Collaborative Research: Recovery of Waste Heat using Efficient Thermoelectric Devices Based on Laser Sintering of Doped SiGe Nanoparticles

A large amount of energy is wasted through heat dissipation in many industrial processes and consumer systems. This waste of energy occurs as many of the current systems such as refrigerators, automobiles, and industrial process are fundamentally very inefficient and power is wasted as heat. Some of this waste heat could be utilized with low-cost recovery technologies. However, current waste heat conversion devices are very inefficient and are relatively expensive. Hence, research needs to be carried out to find low cost and more efficient solutions for waste heat recovery. The proposed research will investigate a new thermoelectric (thermal-to-electric energy conversion) process for developing efficient waste heat recovery at low cost. The research will also train future scientists and engineers in the energy sector. The principal investigator and co-principal investigator will involve teachers and students in the project and will display materials at the local Science Museum and library as part of outreach and educational activities. The growth of alternative energy technologies will have an important impact on society to meet its energy needs and will lower the nation's dependence on foreign oil thus improving the nation's energy security.

Significant progress has been made in thermoelectric power conversion devices with efficiencies reaching over 10%. To realize the commercial potential of thermoelectric devices, further improvements in efficiency, long-term stability at high temperatures and lower cost of fabrication must be realized. A world-wide research effort is being carried out to realize the above goals. Correspondingly, this proposal consists of a multidisciplinary team of a faculty member from the University of Minnesota (Prof. Kortshagen) with research expertise in novel gas phase synthesis of nanoparticles and a faculty member from the University of Virginia (Prof. Gupta) with research expertise in laser processing and device physics. The research plan is to provide understanding of nanograined thermoelectric materials and to achieve further enhancement in efficiency, long-term stability and reduced fabrication costs. The hypothesis of the research is that nanograined materials can enhance the overall thermoelectric device efficiency by reduction of thermal conductivity due to enormous interfacial area causing enhanced phonon scattering and an increase of Seebeck coefficient due to filtering of electron energy producing a higher voltage. Another hypothesis is that nearly fully-dense films and bulk materials can be realized by pulsed laser sintering of nanoparticles to avoid major grain growth by nanosecond heating and cooling rates. The realization of the goals will be achieved through the following tasks: (1) vapor phase synthesis of SiGe nanoparticles of < 20 nm in size, (2) p- and n- type doping of SiGe nanoparticles during vapor phase synthesis, (3) nanosecond pulsed laser sintering of vapor phase synthesized nanoparticles of SiGe to achieve close to theoretical density, (4) fabrication of thermoelectric devices and evaluation of high-temperature performance up to 1000 °C, and (5) enhancement of research through collaboration with DOE funded thermoelectric materials and device laboratory at Oak Ridge National Laboratory for fundamental understanding of material and device properties at very high temperatures using state of the art high-temperature characterization facility for crystal structures, electrical and thermal properties.