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

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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.