Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 39: Nanostructures III

O 39.2: Talk

Thursday, March 30, 2006, 15:15–15:30, PHY C213

Embedded foreign atom interactions and cluster configurations: Co/Cu(001) — •Bene Poelsema, Nuri Öncel, Ronald Van Moere, and Harold J.W. Zandvliet — Solid State Physics; MESA+ Institute for Nanotechnology, University of Twente, P.O.Box 217; 7500 AE Enschede; The Netherlands

At low coverages (~0.03 ML) of Co on Cu(001) and intermediate temperatures (300-380K), small clusters composed of embedded Co atoms coexist with larger adatom islands. The configurations and concentrations of the former have been analyzed, assuming (local) equilibrium. The observations of fluctuations of the shape/confiugrations of small embedded clusters encourage this assumption. Taking into account configuration entropy and assuming pairwise interactions leads to a surprisingly accurate description of the relative occurrence of monomers, dimers, trimers and tetramers. The same applies for the probability distribution of the various configurations of dimers, trimers and tetramers. These findings suggest an à posteriori confirmation of local equilibrium. The embedded Co-Co interactions have been found attractive for both nearest neighbour (NN) and next nearest neighbour (NNN) interactions. The latter (-93+/-5 meV) is twice as strong as the NN-interaction (-45+/-10 meV), which explains the predominance of observed c(2x2) building blocks in the clusters. With inclusion of NN- and NNN-interactions only moderate agreement between calculations and experiments is achieved. Adding a next-next nearest neighbour (NNNN) interaction term of -20+/-10 meV results in a very convincing fit of the configuration distributions of both trimers and tetramers.