Development of illumination system of gun-damage free electron microscope

在现今的电子显微镜下，在灯丝附近会形成某种负离子。这些离子被加速，通过聚光镜，均匀地照射在样品上。离子的能量为200键，这些离子可以在样品中形成位移损伤级联。这些损害被称为“枪支损害”。目前研究人员发现，这种枪炮损伤形成在现有的EM中很重要，这给离子和中子辐照金属的损伤形成研究带来了困难。在本项目中，开发了新的系统来消除样品中的这些火炮损伤地层。建立了两种系统：一种是将电子枪部分垂直移动到EM中的电子光轴上，另一种是在样品室（样品上方）中弯曲电子路径以形成旁路。在直线路径上，插入阻挡板以阻挡成枪离子。将这些设备安装在JEM-2000ES显微镜上，并在200 kV加速电压下测试了它们的性能。这两种仪器都工作得很好。两种装置都能很好地消除火炮损伤的形成，并且显著减少了电子照射时产生的污染。这一事实表明，在电子显微镜观察期间形成的污染是由于来自枪膛的离子。电子显微镜无枪损照明系统将作为标准配置配置到未来的电子显微镜上。

In a present day's electron-microscope (EM)some sort of negative ions is formed near filament. These ions are accelerated, pass through condenser lenses and illuminate uniformly on specimen. The energy of ions is 200 key so that these ions can form displacement damage cascades in specimens. These damages are referred to as "gun damages". The present investigators found that this kind of gun damage formation is significant in presently available EM and make difficult to study the damage formation in ion- and neutron-irradiated metals. In the present project, new system was developed to eliminate these gun damage formation in specimens. Two systems were built : One is the shift perpendicularly the gun part to the optical axis of electrons in EM. Another-is the bend of electron path in a specimen chamber (above specimbns) to form by-pass. In the straight path, the stopping plate is inserted to block gun-forming ions. We have installed these equipments to our JEM-2000ES microscope and tested their performances at 200 kV accelerating voltage. Both of apparatus works very well. Gun damage formation was eliminated perfectly with both of apparatus and moreover contamination formed during electron-illumination was remarkably decreased. This fact suggests that contamination which forms during an elgidtron-microscope observation is due to ions which come from gun chambers. The illumination system of gun-damage free of an electron-microscope will be equipped to a future electron-microscope as standard configuration.