Investigation of tribocharges and their migration in layered model toners by electron holography

The distribution of tribocharges in toner samples is studied by electron holography, a powerful tool for direct observations of the electric field. We carry out both in situ and ex situ observations on triboelectricity using model toner specimens, which are laminated with thin films, and a transmission electron microscopy specimen holder with two piezo-driving microprobes. We investigate specimens with stacking layer-patterns of minus and weak minus and plus and minus. The observed equipotential lines show a simple semi-ellipsoidal shape, regardless of the combination of toner films having different charging characteristics. Computer simulations for quantitative analyses of the electron hologram results with a modulated reference wave by a long-range electric field from the tribocharges are performed. Both the experimental results and the simulations indicate that the tribocharges are not localized at the positions where they are formed; rather they migrate to achieve a gradient charge density in the specimen. The charge quantity of the model toner is also evaluated by the simulation.