Measurement of heat transfer in sub-micron area of thin films by transmission electron microscope

利用透射电子显微镜（TEM）的高空间分辨率（-nm），研究了一种薄膜导热系数的测量方法，并将其应用于厚度为30-300nm的多晶薄膜。电子通过薄膜被晶格的热振动散射，透射电镜图像的光束强度随试样温度的变化而变化。当激光束聚焦在薄膜上时，可以对薄膜进行局部、快速和反复的加热。结合这些函数，我们可以研究这种薄膜的传热机理。在TEM上安装了一个带调幅器的He-Ne气体激光器和聚焦对准光学系统。约10mW的激光束聚焦在直径为10 ~ 20mum的试样上。观察试样的放大图像，并用闪烁体和光倍增器检测小区域（试样上1mumphi）的光束强度。薄膜温度的上升是由热容量和热扩散率延迟到激光功率的。相位差被转换成导热系数。其次，该方法具有不受绝对温度和薄膜厚度影响的优点。制备并测量了不同厚度的真空沉积膜（Al, Sn, Ni, Ge, Cu, Mg, Bi）。在大多数情况下，薄膜电导率为体积电导率的30-80%，并随着晶粒尺寸的增大而接近。薄膜导电性随厚度的减小而减小。在项目期间，我们还没有完成对传热与晶体结构之间关系的研究。这将会被陆续研究。

With the high-spatial resolution (-nm) of transmission electron microscopes(TEM), a measurement method of thermal conductivity of thin films is investigated and it is applied to polycrystalline films whose thickness is 30-300nm.Electrons through a film are scattered by the thermal vibration of lattice and the beam intensity at TEM image changes by the temperature of the specimen. When the laser beam is focused on a film, the film can be heated locally, quickly and repeatedly. combining these functions, we can investigate the mechanize of heat transfer in this films.A He-Ne gas laser with amplitude modulator and an optical system for focusing and aligning are attached to the TEM.The laser beam with about 10mW is focused on the specimen to the area of 10-20mum in diameter. The magnified image of the specimen is observed and the beam intensity in a small area (1mumphi on specimen) is detected by a scintillator and a photo-multiplier.The rise of film temperature is delayd to the laser power by the heat capacity and heat diffusivity. The phase difference is converted to the thermal conductivity. Then, this method has advantage that the deduction is independent to the absolute temperature and the film thickness.Some vacuum-deposited films (Al, Sn, Ni, Ge, Cu, Mg, Bi) with various thicknesses are prepared and measured. In most cases, film conductivity is in 30-80% of bulk conductivity and approaches to it as the grain size increases. The film conductivity reduces as the thickness decreases.In the term of project, we have not finished the investigation to the relation between heat transfer and crystal structure. This will be studied in succession.