Resist-less patterning on SiO2 by combination of X-ray exposure and vapor HF etching

We succeeded in a resist-less patterning of SiO₂/Si substrates by a combination of X-ray exposure and vapor hydrogen fluoride (HF) etching. A 2 μm thick SiO₂ layer was formed on a Si substrate by employing a thermal oxidation process. An X-ray mask consisted of a 1 μm thick Ta absorber on a 2 μm thick Si₃N₄ membrane mounted on a 1 mm thick Si frame, and a honeycomb pattern where 640 nm diameter circle dots arranged in the corners of a hexagon with a pitch of 960 nm was processed. X-ray exposure experiments were carried out on a beamline BL-4 with a peak photon energy of 2 keV at the TERAS synchrotron radiation (SR) facility. When a dose energy was 750 mAh, the transfer of the patterns was confirmed, although irradiations with different dose energy were also conducted. Moreover, heating temperatures and total etching times of SiO₂/Si substrates in vapor HF etching were changed, and the shapes of etched patterns were observed by scanning electron microscope. It was learnt that an appropriate etching time existed between 30 and 60 min. Moreover, we observed discoloration of irradiated area by SR; and this seemed to be caused by changes in the etching rate of SiO₂/Si substrates that led to the development of resist-less patterning technique.     

Self-crack healing ability and strength recovery in ytterbium disilicate/silicon carbide nanocomposites

The SiO₂ volatility and SiC recession in hydrocarbon-rich combustion atmosphere is the main problem of SiC-reinforced ceramics when they are utilized as coating materials for gas turbine blades. The composite of Yb₂Si₂O₇-Yb₂SiO₅/SiC is expected as a self-crack healing material that can avoid this problem because the monosilicate can react with the SiO₂ glass to form disilicate and hence further reinforce the composite. In this study, the composites, fabricated with various morphology of SiC nanofillers, were precracked and then heat-treated in an oxidizing environment to activate their crack healing behavior. The healing effect as a function of filler morphology and annealing time was investigated. Healing mechanism and future applications of these composites were also discussed.     

Bubble formation in cocurrently upward flowing liquid

The effects of liquid velocity, nozzle diameter, gas chamber volume and gas flow rate on volumes, shapes and growth curves of bubbles formed at a nozzle submerged in a cocurrently upward flowing liquid in a bubble column were experimentally investigated. The bubble volume decreases with increasing liquid flow velocity. The effect of liquid flow velocity on the volume of bubble increases with an increase in the gas flow rate. To simulate bubble formation at a nozzle submerged in cocurrently upward flowing liquid, a revised non-spherical bubble formation model was proposed. Bubble volumes, bubble growth curves and shapes experimentally obtained in this study, as well as in previous experimental studies, are well predicted by the present model.     

Fine-structured patterns of porous alumina material fabricated by a replication method

Porous alumina materials with three-dimensional fine-patterning over multiple length scales were fabricated from mixed slurry of polyvinyl alcohol (PVA) and alumina nanosized particles in water by a replication method. The mixed slurry was then filled in a silicon mold with different pattern sizes and dried at room temperature. After the drying, the PVA and alumina dried film were detached from the mold. Through burn-out at various sintering temperatures, alumina porous materials with dot, hole and line and space patterns as small as sub-micrometer in size were successfully fabricated. The results demonstrated possibilities to produce porous inorganic materials with various compositions and structures with a facile approach and a simple method.     

Nutrient dynamics through fine litterfall in three plantations in Sabah,Malaysia, in relation to nutrient supply to surface soil

To investigate soil amelioration effects by older tropical fast-wood plantations, we examined the fine litterfall and accompanying nutrient flux of a 20-year-old Acacia mangium site over 3 years under a wet tropical climate in Sabah, Malaysia. The litterfall of a Swietenia macrophylla site and an Araucaria cunninghamii site was also examined for comparison. Annual nitrogen (N) flux through litterfall (kg N ha⁻¹) was larger in A. mangium (207–223) than in S. macrophylla (126–153) or A. cunninghamii (72–94), whereas annual phosphorus (P) flux through litterfall (kg P ha⁻¹) was considerably smaller in A. mangium (2.7–3.4) than in S. macrophylla (7.5–15.6) or A. cunninghamii (7.8–9.2). N flux through litterfall, forest floor N, and N concentration in topsoil (0–5 cm) were in the order of A. mangium > S. macrophylla > A. cunninghamii, but other element fluxes were not related to concentrations in soils. Our findings suggest that topsoil N increased because of a large N flux from litterfall. We conclude that these plantation trees, including A. mangium have the potential to produce a N flux in litterfall for the rapid return of organic N to soils larger than or equivalent to that in adjacent primary forests. However, the litterfall of a single species may lead to deficits of a particular element and cause nutrient imbalances. Using a mixture of fertilizer tree species or applying mixed litter might be a better solution.     

On the Chemical Origin of the Gap Bowing in (GaAs)<Subscript>1−<Emphasis Type=Italic>x</Emphasis></Subscript>Ge<Subscript>2<Emphasis Type=Italic>x</Emphasis></Subscript> Alloys: A Combined DFT–QS<Emphasis Type=Italic>GW</Emphasis> Study

Motivated by the research and analysis of new materials for photovoltaics and by the possibility of tailoring their optical properties for improved solar energy conversion, we have focused our attention on the (GaAs)_{1− x} Ge_2x series of alloys. We have investigated the structural properties of some (GaAs)_{1− x} Ge_2x compounds within the local-density approximation to density-functional theory, and their optical properties within the Quasiparticle Self-consistent GW approximation. The QSGW results confirm the experimental evidence of asymmetric bandgap bowing. It is explained in terms of violations of the octet rule, as well as in terms of the order–disorder phase transition.     

Microstructure and Mechanical Properties of Sinter–Post-HIPed Si3N4–SiC Composites

The microstructural evolution and mechanical properties of Si₃N₄–SiC composites obtained by the sinter–post-HIP process were investigated. SiC addition prohibited β-Si₃N₄ grain growth; however, the grain growth followed the empirical growth law, with exponents of 3 and 5 for the c - and the a -axis directions, respectively. Mechanical properties were strongly influenced by SiC addition and sintering conditions. Short-crack propagation behavior was measured and analyzed by the indentation-strength in-bending (ISB) method. The present composites had high short-crack toughness, compared with the values for monolithic Si₃N₄. The enhanced short-crack toughness was attributed to crack-tip bridging by the SiC particles.     

Nondestructive high-sensitivity measurement method for activation estimation in accelerator room concrete

This study established a method for easily and quickly estimating the specific activity produced in the concrete walls and floors of accelerator rooms during long-term operation of accelerator,for advanced zoning of activated/non-activated areas in planning the decommissioning of an accelerator.We propose a new,highly sensitive method for nondestructively estimating the specific activity in concrete that can be applied to activation zoning.In this method,instead of direct determination of the specific activities of important long-half-life radionuclides for decommissioning,such as ¹⁵²Eu and ⁶⁰Co,we determine the specific activities of short-half-life radionuclides,²⁴Na and ⁵⁶Mn,in situ to obtain neutron flux.The obtained neutron flux and accelerator operation history yield the specific activities of ¹⁵²Eu and ⁶⁰Co for the advance zoning of activated/non-activated concrete.This method is a powerful long-term prediction tool for concrete activation.     

D住宅

这座超小型集合住宅建筑,打破了日本的常规住宅格局．内部是狭长弯曲的空间,房间只有一个面是封闭的．使用面积因而增多。建筑沿着地形而弯曲．与周边环境自然融合,开创了一种全新的住宅类型。     

Preparation of porous polymer materials using water‐in‐oil gel emulsions as templates

Water‐in‐oil gel emulsions consisting of water and n‐butyl acrylate were successfully prepared using N‐3‐hydroxybutylcarbonyl‐l ‐isoleucylaminooctadecane and sorbitan monooleate (Span 80) as gelator and surfactant, respectively. Stable gel emulsions were formed using aqueous phase fractions (APFs) ranging from 10 to 90 vol%. Creaming, flocculation and coalescence were not observed. Low‐temperature polymerization of the gel emulsions with a redox initiator gave the corresponding low‐density, highly porous poly(n‐butyl acrylate)s (PBAs). The microstructures of the PBAs were observed using scanning electron microscopy. All the porous PBAs comprised numerous spherical structures whose sizes could be controlled by adjusting the gel emulsion APF. The densities and porosities of the porous PBAs decreased and increased, respectively, with increasing APF. The absorption capacities of the porous PBAs in organic solvents were studied. The porous PBAs selectively absorbed kerosene from water instantly and the kerosene could then be recovered by physical compression of the PBAs. Further porous polymers were prepared from gel emulsions containing styrene, methyl methacrylate (MMA) or 2‐ethylhexyl acrylate (EHA) as continuous oil phases. The order of absorption capacity and swelling ratio in kerosene was poly(EHA) > PBA ? poly(MMA). Porous copolymers were also prepared from gel emulsions containing a mixture of EHA and MMA as the oil phase. Their absorption and swelling in liquids could be controlled by changing the ratio of EHA and MMA in the gel emulsions. poly(EHA‐co‐MMA) (6:4) was the best polymer when absorption capacity, swelling ratio and durability were simultaneously considered. © 2018 Society of Chemical Industry