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New nano structure approaches for bulk thermoelectric materials


A sustainable supply of environmentally clean energy is one of the most significant challenges facing the 21st century as fossil fuel supplies are decreasing and world energy demand keeps increasing. The field of thermoelectric (TE) materials and devices, for efficient solid state cooling and power generation, has expanded significantly in recent years partly due to the advent of nanotechnology and the promise of higher efficiencies of electrical energy versus thermal energy inter-conversion. Such solid-state refrigeration and power generation based on thermoelectric phenomenon offer significant promises to technical applications in the computer, energy conversion, and consumer market applications. While the area itself has been investigated since the 1950's, traditional bulk thermoelectric materials, such as Bi₂Te₃ generally had low efficiencies (228}06 %) for commercial energy conversion applications. However, a deeper utilization of nanoscience at the quantum mechanical level and fabrication of lower dimensional materials such as nanowires and quantum wells, has shown promise of greatly increasing the energy conversion efficiency. Lower dimensional materials, such as nanoscale thin films and nanowires, have been predicted to have large thermoelectric figures of merit and conversion efficiencies of waste heat to useful energy for practical application, and there are strong indications that this is possible. However, ultimately one needs large volumes of active thermoelectric material for an overall high efficiency. This is, at the present time, not feasible as the typical manufacturing of bulk volumes from low dimensional structures is time consuming and difficult. In this thesis, we lay out several practical schemes to incorporate nanoscale features in bulk- fabricated thermoelectric materials for easy fabrication and a high thermoelectric figure of merit, ZT. We propose to fabricate a novel nanostructure material to impart low dimensional confinement and nanoscale defects for a high figure of merit. Various unique architectures and associated process techniques as well as device applications are introduced. It is anticipated that these techniques will lead to many novel thermoelectric materials, innovative and useful materials processing technologies, and technical applications for efficient thermal management and energy conversion of sunlight and automobile waste heat

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