The effects of the crystalline orientation of Cu domains on the formation of nanoripple arrays in CVD-grown graphene on Cu

Defect structures such as boundaries, ripples and wrinkles in graphene have been considered as main causes reducing the electrical properties of graphene. Among them, the formation of a periodic nanoripple array and surface roughening intrinsically occurs as graphene grows on the surface of a metal catalyst during chemical vapor deposition, which results in anisotropic charge transport and limits the possible sheet resistance. In this study, we observed that among the various growth factors, the crystalline orientation of Cu domains can play an important role in the occurrence of periodic surface roughening. With the exception of Cu (111) domain, the surfaces of Cu domains are considerably rippled to a particular direction with abundant terrace structure and step edges. Such ripples occur to relax the strain from a large lattice mismatch between graphene and Cu lattice at a high temperature during the CVD process, which remain as rippled regions of graphene after wet transfer. However, a relatively flat surface is observed in the graphene transferred from hexagonal Cu (111) domain. Additional conductivity mapping also reveals that graphene from Cu (111) domain shows highly homogeneous current distribution. On the other hand, degraded conductivity on rippled regions introducing anisotropic transport of current is observed in the graphene from Cu domains except Cu (111) domain. We believe that current observation can contribute to the preparation of graphene with flat structure simply by controlling the crystalline orientation of Cu.