Microstructural analysis of NiInGe ohmic contacts for n-type GaAs

NiInGe ohmic contact materials, which are attractive to use in future GaAs devices, were previously developed in our laboratories. Although the NiInGe contacts provided low contact resistances of about 0.3 Ω-mm and excellent thermal stability, further reduction of the contact resistance (R_C) of the NiInGe contacts was mandatory to use these contacts in submicron devices. In this paper, the microstructural parameters, which influence the R_C values, were investigated by correlating the R_C values with the microstructure at the interface between the contact materials and the GaAs substrate. The R_C values of the NiInGe contacts were found to depend strongly on the volume fraction and the In concentration (x) of the In_xGa_1−xAs compound semiconductor layers, which were formed at the metal/GaAs interface. Both the volume fraction and the In concentration of the In_xGa_1−xAs layers were found to depend on the thickness of the In layer used in the NiInGe contact and the annealing temperature to form the ohmic contact. A R_C value of 0.18 Ω-mm was obtained for the Ni (18 nm)/In (13 nm)/Ge (30 nm) contact (where a slash “/” indicates the deposition sequence) after annealing at temperature of 650°C for 5 sec.     

Effect of vacuum annealing on field emission from heavily phosphorus doped homoepitaxial (111) diamond

Vacuum anneal treatments effects on field emission properties of phosphorus doped diamond are discussed. The C1s core level of diamond is characterized by X-ray photoelectron spectroscopy (XPS). With increasing annealing temperature, firstly oxygen desorption takes place from surface, which induce surface reconstruction followed by graphitization of surface. Field emission properties, therefore, strongly depend on vacuum anneal temperature. The threshold voltage of diamond annealed at 900 °C is the lowest. Fowler–Nordheim plots indicate that diamond annealed at 900 °C has the lowest barrier height, which is in good agreement with electron affinities as measured on carbon reconstructed surface. Further increased annealing temperature induces surface graphitization, which causes a threshold voltage increase of field emission.     

Heterogeneous Multi-Core Architecture That Enables 54x AAC-LC Stereo Encoding

This paper describes a heterogeneous multi-core processor (HMCP) architecture that integrates general-purpose processors (CPUs) and accelerators (ACCs) to achieve exceptional performance as well as low-power consumption for the SoCs of embedded systems. The memory architectures of CPUs and ACCs were unified to improve programming and compiling efficiency. Advanced audio codec-low complexity (AAC-LC) stereo audio encoding was parallelized on a heterogeneous multi-core having homogeneous processor cores and dynamically reconfigurable processor (DRP) ACC cores in a preliminary evaluation of the HMCP architecture. The performance evaluation revealed that 54times AAC encoding was achieved on the chip with two CPUs at 600 MHz and two DRPs at 300 MHz, which achieved encoding of an entire CD within 1- 2 min.     

l-Ascorbic acid as an alternative fuel for direct oxidation fuel cells

l-Ascorbic acid (AA) was directly supplied to polymer electrolyte fuel cells (PEFCs) as an alternative fuel. Only dehydroascorbic acid (DHAA) was detected as a product released by the electrochemical oxidation of AA via a two-electron transfer process regardless of the anode catalyst used. The ionomer in the anode may inhibit the mass transfer of AA to the reaction sites by electrostatic repulsion. In addition, polymer resins without an ionic group such as poly(vinylidene fluoride) and poly(vinyl butyral) were also useful for reducing the contact resistance between Nafion membrane and carbon black used as an anode, although an ionomer like Nafion is needed for typical PEFCs. A reaction mechanism at the two-phase boundaries between AA and carbon black was proposed for the anode structure of DAAFCs, since lack of the proton conductivity was compensated by AA. There was too little crossover of AA through a Nafion membrane to cause a serious technical problem. The best performance (maximum power density of 16 mW cm⁻²) was attained with a Vulcan XC72 anode that included 5 wt.% Nafion at room temperature, which was about one-third of that for a DMFC with a PtRu anode.     

Synthesis of l-theanine using enzyme/mesoporous silica conjugates under high pH conditions

We present a new enzymatic process for synthesis of l-theanine using glutaminase combined with immobilization technique on a mesoporous silica (MPS). The MPS was firstly attempted to modify with zirconia in order to enhance the durability against the reaction under high pH conditions. The glutaminase on the MPS successfully catalyzed the reaction for the synthesis of l-theanine. The glutaminase/MPS conjugate was subsequently recovered and employed for the reaction again. The conjugate showed the corresponding activity to the first synthesis. This indicates that the conjugate functions as a catalyst for synthesis of l-theanine, having the operational stability sufficient for reuse.     

Detection of microbubble position by a digital hologram

This paper reports on a new technique of measurements of microbubble position in three dimensions with high time-resolution. The technique is based on micro digital holographic particle tracking velocimetry. In this technique, an intensity profile is constructed from a holographic image of a microbubble where the profile results in showing two peaks. The distance between the two peaks appears to relate to the size of the microbubble's diameter. The three-dimensional position of the bubble can be detected by the center of the two peaks and the center point of the bubble image focused by a digital hologram. We also theoretically obtained the intensity profile of a microbubble by considering a refraction of light on a bubble surface to a ring-shaped aperture model. The theoretically obtained distance between the two peaks is found to be in good agreement with the values obtained experimentally.     

Quantum Phase Transition in the Infinite Dimensional Hubbard Model

We investigated the ground state of the infinite dimensional Hubbard model for both attractive and repulsive interactions by applying Gutzwiller type variational wave functions. Our variational wave functions have lower energies than the simple BCS wave function for the attractive case, and lower energies than the Brinkman-Rice state for the repulsive case. We found that the system has several phases depending on the density of electrons and the interaction strength. Investigated phases include antiferromagnetic, Fermi liquid, superconducting, charge density wave, and supersolid phases. The last one is a coexistence phase of superconducting and charge density wave states.     

Catalytic performance of K-promoted Rh/USY catalysts in preferential oxidation of CO in rich hydrogen

K-promoted Rh/USY (molar ratio: K/Rh=3) catalyst was found to exhibit high performance in preferential oxidation of CO in rich hydrogen. Such high performance was maintained in the presence of steam and CO₂. The CO oxidation activity of the K-Rh/USY catalyst was independent of the partial pressure of H₂, while the activity of the unpromoted Rh/USY catalyst was decreased significantly in hydrogen-rich stream. The effect of potassium addition on the catalyst structure was investigated and is discussed in terms of the differences in the catalytic performance.