SGER - Pulsed Electron-Beam Deposition of PbTe/CdTe Nanocomposites and Thermal Property Study

Fisk University, Nashville TN

Investigators

Abstract

CBET-0829977 Mu Thermal transport in nanostructures presents novel and exciting phenomena, such as surface and interfacial boundary scattering and phonon spectrum confinement effects, which offer new degrees of freedom to fabricate materials of desirable properties by design. It has been shown that reduced thermal conductivity in superlattices, nanowires, and nanocomposites can lead to a significant enhancement of thermoelectric figure of merit, which could produce transformative impacts to refrigeration and waste heat recovery. Currently, most nanostructured materials under investigation for thermoelectric energy conversion are either single crystalline superlattice thin films fabricated by e-beam epitaxial growth, which is very expensive, or individual nanowires, which pose great challenges in integration into functional composites. Therefore, nanostructured materials that can be fabricated cost-effectively, yet possess nanoconfinement effects on phonon transport are of great interest. This exploratory research project is a novel approach to fabricate nanostructured composite materials for thermoelectric energy conversion. More specifically, we will employ Pulsed Electron-beam Deposition (PED), a new, versatile, cost-effective and user-friendly thin film/nanoparticle deposition technique, to fabricate PbTe/CdTe nanocomposite materials and investigate the thermal transport through the fabricated material with the 3ù technique. We choose to deposit PbTe/CdTe nanocomposite materials because bulk PbTe has shown the best thermoelectric performance in the temperature range of 200 °C and 500 °C. In addition, we have made initial progress in fabricating these materials with the PED system in our lab. The fabricated PbTe/CdTe nanostructured thin films will have relatively thick PbTe layers serving as the matrix and nanometer scale CdTe layers or nanoparticles as the embedded nanostructure in the materials. We expect that in addition to the alloy scattering, the matrix materials will effectively scatter the high energy, short wavelength phonons, and the nanostructured CdTe will provide additional scattering mechanisms to the long wavelength phonons. Therefore, we can effectively reduce the thermal conductivity of the fabricated materials using similar mechanisms to those for single crystalline superlattice thin films or quantum composites. The ultimate goal of this research program is to create a cost-effective approach to fabricate nanostructured high performance thermoelectric materials at large scale. The intellectual merit of the proposed research program resides in the fabrication of the PbTe/CdTe nanocomposite materials with the novel PED system and the understanding of thermal transport through the fabricated nanocomposite materials. If successful, this research will pave the road to cost-effective, large-volume production of high-performance thermoelectric materials. In addition, in this research we will acquire the knowledge on the interactions between the energetic electron beam and the target and how these interactions will affect the material fabrication process and the resulted materials. With regard to broader impacts, the PED system is a relatively new materials deposition technique and the deposition process is not well understood yet, so the acquired knowledge on the deposition process will have extensive impacts on other material fabrication using the PED technique. This SGER support will help Fisk University, an HBCU Institution, to establish a long-lasting research and education program in thermal science. The activities will foster cross-disciplinary interactions between two universities and serve as a major step to enhance underrepresented minority student education.