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O: Oberflächenphysik

O 38: Struktur und Dynamik reiner Oberflächen

O 38.7: Talk

Friday, March 31, 2000, 12:45–13:00, H37

Structure of the clean and the Al₂O₃ covered NiAl(110) surface by measurements of crystal truncation rods — •G.R. Castro¹, X. Torelles², H. Isern³, O. Bikondoa¹, F. Wendler⁴, and W. Moritz⁴ — ¹SpLine, Spanish CRG Beamline, ESRF, B.P.220. F-38043 Grenoble cedex 09 — ²Institut de Ciencia Materials de Barcelona, 08193 Bellaterra, Catalunya, Spain — ³ESRF, BP 220, F-38043, Grenoble Cedex 09 — ⁴Inst. f. Kristallographie und Angew. Mineralogie, U. M"unchen, Theresienstr. 41, 80333 M"unchen

The clean and the Al₂O₃ covered NiAl (110) surfaces have been investigated by synchrotron x-ray diffraction experiments. As the oxide overlayer is incommensurate to the NiAl(110)substrate no-interference from the oxide layer is expected and the crystal truncation rod (CTR) analysis provides

information about the NiAl(110)-oxide interface. The analysis of the CTR-data shows clearly a rippled Ni-Al topmost surface with an amplitude value of 0.13 Å for the clean surface and 0.14 Å for the oxide covered surface. No rippling in deeper layers was detectable. The clean surface relaxation agrees qualitatively with previous reported LEED results but is found to be smaller. The Al sites are expanded by +3% (outwards) and the Ni ones are contracted by −3% (inwards) with respect to the unrelaxed interlayer separation. For the oxide covered surface an increase of the expansion of the outermost Al atoms (+6%) relative to their bulk positions has been found, while the Ni remain at the bulk position. No preferential segregation of one species to the surface was detected in both cases