Synthesis,Optical And Magnetic Properties Of Two-dimensional Group VB Transition Metal Sulfides

Two-dimensional transition metal chalcogenides have attracted extensive attention in the field of electronics,optoelectronics,spintronics,catalysis,and energy storage devices,owing to their abundant structures and unique properties.Among them,group VB transition metal sulfides are promising,which have excellent optical properties,various magnetic states,unique metallicity,and high chemical activity.Moreover,group VB transition metal sulfides have strong compositional compatibility,which can be expanded into multi-element layered materials by introducing elements,such as phosphorus and silver,or form superlattice structure by introducing elements,such as iron and chromium,into van der Waals layers,thus greatly enriching their physicochemical properties.However,the research process on two-dimensional group VB transition metal sulfides with new structures and multi-components,concerning preparation and optical properties,especially in-plane optical anisotropy and magneto-optical properties,is still in the initial stage.After a comprehensive review on the recent development of two-dimensional group VB transition metal sulfides from structure and properties,synthesis methods,to device applications,a detailed discussion will be carried out on our experimental research on group VB transition metal sulfides with new structures and characteristics.（1）H-phase VS₂nanosheets were synthesized by molten-salt assistant chemical vapor deposition,and the nonlinear optics and electrical properties of H-phase VS₂were discussed.The as-synthesized VS₂nanosheets have high crystalline quality and uniform monolayer thickness with lateral size up to 250μm,whose structure was confirmed to be honeycomb-like atomic arrangement by spherical aberration-corrected scanning transmission electron microscopy.Also,H-phase VS₂nanosheets with broken inversion symmetry show strong second-order nonlinear optical responses.The field-effect transistor based on VS₂nanosheets shows intrinsic p-type semiconductor characteristics.Temperature-dependent electrical transport measurement found that the VS₂nanosheets have small activation energy（△E=18.9 me V）,demonstrating their excellent conductivity.（2）Atomic-thin V₂P₄S₁₃nanosheets were prepared by chemical vapor transport and mechanical exfoliation methods.The structure of V₂P₄S₁₃nanosheets was characterized by XRD,TEM,and Raman spectroscopy,which has low symmetry feature and anisotropic atomic arrangement.The optical anisotropy of V₂P₄S₁₃nanosheets was demonstrated by polarized Raman spectroscopy,polarized difference reflection spectroscopy,and polarized absorption spectroscopy.V₂P₄S₁₃nanosheets show interesting linear dichroism behavior with a linear dichroism ratio of～1.55 at 468 nm,and a linear dichroism conversion phenomenon between 468 nm and 600 nm.（3）Two-dimensional VAg P₂S₆nanosheets with linear atomic arrangement were prepared by chemical vapor transport and mechanical exfoliation methods.The VAg P₂S₆nanosheets were constituted by VS₆octahedron,Ag S₆octahedron,and P₂S₆dimer,which are linearly arranged in the two-dimensional plane.Polarized difference reflection spectroscopy and polarized absorption spectroscopy demonstrated the strong reflection and absorption anisotropy of VAg P₂S₆nanosheets with the maximum differential reflection intensity of 0.1 and linear dichroism ratio of～1.49 at 600 nm.Moreover,the VAg P₂S₆nanosheets exhibit significant electrical anisotropy with an anisotropy ratio of 1.26.（4）High-quality Ta₃Fe S₆nanosheets were prepared by chemical vapor transport and gold-assisted mechanical exfoliation methods.Ta₃Fe S₆nanosheets have unique Fe superlattice determined by structural analysis technology.The ferromagnetic-paramagnetic phase transition of Ta₃Fe S₆nanosheets was studied by temperature-dependent Raman spectroscopy,which has abnormal Raman shift during the phase transition process.Giant MOKE response was demonstrated in Ta₃Fe S₆nanosheets with Kerr rotation angle of 48mrad and Curie temperature of～80 K.The Ta₃Fe S₆nanosheets exhibit outstanding air stability and its MOKE signal remains unchanged after 4 months of aging in air.Finally,we summarized our work and provided the challenge and prospect of group VB transition metal sulfides.