两个三角形热电系统的线性TEC，为解决其他热电和其他低对称性材料中的非谐效应提供了令人兴奋的机会。
Spectroscopic techniques, including photoelectron spectroscopy, diffuse reflectance, and x-ray absorption, are used to investigate the electronic structure and the local structure of LaOBiS$_{2-x}$Se$_x$ thermoelectric material. It is found that Se substitution effectively suppresses local distortion, that can be responsible for the increased carrier mobility together with a change in the electronic structure. The results suggest a possible way to control thermoelectric properties by tuning of the local crystal structure of these materials.
Owing to the energy shortages and various severe adverse effects of traditional fossil fuel power generation mechanisms, photovoltaic and thermoelectric materials are considered as the potential candidates for building non-traditional, efficient, and eco-friendly power generation portfolios. Lead-based perovskites have emerged as highly efficient, abundantly available, and low-cost materials for such applications but there are two major challenges i.e. chemical instability and the danger of toxic lead leaching that can badly affect both the environment and human health. Therefore, in search of…
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…
Thermoelectric (TE) materials research plays a vital role in heat-to-electrical energy conversion and refrigeration applications. Bismuth-antimony (Bi-Sb) alloy is a promising material for thermoelectric cooling. Herein, a high figure of merit, ZT, near 0.6 at cryogenic temperatures (100-150K) has been achieved in melt-spun n-type Bi85Sb15 bulk samples consisting of micron-size grains. The achieved ZT is nearly 50 percents higher than polycrystalline averaged single crystal ZT of ~0.4, and it is also significantly higher than ZT of less than ~0.3 measured below 150K in Bi-Te alloys commonly us…
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）
We investigated six heavy element bismuth-based 18-VEC half-Heusler alloys CoTiBi, CoZrBi, CoHfBi, FeVBi, FeNbBi, and FeTaBi by first principles approach, in search of better thermoelectric prospects. The motivation is driven by expected lower thermal conductivity and the recent discovery of CoZrBi-based materials. Significantly, our calculated power factor values of all the systems show an increment of $\sim$40\% in comparison to the reported \textit{p}-type CoTiSb. We propose that doping at Bi-site, on account of electronic features, will be helpful in achieving the proposed power factor val…
Single crystalline bismuth (Bi) is known to have a peculiar electronic structure which is very close to the topological phase transition. The modification of the surface states of Bi depending on the temperature are revealed by angle-resolved photoelectron spectroscopy (ARPES). At low temperature, the upper branch of the surface state merged to the projected bulk conduction bands around the $\bar{M}$ point of the surface Brillouin zone (SBZ). In contrast, the same branch merged to the projected bulk valence bands at high temperature (400 K). Such behavior could be interpreted as a topological …
Bismuth oxyselenide (Bi$_2$O$_2$Se) attracts great interest as a potential n-type complement to p-type thermoelectric oxides in practical applications. Previous investigations were generally focused on polycrystals. Here, we performed a study on the thermoelectric properties of Bi$_2$O$_2$Se single crystals. Our samples exhibit electron mobility as high as 250 cm$^2.$V$^{-1}$.s$^{-1}$ and thermal conductivity as low as $2$ W.m$^{-1}$.K$^{-1}$ near room temperature. The maximized figure of merit is yielded to be 0.188 at 390 K, higher than that of polycrystals. Consequently, a rough estimation …
Cumulative X-ray Damage in Bismuth Selenide Examined by Simultaneous TXM and XRD
Stanford University（斯坦福大学）；SLAC National Accelerator Laboratory（SLAC国家加速器实验室）；PULSE Institute（脉冲研究所）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Pohang Accelerator Laboratory（浦项加速器实验室）；Pohang University of Science and Technology（浦项科技大学）；European Radiation Synchrotron Facility（欧洲辐射同步辐射装置）；Nevada National Security Site（内华达国家安全区）；Sogang University（西江大学）
The optimization of secondary phase in thermoelectric(TE) materials can {helps in improvisation of material's efficiency}. Being a potential {contender} for lower temperature TE application, bismuth telluride(Bi$_2$Te$_3$) nanoparticles were synthesized via different routes and profiles to optimize their pure single phase. Systematic characterizations were performed with the help of X-ray diffraction (XRD), Rietveld refinement and field effect-scanning electron microscopy(FE-SEM) for structural and morphological behavior, while TE properties such as Seebeck coefficient, electrical conductivity…
