SCANNING TYPE ELECTRON MICROSCOPE

摘要

PURPOSE:To keep magnification in an externally preset value even when working distance varies by detecting the current amount applied to an electronic lens and varying the deviation of an electron beam interlocking with the current amount. CONSTITUTION:An electron emitted from an electron gun is accelerated by an anode and an electron beam is converged by a convergent lens and an objective lens 5 and then a sample is irradiated with the electron beam. A focal point current regulator 17 externally operates a knob and varies the current value. The lens 5 varies the current value and focal point position through a constant- current amplifier 18 by the output of the regulator 17. A current detection resistor 19 detects the current value of the lens 5 and amplifies it using a buffer amplifier 20. A magnification setting device 21 varies the size of a deflectionsignal interlocking with an external knob and sets the magnification of a picture. The output of the setting device 21 is issued to an attenuator 22. The attenuator 22. The attenuator 22 reduces attenuation as a signal from the amplifier 20 increases and increases the deflection signal. The output of the attenuator 22 is applied to a deflection coil 9 through a constant-current amplifier 23 and preset magnification can be maintained.