We present spatially resolved Raman images of the G and 2D lines of single-layer graphene flakes. The spatial fluctuations of G and 2D lines are correlated and are thus shown to be affiliated with local doping domains. We investigate the position of the 2D line -- the most significant Raman peak to identify single-layer graphene -- as a function of charging up to |n|~4 10^12 cm^-2. Contrary to the G line which exhibits a strong and symmetric stiffening with respect to electron and hole-doping, the 2D line shows a weak and slightly asymmetric stiffening for low doping. Additionally, the line width of the 2D line is, in contrast to the G line, doping-independent making this quantity a reliable measure for identifying single-layer graphene.
@article{arxiv.0709.4156,
title = {Raman imaging of doping domains in graphene on SiO2},
author = {C. Stampfer and L. Wirtz and A. Jungen and D. Graf and F. Molitor and C. Hierold and K. Ensslin},
journal= {arXiv preprint arXiv:0709.4156},
year = {2008}
}