| Summary: | 博士 === 國立交通大學 === 材料科學與工程學系所 === 102 === Directly and efficiently converting natural or artificial waste heat to electricity by thermoelectric power generators is one of the fundamental solutions for reducing the consumption of fossil fuel and thus suppressing the deterioration of the climate due to global warming. Thus far, realizing practical thermoelectric devices with sufficiently high conversion efficiency, however, remains an enormous challenge. Nanostructuring has been theoretically and experimentally demonstrated as a promising strategy to potentially induce quantum effects on specifically benefiting the Seebeck coefficient (S) and electrical conductivity (σ). The abundantly formed interfaces involving various dimensions, topographies, structures and scales would not only significantly suppress the thermal conductivity (к) via enhanced phonon scattering, but even selectively modulate charge carrier transporting in matters under specific conditions and thus finally achieve an applicable level of thermoelectric figure of merit ZT defined as S2σTк-1.
In this dissertation, under the frame of nanostructuring, we proposed four innovative assembling and interfacial engineering to modify or alternate conventional surfaces and interfaces for simultaneously optimizing the transporting behaviors of charged carriers and phonons in maters and thus approached a greatest enhancement in ZTs.
Orderedly assembling of nanocrystals with various dimensions: We have successfully fabricated a series of bismuth telluride (Bi2Te3) nanostructured films respectively and uniformly composed of orderly aligned zero-dimensional (0-D) nanoparticles, 1-D nanorods, 2-D nanoflakes, and 3-D nanocanyons by using pulsed laser deposition (PLD) with the absence of any template and catalyst. Such many highly-uniform nanostructured Bi2Te3 films are the first time prepared using single facile deposition technique. It is worth noting that the 0-D nanoparticles assembled film exhibits an extremely high power factor which is about 1 to 3 orders of magnitude higher than the reported values. The very clean interfaces and surfaces as well as the orderly aligned nanocrystals play as key roles for the present phenomenon.
Superassembling of hierarchical nanostructures: By precisely controlling the deposition parameters, 0-D to 2-D Bi2Te3 nanocrystals are secondly assembled into a series of hierarchical nanostructures on the epitaxial Bi2Te3 bottom layers. The spontaneously formed innovative superassemblies-on-epitaxy structures exhibit an extremely high surface-to-volume ratio and interface-to-volume ratio. The greatly created surface can effectively scatter phonons to have a relatively low thermal conductivity whereas its effects on the carrier transport are limited. In addition, the bottom single crystalline layer further enhances the electrical conductivity to reach an unexpected value.
Orientedly assembling of nanocrystals with coherent interfaces: An innovative concept of twin-enhanced thermoelectricity was proposed to fundamentally resolve the high electrical resistance while not degrading the phonon scattering of the thermoelectric nanoassemblies. Under this frame, a variety of highly oriented and twinned bismuth antimony telluride (BixSb2-xTe3) nanocrystals were successfully fabricated. The significant presence of the nonbasal- and basal-plane twins across the hexagonal BiSbTe nanocrystals, which were experimentally and systematically observed for the first time, evidently contributes to the unusually high electrical conductivity of ~2700 Scm-1 and the power factor of ~25 μWcm-1K-2 as well as the relatively low thermal conductivity of ~1.1 Wm-1K-1 found in these nanostructured films.
Laterally assembling of nanocomposites with hetero-interfaces: We described an innovative concept and facile approach in fabricating laterally assembled Ga2Te3/Te binary nanocomposite films which comprise 2-D quasi-periodic Ga2Te3 nanoassemblies surrounded by interlocking highly-conductive Te single crystals for comprehensively establishing subnano- to micro-scaled multi-style versatile interfaces. The distinct Ga2Te3/Te nanocomposite film exhibits a power factor about 60 times higher than the conventional Ga2Te3 and Te materials reported mainly due to the 2 to 3 orders improved electrical conductivity. Especially noteworthy, the dense lateral heterogeneous interfaces effectively strengthen hot carrier filtering and phonon scattering for obtaining the comparable Seebeck coefficient and ultralow thermal conductivity.
|
|---|
