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

在许多工程系统中，如汽车和涡轮机械，大量的能量以废热的形式损失掉。通过适当的能量转换机制有效地清除此类废热，可获得显著的能量增益。一个特别有希望的机会在于将时间上的温度梯度转化为电能，这被称为热释电效应。本项目将利用实验和理论建模来探索纳米线中的热释电效应，并将构建基于热释电的能量收集微器件原型。研究将有助于了解纳米线热释电效应的本质，包括从纳米线器件中可能实际收获的能量，性能限制等，这将有助于指导势能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少数民族服务机构，位于人口密集的西班牙裔地区。pi将利用这个机会激励和招募少数民族和女性学生进入新兴的纳米/微尺度能量收集领域。pi将在当地高中开展外展活动，以激发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。这项结合实验和理论模拟研究的技术目标是测量和表征纳米线（GaN， ZnO等）中的热释电效应，以开发用于热能收集和传感器应用的微纳米级器件。尽管热释电效应有将废热转化为可用电的潜力，但它在很大程度上尚未被探索，特别是在微/纳米尺度上。这部分是由于缺乏在小尺度上描述这种效应的方法。最近的理论发现表明，纳米线的热释电系数显着提高，类似于纳米线的热电和压电性能的增强，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特性。此外，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（单个纳米线；纳米线阵列）的热释电响应；(3)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极化分布的强非均匀性和可能的声子和电子限制效应。在实验和理论的基础上，利用单纳米线和纳米线阵列构建基于热释电的能量收集微器件原型。纳米线热释电系数的实验数据以及与纳米线尺寸、温度等的关系将有助于对这一效应的基本理解。对单纳米线中热释电输运的基本理解可能会导致利用纳米级材料工程来优化热释电性能的高效能量转换器件的新范式。

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.