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O: Oberflächenphysik

O 11: Epitaxy and growth I

O 11.8: Vortrag

Montag, 27. März 2006, 16:45–17:00, WIL A317

A LEEM study of structure, morphology and composition of ultrathin Ag/films on Pt(111) — •Esther van Vroonhoven and Bene Poelsema — Solid State Physics; MESA+ Institute for Nanotechnology; University of Twente; P.O.Box 217; AE 7500 Enschede; The Netherlands

The growth of ultra-thin silver films on Pt(111) at 750 K has been studied in real time and - space using Low Energy Electron Microscopy, LEEM. Our results demonstrate that the system is considerably more complex than appreciated so far. The LEEM/LEED results reveal a highly mobile film-substrate system. In the sub-monolayer regime they exhibit an intriguing sequence of surface confined alloying up till θ(Ag) = 0.5 ML and de-alloying (both consistent with existing literature), phase separation, partial strain relieve at θ(Ag) ~ 0.8 ML, reentrant alloying and accompanying build-up of strain as indicated by return of the monolayer film to the pseudomorphic state. During growth of the second layer more Pt is dissolved into the Ag-bilayer until the strain is finally relieved by the formation of wide trenches along <11-2> azimuth directions, in line with <1-10> being the soft direction under compressive strain. The full de-alloying and approach towards the bulk immiscibility of silver and platinum is reached only in third monolayer, accompanied by remarkable rearrangements at the interface.