Clusters on soft matter surfaces

Clusters built from metals, semiconductors and dielectric materials, whether they are bare or coated by ligand molecules, interact in many different ways with soft matter. The ensuing phenomena are of great relevance for technical problems such as metal/polymer interfaces, but also to fundamental questions such as controlled charging of single clusters. Clusters on soft matter may be employed for nanotechnology, when a collective physical property of an assembly of many clusters is aimed at. Most interesting is the fact that the interaction with a solid substrate that supports the soft layer can be suppressed. This means that the clusters are adsorbed, but preserved as entities, and hence their size-dependent physical properties are not affected by coupling to the solid substrate (e.g. optical excitation or electronic properties). Soft matter is anything but a well-defined term, but thin layers and organic molecules assembled on solid substrates can exhibit excellent ordering and conformational stability, and a wide range of highly interesting and finely tunable chemical properties. The layers can be organic monolayers such as self-assembling monolayers, but also two-dimensional arrangements of proteins. The surfaces of polymers and organic crystals are very nicely comparable to such systems. In all cases, the surfaces may show conformational flexibility, but their composition and atomic arrangement (in each molecule) are well defined. Special cases are inert gas layers at low temperature, used for soft landing of clusters, again with the aim of preserving the clusters' properties. Typically a cluster/soft matter system is prepared by vacuum deposition, adsorption from solution, or by electrochemical or chemical synthesis, all of which are considered here. For a proper description of the system, cluster/surface interactions can be treated macroscopically, inspired from colloid science, but also microscopically on the atomic level. (c) 2006 Elsevier B.V. All rights reserved.