Comparison of the stability of free-standing silicene and hydrogenated silicene in oxygen: a first principles investigation

The stability of free-standing silicene in oxygen is worthwhile discussing. In this letter, the oxygen adsorption and dissociation on free-standing silicene is studied using first principles. It is found that free-standing silicene is not stable in oxygen because O2 molecules can be easily adsorbed and dissociated into O atoms on a silicene surface without overcoming any energy barrier. Moreover, dissociated oxygen atoms are difficult to migrate on and desorb from silicene surfaces, leading to the formation of Si–O compounds. To enhance the stability of free-standing silicene in oxygen, fully hydrogenated silicene is used as a stabiliser. Interestingly, compared with no energy barrier on pristine silicene, there are two minor energy barriers of O2 molecule adsorption and dissociation on fully hydrogenated silicene, indicating that hydrogenated silicene has higher stability than free-standing silicene in oxygen. However, once the O2 molecule dissociates into two O atoms on hydrogenated silicene, desorption of O atoms will be very difficult due to its high energy barrier. This work will be helpful to understand the detail of O2 molecule dissociation and dissociation-induced O atoms adsorption on free-standing and hydrogenated silicene in oxygen and will be useful to the application of silicene. (paper)