Effect of charging on silicene with alkali metal atom adsorption

Based on first-principles calculations, we studied the effects of charging on the structure, binding energy and electronic properties of silicene with alkali metal (AM) atom (Li, Na or K) adsorption. In AMSi₂, electron doping enlarges the lattice constant of silicene, while the influence of hole doping is non-monotonic. In AMSi₈, the lattice constant increases/decreases almost linearly with the increase in electron/hole doping. In addition, the AM-Si vertical distance can be greatly enlarged by excessive hole doping in both AMSi₂ and AMSi₈ systems. When the hole doping is as large as +e per unit cell, both AMSi₂ and AMSi₈ can be transformed from metal to semiconductor. However, the binding energy would be negative in the AM⁺ Si₂ semiconductor. It suggests AM⁺ Si₂ is unstable in this case. In addition, the electron doping and the AM-Si vertical distance would greatly influence the band gap of silicene in LiSi₈ and NaSi₈, while the band gap in KSi₈ is relatively stable. Therefore, KSi₈ may be a more practicable material in nanotechnology.