Condensed Matter Physics Seminar

2 p.m., Thursday, September 9, 2004
Room 1201, Physics Building

 Conductance in One Dimension: Nanotubes and Molecules

Michael S. Fuhrer

(Department of Physics and Center for Superconductivity Research, University of Maryland)

Abstract:  Recent advances have allowed the exploration of true one-dimensional electron transport in two new systems: carbon nanotubes and conjugated organic molecules.  In each case electrons are conducted through the extended π-orbital network of carbon.  I will discuss recent experiments in my lab to determine the fundamental conduction properties of semiconducting carbon nanotubes, and recent results from a collaborative effort to synthesize, measure, and model transport through individual organometallic molecules.  Growth of very long (up to 1 millimeter), very clean semiconducting carbon nanotubes has allowed determination of the charge carrier mobility in this material[1].  The mobility may exceed 105 cm2/Vs at room temperature, higher than any other known semiconductor.  Schottky-barrier electrodes allow simultaneous injection of electrons and holes at high bias, with recombination in the nanotube.  A simple model allows determination of the saturation velocity of carriers in the nanotube of 2 x 107 cm/s[2], twice that in silicon.  We have studied the conduction through a ferrocene-based organometallic molecule, and, in excellent agreement with theoretical results, observe a Lorentzian resonance in the bias-dependent conduction with a peak differential conductance of up to 70% of Go, the theoretical maximum.  The results are in sharp contrast to those of our group and other groups on conjugated all-organic oligomers, where a high conductance resonance is also expected, but not observed experimentally.  We suggest some solutions to this dilemma.

[1] T. Durkop, S. A. Getty, E. Cobas, M. S. Fuhrer, “Extraordinary Mobility in Semiconducting Carbon Nanotubes”, Nano Letters 4, 35-39 (2004).
[2] Yung-Fu Chen and M. S. Fuhrer, “Saturation Velocity in Semiconducting Carbon Nanotubes,” submitted.
[3] Stephanie A. Getty, Chaiwat Engtrakul, Lixin Wang, Rui Liu, San-Huang Ke, Harold U. Baranger, Weitao Yang, Michael. S. Fuhrer, Lawrence R. Sita, "Designing a high conductance molecular wire," submitted.

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