In the study of such micro electronic devices as a transistor and an integrated circuit by using a scanning electron microscope the contrast of a secondary electron image reveals potential distribution on the surface of a specimen. The intensity of secondary electrons collected by a detector depends on the potential of the specimen surface because the yield of the secondary electrons is restricted by the surface potential and the trajectory of the secondary electrons from the specimen to the detector is disturbed by the field which is produced by the potential applied to the specimen. The relation between the contrast and the potential of the specimen surface varies according to instruments.
A simple specimen was used in order to obtain the relation. Two copper blocks with flat surfaces were arranged with a narrow gap of about 50 μ. One of them is electrically grounded and the other is variously biased. The intensity of the secondary electrons emitted from each block of the specimen was measured at the output of a photomultiplier of the detector.