過去研究發現，金屬樣品在強烈的紫外光照射下會導致氫原子吸附在樣品表面。在本論文裡面，嘗試找出在薄膜系統中此衰變是否跟薄膜厚度有關。我們在Au(111)鍍上不同厚度的銀膜，而所探討的兩個系統分別是：1.6ML Ag/Au(111)跟2.65ML Ag/Au(111)，並利用角解析光電子能譜術即時地量測表面態的變化。從樣品放在低溫持續照光一段時間跟升溫的實驗中，發現兩系統中低厚度的表面態比高厚度的表面態容易衰變(在1.6ML Ag/Au(111)系統中低厚度為1ML，2.65ML Ag/Au(111)系統中低厚度為2ML)。此實驗結果反應出表面態衰變跟研究系統中哪個薄膜厚度較低有關聯。為了解釋觀察到的現象，我們提出以Ehrlich-Schwoebel barrier為基礎的擴散機制來描述氫原子在階梯邊界附近的運動。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.