▎ 摘　　要

Disorder and doping can strongly affect the properties of graphene. Here we analyze these effects on several samples by Raman spectroscopy. In particular, we show that pristine and unprocessed graphene samples deposited on silicon, covered with a thin silicon oxide layer, show strong variations in their Raman spectra, even in absence of disorder. The variation in the Raman parameters is assigned to charged impurities. This shows that as-deposited graphene is unintentionally doped, reaching charge concentrations up to 10(13) cm(-2) under ambient conditions. The doping varies from sample to sample and the charges are inhomogeneously distributed on a submicron scale. (c) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim