Angular X-ray photoelectron spectroscopy study of N(1s) and O(1s) lines during controlled oxidation of NbN thin film

Abstract

The oxidation of NbN thin film has previously been studied by X-ray photoelectron spectroscopy in connection with Josephson junction technology. The Nb(3d) photoelectron lines were the main point of study. In this work O(1s) and N(1s) photoelectron lines have been analysed as a function of the angle θ between the sample surface and the detector slit, and of the oxygen exposure L. Binding energies, photoelectron linewidths and the concentrations of the various constituents have been plotted versus θ and L. O(1s) and N(1s) spectra have been decomposed into three components and two components respectively, and their relative concentrations have been calculated for each step of the oxidation process. NbN oxidation begins with oxygen diffusion into the bulk of the film with nearly constant niobium and nitrogen concentrations. Then the interface development begins some 60 Å below the surface with an increase in chemisorbed oxygen and in oxides with a large variety of species; the concentration of nitrogen decreases. In the surface of the sample the Nb-O bonding state becomes more pronounced and there is no absorbed oxygen. This develops on the NbN surface when oxygen exposure increases and more niobium oxide with well-defined chemical bonding is formed. There is still nitrogen at low concentration. As long as nitrogen is present, the O(1s) line is broader than that for an oxidized niobium sample.