First-principles Study On Electronic Structure Modulation Of Group Ⅳ Two-dimensional Materials

Since the successful isolation of graphene,the number of 2D materials has continued to increase.The new van der Waals（vd W）heterostructures are constructed by different 2D crystals or the same crystals with the different orientations,the new physical properties and the functional devices are explored.The electronic properties of 2D materials are crucial to their application in devices,so it is essential to tune the electronic structure of 2D materials.The group Ⅳ elements Si,Ge and Sn are of interest because they are in the same main group as C.In this paper,the electronic properties of group Ⅳ materials（graphene,silicene,germanene,stanene,Si Ge,Si Sn,Ge Sn,Si C,Ge C,Sn C）,all-hydrogen adsorbed XCH₂（X=Si,Ge,Sn）and XC/XCH₂ heterostructures are systematically investigated based on first principles calculations.1.The band structures of Group Ⅳ 2D materials were systematically analysed,and the mechanical properties,electronic properties and absorption spectra of XC under uniaxial and biaxial strains were investigated in detail.The results show that XC bandgap undergoes a direct-to-indirect transition by increasing strain,and the absorption spectra are red-shifted.2.Both chair-shaped and boat-shaped types of all-hydrogen adsorption are performed on intrinsic XC materials.H adsorption reduces the maximum stress and critical strain of XC.The effect of H adsorption on the type and size of the XC band gap is analysed and the results show that H adsorption allows the conversion of XC from indirect to direct band gaps.The band gap decreases with increasing uniaxial strain for structures except Ge CH₂（boat）.3.Twelve XC/XCH₂（chair）and six XC/XCH₂（boat）longitudinal vd W heterostructures were constructed.The calculated results show that the XC/XCH₂（chair）vd W heterostructures have a type II band arrangement.This band arrangement facilitates the spatial separation of electrons and holes after photoexcitation,and this heterojunction is expected to be used in photovoltaic devices.In addition,the band gap size of the Si C-Ge C transverse heterostructures can be adjusted by adjusting the component ratio.