Evaluation of zinc self-diffusion at the interface between homoepitaxial ZnO thin films and (0001) ZnO substrates

Isotopic ZnO thin films were deposited on the c-plane of ZnO single crystals by pulsed laser deposition. The isotopic abundance of Zn in the films was determined with a secondary ion mass spectrometry before and after the films was diffusion annealed. The diffusion profiles across the film/substrate interface behaved smooth features. The zinc diffusion coefficient (D_Zn) was obtained by analyzing the slope of the profile in the annealed sample. The temperature dependence of D_Zn was determined to be D_Zn(cm²/s)=8.0×10⁴exp(?417[kJ/mol])/RT, where R and T are gas constant and temperature. The zinc ion diffusion coefficients were of the same order as that in a ZnO single crystal. A comparison of the experimental and theoretical values indicated that the zinc ions diffused in the thin film and the single crystal through a vacancy mechanism.     

High-speed wavelength-division multiplexing quantum key distribution system

A high-speed quantum key distribution system was developed with the wavelength-division multiplexing (WDM) technique and dedicated key distillation hardware engines. Two interferometers for encoding and decoding are shared over eight wavelengths to reduce the system's size, cost, and control complexity. The key distillation engines can process a huge amount of data from the WDM channels by using a 1 Mbit block in real time. We demonstrated a three-channel WDM system that simultaneously uses avalanche photodiodes and superconducting single-photon detectors. We achieved 12 h continuous key generation with a secure key rate of 208 kilobits per second through a 45 km field fiber with 14.5 dB loss.     

Modeling of incorporation of oxygen and carbon impurities into multicrystalline silicon ingot during one-directional growth

We propose a simple numerical model for incorporation of oxygen and carbon impurities into multicrystalline Si during one-directional crystal growth in comparison with experimental results. The model includes parameters that are oxygen and carbon concentrations in the melt in the beginning of the growth, carbon flux form the atmosphere, oxygen fluxes from the crucible and to the atmosphere. Variation of oxygen and carbon concentrations in multicrystalline Si ingots with a diameter of 30 cm and a height of 7.5 cm solidified one-directionally was measured by infra red absorption spectroscopy at room temperature. By fitting the numerical results on the experimental results, the parameters were evaluated. In the modeling we found fruitful suggestions for suppressing and controlling the oxygen and carbon concentrations in multicrystalline Si for solar cells.     

Local structure around phosphorus and silicon in the CaO–SiO2–PO2.5 system

The local structure of phosphorus and silicon in the molten CaO–SiO₂–PO_2.5 slag system was investigated by magic angle spinning nuclear magnetic resonance (MAS-NMR). The ³¹P MAS-NMR spectra revealed that phosphorus was present primarily as the monophosphate complex ion PO₄^3?, with a small amount of diphosphate ion also present. Their relative ratio to total phosphorus was independent of the phosphate concentration of the sample. In the case of the ²⁹Si MAS-NMR, the mean number of the non-bridging oxygen atoms associated with tetrahedrally coordinated silicon decreased as the phosphate concentration increased at a fixed CaO/SiO₂ ratio. This indicates that the nonbridging oxygen atoms around the silicon were replaced by bridging oxygen atoms around the phosphorus as the phosphate concentration in the samples increased.To elucidate the basicity dependence of the structure of slag, the relationship between the structure and optical basicity was also investigated. The relative ratio of Qⁿ (Qⁿ means the silicon atoms tetrahedrally bonded with “n” number of bridging oxygen atoms) strongly depends on the optical basicity. These optical basicity dependencies of the structures of phosphorus and silicon can be explained clearly by the basicity equalization concept (Duffy and Ingram, 1976) [12].     

Scott modules in finite groups with cyclic Sylow p-subgroups

We present a simple method for determining Scott modules of finite groups using just the Brauer tree of the principal block and the values of ordinary characters at non-identity p-elements. Previously, determining Scott modules often involved long calculations. The method is applicable to the case where finite groups have cyclic Sylow p-subgroups. The structure of a Scott module is closely related to the length of the shortest path from the vertex labeled by the trivial ordinary character to the exceptional vertex in the Brauer tree. We classify the structures of the Scott modules and the ordinary characters they afford, by the length of the associated path in the Brauer tree.     

M?ssbauer spectroscopic study on valence-detrapping and trapping of mixed-valence trinuclear iron(III, III, II) fluorine-substituted benzoate complexes

Magnetorheological (MR) fluids are new iron-based materials, whose applications include brakes, dampers, clutches, shock absorbers systems and polishing of optical surfaces (lens and mirrors). They are dependent on the size and shape of particles as the magnetic properties. Interested in the possibility of using iron-rich powders, commonly used in nondestructive testing, ranging in size from a few μm to about 200?μm and lower cost than those commercially used for MR fluids, a study of the structural and magnetic properties of iron-rich metallic particles by X-ray diffraction (XRD) and M?ssbauer spectroscopy (MS) at room temperature has been done. Powders, as received, were separated into particle sizes smaller than 20?μm (sample A) and in the range of 20–38?μm (sample B) because these are the sizes generally required for applications in MR fluids. The particles whose sizes exceed the above values were ground in a high energy planetary mill for 3?h, using different values of rotational speed/time: 200?rpm for one hour, a pause of 10?s, 140?rpm for one hour, pause 10?s and then 175?rpm during the last hour. These powders were sieved to obtain particles smaller than 20?μm (sample C). According XRD results, in all samples, only α-Fe (lattice parameter a = 2,867(2) ?) and Fe₂O₃ (lattice parameter a = 5,037(1) ? and c = 13,755(8) ?) were present. The M?ssbauer spectra were fitted with two sextets. The hyperfine parameters values allowed us to assign the highest relative area spectrum (sextet) corresponding to α-Fe and the second one to Fe₂O₃ in accord to the XRD results. Thus, the preparation method using mechanical milling for diminishing the size of the metallic particles allowed us to get particles with size and magnetic properties that could lead to potentially MR fluids applications.     

Evolved gas analysis of Ti(C5H5)2Cl2 by means of Li+ ion attachment mass spectrometry

Characterization of the compound Ti(C(5)H(5))(2)Cl(2) was studied using Li(+) ion attachment mass spectrometry (IAMS) as an analytical methodology. Since this target compound is used as an anticancer drug in the treatment of leukemia, accurate and rapid monitoring methods for the determination of titanium drugs in a hospital environment are desirable. A quadrupole mass spectrometry system along with a Li(+) ion attachment technique and a direct inlet probe (DIP) produced the Li(+) adduct of Ti(C(5)H(5))(2)Cl(2), Ti(C(5)H(5))(2)Cl(2)Li(+). The DIP also was used to study the temperature-resolved behavior of this compound. The slope of the plot of signal intensity of Ti(C(5)H(5))(2)Cl(2)Li(+) versus temperature for Ti(C(5)H(5))(2)Cl(2) sublimation from 60 to 100 °C was used to determine an apparent activation energy (E(a)) of 124.43 kJ/mol for the sublimation of Ti(C(5)H(5))(2)Cl(2). This value is comparable to the reported value of 118.8 kJ/mol for molar enthalpy of sublimation of Ti(C(5)H(5))(2)Cl(2). These results demonstrate that the IAMS methodology can be used to study the enthalpy of sublimation for d-metal complex materials.     

Chemical methods for degradation of target oligosaccharides using designed light-activatable organic molecules

Carbohydrates play crucial roles in a wide range of biological processes, including serious diseases. The development of novel and innovative methods for selective control of specific oligosaccharide functions has attracted much attention in the fields of chemistry, biology, and medicine. In this feature article, the development of novel chemical tools, which can degrade target oligosaccharides by irradiation with a specific wavelength of light under mild conditions without any additives, is introduced. This novel class of photochemical agents promise bright prospects for finding not only molecular-targeted bioprobes for understanding of the structure-activity relationships of oligosaccharides but also novel therapeutic drugs targeting oligosaccharides.     

Development of an electrochemical cholesterol sensor system for food analysis

In this article, we report on a food-cholesterol monitoring sensor based on a non-enzymatic approach. Amorphous and single-crystal gold electrodes were modified with an alkanethiol self-assembled monolayer to quantify it by voltammetry. We first discuss the basic characteristics of these sensors and provide more information about the instrument developed by JSK Co. This instrument is a battery-operated handheld voltammetric analyzer, which mounts a sensor chip to monitor cholesterol contents in food samples. The sensor showed excellent linearity with the cholesterol concentration; egg-yolk samples were analyzed to give an excellent agreement between the values obtained by the sensor (1.4 mM) and chromatography (1.1 mM).     

Morphology and dispersion control of titania–silica monolith with macro–meso pore system

Macroporous gels with bicontinuous morphology in micrometer range were prepared in a titania?Csilica system containing 5 and 7.6 mass?% titania using tetraethoxysilane and four kinds of Ti precursors, two titanium alkoxides, titanium chloride and titanium sulfate, under coexistence of poly(ethylene glycol) (PEG) with an average molecular weight of 20,000. In all the systems with different Ti precursors, the addition of PEG induced phase separation, and the macroporous morphology was formed when the transitional structure of phase separation was frozen-in by sol?Cgel transition of inorganic components. However, we can see large differences in phase separation tendency and Ti dispersion in silica network depending on the Ti precursors used. When titanium alkoxides were added into pure silica sol?Cgel system, phase separation tendency largely decreased, so that low temperature reaction was necessary for macropore formation. When we used titanium salts, on the other hand, phase separation tendency does not change much from pure silica system. The difference has been tentatively attributed to the difference in the mixing level of Ti in silica network. Although titania tended to aggregate when titanium alkoxides were used as precursors, Ti could be well dispersed in silica gel matrix when acetylacetone was added in the alkoxide system or when titanium salts were used as Ti precursors.