Nakamura Nobutomo, Ogi Hirotsugu, Hirao Masahiko
Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Machikaneyama-cho 1-3, Toyonaka, Osaka 560-8531, Japan.
Ultrasonics. 2004 Apr;42(1-9):491-4. doi: 10.1016/j.ultras.2004.01.048.
We propose an advanced method to determine the elastic-stiffness coefficients Cij of thin films using resonance ultrasound spectroscopy (RUS). It uses free-vibration resonance frequencies of a film/substrate layered solid and derives inversely the film's Cij from the resonance frequencies. We develop a piezoelectric tripod consisting of two pinducers and one support to place the specimen on it and measure the resonance frequencies with high enough accuracy. Furthermore, we achieve mode identification by measuring deformation distributions on the vibrating specimen surface using laser-Doppler interferometry. Accurate measurements of frequencies and correct mode identification are the keys for deducing reliable Cij of the film. We applied this technique to copper thin films deposited of Si substrates. The resulting film's Cij are considerably smaller than the bulk's Cij and show anisotropy between the out-of-plane direction and in-plane direction.
我们提出了一种先进的方法，利用共振超声光谱法（RUS）来确定薄膜的弹性刚度系数Cij。该方法利用薄膜/衬底层状固体的自由振动共振频率，通过共振频率反推薄膜的Cij。我们开发了一种由两个压电换能器和一个支撑体组成的压电三脚架，用于放置试样并以足够高的精度测量共振频率。此外，我们通过使用激光多普勒干涉测量法测量振动试样表面的变形分布来实现模式识别。准确测量频率和正确识别模式是推导薄膜可靠Cij的关键。我们将该技术应用于沉积在硅衬底上的铜薄膜。所得薄膜的Cij远小于块体的Cij，并且在面外方向和面内方向之间表现出各向异性。
