AVS 50th International Symposium
    Nanometer Structures Tuesday Sessions
       Session NS-TuM

Paper NS-TuM9
Electronic Structure and Excited States of One-dimensional Polydiacetylene Nanowire

Tuesday, November 4, 2003, 11:00 am, Room 308

Session: Nanowires
Presenter: M. Akai-Kasaya, Osaka University and SORST JST, Japan
Authors: M. Akai-Kasaya, Osaka University and SORST JST, Japan
K. Shimizu, Osaka University and SORST JST, Japan
A. Saito, Osaka University and SORST JST, Japan
M. Aono, Osaka University and SORST JST, Japan
Y. Kuwahara, Osaka University and SORST JST, Japan
Correspondent: Click to Email
The polydiacetylene (PDA) nanowire can be fabricated at designated positions by using a STM probe tip on a self-assembled monomolecular (SAM) layer.@footnote 1@ The fabricated PDA wire grows out in a straight line and extends to a sub-micrometer length on the surface. The fully extended conjugated backbone of the PDA is not only expected to function as an electrically conducting nanowire but is also interesting in terms of exploring physics in one-dimensional (1D) systems. In this work, the density of states of individual polymers and constituent monomers were studied by STS. The STS spectrum delineating the density of states of PDA wire clearly reveals the theoretically predicted @pi@-band and band edge singularities of the 1D conjugated polymer. We have also observed a fascinating spectrum with a narrow gap, which is suggested to be due to the existence of the charge-carrying polaron states on a polymer backbone. Furthermore, we demonstrated that an exited state took place in an isolated polymer nanowire following the polymerization. The voltage pulse initiates additive polymerization, which proceeds instantaneously to both sides of the monomer array on the SAM layer. Before and after polymerization within the disabled feedback loop, the tunneling current shows the accountable difference due to the steady-state current on the monomer and derived polymer, respectively. However, the anomalous current, which often continues for few hundred micro-seconds, has been observed simultaneously with inception of the polymerization. We have estimated statistically the time of onset and duration of the current and correlation with the length of the derived polymer wire. And then, it can be concluded that the detected anomalous current results from the vibrational excitation states of a derived molecular nanowire. These results are remarkable and interesting in terms of one molecular science. @FootnoteText@@footnote 1@Y. Okawa and M. Aono, Nature 409, 683 (2001).