Hiroyuki Yokoi

Rise and Fall of Surface Level of Water Solutions under High Magnetic Field

Magnetic field effects on the surface profile have been investigated for water and copper sulfate aqueous solutions that have very small magnetic susceptibility. When a field of 10 T is applied in a horizontal superconducting magnet, the surface of distilled water was lowered by 39 mm at the field center, relative to the level at the zero field region (Moses effect). In contrast, the surface of a nearly saturated copper sulfate aqueous solution was raised by roughly the same height at the center (reversed Moses effect). The profiles were systematically explained based on the dia- and paramagnetic volume susceptibility values of distilled water and copper sulfate aqueous solution, respectively.

Sonochemical polymerization of benzene derivatives: the site of the reaction.

Sonochemical polymerization of benzene and halogen-substituted benzenes has been studied. The difference of absorption spectra of polymerization products can be explained qualitatively using bond energies of the primary products. The relative rate constant of the polymerization reaction is apparently proportional to the inverse of the vapour pressure of the liquids. Using this relation, we analysed the relative rate constant of the polymerization in benzene/chrolobenzene mixtures. From this, we conclude that sonochemical polymerization proceeds in the vapour phase of a bubble.

Possible new route for the production of C60 by ultrasound

The production of C60 by ultrasonic irradiation of liquid benzene has been studied. After irradiating 150 ml of liquid benzene for 1 h (600 W, 20 kHz), approximately 1 microgram of C60 is produced.

Magnetic field induced helical structure in freestanding metal silicate tubes

Helical structure on freestanding metal silicate membrane tubes induced by a magnetic field is reported. The phenomenon is observed for iron silicate tubes and cobalt silicate tubes grown under a horizontal field of 2.2T and a field gradient of 20.5T∕m at the room temperature in contrast to nonregular structure observed at the zero field. Direction control of helicity is achieved by changing the field gradient direction with respect to the field direction. The results are explained in terms of the magnetohydrodynamics effect on the flow of anion discharged from a metal salt solution at the growing end of the silicate tube.

Infrared Spectroscopy on Poly(dG)–Poly(dC) DNA at Low Hydration

Infrared absorption measurements have been made on dry samples of poly(dG)–poly(dC) DNA at various relative humidity and temperatures. The water content, controlled by the relative humidity, reduce...

Excitation density effect on the decomposition of liquid benzene by ArF excimer laser (193 nm) irradiation

Abstract The excitation density effect on the decomposition of liquid benzene has been studied using an ArF excimer laser ( λ =193 nm). At low excitation density, biphenyl was primarily produced. At higher laser fluence, large-size aromatic molecules and graphitic carbon were produced. The apparent production yield of biphenyl increases steeply with laser fluence. From the dilution effect of benzene by cyclohexane, we conclude that the steep increase is due to the thermal decomposition induced by the non-radiative decay of optically excited molecules.

Small-Angle Oblique-Incidence Infrared Reflection in Polar Materials: II. Experiment on ZnO

The properties of polar optical phonons in thick single crystals of semi-insulating ZnO have been studied experimentally by infrared small-angle oblique-incidence reflectometry (SAOIR) with the subsidiary measurement of Raman scattering. The infrared light used is s - or p -polarized and incident to the c -face of the crystals at an angle of 10°. Despite such a small angle of incidence, since the principal components of the dielectric tensor are very small around the frequencies of longitudinal optical (LO) phonons, Snells total reflection and Brewsters null reflection take place contiguously to modify the reststrahlen band. Consequently, a pair of line structures due to LO phonons of A 1 and E 1 modes appear in the difference spectrum between the s and p spectra. Analysis of the results in terms of Kuroda and Tabatas theory of SAOIR using the dielectric function of Gervais and Pirious four-parameter semi-quantum oscillator model provides accurate frequencies and damping energies of all the LO and tra...

Infrared study on graded lattice quality in thin GaN crystals grown on sapphire

Transverse-optical (TO) and longitudinal-optical (LO) phonons in Si-doped and undoped n-GaN films have been studied by infrared reflection spectroscopy. The former film has been grown by metalorganic chemical vapor deposition (MOCVD) to a thickness of 2.3 µm, while the latter by hydride vapor phase epitaxy (HVPE) to a thickness of 35 µm. Both films are deposited on the c-surface of sapphire substrates with the surface of the c-plane of the wurtzite structure. Oblique-incidence infrared reflection spectroscopy has permitted us to observe the A1 mode, as well as the E1 mode, of polar optical phonons. The reflection spectra observed for s- and p-polarizations can be described well in terms of Gervais and Pirious four-parameter semi-quantum oscillator model taking account of the LO-phonon–plasmon coupling. It is found that in the MOCVD-grown film, the damping energies of the phonons are markedly graded along the growth direction of the film. It is suggested that the lattice strain is quite large in the interface zone but is reduced rapidly upon going beyond about 1 µm from the interface. Accordingly, the HVPE film has a good lattice quality throughout the film.

Infrared Study of Sapphire α-Al2O3 by Small-Angle Oblique-Incidence Reflectometry

Infrared properties of the multimode polar optical phonons in sapphire have been studied by the small-angle oblique-incidence reflectometry (SAOIR) using the a - and c -face of the crystal. It is found that the reststrahlen reflection accompanies the total reflection due to Snells law and the null reflection due to Brewsters law in the form of line structures at frequencies very close to longitudinal optical (LO) phonons. The analysis of the observations in terms of Gervais and Pirious four-parameter semi-quantum oscillator model yields the frequencies and damping energies of all modes of the polar optical phonons. In addition, three weak bands which are allowed for E ∥ c and ascribed to the multiphonon absorptions are observed on the wing of the reststrahlen band of an A 2u mode.

Oblique-incidence infrared reflection in thin ZnO films deposited on sapphire by gas-source MBE

Properties of polar optical phonons in n‐ZnO thin films are investigated by infrared reflection spectroscopy. Although there exist degenerate electrons in the concentration of 5×1018 cm−3 in the buffer layer, observation of the A1(LO) phonon‐plasmon coupled mode permits us to evaluate the electron concentration in the films grown on the buffer layer. The electron concentration is found to attain to 7×1016 cm−3 in undoped, 500‐nm‐thick films, while the damping energy of the E1(LO) mode remains to be as large as 45 cm−1 in those thin films.