Surface conductivity of insulators: A resistivity measurement technique under vacuum

Abstract

A method of resistivity measurement for insulators, previously described by Liesegang and Senn (1995 J. Appl. Phys. 77 5782; 1996 J. Appl. Phys. 80 6336), has been demonstrated to produce measurements not only in good agreement with established results in the literature but also with improved accuracy. The method is based on monitoring the discharge of a charged sample of an insulator through a grounded boundary. The measurements, however, were performed under atmospheric conditions and so the results were influenced by atmospheric effects such as temperature and moisture. By confining a sample to a vacuum and charging it via a custom built electron gun, we here extend the established method of Liesegang and Senn to a more controlled environment. In this paper, we numerically solve the potential and transport equations for the axial-cylindrical geometry of the system and present comparisons of theory and experiment through derived values of the resistivity, carrier depth and diffusion constant for a range of insulator samples. We also use asymptotic solutions via a theory of Burgers equation shock waves, as discussed in Holcombe et al (2004 J. Phys. Condens. Matter 16 5999), to derive resistivity values and again draw comparisons. The results presented here are also compared with previously obtained or literature measurements of resistivity.