Molecular Switches and Rectifiers: The Electronic Properties of Molecular Junctions

When: Thursday, December 01, 2011 at 12:00 pm
Where: EG 306
Speaker: Kim Michelle Lewis, Ph.D.
Organization: Assistant Professor of Physics, Department of Physics, Applied Physics, & Astronomy, Rensselaer Polytechnic Institute
Sponsor: Nanogroup Meeting

Molecular switches are devices that are able to switch between two or more conductance states.  Although many highly conjugated molecules have been reported to show conductance switching, there continues to be a strong need within the community to pinpoint the origin of this electronic property.  Similarly, an argument can be made for the origin of molecular rectifiers.  These devices have the ability to control current in one direction.  This behavior is attributed to either the asymmetry in the electrodes or in the molecule.  However, it may be possible to observe rectification in a device with symmetry in both the molecule and electrode.

Experimental results are discussed and future experiments are proposed that will provide key insights into a two-state conductance observed in porphyrin molecules and connecting the existence of the conductance to redox states and vibration modes that exist in the molecules.  Results will be discussed that demonstrate how one can simultaneously measure the conductance of a single molecule and control the surface potential near the redox states of the molecules to manipulate conductance in a junction.  In addition, data will be presented that show for the first time rectification observed in porphyrin molecules self-assembled as molecular layers on gold facets using conductive atomic force microscopy.  Studies will be presented to explore another explanation for the existence of rectifying behavior in molecular junctions by investigating the effects of molecular multilayers and the molecule-electrode coupling on rectification observed in porphyrin molecules.