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TT: Fachverband Tiefe Temperaturen
TT 27: CE: Poster Session
TT 27.7: Poster
Mittwoch, 24. März 2010, 14:00–18:00, Poster D1
HAXPES analysis of LaAlO3/SrTiO3 thin films grown under various oxygen partial pressures — •Florian Pfaff1, Andreas Müller1, 3, Götz Berner1, Wolfgang Drube2, Michael Sing1, and Ralph Claessen1 — 1Experimentelle Physik IV, University of Würzburg — 2HASYLAB DESY, Hamburg — 3Inorganic Materials Science, University of Twente
At the interfaces of epitaxially grown oxide heterostructures novel phases with unexpected properties may be generated. E.g., for LaAlO3/SrTiO3 (LAO/STO) a quasi-2DEG is found, if more than four monolayers (ML) of LAO are grown on STO. As possible explanations intrinsic, i.e. electronic reconstruction, but also extrinsic effects like oxygen vacancies are discussed. To analyze the influences of oxygen vacancies, we performed hard x-ray photoelectron spectroscopy (HAXPES) measurements on samples with two and five ML LAO grown under various oxygen partial pressures (10−5 mbar, 10−3 mbar, and 10−1 mbar) by pulsed laser deposition (IMS, U Twente). We used angle-dependent HAXPES on the Ti 2p core level to determine the Ti3+/Ti4+ ratio, which clearly depends on the growth pressure. Unexpectedly, the five ML sample grown at 10−1 mbar - a pressure for which oxygen vacancies should be largely suppressed - shows no Ti3+ at all, which is in agreement with its insulating behavior observed in transport measurements, but casts electronic reconstruction as only possible origin for the 2DEG formation into doubt. However, other explanations for the insulating behavior could be involved, like an increased interface roughness or possible Sr-La intermixing.