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321.
322.
Voltage-current (I-V) measurements in a wide temperature range from 88 to 573 K demonstrated the effects of temperature on the switching behavior of a Cu/Ta(2)O(5)/Pt resistive memory cell that is referred to as a gapless-type atomic switch. After the forming process, the cells were SET from the OFF state to the ON state at a positive bias to the Cu electrode and then RESET from the ON state to the OFF state at a negative bias. In a previous study (Tsuruoka et al 2010 Nanotechnology 21 425205), it was demonstrated that the SET process corresponds to the reformation of a metal filament between the electrodes by the inhomogeneous nucleation and subsequent growth of Cu whereas the RESET process can be attributed to the Joule-heating-assisted dissolution of the metal filament. In the work described here, we observed that the voltages at which the cells are SET and RESET (SET and RESET voltages) decreased in magnitude with an increase in temperature. From calculations of the nucleation rate of Cu nuclei based on the classical nucleation theory, it was found that the observed temperature variation of the SET voltage is primarily determined by supersaturation in the vicinity of the Pt electrode, which is controlled by the application of positive bias. The supersaturation required for spontaneous growth of a Cu nucleus decreases with increasing temperature, resulting in lower SET voltages at higher temperatures. The RESET voltage is determined by the thermal stability of the metal filament formed. Moreover, using the temperature variation in cell resistances of the ON state, the growth speed of the Cu nucleus after the nucleation was found to decease with increasing temperature. These results are consistent with our switching model. 相似文献
323.
Solar cells with a short-circuit current density (Jsc) of 6 mA/cm2, an open circuit voltage (Voc) of 280 mV and a conversion efficiency of 0.5% under a 1000 W/m2 solar radiation were prepared by sequential chemical deposition of Bi2S2 (160 nm) and PbS (400 nm) thin films. The optical band gap (Eg) of Bi2S3 (160 nm) decreased from 1.67 to 1.61 eV upon heating the as-deposited film at 250 °C in air for 15 min to make it crystalline, but also reduced its thickness to 100 nm. Photoconductivity of this film is 0.003 (Ω cm)− 1. The Eg of PbS film (200 nm) deposited at 25 °C (24 h) is 0.57 eV, and is 0.49 eV for the film deposited at 40 °C. The electrical conductivity of the latter is 0.48 (Ω cm)− 1. The photo-generated current density for a Bi2S3(100 nm)/PbS(300 nm) absorber stack is above 40 mA/cm2 under AM 1.5 G (1000 W/m2) solar radiation. However, the optical losses in the cell structure reduces the Jsc. Spectral sensitivity of the external quantum efficiency of the cell establishes the contribution of Bi2S3 and PbS to Jsc. The energy level diagram of the cell structure suggests a built-in potential of 470 mV for the present case. Six series-connected cells gave the Voc of 1.4 V and Jsc of 5 mA/cm2. 相似文献
324.
We have developed a flowing gas phase reaction method for synthesizing ZnO nanotetrapods. The synthesis was carried out in a tube furnace under air pressure using air and nitrogen as reactive and carrying gases. The zinc precursor was provided by carbothermal reduction of ZnO powder. The source material transformation efficiency is higher than 90%. ZnO nanotetrapods were nucleated and grown in the gas phase via a vapor-solid mechanism. The reaction occurred at a temperature controlled to 1050-1200?°C and gas flow rate controlled to 0.7-2?L/min. The high flow rate suppressed the diffusion of growth precursors and productions towards the tube wall, and localized them into a gas phase pipe. The harvested ZnO nanotetrapods were carried by the flowing gas and collected outside of the furnace. The sizes of the nanotetrapods range from several hundred nanometers to more than 10?μm with leg diameters of 30-200?nm. The flowing gas phase reaction method provides a relatively uniformity environment for nanotetrapod growth and simplifies the product collection procedure compared with other techniques. This technique is simple and inexpensive, which is promising for realizing continuous mass production of ZnO nanotetrapods on a factory scale. 相似文献
325.
To convert unutilized plant biomass into a useful energy source, methane production from bamboo was investigated using a steam explosion pretreatment. Methane could not be produced from raw bamboo but methane production was enhanced by steam explosion. The maximum amount of methane produced, i.e., about 215 ml, was obtained from 1 g of exploded bamboo at a steam pressure of 3.53 MPa and a steaming time of 5 min. A negative correlation between the amount of methane produced and the amount of Klason lignin was observed in the methane fermentation of steam-exploded bamboo. 相似文献
326.
Free cells of Serratia plymuthica were used to convert sucrose into isomaltulose and trehalulose reducing sugars. The effects of substrate concentration and temperature were observed in a batch process with flasks shaken at 150 rpm. The experimental design and response surface methodology analysis indicated that the conversion parameters had significant influence (p < 0.05) on sucrose conversion, and that a valid model was obtained after an analysis of variance (Fmodel = 10.48 > Fcharted = 5.79) to obtain a response surface and isocurve. Conversion was favoured when a 30% sucrose solution and temperature of 25 °C were used, which resulted in a high conversion into isomaltulose – over 70% – and 7–8% trehalulose. Small amounts of glucose (5–7%) and fructose (5–8%) were formed in the reaction medium. 相似文献
327.
Guimes Rodrigues Filho Ricardo Chagas da Silva Carla da Silva Meireles Rosana Maria Nascimento de Assuno Harumi Otaguro 《应用聚合物科学杂志》2005,96(2):516-522
In the present work we blended cellulose acetate (taken from sugar cane bagasse) (CA) with polystyrene (taken from postconsumer plastic cups) (PS). The blends were produced in the following ratios (w/w) of the polymers: CA 50%/PS 50%, CA 90%/PS 10%, and CA 10%/PS 90%, using dichloromethane as solvent. The blends were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction. The results show that the presence of polystyrene hinders the organization of regions responsible for the crystallinity originally existing in pure cellulose acetate. We also made measurements of water flux through blends, using the Payne cup technique. The flux properties were compared with those obtained for commercial membranes by Osmonix: nanofiltration (SG) and reverse osmosis (CG). The results show that the blend CA 90%/PS 10% presents water vapor flux comparable with that of commercial membranes for nanofiltration (SG). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 516–522, 2005 相似文献
328.
329.
Adriana Yoshiga Harumi Otaguro Duclerc Fernandes Parra Luís Filipe C. P. Lima Ademar B. Lugao 《Polymer Bulletin》2009,63(3):397-409
Isotactic polypropylene (iPP) undergoes crosslinking and extensive main chain scissions when submitted to irradiation. The
simultaneous irradiation of PP and acetylene is able to control chain scission and produce grafting. The grafted PP further
reacts with PP radicals resulting in branching and crosslinking. In this work, commercial polypropylenes (iPP) of different
molecular weights were irradiated with a 60Co source at dose of 12.5 kGy in the presence of acetylene in order to promote the crosslinking. The mechanical and rheological
tests showed a significant increase in melt strength and drawability of the modified samples obtained from resins with high
melt flow index. The characterization of the molecular modifications induced by gamma irradiation of isotactic polypropylenes
under acetylene atmosphere proved the existence of branching, crosslinking and chain scission in a qualitative way. The G′ and G″ indicated the presence of LCB in all samples. Therefore, PP irradiation under acetylene was proved to be an effective approach
to achieve high melt strength polypropylene (HMSPP). 相似文献
330.
Tsuyoshi Matsumoto Yuki Ichige Takashi Komine Ryuji Sugita Tomosuke Aono Masayuki Murata Daiki Nakamura Yasuhiro Hasegawa 《Journal of Electronic Materials》2011,40(5):1260-1265
We numerically investigated the effect of the surface on the transport properties of Bi nanowires. The effect of the surface was modeled using the surface potential. The energy shift in each band due to the surface potential was calculated by a perturbation method. The effect of the surface potential on the transport properties was estimated using the Boltzmann equation with a constant relaxation time. The results reveal that the surface potential dramatically alters the density of states of T-point holes, whereas it has very little effect on the density of states of L-point holes. This is because the wavefunctions at the L- and T-points have different symmetries. The electrical conductivity increases and the Seebeck coefficient decreases with increasing surface potential. The maximum absolute value of the Seebeck coefficient decreases drastically with increasing surface potential. The Seebeck coefficient has a much stronger dependence on the surface potential than on the wire diameter. These results demonstrate that the transport properties of Bi nanowires are very sensitive to the surface potential. 相似文献