Condensed Matter Physics Seminar
                      Monday, April 8, 2002
         4:10 p.m., Room 224 Physics-Astronomy Building
 
                   SINGLE MOLECULE ELECTRONICS
 
                         Stuart Lindsay
               Department of Physics and Astronomy
            Arizona State University, Tempe, AZ 85287
 
 Understanding the metal-molecule junction is an important step in the
 development of molecular electronics. We have recently developed a
 method for making covalently-bonded metal contacts to each end of a
 single molecule.  A molecule with gold-reactive end groups (thiols) on
 each end is inserted into an inert array on a gold surface.  The
 protruding thiol group is then attached to a gold nanocrystal and used
 to form a metallic bond with a gold-coated AFM tip.  The electronic
 properties of the bonded metal-molecule-metal system are very different
 from the properties of junctions in which a mechanical (nonbonded)
 contact is used.  Current, at a given voltage, is increased by about
 five orders of magnitude.  The current becomes independent of strain in
 the nanojunction, suggesting that the charge transfer mechanism is quite
 different.  Finally, we find that the electronics decay length is both
 larger than expected and also voltage dependent.  These effects are
 accounted for by a large, but unexplained shift in the energy gap
 between the Fermi level and the molecular orbitals that dominate charge
 transfer.