Collaborative Research: EAGER: Enhancing Pyroelectric Effects in Nanostructured Materials for High-Efficiency Energy Conversion

在汽车和透平机械等许多工程系统中，大量的能量以余热的形式损失。通过适当的能量转换机制有效地清除这种废热，可以获得显著的能量收益。一个特别有希望的机会在于将时间上的温度梯度转换为电能，即热释电效应。本项目将利用实验和理论模型来探索纳米线中的热释电效应，并将建立基于热释电的能量收集微器件的原型。研究将有助于理解纳米线中热释电效应的性质，包括基于纳米线的器件可能实际获得的能量值、性能限制等，这将有助于指导潜在能量转换器件的进一步发展。参与这项合作研究的所有三家机构都是位于拉美裔人口稠密地区的少数族裔服务机构。PIS将利用这一机会激励和招收少数族裔和女性学生进入新兴的纳米/微米级能源收集领域。PIS将在当地高中开展活动，激发K-12学生对能源收集的兴趣，并鼓励他们考虑进一步的STEM教育和职业生涯。这项实验和理论模拟相结合的研究的技术目标是测量和表征纳米线(GaN，ZnO等)的热释电效应。用于开发用于热能收集和传感器应用的微米和纳米级设备。尽管热释电有将废热转化为可用电能的潜力，但热释电效应在很大程度上还没有被探索出来，特别是在微/纳米尺度上。这在一定程度上是因为缺乏在小范围内描述这种影响的方法。最近的理论发现表明，纳米线具有显著更高的热释电系数，类似于在纳米线的热电和压电性能方面观察到的增强，尽管这一预测尚未得到实验证实。在这项工作中，将开发一种基于微制造器件的方法来定量测量和表征单个悬浮纳米线的热释电性质。此外，还将开发理论模型和计算工具，用于(I)解释和分析实验热释电数据；(Ii)预测各种纳米结构材料(单独的纳米线；纳米线阵列)的热释电响应；以及(Iii)优化纳米结构参数(材料组成、尺寸、形状、界面)以提高热释电电压。所提出的模型将包括纳米结构中偏振分布的强烈不均匀以及可能的声子和电子限制效应。在实验和理论学习的基础上，将利用单个纳米线和阵列纳米线构建基于热释电的能量采集微器件的原型。纳米线热释电系数的实验数据以及纳米线尺寸、温度等对热释电系数的依赖关系将有助于从根本上理解这一效应。对单根纳米线中热释电输运的基本了解可能会导致一种新的高效能量转换装置的范例，该装置利用材料的纳米工程来优化热释电性能。

A large amount of energy is lost as waste heat in many engineering systems such as automobiles and turbomachinery. Significant energy gains may be obtained by efficiently scavenging such waste heat through appropriate energy conversion mechanisms. One particularly promising opportunity lies in the conversion of temperature gradients in time into electricity, referred to as the pyroelectric effect. This project will utilize experiments and theoretical modeling to explore the pyroelectric effect in nanowires, and will build prototype pyroelectric-based energy harvesting microdevices. Research will help understand the nature of pyroelectric effect in nanowires, including the amount of energy that may be realistically harvested from nanowire based devices, performance limits, etc. which will help guide further development of potential energy conversion devices. All three institutions involved in this collaborative research are minority serving institutions located in highly populated Hispanic areas. PIs will leverage this opportunity to excite and recruit minority and women students to the emerging nano/microscale energy harvesting area. The PIs will carry out outreach to local high schools to excite K-12 students about energy harvesting, and encourage them to consider further STEM education and careers.The technical goal of this combined experimental and theoretical-simulation research is to measure and characterize the pyroelectric effect in nanowires (GaN, ZnO, etc.) for developing micro- and nano-scale devices for thermal energy harvesting and sensors applications. Despite its potential to convert waste heat into usable electricity, the pyroelectric effect has been largely unexplored, in particular at the micro/nanoscale. This is partially due to lack of methodologies for characterization of this effect at small scales. Recent theoretical findings suggest a dramatically higher pyroelectric coefficient in nanowires, similar to enhancements observed in thermoelectric and piezoelectric performance of nanowires, albeit this prediction has not been confirmed experimentally. In this effort, a methodology based on microfabricated devices will be developed to quantitatively measure and characterize the pyroelectric properties of individual suspended nanowires. In addition, theoretical models and computational tools will be developed for (i) interpretation and analysis of the experimental pyroelectric data; (ii) prediction of the pyroelectric response of various nanostructured materials (individual nanowires; nanowires arrays); and (iii) optimization of the nanostructure parameters (material composition, size, shape, interface) for enhancing the pyroelectric voltage. The proposed models will include strong non-uniformity of the polarization distribution in nanostructures and possible phonon and electron confinement effects. Based on the learning from experiment and theory, prototype pyroelectric-based energy harvesting microdevices will be built using a single and an array of nanowires. Experimental data on pyroelectric coefficient of nanowires and dependence on nanowire size, temperature, etc. will contribute to the fundamental understanding of this effect. A fundamental understanding of pyroelectric transport in single nanowires may lead to a new paradigm of high efficiency energy conversion devices that take advantage of nanoscale engineering of materials to optimize pyroelectric performance.