Small organic molecules confined between metal electrodes are in the focus of interest for over three decades now since they offer the prospects of becoming active components in ultra-high density nanoelectronic devices. From a technological point of view, significant progress could be achieved in the last decade in, e.g., the synthesis of appropriate molecules or the ability to produce device structures with nanoscaled dimen¬sions. In contrast, making reliable electrical contacts to molecules (i.e. connecting them to the outside world) has been and still continues to be a challenging problem for both, fundamental as well as preparational reasons. To study this problem, chemists and physicists (experimentalists as well as theoreticians) are trying in a joined effort to unravel the fundamental role of interfaces between small organic molecules and their connection to the outside world. In more detail, molecules are first adsorbed at a metal surface and then metallized in a second step by means of a recently developed electrochemical approach.
To increase the functionality of molecule-based nano-electronic devices in the future, a significant increase in complexity of the device architecture might be required. As a vision, combina¬tions of different molecular layers which can electrically be con¬tacted by individual metal electrodes could serve as a new platform for this ambitious aim. New concepts are developed to extend the usual sandwich design of conventional metal-molecule-metal junctions (one organic layer involved) to a molecular double-decker and, finally, to a molecular multilayer with significantly increased functionality and packing density thus aiming to expand Molecular Electronics to the third dimension.