Raman spectroscopy on hydrogenated graphene under high pressure
Abstract We applied laser heating in diamond anvil cells (LHDAC) to synthesize a hydrogenated single layer graphene (SLG) and to explore the pathway toward graphane (fully hydrogenated SLG) We employed Raman spectroscopy to investigate SLG on a Cu substrate that was compressed up to 8 GPa and 20 GPa with 2.2% and 4.6% compressive strain, respectively, followed by laser heating. After laser heating, G and 2D peaks exhibit a redshift, and then form a hysteresis loop during decompression. This phenomenon can be due to either of two mechanisms, or both; the formation of C H chemical bonds in massive hydrogenated SLG, and a reduction of the frictional stress between SLG and Cu substrate causing a relaxation of SLG lattice toward its free standing equilibrium structure. The correlation between G and 2 D peaks also changes significantly after laser heating at 8 GPa, resembling the correlation measured in hole doping experiments. Finally, residual hydrogen remains bonded to the graphene layer after decompression to ambient pressure, and the amount of hydrogen increases as a function of pressure at which the sample was laser heated.