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711.
Aslam M Gopakumar G Shoba TL Mulla IS Vijayamohanan K Kulkarni SK Urban J Vogel W 《Journal of colloid and interface science》2002,255(1):79-90
Copper and copper (I) oxide nanoparticles protected by self-assembled monolayers of thiol, carboxyl, and amine functionalities [X(CH(2))(n)-CH(3), where X can be -COOH, -NH(2), or -SH] have been prepared by the controlled reduction of aqueous copper salts using Brust synthesis. The optical absorption spectrum (lambda(max)=289 nm) is found to be invariant with the nature of the capping molecule while the particle shape and distribution are found to depend strongly on it. A comparison of the protection efficiency for different capping agents such as dodecanethiol (DDT), tridecylamine (TDA), and lauric acid (LA) suggests that although zerovalent Cu is initially formed for dodecanethiol, all other cases allow oxidation to Cu(2)O nanoparticles. Despite the variation in particle size and relative stability, nanoparticles have been found to form oxides after a few days, especially for the case of LA and TDA surface capping. For all the samples studied, the size has been found to be 4-8 nm by high-resolution transmission electron microscopy. The protective ability is found to be better for dodecanethiol SAM (similar to the case of Au and Ag nanoparticles), while the order of capping efficiency varies as Cu-DDT>Cu-TDA>Cu-LA. In the present study we also demonstrate a reversible metal-insulator transition (MIT) in capped nanoparticles of Cu using temperature-dependent electrical resistivity measurement. However, the LA-capped sample does not show any such transition, possibly due to the oxide formation. 相似文献
712.
713.
B. Wu T. George M. Schneider W. Urban B. Nelles 《Applied physics. B, Lasers and optics》1991,52(3):163-167
CW single-line laser oscillation on theP(7) toP(15) transitions in the fundamental band of CO is reported. Laser operation was obtained with a liquid-nitrogen-cooled dc electrical discharge flow system using a mixture of He, N2, air, and CO. The parameters important for the CO fundamental band laser oscillation are discussed. 相似文献
714.
We have performed electron spin resonance experiments on binary amorphous V2 O5- and MoO3 compounds (V2O5-TeO2, V2O5-BaO, V2O5-PbO, V2O5-GeO2, V2O5-As2O3, MoO3-P2O5, MoO3-TeO2) and determined the parameters of the corresponding spin Hamiltonian by 3 cm-, 1.2 cm- and 8 mm band measurements. These measurements yielded values of the contribution to the mean energy difference of thed 1 levels between different vanadium- or molybdenum sites caused by fluctuations of the crystal field. 相似文献
715.
Nanocomposite crystals, (Ag)(x)(Ag(2)S)(y) with x < y, are synthesized in micellar media. The generation of Ag clusters on Ag(2)S nanocrystals is attributed to the reduction of mobile Ag(+) ions in the Ag(2)S nanocrystals by sulfur derivatives. The proportions in the composite material can be modulated by electron beam irradiation. Using dodecanethiol as surface passivating agent, 2D self-organizations of these nanocomposite crystals are produced. 相似文献
716.
Salzemann C Lisiecki I Urban J Pileni MP 《Langmuir : the ACS journal of surfaces and colloids》2004,20(26):11772-11777
In the chemical reduction of copper ions in mixed reverse micelles it is found that a large excess of reducing agent favors the production of a new generation of copper nanocrystals. At low reducing agent concentration, nanocrystals are mostly spherical, while in the supersaturated regime, they have various shapes such as pentagons, squares, triangles, and elongated forms. The nanocrystal structures, characterized by high-resolution transmission electron microscopy, are based on the face-centered cubic structure. A tentative explanation for the growth mechanism of copper nanocrystals having various shapes is proposed. 相似文献
717.
Reactions of antimicrobial species to imidazole-microwave plasma reacted poly(dimethylsiloxane) surfaces 总被引:1,自引:0,他引:1
Microwave plasma reactions of imidazole, 2-methylimidazole, and 2-ethylimidazole on poly(dimethylsiloxane) (PDMS) surfaces resulted in the formation of species containing conjugated surface domains which can be utilized for further reactions. When imidazole and its derivatives were used, polymerization of imidazole and the formation of C=C and CN conjugated species occurred. However, the extent of reactions for each monomer depends on not only the reaction time but also the molecular structure. For methyl- and ethyl-substituted imidazole, more stable radical species are generated and sustain their excited state in the high-energy plasma environments. Specifically, dehydrogenated 2-methyl, 2-ethylimidazole radicals and (*)N=CR-NH(*) (R = -CH(3), -CH(2)CH(3)) species exhibit higher stability than dehydrogenated imidazole radicals and (*)N=CH-NH(*) species under plasma reaction conditions. Such prepared surfaces are capable of attaching antimicrobial drugs via the Pinner synthesis. These studies show that it is possible to react antimicrobial species such as chloramphenicol, and this promising approach offers numerous applications of microwave plasma reactions in biotechnology. Quantitative analysis of the depth of surface reactions was accomplished by using variable angle ATR FT-IR spectroscopy. 相似文献
718.
The combination of precision-controlled weight loss measurements and spectroscopic surface FT-IR analysis allowed us to identify unique behaviors of poly(methyl methacrylate) (p-MMA). When MMA and n-butyl acrylate (nBA) are polymerized into p-MMA and p-nBA homopolymer blends, MMA/nBA random copolymers, and p-MMA/p-nBA core-shell morphologies, a controlled mobility and stratification of low molecular weight components occurs in films formed from coalesced colloidal dispersions. Due to different affinities toward water, p-MMA and p-nBA are capable of releasing water at different rates, depending upon particle morphological features of initial dispersions. As coalescence progresses, water molecules are released from the high free volume p-nBA particles, whereas p-MMA retains water molecules for the longest time due to its hydrophilic nature. As a result, water losses at extended coalescence times are relatively small for p-MMA. MMA/nBA copolymer and p-MMA/p-nBA blends follow the same trends, although the magnitudes of changes are not as pronounced. The p-MMA/p-nBA core-shell behavior resembles that of p-nBA homopolymer, which is attributed to significantly lower content of the p-MMA component in particles. Annealing of coalesced colloidal films at elevated temperatures causes migration of SDOSS to the F-A interface, but for films containing primarily p-nBA, reverse diffusion back into the bulk is observed. These studies illustrate that the combination of different particle morphologies and temperatures leads to controllable permeation processes through polymeric films. 相似文献
719.
A stability analysis of metal nanowires shows that a Jahn-Teller deformation breaking cylindrical symmetry can be energetically favorable, leading to stable nanowires with elliptic cross sections. The sequence of stable cylindrical and elliptical nanowires allows for a consistent interpretation of experimental conductance histograms for alkali metals, including both the electronic shell and supershell structures. It is predicted that for gold, elliptical nanowires are even more likely to form since their eccentricity is smaller than for alkali metals. The existence of certain metastable superdeformed nanowires is also predicted. 相似文献
720.
Johannes Winkler Ernst Urban Christian R. Noe 《Monatshefte für Chemie / Chemical Monthly》2004,2(3):109-116
A synthesis of the amino sugar 2-amino-2,3-didesoxyribose is described. Starting from D-glucosamine, -methylfuranoside was obtained in eight steps in 20% yield. This carbohydrate is a novel building block for nucleosides and for backbone modified antisense oligonucleotides with 2–5 amide linkages. 相似文献