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O: Oberflächenphysik

O 42: Symposium Electron transfer processes II

O 42.2: Fachvortrag

Donnerstag, 30. März 2006, 15:30–16:00, WIL C207

Image potential states on a finite size adsorbate island — •J.P. Gauyacq and A.G. Borisov — Universite Paris-Sud, 91405 Orsay Cedex, France

When adsorbate islands are grown on a metal surface, image potential states can appear localized at two different places: on the adsorbate islands and on clean substrate patches. Confinement of the image states on islands leads to two phenomena deeply influencing their dynamical behaviour: quantisation on the finite size object and scattering at the island edges. This provides a very appealing opportunity to study finite size effects on a 2D-continuum of states. Results of a theoretical parameter-free study of this problem in the case of Ar islands on a Cu(100) substrate will be presented. Two main points will be addressed : i) quantisation of the image state continuum on the Ar island leading to a series of resonance states and ii) scattering at the edges of the island that results in reflection, or transmission into the image states continua of the clean part of the surface, or decay into the substrate bulk states. Transmission at the island edges is highly probable making the image states on small islands very short-lived. The variation of the image state characteristics (energy and lifetime) with the island size will be presented. The question of the observability of finite size effects and the related question of the minimum island size for an image state to ’look like’ on an infinite layer will be addressed.