Surface charges on alumina in vacuum with varying surface roughness and electric field distribution

We investigated the charging characteristics of alumina in vacuum with varying surface roughness, and the electric field distribution. The charging on the alumina surface in vacuum is, in general, strongly influenced by field electron emission (FEE) and secondary electron emission avalanche (SEEA). We varied the surface roughness and the electric field distribution on the alumina surface in order to control the FEE and the SEEA. Under these conditions, we measured the 2-dimensional distribution of surface charging potential on the alumina surface. From the measurement results, we quantitatively discussed charge polarity and charge density on the surface for various types of electric field distributions. Finally, we successfully propose a concept of a charging control technique on the alumina insulator in vacuum for the improvement of electrical insulation performance on the alumina surface.     

Electron Transfer from Support/Promotor to Metal Catalyst: Requirements for Effective Support

Catalysis Letters - Electron transfer from transition metal (TM) catalysts deposited on support to reaction molecules adsorbed is a key step in many catalysis reactions. Electron donation from a...     

Utilization of (oxalato)borate-based organic electrolytes in activated carbon/graphite capacitors

The electrolyte salts composed of tetramethylammonium (TMA⁺) cation and difluoro(oxalato)borate (DFOB⁻) or bis(oxalato)borate (BOB⁻) anions have been proposed for the application in activated carbon (AC)/graphite capacitors. The electrochemical performance of AC/graphite capacitors has been studied using these electrolyte salts dissolved in propylene carbonate (PC). The intercalation behaviors of anions (BF₄⁻, DFOB⁻, and BOB⁻) at the graphite positive electrodes have been investigated by in situ XRD measurements. The bigger the anion is, the higher the cell voltage is where the intercalation happens. Accordingly, the bigger the anion is, the smaller discharge capacity delivered by an AC/graphite capacitor. The charge mechanism of TMA⁺ at the AC negative side has also been addressed. Compared with other bigger quaternary alkyl ammonium cations, the specific capacitance of the AC negative electrode towards TMA⁺ adsorption is somehow smaller as estimated.     

Origin of diameter-dependent growth direction of silicon nanowires

A nucleation thermodynamic model was developed to clarify the diameter-dependent crystallographic orientation of silicon nanowires (SiNWs) grown via the vapor-liquid-solid (VLS) mechanism with an Au catalyst. The calculated critical energies (E(r*)) and corresponding critical radii (r*) of the SiNWs with <111> and <110> orientations as a function of Au-catalyst size (D(Au)) revealed that the 110-oriented SiNW with r is preferred below D(Au) = approximately 25 nm, but the preferred direction changes to <111> above D(Au) = approximately 25 nm. The model indicated that the nucleated SiNW with a radius (r) above r is stable and continues to grow until the diameter becomes equal to D(Au) but that the crystallographic orientation is maintained. Thus, the predicted growth direction of the final SiNW with a size of D(Au) is <110> for D(Au) < approximately 25 nm and <111> for D(Au) > approximately 25 nm, which is in excellent agreement with reported experimental results.     

Effects of low-temperature ozone annealing on operation characteristics of amorphous In-Ga-Zn-O thin-film transistors

Effects of low-temperature annealing were examined for amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs). In a previous study, we reported that O₂ annealing is effective to improve performances of a-IGZO TFTs when annealed at ≥ 300 °C, but causes large negative threshold voltage shift when annealed at ≤ 200 °C. Here, we examined effects of ozone (O₃) annealing on physical properties and TFT characteristics of a-IGZO in comparison with conventional O₂ annealing. We found little differences in chemical composition, band gap and photoemission spectra between the O₂ and the O₃ annealed films. On the other hand, free electron density was suppressed well by the O₃ annealing even at low temperatures ≤ 200 °C. Moreover, even at 150 °C, the TFTs characteristics were improved to the subthreshold voltage swing of 217 mV/decade, the saturation mobility of ~ 11.4 cm²(Vs)^− 1 and the threshold voltage of 0.1 V by the O₃ annealing. It was also found that the effects of the O₃ annealing is more effective for thicker channel TFTs, which would be due to stronger oxidation power and the larger diffusion constant of oxygen atoms produced from O₃ molecules than those of O₂. These results substantiate that the O₃ annealing is more effective to improve TFT characteristics in particular for low-temperature processes at ≤ 200 °C.     

Photovoltaic properties of n-type amorphous In-Ga-Zn-O and p-type single crystal Si heterojunction solar cells: Effects of Ga content

Photovoltaic properties and electronic structures of n-type amorphous In-Ga_x-Zn-O/p-type Si heterojunction solar cells (x = 1, 2, and 3) were investigated focusing on the effects of Ga content based on expectation that Ga-rich films have larger band gaps and improve open circuit voltages (V_OC) of solar cells. To know the electronic structures such as the conduction band minimums (CBMs) and the valence band maximums (VBMs) of these materials, hard x-ray photoemission spectroscopy (HX-PES) was performed. Contrary to the above expectation, the best result was obtained for x = 1 with an energy conversion efficiency of 5.3%. Although the Ga-rich films had larger optical band gaps and higher CBMs, V_OC were remained low and poorer fill factors were obtained due to larger densities of defects. The low V_OCwere partly resulted from the deep VBM levels of the Ga-rich films. The defect densities are discussed in relation also to near-VBM states and near-CBM states observed in HX-PES and subgap optical absorptions.     

Low acoustic attenuation silicone rubber lens for medical ultrasonic array probe

Effects of heavy density (p = 9.2 x 10³ kg/m³) Yb²O³ fine dopant (16 nm in diameter) on the acoustic properties of a high-temperature-vulcanization (HTV) silicone rubber have been investigated, to develop a new acoustic lens material with a low acoustic attenuation (alpha) for the medical array probe application. The HTV silicone rubber has advantages in that it shows a lower alpha than that of a room-temperature-vulcanization (RTV) silicone rubber and it can be mixed by applying shear stress, using roll-milling equipment. Roll-milling time dependence of the HTV silicone rubber indicates that the alpha is closely affected by the dispersion of nanopowders in the rubber matrix. The 8 vol% Yb²O³-doped HTV silicone rubber mixed for 30 min showed the lowest alpha of 0.73 dB/mmMHz with an acoustic impedance [AI = sound speed (c) times density (p)] of 1.43 times 106 kg/m²s at 37degC. Moreover, simulation results reveal that a 5 MHz linear probe using the HTV silicone rubber doped with Yb²O³ powder showed relative sensitivity around 2.6 to 3.0 dB higher than a probe using RTV silicone rubber doped with Yb²O³ powder or SiO²-doped conventional silicone rubber for the ultrasonic medical application.     

Numerical study of flow and heat-transfer characteristics of cryogenic slush fluid in a horizontal circular pipe (SLUSH-3D)

Cryogenic slush fluids, such as slush hydrogen and slush nitrogen, are two-phase, single-component fluids containing solid particles in a liquid. Since their density and refrigerant capacity are greater than those of liquid-state fluids alone, there are high expectations for use of slush fluids as functionally thermal fluids in various applications, such as fuels for spacecraft engines, clean energy fuels to improve the efficiency of transportation and storage, and as refrigerants for high-temperature superconducting equipment. In this research, a three-dimensional numerical simulation code (SLUSH-3D), including the gravity effect based on the thermal non-equilibrium, two-fluid model, was constructed to clarify the flow and heat-transfer characteristics of cryogenic slush fluids in a horizontal circular pipe. The calculated results of slush nitrogen flow performed using the numerical code were compared with the authors’ experimental results obtained using the PIV method. As a result of these comparisons, the numerical code was verified, making it possible to analyze the flow and heat-transfer characteristics of slush nitrogen with sufficient accuracy. The numerical results obtained for the flow and heat-transfer characteristics of slush nitrogen and slush hydrogen clarified the effects of the pipe inlet velocity, solid fraction, solid particle size, and heat flux on the flow pattern, solid-fraction distribution, turbulence energy, pressure drop, and heat-transfer coefficient. Furthermore, it became clear that the difference of the flow and heat-transfer characteristics between slush nitrogen and slush hydrogen were caused to a large extent by their thermo-physical properties, such as the solid–liquid density ratio, liquid viscosity, and latent heat of fusion.     

Electrochemical evaluation of the interaction between endocrine disrupter chemicals and estrogen receptor using 17,beta-estradiol labeled with daunomycin

A new electrochemical screening method for endocrine disrupting chemicals (EDCs) was developed. To evaluate the binding capacity of EDCs to the estrogen receptor (ER), 17beta-estradiol labeled with daunomycin as an electroactive compound was prepared. The electrochemical sensitivity of the prepared labeled estradiol (LE) was high, as compared with daunomycin. The interaction between LE and ER was observed by the decrease in the electrode response of LE, indicating the specific binding of LE with ER. The competitive reaction between LE and 17beta-estradiol for the limiting binding site on ER produced increases in the peak current of LE. The relative standard deviation at 1 x 10(-8) M 17beta-estradiol was about 10.0% (n = 7). The binding affinity between EDC and ER was also evaluated by comparison with 17beta-estradiol-ER interaction. Bisphenol A, p-nonylphenol and p,p'-DDT was used as a test compound. All test compounds demonstrated some ability to bind with ER. This electrochemical binding assay illustrates a new method for evaluating the binding capacity of EDCs to ER without the need for a separation procedure for the bound and free LE.