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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nanocrystalline silver sulfide was successfully synthesized at room temperature and ambient pressure via a novel, safe, convenient and inexpensive redox reaction, using silver oxide, sulfur and polyformaldehyde as reactants and ethylenediamine as solvent. The products were characterized with XPS, XRD and TEM. XRD spectrum demonstrates a monoclinic Ag2S; TEM shows the products are rod-like nanoparticles with average diameter of 100 nm, its corresponding SAED reveals clear diffraction spots indexed as (120) and (303); XPS confirms the formation of Ag2S and indicates the sample's surface stoichiometry of Ag:S=1:0.453. The control experiments show polyformaldehyde and ethylenediamine are both important in the formation of products. Ethylenediamine accelerates the reactions via dissolving silver oxide and sulfur and neutralizing the by-product formic acid.
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PMID:[Synthesis of Ag2S nanoparticles at room temperature and their characterization with XPS]. 1609 83

The reaction between silver nitrate and poly(N-vinyl-2-pyrrolidone) (PVP) in pyridine at ambient conditions could lead to the formation of spherical nanoparticles or quadrilateral and triangular silver nanoplates, depending on the silver-to-PVP ratio used. It is proposed that the spherical Ag nanoparticles, which were formed early in the reaction, were transformed into nanoplates through an Ostwald ripening process driven by the bridging flocculation of small spherical Ag nanoparticles. This unique and hitherto unreported shape evolution process was carefully followed by a combination of techniques, viz., UV-visible spectroscopy, TEM, and powder X-ray diffraction.
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PMID:Solvent-induced shape evolution of PVP protected spherical silver nanoparticles into triangular nanoplates and nanorods. 1611 24

Water entrapment occurs at resin-dentin interfaces of one-step self-etch adhesives. We hypothesized that by preventing water fluxes from dentin, any water entrapment would be attributed to incomplete removal of adhesive solvents. We tested this hypothesis by bonding to transparent carious dentin containing occluded dentinal tubules. An experimental single-bottle, one-step self-etch adhesive was applied to flat surfaces of caries-affected dentin surrounded by sound dentin, with or without pulpal pressure. Resin-dentin interfaces were examined with TEM after silver-impregnation. Although caries-affected dentin was highly porous, adhesive layers were devoid of silver deposits when tubules were occluded. Conversely, variable extents of water-treeing and water-droplets were identified from adhesive layers in bonded sound dentin. Water-treeing and water-droplet formation, being manifestations of evaporative and convective water fluxes, can be eliminated during bonding to occluded transparent carious dentin. However, the highly porous nature of this clinically relevant substrate after bonding may lead to potentially undesirable consequences.
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PMID:Tubular occlusion prevents water-treeing and through-and-through fluid movement in a single-bottle, one-step self-etch adhesive model. 1618 86

The effects of cations on the absorption spectra of silver sols have been investigated by the UV-vis spectrometry and TEM. Experiments showed that injection of certain amounts of transition metal cations into silver sols resulted not only in the aggregation of silver nanoparticles but also in the appearance of a new band centered near 510 nm in the absorption spectra of silver sols. However, the new band was not observed in the presence of alkaline earth metal cations or the Mv2+ cations. The peak position of the new band depends on the nature as well as the concentration of metal cations used. Comparing the peak positions of the new bands, it was found that the new band induced by the injection of Cr3+ was red-shifted with respect to those induced by Cu2+, Zn2+, or the Cd2+ cations. It is reasonable that this band near 510 nm should be attributed to the coeffects of the adsorption of metal cations onto the surfaces of silver nanoparticles and the aggregation of silver nanoparticles.
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PMID:Adsorption of cations onto the surfaces of silver nanoparticles. 1625 71

In this paper, we present a new method to fabricate carbon microspheres with supported silver nanoparticles on the surfaces. In this method, pollen grains were first treated with AgNO(3) aqueous solution, then preoxidized in air at 300 degrees C and carbonized in nitrogen at 600 degrees C, resulting in the silver/carbon nanocomposites. The silver/carbon nanocomposites were characterized by means of SEM, TEM, TG, and XRD. The size and distribution of the silver nanoparticles on the carbon microsphere surface could be controlled by tuning the AgNO(3) treatment conditions.
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PMID:Carbon microspheres with supported silver nanoparticles prepared from pollen grains. 1626 61

A series of silver colloidal dispersions were prepared by two protocols, i.e., addition of the reductant-NaBH(4) and the stabilizer-thiosalicylic acid (TSA) into Ag(+) solution simultaneously or successively. The products were compared and characterized by TEM, electrochemical measurements, XPS, UV-vis, and FT-IR spectra. The size distributions of the Ag nanoparticles prepared by the former and latter protocols are bimodal and monodisperse, respectively. The analytic results of UV-vis spectra coincide with the TEM observation. A tentative explanation was given to the relationship between particle sizes and different synthetic protocols. The changes of the reduction potential of the reductant invoked a variance in particle diameter and size distribution. Electrochemical measurements corroborated our assumption. The composition information of TSA-derived silver nanoparticles was obtained from XPS and FT-IR spectroscopic measurements.
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PMID:Thiosalicylic acid-functionalized silver nanoparticles synthesized in one-phase system. 1629 Jun 6

We have previously reported that low intensity microwave exposure (0.75-1.0 GHz CW at 0.5 W; SAR 4-40 mW/kg) can induce an apparently non-thermal heat-shock response in Caenorhabditis elegans worms carrying hsp16-1::reporter genes. Using matched copper TEM cells for both sham and exposed groups, we can detect only modest reporter induction in the latter exposed group (15-20% after 2.5 h at 26 degrees C, rising to approximately 50% after 20 h). Traceable calibration of our copper TEM cell by the National Physical Laboratory (NPL) reveals significant power loss within the cell (8.5% at 1.0 GHz), accompanied by slight heating of exposed samples (approximately 0.3 degrees C at 1.0 W). Thus, exposed samples are in fact slightly warmer (by < or =0.2 degrees C at 0.5 W) than sham controls. Following NPL recommendations, our TEM cell design was modified with the aim of reducing both power loss and consequent heating. In the modified silver-plated cell, power loss is only 1.5% at 1.0 GHz, and sample warming is reduced to approximately 0.15 degrees C at 1.0 W (i.e., < or =0.1 degrees C at 0.5 W). Under sham:sham conditions, there is no difference in reporter expression between the modified silver-plated TEM cell and an unmodified copper cell. However, worms exposed to microwaves (1.0 GHz and 0.5 W) in the silver-plated cell also show no detectable induction of reporter expression relative to sham controls in the copper cell. Thus, the 20% "microwave induction" observed using two copper cells may be caused by a small temperature difference between sham and exposed conditions. In worms incubated for 2.5 h at 26.0, 26.2, and 27.0 degrees C with no microwave field, there is a consistent and significant increase in reporter expression between 26.0 and 26.2 degrees C (by approximately 20% in each of the six independent runs), but paradoxically expression levels at 27.0 degrees C are similar to those seen at 26.0 degrees C. This surprising result is in line with other evidence pointing towards complex regulation of hsp16-1 gene expression across the sub-heat-shock range of 25-27.5 degrees C in C. elegans. We conclude that our original interpretation of a non-thermal effect of microwaves cannot be sustained; at least part of the explanation appears to be thermal.
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PMID:A small temperature rise may contribute towards the apparent induction by microwaves of heat-shock gene expression in the nematode Caenorhabditis Elegans. 1634 96

Monodisperse silver nanodisks are synthesized on the gram scale from a well-characterized layered silver thiolate precursor via thermolysis at 180-225 degrees C under a N(2) atmosphere. XRD, TEM, HRTEM, and AFM analyses indicate that the nanodisks generated at 180 degrees C over 2 h have an average diameter of about 16.1 nm (sigma = +/-12%) and a thickness of 2.3 nm (sigma = +/-14%), and they lie on their (111) faces. The disk shape is considered to be predestined by the crystal structure of the precursor. Important aspects regarding the stability of the precursor, the thermolysis temperature, and the annealing time, as well as a possible conversion mechanism, are discussed.
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PMID:Structure-controlled solventless thermolytic synthesis of uniform silver nanodisks. 1636 51

An end-to-end assembly of spherical Ag nanoparticles takes place in the presence of biotin to form long fiberlike microstructures. These microstructures are about 4 mum long with a thickness of 1 mum, obtained from SEM studies. TEM studies showed the presence of spherical silver nanoparticles having an average size of 20 nm. ATR-FTIR studies revealed that silver ions interact with biotin involving the carboxylate group. A weak binding of the silver particles with the thioether and ureido groups helps in connecting the Ag nanoparticles to form long fiberlike structures. Elucidation of the mechanism of formation of the spherical Ag clusters was done by pulse radiolysis.
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PMID:Self-assembly of Ag nanoparticle-biotin composites into long fiberlike microstructures. 1637 26

Mercaptoethane sulfonate protected, water-soluble gold and silver nanoparticles (Au-MES and Ag-MES) are synthesized by one-phase method and characterized by TEM, TGA and XPS techniques, UV-vis and FTIR spectra. Both Au-MES and Ag-MES nanoparticles are soluble in the water up to 2.0 mg/ml and the stability of Au-MES is much better than that of Ag-MES. When dissolved in the water, they behave like a polyanion and can be used to build multilayer films with polyaniline (PANI) by way of layer-by-layer. A new approach is presented to fabricate the multilayer films of Au-MES/PANI and Ag-MES/PANI. The assembly mechanism of these multilayer films is also discussed. We anticipate highly conducting PANI films can be obtained by doping with these nanoparticles.
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PMID:Mercaptoethane sulfonate protected, water-soluble gold and silver nanoparticles: Syntheses, characterization and their building multilayer films with polyaniline via ion-dipole interactions. 1641 29


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