Electrical effects at interfaces and surfaces

Interfaces and surfaces are always involved with electrets and frequently, if not invariably, exert a controlling influence on their properties. Although classical featureless models have often been used to describe the behaviour, especially where contact to metal electrodes is involved, the situation is much more complex. The nature of interfaces and contacts and of charge transfer across them is reviewed using the concepts of modern molecular electronics and electrochemistry. The effect of blocking and non-blocking conditions and the special behaviour at free surfaces is considered. The roles of structure and local order especially for polymeric electrets and the influence of ionic and polar impurities in determining the magnitude, life-time and transport of charges in electret materials will be outlined.