Core-level binding energy shifts as a tool to study surface processes on LaAlO3/SrTiO3

X-ray photoelectron spectroscopy (XPS) is used to study the adsorbed species on LalAlO3/SrTiO3 surfaces combined with computational modeling. Core level binding energy shifts are calculated from first-principles for various terminations of LaAlO3 (LAO) surfaces with adsorbed H and OH in different concentrations and with or without the presence of oxygen vacancies on the surface. Final state relaxation effects in the presence of the core hole are included. Energies of formation and adsorption for the various species and relevant reaction energies are calculated. These are used to interpret the changes in XPS spectra of an LAO film under different growth and annealing treatments. We find a peak with 2 eV binding energy shift toward higher binding energy in the O1s spectrum cannot be associated with OH as is commonly assumed. Instead it is assigned to carbonaceous species by studying the corresponding changes in the C1s spectrum. The OH and H species are found to be too strongly bound to be removed at 500 °C.