Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 39: Epitaxie und Wachstum III

O 39.1: Talk

Thursday, March 11, 2004, 15:45–16:00, H39

A Novel Local Free Energy Minimum on the Cu(001)-Surface — •Herbert Wormeester, Michail Ovsyanko, Georgiana Stoyan, and Bene Poelsema — MESA+ Research Institute, University of Twente, The Netherlands

Glancing incidence Ar+ ion bombardment of the Cu(001) surface leads to the formation of two atom layer deep nanogrooves parallel to the incident ion beam. High resolution LEED patterns show that sputtering along [110] and [100] leads to an intergroove distance that depends on temperature, ionfluence and -energy. Suprisingly, prolonged sputtering along [100] leads at various temperatures (175 to 235 K) to a persistent feature located at 1.0% BZ of the Brillouin Zone (BZ). Annealing at temperatures between 250 and 290 K of nanogrooves prepared after a much shorter sputtertime leads to an increase of their separation distance. Here too, the appearance of this persistent feature at 1.0% BZ is observed. These various preparation routes are indicative of a thermodynamic origin of this 1.0% feature, i.e. a local free energy minimum. Mild annealing above 400K transfers the surface to the global free energy minimum: It suffices to remove both the nanogroove structure and the feature at 1.0% BZ. The occurrence of the 1.0% BZ feature is attributed to the relieve of tensile strain, generally present at (001) fcc metal surfaces, leading to a contraction of the in-plane lattice constant of the (001) surface along the [010] azimuth. The energy balance between gain by stress relieve and cost due to lattice mismatch will be discussed. The presence of the nanogrooves along a <100> azimuth turns out to be essential for the relieve of this strain.