American Vacuum Society - 52st International Symposium, Boston, MA, 10/30 - 11/4/2005

Atomically and Time Resolved Pattern Formation in Strained Metal Films: S on Submonolayer Ag/Ru(0001)

Bogdan Diaconescu and Karsten Pohl

Strained metallic interfaces can lead to highly ordered misfit dislocation networks that can be utilized as a bottom-up patterning method for the growth of cluster arrays of specific size and density. The great potential of this natural templating method is that the characteristic length scales are predicted to depend on the interfacial stress. 2D sulfur cluster growth on the misfit dislocation network of submonolayer Ag on Ru(0001) relaxes the 6nm x 4nm unit cell of the strained Ag film into a large-scale ordered triangular array of S filled vacancy islands, 5nm apart.1

Variable Temperature STM and LEED studies reveal that 2D S cluster growth takes place in two regimes: (1) At low S coverage a dilute phase of S clusters, etched at the threading dislocation sites of the Ag film forms. S clusters have an average size of 1.5nm2 corresponding to two S atoms per cluster, and a highly temperature dependent mobility. (2) At a S coverage above 0.018 ML the solid S cluster phase forms after all the available threading dislocation sites of the Ag film were etched. In this regime the highly ordered S cluster array shows a S coverage dependent cluster size and a p(2x2)S/Ru(0001) structure. In the growth process S partially relieves the strain in the Ag film as seen by the relaxation of the misfit dislocation network. For S coverage beyond 0.33 ML on the Ru(0001) terrace, the compressed S phase pushes Ag atoms into the second layer and the ordering of the S clusters is partially destroyed. It is found that exchange-induced inhomogeneous nucleation of S adatoms modifies the interfacial stress in the submonolayer Ag/Ru(0001) film and, that the size of the S-filled vacancy islands in the ordered self-assembled array can be controlled with S coverage.
Supported by NSF-CAREER-DMR-0134933 and ACS-PRF-37999-G5.

1 K. Pohl et al., Nature 397, 238 (1999)