Effects of Surface Chemistry of Substrates on Raman Spectra in Graphene

We investigated the effects of surface chemistry of substrates on the Raman spectra of graphene flakes that come into contact: with various insulating substrates, such as quartz and sapphire, under ambient conditions at room temperature. The G-peak positions of graphene flakes on such substrates were investigated, and significant blue-shifts of the G-band were observed on a chemically single-phased sapphire (0001) substrate. On a phase-separated sapphire (0001) substrate with Al-terminated (hydrophilic) and O-terminated (hydrophobic) domains, the G-band of graphene flakes was composed of two peaks centered at 1587 cm(-1) (G(1)-peak) and 1593 cm(-1) (G(2)-peak). The G(1)-peak originated from the O-terminated domain and the G2-peak from the Al-terminated one. Since the 2D-peak shifts were small, the Raman shifts in the G-band were attributed to chemical doping from environmental conditions, especially water layers at the graphene/substrate interface that cause hole-doping. The blue-shift in the G-band increased with the increase in the amount of water molecules subject to the surface chemistry of the substrate. Even though Raman spectroscopy is an excellent tool for characterizing the physical properties of graphene, this study indicates that preparation of the substrate surface is important for determining Raman spectroscopy of graphene because its peak positions are easily shifted due to the surface chemistry.