Speaker
Description
Variable energy positron annihilation lifetime spectroscopy measurements using the high intensity positron beam have been performed on high quality SrTiO$_3$, and SrTiO$_3$/LaAlO$_3$, thin films grown by pulsed laser deposition (PLD) and on near surface region of SrTiO$_3$ substrates subjected to PLD growth conditions. The measurements were performed using the NEPOMUC beamline at Heinz Maier-Leibnitz Zentrum (MLZ), Garching. The presence of vacancy-related point defects is detected, at concentrations below approximately 100 ppm. The positron lifetime spectra are deconvolved and the lifetime component characteristic of the two types of peroviskite oxide, ABO$_3$, cation monovacancy, the B-site and A-site vacancies, are identified and are consistent with density functional theory calculated positron lifetime values. Measurements on the process modified near surface region of the SrTiO$_3$ substrate provide evidence for the presence of Ti-vacancy O-vacancy divacancy complexes. Changes in positron trapping with UV illumination are observed. The measurements also observe changes in the vacancy defect content on annealing SrTiO$_3$/LaAlO$_3$ structures, the conductivity of the interface is also changed.
