Surface Science Letters Significant increase in conductivity of polydiacetylene thin film induced by iodine doping Kazuhiro Takami a, * , Yuji Kuwahara a,b,c , Takanori Ishii a , Megumi Akai-Kasaya a,b , Akira Saito a,b,c , Masakazu Aono a,b,c,d a Department of Material and Life Science, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan b Nanoscale Quantum Conductor Array Project, ICORP, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan c Harima Institute, The Institute of Physical and Chemical Research (RIKEN), 1-1-1 Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5148, Japan d Nanomaterials Laboratories, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Received 11 April 2005; accepted for publication 14 June 2005 Available online 28 July 2005 Abstract A significant improvement of the conductivity of polydiacetylene thin films by iodine doping was observed using independently driven double-tip scanning tunneling microscopy. One-dimensional conduction along the polydiacety- lene backbone was obtained and the conductivity of the iodine-doped polydiacetylene thin film was estimated to be (3 ± 0.3) · 10 À3 S/cm, which is three orders of magnitude higher than that of the nondoped polydiacetylene thin film and five orders of magnitude higher than that reported previously. The results of visible light absorption spectroscopy and atomic force microscopy showed that distinct changes in the electronic properties of the polydiacetylene backbone in the absence of a close-packed arrangement of polydiacetylene molecules. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Polydiacetylene; Thin film; Iodine doping; Conductivity; Double-tip scanning tunneling microscopy; Visible light absorp- tion spectroscopy; Atomic force microscopy Nanoarchitectures of organic molecules, partic- ularly organic molecular layers on solid surfaces, are highly attractive in view of the future applica- tions of nanotechnology. It is important to both control their electrical conduction and evaluate their conduction mechanism. Polydiacetylene (PDA) is one of the candidate materials for con- ducting molecular wires used in the interconnection 0039-6028/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2005.06.081 * Corresponding author. Tel./fax: +81 668797299. E-mail address: takami@ss.prec.eng.osaka-u.ac.jp (K. Ta- kami). Surface Science 591 (2005) L273–L279 www.elsevier.com/locate/susc