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.