ELECTRON-TUNNELING IN ELECTROCHEMICAL PROCESSES AND IN-SITU SCANNING TUNNEL MICROSCOPY OF STRUCTURALLY ORGANIZED SYSTEMS

The electronic tunnel factor in homogeneous long-range electron transf er (ET) systems has been characterized experimentally and theoreticall y in great detail. Outstanding questions, however, remain, for example interference in multiple ET routes and environmentally induced barrie r fluctuations. Well characterized electrochemical long-range ET syste ms have also become available where the tunnel factor can be accuratel y deconvoluted from the total current. Intriguing new effects here are associated with the electrode charge or overpotential effects on the tunnel factor and with the feasibility of observation of critical curr ent behaviour near phase transitions in thin films across which electr on tunnelling occurs. In situ scanning tunnel microscopy (STM) offers a conceptual and technical new frame for mapping of molecular ET route s through large adsorbate molecules with low-lying local fluctuating l evels. Such a configuration would be representative of large transitio n metal complexes or redox metalloproteins. High-resolution images and new theoretical approaches to STM mapping of large adsorbates are, mo reover reported. The independent in situ electrode potential control p rovides new, non-monotonous features in the current-voltage relations which differ from electrochemical ET behaviour at a single interface. Copyright (C) 1996 Elsevier Science Ltd.