High-quality schottky and ohmic contacts in planar 4H-SiC metal semiconductor field-effect transistors and device performance

We have fabricated planar 4H-SiC, metal-semiconductor field-effect transistors (MESFETs) with high-quality metal/SiC contacts. To eliminate potential damage to the gate region caused by etching and simplify the device fabrication process, gate Schottky contacts were formed without any recess gate etching, and an ideality factor of 1.03 was obtained for these gate contacts. The interface state density between the contact metal and SiC was 5.7×10¹² cm⁻²eV⁻¹, which was found from the relationship between the barrier height and the metal work function. These results indicate that the interface was well controlled. Thus, a transconductance of 30 mS/mm was achieved with a 3-μm gate length as the performance figure of these MESFETs with high-quality metal/SiC contacts. Also, a low ohmic contact resistance of 1.2×10⁻⁶ Θcm² was obtained for the source and drain ohmic contacts by using ion implantation.     

Generation and application of high-quality supercontinuum sources

Ultrawideband supercontinua have been generated using ultrashort pulses and zero-dispersion highly nonlinear fiber. However, they have inherent large noise and spectral fine structure. We generated a widely and flatly broadened, low-noise, highly coherent, high-quality supercontinuum and used it to demonstrate ultrahigh-resolution optical coherence tomography in several wavelength regions.     

Structural and Thermoelectric Properties of Chimney–Ladder Compounds in the Ru-Mn-Si System

We have investigated phase relationships of the sesquisilicide alloys in the Ru-Mn-Si system. A series of chimney–ladder phases Ru_1−x Mn _x Si _y (0.14 ≤ x ≤ 0.97, 1.584 ≤ y ≤ 1.741) are formed over a wide compositional range between Ru₂Si₃ and Mn₄Si₇. We also investigated thermoelectric properties of the directionally solidified Ru_1−x Mn _x Si _y alloys as a function of Mn content and temperature. The dimensionless figure of merit ZT for alloys with high Mn content (x ≥ 0.75) increases as the Mn content increases. The alloy with x = 0.90 exhibits ZT as high as 0.76 at 874 K.     

Wavelength conversion film with glass coated Eu chelate for enhanced silicon-photovoltaic cell performance

In order to improve the conversion efficiency of a silicon-photovoltaic (PV) module, we investigated the combination with a wavelength conversion film (WCF), which consists of Eu chelate particles encapsulated by the sol–gel derived silica glass. The photoluminescence (PL) excitation spectrum of Eu chelate shows that the violet light below 400 nm is effectively converted to the red emission at 613 nm. Since the PV cell has higher sensitivity at the red wavelength region compared to the violet region, Eu chelate is one of the suitable material for a WCF. The diameter of fabricated sol–gel encapsulated Eu chelate was larger than the wavelength of irradiated sunlight, therefore, the transmittance of a WCF decreased with increasing the concentration of Eu chelate. The short circuit current (J_SC) was increased by inserting the the WCF on the front side of Si-PV cell compared to the reference module (glass/ethylene vinyl acetate/WCF without Eu chelate/Si-PV cell/EVA/back-film), and the maximum increase of ΔJ_SC was 1.03 mA/cm² compared to the reference module. However, the maximum ΔJ_SC of fabricated module was almost same as the conventional Si-PV cell due to the refractive index mismatch of each layers.     

Organic photoconductive device fabricated by electrospray deposition method

We demonstrated a blue-sensitive organic photoconductive device fabricated by an electrospray deposition method. Poly[9,9-dioctylfluorenyl-2,7-diyl]-co-1,4-benzo-(2,1,3)-thiadiazole (F8BT) was chosen as a blue-sensitive polymer, and a maximum external quantum efficiency of 0.22% was achieved at the irradiated optical intensity of 3.9 mW/cm². The absorption spectrum of F8BT neat film showed that the selectivity of spectral responses at the blue wavelength region was good enough to divide the incident light into blue color components. These results indicate the possibility of a color separation without a prism for high resolution cameras by combination of green and red sensitive organic photoconductive devices.     

Investigation of Factors Affecting Vertical Drain Behavior

Some influencing factors on vertical drain behavior were investigated by laboratory tests as well as by back-analyses of test embankments on vertical drain improved subsoil at Saga Airport, Saga, Japan. Based on the results from this study, suggestions are made on determining the design parameters for vertical drain improvement. For the discharge capacity test of a prefabricated vertical drain, confining the drain in clay is essential. Also, due to the creep of the filter and the clogging caused by the fine particles entering the drainage channel, the long-term discharge capacity is significantly smaller than the short-term one, and this should be considered in design. For smear effect, a new equation is proposed for determining the ratio of the hydraulic conductivity of the natural subsoil to that of the smear zone, which considers the fact that laboratory tests normally underestimate the hydraulic conductivity of natural deposits. Regarding the effect of the sand mat, the numerical analysis results in this study show that if the hydraulic conductivity of sand is larger than 10?4 m∕s, the assumption of a free drainage condition in the sand mat may not result in significant error. Finally, a methodology of predicting the behavior of vertical drain improved subsoil is proposed.     

Effects of Oral Administration of Chitin Nanofiber on Plasma Metabolites and Gut Microorganisms

The aim of this study was to examine the effects of oral administration of chitin nanofibers (CNFs) and surface-deacetylated (SDA) CNFs on plasma metabolites using metabolome analysis. Furthermore, we determined the changes in gut microbiota and fecal organic acid concentrations following oral administrations of CNFs and SDACNFs. Healthy female mice (six-week-old) were fed a normal diet and administered tap water with 0.1% (v/v) CNFs or SDACNFs for 28 days. Oral administration of CNFs increased plasma levels of adenosine triphosphate (ATP), adenosine diphosphate (ADP), and serotonin (5-hydroxytryptamine, 5-HT). Oral administration of SDACNFs affected the metabolisms of acyl-carnitines and fatty acids. The fecal organic level analysis indicated that oral administration of CNFs stimulated and activated the functions of microbiota. These results indicate that oral administration of CNFs increases plasma levels of ATP and 5-HT via activation of gut microbiota.     

Diagnosability and Distinguishability Analysis and Its Applications

As systems become more complex, it becomes necessary to understand, simplify, and apply fault diagnosis and fault-tolerant design. Although some graph-theoretical diagnostic models such as self-diagnosis model have been studied, the model can not be applied to most systems due to the assumption that each unit has its own testing capability. This paper presents a graph-theoretical diagnosis model expressed by a set of fallible units, a set of measurements, and an incident matrix indicating binary relation between these two sets. Since this model explicitly separates tested units (fallible units) and testing units (measurements), we can discuss diagnostic aspects from both sides. Diagnosability and distinguishability of the model with multiple faults are discussed from combinatorial point of view. Measures of t-fault diagnosability and t-out-of-s diagnosability which was introduced on the self-diagnosis model are discussed. Conditions for these diagnosabilities are expressed by a topological concept of fault distance. The concept of distinguishability is generalized to multiple fault situations called t-fault distinguishability. A lower bound for the distinguishability is obtained by using fault distance. The new concept of s-distinguishability class (s-dc) is presented. This analysis is recommended in the design of systems to attain a required level of diagnosability and distinguishability as well as in the analysis of present systems to investigate their diagnostic aspects. Two application examples are presented: Diagnosability and distinguishability analysis of error-correcting codes, and design of instrumentation systems of large plants with a required level of diagnosability.