Dynamical properties of 3C-, 4H-, and 6Hsingle bondSiC surfaces

Clean 3C-, 4H-, and 6Hsingle bondSiC 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 6Hsingle bond(√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 6Hsingle bondSiC and 960 cm−1 for 4Hsingle bondSiC. 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.