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  • 1
    ISSN: 1572-896X
    Keywords: nanoparticles ; thermal plasma ; nanostructural film ; particle deposition ; silicon carbide ; film hardness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Nanostructured silicon carbide films have been deposited on molybdenum substrates by hypersonic plasma particle deposition. In this process a thermal plasma with injected reactants (SiCl4 and CH4) is expanded through a nozzle leading to the nucleation of ultrafine particles. Particles entrained in the supersonic flow are then inertially deposited in vacuum onto a temperature-controlled substrate, leading to the formation of a consolidated film. In the experiments reported, the deposition substrate temperature Ts has ranged from 250°C to 700°C, and the effect of Ts on film morphology, composition, and mechanical properties has been studied. Examination of the films by scanning electron microscopy has shown that the grain sizes in the films did not vary significantly with Ts. Micro-X-ray diffraction analysis of the deposits has shown that amorphous films are deposited at low Ts, while crystalline films are formed at high Ts. Rutherford backscattering spectrometry has indicated that the films are largely stoichiometric silicon carbide with small amounts of chlorine. The chlorine content decreases from 8% to 1.5% when the deposition temperature is raised from 450°C to 700°C. Nanoindentation and microindentation tests have been performed on as-deposited films to measure hardness, Young's modulus and to evaluate adhesion strength. The tests show that film adhesion, hardness and Young's modulus increase with increasing Ts. These results taken together demonstrate that in HPPD, as in vapor deposition processes, the substrate temperature may be used to control film properties, and that better quality films are obtained at higher substrate temperatures, i.e. Ts≈700°C.
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  • 2
    ISSN: 1572-896X
    Keywords: emulsion ; combustion ; ceramic ; nanoparticles ; synthesis ; barium titanate powder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The emulsion combustion method (ECM), a novel powder production process, was originally developed to synthesize nano-structured metal-oxide powders. Metal ions in the aqueous droplets were rapidly oxidized by the combustion of the surrounding flammable liquid. The ECM achieved a small reaction field and a short reaction period to fabricate the submicron-sized hollow ceramic particles with extremely thin wall and chemically homogeneous ceramic powder. Alumina, zirconia, zirconia–ceria solid solutions and barium titanate were synthesized by the ECM process. Alumina and zirconia powders were characterized to be metastable in crystalline phase and hollow structure. The wall thickness of alumina was about 10 nm. The zirconia–ceria powders were found to be single-phase solid solutions for a wide composition range. These powders were characterized as equiaxed-shape, submicron-sized chemically homogeneous materials. The powder formation mechanism was investigated through the synthesis of barium titanate powder with different metal sources.
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  • 3
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    Journal of nanoparticle research 1 (1999), S. 267-276 
    ISSN: 1572-896X
    Keywords: nanoparticles ; microemulsions ; reaction engineering ; formation model ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Engineering aspects of the preparation of palladium nanoparticles in non-ionic w/o-microemulsions are examined. In order to achieve reproducible synthesis conditions a semi-batch reactor with a standardized design is used. Influences of the stirring rate and of different ways of concentration control on the product properties are observed. For reproducible synthesis it is important to establish appropriate and defined preparation conditions. Monodisperse palladium particles of around 5 nm size are obtained by adding the microemulsion containing the palladium salt at a constant feed rate to the precharged microemulsion containing the reducing agent. A quantitative kinetic model is proposed to describe particle formation in microemulsions. Unknown parameters of the model have been estimated by independent examinations or can be achieved by fitting to the experimental data.
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  • 4
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    Journal of nanoparticle research 1 (1999), S. 349-352 
    ISSN: 1572-896X
    Keywords: alcohol–aqueous salt solutions ; ZrO2 ; nanoparticles ; aging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Parameters that influence ZrO2 (3-mol% Y2O3 stabilized) nanoparticles prepared by heating of alcohol–aqueous salt solutions were investigated. It revealed that the kind of alcohol used significantly affected the particle size and morphology of the as synthesized nano-ZrO2 powders. The ratio of alcohol to water (R/H) was also important to conduct the gelation process. The dispersion and sintering behavior of the powder could be optimized via aging. By carefully controlling the process, weakly agglomerated ZrO2 nanoparticles with an average particle size of 13-nm (TEM) were achieved. The classical DLVO theory was employed to clarify the effect of solvent on powder morphology, an aging mechanism was proposed as well.
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  • 5
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    Journal of nanoparticle research 1 (1999), S. 411-418 
    ISSN: 1572-896X
    Keywords: isopycnic centrifugation ; buoyant density ; drug delivery ; nanoparticles ; sucrose linear gradient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The development of polymer nanoparticles as drug carriers requires numerous steps including several in vitro evaluations in cell cultures and biocompatibility. To perform these experiments, it is crucial to express the particle concentration as the number of particles per volume unit or as the particle surface area. Calculation of these suspension characteristics can be perfomed knowing the size and the density of the nanoparticles as well as the polymer concentration. While particle size and polymer concentration are parameters being determined routinely, this study proposes to measure the density of the nanoparticle drug carriers by isopycnic centrifugation using linear sucrose gradients. The method was found to be very reproducible and it presents the advantage of being applied on a small sample of nanoparticles.
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  • 6
    ISSN: 1572-896X
    Keywords: nanoparticles ; measurements ; instrumentation ; standards ; aerosols ; colloids
    Source: Springer Online Journal Archives 1860-2000
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  • 7
    ISSN: 1572-896X
    Keywords: nanoparticles ; pulse height analysis ; aerosol ; particle size ; condensation particle counter ; light scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Several of the most common methods for measuring nanoparticle size distributions employ the ultrafine condensation particle counter (UCPC) for detection purposes. Among these methods, the pulse height analysis (PHA) technique, in which the optical response of the UCPC detector is related to initial particle diameter in the 3–10 nm range, prevails in applications where fast sampling is required or for which concentrations of nanoparticles are frequently very low. With the PHA technique, white light is required for particle illumination in order to obtain a monotonic relationship between initial particle diameter and optical response (pulse height). However, the popular, commercially available TSI Model 3025A UCPC employs a laser for particle detection. Here, we report on a novel white-light detection system developed for the 3025A UCPC that involves minimal alteration to the instrument and preserves normal counting operation. Performance is illustrated with pulse height spectra produced by differential mobility analyzer (DMA) – generated calibration aerosols in the 3–50 nm range.
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  • 8
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    Journal of nanoparticle research 2 (2000), S. 199-204 
    ISSN: 1572-896X
    Keywords: nanoscale heat transfer ; nanoparticles ; nanowires ; phonons ; superlattices ; thermal conductivity ; thin films ; microscale effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Heat conduction in nanostructures differs significantly from that in macrostructures because the characteristic length scales associated with heat carriers, i.e., the mean free path and the wavelength, are comparable to the characteristic length of nanostructures. In this communication, particularities associated with phonon heat conduction in nanostructures, the applicability of the Fourier law, and the implications of nanoscale heat transfer effects on nanotechnology are discussed.
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  • 9
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    Journal of nanoparticle research 2 (2000), S. 183-190 
    ISSN: 1572-896X
    Keywords: superlattices ; colloidal particles ; Langmuir–Blodgett films ; electrostatic complexation ; air-water interface ; nanoparticles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The formation of nanoparticle multilayer films by electrostatic immobilization of surface-modified colloidal particles at the air–water interface has been recently demonstrated by us. In this paper, we extend our study to show that multilayer assemblies consisting of metal particles of different chemical nature (hetero-colloidal particle superlattices) and size can be deposited by the versatile Langmuir–Blodgett technique. Multilayer films consisting of a different number of bilayers of gold and silver colloidal particles have been deposited and characterized using quartz crystal microgravimetry and UV–visible spectroscopy measurements. It is observed that while layer-by-layer deposition of the different colloidal particle assemblies is possible by this technique without a detectable variation in the cluster density in the different layers, a degree of post-deposition reorganization of the clusters occurs in the film. In addition to this aging behavior, the effect of different organic solvents on the reorganization process has also been studied.
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  • 10
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    Journal of nanoparticle research 1 (1999), S. 115-126 
    ISSN: 1572-896X
    Keywords: nanoparticles ; aerosol charger ; unipolar charging ; Fuchs theory ; experiments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract A novel aerosol charger has been developed, which has high efficiency and high throughput especially for nanometer particles in the size range of 3–50 nm. Unipolar charging with high ion concentration and long charging time is used to obtain the high charging efficiency. High throughput is achieved by reducing particle loss within the charger. This is accomplished by directing ion flow and aerosol flow in the same direction and by the use of sheath air flow. The charger configuration is of a longitudinal design – the direction of aerosol stream and ion stream are flowing parallel along the longitudinal axis of the charger. The charger consists of four sections: the inlet zone, the ion production zone, the unipolar charging zone, and the exit zone. In the inlet and ion production zones, unipolar ions are generated using Po210 radioactive sources with an electric field designed to separate the positive and negative ions, and to focus the selected unipolar ions into the core region of the charger. The ions with the selected polarity is then attracted to the charging zone by an uniform electric field created by a series of ring electrodes applied with a linear ramped voltage. Aerosol entering the charger is sheathed with clean gas flow in order to keep the aerosol in the core region. A novel exit design with a reversed electric field is incorporated in order to minimize the charged particles loss. The performance of the charger is first evaluated using computer simulation and then constructed for experimental validation. Experiment data have demonstrated that the charger achieves 90% and 95% charged-particles penetration efficiency and with 22% and 48% extrinsic charging efficiency at 3 and 5 nm particle sizes, respectively. These performance data represent significant improvement, over a factor of 10, compared with the existing chargers.
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  • 11
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    Journal of nanoparticle research 1 (1999), S. 317-317 
    ISSN: 1572-896X
    Keywords: nanomaterials ; nanotechnology ; nanoparticles ; World Wide Web
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
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  • 12
    ISSN: 1572-896X
    Keywords: coflow diffusion flame ; light scattering ; thermophoretic sampling ; flame hydrolysis deposition (FHD) ; fractal aggregate ; nanoparticles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The evolution of silica aggregate particles in a coflow diffusion flame has been studied experimentally using light scattering and thermophoretic sampling techniques. An attempt has been made to calculate the aggregate number density and volume fraction using the measurements of scattering cross section from 90° light scattering with combination of measuring the particle size and morphology from the localized sampling and a TEM image analysis. Aggregate or particle number densities and volume fractions were calculated using Rayleigh–Debye–Gans and Mie theory for fractal aggregates and spherical particles, respectively. Using this technique, the effects of H2 flow rates on the evolution of silica aggregate particles have been studied in a coflow diffusion flame burner. As the flow rate of H2 increases, the primary particle diameters of silica aggregates have been first decreased, but, further increase of H2 flow rate causes the diameter of primary particles to increase and for sufficiently larger flow rates, the fractal aggregates finally become spherical particles. For the cases of high flame temperatures, the particle sizes become larger and the number densities decrease by coagulation as the particles move up within the flame. For cases of low flame temperatures, the primary particle diameters of aggregates vary a little following the centerline of burner and for the case of the lowest flame temperature in the present experiments, the sizes of primary particles even decrease as particles move upward.
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  • 13
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    Journal of nanoparticle research 1 (1999), S. 163-167 
    ISSN: 1572-896X
    Keywords: Fe2O3 ; nanoparticles ; low-pressure flame ; Fe(CO)5 ; flame synthesis approach
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract A burner stabilized premixed low-pressure flame has been used to generate iron-oxide (Fe2O3) nanoparticles with sizes in the range 7–20 nm. The H2/O2/Ar flames were doped with different amounts of iron-pentacarbonyl (Fe(CO)5) with concentrations in the range 524–2096 ppm. The influence of precursor concentration on composition, structure, morphology, and size have been studied utilizing transmission electron microscopy (TEM), X-ray powder diffraction (XRD), measurements of the specific surface area (BET), and infrared spectroscopy (FT-IR). The product particles consist of both, the γ- and the α-phase of Fe2O3. Average particle sizes were measured in the range 7.4–16 nm depending on precursor concentration and flame conditions.
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  • 14
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    Journal of nanoparticle research 1 (1999), S. 215-221 
    ISSN: 1572-896X
    Keywords: nanoparticles ; magnetic materials ; microemulsions ; barium ferrite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Magnetic nanoparticles of barium ferrite (BaFe12O19) have been synthesized using a microemulsion mediated process. The aqueous cores of water-in-oil microemulsions were used as constrained microreactors for the precipitation of precursor carbonate and hydroxide particles. These precursors were then calcined at 925°C for 12 h, during which time they were transformed to the hexagonal ferrite. The pH of reaction was varied between 5 and 12, and it was found that the fraction of non-magnetic hematite (α-Fe2O3) in the particles varied with the pH of reaction, thus affecting the magnetic properties of the particles. The same precursor particles were also prepared by bulk co-precipitation reaction for comparison. It was found that the microemulsion derived nanoparticles of barium ferrite had both higher intrinsic coercivity (Hc) and saturation magnetization (σs) than the particles derived from bulk co-precipitation. Particles were analyzed by electron microscopy, X-ray diffraction, differential thermal analysis (DTA), thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The best barium ferrite particles produced by the microemulsion synthesis method yielded an intrinsic coercivity of 4310 Oe and a saturation magnetization of 60.48 emu/g.
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  • 15
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    Journal of nanoparticle research 1 (1999), S. 253-265 
    ISSN: 1572-896X
    Keywords: nanoparticles ; surface state ; reactivity ; aerosol catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Nickel nanoparticles produced by spark discharges were used as aerosol catalyst for the formation of methane. The available surface area of the particles was determined using different methods. It was found that the surface area available for nitrogen adsorption and, therefore, for the methanation reaction remained virtually constant during restructuring of the agglomerates while the surface area based on the mobility was significantly reduced. In general, the reaction parameters such as activation energy and reaction rates agree well with the values for single nickel crystals and foils. At temperatures above 350°C the activation energy and the photoelectric activity of the particles decrease indicating the formation of graphite on the particle surface. Also the change of the work function points to the build up of multiple layers of graphite on the particle surface. The surprisingly low temperature for the surface deactivation may indicate an enhanced formation of carbon atoms at the surface.
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  • 16
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    Journal of nanoparticle research 1 (1999), S. 353-368 
    ISSN: 1572-896X
    Keywords: dendrimers ; nanoparticles ; polymer-inorganic nanocomposites ; templates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Structural types of dendrimer nanocomposites have been studied and the respective formation mechanisms have been described, with illustration of nanocomposites formed from poly(amidoamine) PAMAM dendrimers and zerovalent metals, such as gold and silver. Structure of {(Au(0))n−PAMAM} and {(Ag(0))n−PAMAM} gold and silver dendrimer nanocomposites was found to be the function of the dendrimer structure and surface groups as well as the formation mechanism and the chemistry involved. Three different types of single nanocomposite architectures have been identified, such as internal (‘I’), external (‘E’) and mixed (‘M’) type nanocomposites. Both the organic and inorganic phase could form nanosized pseudo-continuous phases while the other components are dispersed at the molecular or atomic level either in the interior or on the surface of the template/container. Single units of these nanocomposites may be used as building blocks in the synthesis of nanostructured materials.
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  • 17
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    Journal of nanoparticle research 1 (1999), S. 329-347 
    ISSN: 1572-896X
    Keywords: nanoparticles ; self assembly ; nanotechnology ; precipitation ; elastic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The use of strain to direct the assembly of nanoparticle arrays in a semiconductor is investigated experimentally and theoretically. The process uses crystal strain produced by a surface structure and variations in layer composition to guide the formation of arsenic precipitates in a GaAs-based structure grown at low temperature by molecular beam epitaxy. Remarkable patterning effects, including the formation of single and double one-dimensional arrays with completely clear fields are achieved for particles in the 10-nm size regime at a depth of about 50-nm from the semiconductor surface. Experimental results on the time dependence of the strain patterning indicates that strain controls the late stage of the coarsening process, rather than the precipitate nucleation. Comparison of the observed particle distributions with theoretical calculations of the stress and strain distributions reveals that the precipitates form in regions of maximum strain energy, rather than near extremum points of hydrostatic stress or dilatation strain. It is therefore concluded that the patterning results from modulus differences between the particle and matrix materials rather than from other strain related effects. The results presented here should be useful for extending strain directed assembly to other materials systems and to other configurations of particles.
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  • 18
    ISSN: 1572-896X
    Keywords: STM ; nanoparticles ; colloids ; Met-Cars ; photon emission ; spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Scanning tunneling microscopy can be used to isolate single particles on surfaces for further study. Local optical and electronic properties coupled with topographic information collected by the scanning tunneling microscope (STM) give insight into the intrinsic properties of the species under study. Since each spectroscopic measurement is done on a single particle, each sample is ‘monodisperse’, regardless of the degree of heterogeneity of the original preparation. We illustrate this with three example systems – a metal cluster of known atomic structure, metal nanoparticles dispersed from colloid suspensions, and metallocarbohedrenes (Met-Cars) deposited with other reaction products. Au and Ag nanoparticles were imaged using a photon emission STM. The threshold voltage, the lowest bias voltage at which photons are produced, was determined for Au nanoparticles. Electronic spectra of small clusters of Ni atoms on MoS2 were recorded. Preliminary images of Zr-based Met-Car-containing soot were obtained on Au and MoS2 substrates and partial electronic spectra were recorded of these possible Met-Car particles.
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  • 19
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    Journal of nanoparticle research 2 (2000), S. 147-155 
    ISSN: 1572-896X
    Keywords: benzene ; nanoclusters ; ion chemistry ; lasers ; mass spectrometry ; nanoparticles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Molecular clusters represent a nanoscale test tube where chemical reactions can be examined in a unique way for the effects of the local environment and the possibility of size-dependent reactions. Previous experiments have shown that the ionization/dissociation of iron pentacarbonyl clusters can lead to the formation of iron ions and iron cluster ions and that these species can further react with dopant molecules to yield chemically rearranged products. The present experiments characterize similar reactions with benzene molecules and clusters. Heteroclusters of the form [Fe(CO)5]m(C6H6)nArp are created in an expanding supersonic jet of the component molecules. Following ionization by a 30 ps, 266 nm laser pulse, extensive dissociation, aggregation, and chemical rearrangement occurs leading to ionic products which are characterized by mass spectrometry. Cluster ions of the type Fem(C6H6)n + are observed as products. The stability of the sandwich form of the ion, Fe(benzene)2 +, is inferred from the data. Evidence for a similar special stability for the double-decker, Fe2(benzene)3 +, is presented.
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  • 20
    ISSN: 1572-896X
    Keywords: tuberculosis ; nanoparticles ; antituberculosis drugs ; Mycobacterium tuberculosis ; drug delivery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract This is the first report evaluating the nanoparticle delivery system for three antituberculosis drugs: isoniazid, rifampin, and streptomycin. The typical particle size is 250 nm. We studied accumulation of these drugs in human monocytes as well as their antimicrobial activity against Mycobacterium tuberculosis residing in human monocyte-derived macrophages. Nanoparticle encapsulation increased the intracellular accumulation (cell-association) of all three tested drugs, but it enhanced the antimicrobial activity of isoniazid and streptomycin only. On the other hand, the activity of encapsulated rifampin against intracellular bacteria was not higher than that of the free drug.
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  • 21
    ISSN: 1572-896X
    Keywords: hydrothermal synthesis ; nanoparticles ; surface photovoltage ; spectroscopy ; surface state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Two SnO2 nanoparticles were synthesized by hydrothermal method at 170 °C and 180 °C, respectively. Transmission electron microscope observations reveal that the diameters of both the nanoparticles are around 6 nm. At the same time, surface photovoltage spectroscopy measurements show that the nanoparticle synthesized at 180 °C has more surface electronic states at 0.3 eV below the conduction band than the one synthesized at 170 °C. This means that the temperatures chosen in hydrothermal synthesis have significant influence on the surface electronic characteristics of resultant SnO2 nanoparticles but the effect on their sizes is not obvious. However, after being calcined at 500 °C for 2 h, the diameter of the nanoparticle synthesized at 180 °C increased to 23 nm and that of the nanoparticle synthesized at 170 °C increased to 32 nm as calculated from X-ray diffraction pattern.
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  • 22
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    Journal of nanoparticle research 2 (2000), S. 363-373 
    ISSN: 1572-896X
    Keywords: nanoparticles ; ZnO ; Al2O3 ; ZnAl2O3 ; flame ; synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Zinc oxide (ZnO) and alumina (Al2O3) particles are synthesized by the combustion of their volatilized acetylacetonate precursors in a premixed air–methane flame reactor. The particles are characterized by XRD, transmission electron microscopy, scanning mobility particle sizing and by measurement of the BET specific surface area. Pure (γ-)alumina particles appear as dendritic aggregates with average mobile diameter 43–93 nm consisting of partly sintered, crystalline primary particles with diameter 7.1–8.8 nm and specific surface area 184–229 m2/g. Pure zinc oxide yields compact, crystalline particles with diameter 25–40 nm and specific surface area 27–43 m2/g. The crystallite size for both oxides, estimated from the XRD line broadening, is comparable to or slightly smaller than the primary particle diameter. The specific surface area increases and the primary particle size decreases with a decreasing flame temperature and a decreasing precursor vapour pressure. The combustion of precursor mixtures leads to composite particles consisting of zinc aluminate ZnAl2O4 intermixed with either ZnO or Al2O3 phases. The zinc aluminate particles are dendritic aggregates, resembling the alumina particles, and are evidently synthesized to the full extent allowed by the overall precursor composition. The addition of even small amounts of alumina to ZnO increases the specific surface area of the composites significantly, for example, zinc aluminate particles increases to approximately 150 m2/g. The gas-to-particle conversion is initiated by the fast nucleation of Al2O3 or ZnAl2O3, succeeded by a more gradual condensation of the excess ZnO with a rate probably controlled by the cooling rate for the flame.
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  • 23
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    Journal of nanoparticle research 2 (2000), S. 375-380 
    ISSN: 1572-896X
    Keywords: mechanochemical processing ; CaCO3 ; nanoparticles ; ball milling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The synthesis of calcite (CaCO3) nanoparticles by mechanochemical reaction and subsequent heat treatment was investigated. A solid-state displacement reaction CaCl2 + Na2CO3 → CaCO3+2NaCl was induced during mechanical milling of a CaCl2+ Na2CO3 powder mixture. Heat treatment of the as-milled powder at 350°C completed the reaction, forming crystalline CaCO3 nanoparticles separated from each other in a dry-salt matrix. A simple washing process to remove the matrix yielded calcite single phase ultrafine powder. The mean particle size was controlled by changing the volume fraction of CaCO3 in the matrix. 20% volume fraction yielded nanoparticles of ~ 140 nm in size, whereas 10% volume fraction led to ~ 80 nm size nanoparticles.
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  • 24
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    Journal of nanoparticle research 1 (1999), S. 495-499 
    ISSN: 1572-896X
    Keywords: optical tweezers ; nanoparticles ; particle-medium interaction ; dynamic mechanical testing ; dynamic moduli ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract We report a new application of the optical tweezers, where a harmonically driven oscillating tweezer is combined with the forward light scattering and lock-in amplification techniques, for probing the mechanics of nanostructures in soft materials in a broad frequency range. Model independent dynamic moduli G′ and G″ of the material at a localized, sub-micron area can be measured directly from the displacement and the phase shift of the particle in the oscillating trap. The probe particles can be as small as 200 nm and the displacement of the particle was in the range of a few nanometers. To illustrate the new methodology, we show the microscopic viscoelastic properties of a transient polymer network in the vicinity of a silica bead.
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  • 25
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    Journal of nanoparticle research 1 (1999), S. 9-15 
    ISSN: 1572-896X
    Keywords: chain aggregates ; aerosol aggregates ; nanoparticles ; titania nanoparticles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Studies of the behavior of nanoparticle chain aggregates (NCA) have shown properties similar to those of molecular polymers. Like polymer chains, NCA tend to gather up and become more compact when heated. Under tensile stress, folded chain segments pull out and the NCA elongates. When the tension is relaxed, the chains contract. The stretching of NCA may contribute to the ductility of compacts made from nanoparticles, a subject of current research interest. In a well established technological application, carbon black and pyrogenic silica NCA produce remarkable increases in elastic modulus and tensile strength when added to commercial rubber. This may be due to the mechanical interaction between the polymer chains and NCA. However, basic mechanisms of NCA elasticity differ from those of molecular polymers. The alignment of chain segments when the NCA are subjected to tension probably results from rotation and translation at grain boundaries between neighboring nanocrystals. The elastic properties depend on the van der Waals forces between segments of the chain that fold to minimize surface free energy. Under tension, these segments pull out, but tend to reform when the tension is relaxed. The processes that lead to NCA formation and control the strength of interparticle bonds are briefly reviewed.
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  • 26
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    Journal of nanoparticle research 1 (1999), S. 137-139 
    ISSN: 1572-896X
    Keywords: molecular self-assembly ; nanoelectronics ; nanoparticles ; biostructures
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  • 27
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    Journal of nanoparticle research 1 (1999), S. 185-195 
    ISSN: 1572-896X
    Keywords: charged aerosols ; coagulation ; charge distribution ; population balance ; nanoparticles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract We consider the coagulation of an aerosol embedded in a stationary atmosphere of bipolar ions. Particles respond to the ionic environment by developing an instantaneous charge the fluctuations of which may produce attraction or repulsion between the particles. The governing parameter is the charge asymmetry factor which quantifies the relative charging efficiency of positive and negative ions. We use a Monte Carlo method to solve the coagulation equation in the free-molecule regime. We perform simulations for conditions ranging from symmetric and nearly symmetric environments (e.g. flames, ionizers), which result in particles that are on the average neutral to highly asymmetric conditions (low-pressure plasmas), which produce a substantial non-zero net charge. In symmetric ionic atmospheres we find that electrostatic interactions are unimportant and particles grow as if in the absence of charging ions. In asymmetric bipolar atmospheres, electrostatic interactions between particles are repulsive, the mean particle size grows logarithmically in time and the resulting size distributions are significantly narrower than the classical self preserving distributions.
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  • 28
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    Journal of nanoparticle research 1 (1999), S. 243-251 
    ISSN: 1572-896X
    Keywords: gold ; nanoparticles ; size selection ; thermal charging ; particle synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: 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.
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  • 29
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    Journal of nanoparticle research 1 (1999), S. 277-291 
    ISSN: 1572-896X
    Keywords: nanoparticles ; specific surface area ; surface melting ; coalescence ; surface diffusion ; flame particle synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Surprisingly, there is still no rational yet practical method to reliably predict absolute ‘primary’ nanospherule sizes and, hence, specific surface areas, in gas phase flame nanoparticle synthesis. The present paper summarizes our approach to this important problem, using a plausible and tractable coagulation–coalescence (two-rate process) model, but with an important modification to the rate of nanoparticle coalescence. The Smoluchowski equation is used to describe the particle Brownian coagulation rate process (free-molecule regime), together with the assumption that the particle population follows a self-preserving size distribution. The decisive coalescence process, driven by the minimization of surface energy of the coalescing nanoparticles, is presumed to occur via the mechanism of surface diffusion. However, a curvature-dependent energy barrier for surface-diffusion is proposed, taking into account the extended ‘surface-melting’ behavior of nanoparticles. This is shown here to have the effect of accelerating the coalescence rate of touching nanoparticles, leading to absolute sizes (at the predicted onset of aggregate formation) in encouraging agreement with available experiments. It was found that the coalescence rate, especially with a curvature-augmented surface diffusivity, is far more sensitive to particle size than is the Brownian coagulation rate. As a result, when cast in terms of characteristic process times, a distinct crossover generally exists, allowing the determination of observed ‘primary’ spherule sizes within larger aggregates. This approach is successfully applied here to several published synthesis examples of vapor-derived nanosized alumina and titania. Its broader implications for nanoparticle synthesis in non-isothermal reactors, including our own counterflow diffusion flame reactor, are also briefly summarized.
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  • 30
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    Journal of nanoparticle research 1 (1999), S. 393-396 
    ISSN: 1572-896X
    Keywords: magnetite ; nanoparticles ; forced mixing ; wet synthesis approach ; superparamagnetism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Synthesis of magnetite nanoparticles by precipitation with forced mixing is presented. Using this method it is easy to obtain a high product saturation degree and the constant pH value of the reaction system. The TEM and XRD measurments show that the average size of the product magnetite particles is less than 6.0-nm in the condition of [Fe2+]/[Fe3+]=0.5. The magnetic properties of the samples are discussed.
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  • 31
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    Journal of nanoparticle research 1 (1999), S. 379-392 
    ISSN: 1572-896X
    Keywords: nanoparticles ; aero-sol-gel ; aerosol ; sol-gel ; hydrolysis/condensation ; silica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract This paper discusses a new approach to the synthesis of nano-structured oxides where sol-gel reactions are carried out in aerosol droplets. This aero-sol-gel (ASG) reactor allows for manipulation of the structure, chemical composition and surface area of silica powders through variation of process parameters. ASG powders differ in nanostructure from other continuous process powders such as pyrolytic and solution-route powders. ASG powders contain mesopores (〉2-nm) and micropores (〈2-nm), the mesopores being responsible for high surface areas measured by nitrogen adsorption using BET theory. Primary particles of close to molecular scale are believed to lead to exceedingly large specific surface areas on the order of 600-m2/g. These primary particles aggregate into nanometer scale mass-fractal aggregates that cluster in micron scale agglomerates. Under controlled reaction conditions the powder structure is reproducible as measured by small-angle X-ray scattering, SAXS, analysis. The ASG reactor displays transport effects similar to those previously seen in laminar flame reactors as evidenced by the effect of reactor geometry and reactant concentration on product structure.
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  • 32
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    Journal of nanoparticle research 1 (1999), S. 439-458 
    ISSN: 1572-896X
    Keywords: nanoparticles ; quantum size ; photocatalysis ; dopants ; sensitization ; nanocrystalline films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The aim of this review paper is to give an overview of the development and implications of nanotechnology in photocatalysis. The topics covered include a detailed look at the unique properties of nanoparticles and their relation to photocatalytic properties. Current applications of and research into the use of nanoparticles as photocatalysts has also been reviewed. Also covered is the utilization of nanoparticles in doped, coupled, capped, sensitized and organic–inorganic nanocomposite semiconductor systems, with an effort to enhance photocatalytic and/or optical properties of commonly used semiconductor materials. The use of nanocrystalline thin films in electrochemically assisted photocatalytic processes has been included. Finally, the use of nanoparticles has made a significant contribution in providing definitive mechanistic information regarding the photocatalytic process.
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  • 33
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    Journal of nanoparticle research 2 (2000), S. 205-208 
    ISSN: 1572-896X
    Keywords: ultrafine particles ; nanoparticles ; condensation nuclei ; condensation particle counter ; indoor air quality ; sick building syndrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Poor indoor air quality (IAQ) can cause a variety of health problems for building occupants including headaches, respiratory problems, eye irritation and fatigue. Traditional IAQ measurements often fail to identify the root cause of the problems and solutions remain elusive. A new IAQ metric, ultrafine particles, is shown to have a high correlation with complaint areas. Researchers are studying the toxicology of these tiny pollutants on animals and humans. Ultrafine particles are defined as particles smaller than 100 nm diameter; ‘nanoparticles’, those smaller than 50 nm diameter, are a subset of ultrafine particles. A battery-powered, portable condensation particle counter (CPC) can be used to quickly identify the source and transport pathways of ultrafine particle contaminants so they can be eliminated or controlled. The CPC condenses isopropyl alcohol on the particles to grow them to an optically detectable size. The hand-held instrument is fast responding, has a wide concentration range, and can log data to detect trends and short-term excursions. Adding the metric of ultrafine particles may become very important to IAQ investigations in the future.
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  • 34
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    Journal of nanoparticle research 2 (2000), S. 305-308 
    ISSN: 1572-896X
    Keywords: magnetite ; mechanochemical activation ; nanoparticles ; Mössbauer spectroscopy ; particle size effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Using Mössbauer spectroscopy as a function of ball milling time, it was found that nanomagnetite behaves differently than magnetite during mechanochemical activation. The phase sequence is determined by the original particle size of the powder. Magnetite suffers a phase transformation to hematite, while nanomagnetite (d = 19 nm) gives rise to superparamagnetism as effect of prolonged milling.
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  • 35
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    Journal of nanoparticle research 2 (2000), S. 237-248 
    ISSN: 1572-896X
    Keywords: nanoparticles ; nanotubes ; manipulation ; AFM ; friction ; tribology ; mechanics ; nanometer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract In this overview, we will give an introduction to experiments in which manipulation is used a means of uncovering the intrinsic response and dynamical behavior of small objects. Experiments done on individual particles reveal new and rich behaviors that are inaccessible to averaging methods. Experiments exploring the stiffness and toughness of carbon nanotubes will be presented showing that nanometer scale engineered materials can far outperform current engineering materials. Through AFM manipulation, imaging and force measurements, the stiffness of this material was found to equal or exceed diamond. Their toughness is also extraordinary. Due to their near crystalline perfection, carbon nanotubes are able to undergo strains exceeding 15% during bending without damage. Through AFM manipulation experiments, these large deformations have been shown to be highly reversible. Experiments in which the lateral force of manipulation of small objects across surfaces is measured show that friction at the nanometer scale occurs without wear processes and is an intrinsic property of the particular interface. Results are also presented showing anisotropic behavior in friction and movement due to commensurate lattice effects. At the nanometer scale, the contacting surfaces can be nearly perfect so that commensurate effects are not partially averaged out by many differently oriented domains. It has been shown that friction can very over an order of magnitude depending on the relative orientation of the contacting surfaces. The relative orientation of object and substrate lattices also can determine the modes of motion. In some cases the particle is confined to move in one direction. In other cases the relative orientation determines whether the particle rolls, rotates in-plane or slides. These effects may have implications on the fundamental mechanisms of friction. They provide a laboratory for testing different geometrical configurations of atoms sliding on atoms. The results may also have implications in the design of nanometer scale electromechanical mechanisms.
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    ISSN: 0021-9304
    Keywords: poly(lactic acid) ; nanoparticles ; protein adsorption ; two-dimensional polyacrylamide gel electrophoresis ; complement activation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: After intravenous administration, nanoparticles suffer a major drawback in that they are rapidly and massively taken up by the cells of the mononuclear phagocyte system. The mechanisms involved in the opsonization, adhesion, and internalization of biodegradable nanoparticles by the mononuclear phagocyte system are still poorly understood. In this work, the kinetics of blood protein adsorption onto nanoparticles of poly(D,L-lactic acid) prepared by the salting-out technique was investigated. Nanoparticles of 312 nm were incubated for variable periods of time (5-60 min) in human serum and citrated plasma. After incubation, the particles were washed and the proteins detached from them, denatured, and analyzed by two-dimensional polyacrylamide gel electrophoresis. In plasma, the predominant protein was immunoglobulin G (IgG), and the amount adsorbed was not dependent on incubation time. Albumin amounts were high for short incubation periods but decreased as a function of time, whereas apolipoprotein E levels increased significantly as a function of the incubation period. Owing to the possible complement cascade inactivation by addition of citrate to plasma, the kinetics of adsorption was also evaluated in serum. In this medium, adsorption of complement C3 components onto the surface of the nanoparticles was clearly evidenced by spots of increasing intensity and area, reaching levels comparable to those of the omnipresent IgG. This result confirms the important role of complement components in the opsonization process of poly(D,L-lactic acid) particles. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 37, 229-234, 1997.
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    Journal of Biomedical Materials Research 39 (1998), S. 478-485 
    ISSN: 0021-9304
    Keywords: nanoparticles ; protein adsorption ; 2-D PAGE ; drug targeting ; colloidal drug carriers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Plasma protein adsorption patterns on colloidal drug carriers acquired after iv administration depend on their surface characteristics and are regarded as key factors for their in vivo organ distribution. Polymeric latex particles with strongly differing surface properties were synthesized as models for colloidal drug carriers for tissue-specific drug targeting via the intravenous route. Physicochemical characterization was performed for size, surface charge density, zeta potential, and surface hydrophobicity. The interactions with human plasma proteins were studied by way of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). Considerable differences in protein adsorption on the latex particles were detected with regard to the total amount of surface-bound protein on the various particle types as well as specific proteins adsorbed, for example, fibrinogen, albumin, and a recently identified plasma glycoprotein. Possible correlations between protein adsorption patterns and the physicochemical characteristics and topography of the polymeric surfaces are shown and discussed. Knowledge about protein-nanoparticle interactions can be utilized for the rational design of colloidal drug carriers and also may be useful for optimizing implants and medical devices. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 478-485, 1998.
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