First Principles Study Of Silicene-based Materials

Graphene has extremely excellent mechanical,thermal and electronic properties,but its inherent “zero bandgap” feature limits its application in micro and nano electronics. Chemical doping, chemical adsorption and introducing vacancy defects can make grapheme has a small band gap, but the size of band gap is very difficult to regulate, so researchers concentrating on semiconductor devices have begun to turn their attention to other two-dimensional materials such as silicene,germanene,transition metal chalcogenide compounds and so on. With the assistance of Material Studio,we have calculated and discussed the electrial structure and optical properties of the intrinsic graphene, silicene, germanene, the silicene with the single atom vacancy and light atoms(B, C, Al, P) doped the 8×8 silicene supercell. In addition, we also calculated and discussed the electrial, magnetic and optical properties of transition metal atoms(TM = Co, Ru, Tc, Y, Rh, La) doped the 5×5 silicene supercell. By analysing the results of the calculation, wo can obtain the following conclusions:1. Both intrinic silicene and intrinsic germanene are monolayer structure similar to grapheme, so they are also two-dimensional submetallic materials with 0e V band gap and have the Dirac properties. However, the different constituent elements cause silicene and gernanene have other characteristics different from grapheme. the formation of π-bond in silience and germanene is not due to an overlap between 3pz orbitals but an overlap between sp3-like orbitals formed by partial hybridization of 3s and 3pz orbitals. In the part of optical properties, the absorption intensity of infrared, visible and near-ultraviolet light of silicene and germanene is greater than graphene, while the absorption intensity of far-ultraviolet light of silicene and germanene is less than graphene.2. After the geometry optimization, among the SV-silicene the distance between any two atoms of the three nearest Si atoms that are from the center of the vacancy varies from 3.86? to 2.679?. The band gap of SV-silicene is 0.056 e V. Single atom vacancy makes silicene has two additional smooth C, D bands, and single atom vacancy has a small effect on the optical properties of silicene.3. The study found that the band structure and conductivity type can be changed by doping foreign atoms. B, Al-doped silicene belong to the P-type doping, P-doped silicene belongs to the N-type doping. The band gap of the C-doped silicene is 0.028 e V and the C-doped silicene also has the Dirac point. By comparing with the forming energy of B, C, Al, P-silicene and intrinsic silicene, we can know that the stability of B, C, P-silicene is better than intrinsic silicene,the stability of P-silicene is worse than intrinsic silicene. Among the four doped systems, and the stability of C-silicene is the best. Although the binary layers silicene has a 0.372 e V band gap, but it will has not the dirac point of the monolayer. In the aspest of the optical properties, the absorption intensity of ultraviolet light of B, C, Al, P-silicene is much smaller than intrinsic silicene, the absorption intensity of all the lights of the binary layers silicene is much greater than intrinsic silicene.4. The study found that the different transitional metal doped silicene can exhibit the different magnetic properties. By comparing with the forming energy of TM(Co, Ru, Tc, Y, Rh, La)-silicene and intrinsic silicene, Co, Ru, Tc, Y, Rh, La-silicene, we can know that the stability of Co, Ru, Tc, Rh-silicene is better than intrinsic silicene,the stability of Y, La-silicene is worse than intrinsic silicene. Among the six doped systems, and the stability of Ru-silicene is the best. In the spin-polarized condition, the net magnetic moment of Co, Y, Ru, Tc, Rh, La,-silicene are respectively 1μB、1μB、0μB、0μB、1μB、1μB, and the total magnetic moment of Co, Y, Ru, Tc, Rh, La,-silicene are respectively 2.24μB、1.66μB、0μB、0μB、2.19μB、2.07μB,consequently we understand that Co, Y, Rh, La-silicene are ferrimagnetic and Ru, Tc-silicene are paramagnetic. By means of the detailed analysis of the magnetic properties of Co,Y-silicene, we understand that the primary cause that the magnetic of Co atom(0.25μB) in the Co-silicene system is greater than the magnetic of Y atom(0.03μB) in the Y-silicene system is that the 3d orbital of Co atom in the Co-silicene system has the unpaired 3d electron and the 5d orbital of Y atom in the Y-silicene system has not the unpaired 4d electron. In the part of optical properties, the Co, Ru, Tc, La-doped silicene have a significant impact on the optical absorption of silicene and the inelastic interreaction between the foreign incident electrons and the electrons of silicene.