| Summary: | 博士 === 國立臺灣科技大學 === 材料科學與工程系 === 106 === At high operation temperature, the thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. In this work, we take advantage of grain boundary-free structure of thin film metallic glasses (TFMGs) to retard the diffusion between TE materials and metal contact upon thermal aging at 400°C. The room-temperature deformation behaviors of 260 nm-thick TFMGs on bulk metallic glass (BMG) in four-point-bend fatigue and nanoindentation experiments were investigated. During the fatigue tests, TFMGs undergo rubber-like deformation with a large shear strain, estimated to be ∼ 4000%. Additionally, thickness reductions of up to 61.5%, with no shear-banding or cracking, are observed during nanoindentation extending through the film and into the BMG substrate. In both cases, TFMG/BMG samples exhibit film/substrate diffusion bonding at severely shear-deformed regions during deformation.
Then, the 200 nm-thick Zr-based and Ti-based TFMGs were deposited as diffusion barrier layers on Se-doped AgSbTe2 and PbTe-based (including p-type PbTe and n-type I-doped PbTe) TE substrates, respectively. Conventional metals, Ni and Ti, with the identical thickness are also prepared as comparisons. Both TFMGs exhibit good electrical contact resistivity with TE materials (<10-8 Ω∙m^2). For Se-doped AgSbTe2 module, the reaction couples structured with TFMG/TE/Ni are annealed at 400°C for 8–360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion. On the contrary, Ni layer severely reacts with the TE substrate, and forms NiSbxTe2-x IMCs. For PbTe-based TE modules, the reaction couples structured with Cu/TFMG/TE/Ti/Cu annealed at 400°C for 8–96 hours are investigated. Ti-based TFMG layers successfully retard the atomic diffusion from both of PbTe and I-doped PbTe TE substrates. Nevertheless, pure Ti layer reacted significantly with substrate at high temperature and formed TixTe1-x IMCs, resulting in the precipitation of Pb. Hence, the high electrical contact resistivity of Ti/TE is measured which can be ascribed to the vigorous reaction of Ti with PbTe, leading to the formation of IMCs and precipitation of Pb at Ti/PbTe interface as well as the void.
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