▎ 摘　　要

Epitaxial graphene layers thermally grown on Si-terminated 6H-SiC (0 0 0 1) have been probed using Auger electron spectroscopy, Raman microspectroscopy, and scanning tunneling microscopy (STM). The average multilayer graphene thickness is determined by attenuation of the Si (L23VV) and C (KVV) Auger electron signals. Systematic changes in the Raman spectra are observed as the film thickness increases from one to three layers. The most striking observation is a large increase in the intensity of the Raman 2D-band (overtone of the D-band and also known as the G'-band) for samples with a mean thickness of more than similar to 1.5 graphene layers. Correlating this information with STM images, we show that the first graphene layer imaged by STM produces very little 2D intensity, but the second imaged layer shows a single-Lorentzian 2D peak near 2750 cm(-1), similar to spectra acquired from single-layer micromechanically cleaved graphene (CG). The 4-10 cm(-1) higher frequency shift of the G peak relative to CG can be associated with charge exchange with the underlying SiC substrate and the formation of finite size domains of graphene. The much greater (41-50 cm(-1)) blue shift observed for the 2D-band may be correlated with these domains and compressive strain. (C) 2009 Elsevier B.V. All rights reserved.