CMP Seminar

Monday, January 20, 2003
4:10 p.m., Room 1400 Biomedical and Physical Sciences Building
Refreshments served in Room 1400A at 3:45 p.m. 

Title:     Mesoscopic charge transport in organic nanostructures
           and carbon nanotubes

Speaker:   Y. W. Park
           School of Physics and Condensed Matter Research Institute
           Seoul National University
           Seoul 151-747, Korea
           and 
           National High Magnetic Field Laboratory
           Florida State University
           Tallahassee, FL 32310, U. S. A.

Abstract:
Since the magnetic length within which the charge carriers maintain phase 
coherence is LH = (eH/hc)-1/2 > 25.66H-1/2(nm) [H: Tesla], the high 
magnetic field could play a role as a local probe in examining the 
electrical properties of the nanometer scale structure, such as the 
polymer fibril nanojunctions in high-density polyacetylene (PA) film,
the PA nanofibers network and the PA single fiber. The linear 
magnetoresistance (MR) of heavily doped PA bulk film was observed in
7 Tesla < H < 30 Tesla. The anomalous linear MR at high field was 
attributed to the weak localization arising from the inherently 
non-homogeneous character of transport in polymers. It indicates that
the current transport is mainly controlled by a network of point
(interfibrillar) contacts between 'bulk volumes' with higher conductance.

The MR of doped PA nanofibers network was measured at low temperature in
micron scale. The magnitude of MR for nanofibers network was 1/100th of 
that of the bulk film. The MR showed weak oscillatory behavior which 
could be originated from the quantum interference effect in the 
mesoscopic annuli of PA nanofibers network. The low temperature MR of PA
single fiber of 20nm diameter showed a highly nonlinear electric field 
dependence of the Zener type and there was no significant change of MR 
in magnetic field up to H=6 Tesla, to within the accuracy of the data. 

The results could provide signature for the creation of charged 
soliton-antisoliton pairs by quantum-mechanical tunneling. Works on 
other conducting polymer nanofibers, such as Ppy, PANI, PPV, etc. are 
also summarized. The anomalous I-V characteristics of carbon nanotube 
in certain circumstance is presented as well. 

1.  J. G. Park, G. T. Kim, V. Krstic, B. Kim, S. H. Lee, S. Roth, M.
    Burghard and Y. W. Park, "Nanotransport in polyacetylene single 
    fiber: Toward the intrinsic properties", Synth. Met. 119, 53 (2001)
2.  A. B. Kaiser and Y. W. Park, "Conduction mechanism in
    polyacetylene nanofibres", Curr. Appl. Phys. 2, 23 (2002)
3.  D.-S. Suh, J. G. Park, J. S. Kim, D. C. Kim, T. J. Kim, A. N.
    Aleshin and Y. W. Park, "Linear High Field Magnetoconductivity 
    of Doped Polyacetylene up to 30 tesla", Phys. Rev. B 65, 165210 (2002)
4.  V. I. Kozub, A. N. Aleshin, D.-S. Suh and Y. W. Park, "Evidence
    of magnetoresistance for nanojunction-controlled transport in 
    heavily doped polyacetylene", Phys. Rev. B 65, 224204 (2002).