Type of publicationArticle (peer-reviewed) Link to publisher's versionhttp://dx.doi.org/10.1039/c3sm27130gAccess to the full text of the published version may require a subscription. The stability of polystyrene thin films of low molecular weight on a solid substrate is shown to be controlled by the presence of uniformly distributed gold sputtered at the air-polymer interface. Continuous gold coverage causes the formation of wrinkles. High coverage and Au nanoparticle (NP) density leads to the development of a spinodal instability while low coverage and NP density retards the nucleation dewetting mechanism that beads up the thin polymer film into drops when no coverage is 10 present. Heating at temperature larger than the polymer glass transition temperature for extended periods allows the gold NPs to coalesce and rearrange. The area of polymer surface covered by NPs decreases as a result and this drives the films from unstable to metastable states.When the gold NPs are interconnected by polymer chains a theoretically predicted spinodal instability that patterns the film surface is experimentally observed. Suppression of the instability and a return to a flat film occurs when the 15 polymer interconnections between particles are broken. While the polymer films maintain their physical continuity changes in their chemical surface composition and thickness are observed. The observed film metastability is nevertheless in agreement with theoretical prediction that includes these surface changes. Rights

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The stability of thin poly(methyl-methacrylate) (PMMA) films of low molecular weight on a solid substrate is controlled by the areal coverage of gold nanoparticles (NPs) present at the air-polymer interface. As the polymer becomes liquid the Au NPs are free to diffuse, coalesce, and aggregate while the polymer film can change its morphology through viscous flow. These processes lead at the same time to the formation of a fractal network of Au NPs and to the development of spinodal instabilities of the free surface of the polymer films. For thinner films a single wavelength is observed, while for thicker films two wavelengths compete. With continued heating the aggregation process results in a decrease in coverage, the networks evolve into disordered particle assemblies, while the polymer films flatten again. The disordering occurs first on the smallest scales and coincides (in thicker films) with the disappearance of the smaller wavelength. The subsequent disordering on larger scales causes the films to flatten.

Emissive probes are standard tools in laboratory plasmas for the direct determination of the plasma potential. Usually they consist of a loop of refractory wire heated by an electric current until sufficient electron emission. Recently emissive probes were used also for measuring the radial fluctuation-induced particle flux and other essential parameters of edge turbulence in magnetized toroidal hot plasmas [R. Schrittwieser et al., Plasma Phys. Controlled Fusion 50, 055004 (2008)]. We have developed and investigated various types of emissive probes, which were heated by a focused infrared laser beam. Such a probe has several advantages: higher probe temperature without evaporation or melting and thus higher emissivity and longer lifetime, no deformation of the probe in a magnetic field, no potential drop along the probe wire, and faster time response. The probes are heated by an infrared diode laser with 808 nm wavelength and an output power up to 50 W. One probe was mounted together with the lens system on a radially movable probe shaft, and radial profiles of the plasma potential and of its oscillations were measured in a linear helicon discharge.

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