Regensburg 2004 – wissenschaftliches Programm
O 39.1: Vortrag
Donnerstag, 11. März 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  and  leads to an intergroove distance that depends on temperature, ionfluence and -energy. Suprisingly, prolonged sputtering along  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  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.