Oxidation of the hydrogenated diamond (100) surface

The surface composition and structure of natural diamond (100) surfaces sub sequently oxidized with activated oxygen at T(sub)less than or equal to 35 degrees C were investigated with high-resolution electron energy loss spect roscopy (HREELS), Auger electron spectroscopy, electron loss spectroscopy ( ELS) and low-energy electron diffraction (LEED). Complete surface oxidation (oxygen coverage theta = 1 ML) required doses of hundreds of kilolangmuirs of O-2. HREELS vibrational spectra permitted identification of the specifi c surface oxygen species, and also provided information about the diamond s urface states. Most surface sites lost their hydrogen at least once before becoming oxidized. The oxygen coverage theta increased quickly at first, an d then more slowly as saturation was approached; different mechanisms or si tes may have accounted for the decreased rate. The relative distribution of oxygen species varied with the oxidation conditions. Ether, carbonyl and h ydroxyl groups appeared during the initial stages of oxidation, but the hyd roxyl groups disappeared at higher coverages. Bridge-bonded ether groups do minated at saturation coverage, although smaller amounts of carbonyl and hy droxyl were still observed. The carbonyl and C-H stretch frequencies increa sed with oxygen dose due to formation of higher oxidation states and/or hyd rogen bonding between adjacent groups. ELS revealed only a low concentratio n of C=C dimers on the oxidized surfaces, and no evidence of graphitization . Surfaces generated by oxygen addition and then desorption were more reactiv e than surfaces generated by hydrogen desorption. Oxidized surfaces that we re heated in vacuum and then rehydrogenated did not recover the sharp LEED patterns and HREELS spectra of the original plasma-smoothed surface. This e ffect was presumably due to surface roughening caused by oxygen desorption as CO and CO2, and creation of reactive high-energy sites that quickly bond ed to available background gases and prevented large areas of organized sur face reconstruction. (C) 2000 Elsevier Science B.V. All rights reserved.