Direct measurement of charge trap depth in polymer nanocomposites

Abstract

Polymer nanocomposites (PNCs) exhibit excellent electrical properties owing to charge trapping provided by nanofillers. However, the role of nanofillers in trap formation at the microscopic level is poorly understood. In this study, we propose a method to determine the charge trap depth of nanofillers in PNCs using x-ray photoelectron spectroscopy (XPS) measurements and first-principles calculations. The low-density polyethylene (PE)/TiO2 nanocomposite is selected as the measurement target as it was previously reported the charges are trapped by TiO2 loading to PE. We observe TiO2 can serve as a trap for holes, and the trap depth is determined to be 0.9 eV. Furthermore, the computed charge trap depth calculated by G 0 W 0 calculation, which reproduce the experimental band gap, is comparable to the XPS result, which strongly supports the validity of our method. In addition, owing to the quantitative evaluation of the electronic structure, it was shown that the charge trap depth of the nanofiller can be controlled by tuning the surface dipole with surface modification of the nanofiller. The approach proposed in this study to determine the charge trap depth of nanofillers provides the prospect of designing PNCs with desirable properties from the atomic or molecular level.