Sensitive Raman Probe of Electronic Interactions between Monolayer Graphene and Substrate under Electrochemical...

In situ electrochemical Raman spectroscopic measurements of defect-free monolayer graphene on various substrates were performed under electrochemical potential control. The G and 2D Raman band wavenumbers (ω_G, ω_2D) of graphene were found to depend upon the electrochemical potential, i.e., the charge density of graphene. The values of ω_G and ω_2D also varied depending on the choice of substrates. On metal substrates where graphene was synthesized by chemical vapor deposition, a strong blue shift of ω_2D was induced, which could not account for the strain and charge doping. We attributed the blue shift of ω_2D to a change in the electronic properties of graphene induced by distinct electronic interactions with the metal substrates. To explain the unique characteristics in the Raman spectrum of graphene on various substrates, a novel mechanism is proposed considering reduction of the Fermi velocity in graphene owing to dielectric screening from the metal substrates.