We used a pulse-injection method to fix π-conjugated poly(3-hexylthiophene) (P3HT) molecules onto H-terminated Si(100) surfaces. Isolated molecules of P3HT were observed by scanning tunneling microscopy. The P3HT molecules comprised an almost all-trans conformation, reflecting the rigid feature of molecular chains. By quenching the substrate at 135 K, residual solvent molecules were observed. We could control the surface density of fixed P3HT molecules by changing both or either the volume or concentration of the injected P3HT solution.

High Seebeck effects from conducting polymer: Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) based thin-film device with hybrid metal/polymer/metal architecture Appl. Morphology and conductivity modification of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) films induced by conductive atomic force microscopy measurements Appl. Phys. Lett. 93, 241911 (2008); 10.1063/1.3049599 Influence of water on the work function of conducting poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) Appl. Phys. Lett. 90, 043512 (2007);

We measured current–voltage (I–V) characteristics of individual conducting polymers, poly(3-hexylthiophene)s (P3HTs), fixed on hydrogen-terminated Si(100) using scanning tunneling microscopy (STM)∕spectroscopy. The I–V curves reveal rectification characteristics that are attributed to the shift of the energy level of the valence-band maximum of P3HT under bias. The current suppression at positive substrate bias results from the effect of differential charging of the polymer between the opposite bias polarities, indicating the possibility for doping of polymer nanowires by using a STM tip as a gate electrode.

We measured the electrical current-voltage characteristics of DNA in vacuum using fine electrodes with a gap of about 200 nm. It was found that the electrical resistance of DNA molecules between the fine electrodes had a large variation: from 7.8 M to values larger than 1 T. This was consistent with the controversial results given in previous reports. The temperature dependence of conductivity was explained well by the Arrhenius equation. In addition, the conductivity of a single molecule of doublestranded DNA was measured by a ''one-by-one'' cutting method using atomic force microscopy (AFM). The conductivity was determined to be 3 Â 10 1 S/cm, which is about the same order as that of semiconductors.

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