Showing papers on "Nanoparticle published in 1992"

Luminescent Colloidal Silicon Suspensions from Porous Silicon

Abstract: A procedure for generating colloidal suspensions of Si that exhibit luminescence, attributed to quantum confinement effects, is described. Samples of n- or p-type Si that have been electrochemically etched to form porous Si can be ultrasonically dispersed into methylene chloride, acetonitrile, methanol, toluene, or water solvents, forming a suspension of fine Si particles that luminesce. Transmission electron microscopy analyses show that the Si particles have irregular shapes, with diameters ranging from many micrometers to nanometers. Luminescent, composite polystyrene/Si films can be made by the addition of polystyrene to a toluene suspension of the Si nanoparticles and casting of the resulting solution onto a glass slide.

Optimization of polyalkylcyanoacrylate nanoparticle preparation: Influence of sulfur dioxide and pH on nanoparticle characteristics

Abstract: Simultaneous influence of pH and presence of sulfur dioxyde (SO2) on nanoparticle preparation and characteristics have been investigated with poly(isohexylcyanoacrylate) and poly(isobutylcyanoacrylate). Turbidity, nanoparticle size, and molecular weights were followed to understand the exact role of each parameter tested. Results showed the extreme importance of SO2 concentration on nanoparticle characteristics and confirmed its role as a polymerization inhibitor. We also demonstrated that, in certain circumstances, pH could compensate, in a limited way, for the effect of SO2. In fact SO2 was always shown to have such a strong effect on size and molecular weight that reproducible batches could be achieved only with SO2-free monomers. Subsequent work on nanoparticle charges under similar conditions will help to gain a better understanding of SO2 influence.

Electrical conductivity of sol-gel derived metal nanoparticles

Abstract: Electrically conducting films of thickness ∼ 2 μm have been prepared on ordinary glass slides by growing ultra-fine particles of iron and copper, respectively, from a suitable precursor sol. The diameters of metal particles can be varied from 3–13 nm by controlling the heat-treatment schedule of the sol coating. Resistivity measurements (d.c.) have been carried out over the temperature range 80–300 K. The resistivity values in the range 0.0001–0.0039 Ω cm have been obtained depending on the particle diameter and the type of metal used. The effective Debye temperature θD for the different nanoparticle systems have been estimated by fitting the experimental data to the Ziman equation. θD is found to vary from 346–408 K for iron with the particle size in the range 3.4–9.5 nm. The values obtained for copper are 243–307 K with particle diameters covering a range of 5.9–12.6 nm.

Electron Microscopy of Metallic Nano Particles Using High- and Medium-Resolution Techniques

Abstract: The study of systems with dimensions of the order of a few to a hundred nanometers has attracted great attention. The main reason is the peculiar physical and chemical behavior of these systems; they are specially important in catalysts since metal nano particles are the most common constituents of the supported catalysts. The understanding of the structure of nano particles is a crucial step for the understanding of the catalytic activity. In the present work we report a number of transmission electron microscopy techniques that can be used in order to characterize the shape and structure of nano particles. In the last decade electron microscopy has had a dramatic development and at the present time we have a number of techniques from medium-resolution such as selected zone dark-field (SZDF) and weak beam dark-field (WBDF) as well as direct atom imaging by high resolution. In the present work we discuss the theoretical principles of these techniques and their main applications to the field of na...

Preparation of nickel nanoparticles by metalorganic route

Abstract: Nickel particles of sizes in the range 5–11 nm have been prepared by the decomposition of a suitable metalorganic compound on the surfaces of micrometer‐sized potassium bromide crystallites. Infrared absorption spectra of nanocomposites comprising these particles dispersed in potassium bromide matrix have been delineated. Effective medium theory is used to explain the experimental results.

Iron nanoparticles in copper matrix prepared by sol‐gel route

Abstract: Iron particles having diameters around 8 nm and loosely packed with nanosized copper particles have been prepared by a sol‐gel route. The samples exhibit coercivities in the range 200 to 500 Oe that are typical of single‐domain iron grains. The Mossbauer spectrum is consistent with the presence of α‐Fe particles in the system. However, a finite value of the isomer shift is obtained that is ascribed to possible electron transfer between the iron atoms and the surrounding copper matrix.

Nanometer particles synthesis in reverse micelles: Influence of the size and the surface on the reactivity

Abstract: In this paprr we are presenting the synthesss “in situ” of nanoparticles in reverse micelles. In the case of aggregates containing copper ions, it is possible to form metallic particles surrounded or not by an oxide layer. By mixing aggregates containing cadmium and sulphide ions, CdS particles are formed. The size and polydispersity of the particles are controlled. The photoelectron transfer reaction depends mainly on the surface composition. In the range of 1 to 5 nm, the efficiency in the electron transfer does not depend on the size of the particle. The reverse micelles are formed by using either sodium di(2-ethyl hexyl)sulfosuccinate, usually called {AOT} or mixed bivalent and sodium di(2-ethyl hexyl)sulfosuccinate {AOl/M(AOT)2}.

Spontaneous dissolution at room temperature of gold nanoparticles.

Abstract: We have studied gold nanoparticles evaporated on NaCl. We examined the sample before and after an annealing at room temperature for seven months. We found that most of the small particles with square shape disappear after the annealing. Many of the particles remaining correspond to multiple twinned particles (MTP), i.e., particles with icosahedral or decahedral shapes. We also found that the size of the icosahedral and decahedral particles did not change with the room-temperature annealing. The only consistent explanation is a spontaneous dissolution of the square-shaped nanoparticles at room temperature. This indicates that the binding energy of the atoms in such particles is much lower than the bulk value. The reason why such a particle would rather be dissolved instead of undergoing quasimelting is not clear. Room-temperature dissolution of square-shaped particles is another example of nanoparticles instability.

In situ detection of monovalent copper in aerosols by photoemission

Abstract: In situ information on nanoparticle surface chemistry and modes of particle growth is obtained in gas suspension by the technique of photoelectric charging of particles (PCP) which depends on the surface chemical compositon as well as the electronic structure of the particles via the spectral dependence of the photoelectric yield. With CuCl particles, photoelectric charging is about 100 times more efficient compared to other divalent transition metal compounds. Therefore, particles containing monovalent Cu can be detected with extremely high sensitivity of below 10 ng/m3. In atmospheric aerosols emitted from volcanoes, the relation of solid state oxidation/reduction in Fe1−xCuxCl2 resulting in monovalent Cu for x<0.4 is important. As an example of the PCP technique this relation is monitored in laboratory generated aerosols. The nanoparticles are also precipitated onto a substrate where their surface chemical composition is analyzed by XPS which is important for the interpretation of the results obtained by photoelectric charging.

Electron microscopic study of ultra-fine particles of silver resulting from the electron-beam-induced decomposition of silver azide

Abstract: Silver azide is known to decompose to metallic silver and nitrogen gas when irradiated by the beam of a transmission electron microscope. We report here that, under appropriate conditions, the resulting silver product consists of a wide range of particles sizes, varying from several hundreds down to tens of nanometres. The morphology of these particles is varied and includes well defined hexagonal or trigonal crystals as well as polygonized spheres. Some evidence is found for the formation of multiply twinned particles similar to those generated in silver-metal smokes. The electron-beam-induced route described here for producing silver microcrystals is straightforward and offers several advantages over conventional nanoparticle synthesis procedures.

Nanoparticles surface modified drugs.

Abstract: Dispersible particles consisting essentially of a substance DOPE CRISTALINA provided with a surface modifier absorbed into the surface thereof in an amount sufficient to maintain effective PROPORTION OF PARTICLE SIZE LESS THAN 400 NM, methods for preparing such particles and dispersions CONTAINING PARTICLE. PHARMACEUTICAL COMPOUNDS CONTAINING SUCH UNEXPECTED bioavailable particles exhibit and used in methods of treatment of mammals.

Sol-Gel synthesis of ceramic-organic nano composites

Abstract: Sol-gel synthesis can be used for generating nano particles from a variety of compositions. In order to avoid aggregation and undesired gelation, it is necessary to react the particle surfaces with ligands reducing their interaction but allowing the incorporation into desired matrices. Three examples (semiconducting and metal quantum dots, ZrO2 and Al2O3 containing composites) are described, their properties and some applications for optics and protective coatings are discussed.

Method of preparing nanoparticles.

Abstract: The invention discloses a method of preparing nanoparticles by solubilisation of an ethylene and/or propylene polyoxide polylactic copolymer in an organic solvent followed by formation of nanoparticles by mixing the solution containing the polymer with an aqueous solution by precipitation without using additional colloidal protection agent or by microfluidisation and evaporation of the solvent

Quantum Size Effect in Metal Coated Nanoparticles

Abstract: In this paper we report the synthesis of AU2S nanoparticles with a gold coating on the surface; the particles are characterized by transmission electron microscopy (TEM), electron diffraction and absorption data. The absorption spectrum is recorded during the gold coating growth process; this data demonstrates a large resonance shift during the growth process. The results are consistent with the growth of a metal shell around the particles; the theoretical model includes electron quantum confinement in the metal shell. The size dependence of the frequency shift, as well as the width of the resonance are consistent with the model.