Fabrication of single-electron transistors using field-emission-induced electromigration

We report a novel technique for the fabrication of planar-type Ni-based single-electron transistors (SETs) using electromigration method induced by field emission current. The method is so-called "activation" and is demonstrated using arrow-shaped Ni nanogap electrodes with initial gap separations of 21-68 nm. Using the activation method, we are easily able to obtain the SETs by Fowler-Nordheim (F-N) field emission current passing through the nanogap electrodes. The F-N field emission current plays an important role in triggering the migration of Ni atoms. The nanogap is narrowed because of the transfer of Ni atoms from source to drain electrode. In the activation procedure, we defined the magnitude of a preset current Is and monitored the current I between the nanogap electrodes by applying voltage V. When the current I reached a preset current Is, we stopped the voltage V. As a result, the tunnel resistance of the nanogaps was decreased from the order of 100 T(omega) to 100 k(omega) with increasing the preset current Is from 1 nA to 150 microA. Especially, the devices formed by the activation with the preset current from 100 nA to 1.5 microA exhibited Coulomb blockade phenomena at room temperature. Coulomb blockade voltage of the devices was clearly modulated by the gate voltage quasi-periodically, resulting in the formation of multiple tunnel junctions of the SETs at room temperature. By increasing the preset current from 100 nA to 1.5 microA in the activation scheme, the charging energy of the SETs at room temperature was decreased, ranging from 1030 meV to 320 meV. Therefore, it is found that the charging energy and the number of islands of the SETs are controllable by the preset current during the activation. These results clearly imply that the activation procedure allows us to easily and simply fabricate planar-type Ni-based SETs operating at room temperature.     

Permeation measurements for investigating atomic hydrogen flux and wall pumping/fuelling dynamics in QUEST

In order to investigate the overall atomic hydrogen background and the dynamic characteristics of wall pumping/fuelling phenomenon, a permeation probe system has been developed and applied in the spherical tokamak QUEST. Reliability of measurements, within ±3% accuracy and a positive correlation with the hydrogen line emission over three orders of magnitude have been demonstrated for more than 3000 various plasma discharges. By comparison of the experimental permeation (flux) curves with the numerically simulated curves, the net incident atomic hydrogen flux is evaluated in the range of 1 × 10¹⁹ H m^?2 s^?1 to 4 × 10²⁰ H m^?2 s^?1. The atomic flux has been investigated as a function of various plasma operation parameters like RF power, gas pressure and magnetic configuration. Using the static particle balance and permeation measurements, the progress in wall conditioning has been investigated. An inverse correlation between the atomic hydrogen flux and improvement in wall pumping has been observed over the two campaigns.     

Further studies on copper nanocomposite with dispersed single-digit-nanodiamond particles

This paper describes the microstructures and mechanical properties of Cu nanocomposites containing 0–30 at.% diamond nanoparticles. The Cu nanocomposite powders are fabricated by mechanical milling method and are consolidated by spark plasma sintering and hot extrusion. Microstructural observation shows that the homogeneous distribution of diamond nanoparticles in the Cu nanocomposite can be achieved by extrusion with large plastic deformation, in spite of 20 at.% diamond content, and that the nanocomposite with homogeneous distribution of diamond nanoparticles has ultra-fine grain structure, approximately 50 nm. Vickers hardness and compression tests on the SPS-consolidated and hot-extruded samples show that the detonation nanodiamond dispersed homogeneously in the Cu matrix enhances the mechanical properties.     

Deformation behaviour of retained β phase inβ-eutectoid Ti-Cr alloys

Plastic deformation mode and its relation to tensile properties were investigated in retained phase of-eutectoid type Ti-Cr alloys. A plate-like single variant phase is induced during deformation of the most unstable phase having a minimum chromium content required to suppress martensitic transformation. A selected area electron diffraction pattern taken from a boundary region of the stress-induced phase plate can be explained by the idea that a single variant of phase is induced in a {3 3 2} 1 1 3 twin produced during deformation. Anisotropy in population of four phase variants decreases with increasing chromium content. On further increasing chromium content, deformation occurs by slip. Enhanced ductility is obtained in as-quenched Ti-Cr alloys accompanied by phase transformation or {332} 1 1 3 twinning during deformation, phase of as-quenched Ti-Cr alloys changes continuously from commensurate structure with sharp reflections to incommensurate structure with diffuse reflections with increasing chromium content. The obtained results in-eutectoid type Ti-Cr alloys are quite similar to those in-isomorphous type Ti-V alloys.     

Preparation and Elastic Properties of rf-Sputtered Amorphous Films in the System SiO2-Y2O3

Amorphous films in the SiO₂-Y₂O₃ system were prepared by the rf-sputtering method. Transparent amorphous films were obtained in the region between 0 and 66 mol% Y₂O₃ content, only in an oxygen atmosphere. The densities and elastic constants of the films were determined. As the amount of Y₂O₃ addition increased, density and elastic constants increased up to about 45 mol% Y₂O₃, beyond which it held constant. From the relationship between the bulk modulus and the mean atomic volume, a structural change in the present films seems to occur at about 45 mol% Y₂O₃ content.     

Physical Properties and Structure of rf-Sputtered Amorphous Films in the System Al2O3–Y2O3

Amorphous films in the system Al₂O₃–Y₂O₃ were prepared by the rf sputtering method in the range of 0–76 mol% Y₂O₃, and their density, refractive index, and elastic constants were measured. All of the physical properties of the amorphous Al₂O₃–Y₂O₃ films had a similar compositional dependence; that is, they increased continuously, but not linearly with increasing Y₂O₃ content. To confirm the coordination states of aluminum and yttrium ions in the amorphous Al₂O₃–Y₂O₃ films, the Al K α X-ray emission spectra and the X-ray absorption near edge structures (XANES) were measured. The average coordination number of aluminum ions in the amorphous films containing up to about 40 mol% Y₂O₃ content was 5, that is a mixture of 4-fold- and 6-fold-coordinated states. In the region of more than about 50 mol% Y₂O₃, the fraction of the 6-fold-coordinated aluminum ions increased with increasing Y₂O₃ content, while the results led to the conclusion that the coordination number of yttrium ions was always 6, regardless of composition. These results indicate that, in amorphous films in the system Al₂O₃–Y₂O₃, the change of the coordination state of aluminum ions has an important effect on physical properties.     

Properties and Network Constitution of rf-Sputtered Amorphous Films in the System Silicon Dioxide–Aluminum Orthophosphate

Amorphous films in the system SiO₂–AlPO₄ were prepared by means of the rf-sputtering method, and their physical properties, such as density, refractive index, and temperature coefficient of Young's modulus, and infrared spectra were measured. Also, the K α X-ray emission spectra of silicon and aluminum were measured in order to investigate the coordination state of these cations in the amorphous films. The density and the refractive index were close to those of amorphous SiO₂ and AlPO₄ and the compositional dependence showed a small deviation from linearity. The temperature coefficients of Young's modulus were positive for all of the samples. The infrared absorption spectra of all of the samples were similar to those of SiO₂ glass and amorphous AlPO₄ film, and there was no evidence of the presence of P═O bonds. The coordination states of silicon and aluminum ions in the present amorphous films were the same as those in fused silica and AlPO₄ crystal, respectively. The results of the properties, infrared absorption spectra, and X-ray emission spectra suggest that SiO₄ tetrahedrons and AlO₄–PO₄ connecting tetrahedral dimers constitute the network of the present amorphous films. A small deviation of the physical properties from an additive rule was thought to result from the difference in the bond character between the newly formed Si–O–Al and Si–O–P bonds and the bonds in the end members, Si–O–Si and Al–O–P.     

A study of living plant specimens by low-temperature scanning electron microscopy

Young fresh Tradescantia reflexa stamen hair cells were used to clarify the optimal conditions for direct viewing and taking photographs with a scanning electron microscope (SEM) equipped with a cryo-system. The rate of protoplasmic streaming in the cells was measured under an optical microscope after examining and photographing them in the SEM over a period of a few minutes. Almost the same rate of streaming (5.5 μm/second, 20°C) was observed in nonirradiated control cells and irradiated cells photographed in the SEM using an accelerating voltage of 10 kV with the cryo-stage at a temperature of – 15°C. (The specimen holder and specimen were not at this temperature, but, rather, probably somewhat higher.) Fresh plant organs, tissues, and cells were also tested under the same conditions. The fine structure was well preserved in detail. The procedures were as follows: (1) prompt attachment of fresh plant materials on an aluminum specimen holder with double-faced adhesive Scotch tape or a small amount of plastic adhesive for woodcraft; (2) setting the holder on the cryo-stage cooled to –15°C in advance and rapid evacuation; and (3) quick SEM examination and photography (within several minutes). The advantages of this method are summarized as follows: (1) high possibility of viewing living materials; (2) minimal artifacts: freedom from chemical fixation and additional procedures utilized in ordinary SEM specimen preparation; and (3) simplicity, speediness, and economy in preparation for viewing. Since the specimens were not likely to be frozen during quick examination and photography, this method might well be called “low-temperature SEM” (LT-SEM) as distinguished from “cryo-SEM”.     

Associations of visual forms with colors: The minor role of emotion as the mediator

Associations of colors with a wide variety of visual forms were examined. Fifty visual forms were presented to Japanese participants, who were asked to report a color suitable to each visual form out of 15 colors. Correspondence analysis was applied to the responses, and four dimensions of configurations were obtained. The first and second dimensions were related to chromaticity or hue. In these dimensions, red and orange were associated with round symmetric shapes, yellow with shapes with sharp corners, violet and purple with irregular shapes with smooth curves, and cold colors such as blue and green with forms that consisted of simple geometrical elements such as triangles, squares, and circles. The third dimension was related to L* and b* in the CIELAB color space and to the stability of visual forms. Dimension 4 was not significantly related to any of L*, a*, and b*. In another experiment, participants rated the affective impressions of the colors and visual forms on semantic differential (SD) scales. The analyses of the SD data combined with the results of the color‐form associations suggest that the role of emotional meanings of colors and visual forms in mediating the associations was rather minor, and that world‐knowledge contributed considerably to the observed color‐form associations. Kandinsky's color‐form assignment was also examined, and except for the yellow‐triangle association, the assignment was not supported.