DISPERSIONS OF SURFACE-STATES ON DIAMOND(100) AND DIAMOND(111)

We present angle-resolved photoelectron spectra and surface state disp ersions for the clean, 2 x 1 reconstructed (111) and (100) surfaces of diamond. For the (100) surface a surface state is found in the gap of the projected bulk band structure around (Y) over bar, which has a bi nding energy of 2.7 eV at (Y) over bar (relative to the Fermi level) a nd a dispersion in the <(Gamma)over bar>-(Y) over bar direction of 0.5 eV, consistent with theory. At <(Gamma)over bar> a surface resonance is observed at 1.4 eV binding energy. No surface states were observed above the valence-band maximum. Our results on the (111) surface show a strongly dispersing surface state that reaches its maximum 0.5 eV be low the Fermi level at (K) over bar. This result implies a gap of at l east 0.5 eV in the surface electronic structure, which has consequence s for the surface reconstruction in terms of a pi-bonded chain model.