Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 51: Metal Substrates: Adsorption III

O 51.4: Talk

Thursday, March 29, 2007, 12:00–12:15, H39

Subsurface oxygen in Ni on (√2×2√2) R45^∘ O/Cu(001) — •Holger Meyerheim¹, Dirk Sander¹, Radian Popescu¹, Wei Pan¹, Iona Popa², Phil Woodruff³, and Jürgen Kirschner¹ — ¹Max-Planck-Institut f. Mikrostrukturphysik, Weinberg 2, 06120 Halle — ²ESRF, BP 220, F-38043 Grenoble, France — ³Univ. of Warwick, Coventry CV4 7AL, UK

Growth, morphology and magnetic properties of Ni deposited on Cu(001) are distictly influenced by preadsorption of oxygen. The preoxidized Cu(001) surface exhibits a (√2×2√2) R45^∘ reconstruction characterized by a "missing row" geometry. Subsequent Ni-adsorption changes the reconstruction to c(2×2) and previous studies indicated that oxygen acts as a surfactant always floating on the surface. The spin re-orientation transition (SRT) from in-plane to out of plane is shifted from ten monolayers (ML) in the case of the non-oxidized Cu substrate to five ML (1 ML= 1.53×10¹⁵ atoms/cm²). We present an in-depth surface x-ray diffraction analysis of the interface structure of Ni grown on the reconstructed (√2×2√2) R45^∘ O/Cu(001) surface in the coverage range between 1.25 and 5.00 monolayers (ML). In contrast to common belief that oxygen atoms always float on the surface, we find an significant fraction (up to ≈0.17 ML) of oxygen located in octahedral interstitial sites below the surface. Surface stress measurements in combination with density functional calculations support this finding. The implications for the understanding of the oxygen induced SRT in the Ni/O/Cu(001) system are discussed.