PHOTOINDUCED OXIDATION OF INP(110) WITH CONDENSED O2 AT 25K

Photoemission studies of cleaved InP(110) surfaces with multilayers of physisorbed O2 at 25 K demonstrate photoinduced oxidation. The photoemission results show a 4-5-eV chemical shift in the P 2p core level, and the bonding configuration of the oxide is similar to that of InPO4. The amount of oxide formed depends on photon exposure and the quantity of oxygen condensed on the surface. During initial oxide growth, the interaction between photogenerated conduction-band electrons from the substrate and physisorbed oxygen molecules controls the reaction and yields an effective reaction cross section of approximately 6 X 10(15) cm2/photon for 170-eV photons. The growth rate for the thicker oxide is much lower because reaction is limited by diffusion through the oxide layer. This second stage of oxide growth is characterized by dissociation of molecular O2 due to direct photoexcitation and dissociative secondary-electron attachment. Finally, the cross section for photon-stimulated desorption Of O2 by 170-eV photons is measured to be 4 X 10(-17) cm2/photon.