Approaches to a theory of electron transfer reactions at film covered electrodes

Abstract

Electron transfer reactions at metal electrodes covered by insulating or semiconducting films may proceed by several mechanisms. At thick films, corresponding to bulk crystalline or amorphous semiconductors, they include electron transfer via the conduction or valence band of the film, electron transfer via localized bulk or surface states, or electron transfer between trapped polaron states. At thin films the dominating electron transfer mechanism is coherent or incoherent elastic tunnelling, or phonon-induced inelastic tunnelling. A survey of the conditions under which the various mechanisms are likely to prevail is given, and it is shown that in many cases the approach towards a theory of electron transfer reactions at film covered electrodes can be reduced to an analysis of elementary steps for which a theoretical formalism is wholly or partially available.