Flash evaporated cadmium sulfide films

Cadmium sulfide (CdS) thin films were deposited by the flash evaporation technique onto glass substrates kept at temperatures in the range 30–300 °C. The source material was CdS powder synthesized in the laboratory. The films exhibited hexagonal structure with dislocation density and the stress decreased as the substrate temperature increased. An optical band gap of 2.39 eV was obtained for the films deposited at 300 °C. Raman spectra exhibited peaks corresponding to Longitudinal Optical phonons of CdS with the full width at half maximum decreasing with increase of substrate temperature. Room temperature resistivity values are lower than earlier reports on chemically deposited CdS films.     

One step synthesis of ZnO nanoparticles in free organic medium: Structural and optical characterizations

Nano-sized ZnO particles are synthesized by the sol–gel method in aqueous medium without any annealing, ripening treatment or organic additive addition. The structure, morphology, and optical properties of these ZnO nanoparticles are characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Ultraviolet–visible spectroscopy (UV–vis) respectively. The effect of the synthesis temperature on the morphological (shape and size) and optical properties of these nanoparticles have been examined for temperatures varying from 0 to 80 °C. XRD analysis shows that the as-prepared particles crystallize in the Würtzite hexagonal phase even at very low synthesis temperatures. Meanwhile, Transmission Electron Microscopy observations reveal that the particles present a significant change in shape and size as the temperature increases. They take a flower shape, at very low temperatures, a conical or ellipsoidal shape when the temperature is ranging from 20 °C to 50 °C and a rodlike shape with a hexagonal section at elevated temperatures (>50 °C). Moreover, it has been observed that the increasing of the synthesis temperature leads to a net increase in the average particle size. It affects especially the length in the minor axis direction while the length in the major direction (c-axis) remains nearly constant. Optical properties, carried out by spectrophotometric measurements, indicate that increasing the temperature results in lower band gap energy values.     

Control of the crystalline phase and morphology of CdS deposited on microstructured surfaces by chemical bath deposition

Chemical bath deposition (CBD) has been used extensively to deposit thin films of CdS for window layers in solar cells. The microtopography or roughness of the surface, however, can affect the quality of the film by influencing the morphology, uniformity, or crystal phase of the CdS film. Here, we have demonstrated that thin films of CdS can be successfully patterned on surfaces bearing micropillars as a model surface for roughness. The phase purity of CdS deposited on the micropillar surfaces is uniform and conformal with the formation of packed clusters on the micropillars at pH 10 that form flower-like structures at long deposition times. Smaller crystallites were observed on micropillar arrays at pH 8 with “network” like structures observed at long deposition times. Additionally, by controlling the pH of the chemical bath, the hexagonal and cubic crystal phases of CdS were both accessible in high purity at temperatures as low as 85 °C.     

Effect of temperature on crystallite sizes of copper sulfide nanocrystals prepared from copper(II) dithiocarbamate single source precursor

We report the synthesis of CuS nanoparticles using [Cu(butdtc)₂] as single source precursor thermolysed at two different temperatures. The products were characterized by UV–vis absorption spectroscopy, X-ray diffraction, Transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray analysis and atomic force microscopy. The absorption spectra of the CuS nanocrystals are blue shifted and the XRD were indexed to the hexagonal phase of CuS with nanoparticles obtained at 120 °C showing well defined crystalline structure compared to those obtained at 180 °C. Transmission electron microscopy images showed particles that are almost spherical in shapes with average crystallite sizes of 21–38 nm for CuS1 prepared at 180 °C and 3–7 nm for CuS2 prepared at 120 °C and confirms that the chosen reaction temperature determine the crystallite sizes of the nanoparticles.     

Structural,magnetic and dielectric properties of nanocrystalline cobalt ferrite by wet hydroxyl chemical route

Nanopowders of CoFe₂O₄ are synthesized via wet chemical co-precipitation processing at pH 8. The synthesized nanoferrite powders are annealed at various temperatures (350 °C, 700 °C and 1050 °C) and are characterized. X-ray diffraction (XRD) patterns indicate the crystalline nature of CoFe₂O₄ nanopowders. Transmission electron microscope (TEM) investigations show, anisotropic shapes like cubic, hexagonal and spherical morphology of nanoparticles with average particle size 38–85 nm. Dielectric constant decreases as the frequency increases. Low value of dielectric loss at higher frequencies suggests the material is suitable for high frequency applications. AC conductivity increases with frequency. The saturation magnetization (M_s), remanant magnetism (M_R) and coercivity (H_C) increases with applied field.     

Effect of CdS layers on opto-electrical properties of chemically prepared ZnS/CdS/TiO2 photoanodes

In the present work, CdS nanoparticles as a sensitizer were grown on the spin coated nanoporous TiO₂ film by repeated cycles of a Successive Ionic Layer Adsorption and Reaction (SILAR) method. ZnS layer was coated on the CdS/TiO₂ anodes to act as a protection layer on CdS. The crystallite size of CdS nanocrystals is calculated to be 3 nm from XRD spectra. The optical band gap of the film determined from transmittance spectra decreases from 3.46 to 2.15 eV with the increase in the number of CdS SILAR cycles. SEM and TEM analysis depict the enabled penetration of CdS (1 1 1) nanoparticles into the nanoporous TiO₂ (1 0 1) structure. EDX study confirms the presence of all the elements (Ti, Cd, S, Zn and O) found on the photoanode. The attachment of cubic structured CdS on anatase phase of TiO₂ in the photoanode is verified using Raman spectra. Photoluminescence (PL) study shows that the emission peak corresponding to TiO₂ has been slightly blueshifted due to the interaction of CdS nanoparticles in TiO₂ nanoporous structures. The electrical measurement shows that the dark and light illuminated resistivity of the preferred photoanode is 7.91 and 5.65 Ω cm respectively.     

Improved electrodeposition of CdS layers in presence of activating H2SeO3 microadditive

CdS thin films were deposited electrochemically onto indium tin oxide (ITO)/glass substrates from aqueous solutions containing 0.01 M CdCl₂, 0.05 M Na₂S₂O₃ and 0.02 M Edta-Na₂ at −1.2 mV versus saturated sulfate reference electrode. Depositions were carried out at various temperatures (20, 50 and 80 °С) and different pH (2.5, 3.5 and 4.5) in a three electrode electrochemical cell. All above mentioned electrochemical syntheses were reproduced in presence of H₂SeO₃ microadditive to compare resulted CdS layers. Electrodeposited CdS thin films were characterized by different instrumental techniques to know the influence of deposition conditions on the quality of the obtained layers. It was found that the presence of 0.05–0.5 mM of H₂SeO₃ in the electrolyte changes the mechanism of the CdS film formation that facilitates nucleation and a growth of a more dense and uniform polycrystalline CdS film. Addition of 0.5 mM of H₂SeO₃ into the initial solution allowed us to obtain nearly stoichiometric (sulfur content ~52 at%) CdS films at reduced temperature value of 50 °C vs. higher temperature values used in a conventional electrodeposition process of CdS layers. No Se-containing phases were detected by EDX, Raman and XRD analyses in the CdS films. The presence of H₂SeO₃ tends to rearrange polytype crystalline structure of CdS to more stable hexagonal structure. The band gap value of CdS was increased from 2.3 eV to 2.5 eV as a result of H₂SeO₃ addition.     

High thermal annealing effect on structural and optical properties of ZnO–SiO2 nanocomposite

The effect of annealing temperature on photoluminescence (PL) of ZnO–SiO₂ nanocomposite was investigated. The ZnO–SiO₂ nanocomposite was annealed at different temperatures from 600 °C to 1000 °C with a step of 100 °C. High Resolution Transmission Electron Microscope (HR-TEM) pictures showed ZnO nanoparticles of 5 nm are capped with amorphous SiO₂ matrix. Field Emission Scanning Electron Microscope (FE-SEM) pictures showed that samples exhibit spherical morphology up to 800 °C and dumbbell morphology above 800 °C. The absorption spectrum of ZnO–SiO₂ nanocomposite suffers a blue-shift from 369 nm to 365 nm with increase of temperature from 800 °C to 1000 °C. The PL spectrum of ZnO–SiO₂ nanocomposite exhibited an UV emission positioned at 396 nm. The UV emission intensity increased as the temperature increased from 600 °C to 700 °C and then decreased for samples annealed at and above 800^°C. The XRD results showed that formation of willemite phase starts at 800 °C and pure willemite phase formed at 1000 °C. The decrease of the intensity of 396 nm emission peak at 900 °C and 1000 °C is due to the collapse of the ZnO hexagonal structure. This is due to the dominant diffusion of Zn into SiO₂ at these temperatures. At 1000 °C, an emission peak at 388 nm is observed in addition to UV emission of ZnO at 396 nm and is believed to be originated from the willemite.     

Enhancement in the optical and electrical properties of CdS thin films through Ga and K co-doping

In the presented work, Ga-doped CdS and (Ga-K)-co-doped CdS thin films are grown on glass substrates at a temperature of 400 °C through spray pyrolysis. Influence of K-doping on structural, morphological, optical and electrical characteristics of CdS:Ga thin films are examined. K level is changed from 1 at% to 5 at% for CdS:Ga samples just as Ga concentration is fixed 2 at% for all CdS thin films. It is observed from the X-ray diffraction data that all the samples exhibit hexagonal structure and an increase level of K in Ga-doped CdS samples causes a degradation in the crystal quality. Energy-dispersive X-ray spectroscopy measurements illustrate that the best stoichiometric film is acquired when K content is 2 at% in Ga-doped CdS films. Optical transmission curves demonstrate that CdS:Ga thin films exhibit the best optical transparency in the visible range for 4 at% K content compared to other specimens. A widening in the optical bandgap is unveiled after K-dopings. It is obtained that maximum band gap value is found as 2.45 eV for 3 at%, 4 at% and 5 at%. K -dopings while Ga-doped CdS thin films display the band gap value of 2.43 eV. From photoluminescence measurements, the most intensified peak is observed in the deep level emission after incorporation of the 4 at% K atoms. As for electrical characterization results, the resistivity reduces and the carrier density improves with the increase of K concentration from 1 at% to 4 at%. Based on all the data, it can be deduced that 4 at% K-doped CdS:Ga thin films show the best optical and electrical behavior, which can be utilized for solar cell devices.     

Low temperature synthesis of PbS and CdS nanoparticles in olive oil

Heterocyclic dithiocarbamate complexes; bis(dipiperidinyldithiocarbamato)M(II) and bis(ditetrahydroquinolinyldithio-carbamato)M(II), M= Pb and Cd, were used as precursors for the synthesis of PbS and CdS in olive oil. The precursors were thermolysed at a relatively low temperature of 180 °C. Distinct cube shaped PbS nanoparticles were obtained with the X-ray diffraction peaks assigned to the cubic rock salt phase. The optical properties of the olive-oil capped CdS particles synthesized at 180 °C showed evidence of quantum confinement. The CdS particles obtained from both precursors were spherical in shape with evidence of agglomeration in the transmission electron microscopy images.     

Effect of calcination temperature on Cu doped NiO nanoparticles prepared via wet-chemical method: Structural,optical and morphological studies

In the present study, NiO and Cu-doped NiO nanoparticles were successfully synthesized by wet chemical method at room temperature using sodium hydroxide (NaOH) as precipitating agent. The as-prepared Cu-doped NiO powder samples were subjected to three different calcination temperatures such as, 350 °C, 450 °C and 550 °C in order to investigate the impact of calcined temperatures on the phase formation, particle size and band gap evolution. The phase formation and crystal structure information of the prepared nanomaterials were examined by X-ray powder diffraction (XRD). XRD revealed the face-centered cubic (FCC) structure. Average crystalline size of pure and doped samples estimated using Scherer formula was found to be 15 nm and 9 nm respectively. With increase in the calcination temperature from 350 °C to 550 °C for the Cu doped NiO samples the particle size of the nanoparticles was found to increase from 4 nm to 9 nm respectively. The optical study for both pure and doped NiO nanoparticles was performed using an UV–Vis spectrophotometer in the wavelength range of 200–800 nm. The strong absorption in the UV region confirms the band gap absorption in NiO and was estimated from the UV–Vis diffuse reflectance spectra via Tauc plot. Systematic studies were also carried out to study the effect of calcination on the optical transmittance. Samples were also investigated using Raman and Fourier Transform Infrared Spectroscopy (FTIR). Furthermore, morphology of the pure NiO and Cu-doped NiO Nanoparticles were examined by scanning electron microscope (SEM).     

Growth mechanisms and their effects on the opto-electrical properties of CdS thin films prepared by chemical bath deposition

Chemically deposited CdS exhibits high sensitivity in the opto-electrical performance to the growth mechanisms. Hence it is of a great interest to study the effects of growth mechanisms on the opto-electrical performance in such films. Studies were carried out by the means of spectroscopic ellipsometry, and coupled with structural, optical, and electrical characterization. A range of bath temperatures (55 °C–95  °C) were used as the means to alter the growth mechanisms. Ion-by-ion process dominated deposition at lower bath temperatures throughout the length of the deposition. This mechanism produced films composed of single phase cubic crystals with corresponding opto-electrical properties inherent to such structures. Complex formations at higher bath temperatures supplement the sole ion-by-ion mechanisms with the cluster-by-cluster mechanism. This results in a mixed cubic/hexagonal structure, and deviation from stoichiometry. As a result, carrier concentrations and mobility increased nearly eight and four fold respectively. Resistivity decreased more than four times from 33.2 to 7.5 Ω cm. A noticeable decrease of, ~0.2 was observed in the refractive index and an increase of ~0.07 eV in the band gap is also reported. Nuclear magnetic resonance analysis confirms deviation from stoichiometry in the cluster-by-cluster mechanisms, resulting in interstitially trapped Cd⁺² and S⁻² ions. The trapped ions act as donors in the film enhancing its electrical performance.     

Preparation and characterization of pulsed laser deposited CdS/CdSe bi-layer films for CdTe solar cell application

CdS/CdSe bi-layer film was prepared by pulsed laser deposition with different substrate temperatures as an improved window layer for CdTe solar cells. The total thickness of each CdS/CdSe bi-layer film was about 70 nm, which could contribute to comparatively high transmittance of photons and, therefore, improving the photocurrent. Substrate temperature influenced the properties of the CdS/CdSe bi-layer films and the study showed that the bi-layer film prepared at 400 °C achieved the best optical transmittance and crystallinity. The crystal structure and optical transmittance of CdS/CdSe/CdTe stack before and after CdCl₂ annealing treatment were investigated by utilizing X-ray diffraction and UV/Vis spectrophotometer, respectively. It showed that further CdCl₂ annealing treatment improved the inter-diffusion of Se into CdTe, facilitating the formation of a CdTe_1−xSe_x alloy in the absorber layer. Comparing with CdTe, the alloy actually showed a smaller band gap which produced an obvious red shift of the absorption edge in long wavelength region. CdSe window layer was consumed by the inter-diffusion, while enhanced the short wavelength response in the range of 300–500 nm. The device based on CdS/CdSe window layer realized a J_SC enhancement due to the improved collection within both short and long wavelength regions accompany with a V_OC enhancement when compared to CdS/CdTe solar cell. The CdTe cell with CdS/CdSe bi-layer window deposited at 200 °C showed an efficiency of 13.47% with V_OC of 791 mV and J_SC of 27.40 mA/cm².     

The influence of substrate temperature on RF sputtered CdS thin films and CdS/p-Si heterojunctions

Cadmium sulfide (CdS) thin films were deposited onto soda lime glasses and p-Si semiconductors at various substrate temperatures (40, 150 and 275 °C) by radio frequency (RF) sputtering technique. The effect of substrate temperature on morphological, structural and optical properties of CdS thin films were analyzed by means of atomic force microscopy (AFM), x-ray diffraction (XRD) and uv–vis spectrum data. The results showed that the average roughness (R_a) of thin films increased from 2.0 to 4.0 nm and all films had hexagonal wurtzite structure. The optical band gaps of CdS thin films varied between 2.46–2.43 eV. Characteristic parameters of CdS/p-Si heterojunctions including ideality factor, barrier height, series resistance and rectification ratio were measured. It was seen that both ideality factor and barrier height values of the heterojunctions increase with the increase substrate temperature. It was attributed to increase in inhomogenity of the thin films. Furthermore, the photoelectrical parameters of CdS/p-Si heterojunctions were studied.     

Structural and optical properties of CdS/PEO nanocomposite solid films

In this paper solution mixing and casting of Cd(NO₃)₂·4H₂O and poly(ethylene oxide) (PEO) at different molar ratios (1:100–1:600) followed by hydrogen sulfide treatment were employed to fabricate solid films of cadmium sulfide (CdS)/polyethylene oxide (PEO) nanocomposites. The nanocomposites were found to exhibit uniform distribution of CdS nanoparticles in the polymer matrix without any additional capping agent. Systematic investigations on the role of PEO on the optical properties of CdS are presented. The optical properties of the composites examined by UV–vis absorption spectroscopy show that the band gap of CdS nanoparticles increases from 2.45 eV to 2.54 eV with decreasing concentration of CdS in PEO films. X-ray diffraction pattern shows the broadening in shape of the PEO peaks which is induced by the CdS particles in PEO matrix. The CdS particle sizes ranging from 10 to 20 nm are clearly seen in a transmission electron microscope (TEM). The X-ray photoelectron spectroscopic studies (XPS) also confirm the presence of CdS in PEO. Fourier transform infrared spectroscopy studies using attenuated total reflectance (FTIR-ATR) indicate the influence of Cd²⁺ ion on C–O–C stretching in PEO and confirm the presence of CdS nanoparticles within PEO. Photoluminescence spectroscopy (PL) shows the broad emission due to the presence of surface trapped carrier states.     

Electrical and optical properties of sputter-deposited cadmium sulfide thin films optimized by annealing temperature

Cadmium sulfide (CdS) is one of the most widely used materials as a window layer in heterojunction thin film solar cells. Sputtering method for the preparation of CdS thin film was employed for the mass-production of large-area deposited CdS thin films. The electrical and optical properties of sputter-deposited CdS thin films varied with the annealing temperature, which were caused by changes in phase composition, grain size, and stoichiometry of CdS thin films. The improved optical transmittance of 72.25% (at average thickness of 843.93 nm) and the optical band gap energy of 2.43 eV were obtained at the optimum annealing temperature of 400 °C. The resistivity below 10³-order Ω cm and carrier concentration above 10¹⁶ carriers/cm³ are suitable for the requirements of window layers at this optimum annealing temperature.     

Synthesis and characterization of ZnS/ZnO/CdS nanocomposites

Water-soluble ZnS/ZnO/CdS (0.1–0.5 M) nanocomposites were successfully synthesized by the chemical precipitation method in air. X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis), photoluminescence (PL) and thermo gravimetric-differential thermal analysis (TG-DTA) were used to characterize the synthesized products. It is found that the ZnS/ZnO/CdS (0.1–0.5 M) core–shell nanocomposite is cubic and hexagonal mixed structure. TEM results showed the prepared nanocomposites are monodispersed and uniform in size. It is confined within 4.3–5.6 nm range. UV–vis absorption spectra were confined growth process of multi shells on ZnS. It showed a red shift with respect to the shells thickness. Fluorescence measurement showed the emission band which exists in the visible region. Stability and phase transition were identified by TG-DTA analysis. The results show an improved florescence property, indicating their potential applications in biological labeling.     

Taguchi robust design to optimize synthesis of lead oxalate nano-disks

Disk-shaped lead oxalate nanoparticles were synthesized via sol-precipitation in aqueous media without any surfactant, template or catalyst. Significance of reaction conditions such as: lead and oxalate concentrations, flow rate of reagent addition and temperature of reactor on diameter of synthesized lead oxalate disk-shaped particles were investigated and optimized. The participation of the studied variables in the particle size control of lead oxalate was quantitatively evaluated by analysis of variance. The results showed that lead oxalate nano-disks can be synthesized via controlling effective procedure parameters. Under optimum conditions, disk shaped nano-sized lead oxalate particles with two dimensions (95 nm diameter and 35 nm thickness) were synthesized. The structure and morphology of the lead oxalate nano-disks obtained under optimum conditions of synthesis process were characterized by scanning electron microscopy, X-ray diffraction, infrared spectroscopy and thermal analysis techniques. The Thermal analysis of the nanoparticles obtained under optimum conditions indicates that the main thermal degradation of the nano-disks occurs in the temperature range of 310–380 °C; while, submicron particles decomposed exothermally in more wider temperature range of 320–430 °C.     

Spectroscopic studies of sol–gel grown CdS nanocrystalline thin films for optoelectronic devices

CdS is one of the highly photosensitive candidate of II–VI group semiconductor material. Therefore CdS has variety of applications in optoelectronic devices. In this paper, we have fabricated CdS nanocrystalline thin film on ultrasonically cleaned glass substrates using the sol–gel spin coating method. The structural and surface morphologies of the CdS thin film were investigated by X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) respectively. The surface morphology of thin films showed that the well covered substrate is without cracks, voids and hole. The round shape particle has been observed in SEM micrographs. The particles sizes of CdS nanocrystals from SEM were estimated to be～10–12 nm. Spectroscopic properties of thin films were investigated using the UV–vis spectroscopy, Photoluminescence and Raman spectroscopy. The optical band gap of the CdS thin film was estimated by UV–vis spectroscopy. The average transmittance of CdS thin film in the visible region of solar spectrum found to be～85%. Optical band gap of CdS thin film was calculated from transmittance spectrum ～2.71 eV which is higher than bulk CdS (2.40 eV) material. This confirms the blue shifting in band edge of CdS nanocrystalline thin films. PL spectrum of thin films showed that the fundamental band edge emission peak centred at 459 nm also recall as green band emission.     

Photocatalytic degradation of methyl orange and gas-sensing performance of nanosized ZnO

ZnO nanoparticles were synthesized by calcining composites of zinc nitrate and poly(vinyl pyrrolidone) (PVP, molecular weight 30 000) at a mass ratio of 1:2 at 500 °C for 2 h. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used to characterize the as-synthesized ZnO nanoparticles. The particles ranged in size from 30 to 50 nm. Infrared spectra of PVP and the PVP+Zn(NO₃)₂·6H₂O composite revealed coordination between the carbonyl (C=O) of PVP and Zn²⁺ of zinc nitrate, which led to a uniform nanoparticle morphology. The gas-sensing properties and photocatalytic performance of the final product were systematically investigated. The results show that the ZnO nanoparticles exhibit both a high response for ethanol detection and excellent photocatalytic activity for degradation of methyl orange under UV irradiation for 30 min.