| Summary: | 碩士 === 國立中央大學 === 物理研究所 === 100 === The surface states of metallic thin films were found to deteriorate under intense ultraviolet irradiation. The reason of deterioration is photon-induced chemisorption of hydrogen on the surface. In this thesis, we explored the possible thickness-dependence of this deterioration. Atomically flat Ag thin films of various thicknesses were grown on Au(111), and the studied systems were 1.6ML Ag/Au(111) and 2.65ML Ag/Au(111). The evolution of their surface states were monitored realtime with ARPES. In the experiment of putting samples under intense ultraviolet irradiation at low temperature for a period of time and annealing, the data show that the deterioration of surface state of low-coverage is more easier than the high-coverage one (the mentioned low coverage are 1ML and 2ML in 1.6ML Ag/Au(111) and 2.65ML Ag/Au(111), respectively). The results indicate that the film surface of lower coverage is more susceptible to the photon-induced deterioration. To explain the observed results, we propose a diffusion mechanism of hydrogen on silver surfaces based on the existence of the Ehrlich-Schwoebel barrier associated with the surface steps.
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