Structural Instability of Transferred Graphene Grown by Chemical Vapor Deposition against Heating

A heating treatment is often used in graphene research to remove adsorbates and resist materials from graphene. Heating graphene followed by air exposure is also known to result in heavy hole doping in graphene, although the role of heating has been unclear. Here, we demonstrate that a practical graphene sample fabricated using the commonly used growth and transfer techniques is unstable against heating in a high vacuum. Structural disorder likely due to defect formation is induced by heating, and the disorder is accompanied by hole doping. Our analysis shows that the main cause of the defect formation is graphene reacting with O2 and H2O molecules inserted between graphene and the substrate. The hole doping caused by air exposure after heating is explained by gas adsorption at the defect sites.