To investigate the effect of alkyl chain length and adsorption time on the charge-transfer complex formation, ultraviolet-visible absorption and inelastic electron tunneling (IET) spectroscopy measurements were carried out for the tetramethylphenylenediamine (TMPD; donor molecule) adsorbed dodecyl-, pentadecyl- and octadecyl-tetracyanoquinodimethane (TCNQ) Langmuir-Blodgett (LB) films. In the optical absorption spectra, the main peak of LB films shows a red-shift depending on alkyl chain length and adsorption time. Furthermore, the dependence on alkyl chain length and adsorption time are also shown in the IET spectra. These results demonstrate that adsorption LB methods enable to control the adsorption ratio of functional molecules and the CT complex formation.

The doping effect of acceptor molecule tetracyanoquinodimethane (TCNQ) and donor molecule tetramethyltetraselenafulvalene (TMTSF) in an organic semiconductor was investigated by field effect measurements in merocyanine (MC) films. The electrical conductivity and carrier concentration of TCNQ-doped MC films were increased compared with those of undoped MC film. An efficient doping effect was observed at the doping concentration of approximately 9%. The electrical conductivity, on the other hand, was decreased by doping of the donor molecule TMTSF in MC film. However, no inversion of the conduction type was obtained. Furthermore, the transport mechanism of TCNQ-doped MC film and undoped film was elucidated from the temperature dependence of electrical parameters. These results demonstrate that TCNQ and TMTSF molecules act as acceptor and donor impurities in MC film, respectively, and the doping of these molecules is effective to control the electrical properties of organic semiconductors.

We have fabricated printed active antenna for flexible information tag which have a loop antenna combined with step-edge vertical channel organic field-effect transistor (SVC-OFET). Fabrication using printing process, characterization of SVC-OFETs, and performances of active antenna elements are discussed in detail.

We have fabricated a static induction transistor structure by using copper phthalocyanine (CuPc) films. Its layer-structure is Au(drain)/CuPc/Al(gate)/CuPc/Au(source)/glass. The source-drain current is controlled by the Al gate bias-voltage when the drain voltage is positive but is almost independent of it when the drain voltage is negative. The current-voltage characteristics are governed by the space-charge-limited conduction which depends on shallow traps.

Step-edge vertical channel organic field-effect transistors (SVC-OFETs) with a very short channel have been fabricated by a novel selective electrospray deposition (SESD) method. We propose the SESD method for the fabrication of SVC-OFETs based on a 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-pentacene) semiconductor layer formed by SESD. In the SESD method, an electric field is applied between the nozzle and selective patterned electrodes on a substrate. We demonstrated that the solution accumulates on the selected electrode pattern by controlling the voltage applied to the electrode.

We have developed a new type electrical probing system based on an atomic force microscope. This method enables us to measure simultaneously the surface topography and surface potential of thin films containing the crystal grains. The obtained local potential changes give an insight into conduction through the grains and their boundaries.