Speaker: Jun-Feng Gao

Beijing Computational Science Research Center    

Abstract: Based on density functional theory calculations and theory of crystal growth, the nucleation of graphene was investigated by systematically exploring the CN clusters  (with size N ranging from 1 to 24) either on a terrace or near a step edge of transition metal (TM) surface. It is surprising that incorporating one to three pentagons into a graphene island on a TM terrace is required to achieve the most stable structure. A ground state structure transformation is found firstly from a carbon chain to a sp2 carbon network at N ≈ 10−12, which is corresponding to the nucleation size at a wide range of carbon chemical potential. Besides, we found that step of metal surface can help to stabilizing the hexagonal carbon structures and reducing the formation energy. Thus, at a relative low carbon chemical potential, the nucleation preferentially occurred along the step. During the research of graphene growth behaviors, a magic carbon cluster C21 is intriguingly found at four selected TM surfaces (Ni(111), Cu(111), Rh(111) and Ru(0001)), which explained the recent observed uniformed C clusters on TM surfaces. Besides, we investigated the impact of passivation on the graphene edges on three TM surfaces [Cu(111), Co(111), and Ni(111)]. Different from that in vacuum, the pristine zz edge is stable on all TM surface and an undiscovered novel reconstructed ac(ad) edge is high stable on Co(111) and Ni(111) surfaces. The unique edge configuration has a significant impact on the graphene CVD growth behavior.

Date&Time: November 30, 2012 (Friday), 14:30–15:30
Location: 606 Conference Room