Study on surface plasmon thermal wave microscopy for evaluation of thermal characteristics in metal thin films

自1990年以来，我们开展了紧凑型光声(热波)显微镜的研制及其在材料科学中的应用研究，因为它具有对不透明材料的内部裂纹和缺陷进行无损评估和成像的能力。遗憾的是，由于银、金和铝等金属的薄膜对可见光具有很高的反射率，因此不能形成很强的热源，因此很难用于评估这些薄膜。在这项研究项目中，我们提出了一种利用非辐射表面等离子体对金属薄膜进行光声显微的新能力。首先，我们研制了一套表面等离子体热波显微镜系统。该系统由三部分组成，第一部分是表面等离子体波转换系统，第二部分是表面等离子体波测量系统，最后是热波测量系统。这些系统由一台个人计算机进行功能和有效的控制。利用该系统测量了当激光的调制频率从100赫兹连续变化到1000赫兹时，银膜、金膜和盖膜中光声信号的幅度对频率的依赖关系。在大样本情况下，所得到的-0.9相关性接近于-1.0相关性(理论预测和实验证据)。

Since 1990, we have carried out the development of a compact photoacoustic (thermal wave) microscope and the study on its application to material science because it has great capability of nondestructive evaluation and imaging of inner cracks and defects in opaque materials. Unfortunately, it was difficult to employ for evaluation of thin films of metals such as silver, gold, and aluminum since these materials do not form strong heat source because they have high reflectivity for visible light. In this research project, Grant-In-Aid for Scientific Research (C), we propose a new capability of photoacoustic microscopy for metal films using nonradiative surface plasmon. First, we developed a surface plasmon thermal wave (SPTW) microscope system. This system made up three systems ; the first is a system for the conversion of the surface plasmon into the thermal wave the second is a system for surface plasmon measurement, and the final is a system for thermal wave measurement. These systems were controlled functionally and effectivelly by a personal computer. Using this system we measured that the frequency dependence on amplitude of the photoacoustic signal in films of the silver, the gold, and the capper when the modulation frequency of the laser beam was changed continuously from 100Hz to 1000Hz. The obtained -0.9 dependence closed with -1.0 dependence (theoretical prediction and experimental evidence) in the bulk sample cases.