Study on Relationship between Electric Charge Trapping and Dielectric Molecular Structure using Quantum Chemical Calculation

摘要

In order to understand the electric charge trapping site in insulating material, this work studies the electronic structures of small molecular structures and proposes the formation of trapping site in a viewpoint of chemistry using quantum chemical calculation. Through calculating of a small PE chain (C24H50) and some PE chains with chemical groups or structures, the electron energy level, molecular orbital and electric potential were obtained. Energy band gap shows an obviously decrease after employing additional chemical groups, such as conjugated double bond and carbonyl groups. Molecular orbitals (MOs) show a localized distribution around these chemical groups at the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) or near levels, which indicates new energy levels are introduced within the band gap of PE. The special chemical structures and existed dipole moment of these chemical impurities contribute to the formation of new energy levels. Additionally, 3D electric potential distributions demonstrate that an obvious potential distortion occurs around these introduced chemical impurities. It means that the moved electron or hole carries can be captured here, giving rise to formation of charge trapping sites.