Formation of ZnO,MgO and NiO Nanoparticles from Aqueous Droplets in Flame Reactor

Nanoparticles of ZnO, MgO and NiO were produced from droplets of aqueous salt solution in the flame spray pyrolysis reactor. Conventional spray pyrolysis, in which electrical furnace reactor is used, is reported to produce nanoparticles only from acetate precursor. If the reactor pressure is low (60torr), nitrate salt precursor is also known to produce nanoparticles. In this paper, we report that nanoparticles are produced from nitrate as well as acetate salt precursor solution when propane–oxygen diffusion flame is used to decompose aqueous aerosol droplets. At low flame temperature, however, nanoparticles are not formed and the particle morphology is similar to the morphology produced by the conventional spray pyrolysis. At high flame temperature, nanoparticles are formed, regardless of the salt type. Nanoparticles are formed at lower flame temperature from acetate salts than from nitrate salts. All nanoparticle prepared in this work were fully crystallized and the size measured from transmission electron microscopy images was 30nm. This size agreed well with the particle size calculated from X-ray diffraction and specific surface area data.     

In situ electron beam irradiated rapid growth of bismuth nanoparticles in bismuth-based glass dielectrics at room temperature

In this study, in situ control growth of bismuth nanoparticles (Bi⁰ NPs) was demonstrated in bismuth-based glass dielectrics under an electron beam (EB) irradiation at room temperature. The effects of EB irradiation were investigated in situ using transmission electron microscopy (TEM), selected-area electron diffraction and high-resolution transmission electron microscopy. The EB irradiation for 2–8 min enhanced the construction of bismuth nanoparticles with a rhombohedral structure and diameter of 4–9 nm. The average particle size was found to increase with the irradiation time. Bismuth metal has a melting point of 271 °C and this low melting temperature makes easy the progress of energy induced structural changes during in situ TEM observations. This is a very useful technique in nano-patterning for integrated optics and other applications.     

Ultrasound with low intensity assisted the synthesis of nanocrystalline TiO2 without calcination

A novel method has been developed for the preparation of nano-sized TiO₂ with anatase phase. Nanoparticles with diameter about 6 nm were prepared at a relatively low temperature (75 °C) and short time. The synthesis was carried out by the hydrolysis of titanium tetra-isopropoxide (TTIP) in the presence of water, ethanol, and dispersant under ultrasonic irradiation (500 kHz) at low intensity. The results show that variables such as water/ethanol ratio, irradiation time, and temperature have a great influence on the particle size and crystalline phases of TiO₂ nanoparticles. Characterization of the product was carried out by different techniques such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV–vis spectroscopy.     

Size effect on the melting temperature depression of Al12Mg17 complex metallic alloy nanoparticles prepared by planetary ball milling

This research investigates the synthesis and size-dependent melting point depression of complex metallic alloy (CMA) nanoparticles. Al₁₂Mg₁₇ which belongs to this new category of intermetallic materials was initially produced as pre-alloyed ingot, then homogenized to achieve single phase compound and crushed into small size powder and finally, mechanically milled in a planetary ball mill to synthesize nanoparticles. Phase and microstructural characterizations of the as-crushed and milled powders were performed using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Effects of the mechanical milling on thermal behavior of the Al₁₂Mg₁₇ nanoparticles in comparison with as-cast Al₁₂Mg₁₇ ingot has been investigated by differential scanning calorimetry (DSC) measurement. It was found that an average particle size of 24 nm with crystallite size of 16 nm was achieved after 20 h of ball milling process. The size- dependent melting point depression of the Al₁₂Mg₁₇ nanoparticles has been experimentally observed and also comparison of the obtained results with theoretical models was carried out.     

Laser-driven synthesis and magnetic properties of iron nanoparticles

Nanoparticles of iron have been prepared by laser-driven decomposition of iron pentacarbonyl vapor. In this method, an infrared laser rapidly heats a dilute mixture of precursor vapors to decompose the precursor and initiate particle nucleation. It was found that when using SF₆ as a photosensitizer during the synthesis, ferrous fluoride (FeF₂) was produced as an undesired byproduct in the product powder. The particle size, composition, and crystalline structure have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS). Results of magnetization measurements for small iron nanoparticles (about 5 nm diameter) are also presented, showing superparamagnetic behavior at room temperature, and a blocking temperature near 125 K.     

Synthesis by sol–gel process,structural and optical properties of nanoparticles of zinc oxide doped vanadium

We report the elaboration of vanadium-doped ZnO nanoparticles prepared by a sol–gel processing technique. In our approach, the water for hydrolysis was slowly released by esterification reaction followed by a supercritical drying in ethyl alcohol. Vanadium doping concentration of 10 at.% has been investigated. After treatment in air at different temperatures, the obtained nanopowder was characterised by various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL). Analysis by scanning electron microscopy at high resolution shows that the grain size increases with increasing temperature. Thus, in the case of thermal treatment at 500 °C in air, the powder with an average particle size of 25 nm shows a strong luminescence band in the visible range. The intensity and energy position of the obtained PL band depends on the temperature measurement increase. The mechanism of this emission band is discussed.     

Size Tunable Synthesis of Highly Crystalline BaTiO3 Nanoparticles using Salt-Assisted Spray Pyrolysis

Highly crystalline, dense BaTiO₃ nanoparticles in a size range from 30 to 360nm with a narrow size distribution (_g = 1.2–1.4) were prepared at various synthesis temperatures using a salt-assisted spray pyrolysis (SASP) method without the need for post-annealing. The effect of synthesis temperature on particle size, crystallinity and surface morphology of the nanoparticles were characterized by X-ray diffraction and scanning/transmission electron microscopy. The nature of the crystalline structure was analyzed by Rietveld refinement and Raman spectroscopy. The particle size decreased with decreasing operation temperature. The crystal phase was transformed from tetragonal to cubic at a particles size of about 50nm at room temperature. SASP can be used to produce high weight fraction of tetragonal BaTiO₃ nanoparticles down to 64nm in a single step.     

Novel room temperature ionic liquids of hexaalkyl substituted guanidinium salts for dye-sensitized solar cells

Nanoparticles are attracting increasing interest because of their high potential for a great number of practical applications, such as optical and electronic devices, nanoscale storage, and delivery systems. Using Cu-phthalocyanine as precursor material, we have synthesized multi-shell graphitic carbon nanospheres without and with metal encapsulation, depending on the pyrolysis conditions. The encapsulated elemental copper nanocrystals achieved using that route were of the order of 50 nm in size. The particles were characterized in detail by high-resolution transmission electron microscopy (HRTEM) and by energy filtering microscopy (EFTEM). The concentric graphitic carbon shells of the as-grown particles were clearly discernable. After in situ high-temperature annealing, an increase in the degree of order was observed. Under high-voltage electron irradiation and heating, a melting point reduction of the enclosed nanosized copper of more than 200 K could be detected, as compared to the melting point 1083 °C of bulk copper. Time-resolved imaging revealed the displacement of the melting copper by migration through the carbon shells, leaving intact carbon cages with a central hole. At intermediate stages of this process the transformation into a hexagonal morphology of the copper nanocrystals was observed. PACS 61.46.+w; 61.48.+c; 68.37.Lp     

Synthesis of single-crystal Sm-Co nanoparticles by cluster beam deposition

Single-crystal Sm-Co nanoparticles have been successfully produced by a cluster beam deposition technique. Particles have been deposited by DC magnetron sputtering using high Ar pressures on both single-crystal Si substrates and Au grids for the magnetic and structural/microstructural properties, respectively. Oxidation of the particles is prevented by using carbon buffer and cover layers. Nanoparticles have a uniform size distribution with an average size of 4.2, 6 and 7 nm at 1, 1.5 and 2 Torr of Ar pressure, respectively. At 1 Torr, the particles have the disordered 1:7 structure and a high coercivity of 19 kOe at 10 K. These particles show a superparamagnetic behavior with a blocking temperature of T_B = 145 K. From this value of T_B and the particle volume, the value of anisotropy constant K is estimated to be around 2.2 × 10⁷ ergs/cc. Heat is introduced to the particles during their flight to the substrate to increase the particle size. Nanoparticles of SmCo₅ with an average size of 15 nm and high room temperature coercivity have been produced. No change in magnetic and structural properties of the samples has been observed even after 10 months. Cluster beam deposition could play a key role for the production of rare earth nanoparticles for many applications.     

Growth of Co nanoparticles on a nanostructured θ-Al2O3 film on CoAl(1 0 0)

We have investigated the growth of Co nanoparticles on θ-Al₂O₃/CoAl(1 0 0) by means of Auger electron spectroscopy (AES), high-resolution electron energy loss spectroscopy (EELS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Due to Volmer-Weber growth, Co forms particles with a mean diameter of approximately 2.5 nm and height of 0.8 nm. Even on the entirely covered oxide, there is no Ostwald ripening and Co particles stay structurally isolated. The nanoparticles exhibit a small size distribution and tend to form chains, as predetermined by the streak structure of the oxide template. For sufficient high coverages Co-core-CoO-shell nanoparticles may be evidenced, which is explained as a result of surfactant oxygen. The nanostructured particles may open the door to numerous applications, such as in catalysis and magnetoelectronic applications, where large areas of ordered nanodots are desired.     

Size controlled synthesis of ZnO nanoparticles via electric field assisted continuous spray pyrolysis (EACoSP) reactor

ZnO nanoparticles were synthesized by the continuous spray pyrolysis technique (CoSP) and the effect of applied voltage across the spray nozzle and an annular ground electrode during spray has been studied. X-ray diffraction and transmission electron microscopy studies showed that the product has (hexagonal) wurtzite structure with the average particle size decreasing from 18.5?nm to 12.9?nm in the presence of a high DC voltage (1?kV). The higher value of the absorption peak for the nanoparticles synthesized without voltage is supportive of this behavior. The films deposited by spin coating using these nanoparticles can be used for a variety of applications, particularly as photoelectrodes for dye-sensitized solar cells.     

Non-aggregated Pd nanoparticles deposited onto catalytic supports

Nanostructured powders have shown great promise for a variety of applications including chemical gas sensors, high surface area supports for catalysis, tribology, chemical mechanical polishing, and optoelectronics. In this report, highly dispersed Pd nanoparticles with a narrow size distribution, and mean diameter of 2±0.2 nm, were deposited at room temperature onto amorphous carbon and oxide supports (TiO₂, Al₂O₃) by pulsed-laser ablation of a Pd sputtering target. Depositions were performed in Ar at a back-fill pressure of 3 mTorr after reaching a base pressure of 10^-7 Torr. Populations of uniformly dispersed particles with an interparticle spacing of 3 to 10 nm were observed by high-resolution transmission electron microscopy with little evidence of nanoparticle aggregation. The chemical compositions of individual nanoparticles were confirmed by high spatial resolution energy-dispersive X-ray spectroscopy.     

Higher surface energy of free nanoparticles

We present an accurate online method for the study of size-dependent evaporation of free nanoparticles allowing us to detect a size change of 0.1 nm. This method is applied to Ag nanoparticles. The linear relation between the onset temperature of evaporation and the inverse of the particle size verifies the Kelvin effect and predicts a surface energy of 7.2 J/m(2) for free Ag nanoparticles. The surface energy of nanoparticles is significantly higher as compared to that of the bulk and is essential for processes such as melting, coalescence, evaporation, growth, etc., of nanoparticles.     

Characterization of ZnS nanoparticles synthesized by co-precipitation method

ZnS nanoparticles are prepared by homogeneous chemical co-precipitation method using EDTA as a stabilizer and capping agent. The structural, morphological, and optical properties of as-synthesized nanoparticles are investigated using x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible(UV-Vis)absorption, and photoluminescence spectroscopy. The x-ray diffraction pattern exhibits a zinc-blended crystal structure at room temperature. The average particle size of the nanoparticles from the scanning electron microscopy image is about50 nm. The ultraviolet absorption spectrum shows the blue shift in the band gap due to the quantum confinement effect.The photoluminescence spectrum of Zn S nanoparticles shows a blue visible spectrum.     

Effects of synthesis variables on the magnetic properties of CoFe2O4 nanoparticles

Cobalt ferrite nanoparticles (CoFe₂O₄) have been synthesized using precipitation in water solution with polyethylene glycol as surfactant. Influence of various synthesis variables included pH, reaction time and annealing temperature on the magnetic properties and particle sizes has also been studied. Structural identification of the samples was carried out using Thermogravimetric and Differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy, High resolution transmission electron microscopy. Vibrating sample magnetometer was used for the magnetic investigation of the samples. Magnetic properties of nanoparticles show strong dependence on the particle size. The magnetic properties increase with pH of the precipitating medium and annealing temperature while the coercivity goes through a maximum, peaking at around 25 nm.     

Solid-stabilized emulsion formation using stearoyl lactylate coated iron oxide nanoparticles

Iron oxide nanoparticles can exhibit highly tunable physicochemical properties that are extremely important in applications such as catalysis, biomedicine and environmental remediation. The small size of iron oxide nanoparticles can be used to stabilize oil-in-water Pickering emulsions due to their high energy of adsorption at the interface of oil droplets in water. The objective of this work is to investigate the effect of the primary particle characteristics and stabilizing agent chemistry on the stability of oil-in-water Pickering emulsions. Iron oxide nanoparticles were synthesized by the co-precipitation method using stoichiometric amounts of Fe²⁺ and Fe³⁺ salts. Sodium stearoyl lactylate (SSL), a Food and Drug Administration approved food additive, was used to functionalize the iron oxide nanoparticles. SSL is useful in the generation of fat-in-water emulsions due to its high hydrophilic–lipophilic balance and its bilayer-forming capacity. Generation of a monolayer or a bilayer coating on the nanoparticles was controlled through systematic changes in reagent concentrations. The coated particles were then characterized using various analytical techniques to determine their size, their crystal structure and surface functionalization. The capacity of these bilayer coated nanoparticles to stabilize oil-in-water emulsions under various salt concentrations and pH values was also systematically determined using various characterization techniques. This study successfully demonstrated the ability to synthesize iron oxide nanoparticles (20–40 nm) coated with SSL in order to generate stable Pickering emulsions that were pH-responsive and resistant to significant destabilization in a saline environment, thereby lending themselves to applications in advanced oil spill recovery and remediation.     

Growth of β-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles by pulsed laser ablation technique

This work investigates pulsed laser ablation for Ga₂O₃ nanoparticles. Nanoparticles with diameters of 10 to 500 nm were deposited on silicon substrates in large quantities, by KrF excimer laser ablation of a GaN (99.99% purity) target in high purity nitrogen (99.9995%) background gas at room temperature, without a catalyst. The particle size and phase structure of the as-deposited nanoparticles are examined by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), and selected-area electron diffraction (SAD). FE-SEM images show that the nanoparticles aggregate to form micron-size nanoclusters at chamber pressures of 1 and 5 Torr. On the other hand, nanoparticles aggregate with chain-like nanostructures, are synthesized at high chamber pressures (10 Torr). TEM images further reveal that chain-like nanostructures are formed by the aggregation of individual spherical and ellipsoidal nanoparticles. Photoluminescence measurement shows stable and broad blue emission at 445 nm. PACS 81.20.-N; 81.15.Fg; 75.50.Vv     

Elaboration and characterization of TiO2 nanoparticles incorporated in SiO2 host matrix

Nanometer-scale TiO₂ particles have been synthesized by sol-gel method. It was incorporated in a glass-based silica aerogel. The composite was characterized by various techniques such as particle size analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and photoluminescence (PL). The bulk glass presents a strong luminescence at wavelengths ranging from 750 to 950 nm. This PL was attributed to various non-bridging oxygen hole centers (NBOHCs) defects resulting from thermal treatment and crystallization of TiO₂ at the interface between titania nanoparticles and silica host matrix.     

Gold Nanoparticles: Production,Reshaping, and Thermal Charging

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 20nm 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.     

A Rapid Method for Growth of Metal Nanoparticles on Nanowire Substrates

The production of nickel and platinum nanoparticles on silica nanowire substrates using plasma-enhanced chemical vapor deposition has been investigated. Determination of particle size and particle size distribution was done using transmission electron microscopy (TEM). Ni nanoparticle diameters were found to be between 2 and 6 nm, with particle size increasing as the substrate temperature increased from 573 to 873 K. The size of Ni nanoparticles was found to be dependent on the chamber pressure during growth. The results indicate a competition between pressure-related diffusion within the vapor and dissociation of the precursor. Pt nanoparticle diameters were consistently found to be 2.5–3.0 nm at all deposition conditions. Insufficient thermal energy within the studied range results in a minimal contribution from surface diffusion, the primary mechanism for nanoparticle growth.