Hard x-ray photoelectron spectroscopy (HAXPES) and variable kinetic energy x-ray photoelectron spectroscopy (VKE-XPS) analyses have been performed on 10 unit cell La(1−δ)Al(1+δ)O3 films, with La:Al ratios of 1.1, 1.0, and 0.9, deposited on SrTiO3. Of the three films, only the Al-rich film was known to have a conductive interface. VKE-XPS, coupled with maximum entropy analysis, shows significant differences in the compositional depth profile between the Al-rich, the La-rich, and stoichiometric films; significant La enrichment at the interface is observed in the La-rich and stoichiometric films, while the Al-rich shows little to no intermixing. Additionally, the La-rich and stoichiometric films show a high concentration of Al at the surface, which is not observed in the Al-rich film. HAXPES valence band (VB) analysis shows a broadening of the VB for the Al-rich sample relative to the stoichiometric and La-rich samples, which have insulating interfaces. This broadening is consistent with an electric field across the Al-rich film. These results are consistent with a defect driven electronic reconstruction.
@article{arxiv.1503.02969,
title = {Stoichiometry Dependence of Potential Screening at La$_{(1-{\delta})}$Al$_{(1+{\delta})}$O$_3$/SrTiO$_3$ Interfaces},
author = {C. Weiland and G. E. Sterbinsky and A. K. Rumaiz and C. S. Hellberg and J. C. Woicik and S. Zhu and D. G. Schlom},
journal= {arXiv preprint arXiv:1503.02969},
year = {2015}
}