On angle resolved x-ray photoelectron spectroscopy of oxides, serrations, and protusions at interfaces

Oxidized surfaces show smeared out x-ray photoelectron spectroscopy (XPS) lines which cannot be fitted by bulk compounds and by lateral growth. By simultaneously fitting XPS spectra obtained for takeoff angles between 5° and 80° not only is the resolution enhanced, but also a new dimension is gained. Thus, small amounts (<0.5 nm) of interface oxides are identified in level shift, stoichiometry, and spatial distribution, i.e., serration and protrusion of interfaces are revealed. The angle resolved x-ray photoelectron spectroscopy analysis of oxidized (<100 °C) NbN, NbC, and Nb, shows that the metal surface is serrated by metallic (≂1 nm) and dielectric (≊1 nm) interface oxides, where Nb2O5 forms the outermost layer. The serration is deeper for Nb than for NbN, because Nb is weaker and dissolves more O. In contrast, in high-temperature oxidation (900 °C) of Si(100), the interface shows no serration and less interface oxides (<1 nm) but Si clusters at the outer SiO2 surface exist as remnants from low (≪300 °C) temperature oxidation.