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，越来越需要科学研究驱动的可持续清洁能源。 通常，能量生产和利用系统的效率受到热损失的限制;可以使用将热转换为电的固态装置（即热电装置）来实现将废热转换为可用能量。 热电发电机用于为卫星、探测器和漫游者提供动力，但它们在陆地上的广泛使用需要提高设备效率。 该项目探索了一条通往高效热电的途径，使用自然发生的现象，自发垂直相分离，以实现在宏观长度上延伸的纳米线超晶格。 最终目标是了解超晶格中的热传播，以优化几种先进纳米技术的性能。该项目由密歇根大学和本-古里安大学之间的合作组成，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。将通过出版物和介绍以及课程编制广泛传播所获得的新知识。推广活动强调对妇女和代表性不足的少数民族的指导。技术说明：纳米尺度的异质结构材料已被确定为高效率热电器件的有前途的候选者。在声子-玻璃-电子晶体概念的框架中，热电效率可以通过减少维度来增强，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，其中电子被限制在一个狭窄的能量范围内，预计使转换效率接近卡诺极限。该项目的主要目标是探索共晶合金催化剂诱导的垂直相分离过程中的气-液-固纳米线的生长。 除了开发这些机制的预测性理解，纳米线超晶格延伸的宏观长度尺度将制造，空间分辨塞贝克测量将使用扫描热电显微镜证明。最后，将开发新的理解的机制，增强热电优值的纳米线。 特别是，货车霍韦奇异性的状态密度和塞贝克系数的增强之间的相关性将使用掺杂和静电门控来调整纳米线的费米能级。该团队在纳米线生长，结构和热电特性以及器件模拟和制造方面的综合专业知识将用于开发热电发电机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.