Two-step model for contact charge accumulation

In contact electrification of metal against insulator, multiple contacts, n ot a single contact, are always needed for reaching the charge saturation l evel. Many experiments have been done to find out the reason for this. The results are the same: multiple contacts are needed for reaching the saturat ion level. Two-step model is proposed as a tentative explanation of charge accumulation. Charge transfer involves two steps: contact of the two surfac es and their separation. Separation plays a major role. In this two-step pr ocess, interface states are formed when contact is established. They are th en populated with electrons from one or both sides. During separation, befo re the interface states are eliminated, all electrons from these interface states are transferred to either the metal or the insulator. Should more or fewer electrons be transferred to the insulator, it will thus gain or lose some electrons. This two-step cycle is repeated to transfer charge into po lymer until the equilibrium is established. (C) 2001 Elsevier Science B.V. All rights reserved.