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Clean 3C-, 4H-, and 6H SiC surfaces were investigated by low-energy electron diffraction, Auger electron spectroscopy, and high-resolution electron energy-loss spectroscopy. The surfaces were treated in buffered HF and then cleaned in ultrahigh vacuum by heating in the presence of a Si flux at different temperatures. Differently reconstructed surfaces ranging from Si-rich to graphitized were examined. On 3C-5 × 2, 3C-2 × 1, 3C-c(2 × 2), and 6H (√3×√3)R30° surfaces the Fuchs-Kliewer (FK) phonons were found around 940 cm −1 . At 3C-3 × 2 surfaces the FK phonon energy is shifted to about 935 cm −1 and even lower values are found for 3C-3 × 2 samples with excess Si on top and 6H-3 × 3 surfaces. At well-prepared 3C-3 × 2 samples additional loss structures at 380 and 700 cm −1 are detected. They may be attributed to intrinsic surface-localized vibrations. Heating at high temperatures results in 3C-1 × 1- and hexagonal (6√3× 6√3)R30°- reconstructed surfaces. The FK phonon losses of such graphitized samples are asymmetrically-broadened and shifted to higher loss energies of about 950 cm −1 for 3C- and 6H SiC and 960 cm −1 for 4H SiC. In off-specular scattering geometry an energy loss around 1600 cm −1 is detected. It may be attributed to high-energy optical phonons of the graphite layer. |
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