Electrical properties at p-ZnSe/metal interfaces

In order to prepare low resistance ohmic contacts to p-ZnSn by the “deposition and annealing (DA)” technique which has been extensively used for GaAs and Si-based devices, formation of a heavily doped layer by the p-ZnSe/metal reaction is required. For p-ZnSe/Ni contacts, Ni and Se reacted preferentially at the ZnSe/Ni interface upon annealing at temperatures higher than 250°C. However, capacitance-voltage measurements showed that the net acceptor concentration (N_A-N_D) close to the p-ZnSe/Ni interface was reduced upon the Ni/ZnSe reaction, resulting in high contact resistance. For p-ZnSe/Au contacts, neither Au/ZnSe reaction nor reduction of the acceptor concentration were observed after annealing at temperatures lower than 300°C. This indicates that although the metal/p-ZnSe reaction is mandatory to prepare a heavily doped layer, the reaction induced an increase in the compensation donors in the p-ZnSe substrate. In order to increase the acceptor concentration in the vicinity of the p-ZnSe/metal interface through diffusion from the contact materials, Li or O which was reported to play the role of an acceptor in ZnSe was deposited with a contact metal and annealed at elevated temperatures. Ni or Ag was selected as the contact metal, because these metals were expected to enhance Li or O doping by reacting with ZnSe. However, the current density-voltage characteristics of the Li(N)/Ni and Ag(O) contacts exhibited rectifying behavior, and the contact resistances increased with increasing annealing temperature. The present results indicated that, even though the acceptor concentration in the p-ZnSe substrate increased by diffusion of the dopants from the contact elements, an increment of the compensation donors was larger than that of the acceptors. The present experiments indicated that preparation of low resistance ohmic contacts by forming a heavily doped intermediate layer between p-ZnSe and metal is extremely difficult by the DA technique.     

Twin-Related Tetragonal Variants in Yttria Partially Stabilized Zirconia

Crystals of yttria partially stabilized zirconia were grown by the arc-image floating-zone technique and studied by transmission electron microscopy. Crystals annealed at 1700°C consist of tetragonal precipitates and a cubic matrix. The platelike domains in a precipitate are twin-related tetragonal variants stacked alternately parallel to the (011) twin plane. The axial relations between the tetragonal precipitate and the cubic matrix are [100]_tetragonal|[100]_cubic, [011]_tetragonal|[011]_cubic.     

On approximate solutions for the deformation of plane anisotropic beams

Plane deformation of anisotropic beams with narrow rectangular cross sections exhibits coupling of stretching, bending and transverse shearing. For anisotropic cantilever beams with a stiff end-cap under end forces and an end couple, assessments were made for approximate solutions by comparing these with numerically exact finite element (FE) solutions. Specific attention is given to point-wise or approximate satisfaction of the end-fixity conditions. As approximate methodologies, (i) the elementary polynomial form of Airy's stress function for the plane stress problem in a rectangular region, (ii) a Timoshenko-type beam theory, and (iii) the Bernoulli-Euler beam theory were selected. Among these, only the polynomial form of Airy's stress function violates the point-wise end-fixity conditions. Both the polynomial Airy stress function and the Timoshenko-type beam theory successfully model the effects of transverse shear deformation and the coupling of stretching and transverse deflection. Analytical solutions demonstrate that the normal shear coupling effect increases linearly with the thickness-to-span ratios in axial normal stress and axial displacement, while the coupling manifests quadratically in transverse displacement. The comparison of end displacements with the numerically exact FE solutions indicates that the polynomial form of Airy's stress function is no better than the Timoshenko-type beam theory. Similar conclusions were reached for the problem of uniformly loaded cantilever beams. It has been found that the accurate prediction of the deformation of thick anisotropic beams with significant normal-shear coupling requires the use of higher order theories.     

Electrical resistivity and Seebeck coefficient of La1−x M x MnO3 (M = Ca,Sr) single crystals

The temperature dependence of the electrical resistivity and Seebeck coefficient was measured on single crystals of La_1–x Ca _x MnO₃(0 <x 0.3) and La_1–x Sr _x MnO 3 (0 <x 0.4) grown by the arc-image floating zone method. The electrical conduction for La_1–x crystals withx 0.2 was of the activation type aboveT _c and of the degenerate type belowT _c, while that for the crystal withx = 0.1 was of the activation type over the whole measured temperature range between –170 and 400°C. The conduction behaviour of La_{1– x} Sr _x MnO₃ was essentially the same as that of La_1–x Ca _x MnO₃ except that the conduction of the crystals withx = 0.3 and 0.4 was of the degenerate type aboveT _c. A distinct difference in Seebeck data was observed between the calcium and the strontium compounds.     

Preparation of spherical fine ZnO particles by the spray pyrolysis method using ultrasonic atomization techniques

An ultrasonic atomizer was used in the spray pyrolysis method to prepare fine, spherical and uniform ZnO particles. Almost spherical particles were obtained successfully which had a mean particle size of 0.15 m and had a very narrow particle size distribution. By using alcohol as the solvent, it was found that the particles do not have hollow shell layers which could usually be observed in the spray pyrolysis process by using water as the solvent. The morphology of the ZnO particles was strongly affected by the concentration of the starting solution.     

Formation of monodispersed Ta2O5 powders

The Ta₂O₅ powders synthesized by the hydrolysis of tantalum pentaethoxide, Ta(OC₂H₅)₅ in alcoholic solution were monodispersed fine oxide particles, which were a uniform, spherical shape, non-agglomerate, and had a narrow size distribution. They grew to 1.2m after ageing for 1 h after hydrolysis. Powder X-ray diffraction and differential thermal analysisthermogravimetric analysis showed the particles were amorphous and hydrated. These particles lost the water at 290° C and gave well-crystalline Ta₂O at 740° C. Throughout these thermal processes, the particle morphology was kept almost the same.     

Activities of FexO in CaO + CaF2 + SiO2 + FexO quaternary slags by disposable electrochemical oxygen probes

The activities of Fe_xO in CaO + CaF₂ + SiO₂ + Fe_xO quaternary slags were measured by means of solid-oxide galvanic cell. The Fe_xO activities in the slags are influenced by CaF₂ as well as SiO₂. At constant Fe_xO mole fractions, e.g., , at low SiO₂ mole fractions i.e., , the substitution of CaF₂ for CaO has an effect of raising the Fe_xO activity. At higher SiO₂ mole fractions, e.g., , however, such an effect becomes insignificant.     

Effect of Silicon Dioxide on the Thermal Diffusivity of Aluminum Nitride Ceramics

The thermal diffusivity of AlN ceramics was significantly decreased by the addition of SiO₂. The AlN ceramics with 4 wt% SiO₂ could not be densified by pressureless sintering in the temperature range 1400° to 1800°C. The thermal diffusivity of these samples was very low because of their porous structure. The AlN ceramics containing 2, 4, and 8 wt% SiO₂ were densified by hot-pressing and also had low thermal diffusivity. In these samples, the grains of the 27R polytype that resulted from the reaction between AlN and SiO₂ were dispersed, obstructing the conduction of heat. The relation between the amount of 27R polytype and the thermal diffusivity of the AlN ceramics was determined.     

Dynamic compensation by fusing a high-speed actuator and high-speed visual feedback with its application to fast peg-and-hole alignment

This paper presents a dynamic compensation concept to grapple with the dynamic defects of a traditional robot arm, especially while performing high-speed endpoint regulations. The proposed high-speed dynamic compensation concept offers a new point of view for cooperating with a traditional manipulator to realize highly dexterous performance of manipulations. The concept is realized through adoption of a high-speed light-weight actuator as well as endpoint closed loop configured high-speed cameras. The dynamic compensation is analyzed experimentally with 1000 Hz visual feedback and a high-speed finger for a robot arm in the case of one degree of freedom. The advantage of the proposed approach is that the modeling for the robot system’s dynamics is not needed, whereas it is necessary and trivial in order to realize high-speed regulations by traditional approaches. Thus, the control issue becomes easier with the proposed approach. As an application for this concept, fast peg-and-hole alignment with large position and attitude uncertainty is studied. The alignment algorithm is based on a visual compliance strategy. Alignment experiments show that with the proposed concept of dynamic compensation as well as visual compliant motion control, robust and fast convergence was realized for most cases.