AVS 49th International Symposium
    Nanometer Structures Thursday Sessions
       Session NS-ThM

Paper NS-ThM8
Electronic Properties of Individual Defects in Molecular Circuit Elements

Thursday, November 7, 2002, 10:40 am, Room C-207

Session: Single Molecule Devices
Presenter: S.V. Kalinin, University of Pennsylvania
Authors: S.V. Kalinin, University of Pennsylvania
M. Freitag, University of Pennsylvania
A.T. Johnson, University of Pennsylvania
D.A. Bonnell, University of Pennsylvania
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The local property variations of nanowires, nanotubes, and functional molecules dictate the behavior of nanoelectronic devices. Scanning Gate Microscopy (SGM) provides information regarding individual defects during dc transport. To determine local properties of defects during ac transport, we have developed Scanning Impedance Microscopy (SIM). In combination these measurements quantify the electronic structures of individual defects in nanocircuits. A circuit is configured with a molecule or nanotube on an oxidized Si wafer with metal contacts at each end and a back electrode. In the case of a semiconducting single walled carbon nanotube the defects become depleted at a gate voltage that is related to the local electronic structure of the defect. The depletion voltage for each individual defect can be accessed in several ways. In SGM the current through the circuit is measured and the scanning probe tip provides a local gate voltage. In SIM an ac signal is applied across the circuit while the tip measures the local potential amplitude. The gate voltage in this case can be applied both from the back electrode (back gate) and the tip (tip gate). In both SGM and SIM the defects are manifest as sharp discontinuities in the image when they are depleted. The gate voltage dependence of the image contrast is a direct measure of the difference in Fermi energies at these defects. A comparison of results from nanotube circuits and molecular circuits will be presented and implications to local electronic structure and transport mechanisms will be discussed.