▎ 摘 要
Plasmon spectroscopy of the thinnest possible membrane, a single layer of carbon atoms, graphene, has been carried out in conjunction with ab initio calculations of the low loss function. We observe pi- and pi+ sigma-surface plasmon modes in free-standing single sheets at 4.7 eV and 14.8 eV which are substantially red-shifted from their values in graphite. These modes are in very good agreement with the theoretical spectra which find the pi- and pi + pi in-plane modes of graphene at 4.5 eV and 14.5 eV. We also find that there is little loss caused by out-of-plane modes for energies less than about 10 eV. (C) 2008 WILEY-NCH Verlag GmbH & Co. KGaA, Weinheim.