Electron affinity of plasma-hydrogenated and chemically oxidized diamond (100) surfaces

The electron affinity (EA) chi of single crystal diamond (100) is determined as a function of hydrogen and oxygen coverage by a combination of work function and photoemission experiments. For the fully hydrogenated (100)-(2x1):H surface an EA of -1.3 eV and for the oxidized surface C(100)-(1x1):O chi = + 1.7 eV are obtained. These are the lowest and the highest electron affinities, respectively, ever reported for any diamond surface. The variation in chi with O and H coverage is well described by a simple dipole model provided that (he depolarization is properly taken into account for high adsorbate densities. This analysis favors the bridge position (etherlike) for oxygen on C(100). By mixing H and O adsorbates on a microscopic scale the EA of C(100) can be adjusted at will over 3 eV between the extreme values without jeopardizing the chemical passivation of the diamond surface afforded by H or O termination.