Yasushi Matsuda

The long term growth of the protective rust layer formed on weathering steel by atmospheric corrosion during a quarter of a century

Abstract The rust layers formed on weathering and mild steels by atmospheric corrosion in an industrial region for a quarter of a century have been characterized using various analytical techniques. In particular, analysis of a local portion of the rust layers by means of Raman spectroscopy gives important information on the structure of the layers. It is elucidated that the inner stable and protective rust layer which covered the surface of weathering steel mainly consists of nano-particles of α-FeOOH containing a considerable amount of Cr. The relative change of the amount of rust constituents for low alloy steels supports well a newly proposed schematic progress of long term alteration in stable and protective rust layer formed on a weathering steel in an industrial environment, i.e. the γ-FeOOH, as an initial rust layer, is transformed into a final stable rust layer of α-FeOOH, probably via an amorphous oxyhydroxide substance, during the long term atmospheric corrosion of a weathering steel.

Raman studies of orthorhombic YBa2−xSrxCu3O7−y

A Raman scattering study was performed in orthorhombic YBa2-xSrxCu3O7-y at room temperature. It is found that the Raman peak associated with Cu-O-Cu stretching mode along the c-axis (502 nm-1, x=0) increases continuously in frequency with increasing Sr content, while the bending mode of the Cu-O (341 cm-1, x=0) decreases in frequency. These results indicate that larger contraction of the Cu-O-Cu bond distance along the c-axis than that of the lattice constant along the c-axis of the orthorhombic unit cell can be attained by replacing Ba sites with Sr ions.

Raman studies on GaAs epitaxial films on Si

Abstract Raman spectroscopy has been applied to the study of the effects of thermal expansion and lattice mismatch between GaAs and Si on the stress in GaAs films. The amount of stress in GaAs films of various thicknesses has been estimated from the GaAs LO phonon frequency and the half-width. By correcting the measured GaAs LO phonon frequency by using the spatial correlation (SC) model, it is shown that compressive stress exists in GaAs films due to accommodation of the lattice mismatch when the film is very thin. It has been also found that the compressive stress decreases with increased film thickness. The misfit dislocations at theGaAs/Si interface have been investigated by HR-TEM. The density of misfit dislocations increases with increased film thickness. The compressive stress in GaAs films due to accommodation of the lattice mismatch is released mainly by an increase of the density of misfit dislocations at the heterointerface as the film thickness increases.

Low-Temperature Metalorganic Chemical Vapor Deposition of GaAs on Si by Alternate Gas Flow of the Source Materials

GaAs layers were grown on Si substrates at 450°C by alternating the gas flow of trimethyl gallium and arsine. Raman spectra showed that the intensity of the longitudinal optical phonon peak taken from GaAs was increased by this approach. Furthermore, transmission electron microscopy showed the reduction of the lattice turbulence and many threading dislocations, which were observed in GaAs layers grown on Si without this approach.

Characterization of Al rich oxide layers on austenitic stainless steels by fluorescence spectroscopy

Abstract An Al rich oxide passivation technique has been developed to improve the corrosion resistance of the stainless steel to ozone added ultra-pure water. Fluorescence spectroscopy was applied to the study on the selective oxidation of aluminum containing austenitic stainless steel in low oxygen atmosphere at 1,353K. It was found that in the thermal oxidation under low oxygen pressure, the minor alloying constitution of Al resulted in the formation of thin oxide layers. The frequency shifts of fluorescence spectra show that the compressive stresses exist in the oxide layers as a result of the difference of the thermal expansion coefficients between substrate steels and α-Al2O3, and depends on the thickness of the oxide layers. It is confirmed that pure α-Al2O3 protective layers grown on the stainless steels, which remain stable and attached to the stainless steels in ozone added ultra-pure water. These act as a diffusion barrier and protect the stainless steels from the metal dissolution.