Growth Kinetics Of Nanoparticles Research Articles

Growth kinetics of CdSe nanoparticles synthesized in reverse micelles using bis(trimethylsilyl) selenium precursor

Abstract We first focus on the kinetics of nanoparticle growth in a microemulsion synthesis of CdSe semiconductor nanocrystals. The process consists of a fast initial stage of typical time constant of the order of 103 s followed by a slow stage of time constant of the order of 104s. Growth proceeds similarly to that described for the hot-matrix synthesis of CdSe, underlining the generality of the two-stage growth mechanism, irrespective of the matrix type and synthesis conditions. However, the time constant of each stage in the microemulsion synthesis is much larger than in the hot-matrix one. Also, the ratio between the fast and slow time constant is appreciably bigger. We also prove that larger size reverse micelles, obtained by increasing the water:surfactant ratio, generally lead to larger CdSe nanoparticles. Bis(trimethylsilyl) selenium is the crucial precursor for the CdSe nanoparticle synthesis. An intermediate stage of the chemical reaction limiting the bis(trimethylsilyl) selenium production is described theoretically.

Effects of synthetical conditions on octahedral magnetite nanoparticles

By controlling the growth kinetics of nanoparticles, octahedral magnetite nanoparticles were successfully synthesized employing an oxidation–precipitation method with FeSO 4·7H 2O, NaNO 3 and NaOH as starting materials. Magnetite nanoparticles with 40 nm or less can be synthesized under the following conditions: pH 9.5, F = 10–90 ml/min, T = 60–90 °C, C = 0.2–1 mol/l, t = 4 h, R = 200–500 rpm. The saturation magnetizations of octahedral magnetite nanoparticles are in the range from 80 emu/g to 90 emu/g. The remanence magnetizations of the as-prepared samples are lower than that of the bulk magnetite and the coercive forces of the as-prepared sample are around 140 Oe.

Kinetic Study of Gold Nanoparticle Growth in Solution by Brust-Schiffrin Reaction

Nanoparticle growth in solution is a rather complicated process governed by many thermodynamic and kinetics factors. A better understanding of nanoparticle growth kinetics is of primary importance leading to a better control on the nanoparticle size and size distribution. In this work we conducted both experimental and theoretical study on the kinetics of Brust-Schiffrin reaction for the synthesis of gold nanoparticles. Using an excessive amount of thiol ligands, the nanoparticle growth was stopped at different intermediate stages. Our study revealed and confirmed that the reproducibility of Brust-Schiffrin reaction for the synthesis of gold nanoparticles with diameters around 2 nm is rather poor due to the intrinsic complexity of this two-phase reaction. The analysis results of each intermediate product by TEM showed that nanoparticles grew very rapidly at the early stage of reaction and reached a maximum value of 2.6 nm at reaction time of around 10 minutes. Further increase of reaction time led to a decrease of nanoparticle size. In addition to the experimental study, we proposed a kinetic model for nanoparticle growth in solution by assuming that the nanoparticle core expands through incremental addition of gold atoms to the existing nanoparticle nuclei. This model not only gave a relatively good fitting to the experimental data, but also provided further insight into the nucleation and core expansion stage of the nanoparticle growth, which had not been revealed in previous modeling studies.

Synthesis of high-quality semiconductor nanoparticles in a composite hot-matrix

Semiconductor nanocrystals are of a great interest for many practical applications which motivates the search of low cost and environmental-friendly methods for their manufacturing. Here we report the synthesis of CdSe and CdS nanoparticles utilizing composite matrix of liquid paraffin as a non-coordinating solvent and stearic acid as a coordinating ligand. The nanoparticle growth kinetics is compared to that of the classical synthesis in trioctylphosphine oxide matrix. It is found that the nucleation and crystal growth are remarkably affected by the coordinating ligand. The CdSe and CdS nanocrystals can be isolated and purified from the matrix which makes it possible their large-scale synthesis for applications.

Microwave Radiation Effect On The Synthesis Of Cadmium Sulphide Nanoparticles In Water In Oil Microemulsion: A Preliminary Study At Different Frequencies

Cadmium sulphide nanoparticles have been synthesised in water/sodium bis (2-ethylhexyl) sulfosuccinate (AOT)/n- heptane microemulsions kept at 30 °C by microwave irradiation coupled with water-cooling and in conventional thermostatic conditions at the same temperature. The study has been performed exposing the reaction media to microwave radiation at five different frequencies (2.45, 2.85, 8, 12 and 18 GHz). For each frequency, a suitable microwave exposure set-up has been assembled. During the growth process, the dimensions of the nanoparticles have been characterised by means of UV-Vis spectroscopy. At the end of the growth process, the surface morphology of the nanoparticles has been determined by using photoluminescence (PL) measurements. Results indicate that compared to conventional thermostatic conditions, microwave irradiation influences nanoparticle growth kinetics, affecting both the final size and surface morphology structure. The effect is microwave frequency dependent.

Degree of Asymmetry of CdSe Quantum Dots Grown in Glass Probed by Four Wave Mixing

ABSTRACTInformation about quantum dot (QD) asymmetry is derived by analyzing the polarization properties of the time-integrated four wave mixing (FWM) signal. The lowering of QD symmetry results in the splitting of bright J= +/-1 exciton states. This causes the polarization oscillation of circularly excited excitons between these two split states. In a QD ensemble with a random distribution in the exciton level splitting, this results in the decay of the difference in FWM signals observed in scattering of σ+ and σ+ polarized light on the population grating created by two σ+ pulses, the decay time reflecting the degree of QD asymmetry. We have investigated the decay time of the difference in two polarized signals for quantum dots of equal size, grown in a glass matrix under different conditions. Increasing growth temperature and decreasing growth time lead to lowering of QD symmetry. We discuss this experimental result in terms of kinetics of nanoparticle growth in glass.

The Formation and Growth Kinetics of PbS Nanoparticles in Lead Stearate Langmuir-Blodgett Films

The nucleation and growth processes of PbS nanoparticles in lead stearate Langmuir-Blodgett films depending on Pb content and the treatment duration in aqueous solution are presented. It is shown that nanoparticle growth kinetics is different due to different initial Pb concentration in LB films and otwo structure types-flat isolated nanoparticles and domains can be formed.

Plasmon Resonance Shifts of Au-CoatedAu2SNanoshells: Insight into Multicomponent Nanoparticle Growth

In this Letter we present a coherent description of the optical properties of a unique type of nanoparticle, metal-coated dielectric nanoparticles. These structures occur naturally in the form of Au-coated ${\mathrm{Au}}_{2}\mathrm{S}$ nanoparticles. During the course of nanoparticle growth, the plasmon-related absorption peak undergoes very large shifts in wavelength, from $\ensuremath{\sim}650$ to $\ensuremath{\sim}900\mathrm{nm}$. We show that this plasmon peak shift is purely classical in origin and is determined solely by the relative thickness of the Au shell and the ${\mathrm{Au}}_{2}\mathrm{S}$ core diameter. This understanding of the optical properties of these nanoparticles is used to elucidate the nanoparticle growth kinetics.