Paper EM-TuM5
Real-time Conductivity Analysis through Single-Molecule Electrical Junctions

Tuesday, October 16, 2007, 9:20 am, Room 612

We have recently developed a molecular electronic characterization test-bed that utilizes a symmetric pair of gold nanoparticles, 40 nm in diameter, joined together by a single or small group of conjugated oligomeric phenylene ethynylene (OPE) molecules. These nanoparticle/molecule/nanoparticle structures are subsequently assembled between nanoscale test electrodes to enable current through the molecule to be characterized. At low voltage (< ±1.5 V) the observed current is consistent with common non-resonant tunneling (i.e., I vs V is independent of temperature between 80 and 300 K). This molecular analysis approach is unique because it enables the stability of the molecular conductance to be observed and characterized over extended periods (several weeks so far) after fabrication. Conductance through single molecule junctions was monitored in real-time during several process sequences, including dielectrophoretic directed self assembly and post-assembly modification. Assembly faults are directly detected in real-time when non-ideal assembly conditions result in molecular junction failure and nanoparticle fusion in the junction. Real-time conductivity measured through the junction was sensitive to ambient conditions, and changes persisted over several days of exposure. Atomic layer deposition of Al₂O₃ was used to encapsulate and isolate the molecular junctions, and the effect of the deposition process sequence on current through the junction was evaluated in real-time. Results indicate that the current measured during atomic layer deposition is sensitive to the chemical oxidation and reduction reactions proceeding in the 1-2 nanometer confined region between assembled nanoparticles.