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E. Klein, B. Schwarz, C. Eisenmenger-Sittner, C. Tomastik:
"THE INITIAL STATES OF WETTING AND SPREADING OF SN ON";
Poster: Joint Vacuum Conference 10, JVC-10, Portoroz, Slovenien; 28.09.2004 - 02.10.2004.

Tin (Sn) deposited on polycrystalline Aluminium (Al) surfaces shows a Stranski-Krastanov growth mode which means that before Sn-islands nucleate a thin Sn-wetting layer is formed (Eisenmenger-Sittner, J. Cryst. Growth 205, 1999, 441-452). If the wetting layer is removed from the Al-surface by sputter cleaning in UHV it re-forms by a solid state wetting process (Eisenmenger-Sittner at al., Surf. Sci. 489, 2001, 161-168).
The sources of the Sn-atoms forming the wetting layer are the Sn-islands which are not removed from the Al-surface due to their size. Nonetheless it was observed that not every island acts as Sn-emitter.
In this work we show that this selective Sn-emission is a consequence of the chemical composition and the crystallographic structure of the Sn islands. Regarding the chemical composition of the Sn islands each residual trace of Oxygen has to be removed to facilitate the emission of Sn-atoms from the island boundaries. In addition wetting is only initiated if the sputter cleaning process results in a visible damage of the islands thus increasing the roughness of their surface. From this rough interface Sn-atoms can emerge more easily than from a crystallographically smooth surface due to their lower coordination.
By monitoring line-scans obtained from Scanning Auger Electron Spectroscopy the diffusion coefficient of the Sn-atoms could be estimated from the progress of the rim of the wetting layer around the islands.

This work is supported by the Austrian Science Fund (FWF) under grant Nr. P-15739.