There is continued interest in finding quicker and simpler ways to fabricate nanowires, even though research groups have been investigating possibilities for the past decade. There are two reasons for this interest: first, nanowires have unusual properties-for example, they show quantum-mechanical confinement effects, they have a very high surface-to-volume ratio, enabling them to be used as sensors, and they have the ability to connect to individual molecules. Second, no simple method has yet been found to fabricate nanowires over large areas in arbitrary material combinations. Here we describe an approach to the generation of well-defined nanowire network structures on almost any solid material, up to macroscopic sample sizes. We form the nanowires within cracks in a thin film. Such cracks have a number of properties that make them attractive as templates for nanowire formation: they are straight, scalable down to nanometre size, and can be aligned (by using microstructure to give crack alignment via strain). We demonstrate the production of nanowires with diameter <16 nm, both singly and as networks; we have also produced aligned patterns of nanowires, and nanowires with individual contacts.

Chain mobility in a near surface region at a polystyrene/vacuum interface was investigated by embedding of noble metal nanosized clusters. The embedding process was monitored in situ by X-ray photoelectron spectroscopy. The embedding of nanosized clusters needs long-range chain mobility of the polymer. Therefore, the embedding process is a probe for the glass transition in a near surface region. The clusters used in this study are formed by the dewetting of evaporated noble metals onto the polymer surface. First, methodical influences on the embedding process were investigated. An onset embedding temperature T* was defined. T* increases with a heating rate comparable to T g(bulk) determined with a differential scanning calorimeter. Furthermore, T* increases with nominal metal coverage which results in increasing average cluster radius. The cluster size distribution was investigated by transmission electron microscopy. It is shown that T* is an upper limit for T g in a near surface region with a depth of a few nanometers. With optimized probe conditions, embedding processes were performed on monodisperse polystyrene (M w = 3−1000 kg/mol). The T* values fit quite well with the Fox−Flory relation, but with a saturation temperature of approximately 8 K below the bulk value. ΔT = T g(bulk) − T* increases with molecular weight. This molecular weight dependence of T* will be discussed in terms of several models. The chain end segregation model can be ruled out. To investigate the kinetics of the embedding process, isothermal experiments were performed. From these experiments surface viscosities were derived, which are well below bulk values.

We present a combined analysis of the free volume in polyimide membrane polymers by employing experimental measurements as well as computer simulations. The amount and distribution of free volume in polymeric membranes significantly determine the transport and separation properties.In the present work these free volume characteristics were determined directly from simulated atomistic packing models via a new method. Here a "virtual tracer sphere" probes the simulation cell to determine the unoccupied volume. As an experimental approach, positron annihilation lifetime spectroscopy was used to determine the average size of free volume cavities via a well-established correlation between orthopositronium lifetime and cavity size. We show that the results obtained from the combined analysis provide a valuable basis for the investigation of free volume properties; moreover, limitations of the standard model for the evolution of the positron lifetime data will be discussed.

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