Hiromitsu Kawase

Triboelectricity evaluation of single toner particle by electron holography

Understanding electrification is particularly important in materials science since the use of charged particles, e.g., the electrophotographic printer with toner particles, is one of the most successful applications of electrification. However, the charge generation mechanism still remains unclear due to the lack of an appropriate method for evaluating individual fine particles. In this study, we describe an approach for determining the charge of a single toner particle that uses electron holography in combination with a shielding technique. Two long-standing problems in holographic studies—namely, perturbation of the reference electron wave and unwanted charging by illumination—have been overcome by introducing two types of shields in a microscope. Using this method, the amount of charge on a single toner particle was determined, and the surface charge distribution was found to be inhomogeneous. Furthermore, an in situ observation of triboelectricity was conducted inside the microscope.

Split-illumination electron holography for improved evaluation of electrostatic potential associated with electrophotography

Precise evaluation of the electrostatic potential distributions of and around samples with multiple charges using electron holography has long been a problem due to unknown perturbation of the reference wave. Here, we report the first practical application of split-illumination electron holography (SIEH) to tackle this problem. This method enables the use of a non-perturbed reference wave distant from the sample. SIEH revealed the electrostatic potential distributions at interfaces of the charged particles used for development in electrophotography and should lead to dramatic improvements in electrophotography.

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 ...

Electrostatic-Potential Analysis of Charged Particles by Split-Illumination Electron Holography

1. Central Research Laboratory, Hitachi, Ltd., Hatoyama 350-0395, Japan 2. Center for Emergent Matter Science (CEMS), RIKEN, Wako 351-0198, Japan 3. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan 4. Department of Materials Science & Engineering, Dong-A University, Busan 604-714, Republic of Korea 5. System Research & Development Center, Ricoh Institute of Technology, RICOH Co., Ltd., Kanagawa 224-0035, Japan