Theoretical investigation on the healing mechanism of divacancy defect in graphene growth by reaction with ethylene and acetylene

Abstract

Recent experiments have shown that using ethylene (acetylene) as carbon source to obtain graphene can dramatically decrease the defects in prepared graphene. However, the inherent mechanism with regard to reduction of defects is quite unclear. Herein, using density functional theory (DFT) calculations, we disclose the healing mechanism of the divacancy defect in graphene by ethylene/acetylene, i.e., (1) the chemisorption of the ethylene/acetylene, (2) the incorporation of the C atoms of the ethylene/acetylene into the defective graphene, accompanied by the adsorption of the leaving H atoms on the graphene surface, and (3) the removal of the adsorbed H atoms to generate the perfect graphene. The entrance adsorption step of ethylene/acetylene has a barrier of 28.8/25.3 kcal mol⁻¹ and the eventual formation of graphene is strongly exothermal by 189.1/243.2 kcal mol⁻¹. Considering that the graphene growth usually takes place at high temperature conditions, the healing of divacancy defects could be effectively realized in the presence of ethylene or acetylene molecule. Therefore, we propose that the good performance of the ethylene/acetylene-based graphene synthesis methods might be ascribed to the dual role of ethylene/acetylene, i.e., they can act as both the carbon source and as the defect healer.