Interlayer interaction mechanism and its regulation on optical properties of bilayer SiCNSs

Silicon carbide nanosheets(SiCNSs)have a very broad application prospect in the field of new two-dimensional(2D)materials.In this paper,the interlayer interaction mechanism of bilayer SiCNSs(BL-SiCNSs)and its effect on optical properties are studied by first principles.Taking the charge and dipole moment of the layers as parameters,an interlayer coupling model is constructed which is more convenient to control the photoelectric properties.The results show that the stronger the interlayer coupling,the smaller the band gap of BL-SiCNSs.The interlayer coupling also changes the number of absorption peaks and causes the red or blue shift of absorption peaks.The strong interlayer coupling can produce obvious dispersion and regulate the optical transmission properties.The larger the interlayer distance,the smaller the permittivity in the vertical direction.However,the permittivity of the parallel direction is negative in the range of 150-300 nm,showing obvious metallicity.It is expected that the results will provide a meaningful theoretical basis for further study of SiCNSs optoelectronic devices.

Layer-number dependent high-frequency vibration modes in few-layer transition metal dichalcogenides induced by interlayer couplings

Two-dimensional transition metal dichalcogenides（TMDs） have attracted extensive attention due to their many novel properties.The atoms within each layer in two-dimensional TMDs are joined together by covalent bonds,while van der Waals interactions combine the layers together.This makes its lattice dynamics layer-number dependent.The evolutions of ultralow frequency（〈 50 cm^（-1）） modes,such as shear and layer-breathing modes have been well-established.Here,we review the layer-number dependent high-frequency（〉 50 cm^（-1）） vibration modes in few-layer TMDs and demonstrate how the interlayer coupling leads to the splitting of high-frequency vibration modes,known as Davydov splitting.Such Davydov splitting can be well described by a van der Waals model,which directly links the splitting with the interlayer coupling.Our review expands the understanding on the effect of interlayer coupling on the high-frequency vibration modes in TMDs and other two-dimensional materials.