CAREER: Quantifying and Exploiting Knudsen Thermal Forces in Nano/Microsystems

在微观尺度上，即使是适度的温差也会导致气体分子和浸入气体中的固体之间的非平衡能量交换产生显著的克努森力。利用克努森力为纳米/微系统中的驱动、传感和能量收集提供了新的机制。在气体分子平均自由程尺度上存在较大的热梯度时，气体克努森力是显著的。在涉及微米和亚微米尺寸结构以及气体环境的各种应用中，都会出现这种情况。该计划的计算和实验工作将为当前系统（如原子力显微镜和MEMS结构）中的热克努森力的分析和控制以及未来的高精度热传感器和执行器提供途径。热克努森力的预测需要气相输运过程的动力学理论描述，这超出了传统宏观计算模型的能力。计算研究的基础是确定解的波耳兹曼动力学方程的耦合气固热相互作用在亚连续统制度。在广泛条件下的高保真仿真的基础上，开发了克努森力的封闭模型。该模型将通过扫描激光多普勒振动测量技术在控制环境气体压力和真空探测站热条件下集成纳米级加热器的微结构的实验测量来验证。这些实验将提供与实际工程纳米/微系统应用相关的几何形状中克努森力的直接校准测量。研究成果将整合到分子气体动力学和纳米/微系统工程课程中。将创建一个用于模拟N/MEMS中克努森力效应的交互式在线工具，并通过nanoHUB （http://nanohub.org）向全球研究和教育界提供。这项研究还与教育活动相结合，旨在吸引和留住少数民族学生，并为本科学生在职业生涯早期提供研究机会。

1055453Alexeenko At the microscale, even moderate temperature differences can result in significant Knudsen forces generated by the non-equilibrium energy exchange between gas molecules and solids immersed in the gas. Exploiting the Knudsen force offers novel mechanisms for actuation, sensing, and energy harvesting in nano/microsystems. The gas Knudsen forces are significant in the presence of thermal gradients that are large on the scale of the gas molecular mean free path. Such conditions occur and can be created in a wide variety of applications involving micron-and submicron-sized structures and a gas ambient. The aligned computational and experimental efforts in this program will provide a pathway for analysis and control of thermal Knudsen forces in current systems "such as atomic force microscopy and MEMS structures" and for future high-precision thermal sensors and actuators.Prediction of thermal Knudsen forces requires kinetic theory description of transport processes in the gas phase, which is beyond the capabilities of conventional macroscopic computational models. The basis for computational investigation is the deterministic solution of Boltzmann kinetic equations for coupled gas-solid thermal interaction in the subcontinuum regime. Closed-form models for Knudsen force will be developed based on the high-fidelity simulations for a wide range of conditions. The modeling will be validated by experimental measurements using Scanning Laser Doppler Vibrometry of microstructures with integrated nanoscale heaters under controlled ambient gas pressure and thermal conditions in a vacuum probe station. The experiments will provide direct calibrated measurements of Knudsen forces in geometries relevant for applications in practical engineered nano/microsystems. The research results will be integrated into the courses on molecular gas dynamics and nano/microsystems engineering. An interactive online tool for simulation of Knudsen force effects in N/MEMS will be created and made available to a worldwide research and education community through nanoHUB (http://nanohub.org). This research is also combined with educational activities aimed at attracting and retaining minority students and providing research opportunities for undergraduate students early in their careers.