Cadmium Sulfide Nanocrystals Research Articles

Nanocrystal Layer Deposition: Surface-Mediated Templating of Cadmium Sulfide Nanocrystals on Zinc Oxide Architectures

The integration of zinc oxide (ZnO) and cadmium sulfide (CdS) has shown promise in applications such as sensing and photovoltaics. We describe here a room temperature, aqueous synthetic strategy to selectively grow nanocrystalline CdS on ZnO. In particular, we describe an experimentally simple process that selectively grows a conformal nanocrystalline coating only 1 nanocrystal (10−20 nm) thick on planar and three-dimensional extended ZnO structures. We explore the synthesis, characterization, and mechanisms involved in the formation of this composite material, and we demonstrate a promising optical response from these composite structures that may prove valuable for future optoelectronic applications.

Inorganic surface passivation of CdS nanocrystals resulting in strong luminescence

Cadmium sulphide (CdS) nanocrystals have been synthesized by wet chemical route using cadmium chloride, thiourea and sodium hydroxide in ethanol solution. Triethylamine (TEA) is used as a capping agent. The products were characterized by high resolution transmission electron microscope (HRTEM), powder X-ray diffraction (XRD) pattern, UV–visible, FT-Raman, thermal and photoluminescence studies. The spherical morphology of the TEA capped CdS has been observed by TEM. Broadening of the XRD peaks and asymmetrical broadening of longitudinal optical (LO) modes in FT-Raman indicated the nanocrystal formation. Strong photoluminescence was observed in TEA capped nanocrystals. UV spectrum showed blue shift due to size quantization effect. The high temperature behavior of CdS nanocrystallites has been studied using thermal analyses.

Signal‐On Electrochemiluminescence Biosensors Based on CdS–Carbon Nanotube Nanocomposite for the Sensitive Detection of Choline and Acetylcholine

AbstractThis work describes for the first time signal‐on electrochemiluminescence (ECL) enzyme biosensors based on cadmium sulfide nanocrystals (CdS NCs) formed in situ on the surface of multi‐walled carbon nanotubes (MWCNTs). The MWCNT–CdS can react with H2O2 to generate strong and stable ECL emission in neutral solution. Compared with pure CdS NCs, the MWCNT–CdS can enhance the ECL intensity by 5.3‐fold and move the onset ECL potential more positively for about 400 mV, which reduces H2O2 decomposition at the electrode surface and increases detection sensitivity of H2O2. Furthermore, the ECL intensity is less influenced by the presence of oxygen in solution. Benefiting from these properties, signal‐on enzyme‐based biosensors are fabricated by cross‐linking choline oxidase and/or acetylcholine esterase with glutaraldehyde on MWCNT–CdS modified electrodes for detection of choline and acetylcholine. The resulting ECL biosensors show wide linear ranges from 1.7 to 332 µM and 3.3 to 216 µM with lower detection limit of 0.8 and 1.7 µM for choline and acetylcholine, respectively. The common interferents such as ascorbic acid and uric acid in electrochemical enzyme‐based biosensors do not interfere with the ECL detection of choline and acetylcholine. Furthermore, both ECL biosensors possess satisfying reproducibility and acceptable stability.

In situ synthesis and third-order nonlinear optical properties of CdS/PVP nanocomposite films

Cadmium sulfide (CdS) nanocrystals were in situ grown in a polyvinylpyrrolidone (PVP) matrix at room temperature using cadmium nitrate and thioacetamide as the cadmium and sulfur sources, respectively. It was found that the growth of CdS nanocrystals in the PVP matrix was well controlled and the mass concentration of CdS could be up to 18.2 wt% without the formation of large precipitates. The third-order nonlinear optical properties of the composite films were studied at 532 nm in the nanosecond regime by using the Z-scan technique. The results showed that the CdS/PVP nanocomposite film has a promising optical property exhibited by a nonlinear optical refractive index and an absorption coefficient of −1.65 × 10−11 cm2 W−1 and −4.25 × 10−7 cm W−1, respectively. The flexible processing technique allows the production of optical devices with various shapes.

Synthesis of monodisperse CdS nanowires and their photovoltaic applications

Cadmium sulphide (CdS) nanowires with a monodisperse diameter of 3.6 nm and an aspect ratio of 10–170 were successfully synthesized using a simple and reproducible hot coordinating solvents method. The morphology and optical properties of the CdS nanocrystals were investigated using transmission electron microscopy (TEM), high-resolution TEM (HRTEM) ultraviolet–visible (UV–Vis) absorption spectroscopy and photoluminescence (PL) spectroscopy. It was found that using a long alkyl chain phosphonic acid-octadecylphosphonic acid (ODPA) causes a low diffusion rate and low reactivity which help to control the morphology of the nanocrystals. The timing of the injection process was also found to have critical effect on the morphology of the nanocrystals. Sharp peaks in both the UV–Vis absorption and PL spectra indicate that the size distribution of the diameter is nearly monodisperse. The photovoltaic properties of photovoltaic devices made with a blend of our nanowires and poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) were also investigated. Devices made with the nanowires were found to have double the I sc observed in devices made with lower aspect ratio CdS nanorods. The possible reason of low photocurrent and high V oc is maybe due to the presence of ligand in the nanocrystals.

Controlled Synthesis of Pyramid-Aggregated Sphere-like Cadmium Sulfide in the Presence of a Polymer

Large-scale three-dimensional cadmium sulfide (CdS) spheres composed of hexagon-based pyramids were synthesized through a facile solution-phase reaction from CdCl2, thioacetamide, and a polymer, where the polymer acted as both a dispersant and coating agent. The reaction conditions influencing the synthesis of these three-dimensional (3D) CdS nanostructures such as reaction temperature, reaction time, the concentration of the polymer, and the kinds of precursors used were investigated. The phase composition, the morphology, and the structure of CdS nanostructures were examined by X-ray diffraction, X-ray photoelectron spectra, field emission scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The possible formation mechanism of the novel CdS spheres was proposed based on the above analysis. The room-temperature Raman spectrum and photoluminescence spectra of the obtained CdS nanocrystals were also studied.

Synthesis and Characterizations of Bare CdS Nanocrystals Using Chemical Precipitation Method for Photoluminescence Application

Bare cadmium sulfide (CdS) nanocrystals were successfully synthesized by the thermolysis of a single‐source organometallic precursor, cadmium chloride hemipentahydrate (CdCl2 · 2.5H2O) with thiourea in ethanol. The microstructure of the CdS samples was characterized using XRD, TEM, and Raman spectroscopy. The XRD′s results showed that there was a transformation from cubic to hexagonal crystalline phase when higher mass of CdCl2 · 2.5H2O was used. Further experimental with different Cd2+ source showed ion Cl− originated from CdCl2 · 2.5H2O attributed to this crystalline phase transformation. The UV‐Visible analysis indicated that quantum confinement effect took place when compared to the bulk CdS. However, the photoluminescence experiments revealed that the red‐light emission was observed in all samples. This finding could be ascribed to deep trap defects that were due to sulfur vacancies as suggested by XPS and also the fact that the bare CdS nanoparticles are in contact with each other as shown in the TEM images.

Electron Microscopy and Optical Characterization of Cadmium Sulphide Nanocrystals Deposited on the Patterned Surface of Diatom Biosilica

Intricately patterned biosilica obtained from the shell of unicellular algae called diatoms serve as novel templates for fabrication of optoelectronic nanostructures. In this study, the surface of diatom frustules that possessed hierarchical architecture ordered at the micro and nanoscale was coated with a nanostructured polycrystalline cadmium sulphide (CdS) thin film using a chemical bath deposition technique. The CdS thin film was composed of spherical nanoparticles with a diameter of about 75 nm. The CdS nanoparticle thin film imparted new photoluminescent properties to the intricately patterned diatom nanostructure. The imparted photoluminescent properties were dependent on the CdS coverage onto the frustules surface. The intrinsic photoluminescent properties of the frustules were strongly quenched by the deposited CdS. The origin of PL spectra was discussed on the basis of the band theory and native defects.

Hollow strength

Tiny hollow spheres made from cadmium sulphide nanocrystals can withstand incredibly high stresses and strains

CdS NANORODS FABRICATED BY ICP-ASSISTED MAGNETRON SPUTTERING AT ROOM TEMPERATURE

Cadmium sulfide ( CdS ) nanocrystals are successfully fabricated on glass and silicon substrates at room temperature with low-frequency (460 kHz) inductively coupled plasma assisted magnetron sputtering technique. Both size and shape can be controlled by changing deposition parameters and substrates. Field-emission scanning electron microscope, energy dispersive X-ray spectroscopy, and X-ray diffraction are adopted to measure the properties of CdS nanorods.

Optical properties of cadmium sulfide nanocrystals obtained by the sol-gel method in gelatin

Based on analysis of optical absorption data for CdS nanocrystals obtained by sol-gel technology in gelatin, we have studied the effect of technological factors (reagent concentrations, gelatin concentration) on the growth process and size distribution of the synthesized nanocrystals. Depending on the reagent concentration, we synthesized CdS nanocrystals with mean radii in the range \( \bar r = 1.9 - 2.4 nm \) . We have shown that for a low gelatin content (1%), nanocrystals of different sizes are formed (1.7 nm and 2.6 nm). With an increase in the gelatin concentration, the size dispersion decreases and nanocrystals of a single mean radius (2.3 nm) are formed. We have established a correlation between the size dispersion and the shape of the photoluminescence spectrum of the CdS nanocrystals.

Facile Preparation of Impurity Doped CdS Nanoparticles in New Polymeric Templates

Cadmium sulfide nanocrystals (quantum dots) have been prepared using polymer solution as template. The new polymer is a vinyl acetate- maleic anhydride (VAcMA) copolymer obtained by using an original procedure developed in our laboratory. The influence of composition and concentration of the polymer on the size and the optical properties of the semiconductor nanoparticles has been studied. The influence of the reaction parameter was also investigated in order to obtain a versatile procedure to prepare nanocrystals with tunable optical properties. The reaction in polymeric matrix could lead to the formation of wide range of particle size (3–8 nm). In addition to modify the emission properties by controlling the particle size, CdS nanocrystals were doped with Zn, Cu and Mn ions. Both blue and red shifts of the maximum emission wavelength were recorded. QD-polymer composites obtained from CdS nanoparticles prepared in VAcMA matrix have been investigated by UV-VIS, fluorescence and IR spectroscopy, TEM and DLS. The photophysical properties of the semiconductor nanoparticles obtained in polymer matrix was compared for different QD-polymer composites, according to the obtaining procedure.

The effect of solvent on the crystal structure and size distribution of cadmium sulfide nanocrystals

CdS nanocrystals with different structures were synthesized by the method of solution precipitation using thiourea and cadmium acetate as starting materials in different solvents: water, methanol and N, N-dimethylformamide (DMF). Our results show that the solvent has direct effect on the structure and size of the final nanoparticles. It was found that using DMF, as a solvent, results in producing smaller nanoparticles with the cubic structures, while using the other solvents gives rise to larger nanoparticles with the hexagonal structure. It was also found that using heat during washing the precipitate results in a more homogenous size distribution of CdS nanocrystals. On the basis of our experimental results we also suggest a critical structure transformation size.

Photon-induced formation of CdS nanocrystals in selected areas of polymer matrices

We demonstrate light-induced formation of semiconductor quantum dots in TOPAS® polymer matrix with very high control of their size and their spatial localization. Irradiation with UV laser pulses of polymer films embedding Cd thiolate precursors results in the formation of cadmium sulfide nanocrystals well confined in the irradiation area, through a macroscopically nondestructive procedure for the host matrix. With increasing number of laser pulses, we accomplish the formation of nanoparticles with gradually increasing dimensions, resulting in the dynamic change of the spectra emitted by the formed nanocomposite areas. The findings are supported by x-ray diffraction and transmission electron microscopy measurements.

White light

Adding a small amount of manganese to cadmium sulphide nanocrystals can generate a stable shade of white light

Influence of Engineered Peptides Cadmium Sulfide Nanocrystals

AbstractCadmium sulfide (CdS) nanocrystals continue to generate scientific and technological interest, owing to their valuable optical, electronic, and chemical properties. Aqueous nanocrystal syntheses rely on functional capping agents to control nanocrystal form and function. We present a series of linear and dendritic engineered peptides, rich in cysteines and aspartic acids, as CdS capping agents. The chemical composition and peptide geometry were found to significantly influence CdS nanocrystal size, optical properties, and aggregation behavior.

Nonlinear absorption and scattering properties of cadmium sulphide nanocrystals with its application as a potential optical limiter

A systematic study of nonlinear absorption and scattering properties of 4.5nm sized CdS nanocrystals dispersed in dimethylformamide with varying concentrations is reported in this paper. The study is undertaken by performing open aperture Z-scan measurements with 532nm nanosecond and 790nm femtosecond pulse excitations. A modified Z-scan experimental setup is used to collect both nonlinear absorption and nonlinear scattering at different forward angles simultaneously. Optical limiting studies of these nanocrystals show that nonlinear scattering (NLS) is comparable to the two-photon absorption (TPA). Both the TPA and NLS coefficients are estimated by theoretical fit of the observed open aperture Z-scan curves. The variation of NLS coefficients with concentration is discussed in detail, and we estimated the thermo-optic coefficient of CdS nanocrystals. The nonlinear refractive index and limiting threshold (I1∕2) of CdS nanocrystals at different concentrations (at 532nm) are also estimated and reported. Further, we report our observation of the formation of diffraction fringes in the transmitted beam at high intensities.

Growth kinetics and characterization of fluorescent CdS nanocrystals synthesized with different sulfur precursors in paraffin hot-matrix

The present paper describes the influence of the sulfur precursor on the nanocrystal growth rate and optical properties of cadmium sulfide nanocrystals in a hot-paraffin matrix. One of the precursors used is tributylphosphine sulfide; the other one is elemental sulfur. The growth kinetics is studied at various temperatures to estimate the activation energy for the formation of CdS nanocrystals from the temperature dependence of model kinetic parameters. The different sulfur precursors lead to different trends in the limiting nanocrystal radii and the time-constant of growth. The obtained nanocrystals are characterized by UV-absorption and photoluminescence spectroscopy, electrophoresis, X-ray powder diffraction and transmission electron microscopy. The nanocrystals prepared from tributylphosphine sulfide have fewer surface defects and their spectra exhibit a band-edge emission only. In this case the limiting radii of the nanocrystals increase with increasing the temperature of growth. The nanocrystals synthesized from elemental sulfur show in addition a trap-state emission due to much more surface defects. Here the limiting radii of nanocrystals decrease with increasing temperature in contrast to the previous case. In both cases, the semiconductor nanocrystals can be sterically and electrostatically stabilized in non-polar organic solvents by post-capping with tributylphosphine. Our findings are important for the controlled manufacturing of CdS nanocrystals with pre-determined properties and their utilization in a variety of optical devices.

Influence of the matrix on the chemical surface bonds of ZnS and CdS nanoclusters obtained by chemical synthesis

AbstractCadmium sulfide (CdS) and zinc sulfide (ZnS) nanocrystals were grown following three different chemical synthesis routes. In particular, the nanocrystals were synthesized by in situ thermolysis (∼300 °C) starting from a metal thiolate (i) in a solventless way, (ii) by a novel route in trioctylphosphine oxide (TOPO), and (iii) by direct synthesis in a polystyrene matrix. The formation of cadmium sulfide (zinc sulfide) nanocrystals and the chemistry of the organic/nanocrystal (polymer/nanocrystal) composites were investigated in detail by X‐ray photoelectron spectroscopy (XPS). In addition, X‐ray diffraction analyses (XRD) were performed in order to determine the crystallographic structure and the average size of the nanocrystals.The precursor powders (Cd(SR)2 and Zn(SR)2) of both II–VI compounds were analysed after annealing in different atmospheres (air, nitrogen, vacuum) at 300 °C (in situ thermolysis) in order to establish the starting of the nanocrystal formation process.All the three chemical routes employed and investigated here, showed the formation of CdS (and ZnS) nanocrystals. X‐ray diffraction analyses evidenced that under optimized growth conditions single crystal nanoclusters of zinc‐blende structure and of diameter between ${\oslash} = 1.5$ and 3.0 nm (depending on the annealing temperature and time) are formed. Very good and promising results were obtained by the novel route in TOPO that revealed that sulfur has only one component on the S 2p unresolved doublet (at about 161.6 eV ±0.2) associated to the metal‐sulfide bond, i.e. the Cd(Zn)–S nanocrystals are capped by metal‐sulfide‐TOPO chains. CdS and ZnS nanocrystals embedded in a polystyrene matrix were also successfully prepared and the XPS analyses revealed, in particular, that the sulfur doublet signal is split at least into two peaks, compatible with S in CdS structure and with S bonded to organic residues with energies of 161.66 and 166.98 eV respectively. Copyright © 2006 John Wiley & Sons, Ltd.

Fabrication of CdS nanorods in inverse microemulsion using HEC as a template by a convenient γ-irradiation technique

Cadmium sulfide (CdS) nanocrystals were successfully prepared in inverse microemulsion under γ-irradiation at room temperature. Their shape can be controlled by changing the surfactant concentrations and the addition of hydroxyethyl cellulose (HEC) as the template. CdS nanorods were successfully obtained under γ-irradiation using HEC as the template, which was confirmed by the observation of transmission electron microscopy (TEM). Without the addition of HEC, spherical CdS crystals were formed. X-ray powder diffraction (XRD) pattern and electron diffraction (ED) analysis showed the hexagonal lattice of CdS in the nanorods. Additionally, the optical properties of CdS nanorods were characterized by ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy.