Yoshijiro Ushio

Effects of interface states on gas-sensing properties of a CuO/ZnO thin-film heterojunction

Abstract Humidity- and gas (CO, H 2 )-sensing properties of CuO/ZnO thin-film junctions fabricated by different procedures have been investigated. Junctions in which the lower layer surface is exposed to air before stacking the upper layer (type I) and junctions deposted continuously (type II) have been prepared by the sputtering method. The type II junction shows little sensitivity to humidity and flammable gas (CO and H 2 ) compared to the type I junction. The interface capacitance in type I is almost independent of the applied bias. This indicates that the interface state are dominant for determining the electrical properties of the junction. The interface states formed by exposure to air are suggested to play important roles in chemical sensing.

Fabrication of thin-film CuO/ZnO heterojunction and its humidity-sensing properties

Abstract Heterojunctions of CuO/ZnO in array patterns are fabricated by thin solid film deposition and a photolithographic process. Such junction show rectifying current-voltage characteristics and the IV curves are changed by relative humidity changes at room temperature. The forward current of p-n junctions increases with the increase of relative humidity, while changes in reverse current are negligible. Current changes caused by humidity are different depending on the applied bias. These sensing properties are confirmed to be attributed to the ‘open’ junction, where the interface of p- and n-type semiconductors is partly exposed to the atmosphere by patterning of the films.

Degradation of the electrochromic nickel oxide film upon redox cycling

The degradation mechanism of electrochromic nickel oxide films by redox cycles was investigated. Films fabricated by sputtering of an oxide target were driven between the colored (oxidized) and bleached (reduced) states in 1 M KOH solution. With the cycles, the transmittance of the colored state decreased. While the peak potential of the redox became larger at first and then became smaller, the response time became rapid at first and slower afterward. The surface of heavily degraded films became uneven and easy to be removed. A higher oxidation voltage caused faster degradation. Heat treatment during deposition or making a film thicker was shown to affect durability.

Properties of tantalum oxide thin film for solid electrolyte

Abstract Tantalum oxide thin films were prepared by RF ion-plating and RF sputtering. Protonic conductivities of the films varied from 10 −5 to 10 −10 S/cm with the condition of deposition. The high ionic conductive film has low packing density and shows strong O-H absorption. It was concluded that the adsorbed water gives much influence to the protonic conduction.

Photoinduced Current of a CuO/ZnO Thin-Film Heterojunction in Humid Atmosphere

The effects of the light illumination on the humidity sensing properties of a CuO/ZnO thin-film heterojunction where the interface is partly exposed to atmosphere were investigated. When ultraviolet light ( ~400 nm) was applied to the heterojunction, a very large photoinduced current, about two orders of magnitude larger than that in dry air, was observed under humid conditions at the forward bias of the p-n junction above about 1 V. The increase of photoinduced current is assumed to be due to desorption of adsorbed oxygen species on ZnO promoted by the adsorption of water molecules and the application of the forward bias, which caused the changes of interface states.

Gas Detection Utilizing the Interface of a CuO/ZnO Thin Film

The gas sensing function of the interface of CuO (p-type semiconductor) and ZnO (n-type semiconductor) thin films was investigated. Films were prepared by sputtering and the junction showed rectified I–V characteristics originating from the interface of the semiconductors. An array pattern was made in the films ( channels of ∼10 μm were formed ) by photolithography so that the interfaces of the semiconductors could be exposed to the atmosphere. These exposed junctions showed current increases at a p-n forward bias when flammable gases (CO, H2) were introduced. In the temperature range from 100°C to 250°C, the current increase was observed at 0.5 to 1.0 V bias, and at room temperature it occurred at a higher bias than 2.0 V. Little change was observed at a p-n reversed bias. The sensitivity (ratio of the current with and without flammable gas) and gas selectivity were different depending on the applied bias and the heat treatment temperature.

Evaluation of the no-disparity realistic image from a sense of presence and low fatigue

We evaluated an observer’s fatigue and a sense of presence, in observing the no-disparity realistic image (NDR image) [1-3]. NDR image is consisted of two images (right and left image). Right image is created by shifting all pixels in left image same amount. Consequently, there are no disparities in all area of NDR image. NDR image which is reconfigured the contents that contain image with large disparity might have a possibility that it suppress an observer’s fatigue and let him feel high presence. Subjects observed three conditions videos (stereoscopic, NDR and 2D). Subjects observed two videos in each condition. Each video was 30 minutes. There were scenes with large disparity (more than 5 degrees) in videos. Subjects responded SSQ (Simulator Sickness Questionnaire), VAS (Visual Analogue Scale) for fatigue and questionnaire on realism and were measured CFF (Critical Frequency Fusion), accommodation tremor, stereoscopic vision test, ocular position measurement and eye sight test. Results showed that NDR image let observer feel high presence and an observers fatigue was low. NDR image is effective, even if contents which contain large disparity are converted into NDR image.

Optical loss estimation of coatings at the ArF excimer laser wavelength

Abstract A measurement system that estimates the absorption loss of coatings at the wavelength of ArF excimer laser (193 nm) has been developed. Utilizing the photoacoustic waves generated by pulsed laser irradiations, the quantitative measurements with simple procedures became possible. The holder that holds the samples in a liquid led to stable acoustic matching condition and high reproducibility (