金相学史话(6):电子显微镜在材料科学中的应用

A Brief History of Metallography: Ⅵ.Application of Electron Microscopy in Materials Science

Ruska在三十年代研制出第一台电子显微镜 ,战后 (195 4年 )又在极端困难条件下发展出带有电子衍射功能的高分辨电镜ElmiskopI。但是 ,从专利优先权角度看 ,他不是电镜的发明人。直到半个世纪后 ,有关的争议人都已过世 ,他才在 1986年获得这个迟到的但却是当之无愧的诺贝尔物理奖。材料科学的几次突破性进展充分说明电子显微镜的重要性。首先是电子衍射与成像的结合使位错的直接观察得以实现。在双束 (透射束与一个强衍射束 )条件下 ,位错产生的畸变区的衍射强度与基体不同从而显示衬度差异 (衍衬像 )。位错等晶体缺陷因此得以成为六、七十年代的研究热点。选区衍射使晶体结构分析进入到微米甚至到纳米层次。迄今为止 ,八十年代发现的各种类型的准晶 (五重、八重、十重、十二重旋转对称准晶 )都是使用这种手段实现的 ,从而扩大了晶体的范围 ,把无周期性的准晶也包括进去。高分辨电镜已发展到分辨单个原子的水平 ,这就为九十年代发现和研究纳米碳管创造了条件 。

E.Ruska developed the first electron microscope in the thirties and the electron microscope Elmiskop I of fairly high resolution and equipped with electron diffraction devices after the Second World War(1954). However, according to the patent priority he was not the inventor of electron microscope. After about half of a century of the first electron microscope ever made, he finally received righteously the Nobel Prize in Physics in 1986, when all contestants have passed away. Following each development stage of the electron microscope, there is always a big advance in materials science. Under the two\|beam condition(transmit beam and one strong diffraction beam), the distorted region caused by a dislocation line will have a different diffraction intensity compared with the undistorted matrix, thus showing a diffaction contrast(diffraction contrast image). This made the study of crystalline defects such as dislocations a hot spot in the sixties and seventies. Thanks to the selected area electron diffraction made in the micrometer or even in the nanometer range, fivefold diffraction symmetry becomes obvious in an electron microscope. Quasicrystals of different rotational symmetries(fivefold, eightfold, tenfold and twelvefold) were found in the eighties by this method, thus extending the scope of crystallography to include the aperiodic quasicrystals. With the improvement of the resolution of an electron microscope to the atomic level, the carbon nanotube was discovered in the nineties, thus announcing te new era of nanotechnology.