▎ 摘　　要

The authors report results of spectroscopic ellipsometry (SE) measurements in the near-IR, visible, and near-UV spectral ranges using a Woollam dual rotating-compensator ellipsometer, analyzing data in terms of both epitaxial graphene and interface contributions. The SiC samples were cleaned by standard methods of CMP and HF etching prior to mounting in UHV and growing epitaxial graphene by thermal annealing at similar to 1400 degrees C. Most samples were vicinally cut 3.5 degrees off (0001) toward [11-20]. STM measurements show that the initial regular step edges were replaced by somewhat irregular edges after graphene growth. From growth-temperature and Auger data the authors estimate that the graphene is similar to 3-4 ML thick. The authors find significant differences among the spectral features of the interface "buffer" layer and those of graphene. Specifically, the hyperbolic-exciton peak reported previously at similar to 4.5 eV in graphene shifts to a similarly shaped peak at similar to 4 eV in the interface buffer layer. The authors attribute this shift to a significant component of sp(3) bonded carbon in the buffer, which occurs in addition to the sp(2) bonded carbon that is present in the graphene layer. SE data in the terahertz range obtained by Hoffman et al. [Thin Solid Films 519, 2593 (2011)] show that the mobility values of graphene grown on the carbon face of SiC vary with proximity to the substrate. This leads to the question as to whether an interface layer at the Si face has properties (i.e., dielectric function/complex refractive index) that are different from and/or affect those of the graphene layers. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4726199]