Size Of CdS Nanoparticles Research Articles

Size-Dependent Carrier Dynamics in CdS Nanoparticles by Femtosecond Visible-Pump/IR-Probe Measurements

Ultrafast photoexcited carrier dynamics in CdS nanoparticles prepared by an AOT/n-heptane reversed micelle system were investigated by a femtosecond visible-pump/mid-IR probe technique. A mid-IR probe beam was found to mainly probe the ultrafast dynamics of photoexcited electrons in the conduction band. Dispersions of CdS nanoparticles with 8 different mean diameters from 2.9 to 4.1 nm were prepared by tuning the mole ratio between water and AOT (W = [H(2)O]/[AOT]) in the reversed micelle systems. The excited state lifetime strongly depended on the mean size of CdS nanoparticles with a maximum around a mean diameter of 3.5 nm. This result was explained by considering the balance between the carrier recombination rates via surface states and those via interior states. The relationship between the excited state lifetime and the size of CdS nanoparticles was drastically changed when the surface was terminated by thiol molecules.

Fine tuning of the size of CdS nanoparticles synthesized by a photochemical method

In this work, we propose a combined photochemical–chemical methodthat enables us to grow CdS nanoparticles with ångström precision. CdSnanoparticles were formed through a photo-induced reaction betweenCdSO4 andNa2S2O3.Thioglycerol (C3H8O2S) was used as the capping agent. Fine tuning of the size was subsequently carried out bycontrolling the pH of the solution. Optical absorption spectroscopy was mainlyused to monitor the process of particle formation, and to measure the bandgapand size. X-ray diffraction spectra confirmed the optical sizes and demonstratedcrystalline nanoparticles. In the presence of the capping agent there was a darkgrowth that was completely dependent on the pH of the solution. The rate ofdark growth decreased when the pH of the solution increased to 7.0. In pHs of7.5 and 8, we observed a boundary situation where the number of particles wasconstant and only the existing particles grew in size. We proposed a model toexplain this effect. The model is based on the formation of a local higherH+ concentration near the nanoparticle’s surface. Finally, in pHs higher than 8.3 there was no dark growth.In a typical procedure, we showed that fine tuning of the size with ångström precision is possible, i.e. a1.6 Å change in size was obtained in 45 min reaction time.

A Simple Approach to Fabricate CdS-SiO 2 Hybrid Microspheres by Producing CdS Nanoparticles on the Surface of Thiolated SiO 2 Microspheres

We have developed a simple synthetic method to prepare the hybrid microspheres of CdS nanoparticles on the surface of silica microspheres modified by(3-mercaptopropyl)trimethoxysilane(MPS). The—SH groups of MPS can bind with the Cd2+ ions on the surface of SiO2. When thioacetamide releases H2S, the nanosized CdS particles(1–6 nm) will successfully be generated on the silica surface under the experimental conditions. The size of the CdS nanoparticles was found to be related to the concentration of Cd2+ feed and the size of silica spheres, the higher the concentration of Cd2+ and the larger of silica microspheres, the bigger the size of CdS nanoparticles. Techniques including UV, PL, TEM and XPS were used to characterize the CdS-SiO2 hybrid microspheres.

Laser-induced nanocomposite formation for printed nanoelectronics

CdS nanocrystals are formed by regioselective thermal decomposition of metal alkanethiolates in a polymer matrix by selective heating of a polystyrene foil filled with the cadmium-(bis)-thiolate precursor using focused laser beam irradiation. CdS nanocrystal formation in the polymer was investigated by photoluminescence emission and excitation (PL and PLE) spectroscopy and transmission electron microscopy (TEM). The PLE spectra show a band edge at 420 nm for the irradiated area, indicating the presence of nanocrystalline CdS of size of about 2–3 nm. The PL exhibits an emission band at 535 nm that is also characteristic of nanometer-sized CdS. TEM images confirm the presence and size of CdS nanoparticles. The surface temperature was estimated theoretically considering the relationships between the temperature, time and power of the laser pulses. Nanoparticle formation via laser probe is also discussed in terms of possible utilization of other probes (e.g., electrons, etc.), inducing nanocrystal formation for the realization of conducting nanowires embedded in non-conductive matrix materials useful for nanoelectronic devices or conductive plastic.

Effect of chelating functional polymer on the size of CdS nanocluster formation

Chelating poly(acrylates-co-2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) microspheres of diameter 250–310 nm were prepared by the soap-free emulsion polymerization method for varying amounts of GMA-IDA. Then CdS/copolymer composite was generated by chemical deposition on the surface of the copolymer microspheres. By XRD analysis it is found that the chelated CdS nanoparticles are a pure cubic zinc blende structure. The CdS/copolymer composite is examined by UV–vis absorbance, photoluminescence, and TEM observation. Average CdS nanoparticle size calculated from Henglein's empirical curve is in the range of 3.0–8.0 nm and varies according to the GMA-IDA molar ratio during polymerization, pH value during chelation, and postchelation annealing temperature. Higher ratio of chelating group, pH value, and annealing temperature produce larger CdS nanoparticles. As GMA-IDA ratio increases, photoluminescence exhibits a red shift from 510 to 520 nm, photoluminescence increases, and bandwidth decreases. Photoluminescence of the CdS nanoparticle becomes negligible when diameter exceeds 5 nm.

A photochemical method for controlling the size of CdS nanoparticles

The optical and electrical properties of semiconductor nanoparticles are strongly dependenton their size. A flexible control of the size of the nanoparticles is of interest for tuning theirproperties for different applications. Here we use a coupled method to controlthe size of CdS nanoparticles. The method involves the photochemical growthof CdS nanoparticles together with the use of a capping agent as an inhibitingfactor. CdS nanoparticles were formed through a photoinduced reaction ofCdSO4 andNa2S2O3 in an aqueous solution.Mercaptoethanol (C2H6OS) was used as the capping agent, and we investigated the effect of illumination time,illumination intensity and the concentration of capping agent on the nanoparticle size.Transmission electron microscopy (TEM) shows crystalline nanoparticles withrelatively low dispersion. Optical absorption spectroscopy was mainly used to measurethe band gap and size of the nanoparticles. Increasing the illumination time orillumination intensity increases the nanoparticle size, while higher capping agentconcentration leads to smaller nanoparticle size. A band gap range of 2.75–3.4 eV waspossible with our experimental conditions, corresponding to a 3.2–6.0 nm sizerange.

Synthesis, characterization and fluorescence property of CdS/P( N-iPAAm) nanocomposites

A novel nanocomposite in which CdS nanoparticles were embedded in poly( N-isopropylacrylamide) (P( N-iPAAm)) matrix have been fabricated. The particle size of CdS nanoparticles ranged from 10 nm to 40 nm could be adjusted with the varying of the inorganic contents. The nanocomposites have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), thermo-gravimetric analysis (TGA), high resolution transmission electron microscope (HRTEM), UV–vis absorption and fluorescence spectra (FLS) measurements. The cell volume of CdS nanoparticles embedded in polymer matrix was smaller than the standard value and the nanocomposites with 12.0% inorganic content showed a good fluorescence property.

Single w/o microemulsion templating of CdS nanoparticles

We report the synthesis of monodispersed CdS nanoparticle with tunable size by controlling the reaction aging time in a single water in oil (w/o) microemulsion system. The w/o microemulsion system consists of nonionic surfactant poly (oxyethylene)5 nonyl phenol ether (NP5), poly (oxyethylene)10 nonyl phenol ether (NP10), cyclohexane and aqueous solution (cadmium salt and thioacetamide). Thioacetamide (TAA) has been utilized as a source for slow release of sulfur ions in the in situ synthesis of CdS. UV-Visible spectra shows obvious blue shift for the CdS nanoparticles as compared to the bulk material due to quantum size effect. CdS nanoparticle size depends on the reaction aging time where longer reaction aging time yields bigger particles. CdS nanoparticles growth behaviour as a function of reaction aging time in the microemulsion system was characterized by UV-Visible spectroscopy. The particle growth follows a power law with an exponential in the order of 0.17. Energy Filter Transmissions Electron Microscopy (EFTEM) reveals monodispersed CdS nanoparticles with standard deviation, σ less than 8%.

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.

Growth Behavior of CdS Nanoparticles Embedded in Polymer and Sol-Gel Silica Matrices: Relationship with Surface-State Related Luminescence

Chemical techniques were employed to synthesize CdS nanoparticles embedded in polymer (PEG 300) and sol-gel silica matrices. Systematic growth of particles (radius 3–9 nm) was obtained by adjusting post-deposition annealing temperature and time to examine the dependence of surface-state–related luminescence on particle size. Photoluminescence (PL) peak energy showed a linear dependence with a gentle slope in the weak confinement region and a steep slope in the strong confinement region, the divergence being observed near the excitonic Bohr radius for CdS. The empirical relation proposed for the weak confinement region could be used for estimating chemically prepared CdS nanoparticle size with a high degree of reliability from PL peak energy.

Poly(N-vinylcarbazole) (PVK) Photoconductivity Enhancement Induced by Doping with CdS Nanocrystals through Chemical Hybridization

We have functionalized poly(N-vinyl carbazole) (PVK) by controlled sulfonation. CdS nanocystals of 3−20 nm across were synthesized in the sulfonated PVK matrix with the CdS molar fraction of ∼1−18%. The CdS nanoparticle size increased with the molar fraction of CdS. At high CdS molar fractions, the CdS nanocrystals exist in both cubic and hexagonal phases. Photoluminescence efficiency of PVK decreases when the molar fraction of CdS increases due to quenching through interfacial charge transfer. Photoluminescence attributable to the CdS nanocrystals can be observed only at low molar fractions of CdS. Significant enhancement in photoconductivity induced by the chemical doping of CdS in PVK has also been demonstrated.

Kinetic effect in the size-control of CdS nanoparticles

A new method of size control for CdS nanoparticles, called common cation coprecipitation, is reported. In the course of coprecipitation, both CdS and CdSt2(cadmium stearate) formations are diffusion-controlled and their rates are quite different. The size of CdS nanoparticles depends on the ratio of initial concentrations of S2- to St- (stearateion). Chnracterized by UV-Vis absorption, XRD, TEM, fluorescence and XPS, the results obtained show that the coprecipitate is a composite, i.e. CdS particle inserts in the CdSt2, molecular layers to form a sandwirh-like structure. The method reported for size control of CdS nanoparticles might be called kinetic self-assembling.

Control of the size and photochemical properties of Q-CdS particles attached to the inner and/or outer surface of the lecithin vesicle bilayer membrane by the nature of its precursors

Cadmium sulfide nanoparticles have been generated in situ on the inner and/or outer surfaces of monolamellar lecithin vesicles. Chemical agents, strongly chelating or bounding the Cd 2+ cations, are shown to influence dramatically the size of CdS nanoparticles as well as their optical, luminescence and photochemical properties. The more stable is a Cd 2+-containing complex created by these chelating agents, the smaller are the CdS particles formed. In case of CdCl 2 and Cd(NO 3) 2 as the CdS precursors inside the vesicles, a steady rise in the size of growing CdS nanoparticles is observed, while in case of K 2[CdEDTA] the accumulation of mass of growing CdS occurs without a change in the nanoparticles size. The size of CdS particles and their initial growth rate depend also on pH of the vesicle suspension, modification of the lipid membrane, being, however, independent of the CdCl 2 concentration, if CdCl 2 is the CdS precursor. In the presence of a sacrificial electron donor (S 2− or EDTA), the bandgap irradiation of the lipid-vesicle-supported CdS particles yields charge separation and electron transfer to lipophilic cetylviologen bications, C 16V 2+, embedded into the lipid bilayer. The initial quantum yield of C 16V ⋅+ formation depends on the topology of vesicular systems and CdS localization on the inner or outer surface of the lecithin membrane. Presence of EDTA anions enhances sufficiently the initial quantum yield of vectorial electron phototransfer from CdS nanoparticles to cetylviologen.

Preparation of aqueous CdS colloids in the presence of cadmium complexonates: effect of complexonates on the size of CdS nanoparticles

The results of a systematic study of the preparation of CdS colloids in aqueous solutions containing different Cd2+ complexonates are presented. The effects of the ratio of the reagents and the nature and concentration of various stabilizing surfactants and Cd2+ complexonates, including those of some sulfur-containing compounds, on the size of the colloidal particles have been studied. Thermodynamic calculation of the expected equilibrium size of the colloidal particles as a function of the solvent composition, taking into account the increase in the solubility of the CdS phase as the particle size decreases, has been performed. Comparison of the calculated results with the experimental data shows that the size of colloidal particles is determined to a great extent by kinetic factors of their growth rather than by thermodynamic factors. It has been established that when the size of colloidal particles is less than a critical value, their dissolution by adding strong compexing agents to the system does not result in a change in the observed mean-volume size of the particles.