Properties and behavior of dislocations in 4H-SiC are presented based on classical theory of dislocations. 1) A new symbol which is an extension of the famous Frank symbol is introduced to explain complex stacking sequence in SiC polytypes. 2) A basal plane dislocation (BPD) is dissociated into two Shockley partials. Polarity of BPD is described. 3) Principles to assign Burgers vectors and polarity to the individual Shockley partials are derived. 4) Threading screw dislocations (TSD) can be dissociated into four partials, thereby reducing the total energy considerably. 5) Deviation of threading dislocations (TD) from the exact  orientation is reasoned from the viewpoint of energy consideration. 6) Transition from BPD to threading edge dislocations (TED) is explained by taking into account effects of the crystal surface. All of behavior can be explained quite well in terms of classical theory of dislocations.
We demonstrate the characteristics of dc arc plasma to clarify the advantage of reactive plasma deposition with dc arc plasma over the conventional other deposition methods such as magnetron sputtering. Both carrier concentration and crystallographic orientation distribution of Ga-doped ZnO (GZO) polycrystalline films deposited by the reactive plasma deposition can be controllable. The irradiation of electronegative oxygen ions (O−) generated in the afterarc plasma is an effective way for reducing the density of oxygen vacancies (VO) together with an increase in the density of O− trapped at the grain boundaries. VO on and in the vicinity of the surface of ingrains exhibits as just hydrogen-gas adsorption sites, whereas O− reacts with hydrogen gas to create carrier electrons. The hydrogen-gas sensors based on 50-nm-thick GZO films having the reactive O− located at the grain boundaries exhibited high response to 0.25% of hydrogen gas at 330℃.
Graphene: a monolayer sheet of graphite shows many attractive properties, which are expected to be applied to various devices. Development of a high throughput method has been required to realize the applications. Chemical exfoliation via graphene oxide (GO) has been considered one of the promising methods. However, the graphene reduced from GO showed poor crystallinity and mobility than that of mechanically exfoliated graphene. Many reduction methods have been investigated to obtain high mobility graphene from GO lately. In this review, we introduce a novel reduction method which we have developed to convert GO to graphene by explaining their advantages and some flaws to be solved.
A single spin-rotational state-selected [(J,M)=(2,2)] O2 beam allows us to conduct a spin- and alignment -controlled O2 chemisorption experiment. We have recently expanded its available translational energy range to 0.1-0.9 eV. In this study, the beam has been used for the analysis of O2 chemisorption on Pt(111). Although this system has been investigated intensively due to its technological importance, the origin of the low O2 sticking probability and its unusual energy dependence has remained unclear. The present results indicate that, at low translational energy (E0) conditions, direct activated chemisorption occurs only when the O2 axis is nearly parallel to the surface. At high energy conditions (E0>0.5 eV), however, the sticking probability for the parallel O2 decreases with E0 while that of the perpendicular O2 increases, accounting for the nearly energy-independent O2 sticking probability determined previously by a randomly oriented O2 beam.
The effect of nitrogen and aluminum as doped impurities on the stability of SiC polytypes (C- or Si-face 4H and 6H substrates) formed by physical vapor transport (PVT) was investigated. The stability of the polytypes was analyzed using classical thermodynamic nucleation theory with numerical results obtained from a global model including heat, mass and species transfer in a PVT furnace. The results reveal that the formation of 4H-SiC was more stable than that of 6H-SiC when a grown crystal was doped with nitrogen using C-face 4H- and 6H-SiC as seed crystals. In contrast, formation of 6H-SiC was favored over 4H-SiC when Si-face 4H- and 6H-SiC seed crystals were used. Meanwhile, the formation of 4H-SiC was more stable than that of 6H-SiC when aluminum was the dopant and C- and Si-faces of 6H-SiC were used as seed crystals. 6H-SiC was preferred to grow rather than 4H-SiC in the cases of C- and Si-faces of 4H-SiC as seed crystals.
Atmospheric pressure electrospray had been used previously in our laboratory to generate massive cluster ion beam for charged droplet ionization; a method we called electrospray droplet impact (EDI). Previous ion gun that employed atmospheric pressure electrospray lacks adequate beam current and density for surface and interface analysis. To improve the EDI beam performance, we have proposed a technique for producing a stable electrospray of aqueous solution under vacuum. It is well known that vacuum electrospray of volatile liquids is difficult because of the freezing of the liquids by evaporative cooling under vacuum. Vacuum electrospray of aqueous solution was achieved by irradiating the tip of the electrospray emitter with infrared or near-infrared laser to prevent the freezing under high vacuum (<0.05 Pa). A stable and large beam current was also obtained by optimizing the vacuum electrospray conditions. On the basis of these results, the vacuum electrospray can be expected to be a high-performance massive cluster ion gun.
A vacuum system was developed to evaluate the electron emission properties of an image sensor consisting of a field emitter array under high energy X-ray irradiation. Design of the vacuum chamber was conducted with the following requirements: (a) low base pressure less than 1×10−5 Pa to allow operation of field emitter arrays, (b) absorbed dose rate of X-ray of the order of 1∼10 kGy h−1, (c) voltage feeding system for operation of a matrix-driven field emitter array, and (d) introduction of photo-signal to the device. The pressure of the vacuum system reached 2×10−6 Pa when the system was isolated, and was 6×10−6 Pa when the system was connected to the electron accelerator. The absorbed dose rate of higher than 1 kGy h−1 was achieved with an electron beam energy of 1 MeV and a current of 6 μA.
Characteristic of the methane-hydrogen reforming is studied on the plasma reforming effects by the electrode structure and the additional magnetic field using the dielectric barrier discharge plasma actuator (DBD-PA). The hydrogen production rate was improved by using the multiple electrode structure of DBD-PA that achieved high rate of 10.6% as compared with 1.1% on single structure. Moreover, it was found that the DBD plasma confinement was improved by the effect of fluid control around DBD-PA resulting from the addition of the magnetic field and the hydrogen product rate could increase to 13.4% by using the cusp field configuration.