Threading Dislocation Pair Annihilation as a Mechanism for the Growth of Ordered 2D Nanocluster Arrays*

The bottom-up approach of growing nanostructured ordered arrays of clusters on the misfit dislocation networks of strained metallic thin films requires a detailed understanding of the nucleation and film-adsorbate interaction processes. In the case of S adsorption on submonolayer Ag / Ru(0001), the Ag's short herring bone rectangular misfit dislocation unit cell of 54{\AA}x40{\AA} (19x16 Ag atoms) reconstructs into a well ordered triangular array of S filled vacancy islands 50{\AA} apart. Atomically resolved VT-STM measurements show that the S cluster growth mechanism involves a local restructuring of the misfit dislocation network of Ag with the final structure free of threading dislocations. The new symmetry and morphology of the composed S/Ag films is obtained via a threading dislocation annihilation mechanism where adjacent and opposite pairs of threading dislocations are replaced by the S filled Ag vacancy islands. The local character of the annihilation process is shown by the conservation of the unit cell size area of 21.5nm$^{2}$.