Intrinsic Friction of Monolayers Adsorbed on Solid Surfaces
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Intrinsic Friction of Monolayers Adsorbed on Solid Surfaces. O.B´ enichou1 , A.M.Cazabat1 , J.De Coninck2 , M.Moreau3 and G.Oshanin3,4 1 Laboratoire de Physique de la Mati`ere Condens´ee, Coll`ege de France, 11 Place M.Berthelot, 75252 Paris Cedex 05, France 2 Centre de Recherche en Mod´elisation Mol´eculaire, Universit´e de Mons-Hainaut, 20 Place du Parc, 7000 Mons, Belgium 3 Laboratoire de Physique Th´eorique des Liquides, Universit´e Paris 6, 4 Place Jussieu, 75252 Paris, France 4 Max-Planck-Institut f¨ ur Metallforshung Heisenbergstr. 3, 70569 Stuttgart, Germany ABSTRACT We review recent results on intrinsic frictional properties of adsorbed monolayers, composed of mobile hard-core particles undergoing continuous exchanges with a vapor phase. In terms of a dynamical master equation approach we determine the velocity of a biased impure molecule - the tracer particle (TP), constrained to move inside the adsorbed monolayer probing its frictional properties, define the frictional forces exerted by the monolayer on the TP, as well as the particles density distribution in the monolayer. INTRODUCTION Monolayers emerging on solid surfaces exposed to a vapor phase are important in different backgrounds, including such technological and material processing operations as, e.g., coating, gluing or lubrication. Knowledge of their intrinsic frictional properties is important for understanding of different transport processes taking place within molecular films, stability of films, as well as spreading of ultrathin liquid films on solid surfaces [1], spontaneous or forced dewetting of monolayers [2, 3] or island formation [4]. Since the early works of Langmuir, much effort has been invested in the analysis of the equilibrium properties of the adsorbed films [5]. Significant analytical results have been obtained predicting different phase transitions and ordering phenomena. As well, some approximate results have been obtained for both dynamics of isolated non-interacting adatoms on corrugated surfaces and collective diffusion, describing spreading of the macroscopic density fluctuations in interacting adsorbates [6]. Another important aspect of dynamical behavior concerns tracer diffusion in adsorbates, which is observed experimentally in STM or field ion measurements and provides a useful information about adsorbate’s viscosity or intrinsic friction. This problem is not only a challenging question in its own right due to emerging non-trivial, essentially cooperative
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behavior, but is also crucial for understanding of various dynamical processes taking place on solid surfaces. Most of available theoretical studies of tracer diffusion in adsorbed layers (see, e.g., Ref.[7]) exclude, however, the possibility of particles exchanges with the vapor, which limits their application to the analysis of behavior in realistic systems. Here we focus on this important problem and provide a theoretical description of tracer diffusion in adsorbed monolayers in contact with a vapor phase. The model we consider consists of (a) a solid substra
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