NSF/ENG/ECCS-BSF: Self-Assembled Superlattice Nanowires: A Pathway to High Efficiency Thermoelectrics

摘要：非技术性：随着发展中国家继续工业化，能源需求迅速增加；因此，对科学研究驱动的可持续清洁能源的需求越来越大。通常，能源生产和利用系统的效率受到热损失的限制；将废热转换为可用能量可以使用将热能转换为电能的固态设备，即热电设备。热电发电机被用来为卫星、探测器和火星车提供动力，但它们在地面上的广泛使用需要提高设备效率。这个项目探索了一条通往高效率热电材料的途径，使用一种自然发生的现象--自发的垂直相分离--来实现跨越宏观长度的纳米线超晶格。最终目标是了解超晶格中的热传播，以便优化几种先进纳米技术的性能。该项目包括密歇根大学和本-古里安大学之间的合作，将美国研究人员的专业知识(理论和热电表征)与以色列研究人员的专业知识(纳米线制造和表征)相结合。所获得的新知识将通过出版物和演示文稿以及课程编制广泛传播。外展活动强调对妇女和代表不足的少数民族的指导。技术说明：纳米级异质结构材料已被确定为高效率热电设备的有前途的候选者。在声子-玻璃-电子晶体概念的框架内，可以通过降维来提高热电效率，通过形成二维薄膜或超晶格、一维纳米线或零维量子点。事实上，一维导体中的电子被限制在一个很窄的能量范围内，据预测，这种导体的转换效率将接近卡诺极限。该项目的一个主要目标是探索共晶合金催化剂在纳米线的气-液-固生长过程中诱导的垂直相分离。除了发展对这些机制的预测性理解之外，还将制造跨越宏观长度尺度的纳米线超晶格，并将使用扫描热电显微镜演示空间分辨的塞贝克测量。最后，我们将对纳米线中增强热电优值的机理有新的认识。特别是，将使用掺杂和静电门控来研究态密度中的van Hove奇点与Seebeck系数的增强之间的关联，以调节纳米线的费米能级。该团队在纳米线生长、结构和热电表征以及器件模拟和制造方面的专业知识将用于开发一种用于热电发电机的超晶格纳米线的途径。

Abstract:Non-technical: As developing countries continue to industrialize, energy demands are rapidly increasing; thus, there is an increasing need for sustainable clean energy sources driven by scientific research. Typically, the efficiency of energy-production and utilization systems is limited by heat loss; conversion of the wasted heat into usable energy may be accomplished using solid-state devices that convert heat to electricity, i.e. thermoelectrics. Thermoelectric generators are used to power satellites, probes, and rovers, but their widespread terrestrial use would require increased device efficiencies. This project explores a pathway towards high efficiency thermoelectrics using a naturally occurring phenomenon, spontaneous vertical phase separation, to achieve nanowire superlattices that extend over macroscopic lengths. The ultimate goal is to understand heat propagation across the superlattices in order to optimize the performance of several advanced nanotechnologies. The project consists of a collaboration between the University of Michigan and Ben-Gurion University, integrating the expertise of the U.S. investigators (theory and thermoelectric characterization) with that of the Israeli investigators (nanowire fabrication and characterization). The new knowledge gained will be broadly disseminated through publications and presentations, and curriculum development. Outreach activities emphasize the mentoring of women and underrepresented minorities.Technical Description: Nanometer-scale heterostructured materials have been identified as promising candidates for high efficiency thermoelectric devices. In the framework of the phonon-glass-electron crystal concept, the thermoelectric efficiency can be enhanced by reducing dimensionality, through the formation of two-dimensional thin films or superlattices, one-dimensional nanowires, or zero-dimensional quantum dots. Indeed, one-dimensional conductors, in which electrons are restricted to a narrow energy range, are predicted to enable conversion efficiencies approaching the Carnot limit. A primary goal of the project is to explore eutectic alloy catalyst-induced vertical phase separation during vapor-liquid-solid growth of nanowires. In addition to developing predictive understanding of these mechanisms, nanowire superlattices extending over macroscopic length-scales will be fabricated, and spatially-resolved Seebeck measurements will be demonstrated using scanning thermoelectric microscopy. Finally, new understanding of the mechanisms for enhanced thermoelectric figure of merit in nanowires will be developed. In particular, correlations between van Hove singularities in the density of states and enhancements of the Seebeck coefficient will be investigated using both doping and electrostatic gating to tune the Fermi level of the nanowires. The combined expertise of the team in nanowire growth, structural and thermoelectric characterization, and device simulation and fabrication will be used to develop a pathway to superlattice nanowires for thermoelectric generators.