  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$_{(1-{\delta})}$Al$_{(1+{\delta})}$O$_3$ films, with La:Al ratios
of 1.1, 1.0, and 0.9, deposited on SrTiO$_3$. 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.
