Cooling rate dependence of Ni-catalyzed transformation of amorphous carbon into graphene in rapid thermal processing: An experimental and reactive molecular dynamics study

Abstract

Amorphous carbon with Ni as catalyst can be transformed into graphene on the dielectric substrate directly without the subsequent transfer process during rapid thermal processing (RTP). However, the effect of cooling rate on this transformation process is still not fully understood yet, leading to the controversy of underlying mechanism. Here, by the combined reactive molecular dynamics simulation with experimental approach, we investigated the evolution of RTP graphene structure and diffusion behavior of C atoms with cooling rates. Results demonstrated that for each case, there were no C atoms precipitated from C-Ni intermixing layer during the cooling process, which was different from the behavior observed in the Ni-catalyzed CVD growth process of graphene. This confirmed that the a-C-to-graphene transformation mechanism during the RTP process was dominated by the C diffusion and Ni-induced crystallization rather than the traditional dissolution/precipitation mechanism for graphene growth. Most importantly, it was also found that tailoring the cooling rate could achieve the regular arrangement of distorted structure in as-grown RTP graphene and thus promote the high-quality synthesis of graphene, which was confirmed by the experimental result.