Research Activities > Programs > Nonequilibrium Interface and Surface Dynamics 2007

A Mesoscopic View of Surface Diffusion

CSIC Building (#406), Seminar Room 4122.

A Mesoscopic View of Surface Diffusion

Professor Frank Meyer zu Heringdorf

Universitt Duisburg-Essen, Germany

Abstract:   Nanostructures on surfaces can either be formed by means of nano-lithography, or by utilizing self-organisation processes. While lithography is either an ex-situ preparation or requires some cumbersome experimental techniques, self-organisation relies on kinetic effects, surface stress, and anisotropic diffusion. Understanding self-organization requires determination of the relative importance of these parameters and an evaluation of the diffusion in the system a challenging task, considering that often myriads of atoms are involved in the structure formation and very often the self-organization takes place at elevated temperatures. Here, a new method to image diffusion effects on the mesoscopic scale will be presented: If Ag is deposited on Silicon surfaces at ~500C, small and compact islands and wires are formed on a Ag-reconstructed layer. If the Ag flux is stopped, however, and the sample temperature is slightly raised, Ag desorbs from the reconstructed layer. The Ag islands and wires decay while feeding silver into the surface in an attempt to maintain the surface reconstruction. Over time, a reconstructed region of higher Ag coverage can only be preserved in the vicinity of the islands. The perimeter of this region resembles a line of constant coverage and represents a footprint of the diffusion in the vicinity of the island. Photoemission Electron Microscopy (PEEM) allows to directly visualize the formation and decay of such diffusion fields. The specific shape of the diffusion field depends on the particular surface and reflects the anisotropic character of the diffusion as well. For the simple case of a circular geometry, as observed on Si(001) and Si(111), a continuum model links the observation to fundamental diffusion parameters.

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