Radiation damage of SiC Schottky diodes by electron irradiation

The impact of radiation damage on the device performance of 4H-SiC Schottky diodes, which are irradiated at room temperature with 2-MeV electrons is studied. After irradiation the reverse current increases, while the forward current and the capacitance decrease with barrier height and carrier density. The decrease of the barrier height is mainly responsible for the increase of the reverse current, while the decrease of the forward current for a high fluence is caused by the increase of the resistance in the bulk of the crystal. Although no electron capture levels are observed before irradiation, three electron capture levels (E₁, E₂, and E₃) are induced after irradiation. It is noted that the decrease in carrier density is partly caused by the contribution of non-observed electron capture level in the DLT spectrum, which compensates the free carriers.     

Evaporation rate effect on starting point of shrinkage stress development during drying process in solvent cast polymer film

To reveal the effect of drying conditions on shrinkage stress existing between a film and a substrate, a polystyrene/toluene solution was coated on a glass substrate, and the volume fraction of toluene at the time when the stress starts to grow (?_S) was measured at various drying temperatures and evaporation rates. ?_S decreased with increase of drying temperature at a constant evaporation rate, while ?_S increased with increase of evaporation rate at a constant drying temperature. From these results, it was suggested that the dominant factors affecting the starting point of stress were both the chain mobility and the measurement time‐scale. Considering the two factors, the tendency of ?_S with the drying conditions is quite similar to that of the solvent content at glass transition point, and this fact indicates a strong correlation between the starting point of stress and the glass transition of coated solution. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of tacticity of poly(methyl methacrylate) on interfacial region with silica in polymer nanocomposite

The effect of tacticity on the interfacial region between poly(methyl methacrylate) (PMMA) and silica in a PMMA/silica nanocomposite was investigated by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The glass transition temperature (T_g) values of the syndiotactic (st-) and atactic (at-) PMMA/silica nanocomposites are higher than those of the neat PMMA. Conversely, the T_g of the isotactic (it-) PMMA/silica nanocomposite is slightly higher than that of the neat it-PMMA. DSC and XRD results suggest that the restriction of the PMMA chain mobility in the silica nanoparticle interfacial region heightens as the syndiotactic content increases. FT-IR results show that this phenomenon is caused by the interaction between the carbonyl group of PMMA and the silanol group on the silicon dioxide surface. Therefore, it can be concluded that the syndiotactic-rich PMMA has a significantly different molecular mobility from that of the neat PMMA in the interfacial region with silica nanoparticle surface than isotactic-rich PMMA.     

The calculation of particle deposition efficiency due to inertia,diffusion and interception in a plane stagnation flow

The particle deposition mechanism in a plane stagnation flow is investigated analytically and numerically. Particle deposition efficiency η_TID is obtained theoretically by taking into account particle inertia, diffusion and interception. It is compared with various calculated deposition efficiencies, i.e. η_T (due to inertia) + η_I (due to interception) + η_D (due to diffusion), η_TI, (due to inertia and interception) + η_D, etc. In the region where all of the three deposition mechanisms, i.e. inertia, interception and diffusion, act at the same time, real deposition efficiency η_TID is not accurately expressed by η_T + η_I + η_D. However, η_TID is nearly equal to η_TI + η_D unless the interception parameter is zero.The calculated results of particle concentration indicate that a high concentration region is formed near the deposition plate, and that the concentration becomes higher as particle inertia increases.     

Fourier synthesis image reconstruction by use of one-dimensional position-sensitive detectors

An improvement of Fourier synthesis optics for hard x-ray imaging is described, and the basic performance of the new optics is confirmed through numerical simulations. The original concept of the Fourier synthesis imager utilizes nonposition-sensitive hard x-ray detectors coupled to individual bigrid modulation collimators. The improved concept employs a one-dimensional position-sensitive detector (such as a CdTe strip detector) instead of the second grid layer of each bigrid modulation collimator. This improves the imaging performance in several respects over the original design. One performance improvement is a two-fold increase in the average transmission, from 1/4 to 1/2. The second merit is that both the sine and cosine components can be derived from a single grid-detector module, and hence the number of imaging modules can be halved. Furthermore, it provides information along the depth direction simultaneously. This in turn enables a three-dimensional imaging hard x-ray microscope for medical diagnostics, incorporating radioactive tracers. A conceptual design of such a microscope is presented, designed to provide a field of view of 4 mm and a spatial resolution of 400 microm.     

Ultrasonic techniques for imaging and measurements in molten aluminum

In order to achieve net shape forming, processing of aluminum (Al) in the molten state is often necessary. However, few sensors and techniques have been reported in the literature due to difficulties associated with molten Al, such as high temperature, corrosiveness, and opaqueness. In this paper, development of ultrasonic techniques for imaging and measurements in molten Al using buffer rods operated at 10 MHz is presented. The probing end of the buffer rod, having a flat surface or an ultrasonic lens, was immersed into molten Al while the other end with an ultrasonic transducer was air-cooled to room temperature. An ultrasonic image of a character "N", engraved on a stainless steel plate immersed in molten Al, and its corrosion have been observed at 780 degrees C using the focused probe in ultrasonic pulse-echo mode. Because cleanliness of molten Al is crucial for part manufacturing and recycling in Al processing, inclusion detection experiments also were carried out using the nonfocused probe in pitch-catch and pulse-echo modes. Backscattered ultrasonic signals from manually added silicon carbide particles, with an average diameter of 50 microm, in molten Al have been successfully observed at 780 degrees C. For optimal image quality, the spatial resolution of the focused probe was crucial, and the high signal-to-noise ratio of the nonfocused probe was the prime factor responsible for the inclusion detection sensitivity using backscattered ultrasonic signals. In addition, it was found that ultrasound could provide an alternative method for evaluating the degree of wetting between a solid material and a molten metal. Our experimental results showed that there was no ultrasonic coupling at the interface between an alumina rod and molten Al up to 1000 degrees C; therefore, no wetting existed at this interface. Also because ultrasonic velocity in alumina is temperature dependent, this rod proved to be able to be used as an in-line temperature monitoring sensor under 1000 degrees C in molten Al.     

Leaching test of gamma-emitting Cs,Ru, Zr,and U from neutron-irradiated UO2/ZrO2 solid solutions in non-filtered surface seawater

The leaching behaviors of gamma-ray radionuclides, Cs-137, Ru-103, and Zr-95, produced by neutron irradiation of UO₂/ZrO₂ solid solutions, in real surface seawater were investigated under atmospheric conditions. The fraction of radionuclide inventory leached in the seawater was in the order of Cs > Ru (～U) ? Zr, indicating that the fraction was significantly affected by the chemical state of the radionuclides. However, the amount of soluble nuclides was proportional to that of uranium regardless of whether the solid solutions were prepared under an oxidative or reductive environment. A tiny fraction of Ru was filtered out by a 3 kDa nominal molecular weight cut-off filter after the 160 d leaching test, suggesting a different behavior from its ionic form, but Cs and U did not form a colloid-like species in seawater.     

In Situ Observation of Phase Separation of a Barium Borate Melt in a Stable Immiscibility Region under Microgravity

The precipitation of droplets was directly observed on a BaO–B₂O₃ melt in a drop shaft experiment. This is the first time that precipitation of droplets has been observed in a 4.5 s drop test. The melt film of 4BaOz96B₂O₃ (mol%) held on a platinum wire loop was heated above the critical tem-perature to produce uniformity and was cooled down to the phase separation temperature range. Phase separation of the melt was observed directly with a video camera. The IR image of the melt was simultaneously detected with a CCD array and was converted into a two-dimensional thermograph.     

Radiation source dependence of performance degradation in thin gate oxide fully-depleted SOI n-MOSFETs

The degradation of the electrical performance of thin gate oxide fully depleted SOI n-MOSFETs and its dependence on the radiation particles are investigated. The transistors are irradiated with 7.5-MeV protons and 2-MeV electrons at room temperature without bias. The shift of threshold voltage and the coupling effect with the degraded opposite gate are clarified. A remarkable reduction of the floating body effects is observed after irradiation. The degradation of the extracted parameters is discussed by a comparison with the damage coefficients.     

Performance of the first Japanese large-scale facility for radon inhalation experiments with small animals

A radon test facility for small animals was developed in order to increase the statistical validity of differences of the biological response in various radon environments. This paper illustrates the performances of that facility, the first large-scale facility of its kind in Japan. The facility has a capability to conduct approximately 150 mouse-scale tests at the same time. The apparatus for exposing small animals to radon has six animal chamber groups with five independent cages each. Different radon concentrations in each animal chamber group are available. Because the first target of this study is to examine the in vivo behaviour of radon and its effects, the major functions to control radon and to eliminate thoron were examined experimentally. Additionally, radon progeny concentrations and their particle size distributions in the cages were also examined experimentally to be considered in future projects.