Electron microscope for high resistance samples - has secondary sweep discharging main sweep lines between main sweeps

摘要

The electron microscope has an auxiliary sweep to release the local electrostatic charges which the main sweep beam has produced on the surface of a sample. The altenating sweeps are obtained by successive line sweeps such that a line is swept by the spot of the principal beam. The principal beam is switched off and the auxiliary beam spot discharges the line during the time normally used to sweep the following line. The microscope also has a chopper circuit at the output of a detector. The chopper switches off the secondary electron detector during the activation of the auxiliary beam so as to eliminate any noise due to free ions in the vacuum chamber of the instrument. The microscope may be used for insulating material samples which have a high electrical resistivity.