Trivacancy and Stone-Wales defected silicene for adsorption of small gas molecules

The adsorption characteristics of small gas molecules (CO2, CO, H2O, N-2, NO, NH3, NO2 and O-2) on trivacancy and Stone-Wales defected silicene were investigated by density functional theory calculations. The results reveal that CO, H2O and N-2 are absorbed on trivacancy silicene in a physical way via van der Waals forces, whereas CO2, NO, NH3, NO2 and O-2 are chemisorbed on trivancancy silicene via strong covalent (SisbndN or SisbndO) bonds. For Stone-Wales defected silicene, N-2, H2O and CO2 are physisorbed whereas CO, O-2, NO, NH3, and NO2 are chemisorbed. The chemisorption of gas molecules on trivancancy and Stone-Wales defected silicene widens the band gap. In particular, the NO2 chemisorption on trivacancy or Stone-Wales defective silicene shows significant hole doping. Additionally, O-2 is found to be readily decomposed into two O atoms on trivacancy silicene due to the small energy barrier and large exothermic reaction heat. Our work offers a possible method to regulate the electronic properties of silicene for applications at the nanoscale.