Shuji Imazeki

Self-aligned self-assembly process for fabricating organic thin-film transistors

A process for fabricating alignment-free, printable, organic thin-film transistors is presented. This process utilizes a self-assembly phenomenon in which soluble nanomaterials such as metallic nanoparticles and organic molecules are self-assembled into a device structure. To demonstrate this process, solution-processed source∕drain electrodes were self-aligned to a gate electrode using a hydrophobic self-assembled monolayer (SAM) optically patterned onto the gate electrode using a backsubstrate exposure technique. An organic semiconductor film deposited on the patterned SAM was selectively ordered and substantially self-aligned to the gate electrode. This process is called self-aligned self-assembly. A field-effect mobility of 0.15cm2∕Vs and potential minimum channel length of 3μm were experimentally demonstrated when pentacene molecules and silver nanoparticles were used as the semiconductor and electrode materials, respectively.

Surface‐pressure‐induced reversible color change of a polydiacetylene monolayer at a gas–water interface

The photopolymerization properties and the surface pressure dependence of excitonic absorption of polydiacetylene (PDA), i.e., poly‐(heptacosa‐10,12‐diynoic acid), are investigated by in situ reflection spectra of a monolayer at a N2 gas–water (pure water, CdCl2 aqueous solution) interface. The electronic structure of the initially appearing PDA is strongly dependent on the packing condition of diacetylene monomer, the blue‐ and red‐form PDAs that initially appear in loose and close packing conditions, respectively. A reversible color change induced by a change in surface pressure is found for the first time in a partially polymerized PDA monolayer on pure water, in which blue and red form PDAs appear predominantly at low and high surface pressures, respectively. Further, two metastable phases, observed at wavelengths about 40 nm longer than those of the blue form, are thought to be induced by the rheological process of the substitutional sidegroups. Our results suggest that these color changes are closel...

High-resolution full-color LCD driven by OTFTs using novel passivation film

A full-color twisted-nematic type liquid crystal display (TN-LCD) of 1.4-in diagonal size driven by organic thin-film transistors (TFTs) has been fabricated. This TN-LCD has 80/spl times/80/spl times/3 (RGB) pixel arrays addressed by pentacene TFTs with a channel width of 50 /spl mu/m. The contact resistance between the pentacene film and the source/drain electrodes has been reduced by selecting the exposure condition of the photoresist in patterning the electrodes. In addition, a solution-processed passivation film with a novel structure, consisting of photosensitive polyvinylalcohol and organosiloxane glass resin, has been developed to protect the TFTs against degradation induced by integration with TN-LCD devices. Consequently, it has been confirmed that the organic-TFT-driven TN-LCD fabricated in this paper is capable of displaying full-color moving images at a resolution of 80 pixels per inch.

Memory effect of chromophore orientation in merocyanine Langmuir-Blodgett films☆

Abstract The changes in the in-plane spectral anisotropy caused by heat, acidic vapour and basic vapour treatments after deposition are studied for Langmuir-Blodgett (LB) films of merocyanine dye containing a benzoselenazole nuclei mixed with arachidic acid. The as-deposited films exhibit a J-like aggregate band at 597 nm which is strongly polarized along the dipping direction of the substrate. After heat treatment or HCl vapour treatment, the J-like band disappears and the in-plane spectral anisotropy is reduced. NH3 vapour treatment causes the J-like band to be restored in the wavelength region 620–627 nm. The restored J-like band is polarized along the same direction as the original J-like band. This memory effect of chromophore orientation suggests that there is a highly anisotropic structure of J-like aggregates in LB films.

Unusual Orientational Behavior of Anthraquinone Dyes in Nematic Cyanophenylcyclohexane Derivatives

Abstract The optical order parameters of a number of anthraquinone and azo dyes are determined in three nematic liquid crystalline hosts. The results are discussed in terms of the effects of the hosts on the dye order parameters. It is found that the anthraquinone dyes show significantly higher order parameters in the host composed of cyanophenylcyclohexane derivatives. This enhancement of the orientational ordering is tentatively interpreted as being due to the supplement of the orientational cohesive forces with the charge-transfer interaction between the dyes and the host.

Highly oriented polydiacetylene monolayer formed at the air—water interface

Abstract Spectral and structural investigation of soluble polydiacetylene monolayer at the air—water interface is carried out using in situ polarized spectroscopy. The coil-like polydiacetylene that is adsorbed two-dimensionally on the water surface is distinguishable from the usual coil form in a solution and film in terms of the position of the absorption peak and the spectral feature. Through the coil-to-rod transition induced by increasing pressure, the linear conjugated backbone of the rigid rod polydiacetylene is gradually packed and remarkably oriented perpendicular to the direction of uniaxial compression. This orientation mechanism is discussed in relation to the preparation of monolayer and the nature of the rigid linear polymer and its coil-to-rod transition.

High-mobility solution-processed organic thin-film transistor array for active-matrix color liquid-crystal displays

Abstract— A solution-processed organic thin-film-transistor array to drive a 5-in.-diagonal liquid-crystal display has been fabricated, where semiconductor films, a gate dielectric film, and passivation films have all been formed using solution processes. A field-effect mobility of 1.6 cm2/V-sec, which is among the highest for solution-processed organic thin-film transistors ever reported, was obtained. This result is due to semiconductor material with large-grain-sized pentacene crystals formed from a solution and adoption of three-layered passivation films that minimize the performance degradation of organic thin-film transistors.

New Yellow Dyes For Guest-Host Applications

Abstract A study is presented of the optical order parameters and spectroscopic properties of 3′-hydroxyquinophthalone and 3,9-disubstituted perylene dyes in nematic liquid crystalline mixtures. The results of this study are discussed in terms of the effects of the dye structure on the order parameters. From the systematic variation in structure, it is found that a thioester group and a short flexible chain such as an n-butyl group play a significant role in increasing the order parameters. In addition, preliminary data on the solubility and photostahility of the dyes are reported.

Determination of the thickness and distribution of a Langmuir-Blodgett film using soft X-ray reflection

Abstract This paper reports the simultaneous observation of the thickness and distribution of XY-type Langmuir-Blodgett (LB) films by measurement of the reflectivity of soft X-rays using synchrotron radiation. The thickness and distribution are obtained by analysing the oscillation of the reflectivity, which is produced by varying the wavelength λ or grazing angle θ. The thickness obtained is compared with models of the XY-type deposition mechanism. It is shown that the molecular overturning model is the most satisfactory.

Order Parameters of α-Substituted Anthraquinone Dyes in a Nematic Liquid Crystalline Host

Abstract A study is presented of the optical order parameters and spectroscopic properties of α-substituted anthraquinone dyes in a nematic liquid crystalline mixture composed of cyanophenylcyclohexane derivatives. Then, the results of this study are discussed in terms of the effects of the dye structure on the order parameters. From the systematic variation in structure, the order parameters are found to be improved when a biphenylamino group is introduced into the α-position of the anthraquinone nucleus. In addition, preliminary data on the solubility and photostability of the dyes are reported.