AlOx thin film is one of the most promising high dielectric constant (High-k) materials. AlOx thin films were grown by mist CVD using a solution-based fabrication technology operated even under atmospheric pressure. This method is highly suitable due to easy configuration, low cost and environmental friendly operations. This report demonstrates significant improvements in the quality of AlOx thin films by O3 incorporation. AlOx thin films were grown above 400°C with breakdown field (EBD) over 6 MV/cm, static dielectric constant (κ0) over 6, and dynamic dielectric constant (κ∞) around 3. On the other hand, O3 assisted AlOx thin films were grown above 340°C with EBD over 8MV/cm, κ0 over 7, and κ∞ over 3. This work demonstrates that the quality of AlOx thin films could be significantly improved using O3 incorporation. AlOx thin film properties and its degradations were controlled by the OH(-AlOx) residual bonding. High quality AlOx thin films were grown at the temperature range from 400°C to 340°C by controlling OH(-AlOx) bonding decomposition with O3 incorporation.
Zinc oxide (ZnO) thick film growth on n-type gallium nitride (n-GaN) using an electrodeposition was investigated. We supplied electrons to the surface by light excitation using a Xe lamp for a long continuous electrochemical deposition. By using this technique, stable electrochemical reactions for 20h and 120h were realized. The sample grown for 20h had a thickness of 26μm, an averaged optical transmission of 85% in the visible-light region, and no obvious grain boundary from its cross-sectional SEM image. On the other hand, the sample grown for 120h had a thickness of 140μm, an averaged optical transmission of 25%, and many grain boundaries. Optimization of growth conditions for the thickness of above 30∼40μm is necessary.
The dilute bismuthide III-V semiconductor GaAs1-xBix alloys have unusual properties owing to large bowing of the band gap energy caused by Bi incorporation and a reduction of the temperature coefficients of the band gap. Deep- and shallow-level defects in device-quality GaAs1-xBix (χ ≤ 5.4%) are investigated. Deep- and shallow-level defects behave as non-radiative recombination centers and electrical carrier traps. The Bi-related localized states induced by the interaction between spatially localized Bi states and the valence band of GaAs are continuously located up to ∼90meV from the valence band with a density of ∼1 × 1017cm-3. In spite of concerns about the degradation of the hole mobility in GaAs1-xBix due to scattering at these Bi-related localized states near the valence band, the p-type doping masks the contribution of the Bi-related states to the hole mobility, and a high hole mobility of 200 cm2V-1s-1 is demonstrated. Despite low-temperature growth, the deep-level trap density in GaAs1-xBix is suppressed on the order of 1015cm-3 comparable to GaAs because of a surfactant-like effect of the Bi atoms. While the interface state density of ∼8 × 1011cm-2eV-1 in a GaAs/GaAs1-xBix heterointerface cannot be reduced by annealing, it can be reduced by half by the insertion of a Bi graded layer into the heterointerface.
Emission wavelengths of self-assembled InAs quantum dots (QDs) were controlled at around 1.05μm by using the In-flush technique. A rapid annealing (In-flush) process after the growth of the GaAs capping layer, which partially covers the InAs-QDs, reduces the height of the InAs-QDs to the thickness of the capping layer. Using this technique, the emission wavelengths of the QDs were precisely controlled by varying the thickness of the capping GaAs layer. The central emission wavelength was suitably controlled in the range of approximately 0.95-1.22μm. This method enables the realization of a broadband 1.05μm light source with a bandwidth of beyond 200nm via a combination of In-flushed QDs. Such a broadband light source with a wavelength of 1.05μm is applicable to optical coherence tomography (OCT), thereby enabling high resolution and large penetration depth in the OCT images. In addition, we have grown a sample including stacked layers of In-flushed QDs and obtained an emission spectrum with a central peak at 1.09μm and a bandwidth beyond 100nm. These results suggest that an axial resolution of approximately 5μm will be achieved by the use of the light source in OCT.
This article describes characteristics of p-type MgCr2O4-TiO2 ceramics from the viewpoint of the application to gas sensing element. The metal-oxide semiconducting ceramics were made by sintering a mixture powder of MgO, Cr2O3, TiO2, and WO3 as an additive to increase the sensitivity for chemical species. Gas detection performance as well as the structural quality was examined and found to become the highest at around 75mol%MgCr2O4-25mol%TiO2 with 0.5 wt% WO3.
We have developed a gas-fired immersion heater tube for use with melting furnaces for the processing of molten zinc. The tubes are made out of a pressureless sintered silicon carbide. The tubes single-ended have dimensions of either φ230 × φ210 × 2300mm or φ310 × φ290 × 1000mm. In this study, we examined thermal shock resistance upon water quenching, measured the gas temperature along the tubes, and simulated their tube wall temperature strength/stress distributions. Maximum stress of tube occurs just above the ring of contact with the surface of the molten zinc, where the temperature differential is the maximum. By inserting a thermal insulation sleeve (alumina silicate cloth) within the immersion heater tube, stress is decreased from 51.5MPa to 22.5MPa. The stress on dipping slant, which occurred at mechanical fixing part of tube, were not so large. We also checked the resistance of immersion heater tubes to molten zinc corrosion within actual production furnaces. We have found that within industrial zinc furnaces, the tubes can keep to operate on good condition (i.e., corrode only partially) after 6 years of service with normal burners and 4 years of service with regenerative burners.
We develop a new test method for evaluating tensile properties of nano-mateirals and apply it to a single crystalline gold nanorod with a square section of 189nm. The nanorod, which is carved out of a bulk material by focused ion beam processing, is mounted on a lozenge-shaped silicon frame and is pulled by a compressive load on the top face of the frame. Although the applied load increases monotonically in the early stages of deformation, it drops rapidly at a certain displacement. In-situ TEM observation indicates that the rapid decrease of applied load is due to crystallographic slip generation in the nanorod. The critical resolved shear stress on the primary slip system at yielding is evaluated to be 325.8MPa, which is about 600times larger than that of bulk. When the tensile elongation becomes large, the nanorod shows necking and isotropic plastic behavior independent on crystalline structure.
Reinforced concrete (RC) structures deteriorate because of the penetration of chloride ions into the cracks in concrete. Therefore, highly accurate detection of cracks is important. In this study, a pre-detection method for crack occurrence during RC beam bending is developed. The strain on a concrete surface is measured by a digital image correlation method. In addition, a method for detecting crack initiation is developed. In particular, RC beams used in experiments are set in the crack propagation stage based on the actual condition of existing structures. As a result, the location of crack occurrence is detected beforehand by a map of strain with 600μ or above. Hence, an effective pre-detection method for crack occurrence has been proposed for RC beams in the crack propagation stage.
Strengthening mechanism of age-hardenable electrodeposited Ni-P alloy was investigated focusing on the role of Ni3P precipitates in nanocrystalline structures. Specimens were synthesized by electrodeposition followed by aging treatment at temperatures ranging from 200 to 600°C. As-deposited structures were amorphous and became crystallized into nanocrystals by the subsequent aging treatment accompanying Ni3P precipitation. Microstructures, in particular distributions of grain size of Ni matrix and Ni3P particles size were examined in detail by field-emission type transmission electron microscopy. After the aging treatment under 300°C or bellow, average grain size of Ni matrix was approximately 10 nm with finer Ni3P precipitating intra- or intergranulary. On the other hand, after aging at 350°C both the grain size of Ni matrix and Ni3P particle size were grown to be comparable. Maximum hardness was obtained after the aging treatment at 350°C, and it was harder than that predicted by the rule-of-mixture between pure Ni and Ni3P. In both the cases, the additional strengthening may operate, which is not associated with the classical precipitate hardening. Less hardening by the precipitate in nanocrystalline structures is associated with a different deformation mechanism such as grain boundary sliding, which may operate in nanocrystalline domain.