Investigation of the divergence of the radiation emitted by a pulsed CO₂electron-beam-controlled laser

Abstract

The contact charging of insulators is usually attributed to electron states which are characteristic of the material, for example the pendant groups of polymers. However, most materials normally encountered will have been charged by contact with other materials, if only during manufacture. Such charge is eventually neutralised by atmospheric ions (or by conduction in the case of poor insulators) but it is not at all certain that a 'neutralised' surface is equivalent in electronicstructure to a freshly created surface of the material. We report experiments to determine whether the contact charging of insulators is indeed influenced by previous contact and 'neutralisation' or whether it is, on the contrary, an invariant property governed solely by the chemical constitution of the material. We find that charge transfer is influenced by prior charging. Usually the charge transfer is decreased by prior contacts but in a few cases it is increased. Repeated cycles of contact and discharge have a cumulative but diminishing effect on charge transfer; typically about one third of the initial charge transfer is retained even after a large number of such cycles, and this accounts for the fact that even old and much-rubbed samples of a material retain their approximate position in the triboelectric series.