Surface phonons and CH vibrational modes of diamond (100) and (111) surfaces

The surface phonons and CH vibrational structure of diamond (100) and (111) surfaces have been examined using high-resolution electron-energy-loss spectroscopy. Experimental phonon features of (2×1)-reconstructed diamond surfaces [H-free (100) and partially H-terminated (111)] agree well with scaled phonon frequencies of theoretically predicted modes for similarly reconstructed silicon surfaces. Several modes not detected on silicon surfaces are observed on diamond surfaces, in agreement with scaled theoretical calculations. Vibrational spectra from hydrogen-terminated diamond (1×1) surfaces reveal several types of ${\mathrm{CH}}_{\mathit{x}}$ species, including ${\mathit{sp}}^3$ hybridized methyl and methylene groups, and olefinic (${\mathit{sp}}^2$ hybridized) methylene groups. On heating to ∼1473 K, hydrogen desorbs readily from the (100) surface. Complete removal of hydrogen from the (111) surface by repeated annealing to ∼1473 K was impossible, although (2×1) reconstruction had already occurred.