Improved stability of organic field-effect transistor performance in oligothiophenes including β-isomers

Dialkyl quarter- and quinquethiophenes end-capped with β-connected thiophenes are prepared, and the field-effect transistor (FET) properties are investigated. Molecular orbital calculation as well as the redox and optical measurements indicate that the β-isomers have low-lying HOMO levels and large energy gaps compared with the α-isomers. Molecular packing of the dihexylquaterthiophene with β-isomers consists of a typical herringbone motif analogous to the α-isomers. In the single crystal, the alkyl chains are extending in the tilted directions from the core molecular plane, but straightly extending in the thin films, resulting in even more perpendicular molecular arrangement to the substrate than the α-isomers. These β-isomers show p-type FET performance comparable to the corresponding α-isomers, whereas all new oligothiophenes show air stability better than the corresponding α-isomers. In particular, dihexylquinquethiophene with β-isomers has shown significantly improved air stability maintained over 270 days. This stabilization effect is ascribed to the low-lying HOMO level and the dense packing realized by perpendicular molecular arrangement.     

Novel freebase and zinc bilinone dimers with optically active peripheral groups. Synthesis and application to chiral nematic induction in a nematic mesophase

In order to investigate effective dopants to induce chiral nematic liquid crystalline phases, novel freebase (FbBL) and zinc bilinone (ZnBL) derivatives bearing optically active aliphatic groups ((S)-3,7-dimethyloctyls) at the peripheral positions were prepared. From the CD spectra, it was confirmed that M-helicity in the bilinone frameworks was modestly enriched for ZnBLs, whereas helicity was hardly induced for FbBLs except for the o-xylylene-spaced dimer. When N-(4-methoxybenzylidene)-4-butylaniline (MBBA) was doped with the bilinone derivatives, the chiral nematic phase was effectively induced, and the helical twisting powers (β_Ms) ranged from ?95 to ?159 μm^?1. The control experiment using (S)-3,7-dimethyl-1-phenyloctane (β_M = +14 μm^?1) clearly showed that the induced chiral helical frameworks of FbBL and ZnBL predominantly contribute to chiral nematic induction of MBBA.     

Intergranular Stress Corrosion Cracking of Pure Copper 〈111〉 Tilt Bicrystals

Behaviour of stress corrosion cracking (SCC) in a series of pure copper bicrystals with a symmetrical 111-tilt boundary has been investigated. Tests were performed by the slow strain rate technique (SSRT) in 1M NaNO₂ solutions. The small-angle tilt bicrystals fractured in both intergranular and transgranular manners accompanied by a large amount of plastic strain to fracture while the large-angle bicrystals fractured in almost intergranular manner with a smaller plastic strain. Susceptibility of SCC increases with increasing misorientation and becomes relatively constant in large-angle grain boundaries. The local minima appeared at the 7(321) and 3(211) boundaries, suggesting that the susceptibility was partially affected by grain boundary energy. Stress concentration generated by the pile-up of trapped dislocations at the grain boundary could account for the high susceptibility of the intergranular SCC in large-angle grain boundaries.     

Characterization of the optical properties of LPE InxGa1−xAsyP1−y thin layers grown on InP

A series of In_xGa_1?xAs_yP_1?y single-crystal thin layers have been grown on an InP substrate in a vertical liquid phase epitaxy furnace with a rotating slide boat system. The optical properties of these LPE quaternary alloys lattice-matched to InP have been investigated mainly by photoluminescence and electroreflectance measurements. Photoluminescence spectra of In_xGa_1?xAs_y P_1?y epitaxial layers are dominated by a strong luminescence line due to band-edge emission. At low temperatures, around 4.2 K, we have observed complicated luminescence bands with many fine structures. Electroreflectance spectra for the LPE In_xGa_1?xAs_yP_1?y layers are sufficiently broad to fulfil the low-field condition, and the analysis enabled us to determine precisely the band gap energy.     

Liquid phase epitaxy of AlxGa1−xP on GaP and its application to double heterostructure light modulators

Single- and double-heterojunction structures of Al_xGa_1?xP/GaP were grown by liquid phase epitaxy and their opto-electronic properties were characterized. Using a starting growth temperature of 900°C, a background impurity level in undoped Al_0.5Ga_0.5P of 1 × 10¹⁶ cm^-3 (p-type) is obtained. The growth rate of Al_xGa_1?xP was very low. An almost intrinsic layer exists at the p-n Al_xGa_1?xP/GaP heterojunction interface due to the interdiffusion of the dopants. By using a rotating slide liquid phase epitaxial growth technique, we have made a high efficiency light modulator from a Al_xGa_1?xP/GaP double heterostructure. The employment of a dummy crystal resulted in very good reproducibility of the GaP waveguide layer thickness. Light is well confined in the GaP layer and a voltage difference, V_π, of 6 V is enough to obtain the phase difference, π, between TE and TM modes.     

Simplification of determination method for standard materials using post-column reaction GC/FID

For the simple and fast preparation of highly reliable standard materials, a post-column reaction GC/FID system was developed and evaluated on the mixture of oxygen-containing organic compounds. The oxygen-containing organic compounds mixing solution were determined with the post-column reaction GC/FID system using n-dodecane as an internal calibration standard. Required value of relative expanded uncertainty as an original source of SI-traceable standard materials was within 1% and it aimed at this value as accuracy of the quantitative analysis. The results showed good agreement between the prepared concentrations and analytical values using post-column reaction GC/FID system. These results indicated that the post-column reaction GC/FID system would be used for getting SI-traceable values.     

LBI tests of independence in bivariate exponential distributions

The locally best invariant test for the hypothesis of independence in bivariate distributions with exponentially distributed marginals is derived. The model consists of a family of bivariate exponential distributions with probability density function $$f_\theta (x_1 ,x_2 ;\lambda _1 ,\lambda _2 ) = \lambda _1 \lambda _2 \exp [ - (\lambda _1 x_1 + \lambda _2 x_2 )]g(\lambda _1 x_1 ,\lambda _2 x_2 ;\theta )$$ with unknown scale parameter γ _j (j=1, 2) and association parameter ? which includes the independence situation. The locally best invariant (LBI) test is derived and the asymptotic null and nonnull distributions are also derived under some regularity conditions. The results are applied to the Gumbel (1960,J. Amer. Statist. Assoc.,55, 698–707), Frank (1979,Aequationes Math.,19, 194–226, and Cook and Johnson (1981),J. Roy. Statist. Soc. Ser. B,43, 210–218) families.     

Zero-CO2 emission and low-crossover 'rechargeable' PEM fuel cells using cyclohexane as an organic hydrogen reservoir

High performance (open circuit voltage = 920 mV, maximum power density = 14-15 mW cm(-2)) of the PEM fuel cell was achieved by using cyclohexane as a fuel with zero-CO2 emission and lower-crossover through PEM than with a methanol-based fuel cell.     

High-pressure acceleration of the growth kinetics of glucose isomerase crystals

The growth and dissolution rates of glucose isomerase crystals ({1 0 1} face) were measured in situ at 0.1 and 100 MPa. From these data, we determined that the solubilities at 25 degrees C were C(e) = 3.1 +/- 0.9 and 2.6 +/- 0.5 mg mL(-1) at 0.1 and 100 MPa, respectively. At the same supersaturation of sigma = 2.5 (sigma identical with ln(C/C(e)), C = the concentration of glucose isomerase, C(e) = the solubility) and temperature (T = 25 degrees C), the growth rate under 100 MPa was 7.6 times larger than that under 0.1 MPa. This result shows, for the first time, a kinetic acceleration of the growth rates of protein crystals with increasing pressure. The growth rates vs sigma data fitted well with a two-dimensional nucleation growth model of a polynucleation type. The fitting results indicate that the acceleration is mainly due to the decrease in the molecular surface energy of the glucose isomerase crystal with pressure.