Thermal and electrical conductance and thermopower at the nanoscale

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In the previous funding phase, we have set the basis for a detailed study of the electrical and thermal transport properties of hybrid heterostructures consisting of semiconducting materials functionalized by organic molecules. Experimentally, novel methodologies were developed. A new self-assembled monolayers (SAM) soft-contacting method was established which allowed us to obtain the first reliable transport measurements of SAMs contacted by two semiconducting electrodes. We identified different low temperature transport regimes of alkane chains with varying lengths. We also succeeded to "roll-up and press-back" superlattice stacks of different material compositions, mainly semiconducting and metal layers. Preliminary results of the cross-sectional electrical as well as thermal conductivity were obtained using thermoreflectance and local 3ω measurements. In the second period, we will focus on (i) the preparation of micro-patterned contacts to the mesas in order to obtain a complete figure of merit, and (ii) the incorporation of suitable molecular layers with tailored electrical and thermal properties, which will be identified in close cooperation with the theoretical partners. From the modeling point of view, our work progressed in two directions: (a) development of efficient computational methodologies to treat, on a first principle basis, thermal transport in large (experimentally relevant) systems and (b) application of first principle methods combined with Green function techniques to investigate the thermoelectric properties of silicon-molecule-silicon junctions. Hereby a special focus was to demonstrate the possibility of tuning the thermopower of the junction via tailored modifications of the chemical composition of the molecules. In the second funding period, we will apply these methodologies, in close cooperation with the experimental partners, to study (i) electrical and thermal transport in hybrid heterostructures consisting of semiconductor electrodes and pre-defined molecular SAMs, and (ii) to develop a methodology to compute the relevant quantities determining the thermoelectric figure of merit on an atomistic level.