A Novel Non-Contact Technique for Dynamic Loading of Thin Film Materials Using Finite Amplitude Mechanical Stress Waves

该项目旨在开发一种基于激光的新技术，用于产生有限幅度的表面声波应力波。该技术将有助于理解薄膜材料在超声频率下的非线性弹性响应。这一发展将导致使用非线性弹性应力波对各种非线性弹性性质进行定量测量，包括薄膜界面的退粘和断裂强度。该技术使用聚焦在样品表面上的激光光源，通过热弹性效应产生平面表面声应力波。利用路径稳定的迈克尔逊干涉仪监测激光产生的应力波。通过以表面波的相速度扫描样品表面上的激光线源，应力波的幅度随距离不断放大。这项技术将能够以每秒一百万以上的应变率加载应变幅度约为0.01的薄膜材料。该技术的无接触特性允许对应力波的产生和传播过程进行准确的建模，从而可靠地提取薄膜材料的特性。如果该项目成功，该技术将能够对包括MEMS和NEMS器件在内的基于薄膜的小型结构的机械可靠性和稳定性进行定量评估。这些特性对于它们成功集成到更复杂的微电子设备中至关重要。此外，该项目还与各种教育活动相结合，包括研究生课程充实、研究生培训和面向高中生的外联活动。

This project seeks to develop a new laser based technique for the generation of finite amplitude surface acoustic stress waves. The proposed technique would facilitate the understanding of the nonlinear elastic response of thin film materials at ultrasonic frequencies. This development would lead to quantitative measurement of various nonlinear elastic properties including; decohesion and fracture strength of thin film interfaces, using nonlinear elastic stress waves. The technique uses a laser source focused to line on a sample surface to generate plane surface acoustic stress waves through the thermoelastic effect. The laser generated stress waves are monitored using a path stabilized Michelson interferometer. By scanning the laser line source on the sample surface at the phase velocity of the surface wave, the stress wave amplitude is amplified continuously with distance. The technique would enable loading thin film materials with strain amplitudes of the order of 0.01 with strain rates greater than one million per second. The contact-free nature of the technique allows for accurate modeling of the processes of stress wave generation and propagation, leading to reliable extraction of thin film material properties.If the project is successful, the proposed technique would enable the quantitative assessment of the mechanical reliability and stability of film based small scale structures including MEMS and NEMS devices. These properties are critical to their successful integration into more complex microelectronic devices. Furthermore, the project is integrated with various educational activities including, graduate course enrichment, graduate student training, and outreach activities to high school students.