1 Introduction : Molecular Electronics and Molecular Wires

According to the predictions of Gordon Moore in 1965, the number of transistors per square centimeter of silicon doubles every 18 months [1]. This requires that the size of transistors and the interconnecting wires between them decrease at the same rate. Up until now, this miniaturization has been realized by improvements in photolithographic techniques. These techniques will reach their fundamental limit in the near future, as the dimensions of the components drop below tens of nanometers. Therefore, it is of considerable practical and fundamental interest to study the smallest components that are likely to be functional, that is, components consisting of single molecules or groups of molecules. Already in 1959 the eminent physicist Richard Feynman discussed the possibilities of devices of extremely small dimensions in his lecture entitled ‘‘There’s plenty of room at the bottom’’ [2]: