Potential of far-ultraviolet absorption spectroscopy as a highly sensitive analysis method for aqueous solutions. Part II: monitoring the quality of semiconductor wafer cleaning solutions using attenuated total reflection

Far-ultraviolet (FUV) spectroscopy combined with attenuated total reflection (ATR) is employed for direct measurement of the concentrations of semiconductor wafer cleaning fluids such as SC-1 (aqueous solution of NH(3) and H(2)O(2)) and SC-2 (aqueous solution of HCl and H(2)O(2)). FUV spectra of these aqueous solutions in the 170-200 nm region are highly sensitive to changes in both hydrogen bonding and hydration. Although ATR measurement results in lower absorptivity compared to transmittance measurement, it is possible to increase absorption with greater evanescent wave penetration depth using a low refractive index internal reflection element (IRE). We adopt quartz as an IRE material. Since the refractive index of quartz becomes lower than that of water in the low energy side of an intense absorption band due to the n --> sigma* transition of water, the quartz IRE yields non-total reflection wavelength regions. However, near 175 nm the effective absorptivity of the tail of water's absorption band can be successfully enlarged, making the FUV-ATR technique suitable for measuring the concentrations of the components in the semiconductor wafer cleaning fluids. In the present study we prepared the same cleaning fluids as those used in actual semiconductor fabrication and measured their FUV-ATR spectra in the 150-300 nm wavelength range. It was found that even with the quartz IRE one can measure FUV-ATR spectra under total reflection conditions at 175 nm or above. We created calibration models for predicting both NH(3) and H(2)O(2) in the concentration ranges of 0-10% in SC-1 using multiple linear regression (MLR). The standard deviations of the models were 0.033% and 0.265% for NH(3) and H(2)O(2), respectively. The same procedure was repeated under the same conditions for HCl and H(2)O(2) in SC-2, yielding corresponding values of 0.018% for HCl and 0.178% for H(2)O(2).     

Mathematical simulation of liquid food pasteurization using far infrared radiation heating equipment

In this study, pasteurization equipment using far-infrared radiation (FIR) was developed for liquid food. The temperature was measured at various conditions to investigate the heating effect. With the liquid food passing down an angled trough and FIR applied from above, the temperature changed with the radiation intensity (electricity supplied), the angle of the incline, and the flow rate. As the liquid film became thinner, the temperature could be heated to nearly 80 °C. The pasteurization effect was verified using lactic acid bacteria as the target microorganism; the heat resistance of the bacteria was measured, the death of bacteria was confirmed, and the effectiveness of the equipment was verified. Furthermore, a mathematical model for FIR pasteurization was developed using a heat transfer equation and thermal death equation. The simulation could make predictions about temperature and the viable count of bacteria that compared very well with the experimental results. Moreover, the model simulated the change of temperature and viable count of bacteria at different flow rates, and showed that it is possible to sterilize at low temperatures with this equipment.     

A caged progesterone analog alters intracellular Ca2+ and flagellar bending in human sperm

Progesterone is a physiological agonist for mammalian sperm, modulating its flagellar movement and facilitating the acrosome reaction. To study the initial action of progesterone, we developed a caged analog with a photosensitive group: nitrophenylethanediol, at position 20. Using this compound combined with stroboscopic illumination, we performed Ca(2)(+) imaging of human spermatozoa and analyzed the effects of progesterone on the intracellular Ca(2)(+) concentration ([Ca(2)(+)](i)) of beating flagella for the first time. We observed a transient [Ca(2)(+)](i) increase in the head and the flagellum upon photolysis of the caged progesterone and an increase in flagellar curvature. Detailed kinetic analysis revealed that progesterone elicits an increase in the [Ca(2)(+)](i) immediately in the flagellum (mid-piece and principal piece), thereafter in the head with a short time lag. This observation is different from the progesterone-induced Ca(2)(+) mobilization in mouse spermatozoa, where the Ca(2)(+) rise initiates at the base of the sperm head. Our finding is mostly consistent with the recent discovery that progesterone activates CatSper channels in human spermatozoa, but not in mouse spermatozoa.     

Optimization of anti‐reflection moth‐eye structures for use in crystalline silicon solar cells

An anti‐reflection (AR) moth‐eye structure made of acrylic resin and deposited on a polyethylene terephthalate (PET) substrate was optimized in the wavelength range from 400 to 1170 nm; crystalline silicon (c‐Si) solar cells function efficiently in this wavelength range. The rigorous coupled wave analysis (RCWA) method was used for optical simulation, and the Taguchi method was used for efficient optimization. The simulation results showed that the reflectance of the optimized structure over the above‐mentioned wavelength range was less than 0.87% and that a minimal reflectance of 0.1% was observed at 400 nm. Experimental results showed that the reflectance of a fabricated moth‐eye structure was less than 1.0% in the wavelength range and that a minimal reflectance of 0.55% was observed at 700 nm. A c‐Si solar cell, which was enclosed in a polyvinyl butyral (PVB) layer of uniform thickness, was coated with the fabricated moth‐eye film, and it was observed that the moth‐eye film increased electric generation (EG) up to 15%, depending on the incident angle. Further, a daily increase in EG of up to 8.7% was estimated on a clear summer day in Japan when the moth‐eye film was used. Copyright © 2010 John Wiley & Sons, Ltd.     

DRYING MODEL WITH NON-ISOTROPIC SHRINKAGE DEFORMATION UNDERGOING SIMULTANEOUS HEAT AND MASS TRANSFER

A model of simultaneous heat and moisture transfer in a cylindrical sample was coupled with the virtual work principle applicable to a body undergoing shrinkage deformation in two dimensions. Non-constant physical and thermal properties were also incorporated in the model. Governing equations and boundary conditions were solved numerically using Galerkin's finite element method. To check the mathematical model drying experiments were carried out. A cylindrical potato was used as a drying sample. Experimental conditions were as follows: a drying temperature of 333 K, relative humidity of 5.4%, and air velocity of 1.6 m/s. We obtained the central temperature of the sample, average moisture content, and the shrinkage change in the axial and radial directions during drying. It was observed that the shrinkage coefficients in the axial and the radial directions were significantly different during air-drying. Comparison between predicted and experimental results provides satisfactory agreement.     

Measurement of electrical characteristics of ZnO microvaristors

A measurement technique is developed to measure the characteristics of zinc oxide (ZnO) microvaristors directly. We used Cu wires, a micromanipulator, and an optical microscope to gain ohmic contact of the measurement apparatus with ZnO particles. With our system, the I−V characteristics and C⁻²−V characteristics were measured for 25 µm ZnO microvaristors. Our measurements show that these microparticles behave as varistors. Further measurement on the ZnO microvaristors and observation of their fine structure may help to understand the varistor behavior. It also can pave the way to the understanding of the electrical characteristics of grain boundaries as well as the double Schottky barrier formed at the grain boundaries. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

CFD analysis of the convection flow in the pan during induction heating and gas range heating

One difference between induction heating (IH) and gas range heating (GRH) is that, because the heating location of the pan is different, the convection in the pan is different. In particular, in cooking situations in which solids are mixed with liquids, such as the boiling of soup containing solid foods, the natural convection flow in the pan may affect food quality. The convection in the pan during IH and GRH was analyzed by using computational fluid dynamics (CFD), and the temperature distribution and the flow velocity distribution in the pan were obtained. These results were then compared with the measurement results. In GRH, the heat flux at the wall of the pan was obtained by experiment, and it was used for the analysis as a boundary condition. In IH, the heat generation distribution obtained by electromagnetic field analysis was used for the analysis as the boundary condition. Differences in convection flow in the pan during IH and GRH were observed by CFD modeling especially at the initial stage of heating. The simulated convection in the pan showed the same tendency as the captured movement of the tracer particle using flow visualization.     

A Homogeneous Catalyst for Reduction of Optically Active Esters to the Corresponding Chiral Alcohols without Loss of Optical Purities

A ruthenium complex was found to catalyze the hydrogen reduction of esters under mild and neutral conditions. A variety of optically active esters can be reduced to the corresponding alcohols in excellent yield without loss of their optical purity or causing undesirable side reactions. Hydrogen reduction needs such simple operations – reaction, concentration, and purification – that the violent quench step and extraction step, which accompany conventional sodium borohydride or lithium aluminum hydride reduction, can be omitted.     

Decomposition kinetics of umami component during meat cooking

We developed a kinetic model for the decomposition reaction of inosine monophosphate (IMP), which is a umami component, and obtained kinetic parameters based on the amount of IMP in an isothermal experiment. The amount of remaining IMP decreased with heating time, and its reduction rate was the highest at 40 °C. We assumed that the activity of IMP decomposition enzyme is temperature-dependent above 40 °C, and constant below 40 °C. The predicted results using this kinetic model are in good agreement with the experimental ones. Unsteady-state three-dimensional heat transfer analysis of meat during sous-vide cooking was conducted, and the distribution of remaining IMP was predicted. By the end of sous-vide cooking, the ratio of the amount of IMP in the interior of the meat decreased, whereas at the surface region, it was almost the same as the initial value, because the surface temperature reached the inactivation temperature immediately.