Development of illumination system of gun-damage free electron microscope

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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.