Molecule-Based Devices

Introduction. The increasing demand for higher information density and circuit miniaturization is rapidly approaching the limits of device scaling technologies, with potential cost and performance limits being realized within a decade. Fortunately, nanoscale fabrication technology has progressed to the point where single molecules can be incorporated into and function as critical components in electronic circuits, offering the prospect of even smaller, faster, and more efficient devices. Recent reports indicate that spin polarized electron transport (Kondo assisted tunneling) can be observed in electrical devices constructed from physisorbed C₆₀ molecules spanning ferromagnetic nickel electrodes. Moreover, Tunneling Magneto Resistance (TMR) through the fullerene up to 40% was observed at 1.5 K, suggesting that simple resistance measurements can probe the quantum state of an electrically isolated molecule; incorporation of magnetic clusters with efficient spin coupling and high spin ground states should significantly enhance this effect. If engineered clusters with tunable magnetic and spin transport properties can be inserted into these nanoscale junctions, then the superposition of metal spin states could under ideal circumstances, act as a basis for quantum computing, with the output being resistance across the cluster.

Recent Progress in Device Fabrication. We are currently investigating the construction of molecule-based devices derived from magnetic clusters and a key challenge of this research effort is to fabricate nm-scale gaps that correspond to the length scales of molecules.

The Bruce Hinds group has prepared nm-scale electrodes that correspond to the length scales of our magnetic clusters. Synthetic efforts have afforded clusters that chemisorb to nanometer-sized electrodes and span the nanometer-scale electrodes. Recent transport measurements suggest that successful integration and chemisorption of the clusters into these electrodes has been realized.

Future Studies. Subsequent measurements will probe molecule-mediated conduction mechanisms exhibited by the assembled devices (e.g. RKKY, superexchange, etc.). With knowledge of the dominant conduction mechanisms operative between the magnetic clusters and leads, we can investigate the optimal means of switching spin state via applied gate bias, light excitation, applied magnetic field, or chemical coordination. These transport studies are currently underway in collaboration with Bruce Hinds and co-workers.