
 Charge density wave (CDW) strongly affects the electronic properties of two-dimensional (2D) materials and can be tuned by phase engineering. Among 2D transitional metal dichalcogenides (TMDs), H-VTe2 was predicted to require small energy for its phase transition and shows unexpected CDW states in its T-phase. However, the CDW state of H-VTe2 has been barely reported. Here, we investigate the CDW states in monolayer (ML) H-H-VTe2, induced by phase-engineering from T-phase H-VTe2. The phase transition between T- and H-H-VTe2 is revealed with X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) measurements. For H-H-VTe2, scanning tunneling microscope (STM) and low-energy electron diffraction (LEED) results show a robust $2\sqrt{3}\times 2\sqrt{3}$ CDW superlattice with a transition temperature above 450 K. Our findings provide a promising way for manipulating the CDWs in 2D materials and show great potential in its application of nanoelectronics.

Charge Density Wave States in Phase-Engineered Monolayer VTe2

Charge density wave (CDW) strongly affects the electronic properties of two-dimensional (2D) materials and can be tuned by phase engineering. Among 2D transitional metal dichalcogenides (TMDs), VTe2 was predicted to require small energy for its phase transition and shows unexpected CDW states in its T-phase. However, the CDW state of H-VTe2 has been barely reported. Here, we investigate the CDW states in monolayer (ML) H-VTe2, induced by phase-engineering from T-phase VTe2. The phase transition between T- and H-VTe2 is revealed with x-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) measurements. For H-VTe2, scanning tunneling microscope (STM) and low-energy electron diffraction (LEED) results show a robust 23×23 CDW superlattice with a transition temperature above 450 K. Our findings provide a promising way for manipulating the CDWs in 2D materials and show great potential in its application of nanoelectronics.

Charge density wave states in phase-engineered monolayer VTe2

Epitaxial Growth of Monolayer SnSe<sub>2</sub> Films on Gd-Intercalated Quasi-Free-Standing Monolayer Graphene with Enhanced Interface Adsorption

Niobium diselenide (NbSe2) is a layered transition metal dichalcogenide material which possesses unique electrical and superconducting properties for future nanodevices. While the superconducting, electrical, and bulk thermal transport properties of NbSe2 have been widely studied, the in-plane thermal transport property of NbSe2, which is important for potential thermoelectric applications, has not been thoroughly investigated. In this report, we study the lattice in-plane thermal transport of 2D NbSe2 by solving the phonon Boltzmann transport equation with the help of the first principles calculation. The thermal conductivity obtained at room temperature is 12.3 W/mK. A detailed analysis shows that the transverse acoustic phonon dominates the lattice thermal transport, and an anomalously small portion of electron contribution to the total thermal conductivity is observed for this metallic phase. The results agree well with experimental measurements and provide detailed mode-by-mode thermal conductivity contribution from different phonon modes. This study can provide useful information for integrating NbSe2 in nanodevices where both electrical and thermal properties are critical, showing great potential for integrating monolayer NbSe2 to thermoelectric devices.

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Phonon Dominated Thermal Transport in Metallic Niobium Diselenide from First Principles Calculations

材料的电子结构是决定其电、磁、光等性质的关键因素，而能够直接观测材料电子结构的角分辨光电子能谱（Angle-Resolved Photoemission Spectroscopy，ARPES）技术是研究材料的基本物理和化学性质的先进技术手段之一。近年来，各种具有优异性能的二维材料被人们不断发掘出来，并有望成为未来光电、电子和自旋器件的基础材料。在本文中，我们将对ARPES的构成和原理做简要的介绍，并总结了当前利用ARPES技术研究二维材料电子结构及其基本物性的前沿进展。本文所关注的二维材料体系主要包含以下四个部分：石墨烯、氮化硼、单元素二维材料、过渡金属硫族化合物。其中对石墨烯的ARPES研究成果最为丰富，对它的研究直接引领了对其他二维材料的ARPES研究。当前，对基于不同二维材料相互堆叠形成的异质结构的研究正方兴未艾，我们在文中也提及一部分关于二维堆垛异质结构的ARPES研究。 

Qiyuan Li

Papers

Charge Density Wave and Electron-Phonon Interaction in Epitaxial Monolayer NbSe$_{2}$ Films