Secondary emission measurements of semiconductors and dielectrics

A measuring technique is described whereby the secondary emission ratio can be determined using a special experimental set-up employing two electron guns in a demountable vacuum system plus associated electronics. Although originally set up for measurements of semiconductors, the apparatus has also been used for measurement of insulators. The principal features of this technique are: (1) use of a flood electron gun to place the target surface at some voltage, and (2) the use of an amplitude modulated probing electron beam and a narrow-band amplifier at the target to detect the collected probing current at the target. The collection of the probing electron beam occurs when its cathode is more negative than the secondary emitting surface. By positioning the cathode voltage, the surface voltage can be determined as well as the landing energy of the flood electrons. Secondary emission measurements on semiconductors are described for primary energy from 0 eV through first cross-over to several hundred eV. Measurements taken on dielectrics are described from first cross-over to approximately 50 eV above maximum. Advantages of using a measuring technique in which the surface voltage of the target material does not vary are described. This apparatus was used to perform tests on contract DA-44-009-ENG-4868 for U.S. Army Engineer Research and Development Laboratories, Ft. Belvoir, Va.