Electronic structure and photochemistry of adsorbates on ultra-thin metal films

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We have investigated how electronic structures and photochemistry of adsorbates are modified on nano-structured substance such as ultra-thin films and nano-clusters of metals, in comparison with adsorbates on bulk metal surfaces. We have mainly focused on the following topics :1. Photochemistry of methane on palladium nano-clustersNano-clusters of palladium are formed on A1_<22E2O2<reverse surface chemistry arrow>> prepared on a NiAl(110) surface. The size distribution of clusters can be controlled by temperature of the substrate and the deposition rate of palladium. Methane is adsorbed on the clusters and irradiated by 6.4-eV photons. Methane is photodissociated or photodesorbed as in the case of the clean Pd(111) surface. However, the branching ratio is significantly dependent on the2. Photodesorption of rare gas atoms on silicon surfacesRare gas atoms (Kr, Xe) weakly adsorb on a Si(100) surface. We found for the first time that these adsorbates are desorbed by the irradiation of photons whose wavelength range from near infrared to uv. The excitation mechanism and desorption dynamics have been investigated.3. Unoccupied states of CO adsorbed on Pt(111)The unoccupied state of CO adsorbed on Pt(111) has been monitored by 2-photon photoelectron spectroscopy. We found that this state depends on the adsorption site of CO.4. Photochemistry of oxygen adsorbed on Ag(110)Preliminary measurements have been done on photochemistry of oxygen atoms on Ag(110). The chemisorbed oxygen atoms are removed by uv light irradiation. Wavelength dependence of photo-yield has been measured.In addition, we have found that CO_2 is effectively converted into carbonate species on Si(100) by coadsorption of N_2O and O_2