(779i) The Evolution of the Physical and Electronic Structure of Bilayer Graphene Upon Chemical Functionalization

Bilayer graphene is increasingly attractive for electronic applications because of its electric field tunable band structure and band gap. However, while the chemical functionalization of monolayer graphene has been widely explored to date, there is much less known for bilayer graphene. Of particular interest in bilayer graphene is the use of chemical functionalization to generate an external electric field to open a bandgap. In this paper, we show the covalent and non-covalent functionalization of bilayer graphene using an electrochemical process with aryl diazonium salts, and we use Raman spectroscopic mapping and conductive atomic force microscopy (cAFM) to study the resulting changes in the physical and electronic structures. We report that under strong covalent functionalization, the G peak of bilayer graphene splits into two components that broaden in width and shift in position with increasing functionalization, the D peak forms with four components, and the 2D peak decreases in intensity in the 2D₁₂ and 2D₁₁ components but broadens in width in the 2D₂₂ and 2D₂₁ components. These changes suggest a complex interplay between the physical and electronic structures of bilayer graphene. We report for the first time these distinct changes observed in the Raman spectra as a function of degree of covalent and non-covalent functionalization, which can provide a guide for further studies of the chemistry of bilayer graphene.