A surface spectroscopic study of thin layers of U on polycrystalline Pt

Abstract

Thin layers of U on polycrystalline Pt have been prepared by magnetron sputter deposition and studied by X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS, respectively) and Auger electron spectroscopy (AES). The results of this study are compared to those of U deposited on Pd published previously [1]. We studied the mode of growth of U on the substrate, the evolution of the electronic structure of the surface, with special emphasis on the localization-delocalization of the U 5f states, and the diffusion of U into the bulk when the surface was annealed. We found U spontaneously reacting with Pt, immediately after deposition, to form a homogeneous surface alloy. Annealing results in the formation of more diluted surface alloys and, finally, in the diffusion of U into the bulk. A real time study of this process allowed us to follow the formation and disappearance of near surface alloys with decreasing U concentration. With dilution the U 5f band narrows but for all U concentrations we investigated the 5f states stayed itinerant.