Favorable zigzag configuration at etched graphene edges

To control and improve edge quality during etching process is a desired goal for fabricating graphene nanostructure. The preferred edge atomic configurations and shapes when etching pure armchair and zigzag graphene edges have been extensively studied by first-principles calculations. In the beginning stage of etching, it is energetically favorable to remove a specific four-atom carbon segment from flat armchair edge and a three-atom segment from zigzag edge. The subsequent etching on armchair edge shows strong tendency to start from the etched site because of higher chemical reactivity, and a triangle pit with an angle of 120° and zigzag boundary configuration is expected to form on armchair edge. In contrast, the initial etched site on zigzag edge exhibits similar chemical reactivity to other unetched edge atoms. Nevertheless, all created configurations at the etched boundaries are zigzag-edged despite the fact that armchair or zigzag edge could be etched into several shapes. Our results promise that the zigzag chirality be dominating on the edges of graphene nanostructure after patterned under proper etching condition.