Showing papers on "Nanoparticle published in 1999"
TL;DR: In this paper, the surface plasmon absorption of noble metal nanoparticles was studied and the effects of size, shape, and composition on the plasman absorption maximum and its bandwidth were discussed.
Abstract: The field of nanoparticle research has drawn much attention in the past decade as a result of the search for new materials. Size confinement results in new electronic and optical properties, possibly suitable for many electronic and optoelectronic applications. A characteristic feature of noble metal nanoparticles is the strong color of their colloidal solutions, which is caused by the surface plasmon absorption. This article describes our studies of the properties of the surface plasmon absorption in metal nanoparticles that range in size between 10 and 100 nm. The effects of size, shape, and composition on the plasmon absorption maximum and its bandwidth are discussed. Furthermore, the optical response of the surface plasmon absorption due to excitation with femtosecond laser pulses allowed us to follow the electron dynamics (electron−electron and electron−phonon scattering) in these metal nanoparticles. It is found that the electron−phonon relaxation processes in nanoparticles, which are smaller than t...
3,635 citations
TL;DR: In this article, a co-reduction of chlorauric acid HAuCl4 and silver nitrate AgNO3 with sodium citrate is used to form homogeneous gold−silver alloy nanoparticles.
Abstract: Gold−silver alloy nanoparticles with varying mole fractions are prepared in aqueous solution by the co-reduction of chlorauric acid HAuCl4 and silver nitrate AgNO3 with sodium citrate. As the optical absorption spectra of their solutions show only one plasmon absorption it is concluded that mixing of gold and silver leads to a homogeneous formation of alloy nanoparticles. The maximum of the plasmon band blue-shifts linearly with increasing silver content. This fact cannot be explained by a simple linear combination of the dielectric constants of gold and silver within the Mie theory. On the other hand, the extinction coefficient is found to decrease exponentially rather than linearly with increasing gold mole fraction xAu. Furthermore, the size distribution of the alloy nanoparticles is examined using transmission electron microscopy (TEM). High-resolution TEM (HRTEM) also confirms the formation of homogeneous gold−silver alloy nanocrystals.
1,327 citations
TL;DR: In this paper, the interfacial activity of reverse micelles and microemulsions is exploited to couple nanoparticle synthesis and self-assembly over a range of length scales to produce materials with complex organization arising from the interdigitation of surfactant molecules attached to specific nanoparticle crystal faces.
Abstract: Colloidal inorganic nanoparticles have size-dependent optical, optoelectronic and material properties that are expected to lead to superstructures with a range of practical applications1,2. Discrete nanoparticles with controlled chemical composition and size distribution are readily synthesized using reverse micelles and microemulsions as confined reaction media3,4,5, but their assembly into well-defined superstructures amenable to practical use remains a difficult and demanding task. This usually requires the initial synthesis of spherical nanoparticles, followed by further processing such as solvent evaporation6,7,8, molecular cross-linking9,10,11,12,13,14 or template-patterning15,16,17,18. Here we report that the interfacial activity of reverse micelles and microemulsions can be exploited to couple nanoparticle synthesis and self-assembly over a range of length scales to produce materials with complex organization arising from the interdigitation of surfactant molecules attached to specific nanoparticle crystal faces. We demonstrate this principle by producing three different barium chromate nanostructures—linear chains, rectangular superlattices and long filaments—as a function of reactant molar ratio, which in turn is controlled by fusing reverse micelles and microemulsion droplets containing fixed concentrations of barium and chromate ions, respectively. If suitable soluble precursors and amphiphiles with headgroups complementary to the crystal surface of the nanoparticle target are available, it should be possible to extend our approach to the facile production of one-dimensional ‘wires’ and higher-order colloidal architectures made of metals and semiconductors.
1,248 citations
TL;DR: Transmission electron microscopy, quantitative energy-dispersive x-ray analysis, and electron diffraction established that the crystals comprise at least three different types, found both in whole cells and thin sections, in Pseudomonas stutzeri AG259.
Abstract: One mechanism of silver resistance in microorganisms is accumulation of the metal ions in the cell. Here, we report on the phenomenon of biosynthesis of silver-based single crystals with well-defined compositions and shapes, such as equilateral triangles and hexagons, in Pseudomonas stutzeri AG259. The crystals were up to 200 nm in size and were often located at the cell poles. Transmission electron microscopy, quantitative energy-dispersive x-ray analysis, and electron diffraction established that the crystals comprise at least three different types, found both in whole cells and thin sections. These Ag-containing crystals are embedded in the organic matrix of the bacteria. Their possible potential as organic-metal composites in thin film and surface coating technology is discussed.
1,175 citations
TL;DR: In this article, the authors report a rapid, aerosol process that results in solid, completely ordered spherical particles with stable hexagonal, cubic, or vesicular mesostructures, which relies on evaporation-induced interfacial self-assembly confined to a spherical aerosol droplet.
Abstract: Nanostructured particles exhibiting well-defined pore sizes and pore connectivities (1-, 2-, or 3-dimensional) are of interest for catalysis, chromatography, controlled release, low dielectric constant fillers, and custom-designed pigments and optical hosts During the last several years considerable progress has been made on controlling the macroscopic forms of mesoporous silicas prepared by surfactant and block copolymer liquid crystalline templating procedures Typically interfacial phenomena are used to control the macroscopic form (particles, fibers, or films), while self-assembly of amphiphilic surfactants or polymers is used to control the mesostructure To date, although a variety of spherical or nearly-spherical particles have been prepared, their extent of order is limited as is the range of attainable mesostructures They report a rapid, aerosol process that results in solid, completely ordered spherical particles with stable hexagonal, cubic, or vesicular mesostructures The process relies on evaporation-induced interfacial self-assembly (EISA) confined to a spherical aerosol droplet The process is simple and generalizable to a variety of materials combinations Additionally, it can be modified to provide the first aerosol route to the formation of ordered mesostructured films
937 citations
TL;DR: In this article, the reduction of Ag+ in these solutions is brought about by the 1-hydroxyalkyl radical generated in the radiolysis of 2-propanol; citrate does not act as a reductant but solely as a stabilizer of the colloidal particles formed.
Abstract: Colloidal silver sols of long-time stability are formed in the γ-irradiation of 1.0 × 10-4 M AgClO4 solutions, which also contain 0.3 M 2-propanol, 2.5 × 10-2 M N2O, and sodium citrate in various concentrations. The reduction of Ag+ in these solutions is brought about by the 1-hydroxyalkyl radical generated in the radiolysis of 2-propanol; citrate does not act as a reductant but solely as a stabilizer of the colloidal particles formed. Its concentration is varied in the range from 5.0 × 10-5 to 1.5 × 10-3 M, and the size and size distribution of the silver particles are studied by electron microscopy. At low citrate concentration, partly agglomerated large particles are formed that have many imperfections. In an intermediate range (a few 10-4 M), well-separated particles with a rather narrow size distribution and little imperfections are formed, the size slightly decreasing with increasing citrate concentration. At high citrate concentrations, large lumps of coalesced silver particles are present, due to ...
709 citations
TL;DR: In this article, a non-hydrolytic single-precursor approach to the synthesis of dispersable nanocrystals of transition metal oxides is presented, which is of considerable interest to us.
Abstract: The advent of new methods to prepare semiconductor and metal nanocrystals, specifically the injection of molecular precursors into hot organic surfactants, has yielded markedly improved samples with good size control, narrow size distribution, and good crystallinity of individual and dispersable nanocrystals. It is of considerable interest to apply these methods to the synthesis of transition metal oxide nanoparticles, which typically are prepared by methods involving water as solvent or reactant. The authors report the first results of a new nonhydrolytic single-precursor approach to the synthesis of dispersable nanocrystals of transition metal oxides.
703 citations
TL;DR: Extraordinarily stable, monodisperse noble metal nanoparticles can be prepared by using dendrimers as both templates and stabilizers, and the catalytic activity and selectivity of these materials can be controlled by adjusting the d endrimer generation.
Abstract: Extraordinarily stable, monodisperse noble metal nanoparticles can be prepared by using dendrimers as both templates and stabilizers. Dendrimer-encapsulated Pd nanoparticles (see the schematic representation) exhibit high catalytic activity for the hydrogenation of alkenes in water. The catalytic activity and selectivity of these materials can be controlled by adjusting the dendrimer generation.
584 citations
TL;DR: In this article, the authors examined the electrodynamics of silver nanoparticles and of clusters of nanoparticles, with an emphasis on extinction spectra and of electric fields near the particle surfaces that are important in determining surfaceenhanced Raman (SER) intensities.
Abstract: In this paper we examine the electrodynamics of silver nanoparticles and of clusters of nanoparticles, with an emphasis on extinction spectra and of electric fields near the particle surfaces that are important in determining surface-enhanced Raman (SER) intensities. The particles and clusters are chosen to be representative of what has been studied in recent work on colloids and with lithographically prepared particles. These include spheres, spheroids, truncated tetrahedrons, and clusters of two or three of these particles, with sizes that are too large to be described with simple electrostatic approximations but small compared to the wavelength of light. The electrodynamics calculations are mostly based on the discrete dipole approximation (DDA), which is a coupled-finite element approach which produces exact or nearly exact results for particles of arbitrary size and shape if fully converged. Mie theory results are used to study the validity of the DDA for spherical particles, and we also study the validity of the modified long wavelength approximation (MLWA), which is based on perturbative corrections to the electrostatic limit, and of the single dipole per particle approximation (SDA). The results show how the dipole plasmon resonance properties and the electric field contours around the particle vary with particle shape and size for isolated particles. For clusters of particles, we study the effect of interparticle spacing on plasmon resonance characteristics. We also show that the quadrupole resonance is much less sensitive to particle shape and interparticle interactions than the dipole plasmon resonance. These results provide benchmarks that will be used in future comparisons with experiment.
567 citations
TL;DR: This work has determined the relative importance of parameters as well as the optimal conditions for obtaining uncoated stable particles with an average size of 5 nm and interesting relaxivities and proposed model of synthesis, related to spontaneous emulsification of suspensions, is proposed.
549 citations
TL;DR: Aqueous magnetic fluids were synthesized by a sequential process involving the chemical coprecipitation of Fe(II and Fe(III) salts with ammonium hydroxide (NH4OH) followed by resuspension of the ultrafine particles in water using fatty acids.
Abstract: Aqueous magnetic fluids were synthesized by a sequential process involving the chemical coprecipitation of Fe(II) and Fe(III) salts with ammonium hydroxide (NH4OH) followed by resuspension of the ultrafine particles in water using fatty acids. This procedure produced Fe3O4 nanoparticles stabilized against agglomeration by bilayers of n-alkanoic acids with 9−13 carbons encapsulating the metal particles. The magnetic properties and particle size and size distributions of these magnetic fluids, characterized by transmission electron microscopy and superconducting quantum interference device, indicated the formation of single-domain nanoparticles of mean diameter ∼9.3 and ∼7.5 nm, respectively; the difference in values determined by the two methods implies the presence of a nonmagnetic layer on the particle surface. Thermogravimetric analysis measurements showed the existence of two distinct populations of surfactants on the particle surface, each having surfactant coverage of ∼21−24 A2/molecule, that was con...
TL;DR: In this paper, the authors examined the effect of solvent on the optical extinction spectrum of periodic arrays of surface-confined silver nanoparticles fabricated by nanosphere lithography (NSL) and showed that the defect sites that occur as a byproduct of the NSL fabrication process play a negligible role in the macroscale extinction spectrum.
Abstract: In this paper we examine the effect of solvent on the optical extinction spectrum of periodic arrays of surface-confined silver nanoparticles fabricated by nanosphere lithography (NSL). By use of NSL, it is possible to systematically vary the out-of-plane height of the nanoparticles, and by thermal annealing, we can control the nanoparticle shape. We have studied four separate samples of nanoparticle arrays; three samples have nanoparticles that are truncated tetrahedral in shape but that differ in out-of-plane height and one sample has nanoparticles that are oblate ellipsoidal in shape. By performing UV−vis extinction spectroscopy measurements at 12 μm spatial resolution, we show that the defect sites that occur as a byproduct of the NSL fabrication process play a negligible role in the macroscale extinction spectrum. We find that the extinction spectrum of the nanoparticles that are oblate ellipsoidal in shape is least sensitive to the surrounding dielectric medium, and the extinction spectrum of the na...
TL;DR: In this paper, a template-synthesized carbon tubule is used to construct a monodisperse graphitic carbon nanotubule membrane, which can then be filled with nanoparticles of electrocatalytic materials (i.e., Pt, Ru, Pt/Ru).
Abstract: Ensembles of highly aligned and monodisperse graphitic carbon nanotubules have been prepared via the template method using chemical vapor deposition of carbon within the pores of alumina membranes. Tubules with diameters of 200 nm have been prepared, and smaller diameters are possible. Free-standing aligned carbon-tubule membranes are formed by this template method. These novel carbon tubule membranes can be filled with nanoparticles of electrocatalytic materials (i.e., Pt, Ru, Pt/Ru), which can then be used to electrocatalyze O2 reduction and methanol oxidation as well as the gas-phase catalysis of hydrocarbons. Hence, these membranes have potential applications in fuel cell development. Smaller, highly ordered graphitic-carbon tubules can also be prepared within the template-synthesized carbon tubules, using Fe nanoparticles as catalysts. In these novel tube-in-tube structures, both the outer and the inner tubules are electrochemically active for Li+ intercalation, suggesting possible applications such ...
TL;DR: Au, Pt, Pd, Ru and Ir nanoparticles with a narrow size distribution have been synthesized by chemical reduction of their corresponding metal species in ethylene glycol as mentioned in this paper.
TL;DR: In this article, the magnetite core and polymeric shell were synthesized in a single inverse microemulsion and the particle size was varied in the range 80−320 nm by changing of the monomer concentration and water/surfactant ratio.
Abstract: A novel approach to prepare magnetic polymeric nanoparticles by synthesis of the magnetite core and polymeric shell in a single inverse microemulsion is reported. Stable magnetic nanoparticles colloid dispersion with narrow size distribution can thus be produced. The microemulsion seed copolymerization of methacrylic acid, hydroxyethyl methacrylate, and cross-linker results in a stable hydrophilic polymeric shell of the nanoparticles. The preparation of the nanoparticles was carried out also by the two-stage microemulsion process and the seed precipitation polymerization. The particle size was varied in the range 80−320 nm by changing of the monomer concentration and water/surfactant ratio. The magnetic properties and the size distribution of the nanoparticles synthesized by these three methods were compared. The polymeric nanoparticles synthesized in single microemulsion have superparamagnetic properties and the narrowest size distribution.
TL;DR: In this paper, carboxylate-modified gold nanoparticles have been synthesized in a single-phase system based on the reduction of hydrogen tetrachloroaurate(III) by sodium borohydride in methanol using mercaptosuccinic acid (MSA) as the stabilizing thiol ligand.
Abstract: Carboxylate-modified gold nanoparticles have been synthesized in a single-phase system based on the reduction of hydrogen tetrachloroaurate(III) by sodium borohydride in methanol using mercaptosuccinic acid (MSA) as the stabilizing thiol ligand. Five samples with diameters of 10.2, 10.8, 12.8, 19.4, and 33.6 A have been prepared as water-redispersible powders through decreasing the initial MSA/HAuCl4 molar ratio from 2.5 to 0.5. These samples were characterized by X-ray diffraction, transmission electron microscopy, elemental analysis, thermogravimetric analysis, ζ-potential measurement, Fourier transform infrared spectroscopy, and UV−vis spectroscopy. The results show that a large number of the particles are fcc single crystals with the polyhedral morphology of a truncated octahedral motif and that a self-assembled monolayer of thiolates has indeed formed through the adsorption of mercapto groups on the gold particle surface; the maximum packing density of the thiolates is 15.23 A2 per mercapto group. Th...
TL;DR: In this article, colloidal assemblies are used to synthesize FCC cobalt nanoparticles and the magnetic properties are compared when they are dispersed in a solvent and organized in 2D superlattices.
Abstract: Colloidal assemblies are used to synthesize FCC cobalt nanoparticles. The particles are coated, extracted from micelles, and characterized by transmission electron microscopy, small angle X-ray scattering, and electron and X-ray diffraction spectroscopy. These cobalt metal particles are stable in air, have a narrow size distribution, and on deposition on a graphite support, spontaneously form a 2D hexagonal network. The magnetic properties are compared when they are dispersed in a solvent and organized in 2D superlattices. Changes in the hysteresis loop and in the blocking temperature are observed and attributed to collective flip of the magnetization of adjacent particles.
TL;DR: In this article, the authors describe the production of size-selected gold aerosol particles in the 20 nm range made by evaporation in a high-temperature tube furnace and subsequent size selection.
Abstract: Gold nanoparticles are of great interest for various nanoelectronic applications, e.g., for making single electron transistors or very fine leads to molecular size entities. For this and other applications, it is important that all particles have controllable size and shape. In this paper, we describe the production of size-selected gold aerosol particles in the 20 nm range made by evaporation in a high-temperature tube furnace and subsequent size selection. To obtain spherical particles, it was necessary to reshape the particles at high temperature, which was investigated for temperatures between 25°C and 1200°C. High-resolution transmission electron microscopy showed that the degree of crystallinity became higher for higher reshaping temperature. During reshaping at high temperature, an anomalous charging behavior was discovered, whereby negatively as well as positively charged particles became multiply negatively charged. Possible mechanisms for explaining this thermally activated phenomenon are discussed.
TL;DR: In this paper, the electrochemical synthesis of nanoparticles of γ-Fe2O3 was performed in an organic medium, and the size distributions of the particles were narrow, with the average sizes varying from 3 to 8 nm.
Abstract: The electrochemical synthesis of nanoparticles of γ-Fe2O3 was performed in an organic medium. The size was directly controlled by the imposed current density, and the resulting particles were stabilized as a colloidal suspension by the use of cationic surfactants. The size distributions of the particles were narrow, with the average sizes varying from 3 to 8 nm. The amorphous character of the nanoparticles was clearly established by X-ray powder diffraction and TEM analysis. The microstructure of this phase could nevertheless be spectroscopically related to maghemite, γ-Fe2O3. 57Fe Mossbauer spectroscopy and magnetization measurements indicated that the dry powders exhibit superparamagnetic behavior at room temperature.
TL;DR: In this paper, hollow composite silica−polymer spheres were obtained by calcining polymer latex spheres with multilayers of silica nanoparticles (SiO2) bridged by polymer [poly(diallyldimethylammonium chloride) (PDADMAC).
Abstract: Uniform inorganic and hybrid inorganic−organic hollow microspheres have been produced by coating colloidal core templates with alternating layers of oppositely charged nanoparticles and polymer, and thereafter removing the core either by heating or chemical treatment. The multilayers were constructed by consecutively depositing the nanoparticles and polymer onto the colloidal templates, utilizing the electrostatic attraction between the particles and polymer for layer build-up. Hollow silica spheres were obtained by calcining polymer latex spheres coated with multilayers of silica nanoparticles (SiO2) bridged by polymer [poly(diallyldimethylammonium chloride) (PDADMAC)]. Exposure of SiO2/PDADMAC multilayer-coated polymer latex colloids to acidic solutions, dimethyl sulfoxide, or tetrahydrofuran yielded hollow composite silica−polymer spheres. The fabricated hollow spheres have been characterized using scanning and transmission electron microscopy. The approach employed is well suited to generating hollow ...
01 Apr 1999
TL;DR: The variation in the polymeric shell size and the polymer net density can be useful tools for evaluation of the polymer-coated magnetite particles as effective contrast agents.
Abstract: The properties of polymer-coated magnetite nanoparticles, which have the potential to be used as effective magnetic resonance contrast agents, have been studied. The magnetite particles were synthesized by using continuous synthesis in an aqueous solution. The polymer-coated magnetite nanoparticles were synthesized by seed precipitation polymerization of methacrylic acid and hydroxyethyl methacrylate in the presence of the magnetite nanoparticles. The particle size was measured by laser light scattering. It was shown that the particle size, variance, magnetic properties, and stability of aqueous magnetite colloidal dispersion strictly depend on the nature of the stabilizing agent. The average hydrodynamic radius of the magnetite particles was found to be 5.7 nm in the stable aqueous colloidal dispersion. An inclusion of the magnetite particle into a hydrophilic polymeric shell increases the stability of the dispersion and decreases the influence of the stabilizing agent on the magnetic and structural properties of the magnetite particles as was shown by X-ray diffraction and Mossbauer and IR spectroscopy, as well as by vibrating sample magnetometry. The variation in the polymeric shell size and the polymer net density can be useful tools for evaluation of the polymer-coated magnetite particles as effective contrast agents.
TL;DR: In this paper, a general one-phase synthesis for thiol-functionalized gold, palladium, and iridium nanoparticles, using tetrahydrofuran (THF) as the solvent and lithium triethylborohydride (Superhydride) as reducing agent, is presented.
Abstract: A new, facile, general one-phase synthesis for thiol-functionalized gold, palladium, and iridium nanoparticles, using tetrahydrofuran (THF) as the solvent and lithium triethylborohydride (Superhydride) as the reducing agent, is presented. For octadecanethiol-functionalized gold (Au/ODT) nanoparticles, HRTEM of drop-cast particle-films revealed the formation of spherical particles of d = 4 ± 0.3 nm average size. Electron diffraction shows fcc packing arrangement, similar to that of bulk gold. The crystalline gold cores are surrounded with closely packed n-alkyl chains mainly in an all-trans conformation, adopting orthorhombic packing as confirmed by FTIR spectroscopy. Particles are arranged in a discrete solidlike assembly with a correlation length of ∼5 nm, as the interparticle distance (center-to-center) and a constant edge-to-edge distance of 1 nm as shown by FFT analysis. Using the same synthetic procedure gold nanoparticles functionalized with 11-hydroxyundecane-1-thiol and with 4‘-bromo-4-mercaptobip...
TL;DR: In this paper, an X-ray diffraction of the initial zinc sulfide−silica (ZSS) powder yields diffraction peaks corresponding to the ZnS phase.
Abstract: Ultrasonic irradiation of a slurry of amorphous silica microspheres, zinc acetate, and thioacetamide in an aqueous medium for 3 h under ambient air yields zinc sulfide coated on silica. The powder X-ray diffraction of the initial zinc sulfide−silica (ZSS) powder yields diffraction peaks corresponding to the ZnS phase. The TEM image of ZSS shows that the porous ZnS nanoparticles (diameter 1−5 nm) coated the silica (SiO2) surface as thin layers or nanoclusters, depending on the reactant concentration. Infrared spectroscopy illustrates the structural changes that occurred in the siloxane network and surface silanol groups of SiO2 upon the ultrasonic deposition of ZnS. The optical absorption of porous ZnS shows a broad band at around 610 nm, ascribed to unusual surface state transition. The absorption energy of the surface state transition is lower than the band gap of the ZnS particles and probably stems from the dangling surface bonds or defects. On the other hand, the ZSS does not show the surface state tr...
TL;DR: In this paper, inorganic fullerene-like (IF) supramolecules of metal dichalcogenide MX2 (M=Mo, W, etc.; X=S, Se), materials with structures closely related to (nested) carbon fullerenes and nanotubes have been synthesized.
TL;DR: In this paper, a H2-CH4 mixture over oxide spinels containing two transition elements as in Mg0.8MyM'zAl2O4 (M, M' = Fe, Co or Ni, y + z = 0.2) at 1070°C produces small alloy nanoparticles which enable the formation of carbon nanotubes.
TL;DR: The reaction of Ni(COD)2 with H2 (3 bar) in CH2Cl2 in the presence of poly(vinylpyrrolidone) (PVP) K 30 leads to air-stable agglomerates of ≈30 nm, composed of individual 3−4 nm fcc Ni particles.
Abstract: The reaction of Ni(COD)2 with H2 (3 bar) in CH2Cl2 in the presence of poly(vinylpyrrolidone) (PVP) K 30 leads to air-stable agglomerates of ≈30 nm, composed of individual 3−4 nm fcc Ni particles an...
TL;DR: In this paper, metal and metal sulfide nanoparticles are prepared using a method that is based on the rapid expansion of supercritical fluid solution (RESS) into a liquid solution and characterized using transmission electron microscopy and X-ray diffraction methods.
Abstract: Metal and metal sulfide nanoparticles are prepared using a method that is based on the rapid expansion of supercritical fluid solution (RESS) into a liquid solution and characterized using transmission electron microscopy and X-ray diffraction methods. The nanoparticles form solution-like stable suspensions in the presence of a stabilization agent such as poly(N-vinyl-2-pyrrolidone) (PVP) polymer. The stable suspensions allow systematic nonlinear optical measurements. The nanocrystalline silver metal and silver sulfide particles in PVP polymer-stabilized ethanol suspensions of high linear transmittance exhibit excellent optical limiting properties, with the optical limiting responses toward nanosecond laser pulses at 532 nm being much stronger than those of benchmark materials [60]fullerene and chloroaluminum phthalocyanine in solution. A comparison of the results with those of stable suspensions of other nanoparticles including cadmium sulfide, lead sulfide, and nickel suggests that the optical limiting ...
TL;DR: Thermally induced changes in the magnetization direction of superparamagnetic magnetite nanoparticles were observed but with a much slower rate than expected, due to surface anisotropy.
Abstract: The magnetization directions of individual monodomain nanoparticles as small as 5 nanometers in diameter are determined using the Foucault method of Lorentz microscopy. A model is developed to explain the images and diffraction patterns of samarium cobalt nanoparticles as a function of the aperture shift direction. Thermally induced changes in the magnetization direction of superparamagnetic magnetite nanoparticles were observed but with a much slower rate than expected, due to surface anisotropy. When the time scale for magnetization reversal is much shorter than the data acquisition time, as in carbon-coated iron cobalt alloy nanoparticles, the images show an average of such thermally induced changes.
TL;DR: A chemical precipitation method has been used for the synthesis of ZnO nanoparticles with controlled morphology as mentioned in this paper, where the precursor powders were prepared using several precipitation reagents and using ammonium carbamate as a precipitating reagent led to unusual rod shape morphology.
Abstract: A chemical precipitation method has been used for the synthesis of ZnO nanoparticles with controlled morphology. The precursor powders were prepared using several precipitation reagents and using ammonium carbamate as a precipitating reagent led to unusual rod-shape morphology. The precursor was decomposed by heating in air resulting in the formation of spherical or rod-like shapes of zinc oxide. A flow injection synthesis technique has been developed to synthesize nanophase particles of zinc oxide. The precursor and decomposed products were analyzed using IR, SEM, XRD and TGA techniques. The average size of the particles of ZnO obtained using the flow injection technique was approximately 20 nm while the crystallite size as measured from the X-ray pattern was 10–15 nm.
Patent•
IBM1
TL;DR: In this paper, a method of forming nanoparticles includes steps of forming a metal precursor solution from a transition metal, injecting the metal precursors to the surfactant solution, adding a flocculent to cause nanoparticles to precipitate out of solution without permanent agglomeration, and adding a hydrocarbon solvent to redisperse or repeptize the nanoparticles.
Abstract: A method of forming nanoparticles includes steps of forming a metal precursor solution from a transition metal, injecting the metal precursor solution to the surfactant solution, adding a flocculent to cause nanoparticles to precipitate out of solution without permanent agglomeration, and adding a hydrocarbon solvent to redisperse or repeptize the nanoparticles.