Silicon-based nanocomposites for thermoelectric applications

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The main goal of this project is the realization of efficient and sustainable silicon based thermoelectric materials. In this second funding period, the so called “nanoparticle in alloy” approach, theoretically proposed in the literature, forms a guide line. It combines the efficient scattering of phonons with short wavelengths on irregularly positioned atoms in common alloys with the efficient scattering of phonons with long wavelengths on larger structures, like nanoparticles. Metal silicide nanoparticles are considered for this purpose. Two coupled particle reactors, developed during the first funding period, allow for the realization of this concept. The concept includes also the approach of modulation doping, were small areas with very high doping concentrations alternate with areas of low doping concentration. This allows for electronic transport pathways without Coulomb scattering on charged dopants, while the clusters of dopants act as efficient centers for phonon scattering. For bulk samples, a current assisted sintering process has to be developed, in order to maintain the desired “nanoparticle in alloy”-structure and to prevent a general alloying of all components or a phase separation during sintering. For thin films, a multilayer approach will be used, where the laser annealing process will be combined with hydrogenation in DC plasmas or microwave heating. The thermal conductivity of the thin films will be measured with methods developed within this priority program by the Group of Prof. Völklein as well as with an optical non-contact method based on the mirage effect. In order to get a deeper insight into thermoelectric properties and structure forming processes, a 3D-Onsager network model will be developed, where input is taken from the molecular dynamic modelling of the microscopic processes during compaction.