Effect of chemical impurities on charge injection barriers at the interface of copper and polyethylene

Abstract

Chemical impurities in dielectric materials are one of the reasons that reduce the height of charge injection barrier. These impurities create energy states in dielectric band gap, which impact on the injection process. Chemical impurities that are studied in this paper include carbonyl, vinyl, and conjugated double bond impurities. These types of chemical impurities are the most common in technical dielectric polymers such as polyethylene. These impurities are studied using the computational quantum mechanics in the scope of density functional theory (DFT). The computed barrier in the present work is carried out using a new technique based on correcting the underestimation in polyethylene band gap due to the DFT computations. It is found that terminal carbonyl and conjugated double bond produce the lowest injection barrier for electrons and holes, respectively. The depth of these impurity states are compared with that developed in bulk PE and at the interface with other metals. The similarity in calculated barrier for electrons and holes is in agreement with the experimental observations. This paper concludes that chemical impurities cannot alone explain the activation energy of conduction of 1 eV.