Engineering electronic structure of silicene for nano-devices application

Abstract

This study applies density functional theory (DFT) on examination of silicene, which is graphene-like 2-dimensional silicon sheet. Silicene possesses buckled honeycomb lattice. This work involves in the investigation of silicene with different thickness, i.e. one to four layers. We apply 1) compressive strain and electric field, 2) hydrogen adsorption and 3) lithium doping on silicene, respectively. The buckling height is found to rise with increasing strain. The bond length decreases with small strain applied while starts to increases again after the strain exceeds the threshold, i.e. 8%, 6%, 7% and 5% for monolayer, bilayer, tri-layer, and quad-layer, respectively. Almost simultaneously, the metallic bands shift downward, which remain at the Fermi level when strain is under the threshold. The electric field can linearly open gap of those crossings around the Fermi level. Hydrogen adsorption increases the buckling height and gives rise to sp3 hybridization. With different one-side hydrogen coverages, silicene becomes spin-polarized semiconductor with net magnetic moment of 1 μB and the coverage affects band structure significantly. Hydrogen co-adsorption is examined to be unstable by our calculation. The extra H atom contributes to spin-polarization and introduces bands around the Fermi level. With lithium adsorption, monolayer silicene becomes n-type semiconductors. Multilayer silicene is spin-polarized with net magnetic moment of 1 μB. The substitution leads to remarkable distortion in the doped structure. Additionally, monolayer becomes a p-type semiconductor while the multilayer induces metallic conductivity and magnetism with the net magnetic moments of ~ 1 μB. Lithium intercalation can weaken the interlayer bonding and increases the interlayer distance. The silicene becomes n-type semiconductors via intercalation and the tri-layer generates magnetism due to its asymmetry structure. The quad-layer silicene with Li intercalated in the internal site is not affected noticeably since the effect of intercalation is suppressed with the Li atom covered by more layers.