SURFACE VIBRATIONAL STUDIES OF CVD DIAMOND

Using high-resolution electron energy loss spectroscopy (HREELS), the surface vibrations of adsorbed hydrogen were investigated on homoepitaxially grown boron-doped single-crystal (001) and (111) films. As-grown surfaces are terminated by hydrogen and the surface carbon atoms are in the sp(3) hybridized state. Hydrogen desorption by heating affects the long-range and/or short-range ordering of the surface. On hydrogen readsorption the long-range ordering on the (001) surface is not recovered, and even the short-range structure remains disturbed in the (111) case. In contrast, heating the sample in D-2 (H-2) gas results in H-D exchange of the adsorbate without largely disturbing the surface structure. Off-specular HREELS shows two C-H stretching modes and two C-H bending modes on the as-grown (lll) surface, which is consistent with CH, termination. The dispersionless C-H modes indicate weak direct interaction between each adsorbed species. An acoustic surface phonon is observed and shows a small isotope shift, which can be explained by either a CH3 termination or H (monohydride) termination model.