Irradiation with 1.7 and 1.97 eV photons of O2physisorbed on GaAs(110) at 25 K induced strong surface oxidation. The oxidation rate was dependent on photon energy as well as substrate doping type. The 1.97 eV photons induced reaction sim;30 times faster than did the 1.7 eV photons. For fixed photon energy, reaction onphyphen;type substrates was sim;6 times faster than onnhyphen;type substrates. These results stand in contrast from those of room temperature experiments where reaction rate was independent of doping type and the dependence on photon energy reflected only the substrate photon absorption coefficient. We show that photoexcitedhotelectrons are responsible for photohyphen;induced reactions at low temperature. Coupling between hot electrons and physisorbed O2is via resonant tunneling involving the O2electron affinity level.
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