Stranski±Krastanov growth of Sn on a polycrystalline Al ®lm surface initiated by the wetting of Al by Sn C. Eisenmenger-Sittner a, * , H. Bangert a , H. St ori b , J. Brenner b , P.B. Barna c a Institut f ur Angewandte und Technische Physik, E137, Technische Universit at Wien, Wiedner Hauptstrasse 8-10, 1040 Wien, Austria b Technische Universit at Wien, Institut f ur Allgemeine Physik, E134, Austria c Research Institute for Technical Physics and Material Science, H-1121 Budapest, Hungary Received 17 March 2001; accepted for publication 10 May 2001 Abstract The deposition of tin Sn) layers on polycrystalline aluminum surfaces exhibits pronounced islanding. The island formation slightly depends on the deposition rate, substrate temperature and on the surface topography of the Al underlayer. The present study clari®es this islanding mechanism by combined SEM, atomic force microscopy and scanning Auger microscopic SAM) investigations. The detection of a continuous Sn coverage ``wetting layer'') be- tween the islands indicates a Stranski±Krastanov growth mode of the Sn islands despite the polycrystallinity of the underlying Al surface. The wetting of the Al surface by Sn was proved by in situ sputter cleaning of the sample surface in the SAM chamber. It was possible to completely remove the wetting layer by the sputter cleaning process. Surprisingly, the clean Al surface was covered again by Sn after several minutes as observed by a re-appearance of the Sn-AES signal. The Sn coverage of the surface developed at room temperature within some minutes after removing the wetting layer. Spatially resolved SAM measurements proved that the Sn emerged from the Sn islands and not from the Al bulk by surface segregation) and spread over the Al surface uniformly. This process led to the complete wetting of the Al surface by Sn despite the thermodynamic immiscibility of this binary system. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Polycrystalline thin ®lms; Auger electron spectroscopy; Atomic force microscopy; Wetting; Sputtering; Aluminum; Tin 1. Introduction Nucleation and growth of islands in the early stages of thin ®lm formation have extensively been studied both experimentally [1±4] and theoretically [1,5±12] since the seventies. The emergence of scanning probe techniques yielding topographical and chemical information with a lateral resolution on the nm scale has now given new impulses to the ®eld [13±16]. Nucleation and growth phenomena comprise length scales from atomic dimensions interactions and dynamics of single atoms) via the nanometer range formation of critical nuclei) to microscopic extensions stable islands with sizes in the lm range). In the case of polycrystalline substrates one would expect a distinct in¯uence of surface defects e.g. surface steps, grain boundaries and dierence Surface Science 489 2001) 161±168 www.elsevier.com/locate/susc * Corresponding author. Tel.: +43-1-58801-13774; fax: +43- 1-58801-13798. E-mail address: eisenmen@atp6000.tuwien.ac.at C. Ei- senmenger-Sittner). 0039-6028/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0039-602801)01174-8