Native oxide on ultra-thin NbN films

We report study of native oxide formation over NbN ultra-thin films. With a help of XPS, chemical and phase depth profiles of NbN film of 5 nm and 10 nm thickness exposed to room air for more than a month were recorded. The surface of those films were sputtered with Ar+ ions and consequently oxidized in room air for another few days. It was found that an intermediate layer of NbNx was formed between the niobium oxide layer and original NbN material