Charge Transfer Upon Contact Between Metals and Insulators

Abstract

The equilibrium charge distribution between substances in contact is calculated in the one-dimensional approximation for metal-insulstor and insulator-insulator contacts. The direction of charge transfer is such as to equalize the Fermi levels, and the magnitude of charge transferred depends on the positions of the energy bands in the substances in contact. For example, in an insulator it is possible to have a large charge density (∼ 10 11 esu) within a thin layer (∼ 10 -8 cm.) or a small charge density (∼ 10 -1 esu) in a thick layer (∼ 10 -1 cm.), to give the same potential shift (∼ 1 ev), depending on the relative position of the bands. The energy levels in most insulators of high resistivities are too poorly known to allow strict quantitative comparison with experiment, but the results permit a semiquantitative explanation of some observations on static electrification.

Relation of Charge to Frictional Work in the Static Electrification of Filaments

“…None of the findings conflict seriously with recently announced concepts of the transfer of charge due to friction [33,76) . However, the observation that appreciable amounts of one fiber abrade under the conditions of experiment and cling to the other fiber, thereby surely influence ing the net charge transfer, suggests caution in proposing a purely electronic or ionic mechanism of triboelectricity on the basis of experiments of this type.…”

“…Further theoretical treatment based on this model has been given by Van Ostenburg and Montgomery [ 76 ) . Levy and Dillon [ 44 ] , using the Hersh-Montgomery apparatus with certain modifications, gave preliminary results at variance with one of the conclusions of Hersh and Montgomery [ 32 ) ; i.e., under certain conditions the charge developed by rubbing insulator on insulator increased with increasing velocity.…”

The role of bulk traps in metal-insulator contact charging

“…We note that such calculations have been made for trapless insulators by Van Ostenburg and Montgomery (1958) and Harper (1967). As pointed out by Harper, the screening length for the transferred charge to a trap-free insulator is too large for that model to have any practical value.…”

Tunnelling between metals and insulators and its role in contact electrification

“…A number of authors have calculated the charge transferred when a metal and an insulator are brought into contact, assuming that the charge transfer is due to electrons (Van Ostenberg and Montgomery 1958, Davies 1969, Chowdry and Westgate 1974, Carton 1974, Duke and Fabish 1978, Nordhage and Backstrom 1975. Most of these calculations are based on thermodynamics, and have not been concerned with the detailed mechanism of charge transfer.…”