Investigations of two-dimensional transition-metal chalcogenides (TMCs) have recently revealed interesting physical phenomena, including the quantum spin Hall effect1,2, valley polarization3,4 and two-dimensional superconductivity
 5
 , suggesting potential applications for functional devices6–10. However, of the numerous compounds available, only a handful, such as Mo- and W-based TMCs, have been synthesized, typically via sulfurization11–15, selenization16,17 and tellurization
 18
 of metals and metal compounds. Many TMCs are difficult to produce because of the high melting points of their metal and metal oxide precursors. Molten-salt-assisted methods have been used to produce ceramic powders at relatively low temperature
 19
 and this approach
 20
 was recently employed to facilitate the growth of monolayer WS2 and WSe2. Here we demonstrate that molten-salt-assisted chemical vapour deposition can be broadly applied for the synthesis of a wide variety of two-dimensional (atomically thin) TMCs. We synthesized 47 compounds, including 32 binary compounds (based on the transition metals Ti, Zr, Hf, V, Nb, Ta, Mo, W, Re, Pt, Pd and Fe), 13 alloys (including 11 ternary, one quaternary and one quinary), and two heterostructured compounds. We elaborate how the salt decreases the melting point of the reactants and facilitates the formation of intermediate products, increasing the overall reaction rate. Most of the synthesized materials in our library are useful, as supported by evidence of superconductivity in our monolayer NbSe2 and MoTe2 samples21,22 and of high mobilities in MoS2 and ReS2. Although the quality of some of the materials still requires development, our work opens up opportunities for studying the properties and potential application of a wide variety of two-dimensional TMCs.

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A library of atomically thin metal chalcogenides

XPS studies on surface reduction of tungsten oxide nanowire film by Ar+ bombardment

This paper describes a solution-phase synthesis of high-quality vanadium dioxide thermochromic thin films. The films obtained showed excellent visible transparency and a large change in transmittance at near-infrared (NIR) wavelengths before and after the metal−insulator phase transition (MIPT). For a 59 nm thick single-layer VO2 thin film, the integral values of visible transmittance (Tint) for metallic (M) and semiconductive (S) states were 54.1% and 49.1%, respectively, while the NIR switching efficiencies (ΔT) were as high as 50% at 2000 nm. Thinner films can provide much higher transmittance of visible light, but they suffer from an attenuation of the switching efficiency in the near-infrared region. By varying the film thickness, ultrahigh Tint values of 75.2% and 75.7% for the M and S states, respectively, were obtained, while the ΔT at 2000 nm remained high. These results represent the best data for VO2 to date. Thicker films in an optimized range can give enhanced NIR switching efficiencies and e...

Thermochromic VO2 thin films: solution-based processing, improved optical properties, and lowered phase transformation temperature.

This work was financially supported by the National Natural Science Foundation of China (No. 21671096), the Shenzhen Key Laboratory Project (No. ZDSYS201603311013489), the Natural Science Foundation of Shenzhen (Nos. JCYJ20170412153139454, JCYJ20150630145302231, JCYJ20150331101823677), and the Fundamental Research Funds for the Central Universities (No. JZ2016HGTB0725).

/pdf/synergistic-interlayer-and-defect-engineering-in-vs2-2mue6aztg7.pdf

Synergistic Interlayer and Defect Engineering in VS2 Nanosheets toward Efficient Electrocatalytic Hydrogen Evolution Reaction.

https://pubs.rsc.org/en/content/articlepdf/2020/gc/d0gc00940g

Solvometallurgical recovery of cobalt from lithium-ion battery cathode materials using deep-eutectic solvents

XPS study of vanadium surface oxidation by oxygen ion bombardment

Self-formation of a nanonet of fluorinated carbon nanowires on the Si surface by combined etching in fluorine-containing plasma

The states of oxidation of molybdenum, tungsten, niobium, and tantalum in thin oxide films of variable composition were determined by X-ray photoelectron spectroscopy. It was found that the metals occurred in different states of oxidation in thin oxide films prepared by the irradiation of metal surfaces with low-energy oxygen ions under high-vacuum conditions. The concentrations of metals in different states of oxidation essentially depend on the radiation dose and the reactivity of metals.

Determination of the States of Oxidation of Metals in Thin Oxide Films by X-Ray Photoelectron Spectroscopy

The surface modification of oxides MoO3and WO3 under irradiation by Ar+ ions with an energy of 3 keV in high vacuum is investigated by X-ray photoelectron spectroscopy. It is shown that under irradiation by Ar+ ions lower and intermediate oxides and unoxidized metals are formed in the surface layers of higher oxides. It is found that the process of ion-beam reduction of the surface of oxides MoO3and WO3 substantially depends on the irradiation dose and difference in energy of the metal–oxygen bond in oxides. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

XPS study of MoO3 and WO3 oxide surface modification by low‐energy Ar+ ion bombardment

The current state of the art in one of the most promising techniques of X-ray spectral analysis, namely, total reflection X-ray fluorescence analysis (TXRF), is summarized. The underlying physical processes, including reflection, refraction, total external reflection (TER) of X-rays, and formation of standing waves by TER, are considered. The construction and crucial components of a modern energy-dispersive TXRF spectrometer, involving X-ray tubes, monochromators, detectors, and reflectors, are described. Examples of analytical application of TXRF are given. High efficiency of this technique for qualitative and quantitative chemical analysis of liquids and solids of various natures is demonstrated. The main research trends in surface analysis and investigation of surface layers of solids by TXRF are discussed.

Nikolai V. Alov

Papers

XPS study of vanadium surface oxidation by oxygen ion bombardment

Self-formation of a nanonet of fluorinated carbon nanowires on the Si surface by combined etching in fluorine-containing plasma

Determination of the States of Oxidation of Metals in Thin Oxide Films by X-Ray Photoelectron Spectroscopy

XPS study of MoO3 and WO3 oxide surface modification by low‐energy Ar+ ion bombardment

Total reflection X-ray fluorescence analysis: Physical foundations and analytical application (A review)