We report a comprehensive study on the surface structural and electronic properties of TaTe2 at room temperature. The surface structure was investigated using both low energy electron diffraction intensity versus voltage and density functional theory calculations. The relaxed structures obtained from the two methods are in good agreement, which is very similar to the bulk, maintaining double zigzag trimer chains. The calculated density of states indicates that such structure originates from the trimer bonding states of the Ta dxz and dxy orbitals. This work will further provide new insights towards the understanding of the charge density wave phase transition in TaTe2 at low temperature.
Transition metal dichalcogenides (TMDCs) belong to technologically important compounds. We have explored the structural, elastic, bonding, optoelectronic and some thermo-physical properties of ZrX2 (X = S, Se, Te) TMDCs in details via ab-initio technique in this study. Elastic anisotropy indices, atomic bonding character, optoelectronic properties and thermo-physical parameters including melting temperature and minimum phonon thermal conductivity are investigated for the first time. All the TMDCs under investigation possess significant elastic anisotropy and layered structural features. ZrX2 (…
An important step in understanding the exotic electronic, vibrational, and optical properties of the moiré lattices is the inclusion of the effects of structural relaxation of the un-relaxed moiré lattices. Here, we propose novel structures for twisted bilayer of transition metal dichalcogenides (TMDs). For $θ\gtrsim 58.4^{\circ}$, we show a dramatic reconstruction of the moiré lattices, leading to a trimerization of the unfavorable stackings. We show that the development of curved domain walls due to the three-fold symmetry of the stacking energy landscape is responsible for such lattice reco…
Trends in structural, electronic properties, Fermi surface topology, and inter-atomic bonding in the series of ternary layered dichalcogenides KNi2S2, KNi2Se2, and KNi2Te2 from first principles calculations
利用FLAPW-GGA方法，我们系统地研究了四硫属二硫化物KNi_2CH_2（CH = S，Se，Te）的结构和电子性质.结果表明，硫族元素（S -> Se -> Te）的置换导致晶体结构的各向异性变形，这与[Ni_2Ch_2]块内原子间键的强各向异性有关，在[Ni_2Ch_2]块内形成共价-离子-金属混合键，而在相邻的[Ni_2Ch_2]块和K原子片之间形成离子键.我们发现在KNi_2S_2-> KNi_2Se_2-> KNi_2 Te_2的顺序中（i）整个能带结构（其中近费米价带主要由Ni态产生）的能级保持不变，但公共价带的宽度、分立子带和带隙的宽度减小;（iii）对于费米面，当类二维片形成项链状拓扑结构且封闭口袋的体积减小时，类孔片表现出最明显的变化.讨论了ThCr_2Si_2型层状二硫属化合物KNi_2Ch_2、KFe_2Ch_2、KCo_2Se_2的结构和电子参数的变化趋势。
Transition-metal dichalcogenides containing tellurium anions show remarkable charge-lattice modulated structures and prominent interlayer character. Using cryogenic scanning transmission electron microscopy (STEM), we map the atomic-scale structures of the high temperature (HT) and low temperature (LT) modulated phases in 1T'-TaTe$_{2}$. At HT, we directly show in-plane metal distortions which form trimerized clusters and staggered, three-layer stacking. In the LT phase at 93 K, we visualize an additional trimerization of Ta sites and subtle distortions of Te sites by extracting structural inf…
The antiferromagnetic kagome material Na2Ti3Cl8 exhibits a first-order phase transition; the low-temperature phase is characterized by the trimerizations of Ti ions. In this work, we carry out first-principles calculations on the crystal and electronic structure of Na$_2$Ti$_3$Cl$_8$ at the high- and low-temperature phases. The crystal structures, including the lattice constant and the trimerization of Ti ions, are well reproduced by taking account a small Hubbard correction of 1 eV. The calculated total energy landscape reveals a first-order phase transition with the total energy barrier of 8…
Transition metal dichalcogenide (TMD) monolayers and heterostructures have emerged as a compelling class of materials with transformative new science that may be harnessed for novel device technologies. These materials are commonly fabricated by exfoliation of flakes from bulk crystals, but wafer-scale epitaxy of single crystal films is required to advance the field. This article reviews the fundamental aspects of epitaxial growth of van der Waals bonded crystals specific to TMD films. The structural and electronic properties of TMD crystals are initially described along with sources and metho…
Quasi-two-dimensional transition-metal dichalcogenides are a key platform for exploring emergent nanoscale phenomena arising from complex interactions. Access to the underlying degrees-of-freedom on their natural time scales motivates the use of advanced ultrafast probes sensitive to self-organised atomic-scale patterns. Here, we report the first ultrafast investigation of TaTe2, which exhibits unique charge and lattice trimer order characterised by a transition upon cooling from stripe-like chains into a $(3 \times 3)$ superstructure of trimer clusters. Utilising MeV-scale ultrafast electron …
Mono- and few-layer transition-metal dichalcogenides (TMDCs) provide opportunities for ideal two-dimensional semiconductors for electronic and optoelectronic devices. For electronic devices on TMDCs, it is essential to incorporate n- and/or p-type dopants which are stable in positions after patterned doping. Here we investigate hydrogen doping for TMDC (MX2 with M = Mo, W and X = S, Se, Te) nanosheets by first-principles calculations to address diffusion and doping properties. We find that adsorbed hydrogen atoms in TMDCs are energetically most stable at the interstitial site right on the Mo o…
Activating Basal Planes in Transition Metal Dichalcogenides for CO2 Reduction to CO through Alloying
Institute of Materials Science & Engineering, Washington University in St. Louis（华盛顿大学圣路易斯分校材料科学与工程研究所）；Department of Computer Science & Engineering, Washington University in St. Louis（华盛顿大学圣路易斯分校计算机科学与工程系）；Department of Mechanical Engineering & Materials Science, Washington University in St. Louis（华盛顿大学圣路易斯分校机械工程与材料科学系）；Department of Chemistry, Incheon National University（仁川国立大学化学系）
On the origin of diverse interlayer charge redistribution in transition-metal dichalcogenides
Key Laboratory of Optic-Electronic Information and Materials of Hebei Province, Hebei Research Center of the Basic Discipline for Computational Physics, College of Physics Science and Technology, Hebei University（河北省光电信息与材料重点实验室，计算物理基础学科河北研究中心，河北大学物理科学与工程学院）
Metal and magnetic overlayers alter the surface of the topological insulator (TI) bismuth selenide (Bi$_2$Se$_3$) through proximity effects but also by changing the composition and chemical structure of the Bi$_2$Se$_3$ sub-surface. The interface between Bi$_2$Se$_3$ and Mn metal or manganese selenide was explored using x-ray photoelectron spectroscopy (XPS) revealing chemical and electronic changes at the interface. Depositing Mn metal on Bi$_2$Se$_3$ without an external source of Se shows unexpected bonding within the Mn layer due to Mn-Se bonding as Se diffuses out of the Bi$_2$Se$_3$ layer…
A superstructure can elicit versatile new properties of materials by breaking their original geometrical symmetries. It is an important topic in the layered graphene-like two-dimensional transition-metal dichalcogenides (TMDs), but its origin remains unclear. Using diamond-anvil cell techniques, synchrotron x-ray diffraction, x-ray absorption, and the first-principles calculations, we show that the evolution from the weak Van der Waals bonding to the Heisenberg covalent bonding between layers induces an isostructural transition in quasi-two-dimensional 1$\textit{T}$-type VSe$_2$ at high pressu…
Transition metal dichalcogenides (TMDs) in the $1T$ polymorph are subject to a rich variety of periodic lattice distortions, often referred to as charge density waves (CDW) when not too strong. We study from first principles the fermiology and phonon dispersion of three representative single-layer transition metal disulfides with different occupation of the $t_{2g}$ subshell: TaS$_2$ ($t_{2g}^1$), WS$_2$ ($t_{2g}^2$), and ReS$_2$ ($t_{2g}^3$) across a broad range of doping levels. While strong electron-phonon interactions are at the heart of these instabilities, we argue that away from half-fi…
Large optical anisotropy observed in a broad spectral range is of paramount importance for efficient light manipulation in countless devices. Although a giant anisotropy was recently observed in the mid-infrared wavelength range, for visible and near-infrared spectral intervals, the problem remains acute with the highest reported birefringence values of 0.8 in BaTiS3 and h-BN crystals. This inspired an intensive search for giant optical anisotropy among natural and artificial materials. Here, we demonstrate that layered transition metal dichalcogenides (TMDCs) provide an answer to this quest o…
Vanadium oxides have been highly attractive for over half a century since the discovery of the metal insulator transition near room temperatures. Here NaxVO2 is studied through a systematic comparison with other layered sodium metal oxides with early 3d transition metals, first disclosing a unified evolution pattern of Na density waves through in situ XRD analysis. Combining ab-initio simulations and theoretical modelings, a sodium-modulated Peierls-like transition mechanism is then proposed for the bonding formation of metal ion dimers. More importantly, the unique trimer structure in NaxVO2 …
Hyperuniform many-body systems in $d$-dimensional Euclidean space are characterized by completely suppressed (normalized) infinite-wavelength density fluctuations, and appear to be endowed with novel exotic physical properties. In this work, we analyze the effects of localized defects on the density fluctuations across length scales and on the hyperuniformity property of experimental samples of two-dimensional transition metal dichalcogenides. In particular, we extract atomic coordinates from time series annular dark field-scanning transmission electron microscopy imaging data of 2D tungsten c…
Van der Waals layered materials, such as transition metal dichalcogenides (TMDs), are an exciting class of materials with weak interlayer bonding which enables one to create van der Waals heterostructures (vdWH). Recent work has shown that control of the twist angle between layers can have a dramatic effect on vdWH properties. For TMD vdWH, twist angle has been treated solely through the use of rigid-lattice moiré patterns. No atomic reconstruction, i.e. any rearrangement of atoms within the individual layers, has been reported experimentally to date. Here we demonstrate that vdWH of MoSe2/WSe…
Two-dimensional (2D) semiconducting transition metal dichalcogenides such as MoS$_2$ have attracted extensive research interests for potential applications in optoelectronics, spintronics, photovoltaics, and catalysis. To harness the potential of these materials for electronic devices requires a better understanding of how defects control the carrier concentration, character, and mobility. Utilizing a correction scheme developed by Freysoldt and Neugebauer to ensure the appropriate electrostatic boundary conditions for charged defects in 2D materials, we perform density functional theory calcu…
