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991.
The electrical stability of molybdenum disulfide (MoS2) transistors is crucial for their use in various applications. However, it is tricky to evaluate the inherent stability of MoS2 transistors because it is highly dependent on environmental conditions during measurement such as humidity, light, and electrical factors. We studied the threshold voltage instability under negative bias stress at a variety of temperatures in a vacuum and in the dark to eliminate any environmental effects. In particular, the measurement of transfer curves under stress is minimized in order to study the inherent instability of MoS2 transistors, even though the measurement of transfer curves is normally indispensable to check for the evolution of electrical instability. MoS2 transistors have high average effective energy when compared to conventional amorphous Si and oxide semiconductor transistors, which allows for adequate operation at high temperatures. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
992.
993.
Conventional methods of yield stress determination involve extrapolation of shear stress data to zero shear rate, and are thus susceptible to errors. This paper reports the application of a quasi-static technique for direct yield stress measurement, which obviates data extrapolation. Yield stresses of 38%, 42%, and 46% (by weight) SBS block copolymer solutions in a mixed solvent of tetrahydrofuran and methyl ethyl ketone (9:1 by volume) were obtained with a modified Fisher Autotensiomat Surface Tension Analyzer. Values obtained via extrapolation of viscometric data were compared with and found to differ significantly from those measured with the Autotensiomat. Arrhenius plots of the yield stress give straight lines, from which energy barriers to induce breakdown of the phase-separated morphologies are determined. These activation energies increase with solution concentration. The effect of repeated shearing on the apparent yield stress of the solutions was also determined at different temperatures. 相似文献
994.
James Trevey Jum Suk Jang Yoon Seok Jung Conrad R. Stoldt Se-Hee Lee 《Electrochemistry communications》2009,11(9):1830-1833
We report that glass–ceramic Li2S–P2S5 electrolytes can be prepared by a single step ball milling (SSBM) process. Mechanical ball milling of the xLi2S·(100 − x)P2S5 system at 55 °C produced crystalline glass–ceramic materials exhibiting high Li-ion conductivity over 10−3 S cm−1 at room temperature with a wide electrochemical stability window of 5 V. Silicon nanoparticles were evaluated as anode material in a solid-state Li battery employing the glass–ceramic electrolyte produced by the SSBM process and showed outstanding cycling stability. 相似文献
995.
Chang Kee Lee Su Ryon Shin Ji Young Mun Sung‐Sik Han Dr. Insuk So Dr. Ju‐Hong Jeon Dr. Tong Mook Kang Dr. Sun I. Kim Dr. Philip G Whitten Dr. Gordon G. Wallace Dr. Geoffrey M. Spinks Dr. Seon Jeong Kim Dr. 《Angewandte Chemie (International ed. in English)》2009,48(28):5116-5120
Tough and soft : Highly porous, spongelike materials self‐assemble by calcium ion condensation of DNA‐wrapped carbon nanotubes (SWNTs–DNA; see picture, IL=ionic liquid). The toughness, modulus, and swellability of the electrically conductive sponges can be tuned by controlling the density and strength of interfiber junctions. The sponges have compliances similar to the softest natural tissue, while robust interfiber junctions give high toughness.
996.
Hooi Ling Kee James R. Diers Marcin Ptaszek Chinnasamy Muthiah Dazhong Fan Jonathan S. Lindsey David F. Bocian Dewey Holten 《Photochemistry and photobiology》2009,85(4):909-920
The photophysical properties of two energy‐transfer dyads that are potential candidates for near‐infrared (NIR) imaging probes are investigated as a function of solvent polarity. The dyads ( FbC‐FbB and ZnC‐FbB ) contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. The dyads were studied in toluene, chlorobenzene, 1,2‐dichlorobenzene, acetone, acetonitrile and dimethylsulfoxide (DMSO). In both dyads, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of ~(5–10 ps)?1 and a yield of >99% in nonpolar and polar media. In toluene, the fluorescence yields (Φ f = 0.19) and singlet excited‐state lifetimes (τ~5.5 ns) are comparable to those of the benchmark bacteriochlorin. The fluorescence yield and excited‐state lifetime decrease as the solvent polarity increases, with quenching by intramolecular electron (or hole) transfer being greater for FbC‐FbB than for ZnC‐FbB in a given solvent. For example, the Φ f and τ values for FbC‐FbB in acetone are 0.055 and 1.5 ns and in DMSO are 0.019 and 0.28 ns, whereas those for ZnC‐FbB in acetone are 0.12 and 4.5 ns and in DMSO are 0.072 and 2.4 ns. The difference in fluorescence properties of the two dyads in a given polar solvent is due to the relative energies of the lowest energy charge‐transfer states, as assessed by ground‐state redox potentials and supported by molecular‐orbital energies derived from density functional theory calculations. Controlling the extent of excited‐state quenching in polar media will allow the favorable photophysical properties of the chlorin–bacteriochlorin dyads to be exploited in vivo. These properties include very large Stokes shifts (85 nm for FbC‐FbB , 110 nm for ZnC‐FbB ) between the red‐region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (λ f = 760 nm), long bacteriochlorin excited‐state lifetime (~5.5 ns), and narrow (≤20 nm) absorption and fluorescence bands. The latter will facilitate selective excitation/detection and multiprobe applications using both intensity‐ and lifetime‐imaging techniques. 相似文献
997.
In Seo Kee 《Tetrahedron letters》2009,50(51):7116-4049
3-Methyl- and 3-ethyl-1-aza-1,3-butadiene-1-carbonitriles were synthesized by reaction of the corresponding 3-alkylacroleins with bis(trimethylsilyl)-carbodiimide using titanium tetrachloride as catalyst. They were highly reactive and difficult to purify rigorously. Attempted anionic polymerizations gave only oligomers of molecular weight ∼500 Da. These 3-alkyl-azadienecarbonitriles cycloadded to the electron-rich olefins iso-butyl vinyl ether and p-methoxystyrene to give [2+4] cycloadducts with moderate yields. 相似文献
998.
A novel microextraction method making use of commercial polymer fiber as sorbent, coupled with high-performance liquid chromatography-fluorescence detection for the determination of polycyclic aromatic hydrocarbons (PAHs) in water has been developed. In this technique, the extraction device was simply a length (8 cm) of a strand of commercial polymer fiber, Kevlar (each strand consisted of 1000 filaments, each of diameter ca. 9.23 μm), that was allowed to tumble freely in the aqueous sample solution during extraction. The extracted analytes were desorbed ultrasonically before the extract was injected into HPLC system for analysis. Extraction parameters such as extraction time, desorption time, type of desorption solvent and sample volume were optimized. Each fiber could be used for up to 50 extractions and the method showed good precision, reproducibility and linear response within a concentration range 0.05–5.00 μg L−1 with correlation coefficients of up to 0.9998. Limits of detection between 0.4 and 4.4 ng L−1 for seven PAHs could be achieved. The relative standard deviations (n = 3) of this technique were between 2.9% and 12.1%. 相似文献
999.
Chanbasha Basheer Anass Ali Alnedhary B.S. Madhava Rao Hian Kee Lee 《Journal of chromatography. A》2009,1216(2):211-216
We describe a simple and sensitive porous polypropylene membrane-protected micro-solid-phase extraction (μ-SPE) approach for the sample preparation and determination of carbamate pesticides in soil samples by high-performance liquid chromatography. The μ-SPE device consisted of C18 sorbent held within a porous polypropylene envelope. In order to achieve optimum performance, several extraction parameters were optimized. Under the most favorable conditions, the extraction efficiency of the μ-SPE was very high, with detection limits in the range of 0.01–0.40 ng g−1. This is more than two orders of magnitude lower than the limits obtained by the United States Environmental Protection Agency Methods 8321A and 8318. A linear relationship was obtained for each analyte in the range of 2 and 200 ng g−1. The relative standard deviation for the analysis of aged soil samples spiked at 5 ng g−1 was ≤11%. The reproducibility of separate μ-SPE device used for experiments was satisfactory (relative standard deviations ranged from 4 to 11%), indicating that the method is reliable for routine environmental analysis. 相似文献
1000.