Electron Injection Technique for Investigating Conduction Processes in Insulating Liquids and Solids

A dielectric test cell has been constructed in which the cathode of a conventional cell is replaced by a scanning electron beam. This apparatus has been used to study conduction processes in dielectrics, principally liquids, in the absence of the complicating factors normally introduced by a metal cathode. In this apparatus an electron beam is used to inject a uniform electron charge pattern into the top layer of the dielectric. As the charge builds up, the resultant field causes a current to flow through the liquid to the substrate; this current is measured by an electrometer. The surface potential of the liquid is measured by observing the deflection of a second electron beam which passes parallel to the dielectric surface about 7 mm above it. This ``electrometer'' beam can also be used to time-resolve the build up and decay of charges in the dielectric. The injected charges give rise to a mechanical force, which tends to compress the dielectric, so that it is necessary to monitor the thickness of the liquid during a test. This is done optically by using a light slit technique for relatively thick films, and an interferometric method for films thinner than 0.04 mm. Typical results for a hydrocarbon liquid are presented to illustrate the use of the apparatus for dielectric measurements.