Studies on Electrode Surface Conditions and Vacuum Breakdown Phenomena by an Electron Emission Microscope

本课题的目的是利用自行研制的电子发射显微镜，观察真空间隙中电极上电子发射点形貌的变化。所研制的电子发射显微镜的特点是不仅可以在点电极上而且可以在大面积电极上成像电子发射光。获得了电子发射点的图像，验证了电子发射显微镜的工作性能.观察到场致电子发射点的振动。这可能是由于排放地点的移动。为了证实发射点的移动，有必要做进一步的实验.利用该显微镜对真空间隙宽面积无氧铜电极上的场致电子发射点进行了观察，发现宏观上单个发射点是由多个发射点组成的，1998年，即本课题的最后一年，又对真空间隙电极进行了连续的场致电子发射点观察，结果如下：1.显微镜的放大倍数是通过紫外光激发的50 μ m直径的铝丝的光电子发射图像来校准的.对真空间隙无氧铜电极的观察表明，宏观上单个场致电子发射点由多个场致电子发射点组成.此外，对无坑电解抛光铝电极的观察表明，击穿前后电子发射点的方位发生了显著变化，通过本研究可以阐明电子发射点方位的变化。该仪器将提供一个强大的手段来评估电极表面处理，以获得更高的电压保持能力的真空间隙。

The aim of this project is to find changes of the aspect of electron emission sites on electrodes of a vacuum gap by using an electron emission microscope developed by our laboratory. The electron emission microscope developed has the feature that imaging of electron emission sights on not only a point electrode but also a broad area electrode is possible.In 1997, the first year of the research term, followings were clarified.1. The images of electron emission sites were obtained and operating performance of the electron emission microscope was confirmed.2. It was observed that field electron emission sites vibrated. This may be due to moving of emission sites. To confirm moving of emission sites it is necessary to make further experiments.3. Field electron emission sites on broad area oxygen-free copper electrodes of a vacuum gap were observed by this microscope.The observations revealed that macroscopicaly single emission site consists of several sites.In 1998, the last year of this project, observations of electrodes of vacuum gaps were carried in succession, and the results were summarized as follows.1. The magnification factor of the microscope was calibrated by photoelectron emission images of 50 mu m diameter Al wire excited by ultra-violet light.2. Observations of oxygen-free copper electrodes of vacuum gaps clarified that a macroscopically single field electron emission site consists of several sites.3. In addition, observations of pit-free electropolished aluminum electrodes revealed that the aspect of electron emission sites changed significantly before and after breakdowns.By this research it becomes possible to clarify changes of aspect of electron emission sites. The instrument will provide a powerful means to asses electrode surface treatments to obtain higher voltage hold-off capability of a vacuum gap.