PhD defense, Nazanin Davani (March 7, Monday, 11 am, Packard 202)

Electrical and Optical Characterization of Molecular Junctions

Nazanin Davani

Stanford University PhD Dissertation Defense- Department of Chemical Engineering

Research Advisor: Professor Nicholas A. Melosh

 

March 7th (Monday), 2011 @ 11 am

(Refreshments served at 10:45 am)

 

Location: Packard 202

http://ee.stanford.edu/directions.php?bld=packard

Electronic transport through molecules has been intensively studied in recent years, due to scientific interest in fundamental questions about charge transport and the technological promise of nanoscale circuitry. A variety of experimental platforms have been developed to electronically probe molecular junctions. However, it remains challenging to fabricate reliable electronic contacts to molecules, and the vast majority of molecular electronic architectures are not amenable to standard characterization techniques, such as optical spectroscopy. Interesting phenomena like switching and rectification are observed in molecular junctions. However, due to limited quantitative information about the junction, the mechanism remains unknown and many fundamental questions about electronic transport remain unanswered.

The first part of the presentation will introduce the fabrication of Metal-Insulator-Metal (MIM) cross bar junctions using soft deposition technique. In this method, we softly deposit the premade metal contacts that are being supported with a polymer backing layer onto the organic layer. Using this method, we can efficiently fabricate large area, non-shorting devices, which are required for optical characterization of the molecular junctions.

Having established a means of fabricating reliable molecular devices, we have investigated the switching mechanism in molecular junctions based on n-type semiconductor Perylene tetracarboxylic diimide (TE-PTCDI) molecules. Using Surface Plasmon Resonance Spectroscopy (SPRS) we have been able to perform simultaneous optical-electrical measurements to study the molecular behavior quantitatively. Using in-situ optical spectroscopy on active molecular junctions, we find that only a small fraction of the molecules are actually switching in the junction. Finally, I present the results of our studies on the molecular rectification in C60-diamondoid hybrid molecules in large area junctions, as well as in smaller ensemble of molecules. The statistical studies along with a theoretical model show the origin of rectification in such molecular devices.