Experiments and Models on Room Temperature Creep of Nanocrystalline Metallic Films

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。本研究计划将实验与模型相结合，为纳米晶金属薄膜的室温蠕变问题开发基于物理的预测模型。该实验旨在直接提取晶界滑动粘度和晶界扩散系数。模型实验与原子力显微镜测量相结合，将得到位移跳跃作为时间的函数。测量到的局部GB参数将被纳入多晶Au多尺度模型中GB的内聚模型，以量化非弹性GB机制对纳米晶Au薄膜蠕变响应的影响。虽然其他均质方案使用宏观尺度材料行为来拟合微观尺度参数，但所提出的多尺度实验/建模方案使用宏观尺度实验来验证多尺度建模预测。这个项目可以产生重大的技术和教育影响。一些薄膜应用，如射频微机电系统，可变电容器和可调谐滤波器，涉及固定的固定金属结构，由于室温下的蠕变而遭受机械刚度损失。纳米晶金属中GB机制的量化将允许采取缓解策略，以防止室温蠕变，但保持由位错晶体塑性控制的高屈服强度。一旦完善，这些实验将被整合到PI的实验课程“纳米尺度接触力学”中，该课程通过遵循力学“自下而上”的方法，为研究生提供理论和实验教育和培训。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This research project integrates experiments and modeling to develop physics-based predictive models for the problem of room temperature creep in nanocrystalline metallic films. The novel experiments aim at extracting directly the grain-boundary (GB) sliding viscosity and the GB diffusivity. Model experiments augmented with atomic force microscopy measurements will obtain the displacement jumps as a function of time. The measured local GB parameters will be incorporated in cohesive models for the GBs in a multiscale model for polycrystalline Au to quantify the effect of inelastic GB mechanisms on the creep response of nanocrystalline Au films. While other homogenization schemes use the macroscale material behavior to fit microscale parameters, the proposed multiscale experimental/modeling protocol employs macroscale experiments to validate the multiscale modeling predictions.This project can have significant technological and educational impacts. Several thin film applications, such as radio frequency microelectromechanical systems, variable capacitors and tunable filters involve fixed-fixed metal structures that suffer from loss of mechanical stiffness due to creep at room temperature. Quantification of the GB mechanisms in nanocrystalline metals will allow for mitigating strategies to prevent room temperature creep but maintain the high yield strength that is controlled by dislocation crystal plasticity. Once perfected, the experiments will be integrated in the PI's experimental course "Nanoscale Contact Mechanics" that provides theoretical and experimental education and training to graduate students by following a "bottom-up" methodology in mechanics.