Influence of Polymer Residues on the Double Resonance Process of Bilayer Graphene

PMMA is commonly used for graphene transfer and device processing. However, it leaves a thin layer of polymer residues after standard acetone cleaning and causes electrical and thermal performance degradation of graphene devices. In this paper, we present a research of the impact of polymer residues on surface morphologies and electronic properties of bilayer graphene using Raman spectroscopy in combination with atomic force microscopy (AFM). The electronic structure of bilayer graphene is well captured in its Raman spectrum, of which the 2D band reveals four double resonance Raman scattering processes. The Raman analyses show universal blueshifts of the G band and the four 2D sub-bands P11, P12, P21, P22, as well as reduced intensity ratios of the sub-bands to the G band I(Pij)/I(G) after surface contamination by polymer residues, implying an electronic structure modulation in bilayer graphene. The effects are mainly attributed to p-type doping and extrinsic scattering induced by residual impurities and defects.