Diode Measurements with Thick Chloride Layers on Nickel

Abstract

The formation of a thick chloride layer on the surface of a nickel anode has been found to result in a diode characteristic curve which, in addition to lateral displacement due to the surface potential, shows marked nonparallelism with respect to the diode characteristic for the clean surface. This behavior has been interpreted in terms of the electrical conductance of the chloride layer and it suggests a general method for the measurement of the electrical properties of thin insulating layers on metal surfaces. Confirmatory conductance measurements have been made with bulk nickel chloride. Some kinetic data have been obtained for the formation of thick cloride layers on the surface of nickel and a technique is described for the preparation of uncontaminated sintered nickel films of small area. It is concluded that the conductivity of stoichiometric nickel chloride is ≲10−15 Ω−1 cm−1 at room temperature, but that after heating in vacuum the conductivity rises and feeble semiconductivity results, with an activation energy for conduction of about 16 kcal mole−1. Both the conductance and the surface potential for a chloride layer on nickel increase on heating in vacuum and it is suggested that this is due to the incorporation of nickel from the substrate.