Tetsuyuki Kurata

Macromolecular Electronic Device

Abstract A thin-film transistor (TFT) with high carrier mobility has been fabricated using poly(2,5-thienylenevinylene)(PTV) as semiconductor. The carrier mobility has been obtained to be 0.22cm2/Vsec, which is in the same level as that of amorphous silicon TFT. It has been indicated that the enlargement of the π-conjugation length is crucial for the improvement of the carrier mobility. It has been also demonstrated that the molecular orientation is another important factor in terms of the device characteristics.

Organic Molecular Beam Deposition of α-Sexithienyl

We fabricated the molecular-oriented thin films of α-sexithienyl (6T) by an organic molecular beam deposition (OMBD) technique. The molecular orientations were evaluated from electronic spectra. The 6T molecules were aligned almost exactly parallel to the surface normal in the film deposited at a low deposition rate under 10-9 Torr. Furthermore, the 6T molecules in the film fabricated under 10-9 Torr have been found to form uniform aggregates. The aggregation has been analyzed by a molecular exciton model to give the molecular tilt angle of 85.7°.

NEXAFS spectroscopic studies of molecular orientation in α-sexithienyl evaporated thin films on metal films

Abstract The molecular orientation of evaporated α-sexithienyl (6T) films on gold (Au), silver (Ag) and copper (Cu) films at room temperature were studied by polarized near edge X-ray absorption fine structure (NEXAFS) spectroscopy and infrared reflection absorption spectroscopy (IR-RAS). The polarized NEXAFS spectra of 6T on Ag and Cu films exhibit a strong angular dependence of C1s → π∗ resonance intensity. Combining the results with theoretical simulations and auxiliary information from IR-RAS, it was found that 6T molecules in the film on Ag and Cu films are highly oriented with their molecular axes inclining by about 70° to the substrate surface. On the other hand, NEXAFS of 6T on Au film showed only a little dependence, indicating that 6T molecules are in nearly random orientation.

Electrooptical Study of an In-Plane Switching Mode Using a Uniaxial Medium Model

A new modeling method using a uniaxial medium model has been proposed to obtain a simple and quantitative expression for the transmittance of an in-plane switching (IPS) mode. In this model, the effective birefringence (Δneff) and the apparent optic axis rotation angle (app) are used instead of the original birefringence and the director profile, and Δneff changes when an electric field is applied to the IPS mode cell. The dependences of Δneff (measured as a retardation) and app on the applied voltage have been evaluated first by experiment. Δneff was reduced to 80% of the original value and app rotated 45° at the maximum transmittance (Tmax). It has been confirmed that the transmittance can be reproduced satisfactorily by employing the models expression using the observed Δneff and app values. Theoretical simulation has also been executed and the results supported the experimental results. The simulation has also shown that both the Δneff–Δn ratio and app at Tmax are almost constant and do not depend on either the cell gap or liquid-crystal properties. Tmax can be easily calculated using the uniaxial medium model.

Preparation and Characterization of 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) Films Deposited by Organic Molecular Beam Deposition Method.

The optical and structural properties for 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) films deposited on Au-coated substrates at the various growth temperatures by the organic molecular beam deposition (OMBD) method have been studied. The planar PTCDA molecules were oriented almost parallel to the substrate surface in the films deposited at the growth temperature of -160° C. Orientational disorder of the molecular planes occurred especially in the films grown at higher substrate temperatures. These films had basically large anisotropy of refractive indices which were evaluated by the prism attenuated total-reflection (ATR) method. The anisotropy of indices decreased for the film grown at the substrate temperature of 100° C. The optical anisotropy has been understood in terms of the molecular orientation.

Studies on Langmuir-Blodgett films fabricated from the monolayers containing polydiacetylene and polythiophene derivatives

Abstract A stable mixed monolayer, composed of a soluble conducting polymer, poly(3- hexylthiophene) (PHT), and a topochemically polymerizable amphiphilic diacetylene derivative, pentacosa-10, 12-diynoic acid (DA), was formed on an aqueous subphase. The structure of the deposited Langmuir-Blodgett (LB) films has been investigated by X-ray diffraction and second harmonic generation. It has been shown that the LB films have a well-defined layered structure, which is considered to contain partly a double-layered structure of PHT and DA. The PHT chain is well oriented in the LB films, so that its total dipole moment is perpendicular to the substrate when the ratio of PHT repeating unit to DA is less than unity.

Novel Pretilt Angle Measurement Method for Twisted-Nematic Liquid-Crystal Cells by Apparent Retardation Measurement

We have proposed a novel pretilt angle measurement method for twisted-nematic (TN) liquid-crystal (LC) cells. In this method, the dependence of the apparent retardation of the TN cell on the cell rotation angle is analyzed by the simple mathematic equations derived here to determine the pretilt angle and the gap. This method can be applied to the TN LC display panel. The necessary range of the cell rotation angle is from -3° to 3°. This provides an advantage for both constructing a compact measurement system and measuring a small-size pixel.

Study of α-Sexithienyl Thin Film by Polarized Near Edge X-ray Absorption Fine Structure

An ultrathin α-Sexithienyl (6T) film prepared by an organic molecular beam deposition method on a silver (Ag) film was studied by polarized near edge X-ray absorption fine structure (NEXAFS) spectroscopy using synchrotron radiation and IR-reflection absorption spectroscopy. The carbon K-edge NEXAFS spectrum of 6T was similar to those reported for poly-(3-methylthienylene) and thiophene. Polarized NEXAFS spectra of 6T exhibit strong angular dependence of 1 s→π* resonance intensity, showing that 6T molecules in the film deposited on the Ag film at room temperature had a highly oriented structure. To obtain quantitative information about molecular orientation, this dependence is analyzed by a comparison with theoretical calculation, indicating that the molecular axis is inclined by about 71° to the substrate surface. This angle is almost the same as that reported for 6T film on quartz.

Device characteristics and its operation mechanism of a FET-type waveguide modulator using α-sexithienyl

An optical waveguide modulator having a field-effect transistor-type electrode using a thiophene oligomer, α-sexithienyl (6T), has been fabricated and has functioned as an electro-absorption modulator with the modulation ratio of 20%. The optical modulation is directly related with the FET device operation, and has shown a maximum at 830 nm for propagating light wavelength. Therefore, the mechanism of the optical modulation has been clarified to be the increasing absorption due to polarons induced by negative bias. The linear relationship between the modulation ratios and the FET source currents has led to the conclusion that the polaron conversion efficiency η was introduced as the new parameter to understand the device operation, which has become clear. From the analysis, the nearly intrinsic value of carrier mobility of 6T was extrapolated, and the limit of the improving the carrier mobility was also shown. The possibility of enlarging the modulation ratio and its frequency dependence is also discussed.

25.3: The High Performance Scalable Display with Passive OLEDs

This paper describes a newly developed scalable Passive OLED Display System. The display dimension is no longer limited due to the seamlessly linked module structure. In the class of flat displays over 100 inches in dimension, passive OLED offers potentially significantly lighter weight as well as thinner thickness. A new design technology encompasses passive OLED units linked together to form a larger display without showing joint seams. The development also incorporates a technique to equalize individual display panel. A 155 inch (3.93m) prototype using 2,880 OLED panels have been fabricated. The display can offer the clear character and HD-TV images with wide-viewing angle.