Makoto Harada

Infrared and XAFS study on structure and transition behavior of zinc stearate

Structure and transition behavior of zinc(II) stearate crystal were investigated by infrared and XAFS spectroscopies. Structure of zinc stearate at room temperature was estimated as follows. From XAFS analysis, the coordination number of the carboxylate groups around the zinc atom was evaluated as 4 and the Zn-O distance as 1.95 A. Based on the infrared spectrum and a normal mode analysis, the conformation of the alkyl chain was confirmed as all-trans and the sub-cell packing was considered as parallel type, and also the coordination form of the carboxylate groups was determined as bridging bidentate type. As increasing temperature, zinc stearate has a solid liquid phase transition at 130 degrees C. At the transition, the alkyl chains goes into liquid like state as reported by Mesubi but the coordination structure was confirmed to be maintained.

Highly efficient oxidation of silicon at low temperatures using atmospheric pressure plasma

Silicon oxide (SiO2) layers were formed with initial oxidation rates in the range of 6.2–14.1nm∕min in the temperature range of 150–400°C by oxidizing Si(001) wafers. Such a high-rate and low-temperature oxidation was realized by using a stable glow He∕O2 plasma excited at atmospheric pressure by a 150MHz very high-frequency power. Increasing the temperature led to both the higher oxidation rate and the better quality of SiO2 and SiO2∕Si interface. The oxidation at 400°C showed an interface trap density of 6.2×1010eV−1cm−2, which is considerably lower than that in a radical oxidation process using low-pressure He∕O2 plasma at the same temperature.

X-ray absorption spectroscopy of liquid surface

An apparatus has been constructed for x-ray absorption spectroscopy of elements at air/aqueous solution interface. Its surface sensitivity is gained from glancing incidence of synchrotron radiation under total reflection condition. The absorption is detected by total conversion He ion-yield method. This apparatus was operated at the beam line 7C of Photon Factory, where the incident photon beam comes from a sagittal focus double-crystal monochromator via a 70-cm-long bent mirror. The mirror focuses the beam vertically and changes the beam direction downward by 1 mrad to irradiate solution surface. The essential requirement of this technique, ripple-free liquid surface at accurate position, was attained by introducing a trough on a floating boat, continuous surface level monitoring, and an automatic Z-stage control. The x-ray absorption edge jump demonstrated that surface concentration of bromide ion follows the Langmuir type adsorption for tetraalkylammonuim bromide solution. By comparing the jump values ...

Calculation of electrostatic solvation energies for polycyclic aromatic hydrocarbon mono-cations in acetonitrile

Abstract A modified generalized Born equation is incorporated with a semiempirical molecular orbital method to calculate electrostatic solvation energies for solute ions. A parameter corresponding to the atomic radius is introduced as a function of size of the solute ion and the position of the atom with respect to the solute surface. This method is applied to benzene and 17 polycyclic aromatic hydrocarbon mono-cations with various sizes and shapes in acetonitrile. The results are compared with experimental values obtained from the data of oxidation and ionization potentials. The present calculations based on the simple dielectric continuum model can predict the solvation energies with an average error of 0.07 eV.

Significant enhancement of Si oxidation rate at low temperatures by atmospheric pressure Ar∕O2 plasma

Using stable atmospheric pressure plasma, the effect of inert gas (He, Ar, and Kr) mixed with O2 on the oxidation process of Si(001) wafers was investigated. Ar∕O2 plasma was shown capable of generating atomic oxygen most efficiently and significantly enhanced the oxidation rate in comparison with He∕O2 plasma, while Kr∕O2 plasma was not suitable for the low-temperature and high-rate oxidation of Si. As a result, by using Ar∕O2 plasma, oxide layers having equivalent quality to that by He∕O2 plasma could be formed with a drastically high initial oxidation rate of 28.0nm∕min.

Ionization energies for solvated polycyclic aromatic hydrocarbons

Abstract Vertical ionization energies for a series of polycyclic aromatic hydrocarbon molecules in acetonitrile, measured as E t values by photoelectron emission spectroscopy, are compared with theoretical values derived by a semiempirical MO method, MOMGB, incorporating the solvent effect based on the dielectric continuum model. The calculation reproduces the E t values with errors less than 10%.

Formation of silicon dioxide layers at low temperatures (150?400??C) by atmospheric pressure plasma oxidation of silicon

abstract The formation of silicon dioxide (SiO2) layers at low temperatures (150–400°C) by atmospheric pressure plasma oxidation of Si(0 0 1) wafers have been studied using a gas mixture containing He and O2. A 150 MHz very high frequency (VHF) power supply was used to generate high-density atomic oxygen in the atmospheric pressure plasma. Oxidation rate, structure, and thickness and refractive index profiles of the oxidized layers were investigated by ellipsometry and infrared absorption spectroscopy. Atomic force microscopy was also employed to observe atomic-scale morphologies of the layer surface and wafer Si surface, after chemical removal of the oxidized layers. It was found that stoichiometric SiO2 layers were obtained at higher oxidation rates than conventional dry O2 thermal oxidation and radical oxidation processes, even at a very low substrate temperature of 150°C. Although thickness variations were observed in the plasma region, the refractive index was independent of both substrate temperature and VHF power. In addition, the SiO2 surface and SiO2/Si interface roughnesses were comparable to those obtained in conventional dry oxidation at high temperatures.

AlON/SiO2 Stacked Gate Dielectrics for 4H-SiC MIS Devices

We propose the use of an aluminum oxynitride (AlON) gate insulator for 4H-SiC MIS devices. Since direct deposition of AlON on 4H-SiC substrate generates a large amount of interface charge due to an interfacial reaction, a thick AlON layer was deposited on underlying thin SiO2 thermally grown in N2O ambient. To reduce the negative fixed charge density in the aluminum oxide (Al2O3) film, we used reactive sputtering of Al in an N2/O2 gas mixture. The fabricated MIS capacitor with AlON/SiO2 stacked gate dielectric shows no flat band voltage shift and negligible capacitance-voltage hysteresis (30 mV), indicating the dielectric is almost free from both fixed charges and electrical defects. Owing to the high dielectric constant of AlON (k=6.9), as compared to single N2O-SiO2 gate insulator, significant gate leakage reduction was achieved by AlON/SiO2 stacked gate dielectrics even at high-temperature, especially in a high electric field condition (>5 MV/cm).

Low-temperature formation of SiO2 layers using a two-step atmospheric pressure plasma-enhanced deposition-oxidation process

Silicon oxide (SiO2) layers were fabricated at low temperatures (⩽400°C) by combining the deposition of hydrogenated amorphous Si (a-Si:H) with its oxidation using atmospheric pressure plasmas excited by a 150MHz very high-frequency (VHF) power. The surface excitation by the atmospheric pressure VHF plasma was capable of reducing the temperature for the hydrogen effusion from a-Si:H. As a result, a porous a-Si:H film containing a large amount of hydrogen could be transformed into a stoichiometric SiO2 with an approximately 24% increase in oxidation rate compared with the oxidation of Si(001) at a temperature of 400°C.

SiO2 Formation by Oxidation of Crystalline and Hydrogenated Amorphous Si in Atmospheric Pressure Plasma Excited by Very High Frequency Power

Silicon oxide (SiO2) layers were fabricated at a low temperature of 400 °C by the oxidation of single-crystal Si substrates and hydrogenated amorphous Si (a-Si:H) films using stable plasma excited at atmospheric pressure with a 150 MHz very high frequency (VHF) power. The utilization of Ar/O2 plasma led to an oxidation rate higher than that using He/O2 plasma while maintaining both SiO2/Si interface and SiO2 bulk qualities. The oxidation of a-Si:H was also effective in increasing the oxidation rate than the oxidation of single-crystal Si. Although the a-Si:H film contained a large amount of H atoms bound to Si atoms, the atmospheric-pressure VHF plasma significantly induced the hydrogen evolution from the film and the transformation of the film into a SiO2 layer. As a result, this study showed that the utilization of atmospheric-pressure VHF plasma was beneficial to the realization of a highly efficient formation process of stoichiometric and pure SiO2 layers at low temperatures.