AVS 52nd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM1-ThM

Paper EM1-ThM1
Molecular Conductance and Contact Resistance Measured in Nanoparticle-Bridged Nanogap Structures

Thursday, November 3, 2005, 8:20 am, Room 309

Session: Molecular Electronics
Presenter: C. Chu, North Carolina State University
Authors: C. Chu, North Carolina State University
G.N. Parsons, North Carolina State University
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Understanding molecular conduction and contact resistance at organic-metal junctions is crucial for advanced organic electronic materials and devices. We have developed an angled metal evaporation technique to form planar metal (Au and Al) electrodes with separation distances of <50nm and electrode width of several microns, and used 80nm Au nanoparticles to form conductance pathways between the nanometer-spaced electrodes. Multiple nanoparticles can be measured in parallel, and the conductance increases with the number of nanoparticles in the gap. Before Au nanoparticle deposition, various molecular monolayers were adsorbed onto the Au electrodes, resulting in bridging structures that enable conductance of sets of molecules to be characterized. The conductance and contact resistances are evaluated from current-voltage characteristics and compared to results obtained by conductive probe AFM (CP-AFM) on the same monolayers. Molecules studied include various length alkanethiols and alkylamines, as well as conjugated molecules including xylyl thiol and phenylene derivatives. Current vs voltage is observed to follow the coherent tunneling model, and contact resistance (R@sub o@) was evaluated by measuring the effect of alkyl chain length for both thiol and amine head groups. Alkanethiols show R@sub o@ of ~18 k@OMEGA@, whereas amine head groups give R@sub o@ ~1k@OMEGA@. The number of molecules probed is not precisely known, but resistance for the nanoparticle bridge is larger than measured by CP-AFM, suggesting a smaller number of molecules are probed in the bridge structure. Furthermore conjugated molecules show conductivity that is ~400 times larger than for alkanedithiols. Results show that the bridged nano-gap structure can be used to evaluate conductance and resistance on the molecular scale, and it is capable of characterizing a variety of molecular and nanostructured elements.