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Phys Rev Lett. 2013 Aug 30;111(9):096103. Epub 2013 Aug 27.

Unusual two-stage kinetics of ethylene adsorption on Si(100) unraveled by surface optical spectroscopy and Monte Carlo simulation.

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Institut des NanoSciences de Paris, CNRS and UPMC University of Paris 06, UMR 7588, 4 place Jussieu, 75005 Paris, France and Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, University of Lorraine and CNRS, UMR 7564, 405, rue de Vandoeuvre, 54601 Villers-lès-Nancy, France.


The adsorption of ethylene on a Si(100)-2×1 surface in an ultrahigh vacuum has been monitored at room temperature by use of real-time surface differential reflectance spectroscopy, which clearly demonstrated that the adsorption follows a two-stage process. About half a monolayer is obtained for 1 L, while the second stage is much slower, yielding the complete monolayer for an exposure of ∼400  L. The kinetics over the full range has been successfully reproduced by a Monte Carlo calculation. The key point of this two-stage adsorption kinetic lies in the reduced adsorption probability (by a factor of several hundreds) on the Si dimers, neighbors of dimers which have already reacted, with respect to the adsorption probability on isolated dimers. This new kind of adsorption kinetics, due to a repulsion between already adsorbed molecules and additional molecules impinging on the surface, makes it a textbook case for a "cooperative" adsorption process.

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