Effect Of Precursor Concentration Research Articles

The Effect of Precursor Concentration, Temperature and Capping Group on the Morphology of CdS Nanoparticles

A novel ligand to the synthesis of nanoparticles has been employed in this study. A Tetramethylthiuram disulphide cadmium complex (abundant in sulphur atoms) was used as a single-source precursor for the synthesis of CdS nanoparticles. The CdS nanoparticles were synthesized under various conditions and were characterized using UV/Vis, PL, XRD and TEM. The influence of the precursor concentration, temperature and capping environment as factors affecting the morphology and size of the nanoparticles was investigated. We observed that with an increase in precursor concentration, there was an increase in particle sizes and the morphology evolved from spherical to rod-shaped nanoparticles. An increase in temperature showed only evidence of increasing the particle sizes whilst the capping environment had a profound influence on the morphology of the nanoparticles. The work reported in this paper demonstrate that factors such as temperature, concentration and the capping group affects the growth of nanoparticles either in size and/or shape.

High pressure hydrothermal synthesis of cuprous oxide microstructures of novel morphologies

In this paper, “fiber-like” Cu 2O bundles and “tower-like” Cu 2O were successfully synthesized from a Cu(CH 3COO) 2 precursor under hydrothermal conditions related with pressure, examined by means of scanning electron microscopy, and X-ray diffraction. The effects of precursor concentration, pressure on the evolution of Cu 2O synthesis and morphology were investigated. The pressure were found to play a key role in the formation of “fiber-like” bundles, and “tower-like” Cu 2O. A possible mechanism was used to explain the formation of the resultant Cu 2O. As claimed by the results, pressure could offering a very powerful way for the synthesis of novel morphologies. The present study attempts to shed some light on the roles that pressure play in influencing the microstructures of the cuprous oxide particles.

Dependence of the properties of hydrothermally grown ZnO on precursor concentration

This study evaluated the effects of precursor concentration ranging from 0.06 to 1.5 M on the properties of hydrothermally grown ZnO on annealed ZnO buffered Si substrates. At relatively low concentrations (no more than 0.5 M), well-aligned ZnO arrays were grown on ZnO/Si(1 0 0) due to heterogeneous nucleation. As the concentration was increased to 1.0 M, the morphologies changed to randomly accumulated particles as a result of homogeneous nucleation. The crystal and optical properties of the materials were investigated by X-ray diffractometer (XRD) and photoluminescence (PL) measurement, respectively. It was found that the best crystal and optical properties were obtained with concentrations of 0.5 and 0.3 M, respectively. These properties were observed to degrade when the concentration was raised to more than 1.0 M.

Microwave-assisted synthesis of ZnO micro-javelins

The microwave (MW)-assisted formation of ZnO micro-javelins from zinc nitrate and urea in aqueous solution is described. The particles (named as ‘micro-javelins’ because of their high aspect ratio and needle-like tips) grow hexagonally with well-defined facets in the 〈010〉 direction and pointed tips in (0001) direction. Powder X-ray diffraction patterns show the appearance of a strikingly dominant (1000) orientation. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations reveal the morphological evolution of these hexagonal ZnO particles with time. The effect of precursor concentrations, counterion type and MW irradiation power and their consequent influence on pH and Zn2+ ion concentration are investigated. A mechanism for the formation of the micro-javelins is postulated. The microwave induced supersaturation of Zn(OH)+ species under the weakly basic pH condition and the initial growth through the (000) direction (oxygen-rich face) are proposed to be the key factors that dictate the formation of these ZnO micro-javelins. The present one-step microwave process is a straightforward and a reproducible method for the bulk synthesis of defect-free ZnO micro-javelins, which would find potential applications in microelectronic devices (e.g. lasers, cantilevers in surface probing equipment, etc.).

Effect of precursor concentration on the properties of ITO thin films

Abstract Tin-doped indium oxide (ITO) thin films have been prepared by the spray pyrolysis method using indium chloride as a precursor and stannic chloride as a dopant. The effect of a precursor concentration on the structural, morphological, electrical and optical properties of films has been studied. The concentration of InCl 3 in the spraying solution is varied from 6.25 to 37.5 mM keeping doping percentage of tin fixed at its optimized value of 5 wt.%. Bare glass is used as a substrate and oxygen as the carrier and reaction gas. X-ray diffraction (XRD) patterns show that films are polycrystalline and their crystallinities are dependent on the precursor concentration. A surface morphology has been observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The typical ITO film has minimum resistivity value of 2.71 × 10 −3 Ω cm, whose carrier concentration and mobility were 7.45 × 10 19 cm −3 and 31 cm 2 /(V s), respectively. In addition, the best ITO film has optical transmittance of 94.4% and figure of merit 1.20 × 10 −3 Ω −1 .

Preparation of prussian blue nanoparticles with single precursor

Fe 4[Fe(CN) 6] 3 nanoparticles were prepared with potassium ferrocyanide as the single precursor. The effects of precursor concentration and temperature on the particles were investigated. The reaction mechanism was explained. Calculation showed that formation of Fe 4[Fe(CN) 6] 3 precipitates and volatile HCN greatly reduce the electron potential of Fe 3+/Fe 2+ and increase the reaction extent of the oxidation of ferrous ions.

Growth mechanism of lanthanum phosphate particles by continuous precipitation

Lanthanum phosphate, a matrix material of green phosphor, was synthesized by using a T-shaped mixer-type tubular reactor which enabled continuous precipitation of the particles having a uniform diameter. Effects of precursor concentrations and residence time on the yield, number density, diameter, and aspect ratio of particles were investigated for discussing the particle growth mechanism. Particularly, in order to observe the initial stage of particle growth, the residence time was varied over six orders ranging from 0.4 ms to 120 s by employing tubes of 250 μ m in inner diameter and a newly developed fast particle sampling device. The lanthanum phosphate yield was proportional to the concentration product of the precursors, lanthanum ion and dihydrogen phosphate ion, at the inlet of the reactor, while the number density of the particles was proportional to the 2.3th power of the precursor concentration product. The particles formation was practically completed within 0.01 s. Then, the particles grew slowly up to a few micrometers in diameter by growth of radiating acicular crystallites.

Hydrothermal synthesis and characterization of rare earth doped ceria nanoparticles

Ceria (CeO 2) and rare earth doped ceria (RE = Pr, Gd and Sm) of different doping concentration (10, 20 and 30 mol%) were synthesized by hydrothermal synthesis method, achieving nano-particles with weak agglomeration. The nano-particles were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), BET specific surface area measurement and thermal analysis. The size of all doped nano-particles was in the range of 13–25 nm, while the un-doped ceria nano-particles were in the range of 12–16 nm. The effect of precursor concentration on microstructure and morphology of the final powder is reported in this paper. The increase of precursor concentration led to decreases in crystallite size, increase in lattice parameter and increase in the BET specific surface area with Ce 3+ from 0.005 to 0.015 M. The highest rare earth doping ratio is found to be 20, 10 and 20 mol% for Pr, Gd and Sm, respectively.

Low temperature wet chemical synthesis of good optical quality vertically alignedcrystalline ZnO nanorods

The growth of ZnO nanorods on Au-coated ITO substrates using a low temperature wetchemical process is presented. Electron microscopy and x-ray diffraction observationsreveal that the crystalline ZnO nanorods are preferentially oriented along thec axis. Room temperature photoluminescence (PL) measurements reveal a strong band edgeemission at 382 nm, a signature of good crystallinity, with a weak and broad orange–redemission, which is typically attributed to the oxygen interstitials, in the range between 520and 720 nm. Other than the second order feature of the band edge emission at 760 nm, nored or near-infrared bands are observed. The effect of precursor concentration on themorphological, structural and PL properties are studied, and the results are discussed.

Effect of precursor concentration on the characteristics of nanoscale zerovalent iron and its reactivity of nitrate

Differing precursor concentrations, 1.0, 0.1, and 0.01 M FeCl 3·6H 2O, were performed to produce nanoscale Fe 0 and the results were discussed in terms of the specific surface area, particle size and electrochemical properties. The results indicated that the nanoscale Fe 0 prepared by 0.01 M FeCl 3 had absolutely reduced in size (9–10 nm) and possessed the greatest specific surface area (56.67 m 2 g −1). These synthesized nanoscale Fe 0 particles were attempted to enhance the removal of 40 mg-N L −1 unbuffered nitrate solution. The first-order degradation rate constants ( k obs) increased significantly (5.5–8.6 times) with nanoscale Fe 0 prepared by 0.01 M precursor solution ( Fe 0.01 M 0 ) . When normalized to iron surface area concentration, the specific rate constant ( k SA) was increased by a factor of approximately 1.7–2.4 using Fe 0.01 M 0 (6.84×10 −4 L min −1 m −2 for Fe 0.01 M 0 , 4.04×10 −4 L min −1 m −2 for Fe 0.1 M 0 and 2.80×10 −4 L min −1 m −2 for Fe 1 M 0 ). The rise of reactivity of the reactive site on the Fe 0.01 M 0 surface was indicated by the specific rate constant ( k SA) calculation and the i 0 value of the electrochemical test.

Directed Mineralization on Polyelectrolyte Multilayer Films

ABSTRACTSilica formation aided by polypeptides is being actively investigated for a wide range of applications including biomaterials synthesis, ceramics and controlled release systems. We envision that biocatalyzed mineralization could have application as a dental material where in situ formation of mineral layers could provide needed wear-resistance or sealing capability. The approach would be more clinically relevant, if a polymer host could be used to carry and specifically position the biocatalyst on a surface and additionally maintain the catalyst activity.Accordingly, we studied the influence of simple catalytic polypeptides on silica formation from prehydrolyzed alkoxide precursor solutions onto a surface. The polypeptides were localized on to the surface as multilayered thin films using the layer-by-layer (LbL) assembly of polyelectrolytes. Polylysine (PLL) or another biocatalytic polycation, poly(ethyleneimine) (PEI), was adsorbed layer-by-layer up to 10 bilayers on silicon wafers in combination with a negatively charged polyelectrolyte polymer host, poly(sodium-4-styrene sulfonate) (PSS) to prepare PEI-(PLL/PSS)10, PEI-(PEI/PSS)10 and PEI-(PEI/PSS/PLL/PSS)10 multilayer films. Pre-hydrolyzed alkoxysilane solutions were placed dropwise on the catalytic films for silicification. Additionally, the effects of precursor concentration, solvent and drying were evaluated. The morphology, roughness and contact mechanical stiffness of the formed silica were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM).The resulting silica morphology was plate-like or spherical, and porous with average particle size depending on the catalyst and its positions on the surface. Without a catalyst the silica formed over longer times with a fine, gel-like appearance. The morphology of silica produced on the substrate was different from that of particles catalyzed in solution with the same polypeptide catalyst. Additionally, it was found that the homogeneity of PEI-(PLL/PSS)10 films increased with drying temperature, silica precursor concentration and the presence of ethanol. The contact mechanical stiffness of the silica particles (40 N/m) catalyzed from PEI-(PLL/PSS)10 films was lower than the non-silicified areas (48 N/m) suggesting that regions of the silica were amorphous and hydrated. These results show that a polypeptide applied to a surface as a multiple layer with an oppositely charged polymer host (PSS) maintains its activity for silicification. The generally coherent nature of the mineral coating suggests its potential for enhancing critical restorative dental interfaces; however properties like porosity, hydration and their effect on hardness and permeability will need further study.

High-Growth-Rate Chemical Vapor Deposition of Silicon: an Experimental and Modeling Approach

Abstract The chemical vapor deposition (CVD) process of silicon from silane has been analyzed by a combined experimental and modeling approach with the aim to optimize growth rate, yield and deposition quality of polycystalline silicon while minimizing gas phase nucleation. The effects of precursor concentration, flow rate and buffer gas have been investigated. Modeling of the gas phase and of the deposition process has been used in a parameter screening to select appropriate deposition conditions in a stagnation-point cold-wall CVD reactor. Deposition experiments have been performed for several silane concentrations with helium, nitrogen and hydrogen as the buffer gases. Polycrystalline films of good quality were obtained with growth rates up to 8 μm/min. The observed trends in the experiments are in good qualitative agreement with model predictions. To achieve high film growth rates and minimal gas phase nucleation, hydrogen is suggested as the diluent gas, potential reasons for this being its involvement in gas phase and surface reactions.

Palladium nanoparticles on silicon by photo-reduction using 172 nm excimer UV lamps

We report a photochemical procedure induced by ultraviolet (UV) radiation for the preparation of palladium (Pd) nanoparticles on silicon surface at room temperature. Palladium acetate (Pdac, Pd(OCOCH3)2) was used as the precursorwhich was sprayed-on to the Si and irradiated by UV light at a wavelength of 172nm. Scanning electron microscope (SEM), AFM, XRD, and UV-Vis spectroscopy have been used to characterize the as-prepared nanoparticles. The mechanism of growth of Pd particles and the photo-reduction induced by UV radiation are discussed. The effects of precursor concentration, UV-irradiation time, and annealing conditions on the size and distribution of the palladium nanoparticles on Si are also reported.

Water-in-Oil Microemulsion Synthesis of Platinum−Ruthenium Nanoparticles, Their Characterization and Electrocatalytic Properties

Mixed platinum−ruthenium nanoparticles are prepared by water-in-oil reverse microemulsions of water/Triton X-100/propanol-2/cyclohexane. Nanoparticles formed in the microemulsions are characterized by transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffractometry (XRD), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). TEM results show a narrow distribution of Pt−Ru nanoparticles. A homogeneous alloy structure in the bimetallic nanoparticles is indicated by XRD analysis and ED analysis. The composition of the Pt−Ru nanoparticles can be easily controlled by the relative concentration of Pt and Ru in the initial precursor solution. The composition that was in the Pt−Ru nano-alloy is found to be the same as that in the original precursor solution. XPS analysis reveals the presence of Pt and Ru metal as well as some oxide of ruthenium. The effect of precursor concentration on microemulsion drop size was investigated by photo correlation spectroscopy (...

Growth of hex-pod-like Cu 2O whisker under hydrothermal conditions

In this paper, hex-pod-like Cu 2O whiskers were successfully synthesized from a Cu(CH 3COO) 2 precursor under hydrothermal conditions, and examined by means of scanning electron microscopy, X-ray microprobe analysis, and X-ray diffraction. The effects of precursor concentration and pH, reaction temperature and time on the evolution of Cu 2O synthesis and morphology were investigated. The whiskers were composed of a nucleus and six pods. The pods grow along the 〈0 0 1〉 directions, and are bounded to {0 0 1} faces. The adjacent pods are perpendicular to each other. The dipolar characteristics of the Cu 2O {0 0 1} faces are the critical factors in the synthesis of the peculiar Cu 2O whiskers. Finally, a possible growth mechanism is proposed.

The effect of precursor concentration on the size of the CdS nanoparticles synthesized in a chicken egg membrane

Results of the studies on the effect of concentration of the precursors on the size of CdS nanoparticles formed in a chicken egg membrane are presented in this article. CdS is formed by the diffusion of aqueous solutions of cadmium acetate and thiourea across the membrane. The optical absorption spectra of the samples exhibit a blue shift in the absorption edge indicating the formation of CdS particles with the size lying in the nanoscale regime. The band gaps of the samples with small reaction times were higher than that of the bulk value, approaching the bulk band gap value with the increase in reaction time for a fixed concentration. Particle sizes were estimated from the band gap values. At lower concentrations, smaller particles are formed even at large reaction times and offer a better control over the size of the particles. At very low concentrations, it takes some time for the absorption edge to evolve after the membrane is removed from the reaction bath. The particle size saturates at higher reaction time possibly due to an equilibrium being established in the system, resulting in stoppage of the diffusion of the reacting ions. Absorption edge could not be detected even days after the removal of the membrane from the reaction bath at still lower concentrations, despite allowing the reaction to take place for large periods of time.

Effects of precursor concentration on the optical and electrical properties of SnXSY thin films prepared by plasma-enhanced chemical vapour deposition

We have carried out the electrical and optical characterization of thin films of compounds based on Sn–S bonds (SnS2, Sn2S3), prepared by plasma-enhanced chemical vapour deposition (PECVD), as a function of the relative concentration of the precursor vapours, SnCl4 and H2S, keeping all other deposition parameters constant. In all studied cases, the deposited films were formed by polycrystalline materials. The optical bandgap values of deposited materials were calculated from optical transmittance and reflectance measurements. The SnS2 compound produced under certain deposition conditions has a forbidden bandgap around 2.2 eV. This compound shows n-type electrical conductivity, whose dark value at room temperature is 2 × 10−2 (Ω cm)−1. Also, it shows the typical semiconductor dependence of its electrical conductivity on the temperature with an activation energy of about 0.15 eV. However, thin films of a mixture of SnS2 and Sn2S3 compounds were deposited with higher values of the relative concentration of source vapours than those used to obtain the SnS2 compound. The optical bandgap shows a decreasing trend as the relative concentration increases. A similar trend is observed for dark electrical conductivity. These results create the opportunity to use SnX SY compounds in thin films for building heterojunction solar cells prepared completely by PECVD.

Trends in near-surface ozone concentrations in Switzerland: the 1990s

A time series analysis of ozone monitoring data from several locations in Switzerland from 1991 to 1999 is presented. Different methods are used to address changes in the ozone level during these years and to account for the influence of changing meteorological conditions. The results show a slight decrease of the peaks but a highly significant increase of the mean value of around 0.5–0.9 ppb yr −1. The frequency distribution has changed in the sense that very low values have become less frequent and that there is a strong increase in frequency of occurrence of half-hourly mean values between about 45 and 55 ppb. A selection procedure reveals slight tendencies towards different trends of afternoon ozone peaks in summer depending on weather and pollution situations. Ozone peaks tend to decrease on fair weather days at rural sites (but increase at urban sites) and show a small increase on cloudy and windy days. A non-linear regression model is used to estimate trends of summertime afternoon ozone peaks in the presence of meteorological variability. In the model, the long-term signal is additively split into a linear part and a part which is modulated by global radiation. The coefficients for both terms are statistically significant at many sites, with an increasing linear trend at the sites north of the Alps of around 1 ppb yr −1 and a decrease of ozone peaks under fair weather conditions relative to cloudy conditions. When additionally considering the effect of precursor concentrations in the regression models, both trends are weakened, which means that they can partly be explained by changes in local to regional emissions. However, at the sites north of the Alps remains a tendency towards a positive linear “base trend” of around 0.4 ppb yr −1. This could possibly be due to increasing background ozone concentrations.

Characterization and properties of lignocellulosic fibers with thin-film deposited cationic precursor

Cationic pulp has been prepared by depositing ultra-thin films of a cationic silane precursor on the pulp surface. The deposited thin film has been characterized by relative measurement of film thickness and also by determining the charge behavior of the modified fiber surface in an aqueous suspension by streaming current, ionic mobility and charge density measurements. Although the calculated film thickness was found to be less than 30 Å, a significant difference in the calculated thickness values between X-ray photoelectron spectroscopy and ellipsometry was observed. Streaming current measurements confirmed that the cationic charge carrying capacity of cellulosic fibers depends on the hydrophobicity of the fibers. The charge density of the cationic fibers was found to be lower than conventional polyelectrolytes that are used as flocculants in wet-end papermaking. Effect of pH on the ionic mobility of the precursor deposited fibers demonstrated the more pH tolerant character of the cationic fibers compared to the unmodified fibers. Effect of precursor concentration on cationic charge behavior of cellulose, stoned ground wood and thermomechanical pulp demonstrated that, for most of the cation modified fibers, there was a marginal increase in charge with higher precursor concentration. Temperature and pH have little effect on charge properties. A partial replacement of anionic fiber by silane deposited cationic fiber in a fiber slurry improved fines and filler retention properties. Microscopic analyses of floc structure suggested that the improved retention properties exhibited by the cationic fibers could be due to the formation of smaller but stronger flocs at higher shear rates.

Scaling behavior: Effect of precursor concentration and precursor molecular weight on the modulus and swelling of polymeric networks

End-linked poly(dimethylsiloxane) (PDMS) networks, containing a minimal number of defects, are prepared from vinyl-terminated PDMS chains in the presence of a theta (θ) solvent. Unreactive tri-methyl terminated PDMS of the same molecular-weight distribution as the reactive PDMS precursors were chosen as the θ solvent. Four precursor molecular weights ranging from 10 000 to 100 000 daltons were studied. The dependence of the initial modulus after cure, the dry modulus after solvent extraction, and the degree of equilibrium swelling on precursor concentration during cure were compared to recent scaling predictions. The experimental scaling exponents were found to be strong functions of the molecular weight of the precursor chains and their values approach the theoretical predictions for high-molecular-weight precursors. The relationship between the modulus of the fully swollen network and the degree of equilibrium swelling is found to be independent of precursor molecular weight and precursor concentration during cure and in better agreement with the corresponding, more robust, theoretical prediction.