Investigation of thermoelectric nanomaterials

Thermoelectric conversion remains an active research field in light of its potential to enhance energy efficiency by waste heat recovery in a noise and wear-free manner.Nanostructuring is responsible for most of the recently reported improvements of the figure of merit. Measuring thermoelectric properties of such materials on the microscale is advantageous. But although elaborate microdevices for complete thermoelectric characterization have been fabricated, a demanding transfer of the samples onto these devices is generally required and establishing sufficient electrical contact is challenging in this case. Therefore considerable effort was made first to develop a complete and transfer free in-plane characterization method for samples obtained by deposition processes. The accuracy of the method was verified by numerical studies closely mimicking the actual measurement process, comparison to measurements on simultaneously deposited reference samples and results from literature.The developed devices were then applied to samples of interest, i.e. thin films, bismuth rich deposits and composition modulated multilayers, resulting in improvements compared to as-deposited bulk samples in some cases. First attempts at fabricating bismuth telluride - polypyrrole multilayers by electrodeposition are also presented. Based on modeling of the electronic properties of multilayers, upon further refinement, improved conversion efficiency in these structures is expected due to quantum confinement effects. Modeling results of size effects on the lattice thermal conductivity are also discussed and a two-band model describing the bulk electronic properties of bismuth telluride is used to determine the level of doping.