Simultaneous formation of p- and n-type ohmic contacts to 4H-SiC using the ternary Ni/Ti/Al system

Fabrication procedures for silicon carbide power metal oxide semiconductor field effect transistors (MOSFETs) can be improved through simultaneous formation (i.e., same contact materials and one step annealing) of ohmic contacts on both the p-well and n-source regions. We have succeeded with the simultaneous formation of the ohmic contacts for p- and n-type SiC semiconductors by examining ternary Ni/Ti/Al materials with various compositions, where a slash symbol “/” indicates the deposition sequence starting with Ni. The Ni(20 nm)/Ti(50 nm)/Al(50 nm) combination provided specific contact resistances of 2 × 10⁻³ Ω-cm² and 2 × 10⁻⁴ Ω-cm² for p- and n-type SiC, respectively, after annealing at 800°C for 30 min, where the doping level of Al in the SiC substrate was 4.5 × 10¹⁸ cm⁻³ and the level of N was 1.0 × 10¹⁹ cm⁻³.     

Characterization of 2-dimensional crack propagation behavior by simulation and analysis

Crack propagation behavior in 2-dimensional polycrystals is simulated and analyzed as a function of the fracture toughness of the grain boundary. The path of a crack impinging on a grain boundary is determined by the competition theory between intergranular and transgranular propagation. With decreasing boundary toughness, the tendency of intergranular propagation increases and the apparent fracture toughness of the polycrystal decreases. The results of the 2-dimensional analysis are compared with the simulation, and the advantages and limitations are discussed. The grain boundary toughness is evaluated by comparing the simulated crack paths with direct observations, resulting in a reasonable value for alumina ceramics. The fracture behavior is characterized in a macro-scale by the percentage of transgranular fracture and also in a micro-scale by the distribution of crack deflection angles.     

Suppressive effects of magnesium oxide materials on cadmium uptake and accumulation into rice grains I: Characteristics of magnesium oxide materials for cadmium sorption

The objective of this study is to assess the applicability of a commercial magnesium oxide (MgO) and a composite material containing MgO and natural minerals ('MgO-SH-A') as the soil amendments for suppression of cadmium (Cd) uptake and accumulation into rice grains. Firstly, the mineralogical and physicochemical properties, soil neutralizing capacities and Cd sorption characteristics of these materials were investigated. Both materials were strongly alkaline and possessed large surface areas. The X-ray diffraction pattern of MgO-SH-A indicated the presence of MgO and a magnesium-silicate mineral (antigorite) as the main components. MgO-SH-A showed a milder soil neutralizing capacity as compared to commercial MgO. The sorptions of Cd on commercial MgO and MgO-SH-A both fitted Langmuir isotherm. The maximum Cd sorption capacity of commercial MgO (46.8 mmol g(-1) DW) was higher than that of MgO-SH-A (5.87 mmol g(-1) DW), although the latter material showed higher affinity to Cd as compared to the former one. The dominant reaction involved in the Cd sorptions was suggested to be precipitation of Cd(OH)2 on the material surface. About 40% of Cd sorbed on MgO-SH-A was resistant to desorption by 0.1 M HCl, implying that this portion was strongly retained on the material surface.     

Submicron-sized anatase,TiO2 with high photocatalytic activity,and (Ti,Sn)O2 nanocrystals formed via hydrothermal technique

The compositional dependence of the crystalline phase and properties of precipitates (Ti _x Sn_1?x O₂) in the TiO₂–SnO₂ system, which were hydrothermally formed at 100–200 °C from the precursor solutions of TiCl₄ and SnCl₄ under weakly basic conditions in the presence of tetramethylammonium hydroxide (TMAH) was investigated. Rutile-type (Ti, Sn)O₂ solid solutions with nano-sized crystallite were directly formed at 180 °C in the composition range of x = 0–0.8. Nanoparticles with anatase crystallite around 10 nm as a main crystalline phase of precipitates that were formed in the compositions x = 0.9 and 1.0 showed similar photocatalytic activity. As the hydrothermal treatment temperature rose from 100 to 200 °C, the crystallite size of rutile solid solution, Ti_0.5Sn_0.5O_2, increased from 2.5 to 8.0 nm. The optical band gap of the samples changed in the range of 2.93–3.25 eV depending on their composition in the system. At the composition of x = 1.0, submicron-sized anatase-type pure TiO₂ particles (sizes of cuboid sides are around 100–120 nm) with pretty high crystallinity and superior photocatalytic activity were formed from the aqueous solution of TiCl₄ under basic hydrothermal condition at 180 °C in the presence of TMAH with concentration as 1.3 times high as the condition in the case of the nano-sized anatase.     

Suppressive effects of magnesium oxide materials on cadmium uptake and accumulation into rice grains II: Suppression of cadmium uptake and accumulation into rice grains due to application of magnesium oxide materials

The objective of this study is to assess the applicability of a commercial magnesium oxide (MgO) and a composite material containing MgO and natural minerals ('MgO-SH-A') as the soil amendments for suppression of cadmium (Cd) uptake and accumulation into rice grains. A cultivation experiment of rice plants (Oryza sativa L. cv. Kinuhikari) was conducted in an actual Cd-contaminated alluvial paddy field to evaluate the effectiveness of these materials. The 'plant available' fractions of Cd in the paddy soil significantly decreased by application of commercial MgO at 2250 kg ha(-1) or MgO-SH-A at 4500 kg ha(-1). These decreases would be primarily attributed to the increase in soil pH due to applications of the MgO materials because these soil Cd fractions were significantly negatively correlated with the soil pH. Even under a suppressive condition for Cd uptake by rice plants, i.e., continuous flooding of the paddy field around the heading stage, applications of these materials further reduced Cd concentration in brown rice as compared to that from the control. It was concluded that the two MgO materials examined would be effective in preventing Cd contamination of rice grains grown in Cd-polluted paddy fields.     

Ab initio perspective of the 〈110〉 symmetrical tilt grain boundaries in bcc Fe: application of local energy and local stress

The mechanical properties of polycrystalline metals are strongly dependent on the microscopic structure, stability, and elastic properties of grain boundaries (GBs). By using ab initio local energy, local stress, and local Young’s modulus, we attempt to provide a comprehensive view on the stability and structural properties of a series of 〈110〉 symmetrical tilt GBs (STGBs) in bcc Fe. We deal with four representative STGBs, the Σ3 (112), Σ3 (111), Σ11 (332), and Σ9 (221) GBs with the rotation angles ranging from 109.47° to 38.94°. The Σ3 (112) GB shows special stability due to stable structural units of four-membered rings with negligible bond-length changes except for substantial bond-direction changes, like stacking faults or twins. The other GBs are constructed by periodic arrangement of 5–3 and bulk structural units as usual coincidence GBs, while the 5–3 unit in the Σ9 (221) GB has an aspect of an edge-dislocation array in a small-angle tilt GB such as alternate compressive and tensile stresses at both the edges and relatively wide spread of local energy and local stress on both sides. In the GBs other than the Σ3 (112) GB, there exist commonly two kinds of interface atoms; atoms with larger atomic volumes reveal higher local energies, tensile stresses, and enhanced magnetic moments, while the other kind of atoms forming compressed bonds reveal lower local energies, compressed stresses, and reduced magnetic moments. For the four GBs, the local Young’s modulus averaged in the structural units ranges from 60 to 90 % of the bulk Young’s modulus in accordance with the degree of structural disorder or GB energies. There exists clear correlation among the local Young’s modulus, local energy, local stress, local magnetic moment, and local bonding nature at the structural units in the Fe GBs.     

Hydrothermal formation and characteristics of rare-earth niobate phosphors and solid solutions between YNbO4 and TbNbO4

Monoclinic fergusonite-type niobate, YNbO₄:Tb³⁺ and complete solid solutions with luminescent properties in the YNbO₄–TbNbO₄ system were directly formed as nanocrystals from the precursor solutions of NbCl₅, TbCl₃, and YCl₃ under hydrothermal conditions at 240 °C. The niobate nanocrystals possessed distinguishing feature of ellipsoidal morphology. The optical band gap of the as-prepared samples, Y_1−xTb_xNbO₄, x = 0–1.0, decreased from 3.7 to 2.9 eV as the terbium concentration increased from x = 0 to 1.0. The photoluminescence spectra of the as-prepared nanocrystals containing terbium are responsible for the characteristic blue (490 nm) and green (545 nm) luminescence, associated with ⁵D₄ → ⁷F₆ and ⁵D₄ → ⁷F₅ transitions, respectively. The strongest emission bands in the green spectral domain corresponding to ⁵D₄ → ⁷F₅ transition of Tb³⁺ are located at 545 and 550 nm under excitation at 240 nm Xe lamp. By heat treatment at 1300 °C, the luminescence intensity of the as-prepared solid solution x = 0.10 that presented the highest photoluminescence intensity increased more than 8 times as high as that before heat treatment.     

Correlation between temperature coefficient of elasticity and fourier transform infrared spectra of silicon dioxide films for surface acoustic wave devices

We investigated the correlation between the temperature coefficient of elasticity (TCE) and Fourier transform infrared (FT-IR) absorption spectra of SiO(2) for SAW devices. The measurement indicated that the TCE is strongly correlated with peak frequencies; that is, with the fractional change of the Si-O-Si bond angle with temperature.     

Expression of bcl-2 protein and APO-1 (Fas antigen) in the lung tissue from patients with idiopathic pulmonary fibrosis

Between 1974 and 1995 we encountered 19 cases of bronchial stricture or obliteration caused by endobronchial tuberculous lesions. In 11 the involvements were located at the right bronchus (including involvements of segmental and middle lobe bronchi) and in 8 at the left bronchus. On bronchoscopic biopsy of the stenosed bronchus, 7 patients showed histopathologic findings of tuberculous bronchitis, but 12 patients showed nonspecific inflammatory granular tissue. Five patients were kept under conservative observation because of mild subjective symptoms or refusal to undergo operation. Two patients underwent stent procedures but had poor outcomes. Twelve patients underwent operation. As the bronchial lesions in four of them were confined to the lobar or segmental bronchus, lobectomy was performed. One patient with a history of infantile tuberculosis had developed complete obliteration of the left main bronchus and cystic bronchiectasis in the entire lung parenchyma; pneumonectomy was essential. Seven patients who had strictures involving the main bronchus underwent bronchoplastic surgery with right (n = 4) or left (n = 3) upper sleeve lobectomy. None of the patients treated surgically showed any postoperative complication or recurrence of the tuberculosis. These surgical results for endobronchial tuberculosis indicate the need for early detection and operation. Bronchoscopy and computed tomography are the methods of choice for accurate diagnosis of bronchial involvement and assessment of the surgical indications. It is emphasized that bronchoplastic surgery is the best treatment for bronchial stricture involving bilateral main bronchi.     

Deformation-driven electrical transport of individual boron nitride nanotubes

In contrast to standard metallic or semiconducting graphitic carbon nanotubes, for years their structural analogs, boron nitride nanotubes, in which alternating boron and nitrogen atoms substitute for carbon atoms in a graphitic network, have been considered to be truly electrically insulating due to a wide band gap of layered BN. Alternatively, here, we show that under in situ elastic bending deformation at room temperature inside a 300 kV high-resolution transmission electron microscope, a normally electrically insulating multiwalled BN nanotube may surprisingly transform to a semiconductor. The semiconducting parameters of bent multiwalled BN nanotubes squeezed between two approaching gold contacts inside the pole piece of the microscope have been retrieved based on the experimentally recorded I-V curves. In addition, the first experimental signs suggestive of piezoelectric behavior in deformed BN nanotubes have been observed.