Regensburg 1998 – wissenschaftliches Programm
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SYC: Symposium Raster-Sonden-Mikroskopie und -Spektroskopie bei tiefen Temperaturen
SYC 5: Poster
SYC 5.6: Poster
Dienstag, 24. März 1998, 17:00–19:00, A
Surface Analysis and Ageing of YBa2Cu3O7−δ – Single– and Polycrystals — •M. Regier1, E. Keskin1, D. Schild1, A. Erb2, and J. Halbritter1 — 1Forschungszentrum Karlsruhe, Institut für Materialforschung 1 and Institut für Nukleare Entsorgungstechnik, Postfach 3640, D-76021 Karlsruhe — 2DPMC, Universität Genf, 24, quai Ernest Ansermet, CH-1211 Genf
Because clean is defined by the knowledge of Schmutz, we carried out angle
resolved X-ray photoelectron spectroscopy (ARXPS)-measurements on best
available single crystals and on polycrystals. Despite superconductivity
being observed by STM and STS at single crystal surfaces, reaction cinder
in thicknesses above 1–2 nm has been observed. By careful ARXPS analysis
using the Ba-4d core level and its chemical shifts, taking the surface
reconstruction into account, which yields the large leakage current on
those YBCO-ĉ-axis surface, YBCO-material of a comparable thickness has
been identified. This material may be located at steps.
With time
t in air or in water a diffusion controlled
formation of an insulating YBCO corrosion surface layer of thickness
d is observed, following the Tamann relation
d=k*√t . The coefficient k for our single
crystal in air is at least 20 times smaller and for polycrystals in water
about 1000 times higher than for epitaxial films (kfilm= 0.1 nm/
√h).