NO2 ADSORPTION ON A CYLINDRICAL GE CRYSTAL

The adsorption of NO2 on a cylindrical Ge crystal with [110BAR] as the cylinder axis was studied by photoelectron (UPS, XUPS, XPS) and Auger electron spectroscopy. At 300 K, NO2 decomposes into NO and O on the surface but only oxygen adsorbs. Discrete chemical shifts towards higher binding energy are observed in the Ge 3d emission, related with Ge atoms with 1, 2 or 3 oxygen ligands. Compared to the adsorption of O2 and NO, the oxidation with NO2 is faster and shows a comparatively weak dependence on the crystallographic orientation. Also at low temperatures (60, 100 K), NO2 molecules dissociate into NO and O in the first layer. Both species are adsorbed. On top of this layer, NO2 is condensed in form of N2O4. The condensate is desorbed and decomposed by annealing, electron or photon irradiation. The irradiation effects involve most likely secondary electrons.