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41.
采用SCF-X_α-MS方法, 对于C(2×2)S/Fe(001)吸附体系, 选择Fe_5S和Fe_9S两种原子簇模型, 研究了该吸附体系的电子结构、吸附成键特征及其相互作用图象。结果表明, S吸附于Fe(001)单晶表面具有较强的定域性质, S原子与底物Fe原子之间的吸附相互作用主要表现为S(3p)-Fe(4s,3d)之间的轨道相互作用。通过对表面吸附键长的优化, 其结果与X.S.Zhang等的ARPEFS的实验结果一致。 相似文献
42.
43.
The coordination of silver cation to diphosphene Mes*P=PMes* ( 1 , Mes* = tBu3C6H2) was investigated in detail. The reaction of 1 with Ag[Al(ORF)4] (ORF = OC(CF3)3) in the ratios of 2 : 1, 3 : 2 and 1 : 2 led to the formation of the first cationic silver linked diphosphene complexes 2 — 4 . Complexes 2 and 3 contain two and three diphosphene molecules linked by the linear Ag(I) cation, respectively, and they feature unusual zig‐zag topologies. Complex 4 is a dinuclear silver complex, and each Ag(I) center features a tetrahedral geometry, coordinated by one phosphorus atom of diphosphene 1 and three chloro atoms of two CH2Cl2 molecules. 相似文献
44.
45.
We report measurements of fluorescence resonance energy transfer (FRET) for glucose sensing in an established concanavalin A–dextran affinity system using frequency‐domain lifetime spectroscopy. A dextran (MW 2000000) labeled with a small fluorescent donor molecule, Alexa Fluor 568, was used to competitively bind to a sugar‐binding protein, concanavalin A, labeled with acceptor molecule, Alexa Fluor 647, in the presence of glucose. The FRET‐quenching kinetics of the donor were analyzed from frequency‐domain measurements as a function of both glucose and acceptor‐protein concentrations using a Förster‐type decay kinetics model. The results show that the frequency‐domain measurements and donor decay kinetics can quantitatively indicate changes in the competitive binding of 0.09 μM dextran to labeled concanavalin A at a solution concentration of 10.67 μM in the presence of glucose at concentrations ranging from 0 to 224 mg/dL. 相似文献
46.
Su M Pan Z Dravid VP Thundat T 《Langmuir : the ACS journal of surfaces and colloids》2005,21(24):10902-10906
The formation of a water meniscus between a sharp tip and a solid surface is one of the prevailing requirements for scanning probe microscope (SPM)-based lithographies, such as dip-pen nanolithography (DPN) and conductive tip induced oxidation. The water meniscus functions as a medium for the oxidation of or mass transfer to the solid surface. Here we report a simple, efficient, and effective approach to enhance the local relative humidity and thus increase the size of the water meniscus by bringing a water-containing capillary tube to the proximity of the tip-surface contact area. The enhancement in local relative humidity is confirmed via an increase in the measured tip-surface adhesion forces and the widths of DPN generated parallel lines. Compared to the global control of relative humidity for the whole lithography system, the short distance between the "water reservoir" and the tip-surface contact area enables rapid increase in the local vapor pressure of water, less perturbation, and minimal erosion to the state-of-the-art electronics. As a result, most scanning probe lithography experiments at high relative humidity can now be performed in a reasonable time frame. 相似文献
47.
近些年来,无铅低熔点填料日渐引起人们的兴趣,且将得到广泛的应用。Cu-Zn-Sn合金正是无铅低熔点填料的一种基本合金。该体系相图虽有一些报道,但他们的研究只涉及富铜区(>50Wt%)的液相限和等温截面(500℃)。我们颇感兴趣的富Sn区的液相限,尚未见文献报道,因此测定该体系富Sn区的液相限是必要的。关于Cu-Zn-Sn体系的三个相关二元体系,已有文献报道,也较成熟。对于Cu-Zn体系,富Zn区600℃以下存在两个转熔反应,其转熔点分别为Q(~88Wt%Zn,598℃),W(97.5-98.5Wt%Zn,424℃);Cu-Sn体系富Sn区有一个转熔反应,其转熔点 相似文献
48.
Ion-exchanger phase Spectrophotometry withp-nitrochlorophosphonazo (CPApN) has been developed for the determination of scandium. The linear range is 1–8 g of scandium in 50 ml of solution, using 0.8 g of resin, with an apparent molar absorptivity of 2.76 × 105 1 mol–1 cm–1. Aluminum and rare earth elements in reasonable amounts do not interfere. The method has been applied successfully to the determination of scandium in alloys, with relative standard deviations of 2–4%. 相似文献
49.
Wanxing Wei Yuanjiang Pan Yaozu Chen Cuiwu Lin Tengyou Wei Shukai Zhao 《Chemistry of Natural Compounds》2005,41(1):17-21
Five compounds, terephthalic acid mono-[2-(4-carboxy-phenoxycarbonyl)-vinyl] ester (1), (E)-3-(5′-hydroperoxy-2,2′-dihydroxy[1,1′-biphenyl]-4-yl)-2-propenoic acid (2), 3,4,5-trihydroxybenzoic acid (3), succinic acid (or butanedioic acid) (4), and 2,3,4,5,6-pentahydroxybenzoic acid (5), were isolated from Phyllanthus urinaria. The structures of these compounds were elucidated by means of spectral techniques including IR, MS, and 1D/2D NMR. 1 and 2 are new compounds.__________Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 14–17, January–February, 2005. 相似文献
50.
Pan F Wang P Lee K Wu A Turro NJ Koberstein JT 《Langmuir : the ACS journal of surfaces and colloids》2005,21(8):3605-3612
We report a simple photolithographic approach for the creation and micropatterning of chemical functionality on polymer surfaces by use of surface-active block copolymers that contain protected photoactive functional groups. The block copolymers self-assemble at the substrate-air interface to generate a surface that is initially hydrophobic with low surface tension but that can be rendered hydrophilic and functional by photodeprotection with UV radiation. The block copolymer employed, poly(styrene-b-tert butyl acrylate), segregates preferentially to the surface of a polystyrene substrate because of the low surface tension of the polyacrylate blocks. The strong adsorption of block copolymers causes a bilayer structure to form presenting a photoactive polyacrylate layer at the surface. In the example described, the tert-butyl ester groups on the polyacrylate blocks are deprotected by exposure to UV radiation in the presence of added photoacid generators to form surface carboxylic acid groups. Surface micropatterns of carboxylic acid groups are generated by UV exposure through a contact mask. The success of surface chemical modification and pattern formation is demonstrated by X-ray photoelectron spectroscopy and contact angle measurements along with imaging by optical and fluorescence microscopy methods. The resultant chemically patterned surfaces are then used to template patterns of various biomolecules by means of selective adsorption, covalent bonding and molecular recognition mechanisms. The surface modification/patterning concept can be applied to virtually any polymeric substrate because protected functional groups have intrinsically low surface tensions, rendering properly designed block copolymers surface active in almost all polymeric substrates. 相似文献