부산대학교 도서관

Sb2Te3, Bi2Te3 and their alloys have been actively investigated as near-room temperature thermoelectric materials since the first demonstration almost sixty years ago. These materials stirred further interest as the third generation topological insulators in recent past. Nanostructured bulk thermoelectric modules employ these materials for power generation using the thermoelectric effect, where heat can be converted into voltage or vice versa. Thin-films of Sb2Te3 and Bi2Te3 and their hetero-structures are also widely investigated for thermoelectric, topological insulators and memory device applications. In this thesis, Sb2Te3 was chosen to investigate its growth mechanism on supported graphene templates via facile and inexpensive wet chemical bottom-up route. The thermal and electrical transport across the interface of Sb2Te3 and graphene was explored. Bi2Te3, from the same family of materials was employed to study the application to power generation using thermopower wave propagation. Sb2Te3 nano-plates (NPs) were grown directly on graphene templates using microwave assisted solvothermal method. A control over the size of Sb2Te3 NPs was achieved by varying the grain size of the underlying graphene template. The successful growth was realized due to a low lattice mismatch between Sb2Te3 and bridge-sites of graphene and the superior microwave heating of graphene. The interface constructed by the direct growth method was electrically Ohmic, whereas the interface constructed between same materials by a simple drop-casting method was electrically non-conductive exhibiting zero current. The thermal boundary conductance (TBC) of the interface was significantly improved compared to that of Sb2Te3 graphene interface constructed by simple drop-casting method. However, the TBC was not very large due to the very huge acoustic mismatch between Sb2Te3 and graphene based on the difference in the Debye temperatures. In this study, I realized that the mode of synthesis used for constructing an interface is very crucial for superior electrical and thermal transport. I selected Bi2Te3 as a thermal conduit to investigate thermopower wave propagation. Bi2Te3 seemed like an ideal candidate due to its fairly high Seebeck coefficient along with its affinity towards chemical doping. Power generation by thermopower wave propagation was explored and a giant unprecedented peak voltage was achieved. This was due to the right combination of thermal conduit with high Seebeck coefficient, high chemical doping of the conduit by solid fuel and the high aspect ratio device geometry. I also investigated the effect of change of grain size of the thermal conduit on the thermopower wave propagation both experimentally and supported my experimental results by theoretical simulations.