Synthesis and transport properties of interconnected BiSb nanowire networks

This master thesis focuses on the synthesis and transport properties of interconnected BiSb nanowire networks, with a particular emphasis on the thermoelectric properties. The use of track-etched polymer membranes with crossed nanopores has proven to be an effective template for the growth of interconnected nanowire networks by electrodeposition from a single electrolytic bath. The resulting structure offers mechanical stability and electrical conductivity within a self-supported sample, while the polymer template provides flexibility and thermal stability. Additionally, electrons flow along the nanowire axis, while the global transport of heat and charges occurs in the centimeter-scale film plane. This configuration allows for suitable macroscopic electrical and thermal measurements to be performed by creating a four/two-probe design after removing a part of the metallic cathode via chemical etching. Through various experiments, it was discovered that the Seebeck coefficient of networks made of interconnected BiSb nanowires of 230 nm diameter and 4.5% Sb is larger in absolute value (S ~ -69 [µV/K]) than pure Bi (S ~ -61 [µV/K]) at room temperature. Moreover, it was found that the Seebeck coefficient of these nanowire networks can be significantly enhanced through annealing, thereby improving their overall thermoelectric properties. Indeed, by annealing at 210°C or at 250°C for one minute, an increase of 14.3% was observed (S ~ -80 [μV/K]). These findings highlight the potential for utilizing interconnected BiSb nanowire networks in thermoelectric applications, and the importance of optimization techniques such as annealing in achieving optimal performance. Overall, this thesis contributes to the ongoing research efforts in the field of thermoelectricity and provides valuable insights into the properties and behaviour of interconnected BiSb nanowire networks.