Preparation and Properties of Glass-Ceramics Derived from Nitrogen-Containing β-Spodumene Glasses

Crystallization of Li-Al-Si-O-N oxynitride glasses based on the β-spodumene composition and the properties of the resultant glass-ceramics have been studied. The onset of the precipitation of metastable high-quartz solid solution and its transformation to β-spodumene shift to higher temperatures with increasing nitrogen content of the oxynitride glasses. Nitrided glass-ceramics crystallized at 1200°C have negative thermal expansion coefficients, since high-quartz structure is maintained up to 1000° and 1200°C. Knoop hardness and density of the glass-ceramics increase with increasing nitrogen content. There was evidence that part of the nitrogen atoms were incorporated into the high-quartz solid-solution structure and that a small amount of the minor phase of Si₂N₂O was precipitated in highly nitrided glass-ceramics.     

Ionic effects on the transport characteristics of nanowire-based FETs in a liquid environment

For the development of ultra-sensitive electrical bio/chemical sensors based on nanowire field effect transistors （FETs）, the influence of the ions in the solution on the electron transport has to be understood. For this purpose we establish a simulation platform for nanowire FETs in the liquid environment by implementing the modified Poisson-Boltzmann model into Landauer transport theory. We investigate the changes of the electric potential and the transport characteristics due to the ions. The reduction of sensitivity of the sensors due to the screening effect from the electrolyte could be successfully reproduced. We also fabricated silicon nanowire Schottky-barrier FETs and our model could capture the observed reduction of the current with increasing ionic concentration. This shows that our simulation platform can be used to interpret ongoing experiments, to design nanowire FETs, and it also gives insight into controversial issues such as whether ions in the buffer solution affect the transport characteristics or not.     

Transparent conducting film: Effect of mechanical stretching to optical and electrical properties of carbon nanotube mat

We describe in this paper a transparent conducting film (TCF). It is a fibrous layer of multiwalled carbon nanotubes (MWNTs), labeled a dilute CNT mat, that was prepared and unidirectionally stretched to improve both the optical and electrical properties. After stretching by 80% strain, transmittance at 550 nm wavelength was improved by 37% and sheet resistance was reduced to 71% of the original value. The improvement of the transmittance can be explained by increased area of the CNT mat after stretch, and the reduced sheet resistance can be explained by increased density of the CNT alignment in lateral direction due to contraction. Based on the microscopic observation before and after stretch, models to describe the phenomena are proposed. By further expanding on this method, it may be possible to obtain a transparent conducting carbon nanotube film which is crack-resistant for solar cell applications.     

Uniform culture in solid-state fermentation with fungi and its efficient enzyme production

Solid-state fermentation (SSF) has attracted a lot of interest for carrying out high-level protein production in filamentous fungi. However, it has problems such as the fermentation heat generated during the culture in addition to the reduced mobility of substances. These conditions lead to a nonuniform state in the culture substrate and result in low reproducibility. We constructed a non-airflow box (NAB) with a moisture permeable fluoropolymer membrane, thereby making it possible to control and maintain uniform and optimal conditions in the substrate. For the NAB culture in Aspergillus oryzae, temperature and water content on/in the whole substrate were more consistent than for a traditional tray box (TB) culture. Total weight after the culture remained constant and dry conditions could be achieved during the culture. These data demonstrate the possibility of growing a uniform culture of the whole substrate for SSF. The NAB is advantageous because it allows for the control of exact temperature and water content in the substrate during the culture by allowing vapor with latent heat to dissipate out of the box. In addition, several enzymes in the NAB culture exhibited higher production levels than in the TB culture. We believe that culturing in the constructed NAB could become a standard technique for commercial SSF.     

Multiscale modeling of nanowire-based Schottky-barrier field-effect transistors for sensor applications

We present a theoretical framework for the calculation of charge transport through nanowire-based Schottky-barrier field-effect transistors that is conceptually simple but still captures the relevant physical mechanisms of the transport process. Our approach combines two approaches on different length scales: (1) the finite element method is used to model realistic device geometries and to calculate the electrostatic potential across the Schottky barrier by solving the Poisson equation, and (2) the Landauer-Büttiker approach combined with the method of non-equilibrium Green's functions is employed to calculate the charge transport through the device. Our model correctly reproduces typical I-V characteristics of field-effect transistors, and the dependence of the saturated drain current on the gate field and the device geometry are in good agreement with experiments. Our approach is suitable for one-dimensional Schottky-barrier field-effect transistors of arbitrary device geometry and it is intended to be a simulation platform for the development of nanowire-based sensors.     

High-performance antireflective coatings with a porous nanoparticle layer for visible wavelengths

Ghosts and flares are well-known problems that are caused by reflections from lens surfaces when we take photographs. It is more difficult to prevent such stray light in a digital camera than in a film camera because of high reflectance from the low-pass filter and diffraction from the image sensor. To prevent such stray light, we introduce an ultralow refractive index layer into the antireflective (AR) coatings. We used the solgel method to form porous fluoride layers with ultralow refractive indices, and we succeeded in developing a unique process to form AR coatings with superior performance.     

Thin reduced graphene oxide interlayer with a conjugated block copolymer for high performance non-volatile ferroelectric polymer memory

Polymer ferroelectric-gate field effect transistors (Fe-FETs) employing ferroelectric polymer thin films as gate insulators are highly attractive as a next-generation non-volatile memory. For minimizing gate leakage current of a device which arises from electrically defective ferroelectric polymer layer in particular at low operation voltage, the materials design of interlayers between the ferroelectric insulator and gate electrode is essential. Here, we introduce a new solution-processed interlayer of conductive reduced graphene oxides (rGOs) modified with a conjugated block copolymer, poly(styrene-block-paraphenylene) (PS-b-PPP). A FeFET with a solution-processed p-type oligomeric semiconducting channel and ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) insulator exhibited characteristic source–drain current hysteresis arising from ferroelectric polarization switching of a PVDF-TrFE insulator. Our PS-b-PPP modified rGOs (PMrGOs) with conductive moieties embedded in insulating polymer matrix not only significantly reduced the gate leakage current but also efficiently lowered operation voltage of the device. In consequence, the device showed large memory gate voltage window and high ON/OFF source–drain current ratio with excellent data retention and read/write cycle endurance. Furthermore, our PMrGOs interlayers were successfully employed to FeFETs fabricated on mechanically flexible substrates with promising non-volatile memory performance under repetitive bending deformation.     

Effect of axial reflector on radial uniformity in neutron transmutation doping of silicon

Significant axial variation of radial uniformity is observed in Si-ingot neutron transmutation doping in the flux screening method, and leads to non-uniform resistivity distribution for a certain part of Si-ingot. This axial variation of radial uniformity is caused by the installation of a partial neutron screen which decreases the reaction rates differently in the center and surface at the region not surrounded by the partial neutron screen. For the improvement of the specific distribution of radial uniformity in the axial direction, a new concept of axial reflector is introduced to partly change the reaction rate at a certain region of Si-ingot, and neutron irradiation experiments are carried out at the heavy water neutron irradiation facility in the Kyoto University Research Reactor. Based on the experimental and numerical results, the new axial reflector is proved to be effective for improving the axial variation of radial uniformity.     

Alteration of ryanodine receptor in the hippocampus CA1 after hemispheric cerebral ischemia

Alterations in ryanodine binding and local cerebral blood flow (LCBF) were examined at 30 minutes and 2 hours post-ischemia in the gerbil brain in order to evaluate the influence of cerebral ischemia on the intracellular channels of Ca2+-induced Ca2+ release (CICR). Severe hemispheric cerebral ischemia was induced by occluding the right common carotid artery. LCBF was measured at the end of the experiment using [14C]iodoantipyrine method, and the ryanodine binding was evaluated in vitro using [3H]ryanodine as a specific ligand for CICR channels. An autoradiographic method developed in our laboratory enabled us to determine both parameters within the same brain. A group of gerbils who underwent a sham procedure served as controls. LCBF was found to be significantly reduced in most of the cerebral regions on the occluded side at both 30 minutes as well as 2 hours post-ischemia. In contrast, a significant reduction in ryanodine binding was noted only in the hippocampus CA1 on the occluded side at 30 minutes and 2 hours after the occlusion. These findings suggest that regionally specific changes of CICR may be the cause of decreased ryanodine binding in the hippocampus CA1, and that these changes may be related to the pathophysiological mechanisms that cause this region to be particularly vulnerable to ischemia.