A photoelectron study of the oxidation of Ta(110) and thin aluminum layers on Ta(110)

Photoelectron spectra were used to characterize the oxidation of thin aluminum films on Ta(110). The exposure of bare Ta(110) to langmuir amounts of O2 generates Ta 4f spectral components related to chemisorbed atomic oxygen and a thin oxide layer. For a Ta-supported Al monolayer, the Al oxidizes first and forms small oxide clusters on the Ta substrate. Once the Al begins to cluster, the uncovered Ta(110) surface oxidizes like the bare Ta(110) surface. When the aluminum layer is made two atomic layers thick, the surface and sub-surface sites of the Al film are filled by atomic oxygen, then oxygen goes into the tantalum substrate and causes the Al2p core level to shift ∼ 0.5 eV to lower binding energy. The oxidation behavior of the thickest (∼ 5 ML) Al layers on Ta(110) is the same as that reported for similar Al layers on polycrystalline Nb films where the presence of unreacted aluminum at the interface acts to inhibit the entry of oxygen into the substrate.