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E. Klein, B. Schwarz, C. Eisenmenger-Sittner, C. Tomastik, A. Kovács:
"PASSIVATION OF ALUMINIUM (Al) SURFACES AGAINST OXIDATION BY A MONOATOMIC TIN (Sn) WETTING LAYER";
Poster: International Vacuum Congress 16, IVC-16, Venedig, Italien; 28.06.2004 - 02.07.2004.

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).
In this work we show that the monoatomic Sn-wetting layer protects the Al-surface from oxidation to a certain degree. The oxidation process was monitored by Auger Electron Spectroscopy (AES) for both, Al-surfaces covered by the Sn-wetting layer and bare Al-surfaces. Both surface types were exposed to an elevated Oxygen partial pressure of 10-4 Pa in an AES chamber with a total background pressure of 10-9 Pa. The surfaces covered by the Sn-wetting layer were oxidized significantly slower than the bare Al-surfaces.
This inhibition of oxidation also has consequences on the nucleation and growth of Sn-islands on an Al-surface: 400 nm thick polycrystalline Al-films deposited on natively oxidized Si-wafers by magnetron sputtering at a temperature of 180°C were covered by 10 nm Sn by two different procedures:
(i) the bare Al-layer was kept in the deposition chamber at an Oxygen pressure of 2.10-4 Pa for 30 minutes at 180°C. Then 10 nm Sn were deposited on this layer.
(ii) immediately after the Al-deposition 2 nm Sn were deposited on the bare Al-surface, then this system was also exposed to an Oxygen pressure of 2.10-4 Pa for 30 minutes at 180°C. Then the remaining 8 nm Sn were deposited.
While the Sn-films deposited following procedure (i) showed significant signs of secondary nucleation which is induced by the oxidation of the Al-surface no secondary nucleation could be detected if the Sn-overlayers were deposited following procedure (ii).
This work is supported by the Austrian Science Fund (FWF) under grant Nr. P-15739 The financial support of the Hungarian National Science Foundation under contract No. OTKA T033075 and to EU under contract No. ICAI-CT-2000-70029 is acknowledged.