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

摘要：非技术：随着发展中国家工业化进程的不断推进，能源需求快速增长；因此，在科学研究的推动下，对可持续清洁能源的需求日益增加。通常，能源生产和利用系统的效率受到热损失的限制；将废热转化为可用的能量可以通过使用将热转化为电的固态装置，即热电装置来完成。热电发电机用于为卫星、探测器和漫游者提供动力，但在地面上广泛使用热电发电机需要提高设备效率。该项目探索了一条通往高效热电的途径，利用自然发生的现象，自发垂直相分离，来实现延伸到宏观长度的纳米线超晶格。最终目标是了解热在超晶格中的传播，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）结合起来。获得的新知识将通过出版物、演讲和课程编制广泛传播。外联活动强调对妇女和代表性不足的少数民族的指导。技术描述：纳米级异质结构材料已被确定为高效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下，通过二维薄膜或超晶格、一维纳米线或零维量子点的形成，可以通过降维来提高热电效率。事实上，一维导体，其中的电子被限制在一个狭窄的能量范围内，预计可以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纳米线在气-液-固生长过程中的垂直相分离。除了发展对这些机制的预测性理解，纳米线超晶格在宏观长度尺度上的延伸将被制造出来，空间分辨塞贝克测量将使用扫描热电显微镜进行演示。最后，对纳米线中热电性能图增强的机理有了新的认识。特别是，范霍夫奇点在态密度和塞贝克系数增强之间的相关性将被研究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、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.