In this review, the following epitaxial systems are adopted: GaAs on Si, SiC on Si, GaAs on CaF₂ and Ni-silicide on Si studied by photoemission spectroscopy using synchrotron radiation, medium energy ion scattering, low energy electron loss spectroscopy, and X-ray standing wave method, respectively. Importance of fundamental studies is emphasized for the development of reliable and useful devices with new functions.

View full abstract

Historical review of the experiments and theories of dendritic crystal growth and also the review of recent studies of pattern formations in diffusion field are presented. In early experiments the relation between tip-veiocity (υ) and supersaturation or supercooling (Delta;) were concerned. The theoretical analysis on the above relationship was made for a needle crystal and by using the Gibbs-Thomson's boundary condition. The maximum velocity condition was assumed, but was found to be incorrect later. In Muller-Krumbhaar theory, dendritic growth are considered as non-linear and non-equilibrium phenomena. The theory could explain the results of 3-dimensional dendritic growth experiments. However, the marginal stability condition assumed in the theory has not been proved mathematically yet. The next theoretical development was achieved by finding the importance of anisotropy and the solvability condition of the steady state. The origin of the side-branches was then discussed. The possibility of the noise-indused mechanism was reported theoretically and experimentally. The recent experimental understandings of pattern formations in diffusion field are also reviewed. The dendritic problem is not limited only to crystal growth. Finally, various modes of dendritic growth are discussed and the necessity of measurement of diffusion field in dendritic crystal growth is emphasized.

View full abstract

Ceramics are useful materials for humidity sensing device because the electric impedance of porous ceramics is strongly affected by the humidity in atmosphere. The sensitivity could be controlled by the pore structure, surface area and/or chemical modification of the pore wall surface. For the sample where the surface occupancy area of acidic protons was larger than ca. 0.1nm², the impedance value at 90% r.h. was controlled by the surface area and the morphologies of pores. In the range below 0.1nm², the impedance especially for >40% r.h. could be lowered without any increase in the surface area and was reciprocally proportional to the concentration of acidic protons. The introduction of alkali ions to the pore wall surface instead of protons is a preferable method to improve the humidity sensitivity and durability. It is difficult to lower the impedance for <30% r.h. by the introduction of acidic protons and/or alkali cations. To lower the impedance for the lower humidity region, the use of super ionic conductor or ferroelectrics instead of usual insulating metal-oxide was proposed.

View full abstract

The gel structure in the ZrO₂-SiO₂ system, produced by the sol-gel process and the ultrasonic spray pyrolysis method using a solution of ZrOCl₂·8 H₂O-Si(OC₂H₅)₄-C₂H₅OH-H₂O system (mother solution), was investigated in relation to the phase crystallized by heating, from the standing point of the surface and the interface of ZrO₂ and SiO₂. The siloxane polymer of compound system changed from linear to three dimensional type with an increase in the molar ratio 'r' of added H₂O. In this case, the crystallization temperature of SiO₂ increased and the transformation rate of T-to M-ZrO₂ decreased, due to the mutual 'block effect' of SiO₂ and ZrO₂. Without the block effect, T-ZrO₂ was converted utterly to M-ZrO₂. The strain energy caused by the crystallization of SiO₂ at the interface preserved the metastable T-ZrO₂. The morphology such as the dispersive state of two oxide components should be considered for the study on the transformation of ZrO₂. The spherical ZrO₂-SiO₂ system particles were successfully produced by the ultrasonic spray pyrolysis method from the mother solution which had been preliminarily hydrolyzed.

View full abstract

Gas liberation from electron-bombarded electrode surface during prebreakdown situation is one of important factors that cause electrical breakdown in a vacuum gap. Changes in residual gas components were monitored with a quadrupole mass specrometer, and electron-bombarded electrode surfaces were analyzed with an X-ray photoelectron spectrometer. The ions formed in the prebreakdown gap were also analyzed by a time of flight mass spectrometer installed in a prebreakdown measurement apparatus. It was found that the residual gas components in the prebreakdown situation are H, H₂, H₂O, CO, and CO₂, and the mass numbers of the carriers formed in the vacuum gap were the same as those of the residual gas components. The reaction of the electron bombarded surface and the effect of the reaction on vacuum breakdown phenomena are also discussed.

View full abstract

Some experimental results of solid surface studies using synchrotron radiation are described. Experiments were carried out with the light monochromatized by a grazing incidence monochromator at the BL 8A the Photon Factory. As a result, photoemission spectroscopy with an energy resolution of 0.3 eV has been achieved. Using this method, oxidation process of Si (100) surface has been examined. The results of SEXAFS and XANES for various oxide compounds are also presented.

View full abstract

In order to clarify adsorption and reaction on the fine ZnO particle surfaces in the atmosphere, the heating desorption analysis of the particles, which had previously adsorbed CO₂ gas or CO₂ gas containing water, was carried out using FID and TCD gas chromatography. The prism-like and the needle-like ZnO fine particles were synthesized by gas phase oxidation of zinc vapor. The effects of water vapor and of the surface crystal structure of these particles were examined, and the reaction of CO₂ gas with H₂O adsorbed on the crystal surface was studied. The results revealed that adsorption of H₂O on the ZnO surface gave great influence upon the reaction with CO₂ in the atmosphere. It was concluded that a thin layer of hydrozincite or smithsonite, depending upon the degree of stabilization of crystal surface, was probably formed.

View full abstract

The conversion-coated hopeite Zn₃(PO₄)₂·4H₂O films on galvannealed steel sheets, containing Mn²⁺ or Ni²⁺ from the bath, have been investigated using electron spin resonance for the purpose of determining the chemical structure of the films. Zn(II) in the hopeite crystals, the electron state of which is 3 d¹⁰ did not responded to ESR, but manganese and nickel ions in the films did. Six peaks in the spectrum for manganese indicate that the component is Zn₃-_xMn_x(PO₄)₂·4H₂O, and from the spectrum of nickel the component was thought to be Ni₃(PO₄)₂·7H₂O. However, since the g value of the hopeits film containing nickel ions was different from that of Ni₃(PO₄)₂·7H₂O, the most probable structure would be Zn₃-_xNi_x(PO₄)₂·4H₂O. In this research, it was confirmed that ESR analysis to determine the chemical structure of zinc phosphate films containing metal components were very effective and useful.

View full abstract

Hydrogen-absorbing intermetallic compounds have to be activated prior to hydrogen absorp-tion. Recent topics relating to the alloy surfaces, which are involved in this activation, are disc-ribed here. LaNi₅ exhibits strong oxygen induced surface segregation. The segregation occurs with each hydrogenation-dehydrogenation cycle, for-ming fresh active surface. TiFe is considered to be special in the sense that no significant segregation occurs at room temperature. For amorphous Pd₃₀Zr₇₀ and Cu₇₀Zr₃₀, hydrogen induces segregation.

View full abstract