The influence of finite size on phase behavior

Max Wolff (Uppsala University, Sweden)

From every days life one knows that the friction, while skating or skiing on ice or snow, is relatively low. This is an interesting phenomena, since one would assume a much higher friction coefficient for two solids in contact to each other. During the scientific debate different explanations, like pressure or heat induced melting, were proposed but it turned out that skating and skiing is facilitated by the fact that even for temperatures below 0 °C a thin layer of water is still liquid close to the surface and one actually slides on a liquid lubrication layer.

The example of skating on water deals with two semi-infinite materials in contact to each other. If two interfaces come close to each other confinement is introduced and the question arises whether a thin layer of water would freeze at all. From thermodynamic considerations it is known that the physical properties of a system are altered whenever the size approaches the length scales of a certain interaction. A systematic way of studying boundary and finite size effects is to confine a material by well defined boundaries in a specific volume or layer thickness.

For solid materials artificial confinement can be generated by growing extremely thin layers, e.g. by magnetron sputtering or molecular beam epitaxy (MBE), and sandwich them between two layers. Such a configuration is a useful root to enhance interface and finite size effects, since the material of interest in confined, with full control of the layer thickness and boundary conditions. In this presentation an overview of the recent research activities in the Material Physics division at Uppsala University will be given. Examples are taken from magnetic thin films, transition metal hydrides and liquid/polymer systems. Particular emphasis will be directed towards the use of neutron beams for the investigation of such systems.

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