Growth of CdS nanoparticles in Y- and Z-type Langmuir–Blodgett thin film using 1,3-bis-(p-iminobenzoic acid)indane

Cadmium sulphide (CdS) nanoparticles were formed in 1,3-bis-(p-iminobenzoic acid)indane by exposing Cd²⁺ doped Y- and Z-type multilayered Langmuir–Blodgett (LB) films to H₂S gas. The growth of CdS nanoparticles were monitored by UV–visible spectroscopy measurements. It was observed that CdS nanoparticles in both Y- and Z-type LB films cause a blue-shift in absorption spectra. The surface morphology of LB films were characterized with atomic force microscopy DC electrical measurements were carried out for these LB films grown in a metal/LB film/metal sandwich structures with and without CdS nanoparticles. By analyzing I–V curves and assuming Schottky conduction mechanism the barrier height was found to be as 1.25 and 1.17?eV for Y-type unexposed and exposed samples; 1.18 and 1.25?eV for Z-type unexposed and exposed samples, respectively.     

Ultrasound-assisted fabrication of nanoporous CdS films

A new method for fabricating nanoporous CdS films is reported. It involves exposing the CdS solution with ultrasound waves during the process of dip coating. Indium tin oxide (ITO)-coated glass and plastic (commercial transparency) were used as substrates. In each case three different precursors were used for dip coating. The precursors used were CdCl2 and thiourea in one case and CdS nanoparticles prepared by sonochemical and microwave-assisted methods in the other two cases. X-ray diffraction studies performed on these powders show a phase corresponding to cubic CdS. The Field Emission Scanning Electron Microscopy (FE-SEM) images of the films on plastic showed uniform pores with a diameter of 80 nm for all three methods. Optical absorption measurements indicated a blue shift and multiple peaks in the absorption curve. The FE-SEM observations of the films on an ITO/glass substrate indicated a crystalline film with voids. The UV-vis absorption results indicated a blue shift in the absorption with an absorption edge at 435, 380, and 365 nm for CdS films made by solution growth, sonochemical, and microwave routes, respectively. The magnitude of the absorption is dependent on film thickness, and the observed blue shift in the absorption can be explained on the basis of quantum confinement effects.     

CdS nanoparticles grown in a polymer matrix by chemical bath deposition

Nanocrystallites of CdS have been grown by chemical bath deposition within the pores of poly(vinyl alcohol) (PVA) on glass and Si substrates. The CdS-PVA composite films are transparent in the visible region. XRD and TEM diffraction patterns confirmed the nanocrystalline CdS phase formation. TEM study of the film revealed the manifestation of nano CdS phase formation and the average particles size was varied in the range 5-12 nm. UV-vis spectrophotometric measurement showed high transparency (nearly 80% in the wavelength range 550-900 nm) of the films with a direct allowed band gap lying in the range 2.64-3.25 eV. Particle sizes have also been calculated from the shift of band gap with respect to that of bulk value and were found to be in the range 3.3-6.44 nm. The high dielectric constant (lies in the range 120-250 at high frequency) of PVA/CdS nanocomposite compared to that of pure PVA (-28) has been observed. The dielectric constant decreases with increase of dispersibility of the CdS nanoparticles within PVA. The nanocrystalline PVA/CdS thin films have also showed field emission properties with a turn-on field of approximately 6.6 V/microm, whereas only PVA thin film and bulk CdS on PVA have shown no field emission.     

Quantum confinement effect of CdS nanoparticles dispersed within PVP/PVA nanocomposites

Nanocomposite films of CdS nanoparticles within PVP/PVA blend were prepared. The prepared films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and photoluminescence (PL) spectra. The amount of Cd⁺ used strongly influenced the size of the CdS nanoparticles, which was confirmed by XRD, UV–vis absorption spectra, PL emission spectra and TEM images. Smaller sized CdS nanoparticles were formed in higher content of cadmium. The results of XRD indicate that CdS nanoparticles were formed with hexagonal phase in the polymeric matrix. PL and UV–vis spectra reveal that nanocomposite films shows quantum confinement effect. Optical band gap and particle size were calculated and is in agreement with the results obtained from TEM data. The direct energy band gap was increased up to 2.86 eV.     

Biotemplated preparation of CdS nanoparticles/bacterial cellulose hybrid nanofibers for photocatalysis application

In this work, we describe a novel facile and effective strategy to prepare micrometer-long hybrid nanofibers by deposition of CdS nanoparticles onto the substrate of hydrated bacterial cellulose nanofibers (BCF). Hexagonal phase CdS nanocrystals were achieved via a simple hydrothermal reaction between CdCl(2) and thiourea at relatively low temperature. The prepared pristine BCF and the CdS/BCF hybrid nanofibers were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), UV-vis absorption spectroscopy (UV-vis), and X-ray photoelectron spectroscopy (XPS). The results reveal that the CdS nanoparticles were homogeneously deposited on the BCF surface and stabilized via coordination effect. The CdS/BCF hybrid nanofibers demonstrated high-efficiency photocatalysis with 82% methyl orange (MO) degradation after 90 min irradiation and good recyclability. The results indicate that the CdS/BCF hybrid nanofibers are promising candidate as robust visible light responsive photocatalysts.     

Electrical properties of a novel 1,3-bis-(p-iminobenzoic acid) indane Langmuir-Blodgett films containing ZnS nanoparticles

ZnS nanoparticles have been formed in a newly synthesized 1,3-bis-(p-iminobenzoic acid) indane (IBI) by exposing Zn2+ doped multilayered Langmuir-Blodgett (LB) film to H2S gas after the growth. The formation of ZnS nanoparticles in the LB film structure was verified by measuring UV-Visible absorption spectra. DC electrical measurements were carried out for thin films of IBI prepared in a metal/LB films/metal sandwich structure with and without ZnS nanoparticles. It was observed that ZnS nanoparticles in the LB films cause a blue-shift in the absorption spectra as well as a decrease in both capacitance and conductivity values. By analysing I-V curves and assuming a Schottky conduction mechanism the barrier height was found to be about 1.13 eV and 1.21 eV for IBI LB films without and with ZnS nanoparticles, respectively. It is thought that the presence of ZnS nanoparticles influences the barrier height at the metal-organic film interface and causes a change in electrical conduction properties of LB films.     

Chemical synthesis of CdS nanoparticles and their optical and dielectric studies

Cadmium sulphide nanoparticles were synthesized by chemical displacement reaction method using cadmium nitrate as cadmium source and ammonium sulphide as sulphur source. The CdS samples are characterized using X-ray diffraction, UV–Vis spectroscopy, FTIR spectroscopy, scanning electron microscopy and impedance spectroscopy. CdS nanoparticles are found to possess cubic structure with the crystallite size ~10 nm. The absorption spectra of synthesized CdS nanoparticles revealed the blue shift in excitonic transitions with respect to CdS bulk material, clearly confirming the formation of nanoparticles. The dielectric properties of CdS nanoparticles are studied in the frequency range 10³–10⁷ Hz at room temperature. The dielectric properties of CdS nanoparticles are found to be significantly enhanced specially in the low frequency range due to confinement.     

Study of Sago starch-CdS nanocomposite films: fabrication, structure, optical and thermal properties

A synthetic procedure for the preparation of nanocomposite films of sago starch and CdS nanoparticles was introduced. The films were characterized using optical, structural, and thermal techniques. The formation of nanostructured CdS in the starch matrix was confirmed by a blue shift in the onset of absorption in the UV-VIS spectra of the nanocomposites. The average size of the nanoparticles varied from 3.6 to 5 nm, depending on the initial concentration of cadmium acetate during the nanocomposite preparation. Fluorescence measurements of the sago-CdS nanocomposite film showed broad emission in the orange-red part of the spectrum. DSC and TGA analyses revealed significant effects of CdS nanoparticles on the thermal properties of the starch matrix.     

Nanocomposite organic films on silicon

Metal-insulator-semiconductor structures were fabricated using 40-layers-thick Langmuir-Blodgett (LB) films of stearic acid (SA) on hydrophobic n-type silicon (n-Si) substrates. Cadmium sulphide (CdS) nanoparticles were introduced by exposure to H/sub 2/S gas for a period of 12 h. Samples containing CdS nanoparticles exhibit lower dc leakage current but higher effective dielectric constant. The effective dielectric constant of the CdS embedded SA matrix is found to be 5.1. The Poole-Frenkel effect is prevalent for charge transport in the LB films containing CdS nanoparticles at the field higher than 10/sup 7//spl middot/ Vm/sup -1/. The effect becomes saturated at higher fields.     

Synthesis and characterization of sol-gel silica films doped with size-selected gold nanoparticles

Homogeneous nanocomposite silica films uniformly doped with size-selected gold nanoparticles (AuNPs) have been prepared by a combined use of colloidal chemistry and the sol-gel process. For this purpose, stable thiol-functionalized AuNPs (DDT-AuNPs) were first synthesized by a two-phase aqueous/organic system and, subsequently, dispersed in an acid-catalysed sol-gel silica solution. The microstructural morphology of the samples was investigated by x-ray diffraction and field emission scanning electron microscopy. X-ray photoelectron spectroscopy (XPS) and UV-vis optical spectrophotometry were instead employed to investigate the elemental chemical behaviour and the evolution of the surface plasmon resonance (SPR) band of the AuNPs from their synthesis up to the formation of the Au-doped silica films. The results show that the size, shape and crystalline domains of the AuNPs remain unchanged during the entire preparation process, indicating that their aggregation or decomposition was prevented. XPS results show that the DDT-AuNPs lose the capping shells and oxidize themselves when dispersed in acid-catalysed sol-gel solutions, and that bare AuNPs are embedded in the SiO(2) films. A large broadening of the SPR band, observed for systems with DDT-AuNPs, suggests the presence of interface effects which cause a surface electron density lowering. Thiol chain detachment from the AuNPs determines an increase of the SPR peak intensity while the oxidation of the Au surfaces causes a red shift of its position. The latter is no longer observed in doped films, suggesting that no interfacial effects between bare AuNPs and the host medium are present.     

Preparation of ultrafine chalcopyrite nanoparticles via the photochemical decomposition of molecular single-source precursors

The synthesis and characterization of ultrafine CuInS2 nanoparticles are described. Ultraviolet irradiation was used to decompose a molecular single source precursor, yielding organic soluble approximately 2 nm sized nanoparticles with a narrow size distribution. UV-vis absorption, 1H and 31P{1H} NMR, and fluorescence spectroscopies and mass spectrometry were used to characterize decomposition of the precursors and nanoparticle formation. The nanoparticles were characterized by high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy energy dispersive X-ray spectroscopy, powder X-ray diffraction (XRD), electron diffraction, inductively coupled plasma analysis, UV-vis absorption spectroscopy, and fluorescence spectroscopy. They have a wurzite-type crystal structure with a copper-rich composition. The hypsochromic shift in their emission band due to quantum confinement effects is consistent with the size of the nanocrystals indicated in the HRTEM and XRD analyses.     

Interphase synthesis of Fe3O4/CdS core-shell nanoparticles

CdS and Fe₃O₄/CdS core-shell nanoparticles were synthesized by a simple interphase method. The obtained nanoparticles were characterized by TEM, XRD and spectroscopy techniques (fluorescence and UV-vis absorption). The effects of reagent concentration on the properties of obtained nanoparticles were investigated. It was shown that the UV-vis spectra of the Fe₃O₄/CdS colloidal toluene solutions have the sharp edge at 311 nm and the long tail. The broad emission bands in the photoluminescence spectra of the Fe₃O₄/CdS organosols observed at 506, 560 and 568 nm with the increasing of cadmium oleate concentration. The thickness of CdS shell was ranged from 0.2 to 1.0 nm while the average size of the magnetite core is about 9.9 nm.     

Effect of cadmium sulphide quantum dot processing and post thermal annealing on P3HT/PCBM photovoltaic device

The present study demonstrates the effect on photovoltaic performance of poly(3-hexylthiophene) (P3HT) on doping of cadmium sulphide (CdS) quantum dots (QDs). The P3HT/CdS nanocomposite shows a 10 nm blue shift in the UV-vis absorption relative to the pristine P3HT. The blue shift in the absorption of the P3HT/CdS nanocomposite can be assigned to the quantum confinement effect from the CdS nanoparticles. Significant PL quenching was observed for the nanocomposite films, attributed to additional decaying paths of the excited electrons through the CdS. Solar cell performance of pure P3HT and dispersed with CdS QDs have been studied in the device configuration viz indium tin oxide (ITO)/poly(3,4-ethylendioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS)/P3HT:PCBM/Al and ITO/PEDOT:PSS/ P3HT:CdS:PCBM/Al, respectively. Incorporation of CdS QDs in the P3HT matrix results in the enhancement in the device efficiency (?) of the solar cell from 0.45 to 0.87%. Postproduction thermal annealing at 150 °C for 30 min improves device performance due to enhancement in the device parameters like FF, V_OC and improvement in contact between active layer and Al.     

Self assembling of porphyrin-fullerene dyads in the Langmuir and Langmuir-Blodgett films: formation as well as spectral, electrochemical and vectorial electron transfer studies

Donor-acceptor dyads of water-soluble Zn porphyrins and C60 bearing either pyridine or imidazole ligand were self assembled via axial coordination in Langmuir and Langmuir-Blodgett (LB) films. Compression and surface potential versus area per molecule isotherms as well as ellipsometry and BAM measurements showed that molecules were aggregated in all Langmuir films before compression. The area per molecule in the absence of aggregation was determined by linear extrapolation of the area at the zero surface pressure to infinite adduct dilution. Comparison of the extrapolated and theoretically calculated areas, being dependent on the composition of the subphase solution, indicated that dyads were oriented with their porphyrin macrocycles in plane of the air-solution interface. Calculated by molecular modeling thickness of the Langmuir films was in accord with that determined by ellipsometry. The Langmuir films were transferred, by using the LB technique, onto different solid substrates for spectroscopic, microscopic, electroanalytical, and photochemical characterization. From the IR spectroscopy investigations it followed that the porphyrin macrocycle of the dyad was either nearly parallel or tilted with respect to the substrate plane. Molecularly modeled pseudo-hexagonal packing and thickness of the LB films were in accord with that imaged by STM and determined by ellipsometry, respectively. The electrochemical redox states of the dyads were established by performing simultaneous cyclic voltammetry and piezoelectric microgravimetry measurements of the LB films on Au-quartz electrodes. Both steady-state and time-resolved emission studies of the zinc porphyrin-fullerene LB films revealed efficient quenching of the singlet-excited Zn porphyrin. Based on the free-energy calculations and dyad orientation in the film, this quenching was attributed to vectorial electron transfer within the dyad.     

Semiconductor/metal nanocomposites formed by in situ reduction method in multilayer thin films

A layer-by-layer adsorption and in situ reduction method was adopted for synthesizing semiconductor/metal nanocomposites in multilayer ultra-thin films. Alternate adsorption of ZnO nanoparticles modified with poly(ethyleneimine), hydrogentetrachloroaurate and poly(styrenesulfonate) sodium results in the formation of ZnO/AuCl₄⁻-loaded multilayer films. In situ reduction of the incorporated metal ions by heating yields ZnO/Au nanocomposites in the films. UV-vis absorption spectroscopy and X-ray photoelectron spectroscopy were used to characterize the components of the composite films. UV-vis spectra indicate regular growth of the films. The electrochemistry behavior of the multilayer films was studied in detail on indium tin oxide electrode. The combined results suggest that the layer-by-layer adsorption and subsequent reduction method used here provides an effective way to synthesize ZnO/Au nanocomposites in the polymer matrix.     

Synthesis of CdS nanoparticles based on DNA network templates

CdS nanoparticles have been successfully synthesized by using DNA networks as templates. The synthesis was carried out by first dropping a mixture of cadmium acetate and DNA on a mica surface for the formation of the DNA network template and then transferring the sample into a heated thiourea solution. The Cd(2+) reacted with thiourea at high temperature and formed CdS nanoparticles on the DNA network template. UV-vis spectroscopy, photoluminescence, x-ray diffraction and atomic force microscopy (AFM) were used to characterize the CdS nanoparticles in detail. AFM results showed that the resulted CdS nanoparticles were directly aligned on the DNA network templates and that the synthesis and assembly of CdS nanoparticles was realized in one step. CdS nanoparticles fabricated with this method were smaller than those directly synthesized in a thiourea solution and were uniformly aligned on the DNA networks. By adjusting the density of the DNA networks and the concentration of Cd(2+), the size and density of the CdS nanoparticles could be effectively controlled and CdS nanoparticles could grow along the DNA chains into nanowires. The possible growth mechanism has also been discussed in detail.     

Photoluminescence and raman study of CdS-Al2O3 nanocomposite films prepared by sol-gel techniques

The optical and microstructural properties of CdS-Al2O3 nanocomposite (CdS-Al2O3 = 20:80 to 50:50) thin films synthesized by sol-gel techniques were studied. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement. Band gaps of CdS-Al2O3 nanocomposites were found to vary in the range 3.69-2.61 eV. The sizes of the nanocrystals, estimated from the blue shift (0.2-1.2 eV) of the absorption edges and transmission electron microscopy, were found to vary in the range 2.8-7.0 nm. X-ray diffraction studies showed reflections from (111), (200), (220), and (311) planes of CdS in the cubic phase. Microstructural characterization by high-resolution transmission electron microscope (HRTEM) indicated well crystallinity of the nanoparticles and lattice fringes supported the cubic phase of CdS. Raman spectroscopy was carried out for CdS-Al2O3 nanocomposites, which indicated a prominent peak at approximately 299 cm(-1). Significant changes in the peak position and intensity of the Raman peak were observed with varying the annealing temperature (373-573 K). Photoluminescence measurements indicated a prominent broad peak at approximately 1.81 eV due to the surface defects in the CdS nanocrystallites. The present study revealed Al2O3 to be a good capping material for CdS nanoparticles.     

Facile synthesis of near-monodisperse Ag@Ni core-shell nanoparticles and their application for catalytic generation of hydrogen

Magnetically recyclable Ag-Ni core-shell nanoparticles have been fabricated via a simple one-pot synthetic route using oleylamine both as solvent and reducing agent and triphenylphosphine as a surfactant. As characterized by transmission electron microscopy (TEM), the as-synthesized Ag-Ni core-shell nanoparticles exhibit a very narrow size distribution with a typical size of 14.9 ± 1.2 nm and a tunable shell thickness. UV-vis absorption spectroscopy study shows that the formation of a Ni shell on Ag core can damp the surface plasmon resonance (SPR) of the Ag core and lead to a red-shifted SPR absorption peak. Magnetic measurement indicates that all the as-synthesized Ag-Ni core-shell nanoparticles are superparamagnetic at room temperature, and their blocking temperatures can be controlled by modulating the shell thickness. The as-synthesized Ag-Ni core-shell nanoparticles exhibit excellent catalytic properties for the generation of H(2) from dehydrogenation of sodium borohydride in aqueous solutions. The hydrogen generation rate of Ag-Ni core-shell nanoparticles is found to be much higher than that of Ag and Ni nanoparticles of a similar size, and the calculated activation energy for hydrogen generation is lower than that of many bimetallic catalysts. The strategy employed here can also be extended to other noble-magnetic metal systems.     

Comparison of CdS thin films prepared by different techniques for applications in solar cells as window materials

CdS thin films as window materials for solar cells have been prepared by three procedures; chemical bath deposition, electrodeposition in an aqueous medium at 80 °C and electrodeposition in a non-aqueous medium at 170 °C. As deposited films along with those obtained after annealing in air at 400 °C for 15 min were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES), scanning electron microscopy (SEM), optical absorption spectra and photoelectrochemical spectroscopy (PEC) techniques under identical experimental conditions. X-ray diffraction data indicate the formation of hexagonal CdS as the predominent phase, but the SEM studies show that their textures are widely dependent on the conditions employed. GDOES profiling indicates the incorporation of Na and Si into CdS films prepared by all three techniques. Annealing of chemical bath deposited films causes a red shift of the absorbance edge and also a shift in the maxima of the photocurrent action spectra towards the low energy side. However, this effect was comparatively negligible for the samples prepared by the other two techniques. PEC studies indicate that CdS materials grown by all three techniques are all n-type. All studies indicate that the films grown at 170 °C using non-aqueous solutions are of better crystallinity and of improved electrical properties. © 1998 Kluwer Academic Publishers     

C60/PVK/CdS纳米粒子功能复合 LB 膜研究

目的 尝试用Ｌａｎｇｍｕｉｒ－Ｂｌｏｄｇｅｔｔ（ＬＢ）技术组装Ｃ６０技术组装Ｃ６０功能复合体系的新方法。方法 采用（ＬＢ）技术制备Ｃ６０／ＰＶＫ／ＣｄＳ花生酸混合ＬＢ膜并利用界面化学反应技术将混合膜与硫化氢气体反应制得Ｃ６０／ＰＶＫ／ＣｄＳ纳米粒子功能复合ＬＢ膜并进行紫外光谱表征。结果 含不同比例Ｃ６０的Ｃ６０ＰＶＫ／ＡＡ体系可以在辐亚相上形成稳定的单层膜并转移到固体基片上得到了ＬＢ多层膜,ＬＢ混