High Resolution Transmission Electron Microscopy Study of Calcium Fluoride Single Crystal (111) Surfaces Processed by Ultraprecision Machining
High Resolution Transmission Electron Microscopy Study of Calcium Fluoride Single Crystal (111) Surfaces Processed by Ultraprecision Machining
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DOI：
10.2320/matertrans.47.267
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发表时间：
2006-02
影响因子：
1.2
通讯作者：
N. Ohnishi;S. Yoshida;Y. Namba
中科院分区：
文献类型：
--
作者：
N. Ohnishi;S. Yoshida;Y. Namba
用透射电子显微镜研究了机械加工氟化钙(CaF2)的微观结构。采用超精密机械抛光技术，将高纯CaF2单晶的(111)取向表面抛光为平整表面。采用了一种浮法抛光方法--用7 nm直径的二氧化硅粉末、纯水和锡圈进行抛光。在浮法抛光之前，先进行超精密磨削作为初步处理。横截面透射电子显微镜研究表明，与常规光学抛光工艺相比，超精密磨削引起的亚表面损伤厚度相对较小。此外，浮法抛光工艺没有对CaF2晶体造成任何机械损伤。透射电子显微镜照片表明，浮法抛光表面具有由(111)阶面和纳米级台阶组成的刻面结构。单个平台的大小取决于样品表面和(111)面之间的失配角。高分辨率的电子显微镜观察表明，在较大的梯形平面上获得了原子光滑的(111)面，具有块状的萤石结构。
The microstructure of a mechanically finished calcium fluoride (CaF 2 ) was studied by transmission electron microscopy (TEM). The (111) oriented surfaces of high-purity CaF 2 single crystals were finished to a flat surface by ultra-precision mechanical polishing. A float polishing method-with 7-nm-diameter silicon dioxide powder, pure water, and a tin lap-was employed for the finishing. Prior to the float polishing, ultraprecision grinding was performed as the preliminary treatment. A cross-sectional TEM study indicated that the thickness of the subsurface damage introduced by ultraprecision grinding was relatively small when compared with that by the conventional optical polishing process. Further, the float polishing process did not introduce any mechanical damages in the CaF 2 crystals. The TEM images showed that the float-polished surface had a faceted structure consisting of (111) terrace planes and nanometer-sized steps. The size of a single terrace depends on the mismatch angle between the sample surface and the (111) plane. The high-resolution TEM observation suggested that an atomically smooth (111) surface with a bulk fluorite structure was obtained over a relatively wide area on the large terrace planes.