American Vacuum Society - 53st International Symposium, San Francisco, CA, 11/12 - 11/17/2006

2D Ordered Nanocluster Arrays Growth via Threading Dislocation Pair Annihilation

Bogdan Diaconescu and Karsten Pohl

The process of growing nanostructured ordered arrays of clusters on the misfit dislocation networks of strained metallic thin films1,2 requires a detailed understanding of the nucleation and film-adsorbate interaction at the atomic level. In the case of sulfur adsorption on submonolayer silver films on the 0001 surface of ruthenium, the Ag's short herring bone rectangular misfit dislocation unit cell of 54Å x 40Å (19 x 16 Ag atoms) reconstructs into a well-ordered triangular array of S filled vacancy islands 50Å apart.

Atomically and time resolved measurements from our home-built variable-temperature scanning tunneling microscope reveal that the S cluster growth mechanism involves a local restructuring of the highly dynamic misfit dislocation network of Ag with the final structure free of threading dislocations. Adsorbed S atoms will preferably bind on the Ru substrate thus displacing Ag atoms and creating two-dimensional S filled Ag vacancy islands while the strain of the misfit dislocation network of Ag assures the long-range order of the vacancies. The new morphology and symmetry of the composed S/Ag/Ru(0001) system is obtained via a threading dislocation annihilation mechanism in which adjacent and opposite pairs of threading dislocations are replaced by the S filled Ag vacancy islands. The driving force of this process is the strain relaxation whose local character is shown by the conservation of the unit cell size area of 21.5nm2.
Supported by NSF-CAREER-DMR-0134933 and ACS-PRF-37999-G5.

1 K. Pohl et al., Nature 397, 238 (1999)
2 K. Thürmer et al., Science 311, 1272 (2006)