We report rapid deterioration of metallic surfaces on irradiation with ultraviolet light. Very fast degradation of the Shockley state of Cu͑111͒ is observed during photoemission at low temperature. A different evolution of the Shockley states during annealing and cooling was also discovered. These observations seem to favor a mechanism based on photon-stimulated chemisorption of hydrogen on the surface. We suggest that this mechanism affects all experiments involving intense radiation and might become a major obstruction for future experiments with microfocused beams.Angle-resolved photoelectron spectroscopy ͑ARPES͒ ͑Ref. 1͒ is a powerful tool to probe system properties that are closely related to electronic structure such as superconductivity, electron-phonon coupling, work function, surface reactivity, etc. Along with many other techniques, ARPES benefits from constant advances in the technology of synchrotron radiation. The beamlines and insertion devices of third-generation storage rings generate intense monochromatic radiation that greatly decreases the duration needed to collect data and allows tests of dynamic modifications of the system properties of small samples. Nevertheless, the possible alteration of samples resulting from prolonged exposure to radiation is always a concern. An extensive literature has been published on radiation-induced modification of, and damage to, sensitive samples such as macromolecular crystals 2 and photoresists. 3 Although metallic samples are considered to resist radiation damage, earlier studies have shown that metallic surfaces exhibit deterioration under irradiation with ultraviolet photons at low temperature but with contradictory conclusions. 4,5 Surface deterioration is typically accompanied with broadening or disappearance of surface-related signals. Overlooking the influence of surface deterioration during measurements can produce improper or even erroneous interpretation of experimental data.In this paper, we report a mechanism for rapid deterioration of metallic surfaces during photoemission. Depending on the surface temperature, the rate of deterioration that this mechanism causes can be much greater than that caused by adsorption of contaminants, which is a common mechanism for surface deterioration in an ultra-high-vacuum ͑UHV͒ environment. The surface of interest is Cu͑111͒, but a Cu͑111͒ surface partially covered with Ag was chosen for testing. The surface of Ag-covered Cu͑111͒ served as an internal reference, and this advantage of the choice became obvious while analyzing the deterioration of the Cu͑111͒ surface. The surface of Ag/Cu͑111͒ is characterized with its Shockley states. The Shockley-type surface states are electronic states that appear in the projected energy gap of the bulk band around the ⌫ point on the ͑111͒ surface of noble metals due to the termination of the crystal by the surface. 6 The binding energy and linewidth of the Shockley states are very sensitive to surface order and composition; 5,7-9 the evolution of the surface can be character...

The wetting of thin Ag films on Cu͑111͒ is characterized in detail with angle-resolved photoelectron spectroscopy. After constructing disordered Ag films on Cu͑111͒, we monitored the evolution of their layer-resolved Shockley states during wetting. Our results provide the first observation of a transitional state, which implies a coexistence of clean Cu͑111͒, 1 ML of Ag on Cu͑111͒, and 2 ML of Ag on Cu͑111͒. The evolution of these Shockley states indicates a two-process model of wetting.