Photoelectron spectroscopy study of U–Ni alloys: a comparison of thin films and bulk systems

We present a comparative study of UNi2 and UNi5 intermetallic compounds and U–Ni thin films prepared by sputter deposition. The aim of this work was to study the electronic structure of the U–Ni alloys, and in particular to investigate to what extent thin films are representative of the corresponding bulk materials. Electronic structure and surface composition was investigated by X-ray and ultra-violet photoelectron spectroscopies respectively, and X-ray induced Auger electron spectroscopy. The composition of thin films, sputter deposited from a UNi5 target, was strongly dependent on deposition conditions (pressure, target voltage), and ranged from U20Ni80 to U14Ni86. Deposition at room temperature resulted in amorphous films, while deposition at a substrate temperature of 473 K lead to the formation of crystalline phases. In all phases, the U 5f electrons are itinerant and remain pinned at the Fermi-level. With increasing U content, the Ni 3d band shifts towards higher binding energies and becomes narrower than in elemental Ni.