PURPOSE:To produce a lead image, which is clear and easily observable, by providing three metal net electrodes and by applying an AC perturbation voltage between a sample surface and the earth. CONSTITUTION:When an AC perturbation voltage 9 is applied between a sample surface 1 and the earth, the energy of the secondary electrons generated at the sample surface are subjected to the influences therefrom. When the varied portions of the secondary electrons by the perturbation voltage pass through metal net electrodes 2 to 4, they act with a DC blocking voltage 8 impressed so that the Auger signals contained in the secondary electrons are detected by a collector electrode 6. Thus, the leak of the perturbation voltage 9 to the collector electrode is triply prevented by the three metal net electrodes 2 to 4, which are all alternately grounded to the earth, so that a clear lead image can be observed.
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