CdS Clusters Research Articles

The Monolayer Behavior of Amphiphilic Polymer and Heterostructure of Polymer LB Film/CdS Clusters

In this paper we report the behavior of an amphiphilic polymer monolayer on pure water and Cd2+ subphase. This polymer was composed of hydrophilic ethylene diamine epichlorohydrin slightly crosslinked microgel and hydrophobic stearic chains, noted as ES-1. The introduction of Cd2+ ions in subphase had a marked effect on the process of the organization of the amphiphilic polymer at the air/water interface due to the association of Cd2+ ions with the hydrophilic network, which could be indicated by the pressure–area isotherms and Brewster Angle Microscopy. Ordered ES-1/Cd2+ LB multilayers were fabricated. After the multilayers reacted with H2S gas, CdS clusters were synthesized within the film, which was characterized by X-ray diffraction and UV–visible spectroscopy.

Combinatorial Approaches to Peptide-Encapsulated CdS Nanoclusters

AbstractAs many properties of group II-VI semiconductor nanocrystallites arise from their quantum confined nature, the synthesis of these clusters is of great interest. The challenge of synthesizing functional nanoclusters is, however, complicated by the limited stability of metalchalcogen surfaces under highly oxidizing conditions and Ostwald ripening. Our objectives are to develop methods for the synthesis of biogenic CdS semiconductor nanocrystallites that address the following issues: (1) What properties of the ligand peptide are important in stabilizing and producing CdS particles of any desired size? (2) Will hybrid peptides using nonnatural amino acids stabilize the nanoclusters while incorporating new surface functionality? (3) Is it possible to use novel peptides to modify the particle surface, thereby, controlling the photophysical properties of the CdS cluster? Our approach consists of parallel combinatorial techniques and computational methods for the discovery and optimization of peptide and peptidomimetic ligands to stabilize size-defined clusters of CdS. The effects of cysteine separation on CdS particle size by varying the number of bonds with rotational freedom within the spacer amino acids is examined. Furthermore, the properties of the resulting CdS nanoclusters are reported.

A novel electrolyte: CdS nanoparticle capped with 2,2′-bipyridine

The use of an electroneutral ligand modified the Cd 2+-rich surface of CdS leads to the surrounding of CdS/2,2′-bpy by the counter ion (anion) to balance the charge of the Cd 2+ ions, resulting in the CdS cluster with strong electrolyte behavior.

Crystallography of Clusters

Crystallographic characterization of small metal clusters, oxide clusters of Cu and molecular clusters of CdS in the size range of 1 to 10 nm diameter is performed by using HRTEM. This is achieved by comparing experimentally obtained and digitised images and their calculated power spectra with computer simulations performed by the multislice technique for relevant cluster models. Typical structures are being discussed, such as fcc cuboctahedra, hexagonal structures, multiply twinned particles such as decahedra and icosahedra with 5-fold symmetries. Following a brief outline of the multislice technique, the calculations were performed for typical orientations depending on the different models. For most structural orientations, examples of experimental results are given. Finally, two examples for the reduction of oxidised Cu particles under the electron beam of high dose are presented.

A Blue-Emitting CdS/Dendrimer Nanocomposite

CdS/dendrimer nanocomposites that emit blue light are formed by the arrested precipitation of nanometer-scale CdS quantum dots in the presence of Starburst (poly(aminoamine)) dendrimers as the stabilizing host. The authors report a strong photoluminescence with emission maxima at about 450 nm. The optoelectronic properties of the CdS clusters are shown to be sensitive to synthesis conditions, including dendrimer type, solvent type, and the concentration of dendrimer and other solutes. Thin films of these materials prepared by solution casting retain the optoelectronic properties of the parent solutions.

Size-quantization in extremely small CdS clusters formed in calixarene LB films

CdS nanoparticles have been formed within Y-type Langmuir-Blodgett (LB) films of cadmium salts of calix(8)- and calix(4)-arene by reaction with H 2S. UV-vis absorption spectra of the LB films, measured at room temperature, show well-resolved transitions between size-quantization levels in CdS clusters. The size of the CdS particles, obtained by Gaussian fitting of the experimental spectra, is 1.5±0.3 nm, which is much less than those reported for fatty acid LB films. The particle size does not depend either on the type of calixarene or the number of LB layers. LB films were also characterised by X-ray diffraction and ellipsometry which show the film thickness do not change substantially after treatment with H 2S. The mechanism of CdS nanoparticles formation is discussed.

TOTAL AND SURFACE DENSITY OF STATES IN CdS SEMICONDUCTOR CLUSTERS

The total and partial density of states of different symmetries or at different shells in a fairly large CdS cluster (5305 or diameter 63 Å) are presented. Different from many other theoretical calculations on semiconductor clusters, which are mainly interested in the behavior of the near gap states, this work concentrates on the distributions of all electronic states of different symmetry in the energy space and real space. In particular, we found the surface density of states of the CdS clusters calculated here to strongly depend on whether the surface atoms of the cluster are Cd atoms. The results reveal some unique features of the behavior of the total electronic states in semiconductor clusters.

FIR optical study of CdS nanocrystals embedded in SiO2 films

A dielectric response due to polar optical phonons in CdS-doped SiO2 films (semiconductor volume fraction f≈6–15%) was studied experimentally by means of FIR and Raman spectroscopies. FIR reflectivity spectra taken at 80–300 K show a broad bulk CdS-like reflection band inconsistent with the relatively low f(≪1). To explain this, a model of fractal aggregates consisting of small crystalline particles was proposed and an effective dielectric function was calculated which fits well with the experimental FIR spectra. The asymmetric Raman lineshape of the 1LO peak observed experimentally can be fairly well fitted by the usual model considering LO-type phonon modes perfectly confined in nanocrystalline spheres. It is argued, however, that in accordance with the aggregate hypothesis, there is not much reason to consider the nanocrystals as regular spheres. Model lattice dynamics calculations for CdS clusters of irregular shape have been performed, and the results are shown to be able not only to fit equally well the LO Raman lineshape, but also to explain an extra feature appearing in the experimental spectra, interpreted as a disorder-activated acoustic mode.

ChemInform Abstract: Quantum Dots from the Bottle. Preparation and Properties of CdS and Other Semiconductor Clusters

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Characterization of CdS-NaX composite material synthesized in alkaline solution

The composite material consisting of CdS in a NaX zeolite host was synthesized in an alkaline aqueous solution at temperatures ranging from 25 to 70 °C, using cadmium chloride and thiourea as reactive substances. We found that CdS loading in the zeolite is controlled by the reaction temperature. This method allows the room temperature synthesis of CdS clusters and superclusters in the zeolite, stable at ambient conditions. X-ray diffraction patterns, scanning and transmission electron microscopy images and diffuse reflectance spectra of the samples were measured as a function of the reaction temperature. The evolution in the formation of CdS superclusters and the transition to CdS aggregates in the zeolite matrix was studied. The absorption spectrum of the samples prepared at the lowest temperature (25 and 30 °C) shows the transitions due to CdS clusters and superclusters in the zeolite matrix. In the samples prepared at higher temperatures CdS synthesizes in the zeolite matrix as a polycrystalline material with crystallite size depending on reaction temperature. A blue shift in the absorption edge of CdS is observed as a consequence of particle size effects.

Formation, structure and fluorescence of CdS clusters in a mesoporous zeolite

CdS clusters are formed in the pores of a mesoporous zeolite in which the size of the clusters may be adjusted. The size of the clusters increases as the CdS loading is increased. X-ray diffraction investigation shows that the lattice constants of the clusters contract upon increasing size. This contraction is attributed to an increase of the static pressure exercised by the zeolite framework as the clusters grow bigger. Both the excitonic and trapped emission bands are detected and become more intensive upon decreasing size. Three absorption bands appear in the photoluminescence excitation (PLE) spectra and they shift to the blue as cluster size decreases. Based on the effective-mass approximation, the three bands are assigned to the 1 S-1 S, 1 S-1 P and 1 S-1 D transitions, respectively. The size-dependence of the PLE spectra can also be explained.

Inorganic- Organic Hybrid Materials For Photonics

AbstractMolecular materials comprised of inorganic:organic composites are of considerable interest in photonics, optoelectronics and biophotonics. We report broad band lasing and tunable filters in sol-gel processed poly (p-phenylene vinylene) PPV: Silica composites. Optical power limiting in near IR wavelength region is also reported in dye doped PPV: silica multiphasic nanocomposites. For making hybrid inorganic: organic composites the reverse micelle mediated synthesis technique has been exploited to synthesize dye encapsulated metal oxide particles, thiocresol capped CdS clusters, Cul and AgI nanoparticles. These particles were dispersed in polymeric matrix for applications in photoconductivity and photorefractive measurements.

Fabrication and Characterization of CdS Nanostructure Doped Glass Thin Films by Pulsed Laser Evaporation

CdS doped glass thin films were grown by pulsed laser evaporation from sol–gel prepared targets. The sol–gel process was carried out under basic catalysis to contain more CdS dopants than those acid catalyzed. The structure of the CdS nanocrystallites in the film is determined to be wurzite by X-ray diffraction. The blue shift of the absorption edge and photoluminescence spectra, as well as the softening of the longitudinal optical phonon Raman mode, exhibit a quantum size effect. The diameter of CdS clusters embedded in the glass film is measured by these spectra to be 300 Å. The composition of the film determined by an electron probe microanalyzer and energy-dispersive spectrometer indicates that the amount of S atoms is greater than that of Cd atoms.

Electrospray Mass Spectrometry of Thiophenolate-Capped Clusters of CdS, CdSe, and ZnS and of Cadmium and Zinc Thiophenolate Complexes: Observation of Fragmentation and Metal, Chalcogenide, and Ligand Exchange Processes.

Electrospray mass spectrometry provides a rapid, convenient technique for characterizing and studying the chemistry of anionic metal sulfide thiolate clusters. Negative-ion electrospray mass spectra have been recorded for the thiophenolate-capped clusters [Me(4)N](4)[E(4)Cd(10)(SPh)(16)] (E = S, Se), [Me(4)N](4)[S(4)Zn(10)(SPh)(16)], and [Me(4)N](2)[S(4)Cd(17)(SPh)(28)] and of the metal thiophenolate complexes [Me(4)N](2)[M(SPh)(4)], [Me(4)N](2)[M(4)(SPh)(10)] (M = Cd, Zn), and [Et(4)N](2)[Cd(4)X(4)(SPh)(6)] (X= Cl, Br, I). The exchanges of M, E, and X which occur in various mixtures of these clusters and complexes and the fragmentation processes have been investigated. In the clusters the M-E bonds involving the sulfide or selenide core remain intact during the observed fragmentation at low cone voltages. At high cone voltages, monoions are ultimately formed by loss of charged species and neutral M(SPh)(2), resulting in almost complete removal of the SPh(-) ligands from the cluster core. Fragmentation of the ME core unit itself occurs only at very high voltages. The exchange of X in [Et(4)N](2)[Cd(4)X(4)(SPh)(6)] (X = Br, I) gives peaks due to the ions [Cd(4)I(n)()Br(m)()(SPh)(10)(-)(()(n)()(+)(m)()())](2)(-) (n + m = 0-4) and fragment ions with mixed ligands. The nature of the detected species suggests that the halides only exist as terminal ligands. The exchange of M in [Me(4)N](2)[M(4)(SPh)(10)] and [Me(4)N](4)[S(4)M(10)(SPh)(16)] results in the mixed-metal complexes [Cd(4)(-)(n)()Zn(n)()(SPh)(10)](2)(-) (n = 0-4) and the mixed-metal clusters [S(4)Cd(10)(-)(n)()Zn(n)()(SPh)(16)](4)(-) (n = 0-10). The exchange follows random statistics in [M(4)(SPh)(10)](2)(-) but is biased toward equilibrium association of the same metal in [S(4)M(10)(SPh)(16)](4)(-). The rates of exchange within the different structural elements of [S(4)M(10)(SPh)(16)](4)(-) and [S(4)M(17)(SPh)(28)](2)(-) decrease for the atoms located toward the center of the clusters.

Functionalization and Capping of a CdS Nanocluster: A Study of Ligand Exchange by Electrospray Mass Spectrometry

Electrospray mass spectrometry is a powerful technique for investigating the capping and the functionalization of the surface of a CdS nanocluster, via ligand-exchange reactions. The reactions of the thiophenolate-capped CdS cluster [S4Cd17(SPh)28]2- with thiols (HSR), dithiols (HSRSH), thiol acids (HSRCOOH), thio acids (RCOSH), thiol alcohols (HORSH), diethyldithiocarbamate [Et2NCSS]-, isopropylxanthate [(CH3)2CHOCSS]- and 3-mercaptopropyltrimethoxysilane [HS(CH2)3Si(OCH3)3] have been investigated. Information about the extent of exchange, bonding modes and cluster transformations is obtained. Almost complete exchange was observed for p-toluenethiol while the exchange with o-toluenethiol and 1-dodecanethiol was restricted owing to steric hindrance. The thiol acids HSRCOOH bind as the doubly charged [R(S)COO]2- ligand, chelating to neighboring cadmium atoms through both the thiol group and one of the oxygen atoms of the carboxylic acid group. The exchange with the thio acids [RCOSH] involves terminal [RCOS]- ions. Diethyldithiocarbamate [(C2H5)2NCSS]- and isopropylxanthate [(CH3)2CHOCSS]- remove cadmium atoms from the surface of the cluster due to the formation of terminal S,S-chelating bonds. 3-Mercaptopropyltrimethoxysilane HS(CH2)3Si(OCH3)3 readily exchanged to yield the silane-functionalized clusters [S4Cd17(SPh)28-n{S(CH2)3Si(OCH3)3}n]2- (n = 1−11).

The Surface Capping of the CdS Nanoparticle with the Electroneutral Group of 2,2′-Bipyridine in AOT Reverse Micelle

Abstract The CdS nanoparticles capped with 2,2′-bipyridine (bpy) had been synthesized in AOT reverse micelle. Bpy molecules adsorb on the Cd2+-rich surface of the CdS cluster via the nitrogen σ donation, which was elucidated by the FT-Raman spectroscopy. AOT exists as an anion ion of AOTSO3− in the CdS/bpy composite.

XAFS Study of CdTe1-xSxSemiconductor Glass Composites

We have measured the X-ray absorption spectra of CdTe 1-x S x nanocrystals grown in a borosilicate matrix, for x = 0, 0.1, 0.4 and 0.7. The appearance and the growth of the nanocrystals in isothermal heat-treatment at 580°C, observed in optical measurements, were correlated to the evolution of the XANES at the cadmium edge corresponding to the progressive substitution of oxygen atoms by chalcogens atoms. The final mean environment of the cadmium atoms in nanocrystals seems to be closer to CdS than to CdTe, for any value of x. On the other hand significant deviations from CdO pure environment were observed in non-treated samples, correlated to the increase in the sulfur content in the initial glass. These features were ascribed to the existence of early CdS clusters.

EXAFS study of functionalized nanoclusters and nanocluster assemblies

Extended X-ray absorption fine structure spectroscopy and X-ray diffraction were used to investigate the structure of CdS nanocrystals capped with different ligands. Nanocrystals capped with acetate and thiolate do exhibit the rock-salt structure, a high pressure type phase. These nanocsystals undergo a rock-salt to hawleyite transition after the thermal removal of the ligands at 200°C. Changes in coordination and distances as well as second-neighbor shells in differently capped CdS clusters are discussed in comparison with ZnS-clusters.

Thermoluminescence of CdS clusters in zeolite-Y

Thermoluminescence (TL) of CdS clusters encapsulated in zeolite-Y is reported for the first time. The TL of the clusters is much stronger than that of the bulk CdS and increases as the CdS loading decreases. This inverse dependence of TL intensity upon CdS loading is caused mainly by the size-effect of the clusters. All samples exhibit almost the same glow peak position and shape, indicating that traps or surface states are not sensitive to the cluster sizes.

New observation on the luminescence of CdS clusters in zeolite- Y

The excitation spectrum of CdS clusters in zeolite- Y is consistent with their absorption spectrum, both showing two absorption bands that are assigned to the 1 s−1 s and 1 s−1 p transitions, respectively. A new emission at 400 nm is considered to be the recombination of the bounded excitons. The emission firstly increases then decreases with increasing cluster size or loading. The emission by excitation into the 1 s−1 s band is stronger and sharper than that by excitation into the 1 s−1 p band. This phenomenon is attributed to the size inhomogeneity and the strong electron-phonon interaction of the clusters.