Advanced functional materials: submillimeter single-layer p-type h-phase VS2

transition metal chalcogenides (TMDs) have attracted much attention due to their novel abundant optical electrical magnetic properties abundant phase structures. The phase structure of TMDs plays a decisive role in their physicochemical properties. Layered TMDs crystals are usually composed of s-m-s (s: chalcogenides M: transition metal elements) structures stacked by van der Waals interactions. According to the difference of atom arrangement in s-m-s layer TMDs have two different structural elements i.e. triangular prism (H phase) octahedral (t phase). The TMDS have the property of metal to metal. Semiconductor h-phase TMDs with broken symmetry structure suitable b gap high mobility have broad application prospects in the field of electronic optoelectronic devices.

vanadium disulfide (VS2) is a typical TMDs of the fifth sub group which has become a research hotspot due to its metal insulator transition room temperature ferromagnetism. There are two kinds of phase structure in VS2 namely t phase H phase. T phase VS2 which has been widely reported has ultra-high conductivity excellent electrocatalytic activity room temperature ferromagnetism. It is worth noting that h-phase VS2 has semiconductor properties larger magnetic moment than T-phase which creates more opportunities for the development of electronic devices spintronic devices. The theoretical prediction shows that the H phase VS2 is a low energy ground state which means that the H phase VS2 may have intrinsic ferromagnetism. At the same time the electronic density of states of h-phase VS2 indicates that there is no overlap between the valence b conduction b the Fermi level is adjacent to the valence b which indicates its p-type semiconductor characteristics. However there is no report about h-phase VS2 experiment. There are two challenges in the preparation of h-phase VS2: on the one h vanadium sulfide has various stoichiometric ratios (such as v2s3 v5s8 VS2) different components are easy to transform each other which makes the preparation of pure VS2 very difficult; on the other h h-phase VS2 is a thermodynamic metastable phase its growth conditions are harsh. In view of this it is of great significance to synthesize high quality h-phase VS2 promote the research of its electrical photoelectric properties.

recently Professor Zhai Tianyou's team from school of materials science engineering Huazhong University of science technology has successfully synthesized sub millimeter (up to 250 μ m) monolayer (0.6 μ m) by molten salt assisted chemical vapor deposition (CVD) In addition the size morphology of VS2 phase can be finely controlled which provides a new idea for the controllable preparation of new two-dimensional materials with atomic thickness large size. Transmission electron microscopy with spherical aberration correction showed that the V S atoms were honeycomb which confirmed that the synthesized VS2 was h-phase structure. Due to the inversion symmetry of h-phase breaking single-layer VS2 has strong second-order nonlinear optical (SHG) properties. At the same time electrical transport measurements show that h-phase VS2 has typical p-type semiconductor characteristics. This achievement has found a new member of TMDs h-phase VS2 which paves the way for further research based on this material such as high-performance photodetectors ferromagnetic semiconductor spin devices etc.

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