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

在许多工程系统中，如汽车和内燃机，大量的能量以废热的形式损失。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增益。一个特别有希望的机会在于将温度梯度及时转换为电力，称为热电效应。该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，并将建立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中热释电效应的性质，包括从基于纳米线的器件中实际收集的能量的量、性能限制等，这将有助于指导潜在能量转换器件的进一步开发。参与这项合作研究的所有三个机构都是位于人口稠密的西班牙裔地区的少数民族服务机构。PI将利用这个机会激发和招募少数民族和女性学生到新兴的纳米/微米级能量收集领域。PI将在当地高中开展推广活动，激发K-12学生对能量收集的兴趣，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。用于开发用于热能收集和传感器应用的微米和纳米级器件。尽管它有潜力将废热转化为可用的电力，但热释电效应在很大程度上尚未开发，特别是在微米/纳米级。这部分是由于缺乏在小尺度上表征这种影响的方法。最近的理论研究结果表明，纳米线中的热释电系数显着更高，类似于纳米线的热电和压电性能中观察到的增强，尽管这一预测尚未得到实验证实。在这项工作中，将开发一种基于微加工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;以及（iii）优化纳米结构参数（材料成分，尺寸，形状，界面）以提高热释电电压。所提出的模型将包括强烈的非均匀性的偏振分布在纳米结构和可能的声子和电子约束效应。基于实验和理论的学习，将使用单个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。纳米线的热释电系数以及热释电系数与纳米线尺寸、温度等的关系的实验数据将有助于对这种效应的基本理解。对单根纳米线中热释电传输的基本理解可能会导致一种新的高效能量转换器件的范例，该器件利用材料的纳米级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.