Interface properties and built-in potential profile of a LaCrO3/SrTiO3 superlattice determined by standing-wave excited photoemission spectroscopy

Author(s): Lin, S-C; Kuo, C-T; Comes, RB; Rault, JE; Rueff, J-P; Nemsak, S; Taleb, A; Kortright, JB; Meyer-Ilse, J; Gullikson, E; Sushko, PV; Spurgeon, SR; Gehlmann, M; Bowden, ME; Plucinski, L; Chambers, SA; Fadley, CS | Abstract: © 2018 American Physical Society. LaCrO3(LCO)/SrTiO3(STO) heterojunctions are intriguing due to a polar discontinuity along [001], exhibiting two distinct and controllable charged interface structures [(LaO)+/(TiO2)0 and (SrO)0/(CrO2)-] with induced polarization, and a resulting depth-dependent potential. In this study, we have used soft- and hard-x-ray standing-wave excited photoemission spectroscopy (SW-XPS) to quantitatively determine the elemental depth profile, interface properties, and depth distribution of the polarization-induced built-in potentials. We observe an alternating charged interface configuration: a positively charged (LaO)+/(TiO2)0 intermediate layer at the LCOtop/STObottom interface and a negatively charged (SrO)0/(CrO2)- intermediate layer at the STOtop/LCObottom interface. Using core-level SW data, we have determined the depth distribution of species, including through the interfaces, and these results are in excellent agreement with scanning transmission electron microscopy and electron energy-loss spectroscopy mapping of local structure and composition. SW-XPS also enabled deconvolution of the LCO and STO contributions to the valence-band (VB) spectra. Using a two-step analytical approach involving first SW-induced core-level binding-energy shifts and then VB modeling, the variation in potential across the complete superlattice is determined in detail. This potential is in excellent agreement with density functional theory models, confirming this method as a generally useful tool for interface studies.