We demonstrate the excitation of dark plasmon modes with linearly polarized light at normal incidence in self-assembled layers of gold nanoparticles. Because of field retardation the incident light field induces plasmonic dipoles that are parallel within each layer but antiparallel between the layers resulting in a vanishing net dipole moment.Using micro-absorbance spectroscopy we measured a pronounced absorbance peak and reflectance dip at 1.5 eV for bi-and trilayers of gold nanoparticles with a diameter of 46 nm and 2 nm interparticle gap size. The excitation was identified as the dark interlayer plasmon by finite-difference time-domain simulations. The dark plasmon modes are predicted to evolve into standing waves when further increasing the layer number which leads to 90% transmittance of the incident light through the nanoparticle film. Our approach is easy to implement and paves the way for large-area coatings with tunable plasmon resonance.

High thermal conductivity, low thermal expansion and low density are three important features in novel materials for high performance electronics, mobile applications and aerospace. Spark plasma sintering was used to produce light metal–graphite composites with an excellent combination of these three properties. By adding up to 50 vol.% of macroscopic graphite flakes, the thermal expansion coefficient of magnesium and aluminum alloys was tuned down to zero or negative values, while the specific thermal conductivity was over four times higher than in copper. No degradation of the samples was observed after thermal stress tests and thermal cycling. Tensile strength and hardness measurements proved sufficient mechanical stability for most thermal management applications. For the production of the alloys, both prealloyed powders and elemental mixtures were used; the addition of trace elements to cope with the oxidation of the powders was studied.

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High thermal conductivity (TC) and a tunable coefficient of thermal expansion are essential properties for heat management materials operating in a wide temperature range. We combine both properties in a composite with a low-density metal matrix reinforced with pitch-based carbon fibres. The thermal conductivity of the metal matrix was increased by 50%, the thermal expansion coefficient was reduced by a factor of five. The samples were produced by powder metallurgy and have a planar random distribution of fibres, leading to high performance in two dimensions.Surface of a metal matrix composite with 50% carbon fibre (CF) strengthening (optical microscope, 20Â magnification). RapidResearch Letter 1700090 (4 of 5) V. Oddone and S. Reich: Thermal properties of metal matrix composites ß

Light materials with high thermal conductivity and low thermal expansion have a wide application potential for the thermal management of high performance electronics, in particular in mobile and aerospace applications. We present here metal matrix composites with a mixture of graphite flakes and pitch based carbon fibres as filler. The production by Spark Plasma Sintering orients the filler particles on to a plane perpendicular to the pressing axis. The obtained materials have lower density than aluminium combined with a thermal conductivity significantly outperforming the used metal matrix. Depending on the ratio of the filler components, a low thermal expansion along the pressing direction (high graphite flakes content) or across the pressing direction (high carbon fibre content) is achieved. For a 1:3 ratio of carbon fibres to graphite we measured an isotropic reduction of the thermal expansion of the matrix by up to 55%. We present a detailed characterisation of composites with two aluminium alloys as matrix and an overview of the properties for six different metal matrices including magnesium and copper. With the goal of a technical application, we show that the described properties are intrinsic to the material compositions and are achieved with a wide spectrum of production methods.