It is possible to prepare high-density, moisture-resistive and optically transparent SiNx films by a catalytic chemical vapor deposition (Cat-CVD, often called Hot-Wire CVD) technique at low substrate temperatures such as 353K. The key point is the addition of a large amount of H2 to the SiH4/NH3 system. Gas-phase diagnoses show that, in Cat-CVD processes, the H-atom density in the gas phase is typically more than one order of magnitude higher than that in plasma processes; these H atoms abstract atomic hydrogen on the growing surface and also contribute to the local heating of the substrate surface due to their recombination reactions. In addition, H atoms re-activate the catalyzer surfaces poisoned by SiH4 to increase the decomposition efficiency of NH3. Pressure cooker tests combined with FTIR measurements show that SiNx films thus prepared are highly moisture-resistive even when the substrate temperature is as low as 293K. The water vapor transmission rate of plastic substrates covered with thin SiNx films is less than the detection limits of a MOCON or a cup method. The transmission rate was decreased by more than two orders of magnitude by the SiNx coating. The stress of the SiNx films was typically less than 100 MPa and can be controlled from compressive to tensile by choosing the appropriate deposition conditions. It is concluded that SiNx films prepared by Cat-CVD from SiH4, NH3 and an excess amount of H2 can be used as passivation films for organic materials, including organic light-emitting diodes.
A few problems are still remained in a single bulk β-FeSi2 formation from liquid phase. As the first step of a single bulk β-FeSi2 formation from a solid reaction between highly oriented two phases, unidirectional solidification method was applied to the FeSi2 composition alloy. The growth rates were changed from 1.7μm/s to 5.4μm/s. The typical rod type eutectic was formed and the matrix was α phase and the rod was ε phase. The size of the phase increased with decrease of the growth rate. The matrix phase was a single crystal below 3.4μm/s and its orientation was <100>. All of phase were alligned to <100> independent of growth rate.
The fine channel mist (FCM) method has been developed, as a safe and economical growth technology of zinc oxide (ZnO) thin films. This technique utilized aqueous solution of zinc acetate, which is a safe material, as a zinc source, and this solution is supplied to the growth as a form of micro-sized mist by applying ultrasonic-power with the carrier gas of nitrogen. ZnO thin films were grown in an open system, where the mist of zinc acetate reacted with oxygen or water on a glass substrate at the temperature of 270 to 500°C. One of the key technologies was to flow the reactant gases in a micro-channel on the substrate. This allowed effective growth of ZnO by “condensing” the flow to the substrate neighborhood and by rapidly improving collision probability of the source gases, resulting in the high efficiency (as high as 10%) for the zinc source to form ZnO. The ZnO thin film hence grown was transparent with the naked eyes, that is, the optical transmission was higher than 90% in the visible light region. Photoluminescence spectra exhibited near-band edge emission around 3.3eV (375nm) at room temperature, with weak deep level emissions. The surface morphology changed in terms of the growth conditions, reflecting different crystallographic properties. The thickness, the electrical conductivity, and the growth rate were 50-5000nm, 1-5Ωcm, and 1-200nm/min respectively. The overall properties of ZnO thin films grown here suggested the potential of this novel growth technology being utilized to fabricate transparent conducting films, ultraviolet absorbers, and so on.
Toward the fabrication of biosensing medical devices with enzyme-modified field effect transistors based on zinc oxide (ZnO), surface modifications using organic molecules were employed. In case of molecules containing thiol groups, it was found that molecules on ZnO surfaces were desorbed during water immersion, while ZnO surfaces modified by a silane-coupling agent were stable in water. Glucoseoxidase (GOX), an enzyme, specifically reacting with glucose, could be immobilized on molecular modified ZnO surfaces.
We have measured the SnO2 gas sensor response for several alcoholic and carboxylic gases to discriminate smells. The experimental results show that each alcoholic gas gave the peculiar response of the sensor and the secondary polarization of the gases molecules affected strongly to the transient response of the sensor. The total heats of formations were calculated by molecular orbital method using SnO2 cluster to examine the surface reaction of the sensor. The calculating results show that the adsorption distance of the gas molecular from the sensor surface affected to the sensor sensitivity. We operated the sensor heated by rectangular and triangular pulse voltages to discriminate several kinds of smell. The triangular pulse with a rise velocity of 43 [mV/sec] gave us the largest delay time difference for various alcoholic gases. These results suggest that the smell selective sensor will be realized by using the SnO2 gas sensor.
Using first-principles calculations we have analyzed the dependence of spontaneous polarization on lattice parameters and tetragonality ratio in natural and artificial structures of tetragonal BaTiO3 (BTO) and PbTiO3 (PTO), in order to establish the conditions needed for obtaining increased spontaneous polarization. Conventional knowledge of the polarization in PTO being higher than in BTO due to its larger tetragonality ratio and increased chemical activity of the A-site cation has been confirmed. In addition, a peculiar dependence of the spontaneous polarization on unit cell volume has been revealed. Specifically, at the equal tetragonality ratio, a given ferroelectric material (be it BTO or PTO), with a larger unit cell volume will have a larger spontaneous polarization. This may be related to the augmenting or reduction of short-range repulsion forces that tend to stabilize a centrosymmetrical structure. Therefore, a large tetragonality ratio is not absolutely necessary for obtaining increased spontaneous polarization, if the unit cell volume is large. The present results might partly explain why one should expect that BiFeO3, with a rather modest tetragonality ratio in thin film form, should have very large spontaneous polarization. That is, the chemical bonding and the unit cell volume are similar to PTO, whose polarization is close to 100μC/cm2.
A ceramic micro fabrication process has been developed for the 1-3 piezo-electric composites which is suitable for high frequency, wideband ultrasonic transducer. This process employs synchrotron radiation (SR) lithography and a micro molding process. This process realized an array of lead zirconate titanate (PZT) rods whose cross section is 25 microns. The material is expected to improve the resolution of the ultrasonic diagnosis, because composites can transmit a short ultrasonic pulse and have high sensitivity. In addition, when circular shape PZT rods is arranged at the apex of the regular triangle, the internal resonant mode became clear to be suppressed.
Electron beam lithography simulation is presented. A line pattern edge roughness of a resist after development process is discussed based on simulations of electron scattering in the resist film and the resist development process. Fixed threshold energy model is applied for the simulation and variations of a line width and the line edge roughness are obtained as functions of the incident electron energy, resist thickness and electron doses. The minimum line edge roughness is obtained, when the dose is more than that can be produced just the designed width of lines. As the dose increases more than that to obtain the minimum edge roughness, the roughness increases with increasing the dose. On the contrary, the roughness decreases with the dose as the statistical nature at very large doses as 100μC/cm2. Variable threshold energy model is applied and a dose variation of the line edge roughness is obtained. The LER is just reproduced by the statistical fluctuation, and it shows a linear relationship with 1/√dose Although the results obtained by present analyses agree qualitatively with experiments, the edge roughness obtained by experiment shows much smaller than the results, and some other mechanisms should be taken into account for the quantitative agreement.
It was presented that the effect of Photocatalysis coating of TiO2 to the body shell of Shinkansen vehicles in this issue. The results indicated that the coating performance was maintained only few months and the application of the present titanium oxide photocatalysis coating was difficult. The reason of loss of performance was contamination of metal powder into coating layer. It was necessary for application of photocatalysis coating to the Shinkansen vehicles that protection on surface from the wear powder of metals which were generated during a running of vehicles.
Fully reversed axial fatigue tests were conducted using plate specimens of a cast aluminium alloy, AC4CH, at three different temperatures of room temperature (R.T.), 150°C (423K) and 250°C (523K), and crack initiation and small crack growth were studied in detail by means of replication technique. At 150°C and 250°C, fatigue strength was nearly the same as, or significantly lower than, at R.T., respectively. The fatigue strength characterized in terms of fatigue ratio, σ/σB, was the same at all temperatures in high stress region, but slightly lower at 250°C in low stress region. Cracks invariably initiated from a casting porosity at R.T., while crack initiation due to slip deformation became dominant at elevated temperatures. At 250°C, a number of cracks were initiated due to slip deformation and the coalescence of the main crack and other cracks occurred very frequently, particularly in low stress region. At a fixed maximum stress intensity factor, Kmax, small crack growth rates were faster with increasing test temperature. When characterized in terms of Kmax/E (E : Elastic modulus), crack growth rates became similar at R.T. and 150°C, but still faster at 250°C. It was indicated that such enhanced crack growth at 250°C was attributed to most frequent coalescence of the main crack and other cracks, resulting in the lowest fatigue strength at this temperature.
The influence of the stress intensity factor on the microstructure near fatigue crack tips in rail steels was investigated by the orientation analysis using high-resolution EBSP. Large changes in crystal orientation and formation of cell structure were observed around the crack, and a plastic deformation zone was confirmed to be formed by the stress concentration at the crack tip. The size of the maximum plastic zone perpendicular to the crack was quantitatively determined based on the Kernel Average Misorientation, which is the average misorientation between all neighboring pairs of measurement points in the grain, to be 6.9, 8.2 and >50μm for Kmax = 9.55, 10.88 and 15.84 MPa·m1/2, respectively. For ΔKeff = 10.39 MPa·m1/2, a strongly plastic deformation zone of size in 1.3μm formed around the crack, and maximum plastic deformation zone was found outside the strongly plastic deformation zone. Although large misorientation (Δθ - 37.5°) was observed between the strongly plastic deformation zone and the maximum plastic deformation zone, the fluctuation of the crystal orientation inside the strongly plastic deformation zone was comparatively small, and the dislocation density was considered to have been small as well. On the other hand, cell structure was observed in the maximum plastic zone. A large difference in the development of cell structure was observed between the grain having a crack and neighbor grain, indicating that the size of the plastic deformation zone depends strongly on the grain size.
Both the acoustic emission (AE) and corrosion potential fluctuation were monitored for chloride SCC of sensitized Type-304 steel plate under bi-axial stress state. Branched SCCs were produced from rectangular-shaped corrosion pits initiated by falling-off of surface grains and filled with chromium oxide in 30mass% MgCl2 solution (363K). Both the AE and potential fluctuation were simultaneously detected at corrosion pit formation and SCC propagation. Two types of AE (Type-I and Type-II) were monitored. Type-I AEs with higher frequency components were detected during the pit growth and supposed to be produced by falling-off of surface grains due to intergranular attack, while a number of Type-II AEs (about 12,500 counts) with low frequency components were detected at SCC progression and supposed to be produced by cracking of the oxides. Though the AEs detected during SCC test are not the primarily signals from the SCC itself, secondary AE can be usefully utilized to monitor the SCC initiation and propagation as well as the corrosion potential fluctuation.
In this study, theoretical bi-elastic constant α for an interface crack between dissimilar anisotropic composite materials has been obtained. The obtained theoretical solution has been settled to the equation which defines conventional α for an interface crack between isotropic materials, when it brings each material property close to the characteristic of isotropic composite ones. The remarkable conclusion is to determine α regardless of the direction of the boundary surface, if angle difference between anisotropic strongest axes in both sides is fixed.
This paper presents experimental view of damage initiation and growth in plain woven fabric composites, which has several types on woven structure. Plain woven glass fabric composites were fabricated with tensioning the warp during the cure process. Microscopic damage progress was observed by a replica method. Binarization was applied in order to evaluate cracks in the weft and amplitude and curvature radius in plain woven fabric composites. It was found that the amplitude of the warp decreased and the fiber volume fraction in the weft became uniform in order to tension the warp during cure process. In addition, it was clear that the occurrence of cracks in the weft was delayed and the crack was developed slowly on these effects in comparison with the controlled type.
Shape memory alloys (SMAs) possess both sensing and actuating functions due to their shape memory effect, pseudo-elasticity, high damping capability and other remarkable properties. Combining the properties of SMAs with other materials can create intelligent or smart composites by utilizing the unique properties of SMAs. In this paper, ER3 epoxy resin composites filled with NiTi alloy particles were fabricated and their mechanical properties were investigated. As a result, owing to the addition of SMA particles, the flexural rigidity of SMA/ER3 composites raises. Especially, the storage modulus increases remarkably with increasing filler content at higher temperature region. The experimental results show that the addition of just 3.5% of SMA fillers to epoxy resin resulted in increased storage modulus larger than epoxy resin bulk by about four times. The storage modulus reaches to the maximum at the SMA phase transform temperature of approximate 120°C. The loss factor of SMA/ER3 composites increases with the increment of SMA particles contents. Moreover, a model of the laminated plates with SMA particles is presented to predict the dynamic mechanical properties based on the Hashin-Shtrikman’s theory. Compared to the experimental results, the reasonable prediction of the dynamic behaviors is obtained.