Nondestructive evaluation of thin layers and films by a Brillouin scattering spectroscopy

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The purpose of this project is to achieve the nondestructive evaluation of elastic properties in thin metal layers and polymer films by a Brillouin scattering spectroscopy, which cannot have been performed by the conventional ultrasonic techniques. By introducing new measurement apparatus and precise temperature control, we could succeed in long time and continuous measurement of sample velocity, under different physical conditions such as temperature and stress.A continuous measurement of longitudinal wave velocity in thin polymer films (thickness several microns) could be performed by using the 90A optical geometry and tensile test apparatus. The ultra-drawing process in a film was clearly observed as an increase of velocity and showed the appearance of anisotropy. By changing the polarization of incident laser light, we also succeeded in the continuous and nondestructive measurement of birefringence in a film. This method was also applied to the evaluation of adhesive polymer layer under the tensile stress.As for Sic nano layers on the Si wafer, the very weak Brillouin scattering peaks owing to the surface Rayleigh waves could be observed. Although the thickness of the layer was much smaller than the wavelength of the light, the Rayleigh wave velocity clearly depended on the crystalline structure of Sic layer, showing the similar behavior with the velocity of bulk Sic. The scattering peaks of Surface wave were also clearly observed from the one dimensionally aligned ZnO layer on glass plate, showing the anisotoropy of the layer.