The mastered electron: molecular electronics and spintronics, molecular machines

After a historical account of the evolution which led to the concept of Molecular Electronics, the “Hybrid Molecular Electronics” approach (that is, molecules connected to nanosized metallic electrodes) is discussed. The different types of transport (one-step, two-step with different forms of tunnelling) are described, including the case where the molecule is paramagnetic (Kondo resonance). Several molecular achievements are presented: wires, diodes, memory cells, field-effect transistors, switches, using molecules, but also carbon nanotubes. A spin-off result is the possibility of imaging Molecular Orbitals. The emerging field of molecular spintronics is presented. Besides hybrid devices, examples are given of electronic functionalities using ensembles of molecules, either in solution (logical functions) or in the solid state (memory elements). The relation with the domain of Quantum Computing is presented, including the particular domain of Quantum Hamiltonian Computing. The chapter finishes by an introduction to molecular machines, with the problem of the directional control of their motion.