Spatial distributions of densely contact-electrified charges on a thin silicon oxide

The spatial distributions of densely contact-electrified charges on silicon oxide were investigated in air with an atomic force microscope. We found that the spatial distributions immediately after contact electrification significantly depended on the sign of the charge. The spatial distributions showed sharp peaks for positive charge but round peaks for negative charge. We conjectured that the sign dependence of the spatial distributions was induced by the forced tunneling process. We also found the other feature of the spatial distributions of the dissipated charge, which seemed to be related to premonitory phenomena of dielectric breakdown for silicon oxide.