Haruo Hirose

Polarity‐dependent memory switching and behavior of Ag dendrite in Ag‐photodoped amorphous As2S3 films

High cyclical reproducibility in polarity‐dependent switching and memory function was obtained. Switching and memory effect seem to occur when both electrodes (Mo and Ag) are bridged by Ag dendrite which originates as the result of Ag photodoping. The combination of Ag electrode and another kind of electrode material may be responsible for the polarity‐dependent switching and memory by the help of appropriate voltage shapes. Behavior of Ag dendrite was observed in relation to the similar electrical characteristics in a modified device structure. No thermal effects may be contained in the functional processes. Temperature dependence and frequency characteristics of the device resistances are measured and found to support the existence of the Ag dendrite and its role in the function in the original device. Switching transients in addition to the durability show the availability of the device in the compatibility with the magnetic core memory.

Backscattering measurements on Ag photodoping effect in As2S3 glass

350‐keV He+ backscattering analysis was applied to the investigation of Ag photoinduced diffusion into As2S3 glass and proved to be suitable for the present purposes. Silver atoms diffuse into As2S3 by photoirradiation (termed ’’photodoping’’). Photodoped Ag concentration is nearly uniform and falls abruptly beyond a certain depth. The concentration of S in the photodoped region is nearly equivalent to that in As2S3. Preirradiation of As2S3 before Ag deposition enhances Ag diffusion, which results in a tailing of the Ag concentration. The preirradiation effect disappears after a long period. Thermal diffusion of materials was also investigated for comparison.

Arsenic-free GaAs substrate preparation and direct growth of GaAs/AlGaAs multiple quantum well without buffer layer

Abstract High-temperature treatment of GaAs substrate without As flux in a preparation chamber was investigated as a substrate surface cleaning method for molecular beam epitaxial (MBE) growth. Oxide gases such as CO and CO 2 were almost completely desorbed at a temperature above which Ga and As started to evaporate from the substrate. During the cleaning at a temperature as high as 575°C for 30 min, about 100 nm thick GaAs was evaporated from the substrate, but its surface maintained mirror-like smoothness and showed streak pattern with surface reconstruction pattern in the reflection high energy electron diffraction (RHEED) observation. Direct growth of GaAs/Al GaAs quantum well (QW) structures was tried on such surfaces without introducing any buffer layers. The QW structure showed photoluminescence with both intensity and full width at half maximum comparable with those for the QW grown on the substrate cleaned by the conventional method with introducing a GaAs buffer layer.

SUPERCONDUCTIVE FILMS BY LASER POST-TREATMENT OF THERMAL-SPRAYED FILMS

Abstract In an attempt to produce a thick superconductive film of large area, an experimental study was conducted on the preparation of the film through laser post-treatment of thermal-sprayed oxide ceramic film. The ceramic powder of Bi-(Pb)-Sr Ca-Cu-O system was used as raw material. The powder was sprayed onto a stainless steel substrate using two types of spraying systems, conventional plasma spraying system and lower temperature hypersonic spraying system both followed by CO2 laser beam irradiation with oxygen gas flow to remodify the superconductive crystals in the films. The results showed that, though laser post-treatment can produce superconductive crystals in both sprayed films, higher critical temperature Tc (end) was obtained for the film prepared by the hypersonic spraying system.

Observation of dark line defects in InGaAs/GaAs strained layer superlattices by photoluminescence topography

Abstract The behavior of dark line defects (DLDs) in molecular beam epitaxy grown InGaAs/GaAs strained layer superlattices (SLSs) has been studied by photoluminescence (PL) topography. The density of DLDs parallel to the [011] was larger than that of those perpendicular to the [011] and increased with increasing number of SLS periods. These DLDs were considered to be originated from the locally deformed lattices by the misfit stress. The relaxation model of stress in MBE-grown InGaAs/GaAs SLSs was proposed from the obtained results.

Improvement of superconductive characteristics by laser surface treatment

Abstract The effect of laser beam irradiation onto the surfaces of superconductive materials of Bi system is discussed. Results of SEM observation, XRD analysis and measurement of critical temperature of laser treated surfaces indicate that the treatment can improve crystal conditions of the system.

Possibility of connecting bulks of Bi system by the laser irradiation

Abstract Laser treatment has been successful in rapidly realizing superconductors of Bi system. We applied this to easy connection between two bulks and obtained indication of successful result.

Actively generated noise liquid flowmeter

A new noise flowmeter with two transducers has been tested experimentally in water. It detects the noises generated by the interaction between artificially introduced air bubbles and a built-in obstacle with a downstream transducer, and differentiates them from the external noises detected by the upstream transducer in a pipe. The system includes processing instrumentation with functions such as averaging and difference-operating for reduction of external noise effects.<<ETX>>

Behaviour of the superconductivity characteristics of the Bi system during water soaking

Samples of a bulk Bi-Pb-Sr-Ca-Cu-O system and a thick film of the Bi-Sr-Ca-Cu-O system are soaked in distilled water and the change in the superconductivity characteristics is measured. For the bulk samples, the maximum magnetization in the magnetization curve and the critical current density increase for the first 18 hours of soaking and then decrease during the subsequent soaking time. The critical temperature shows monotonic decrease throughout the soaking. A thick-film sample is almost the same as a bulk sample, i.e. the critical current density of the thick film first tends to increase for a short time due to its greater surface area then tends to decrease during the subsequent soaking. The critical temperature of the film sample also shows a slight deterioration as a result of the water soaking.

Preparation of superconductive films using plasma spraying technique with laser post-treatment

In an attempt to produce superconductive films of large area, a study was made on the preparation of the films through laser post-treatment of plasma-sprayed oxide ceramic films. The ceramic powders of Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O systems were used as raw materials. Each ceramic powder was sprayed onto a stainless steel substrate followed by CO2 laser beam irradiation with oxygen gas flow to remodify the composition and provide superconductive crystals on the film. The results showed that laser post-treatment can recover superconductive crystals on both films and can provide the transition temperatures Tc(on) on both systems and the critical temperature Tc(end) on the Bi-Sr-Ca-Cu-O system.