Molecules and oligomers hold great promise for electronics, but electron transport across them are poorly understood.  To enable better understanding, it is necessary to study transport through single molecules.  We have developed the capability of studying transport through single molecules using scanning probe microscopy.  Furthermore, we are also developing techniques to measure the thermopower of single molecules.  This measurement will provide additional knowledge of whether the transport is mediated by electrons or holes, and also provide band offsets, which are key in understanding the role of contacts in molecule electronics.  We study transport of charge and energy in metal-molecule-metal junctions. We primarily work on thiol terminated organic molecules that bind to gold electrodes. The metal-molecule-metal junctions are formed using a scanning tunneling microscope by repeatedly contacting a gold coated mica substrate with a gold STM tip in a solution containing the thiol terminated molecules as shown in the figure.

Molecular Transport for Thermoelectrics

Chemically bonded solid-solid interfaces have thermal conductances in the range of 0.1-1 GW/m2-K over a wide temperature range. It is often desirable to reduce the thermal conductance of interfaces such that when multiple such interfaces are stacked together, one can reduce the effective thermal conductivities to very low values. To reduce thermal interfacial conductance, one should use materials with large mismatches in acoustic impedances. We are studying molecular interfaces since molecules are discrete objects that have discrete vibrational spectra and solids have continuous vibrational spectra. Hence, the mismatch in vibrational spectra would lead to a large impedance for acoustic waves and thereby reduce the thermal conductance. Furthermore, the structure of certain molecules may be switched externally using an electrical or an optical field. This may lead to the development of electrically or optically actuated thermal switches.