▎ 摘　　要

We investigated the inhomogeneities in the charge density of unintentionally doped graphene on SiO(2) prepared by mechanical exfoliation. From the analysis of the G, D, and 2D phonon modes of the Raman spectra after displacing contaminants on graphene surface, and measuring the separation monolayer-substrate distance among zones with different doping levels, we deduce that the interaction with the substrate is the main cause of doping in graphene rather than particle contamination. In particular, we show how graphene doping levels vary within the same flake depending on the distance between graphene and the substrate. (C) 2010 American Institute of Physics. [doi:10.1063/1.3500295]