Density of states evaluation of an insulating polymer by high-sensitivity ultraviolet photoemission spectroscopy

Although the contact electrification of insulating polymers has been widely used in various technologies, the mechanism of electrification is still not well understood and several models have been proposed to explain the mechanism. Some of the models assume the existence of bandgap states that can store or release electrons to charge the polymer; however, the density of states in the bandgap region is not well examined. In this study, an approach to directly measure the density of state of insulating polymers using hν-dependent high-sensitivity ultraviolet photoemission spectroscopy is proposed. Demonstration of the approach to a representative insulating polymer, nylon-6,6, is reported with the estimation of the charge density and charge penetration depth as a function of the work function difference.