Nanoadhesion layer for enhanced Si–Si and Si–SiN wafer bonding

Direct wafer bonding of Si–Si and Si–SiN wafers was demonstrated using a nanoadhesion layer at room temperature. The two mating surfaces were cleaned by an Ar-ion beam and simultaneously deposited with ultrathin Fe layers (known as nanoadhesion layers). The ultrathin Fe layers imparted high bond strengths to Si–Si and Si–SiN bonds without heat treatment. Transmission electron microscopy revealed that the Si–Si and Si–SiN interfaces were tightly bonded and defect free. Moreover, the formation of crystalline iron silicide across the interface was found to enhance Si–Si wafer bonding. In addition to FeSi, an amorphous layer formed at the Si–SiN interface, resulting in a high bond strength at room temperature.     

Residual powders from Shochu distillation remnants induce apoptosis in human hepatoma cells via the caspase-independent pathway

Shochu distillation remnants (SDR) are by-products in the manufacturing process of the Japanese liquor Shochu and include various useful organic compounds derived from the fermentation of grains. We have obtained valuable powder (PSDR) from freeze-dried SDR by the treatment with ethanol. In this study, we examined the anticancer effects of barley-, rice-, and sweet potato-PSDR against HepG2 and HuH-7 cells of human hepatocellular carcinoma (HCC) in?vitro. All PSDR inhibited the growth of both these HCC cells through the induction of apoptosis. Especially, barley-PSDR was the most effective for the growth inhibition and apoptosis induction of HCC cells of all PSDR. We next examined the apoptotic mechanisms induced by barley-PSDR. Decrease in mitochondrial membrane potential and release of cytochrome c from mitochondria were observed in HCC cells after the treatment with barley-PSDR. Furthermore, barley-PSDR induced the nuclear translocation of apoptosis-inducing factor (AIF) from mitochondria, while it did not significantly affect the activities of caspase-3, -8, and -9. The results suggested that barley-PSDR induced apoptosis against HCC cells via the caspase-independent mitochondrial pathway. The findings in this study suggest that PSDR has the possibility of therapeutic and/or preventive agents of HCC.     

Construction of membrane-anchoring fusion protein of Thermococcus kodakaraensis glycerol kinase and its application to repetitive batchwise reactions

We previously demonstrated the stoichiometric conversion of glycerol to glycerol-3-phosphate (G3P) using Escherichia coli recombinants producing the ATP-dependent glycerol kinase of the hyperthermophile Thermococcus kodakaraensis (TkGK) and the polyphosphate kinase of Thermus thermophilus HB27 (TtPPK). TtPPK was associated with the membrane fraction of E. coli recombinants, whereas TkGK was released from the cells during the reaction at 70°C. In this study, TkGK was fused with either TtPPK or an E. coli membrane-intrinsic protein, YedZ, to minimize the heat-induced leakage of TkGK. When the E. coli recombinants having these fusion proteins were incubated at 70°C for 2h, more than 80% of TkGK activity was retained in the heated E. coli cells. However, the yields of G3P production by E. coli having the fusion proteins of TtPPK and TkGK were only less than 35%. Polyphosphate is a strong chelator for metal ions and has an inhibitory effect on TkGK which requires magnesium. Insufficient space between TtPPK and TkGK might enhance the inhibitory effect of polyphosphate on TkGK activity of the fusion protein. The mixture of E. coli cells having TtPPK and those having TkGK fused with YedZ converted 80% of glycerol into G3P. These recombinant cells could be easily recovered from the reaction mixture by centrifugation and repeatedly used without a significant loss of enzyme activities.     

Efficient decomposition of environmentally persistent perfluorooctanesulfonate and related fluorochemicals using zerovalent iron in subcritical water

Decomposition of perfluorooctanesulfonate (PFOS) and related chemicals in subcritical water was investigated. Although PFOS demonstrated little reactivity in pure subcritical water, addition of zerovalent metals to the reaction system enhanced the PFOS decomposition to form F-ions, with an increasing order of activity of no metal approximately equal Al < Cu < Zn < Fe. Use of iron led to the most efficient PFOS decomposition: When iron powder was added to an aqueous solution of PFOS (93-372 microM) and the mixture was heated at 350 degrees C for 6 h, PFOS concentration in the reaction solution fell below 2.2 microM (detection limit of HPLC with conductometric detection), with formation of F-ions with yields [i.e., (moles of F- formed)/(moles of fluorine content in initial PFOS) x 100] of 46.2-51.4% and without any formation of perfluorocarboxylic acids. A small amount of CHF3 was detected in the gas phase with a yield [i.e., (moles of CHF3)/(moles of carbon content in initial PFOS) x 100] of 0.7%, after the reaction of PFOS (372 microM) with iron at 350 degree C for 6 h. Spectroscopic measurements indicated that PFOS in water markedly adsorbed on the iron surface even at room temperature, and the adsorbed fluorinated species on the iron surface decomposed with rising temperature, with prominent release of F- ions to the solution phase above 250 degrees C. This method was also effective in decomposing other perfluoroalkylsulfonates bearing shorter chain (C2-C6) perfluoroalkyl groups and was successfully applied to the decomposition of PFOS contained in an antireflective coating agent used in semiconductor manufacturing.     

Selective hydrobromination of metallurgical-grade silicon in a flow reactor system

Reactions of metallurgical-grade silicon (MG-Si) with gaseous hydrogen bromide (HBr) has been monitored by means of online gas chromatography in a flow reactor system. The formation of tri-bromosilane started to occur at 380 °C, accompanied by the consumption of HBr. The conversion of HBr into bromosilanes increased with an increase in reaction temperature and reached a maximum at 440 °C. An increase of the HBr concentration in a HBr-N₂ mixed gas led to an increase in the consumption of MG-Si, while it reduced the selectivity of the tri-bromosilane formation. An increase in total flow rate of the reaction gas caused a dramatic decrease in the HBr conversion and enhanced the selectivity of the tri-bromosilane formation. The rate constant for overall bromination reaction at 400 °C was measured to be 0.46 s⁻¹. Concentrations of impurities in the product were much less than those in MG-Si. Moreover, kerf loss silicon was subjected to the bromination reaction under the optimized conditions.     

Efficiency of the symmetry bias in grammar acquisition

It is well known that the symmetry bias greatly accelerates vocabulary learning. In particular, the bias helps infants to connect objects with their names easily. However, grammar learning is another important aspect of language acquisition. In this study, we propose that the symmetry bias also helps to acquire grammar rules faster. We employ the Iterated Learning Model, and revise it to include the symmetry bias. The result of the simulations shows that infants could abduce the meanings from unrecognized utterances using the symmetry bias, and acquire compositional grammar from a reduced amount of learning data.     

Recent progress in research and development of crystalline silicon solar cells in Japan

Recently, the research and development of crystalline silicon solar cells in Japan has greatly advanced. Fundamental research has been conducted on the recombination and passivation of minority carriers at Si/SiO₂ interfaces and in those bulk regions containing grain boundaries. Qualities of silicon feedstock and substrates have been improved and large-area cell efficiencies using Czochralski single and cast polycrystalline substrates have reached 20% and 17%, respectively, by using low-cost cell fabrication processes. Such high efficiency values are realized by tenacious improvement of substrate quality and the development of new processes for fabricating solar cells.