4.4
4-7
4.4.1 About shutting down the Electron gun
The electron source of SU8700 is a Schottky emitter type. The emission current is extracted by
applying an extracting electric field to the emitter point heated to about 1700 K. In normal
operation, maintain the instrument as started and use is continuously. Perform the shut down
and start-up operation described below only when the instrument will not be used for a long
period or a full-off of the power. Flow the Filament current If through the emitter to heat and
impress a steady electric field by applying the extraction voltage Vext to maintain the emission
state of the emission current Ie. When observing with SEM, open the electron gun isolation
valve GV installed between the electron gun chamber and the specimen chamber and apply
the accelerating voltage Vacc. For a stable Schottky emission, the balance between the heating
temperature and the extraction electric field is an important matter. Therefore, the start-up
and shut down of the electron gun should be performed over a period of time along the
predetermined operational sequence. Note that the emission current Ie stabilizes with a
gradual increase for a few hours after the completion of the start-up of the electron gun. To
maintain a stable performance, it is recommended that the electron gun should be maintained
always in a start-up state.
NOTE:● The emitter is used in a state heated to high temperature. A sharp temperature
variation imposes unnecessary load on the emitter inviting performance
deterioration or shortened service life. Do not start nor shut down the electron gun
unnecessarily.
● Each of the Schottky emitter has specific values of the Filament current If and the
Extraction voltage Vext for a stable emission. These values are set by our service
engineer at the time of the emitter replacement. If such specific value setting for the
filament current (Heating temperature) or for the extraction voltage is altered, the
life-time of the emitter may be influenced, or the resolution may be affected due to
the emitter shape change. When changing the settings is desired, contact our
service engineer of Hitachi High-Tech Corporation.
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