A new technique for studying ions striking insulating surfaces

Abstract

This paper presents a new technique that employs an ultra-violet excited phosphor for studying the interaction of air ions with insulating surfaces. This technique has an important advantage over more traditional methods as it produces dynamic images of surface electric fields in the form of changing patterns of light from the phosphor. Such fields might arise from changes in surface charge density due to the arrival of air ions, or from the redistribution of surface charge due to local breakdown phenomena. The type of light modulation exhibited by the phosphor layer is known as electromodulated photoluminescence. This phenomenon is more commonly referred to as the Gudden-Pohl effect (GPE). Bertein [1] employed the classical point-to-plane arrangement for generating an asymmetrical electric field and produced circles on an insulating layer when dusted with a dielectric powder. These circles display the surface field intensities that remain after removal of the ion source (the point). When the new technique is employed in a similar setup to that of Bertein, expanding rings of light are observed. This paper shows that these dynamic rings are related to the circles visualised by dusting, this latter method revealing the ring at a powder circle only at its final diameter.