Molecular Electronics is recognized as a key candidate to succeed the silicon based technology once we have arrived at the end of the semiconductor roadmap. The use of organic molecules in nanoscale nonlinear circuits offers many opportunities for new types of devices, which will differ in fabrication, functionality, and architecture. But even the fundamental question how electrical current flows across a single molecule is not satisfactorily understood. The common goal of this SPP is to strengthen the obligatory fundamental research activity in the field by combining different theoretical approaches, experimental techniques and to develop a full physical picture of molecular-scale charge transport. Funding will be provided for the following subtopics:
Molecular junction experiments: Different techniques to contact molecules have to be further developed, improved and calibrated. In addition to present charge transport measurements, new probes and additional control parameters are requested such as inelastic tunneling spectroscopy, the controlled treatment of environmental coupling, noise, and light-induced phenomena in transport.
Scanning-probe experiments with molecules on surfaces: Experiments are requested, which correlate detailed spatial information (including engineering of the molecule-substrate coupling) with electronic transport properties. In addition, tip manipulations to achieve molecular junctions are supported. Purely structural information without the link to charge transport properties is disregarded.
Hybrid structures and biomolecules: bio-inspired routes to molecular self-assembly are of interest and their link to electronic functionality. This may include new concepts to control charge transport in DNA and in DNA hybrids. Carbon nanotubes might be employed as electrodes for molecular contacts.
The ultimate theoretical goal is to devise new concepts and to design a computational machinery that allows for a quantitative prediction of electronic transport properties of individual molecules contacted to electrodes/substrates of a given material.
On the analytical side, model-based approaches familiar from mesoscopic physics (quantum dots) and theoretical chemistry (intramolecular charge transfer) are to be adapted to the molecular electronics context. In particular, this implies that analytical approaches and solutions should be developed by explicitly considering molecular properties and by accessing new parameter regimes appropriate for molecules.
First-principle-based atomistic approaches to quantum transport of complete molecular devices (including coupling to leads/substrates) are highly requested to feed the model calculations in the SPP and to achieve a predictive power relevant to experiment. This includes Density-Functional-Theory methods with improved functionals and more advanced many-particle/quasiparticle methods for accurate calculations of energies, couplings, and conductances. While the molecule itself has to be treated as a strongly inhomogeneous many-body system, the coupling to the leads induces nonequilibrium conditions. Finally, the environmental embedding known to influence the transport through the molecule in experiment should be addressed.
Architecture: Alternative routes to electronic circuitry, which meet special conditions for molecular devices, should be part of the PP as well.
Not supported are systems with all-carbon molecules (fullerenes/nanotubes) and inorganic clusters, except that they are used as a tool for transport across organic molecules. Further, purely synthetic chemistry projects will not be funded, the immediate connection to transport experiments is requested. Molecular films are of interest only when charge transport across molecules in self-assembled mono-layers is studied.