Ichiro Nakabayashi

Transparent conductive ZnO film preparation by alternating sputtering of ZnO:Al and Zn or Al targets

Abstract Multilayered ZnO:Al and ZnO:O v film was prepared by alternately sputtering ZnO:Al(2% wt.) and Zn targets. The films obtained were optically transparent and had lower resistivity than those prepared by ZnO:Al sputtering. Deposition from the Zn target gave a ZnO film containing native donors (a ZnO:O v film). The carrier concentration increased in the ZnO:Al/ZnO:O v multilayered film. Our results cannot be explained by the redistribution of the carrier between ZnO:Al and ZnO:O v . This result indicates an improvement in the doping efficiency. Multilayered films of ZnO:Al and Al oxide compounds were also prepared. In this case, with increasing thickness of the Al oxide film, a decrease was observed in the carrier mobility, due to the scattering at the interface.

Transparent conducting amorphous Zn–Sn–O films deposited by simultaneous dc sputtering

The films of ZnO–SnO2 system were deposited on glass substrates by simultaneous dc magnetron sputtering apparatus, in which ZnO and SnO2:Sb (Sb2O5 3 wt % doped) targets faced each other. The substrate temperatures were maintained at 150, 250, and 350 °C, respectively. As an experimental parameter, current ratio δ=IZn/(IZn+ISn), which corresponds to ZnO target current (IZn) divided by the sum of ZnO and SnO2:Sb target currents (IZn+ISn), was adopted. Amorphous transparent films appeared for 0.50⩽δ⩽0.73, which could be correlated to compositions as [Zn]/([Sn]+[Zn])=0.33–0.67 by x-ray fluorescent analysis. At [Zn]/([Sn]+[Zn])=1/2 (δ=0.62), 2/3 (δ=0.73) and all other ratios in as-deposited films, neither crystalline ZnSnO3 nor Zn2SnO4 was obtained. Minimum resistivity of 4–6×10−2 Ω cm was found at δ=0.50, whose composition was approximately SnO2⋅ZnSnO3. Resistivity increased linearly with an increase of the current ratio, until the composition reached Zn2SnO4. The amorphous phase showed a constant Hall mobili...

On the diffusion of Li+ defects in LiCoO2 and LiNiO2

Abstract NMR spectra of 7 Li nucleus have been measured in LiCoO 2 and LiNiO 2 . Line widths of the spectra decreased with increasing temperature above 400 K. The decrease obviously indicates the motional narrowing originating from diffusing Li + defects. A simple ion hopping model revealed that the diffusion constant of LiCoO 2 with an activation energy of 0.3 eV is larger than that of LiNiO 2 with the activation energy of 0.6 eV. This suggests that lithium ions are easier to diffuse in LiCoO 2 than in LiNiO 2 at high temperatures.

Film properties of ZnO:Al prepared by cosputtering of ZnO:Al and either Zn or Al targets

ZnO:Al and ZnO with oxygen vacancies (ZnO:OV) films were prepared by co-sputtering Zn and either ZnO:Al (Al2O3 2 wt %) or ZnO. The influence of the additional Zn supply on ZnO:Al film properties was investigated and compared with the data of ZnO:OV films. The additional Zn supply improved the film crystallinity and reduced the film resistivity. This was ascribed to the decrease of defects in ZnO:Al films due to the improvement of crystallinity, because the maximum carrier concentration in a ZnO:OV film was much smaller than that in a ZnO:Al film where the carrier concentration was created by Al donors. ZnO:Al films prepared by co-sputtering of ZnO:Al (2 wt %) and either ZnO:Al (6 wt %) or Al targets were also investigated. The doping of Al donors, in the first case, decreased the carrier mobility and increased the carrier concentration, in the second case, the carrier mobility increased with further doping.

Characterization of oxygen-deficient phases appearing in reduction of the perovskite-type LaNiO3 to La2Ni2O5

Abstract Topotactic vacuum reduction of the perovskite-type LaNiO 3 was performed with aluminum metal powder as a reducing agent. An orthorhombic single phase of oxygen-deficient LaNiO 2.5 + x (0.1 ≤ x ≤ 0.15) was successfully prepared. LaNiO 3 − z ( z ≤ 0.25) with the rhombohedral perovskite-type structure showed metallic conductivity and Pauli paramagnetism, whereas the oxygen-deficient phase LaNiO 2.60 was semiconductive and was considered to be ferromagnetic below 230 K. The effective magnetic moment of LaNiO 2.60 was 1.7 μB, which suggests that LaNiO 2.60 is composed of octahedrally-coordinated Ni 3+ ions and square-planarly-coordinated Ni + ions, as seen in La 2 Ni 2 O 5 .

Properties of ZnO:In film prepared by sputtering of facing ZnO:In and Zn targets

ZnO:In films were prepared by a sputtering method with targets facing. The lowest resistivity film is obtained at a substrate temperature of 150 °C using a ZnO target doped with 3 wt % In2O3. At substrate temperatures above 300 °C the resistivity of the film increases as the carrier concentration decreases. This implies a significant decrease in the donor impurity, ascribed to evaporation of the indium during film growth. From experiments with an additional Zn supply during deposition, we found that all of the doped indium is ionized as donor in ZnO:In, and that evaporation of depositing indium atoms is enhanced above 250 °C.

Glucose sensor based on titanium dioxide electrode modified with potassium hexacyanoferrate(III)

Abstract A potassium hexacyanoferrate(III) modified titanium dioxide electrode with immobilized glucose oxidase (GOD) was developed for measuring glucose. With this electrode, glucose concentration (1×10 −5 to 1×10 −3 M) could be determined accurately in the presence of ascorbic acid or uric acid. Glucose in human serum was determined after diluting the serum 10-fold with phosphate buffer of pH 5.5. The glucose concentrations of 70.5–72.7 mg dl −1 were determined in good agreement with those usually found in human serum.

Effect of insertion of thin ZnO layer in transparent conductive ZnO:Al film

Abstract The effects of the insertion of non-doped ZnO layers on the electrical properties of transparent conductive ZnO:Al films are investigated. Layered films of ZnO and ZnO:Al, ZnO:Al/ZnO films, were deposited by sputtering alternatively ZnO:Al and ZnO targets. By inserting ZnO layers in ZnO:Al layers, both the carrier concentration and Hall mobility were increased, and the film resistivity was lower than that of a single ZnO:Al film. Optical transmittance at the absorption edge was increased and grain growth was enhanced for the ZnO:Al/ZnO layered films. These data indicate that the insertion of ZnO in ZnO:Al decreased the defects in ZnO:Al/ZnO film which causes low carrier concentration and mobility

Surface characteristics and activities of plate-type Raney nickel catalyst

Abstract Analytic and morphological studies using SEM, EPMA, and XPS were made on plate-type Raney nickel catalyst with varying contents of aluminum. The surface characteristics and hydrogenation and adsorption behavior of Raney nickel catalysts are discussed. Although the amount of residual aluminum in the catalyst (mainly Al 2 O 3 n H 2 O) remains almost constant on its outermost surface, regardless of the leaching time, it decreases in the interior phases up to a depth of 600 A with leaching times over 9 min. The activities of catalysts with average content of aluminum relative to nickel, i.e., 11.6 and 6.8 wt%, in their surface layers (ca. 0.4 μm thick) were 2.7 and 2.1 mmol/h BET m 2 for the hydrogenation rates of allyl alcohol and 3.6 × 10 −3 and 2.4 × 10 −3 mmol/ BET m 2 for the adsorption amounts of I − ion, respectively. These results suggest that the activities for hydrogenation and adsorption were enhanced when the content of the residual aluminum in the catalyst was increased, and that the role of the residual aluminum in catalytic reactions can be classified into two types: to provide an increase in active sites due to formation of interstitial lattice defects, and to make a negligible contribution to the formation of active sites because of deposition of Al 2 O 3 n H 2 O on the Raney nickel catalyst.

Crystallization process of transparent conductive oxides ZnkIn2Ok+3

Crystallization process of the homologous compounds Zn(k)In2O(k+3) from the coprecipitants was examined by XAFS spectroscopy and X ray diffractometry. Interesting crystallization behavior could be observed. Though zinc oxide already crystallized as the wurtzite-type ZnO at 573K, indium oxide remained amorphous. Subsequently bixbyite-type In2O3 appeared at 873K for k=5 and 7 and at below 773K for the other k-members, respectively. The InO distance in the amorphous In2O3 was a little shorted than that in the bixbyite-type In2O3 by 0.06-7A. The distance remained constant but abruptly increased to that observed in the bixbyite-type In2O3 in accordance with the progress of crystallization. Then the distance gradually decreased and converged to ca. 2.12A at the temperature range of 1173-1373K, due to the reaction between In2O3 and ZnO to form the homologous compound.