Development of illumination system of gun-damage free electron microscope

在当今的电子显微镜(EM)中，某种负离子在灯丝附近形成。这些离子被加速，穿过聚光镜，均匀地照射在样品上。离子的能量是200key，这样这些离子就可以在试件中形成位移损伤级联。这些损害被称为“枪支损害”。目前的研究人员发现，这种枪的损伤形成在目前可用的电磁环境中是重要的，并使研究离子和中子辐照金属的损伤形成变得困难。在本项目中，开发了一种新的系统来消除样品中的这些枪支损伤形成。建立了两个系统：一个是电子枪部分垂直于电子在电磁中的光轴移动。另一种是样品腔(样品上方)中电子路径的弯曲以形成旁路。在直线路径中，插入止动板以阻止成枪离子。我们将这些装置安装在我们的JEM-2000ES显微镜上，并对它们在200千伏加速电压下的性能进行了测试。这两台仪器都工作得很好。两种装置都很好地消除了枪伤的形成，并且显着减少了电子照射过程中产生的污染。这一事实表明，在电子显微镜观察期间形成的污染是由来自枪室的离子造成的。无枪伤电子显微镜照明系统将作为未来电子显微镜的标准配置。

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.