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

本项目的目的是通过布里渊散射谱实现对金属薄层和聚合物薄膜弹性性能的无损评估，这是传统的超声波技术所不能实现的。通过引入新的测量仪器和精确的温度控制，我们可以在不同的物理条件下，如温度、应力等，成功地实现样品速度的长时间连续测量。利用90A光学几何和拉伸测试仪可以连续测量厚度为几微米的聚合物薄膜的纵波速度。观察到薄膜的超拉伸过程随速度的增加而明显增加，表现出各向异性。通过改变入射激光的偏振，我们还成功地实现了薄膜双折射的连续无损测量。对于硅片上的碳化硅纳米层，由于表面的瑞利波，可以观察到很弱的布里渊散射峰。尽管薄膜的厚度远小于光的波长，但瑞利波速度明显依赖于碳化硅薄膜的晶体结构，表现出与块体碳化硅的相似行为。玻璃基片上一维取向的氧化锌薄膜的表面波散射峰也清晰可见，显示了该薄膜的各向异性。

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.