First principles calculations on Na and K-adsorbed diamond(1Â 0Â 0) surface

Self-consistent, periodic, density functional theory calculations, using PW91 functional, have been performed to investigate Na and K adsorption on the C(1 0 0)(2 × 1) surface. Our calculations showed that Na and K adatoms preferred to occupy valley-bridge sites at the coverage (Θ) of 0.5 ML. For the coverage of 1 ML, the combination of pedestal site and valley-bridge site turned out to be energetically favored. These findings are found to be consistent with those obtained for alkali-metal adsorption on silicon and germanium surfaces. Two desorption peaks named α and β for K adsorption have been observed and assigned to pedestal or bridge site and valley-bridge sites experimentally, while our results showed that the α and β states should be ascribed to pedestal site and valley-bridge sites and the combination of bridge and valley-bridge site is not the local minima. Work function analysis showed that when Na and K are adsorbed on diamond surface, the work function will decrease linearly with increasing coverage, up to a minimum, and finally increase again because of the depolarization of the adsorbate, agreeing well with experiments.