Toshiyuki Endo

Solution-Processed Dioctylbenzothienobenzothiophene-Based Top-Gate Organic Transistors with High Mobility, Low Threshold Voltage, and High Electrical Stability

Dioctylbenzothieno[2,3-b]benzothiophene (C8-BTBT)-based organic field-effect transistors (OFETs) with a top-gate configuration, having fluoropolymer gate insulators, are fabricated by means of a spin-coating technique. The device fabrication is simple, and it enables us to obtain C8-BTBT FETs having high field-effect mobility (?FET), low threshold voltage (Vth), and high electrical stability. We fabricate 116 top-gate C8-BTBT FETs having ?FET of 1.59?0.40 cm2 V-1 s-1 and Vth of -1.48?3.02 V, and the maximum ?FET is approximately 3 cm2 V-1 s-1. No changes in the devices characteristics are observed after applying a negative gate bias stress of -1.2 MV/cm for 104 s.

Preparation and Optical Properties of Aligned β-Phase Polyfluorene Thin Films

Aligned β-phase poly(9,9-dioctylfluorene) (F8) thin films have been prepared and their optical properties have been examined. Aligned β-phase F8 thin films are obtained by exposing aligned crystalline F8 thin films to toluene vapor. The polarization ratio in photoluminescence (PL) of the aligned β-phase F8 thin films is 30, which is almost the same as that of the aligned crystalline F8 thin films, while PL quantum efficiency of the aligned β-phase F8 thin films is much higher than that of the aligned crystalline F8 thin films. These results suggest that high performance is expected in polarized organic light-emitting diodes based on the aligned β-phase F8 thin film.

NMR Study of NdB6.

The staggered local field at boron nuclei in the anti-ferromagnetic phase of NdB 6 has been measured by 11 B-NMR. The angular dependence of the local field is explained as a type I anti-ferromagnetic structure by taking the domain distribution into account, which is consistent with that obtained by the neutron scattering measurement. The origin of the local field is explained as mainly the dipolar field from the magnetic moment at the Nd site. The saturated magnetic moment is estimated to be 1.6 µ B /Nd.

Highly Oriented Polymer Field-Effect Transistors with High Electrical Stability

Oriented polymer field-effect transistors (FETs) with a top-gate configuration have been fabricated using amorphous fluoropolymers as gate insulators. The oriented poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) FETs exhibit a high mobility anisotropy of 13 and a high mobility of 0.043 cm2V-1s-1 for charge transport parallel to the alignment direction. The temperature dependence of the mobility reveals small disorder in the oriented F8T2 microstructure at the interface with the fluoropolymer gate insulator. The transfer characteristics show no hysteresis or threshold voltage shift after applying a gate bias stress.

Oscillatory Structure in the Electroabsorption Spectrum of π-Conjugated Polymer Thin Films: How to Identify the Franz–Keldysh Oscillation

The nature of the oscillatory structure observed in the electroabsorption spectrum of highly ordered thin films of poly(9,9-dioctylfluorene) has been investigated and compared with that of the theoretically expected one-dimensional Franz–Keldysh (FK) oscillation. Although the observed oscillatory structure is not an FK oscillation, there are some similarities. From this comparison, we have discovered some features that can be used to distinguish whether the oscillatory structure is an FK oscillation, which include the field dependence of the oscillatory structure measured at four times the frequency of the applied electric field.

Enhancement of Third-Order Optical Susceptibility in Polythiophene Thin Films Fabricated by Drop Casting Using Anhydrous Solvent

To maximize the potential of poly(3-hexylthiophene) (P3HT) as a nonlinear optical material, we examined the conditions for fabricating thin films. The results indicate that the third-order optical susceptibility χ(3), which was determined by electroabsorption spectroscopy, is fourfold enhanced when thin films are drop cast from an anhydrous chloroform solution in an inert atmosphere, compared with the χ(3) of spin-coated thin films prepared in an ambient atmosphere. Fabricating the thin films in an O2- and water-free environment is essential for obtaining large χ(3) values. Under these conditions, we determined the maximum value of the imaginary part of χ(3) for P3HT to be 2.2 ×10-9 esu.

Rapid suppression of the metamagnetic transition for H || (111) in NdB6 by La doping

We have studied the specific heat, magnetization and magnetoresistance of Nd x La 1- x B 6 ( x =0.9, 0.8, 0.7) single crystals and obtained their magnetic phase diagrams. The antiferro (AF) magnetic phase for H ∥ is divided into two phases of AFI below H c1 and AFII * (or AFII) above H c1 . In the AFI phase, there exists the component of the parallel magnetic susceptibility up to H c1 . The intermediate metamagnetic AFII phase in NdB 6 disappears already for x =0.9 and in place, new AFII * phase appears. The AFII * phase is considered to be the spin-canted phase characterized by the perpendicular magnetic susceptibility. However, the magnetization in the AFII * phase for x =0.9 and 0.8 exhibits the unusual behavior that the extrapolation of the magnetization curve down to H =0 takes a large negative magnetization value. This unusual behavior disappears at x =0.7. These results indicate that the interaction forming the interamediate metamagnetic AFII phase is rapidly suppressed by the La doping and di...