Graphene Layer Morphology and Oxidation Behavior Induced by Step Bunches Created on Copper Substrate

Graphene layer properties in graphene-coated copper are highly influenced by the characteristics of the substrate. Step bunch formation is a common phenomenon for graphene grown by chemical vapor deposition on copper substrates, and it has a significant impact on its chemical, mechanical, and electrical properties. In this study the effect of copper step bunches (SBs) on the formation of wrinkles in graphene-coated copper and their effects on oxidation resistance of graphene were studied. The number of graphene layers was determined using Raman spectroscopy. The characteristics of the surface layer, as well as the distribution of SBs, were studied by scanning electron microscopy and atomic force microscope. Furthermore, optical microscope was used to examine the oxidation caused by the presence of wrinkles. The number of graphene layers was found to affect the distribution of SBs. The average height of copper steps and the average distance between two successive steps (lambda) were about 6 and 3.5 times larger, respectively, in multilayer graphene compared with the monolayer graphene. Considering the fact that in the presence of step bunches, the wrinkles are observed to be mainly perpendicular to the step bunches, it could be supposed that there is an orientation relationship between the wrinkles and SBs. Moreover, it was found that creation of the copper SBs not only induce no cracks or damage to the graphene layer, but also it could relax the internal stress of the graphene leading to decrease the wrinkles number density.