The effects of process parameters on graphene growth on copper surface via chemical vapor deposition

Graphene, a two-dimensional material with a single carbon atom thickness, allows for innovation in many technological areas such as touch screens, photodetectors, flexible electronics, solar cells, supercapacitors, high frequency transistors and more. However, these technologies require that the graphene is produced in a controlled manner. In this direction, among other methods, chemical vapor deposition (CVD) on copper foil substrate has emerged as the most promising and economically scalable production method for high-quality graphene in recent years. In the CVD method, a hydrocarbon gas is passed through the system under high temperature (~1100°C) and vacuum conditions (~10 - 10-3 Torr). The gas breaks down to carbon and hydrogene on the surface of the copper and carbon atoms initiate the graphene nuclei on the surface of the substrate. Two-dimensional lateral growth of the nuclei creates the graphene domains and the domain boundaries. These domain boundaries play an important role in determining the properties of the resulting structure (such as thermal, electrical, and mechanical), similar to the grain boundaries in three-dimensional materials. Therefore, in order to improve the quality of the graphene produced by the CVD method, it is necessary to control the mechanism of graphene formation by optimizing the parameters related to the substrate surface and synthesis process. The parameters that are important in the production process are the temperature, duration, gas composition, partial pressures and the substrate (impurity, orientation, thickness, process history, etc.). Studies in the literature found to be reporting many uncertain and inconsistent results about the effects of these parameters. The main reason for this, is the susceptibility of the CVD process to differences in the furnace and the reactor type used. Therefore, it is of high importance to study all of these parameters systematically on the same CVD setup to understand the true effect of each parameter. In this direction, in this work, effects of CVD parameters such as substrate thickness, substrate placement, acid pretreatment, temperature, duration, gas composition and surface stresses were investigated systematically. Especially, the surface impurities and the effects of mechanical stresses on the substrate, which are rarely studied in the literature, were examined in detail. To understand the graphene growth mechanism and the effects of the parameters, the changes on the copper substrate surface and the morphology of the formed graphene are characterized using Scanning Electron Microscope (SEM – EDX/EBSD), Raman Spectroscopy, Atomic Force Microscopy (AFM), Electron Backscatter Diffraction (EBSD), X - Ray Diffraction (XRD) and Optical Microscope (OM) and the results have been compared and discussed.