Observation of the unexpected morphology of graphene wrinkle on copper substrate.

Graphene, a two-dimensional material, has a wide range of unique properties and could be used in the development of varieties of mechanic, electronic and photonic devices, therefore methods to synthesis large-area high-quality graphene films are urgently required. Chemical vapor deposition (CVD) has been of particular interest recently due to its simplicity and low cost. However, because of the mismatch of thermal expansion coefficients, high densities of wrinkles are commonly observed. Despite their prevalence and potential impact on large-scale graphene properties, relatively little is known about their structural morphology and formation mechanism. In this article, morphologies of graphene obtained by CVD are experimentally investigated by an atomic force microscope (AFM) and results show that the profiles of wrinkles are much larger than they should be. By using theoretical methods and molecular dynamics simulations (MD), we find internal molecules created during CVD process which supply additional pressure is the main mechanism.