ESCA study on the mechanism of adherence of metal to silica glass

Indium oxide films formed on the surface of silica glass samples by selective oxidation have been shown to greatly improve the adherence of gold-indium alloy to the silica glass. In order to clarify the role that the oxide films play in the reaction, thin indium films have been evaporated onto silica glass and heated at temperatures of between 973 and 1473 K, both in air and in hydrogen gas. Electron spectroscopy for chemical analysis (ESCA) measurements have then been made to investigate the chemical environments around oxygen and indium atoms at the reacting interface between the oxide and glass. Measured 01s and In3d _5/2 spectra reveal the formation of non-bridging oxygen atoms at the interface, in addition to the original bridging oxygen atoms in silica glass. Introduction of the non-bridging oxygen atoms and indium ions into the silica glass is concluded to be an essential factor in promoting good adherence between the gold alloy and silica glass.     

Marangoni convection driven by thermocapillary and solutocapillary forces in the Fe-O alloy pool during the solidification or remelting process

Marangoni convection during the solidification or remelting process was investigated in a small pool of a liquid Fe-O alloy, by experiments and numerical simulations. Most of the studies of such a system, with a low Prandtl number but a high Schmidt number, have taken into account thermocapillary convection but have left the solutocapillary effect out of consideration. However, our experimental and numerical approaches revealed that solutocapillary convection also plays an important role in the generation of peculiar flow patterns with a single roll cell or two roll cells. The Marangoni convection observed was classified into at least four categories based on the thermocapillary and solutocapillary forces.     

Field emission from diamond particles studied by scanning field emission microscopy

Field emission properties from diamond particles (DPs) are studied. The DPs with thin chemically vapor deposited (CVD) diamond overcoat, dispersed onto metal substrate, essentially exhibit negative electron affinity (NEA). Field emission, approximately 1mA/cm(2) under a macroscopic electric field of 3.5kV/mm are observed. Microscopic electrical properties were studied by scanning tunneling microscopy/spectroscopy. Most parts of the DP surface exhibit narrow gap and p-type characteristics. The localized regions, which have wide gap like bulk diamond properties, are randomly distributed near the top of DP. The field emission current distribution depicted by scanning field emission microscopy (SFEM) show that the electron emission is originating from a localized region on the selected DPs. We found, through SFEM measurement, some favorable field emission spots ("hot spots") where measured emission current is several orders higher than that of the other DPs ("normal spots"). Field emission spectroscopy (FES) results suggest that a poorly conducting layer is present along the electron path from the metal electrode to vacuum.We propose two models for field emission from "hot spots", which involve two main mechanisms. One is electron injection from the metal substrate to the DP, which is attributed to the electric field enhancement at intrinsic non-doped diamond (i-diamond) layer sandwiched between the metal substrate and the surface conductive layer (p-diamond) of the CVD diamond overcoat on the DP. The other is electron emission at the top site of NEA DP through the local i-diamond region or the depletion region of the p-diamond, which is caused by the applied electric field.     

Preparation of luminescent nanosized NaEu(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> incorporated in amorphous matrix originated from zeolite

Novel luminescent material has been prepared by the reaction of Eu³⁺ and molybdate species in the matrix of faujasite (FAU) type zeolite X and successive calcination. Eu³⁺ exchanged FAU was reacted with MoO₃ in the solid-state at 723 K, giving a precursor. By calcining it at 1073 K, different crystalline phases were derived depending on MoO₃-loading levels. Scheelite type crystal of NaEu(MoO₄)₂ was formed at high MoO₃-loading levels, whereas europium sodalite was formed at low loading levels. For the former sample, X-ray diffraction analysis and transmission electron microscopy revealed that the nanosized NaEu(MoO₄)₂ was dispersed homogeneously within amorphous aluminosilicate matrix originated from FAU. The amorphous particles containing NaEu(MoO₄)₂ maintained the original morphology, which the starting FAU particles possessed. The emission intensity of nanosized NaEu(MoO₄)₂ in the matrix was one order higher than that of europium sodalite. The emission lifetime of nanosized NaEu(MoO₄)₂ (0.39 ms) in the matrix was longer than that of bulk NaEu(MoO₄)₂ (0.35 ms) fabricated by conventional solid-state processes.     

Effect ofin Situ cooling on superconductivity of artificially layered BSCCO films with 2223 structure

Thin BSCCO films with the 2223 structure were deposited onto MgO substrate kept at 665°C by applying a sequential sputtering method using metallic Bi and Sr-Ca-Cu-O targets. The resultant films were then cooled under various oxygen partial pressures and cooling rates. It was found that the oxygen partial pressure and substrate temperature during cooling affect significantly the development of superconductivity of the as-deposited films. When the films were cooled stepwise under a critical oxygen partial pressure around 0.3 torr, the as-deposited films showed either superconductivity or nonsuperconductivity behavior. HRTEM images of the films showed no essential difference in the modulated structure, suggesting that the excess oxygen in the Bi-O double layers is the same and not the cause of the different superconducting behavior in the as-deposited films.     

Development of a guide-dog robot: human�Crobot interface considering walking conditions for a visually handicapped person

The repletion rate of guide dogs for visually handicapped persons is roughly 10% nationwide. The reasons for this low rate are the long training period and the expense for obtaining a guide dog in Japan. Motivated by these two reasons, we are developing guide-dog robots. The major objective is to develop an intelligent human?Crobot interface. This paper describes two novel interface algorithms and strategy to guide visually handicapped person. We developed new leading edge searching method, which uses a single laser range finder (LRF) developed to find the center of the corridor in an indoor environment. We also developed a new twin cluster trace method that can recognize the led-person??s walking conditions measured by the LRF. The algorithm allows the guide-dog robot to accurately estimate and anticipate the led-person??s next move. We experimentally verified these algorithms. The results show that the algorithms are reliable enough to enable the guide-dog robot and the led-person to maneuver in a complex corridor environment.     

Properties and mechanisms of fast-setting calcium phosphate cements

The setting time of a calcium phosphate cement consisting of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) was reduced from 30 to 5 min by use of a cement liquid that contained a phosphate concentration of 0.25 mol/l or higher. The diametral tensile strength and conversion of the cement ingredients to hydroxyapatite (OHAp) during the first 3 h were also significantly increased by the phosphate. However, the phosphate produced no significant effects on the properties of the 24-h cement samples. Results from additional experiments in a slurry system verified that the high phosphate concentration in the solution accelerated the formation of OHAp in the TTCP + DCPA system, and this reaction could explain the fast-setting properties of the cements.Certain commercial materials and equipment are identified in this paper to specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by the American Dental Association or National Institute of Standards and Technology or that the materials or equipment identified is necessarily the best available for the purpose.     

Microstructural changes of Al/amorphous SiC layered films subjected to heating

Layered specimens composed of aluminium and a-SiC films were prepared at room temperature by r.f. magnetron sputtering. a-SiC/Al/a-SiC triple-layered films were heated in the trans mission electron microscope (TEM), and thein-situ microstructural changes were observed continuously. In order to estimate the interfacial reaction process kinematically, electrical resistance measurements were conducted on Al/a-SiC double-layered films heated isothermally at 573, 598 and 623 K. Thein-situ TEM observations showed that no pronounced interfacial reactions occurred up to about 600 K, that silicon precipitates were formed and grew around 673 K, and that Al₄C₃ compounds were produced during heating at temperatures above about 753 K. The electrical resistance of Al/a-SiC double-layered film heated isothermally increased gradually with heating time, and this increase was closely related to the volume fraction of silicon precipitates in the aluminium film. From the kinematical analyses of the results of electrical resistance measurements, an activation energy of the interfacial reaction process of aluminium with a-SiC films in the temperature range 573 to 623 K was found to be about 2.6 eV, being close to the bond energy of Si-C.