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

纳米结构中的热输运呈现出新颖且令人兴奋的现象，例如表面和界面边界散射以及声子谱限制效应，这为通过设计制造具有所需特性的材料提供了新的自由度。已经表明，超晶格、纳米线和纳米复合材料中的热导率降低可以导致热电优值的显著增强，这可以对制冷和废热回收产生变革性影响。目前，大多数纳米结构材料的热电能量转换的研究是单晶超晶格薄膜制造的电子束外延生长，这是非常昂贵的，或单独的纳米线，这构成了巨大的挑战，在集成到功能复合材料。因此，纳米结构的材料，可以制造成本效益，但具有纳米约束效应的声子输运的极大兴趣。 该探索性研究项目是制备用于热电能量转换的纳米结构复合材料的新方法。更具体地说，我们将采用脉冲电子束沉积（PED），一种新的，多功能的，具有成本效益和用户友好的薄膜/纳米颗粒沉积技术，以制造PbTe/CdTe纳米复合材料，并研究通过制造的材料与3D技术的热输运。我们选择存款PbTe/CdTe纳米复合材料，因为块体PbTe在200 °C和500 °C的温度范围内表现出最好的热电性能。此外，我们已经取得了初步的进展，在我们的实验室与PED系统制备这些材料。所制造的PbTe/CdTe纳米结构薄膜将具有用作基质的相对厚的PbTe层和作为材料中的嵌入纳米结构的纳米尺度CdTe层或纳米颗粒。我们预计，除了合金散射，基质材料将有效地散射高能量，短波长的声子，和纳米结构的CdTe将提供额外的散射机制的长波长的声子。因此，我们可以有效地降低所制造的材料的热导率使用类似的机制，为单晶超晶格薄膜或量子复合材料。该研究计划的最终目标是创造一种具有成本效益的方法来大规模制造纳米结构的高性能热电材料。建议的研究计划的智力价值在于与新的PED系统的PbTe/CdTe纳米复合材料的制造和通过制造的纳米复合材料的热传输的理解。如果成功，这项研究将为高性能热电材料的成本效益，大批量生产铺平道路。此外，在本研究中，我们将获得有关高能电子束和靶之间的相互作用以及这些相互作用将如何影响材料制造过程和所得材料的知识。关于更广泛的影响，PED系统是一种相对较新的材料沉积技术，并且沉积工艺尚未得到很好的理解，因此所获得的关于沉积工艺的知识将对使用PED技术的其他材料制造产生广泛的影响。这SGER支持将帮助菲斯克大学，HBCU机构，建立一个长期的研究和教育计划，在热科学。这些活动将促进两所大学之间的跨学科互动，并作为加强代表性不足的少数民族学生教育的一个重要步骤。

CBET-0829977MuThermal 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.