The coating of solid surfaces with polyelectrolyte (PEL) multilayers is of potential interest for applications in many fields ranging from chemistry to material science and biology [1-13]. A simple and powerful method that relies on the alternate adsorption of oppositely charged polyelectrolytes to form PEL multilayers with well-defined structure was introduced by Decher et al [14]. The term layer-by-layer (LbL) deposition is commonly used for this technique. To generate the multilayers the substrate is dipped alternately into solutions of the polyanions and - cations and during each dipping step a new PEL monolayer is adsorbed. Charge overcompensation during adsorption is usually identified as the driving force for the deposition of a new layer. Since attractive electrostatic interactions govern the formation of the PEL multilayers, the conformation of the polymer molecules in the layer and thus the thickness of the multilayer assembly depend on surface charge density, charge density of the PEL and the pH value and ionic strength of the medium during deposition [15-16]. The increase in film thickness through deposition of one additional layer is independent of the number of already deposited layers and is on the order of 0 nm per layer [1,17], the exact value depending on the system used and the deposition
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