Nobuo Sonoda

Novel organosynthetic routes to polythiophene and its derivatives

Abstract Polythiophene and its 3-alkyl derivatives have been synthesized by novel organosynthetic techniques. The organochemical syntheses were carried out by dehydrohalogenation of 2-halogenothiophene (or its 3-alkyl derivatives) or by dehydrogenation of thiophene (or its 3-alkyl derivatives). Copolymers can also be obtained from a solution involving two (or more) kinds of thiophene monomer species. The resulting polythiophene and its derivatives have well-defined chemical and electronic structure and molecular weights as large as 2.5 × 10 5 . The poly(3-alkylthiophenes) with long alkyl side groups, typically poly(3-hexylthiophene), are readily soluble in common organic solvents and can subsequently be processed into uniform films from their solution. These solution-cast films, furthermore, can be easily stretched up to a stretching ratio of about five. The stretched films exhibit excellent conductivity (as high as 200 S/cm) after doping. The effect of the copolymerization between two thiophene monomers is also discussed.

Outdiffusion of the excess carbon in SiC films into Si substrate during film growth

The excess of C atoms diffused into the (111) Si substrate during the growth of the cubic SiC films are detected by Auger electron spectroscopy, infrared absorption, and x-ray photoelectron spectroscopy. The diffusion coefficient of the C atoms into the Si substrate at 820 °C is 8.4×10−15 cm2 s−1, which is close to the value of the diffusion of the C atoms into Si crystal using solid source. The C atoms mainly occupy substitutional sites in the Si substrate when the substrate temperature is below 750 °C, and both substitutional and nonsubstitutional sites when it is above 820 °C.

CHARACTERIZATION OF 3C-SIC FILMS GROWN ON MONOCRYSTALLINE SI BY REACTIVE HYDROGEN PLASMA SPUTTERING

Detailed characterization using x-ray diffractometry, scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, and Auger infrared and focused ion-beam spectroscopy, was carried out on cubic SiC films grown on single-crystal (100) Si substrates by reactive hydrogen plasma sputtering over a range of growth temperatures between 700 and 1000 °C. It was found that the first few deposited atomic layers were always amorphous. The subsequent SiC films showed well-defined (111) growth at the lowest temperatures, becoming randomly oriented by 1000 °C. The measured C:Si ratio was always >1, and varied with depth inside a film and also with temperature. At higher temperatures, the presence of “hollow voids” was observed, our data being consistent with their formation by outdiffusion of Si atoms from the substrate through the SiC layer. Associated with the hollow voids we observed the presence of a porous, highly C-rich region at the Si–SiC interface. We propose that this was d...

Intracavity second‐harmonic generation using a deuterated organic ionic crystal

A large organic ionic crystal (10×28×15 mm3):4‐nitrophenol sodium(:Na) salt dihydrate (NPNa) crystal, which had good optical, mechanical, and thermal properties, was grown for the second‐harmonic generation (SHG) device. Its effective nonlinear constant was found to be 5.0 pm/V at 1064 nm. The Vickers hardness and thermal conductivity were about two times larger than those of molecular crystals. The SHG device made of DNPNa, in which the water of crystallization of NPNa was deuterated, was used for the intracavity SHG of a diode‐pumped cw Nd:YVO4 laser. High SHG power of 4.4 mW at 532 nm was obtained for the first time with an organic nonlinear material.

Crystal growth and the nonlinear optical properties of 4‐nitrophenol sodium salt dihydrate and its deuterated material

Large organic ionic crystals on the order of a few centimeters of 4‐nitrophenol sodium(:Na) salt dihydrate (NPNa) and DNPNa, in which the water of crystallization of NPNa was deuterated, were grown for second‐harmonic generation (SHG). The Vickers hardness and thermal conductivities of NPNa were about two times larger than those of conventional organic molecular crystals. The effective nonlinear optical constants of NPNa and DNPNa were estimated to be 5.0 and 5.5 pm/V, respectively. The optical loss coefficients, measured by spectrophotometry, of NPNa and DNPNa were 1.8 and 0.6 dB/cm at 1064 nm, respectively. The substitution of D2O for H2O in NPNa crystal is very effective in reducing the optical loss coefficient. High power of 4.4 mW green SH light was obtained using a 1.5‐mm‐thick DNPNa crystal as the intracavity SHG device of a diode‐pumped Nd:YVO4 laser.

Low-Temperature Growth of Oriented Silicon Carbide on Silicon by Reactive Hydrogen Plasma Sputtering Technique

Highly oriented β-SiC film is prepared on (100) Si substrate at 800°C by reactive hydrogen plasma sputtering of a ceramic SiC target. The highly oriented β-SiC film can be grown on (100) Si substrate without void formation at the SiC film/Si interface. Hydrogen plasma etching of the growing film plays an important role in the growth of the oriented β-SiC films. Voids at the SiC film/Si interface are formed at a temperature of about 800°C due to the reaction of SiC film with Si substrate. Also, a thin amorphous buffer layer of 5 nm thickness is formed at the SiC film/Si interface. The results of this study indicate that the buffer layer can be eliminated by a suitable surface treatment of Si substrate before film growth.

Compositional Changes of SiC/Si Structure during Vacuum Annealing

Compositional changes of SiC/Si structure during vacuum annealing are investigated by Auger electron spectroscopy. An amorphous SiC film is grown on the (111) Si substrate at 600°C by hydrogen plasma sputtering. The obtained SiC/Si structure is annealed in the temperature range of 650–950°C in vacuum. When the annealing temperature is lower than 800°C, no significant compositional or structural changes are observed in the SiC/Si structure. On the other hand, when the annealing temperature is higher than 800°C, crystallization of the amorphous SiC film takes place, resulting in both shrinking and subsequent stress in the SiC film. The stress leads to the crack in the film, and may enhance the gasification of Si and C atoms in the structure.

Observation of the Formation Processes of Hollow Voids at the Interface between SiC Film and Si Substrate

The formation processes of hollow voids which appear at the interface of cubic SiC film/Si substrate are observed using scanning and transmission electron microscopy. The cubic SiC films are prepared on a (100) Si substrate which is kept at a temperature ranging from 700°C to 1000°C by means of reactive hydrogen plasma sputtering of a ceramic SiC target. We found that the hollow voids are first formed at lattice defects near the Si substrate surface due to the high reactivity of the defects, and are later formed at reaction zones which form by the film growth nuclei with the Si substrate surface. Formation and growth of the hollow voids are complex processes that depend on conditions such as substrate temperature, areal density of both the lattice defects and the film growth nuclei at the Si substrate surface, and diffusion rate of gas atoms through the growing film.

Evidence for the appearance of carbon-rich layer at the interface of SiC film/Si substrate

A porous carbon-rich layer with the thickness in submicron order is found to form at the interface between polycrystalline cubic SiC film and (100) Si substrate during the film growth using a reactive hydrogen plasma sputtering of ceramic SiC target. The appearance of the porous carbon-rich layer at the interface is due to an indiffusion of carbon atoms through the growing SiC film, and is related to the existence of a hollow voids at the interface. The results obtained in the present study suggest that the indiffusion of carbon atoms through the film may result SiC film growth at the interface.

Intracavity Second-Harmonic Generation and Influence of Optical Loss of Organic Nonlinear Optical Materials

We propose two different methods to estimate the optical loss of organic nonlinear optical (NLO) materials, which significantly reduces the efficiency of intracavity second-harmonic generation. One method is the estimation of the optical loss from the intracavity optical power at 1064 nm. The optical loss of the 4-nitrophenol sodium (:Na) salt dihydrate (NPNa) crystal was 1.3 dB/cm, and that of the DNPNa crystal, in which the water of crystallization of NPNa was deuterated, was 0.15 dB/cm. Another method is the estimation of the optical absorption loss from a liquid, the molecular structure of which has the same particular structural groups as those of the organic NLO materials. This latter method is very useful when new organic NLO materials are designed. The optical absorption losses at 1064 nm for the particular structural groups of the benzene ring were found to increase in the following order: -Cl<-NO2<-CH3=-OCH3<-OC2H5<-NH2.