Resistivity, charge diffusion, and charge depth determinations on charged insulator surfaces

Abstract

A method and theory presented earlier by the authors, for the straightforward measurement of resistivity in the surface region of charged insulators, in the initial phase of charge decay, is demonstrated also to be valid for much longer time scales. This is achieved with the use of a theoretical charge transport model, enabling a direct comparison between experimental and theoretical data. This comparison enabled the accurate determination of both the diffusion coefficient (D) and the layer of surface charge (Δz). Results are presented for glass, plexiglas (perspex), and polyethylene covering a useful resistivity range in the insulator class. The surface charge transport behavior of small rectangular samples is also studied using this computational model, focusing on the potential and charge distributions involved. From this study, some insight is gained into the way the charge in the surface region of insulators decays away with time when one end of a charged sample is earthed. The method provides a ready means of measuring the resistivity, carrier diffusion coefficient, and carrier occupancy depth in surface charged insulators.

Surface charge carrier motion on insulating surfaces: One dimensional motion

“…Previous attempts [1][2][3] to model charge carrier motion on the surface of insulators via the Mott-Gurney mechanism [4] have given reasonably good agreement with experimental data. This mechanism of charge motion on an insulator (dielectric) surface assumes that the current J of a mobile charged species on the dielectric surface is entirely driven by a particle current of the form J(x, y, t) = µN (x, y, t)E(x, y, t) (1.1) where N is the time and space dependent particle density of charge carriers and E is the component of the electric field in the plane of the dielectric surface.…”

“…[1][2][3]), that the electric potential satisfies a one dimensional Poisson equation. The resulting equations for the charge carrier density are non-linear partial differential equations which may be solved by the method of characteristics, that is by finding the curves in the (x, t) plane on which the carrier density (or electric field) is constant.…”

Electrical conductivity study of surface-modified polymers

“…As mentioned above, the resistivity methodology of Liesegang et al 3,4 was used for these measurements. Briefly, a rectangular film sample (typically 3 ð 5 cm) is frictionally charged and placed inside a cylindrical capacitor arrangement.…”

“…designated functional groups may be incorporated into polymer surfaces, allowing subsequent surface functionalization. We investigate the effect of such grafts on the electrical conductivity in the nearsurface region of a series of polymer films-polyaniline (PAN), low-density polyethylene (LDPE) and polytetrafluoroethylene (PTFE)-using the resistivity methodology of Liesegang et al 3,4 These particular polymers are widely used for industrial applications (in packaging and as nonstick coatings) and were chosen for measurement because of their various chemical and physical properties. The LDPE is known to be highly electrically insulating; PAN has conducting and interesting redox properties; and PTFE is recognized for its inertness.…”

Surface electrical resistivity and wettability study of fused silica

“…The relationship between water adsorption and the electrical conduction mechanism of silica is of particular importance in emerging ionic humidity sensor applications. 4 In this study a fused silica plate was investigated using an electrical conductivity technique developed in previously reported work 5,6 in order to study the effect of surface modification on electrical conduction in the surface region. The results have been used to determine the nature of charge carrier transport in the surface region of the material.…”