Investigation of polycrystalline silicon layers by electron microscopy and x-ray diffraction

The structure of polycrystalline Si layers deposited by pyrolysis of silane in a hydrogen ambient has been investigated by replica electron microscopy and X-ray diffraction. When the gas flow ratio (SiH₄/H₂) is 3·64 × 10⁻⁴ the temperature region below 900°C is a surface reaction control region and the activation energy of the chemical surface reaction rate is 1·6 eV. The temperature range above 900°C is a mass transfer region and the deposition rate is about 500 Å/min. The grains become larger and the texture of the surface of the poly Si layers becomes coarser with the deposition temperature. Some phase change was found to occur around 900°C by replica electron microscopy. The X-ray diffraction experiments show that there exist three preferred orientations of (220), (111) and (311) in the poly Si layers. The decrease of the relative intensity of the (311) orientation might have a relation to the phase change around 900°C.     

Microfluidic device for airborne BTEX detection

We fabricated a microfluidic device for the optical detection of airborne benzene, toluene, ethylbenzene and xylenes (BTEX). The device consists of concentration and detection cells formed of 3 cm x 1 cm Pyrex plates. The concentration cell is composed of an adsorbent to concentrate the BTEX gases and a thin-film heater todesorb the concentrated gases from the adsorbent thermally. The collected gases are introduced into the detection cell, which is connected to optical fibers, to measure their absorption spectra. We optimized the device's operating conditions by studying the thermal characteristics of the concentration cell and the time profile of the gas concentration flowing in the detection cell. We used the device under optimized operating conditions to detect toluene gas as a typical example BTEX. The gas concentration amplification rate was approximately 2 orders of magnitude, and we successfully measured parts-per-million levels of toluene gas with this device.     

Projection lithography to print thick resist patterns with triangular and semi-circular cross-section profiles

Patterning technology to print thick resist patterns with triangular and semi-circular cross-section profiles was investigated for applying to fabrication of light-guide plates and lens arrays, surface texturization of solar cells, and others. Positive novolac resist PMER P-LA900PM with an initial thickness of 10 μm was used and the patterns were mainly printed by the exposure light with a wavelength of 405 nm. At this wavelength, the light transmittance through the resist film was 0.5% and 80% before and after the exposure, respectively. Caused by this moderate transmittance characteristics, pattern sidewalls suitably inclined or roundly curved. When 400 μm line-and-space reticle patterns were printed using a projection exposure lens with a reduction ratio of 1/19 and a numerical aperture of 0.125, triangular patterns were obtained under the defocus conditions of around ?100 μm. The sidewall angle was widely controlled between 20° and 55° by mainly changing the exposure time. On the other hand, semi-circular profiles were obtained when patterns were printed at the defocus position of +100–200 μm. It was clarified that the circular radius depended only on the defocus position and did not depend on the exposure time. Patterns with circular radiuses of 9–34 μm were successfully obtained.     

Basic operation of novel ferroelectric CMOS circuits

A nonvolatile ferroelectric complementary metal-oxide-semiconductor (CMOS) circuit with both logic and memory functions is proposed as a new application of ferroelectric field effect transistors. The logic and memory operations of a NOT-logic ferroelectric CMOS device is demonstrated. Nondestructive readings of high and low output voltage levels of the device were performed. Data retention was measured up to 10⁵ s (1.2 days).     

Effective use of fly ash slurry as fill material

A lot of effort has been put into increasing coal ash utilization; however, 50% of total amount is disposed of on land and in the sea. Several attempts have been reported recently concerning slurried coal fly ash use for civil engineering materials, such as for structural fill and backfill. The authors have studied this issue for more than 15 years and reported its potential for (1) underwater fills, (2) light weight backfills, and (3) light weight structural fills, through both laboratory tests and construction works. This paper is an overview of the results obtained for slurry, focusing on the following. (1) Coal fly ash reclaimed by slurry placement shows lower compressibility, higher ground density, and higher strength than by the other methods. This higher strength increases stability against liquefaction during earthquake. (2) Higher stability of the fly ash ground formed by slurry placement is caused by higher density and its self-hardening property. (3) Stability of fly ash reclaimed ground can be increased by increasing density and also by strength enhancement by cement addition. (4) Technical data obtained through a man-made island construction project shows the advantages of fly ash slurry in terms of mechanical properties such as higher stability against sliding failure, sufficient ground strength, and also in terms of cost saving. (5) Concentration in leachates from the placed slurry is lower than the Japanese environmental law. (6) In order to enlarge the fly ash slurry application toward a lightweight fill, mixtures of air foam, cement and fly ash were examined. Test results shows sufficient durability of this material against creep failure. This material was then used as lightweight structural fill around a high-rise building, and showed sufficient quality. From the above data, it can be concluded that coal fly ash slurry can be effectively utilized in civil engineering projects.     

Carbon Stable Isotope Analysis for Glucose in Sake: Simple Freeze-Dried Sake Can Substitute for Glucose Following HPLC Isolation

Carbon stable isotope analysis of ethanol is an established method for determining the authenticity of alcoholic beverages, but there is no accepted method for measurements of glucose carbon stable isotopic composition (δ ¹³C). This study aims to establish two methods to determine accurately the δ ¹³C value of glucose isolated from sake by high-performance liquid chromatography (HPLC) after three clean-up steps using ion exchange chromatography and in simple freeze-dried sake (total nonvolatile matter) and to examine two methods that yield different δ ¹³C values. In the glucose isolation procedure, the δ ¹³C values of glucose were not significantly affected by the glucose concentration, solvent (water or aqueous acetonitrile), drying method (freeze-dry or nitrogen-spraying), the clean-up step using ion exchange chromatography (weakly acidic cation-exchange, strongly acidic cation-exchange, and weakly basic anion-exchange resins), or HPLC isolation. Glucose nitrogen spray-dried after isolation by ion exchange chromatography and HPLC showed a carbon isotope discrimination value of <0.1 ‰. The glucose δ ¹³C values ranged from ?26.8 to ?25.5 ‰ in authentic sake and from ?27.0 to ?11.0 ‰ in commercial sake samples. This HPLC isolation approach may provide a first step toward visualizing the brewing process via isotopic carbon flow during fermentation. Additionally, there was no significant difference between the δ ¹³C values of glucose and total nonvolatile matter from sake. The δ ¹³C measurement of simple freeze-dried sake can substitute for glucose δ ¹³C measurement using HPLC isolation, thus aiding high-throughput detection of carbon derived from C₄ plants in sake.