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Characterization of the Fe doped CDS Thin Films Produced by Ultrasonic Spray Pyrolysis Technique
Abstract
e doped CdS thin films are covered on glass substrates at 340±5ºC by ultrasonic spray pyrolysis technique. Fe element incorporated into CdS precursor at volume percentages of 0 to 50% step 10. Structural, compositional, optical, surface and electrical properties of samples are analyzed using X-ray powder diffraction, scanning electron microscope, a spectroscopic ellipsometer, atomic force microscope, four-probe technique, UV/Vis and photoluminescence spectroscopy. All the samples are found to be of single-phase and crystallized in a hexagonal lattice. The x-ray diffraction peaks position of Fe doped CdS shifts to higher angle with increasing Fe concentration indicating a decrease in cell volume. It is observed the optical bandgap changes due to Fe addition. Photoluminescence technique displayed the occurrence of red emission in the CdS nanoparticles. There was a noticeable increase in the PL intensity when Fe concentration increased. Fe doped CdS samples for photovoltaic solar cells could be used as windows layer.
Fe 3+ doped CdS nanoparticles using Mercaptoethanol as a capping agent were prepared by colloidal wet-chemical method. UV-VIS spectra show that Fe-doping can effectively tune energy band structure, i.e. a large blue shift (∼ 30 nm) with increasing Fe concentration. PL measurement of doped CdS nanoparticles shows an additional emission band at ∼ 532 nm, which can be due to radiative transition of dopant level to ground state. X-ray diffraction patterns studies revealed cubic crystal phase. TEM micrographs show a spherical shape and nearly well distribution with an average particle size of ∼ 4 nm.
CdS and Gd-doped CdS nanoparticles have been synthesized by chemical precipitation technique. The X-ray diffraction patterns show that the CdS and Gd-doped CdS nanoparticles exhibit hexagonal structure. The high resolution transmission electron microscope image shows that CdS and Gd-doped CdS nanoparticles have particle size lying in the range of 3.5 to 4.0 nm. Raman spectra show that 1LO, 2LO and 3LO peaks of the Gd-doped CdS nanoparticles are slightly shifted to lower wavenumber side when compared to that of CdS. Optical absorption spectra of Gd-doped CdS nanoparticles shows that absorption edge is slightly shifted towards longer wavelength side (red shift) when compared to that of CdS and this shift is due to the quantum confinement effect present in the samples.
CdS and CdS:Ni films (at the Ni percentages of 10 and 20) were deposited on glass substrates by ultrasonic spray pyrolysis (USP) technique at a substrate temperature of 300±5 °C. The effect of Ni incorporation on the film properties is presented. The variations of conductivities of CdS and CdS:Ni films were investigated depending on the temperature and applied voltage in dark and light conditions. The film structures were studied by X-ray diffraction (XRD). The crystallinity was spoiled with increasing Ni concentration, and a shift to amorphous structure was seen. Surface morphologies of the films were studied by scanning electron microscopy (SEM). The most homogeneous surface was seen in CdS films. Elemental analyses of all films were also studied by energy dispersive X-ray spectroscopy (EDS).
Cu and Fe doped cadmium sulfide nanoparticles were prepared with a wet chemical synthesis
by mixing the reactants in double distilled water solvent. Thioglycerol (TG) was employed as
the capping agent and also the reaction catalyst. The estimated particle size of prepared samples
was found in the range 3–4 nm. Properties of particles were investigated using photoluminescence
spectroscopy (PL) and X-ray diffraction analysis (XRD). XRD pattern of samples reveals
a hexagonal crystal structure at room temperature. We have studied effect of doping and
TG concentration on the luminescence of doped CdS nanocrystals. There is a noticeable increase
of the PL intensity when TG concentration increased. The PL spectra include two bands, due to
emission of traps and surface state.
High aspect ratio (up to 100) CdS nanowires having average diameter of 15 nm and length varying from 0.5-1.5 μm have been synthesized using solvothermal technique in ethylenediamine as a solvent at 120℃ and the effect of Mn dop-ing on morphology and optical properties has been studied. X-ray diffraction analysis shows the typical inter-planar spacing and the diffraction peaks corresponding to the hexagonal wurzite phase of CdS. Morphological study has been done through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and the optical studies have been conducted through absorption spectra and room temperature photoluminescence (PL).
In the quest for an electroplated selective black coating stable to 500 °C in air, black cobalts have been prepared by three techniques to yield (a) plated cobalt sulphides, (b) plated cobalt oxide‐hydroxide, and (c) cobalt oxide prepared by thermal oxidation of electropolated cobalt metal. The optical properties of the various coatings are analyzed before and after exposure to air for extended periods of time at temperatures in the 300 °–500 °C range. The sulfide black cobalt is not acceptable as a high‐temperature selective absorber due to severe thermal degradation. The plated oxide is a good selective absorber to about 400 °C, and the thermally oxidized black to a slightly higher temperature, but degrades at 500 °C. Structure studies via scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and x‐ray photoemission spectroscopy (XPS) are reported which yield a full account of the coating chemistry before and after heating. The studies reveal that the high solar absorptance of the acceptable black cobalt coatings is due to a continuation of a porous outer layer grading into nondense oxides of cobalt; either CoO or Co 3 O 4 , depending on the film. Absorption is intrinsic but not due to metal particles as in black chrome. A limited amount of optical degradation occurs upon heating the oxide black cobalt in air due to oxidation of hydroxide. However, the major degradation problem is shown to be substrate oxidation in contrast to black chrome where film oxidation is the principal problem.
Spectral photoconductivity, photoconductive quenching, photoluminescence, and thermally stimulated current measurements, have been carried out in order to study the evolution of defect energy levels in CdS thin films, grown in cubic phase by chemical bath deposition, as a function of thermal annealing temperatures in Ar+S <sub> 2 </sub> atmosphere. The results are influenced by a cubic-to-hexagonal phase transition. From those measurements, a number of trap levels and deep levels in the forbidden band are determined. The results can be explained in terms of the evolution of native and phase transition generated defects in the sample structure. © 1997 American Vacuum Society.
We have examined steady-state and time-resolved luminescence properties of CdS:Te quantum dots (QDs). The transient emission spectra have a red shift along the emission process. Using singular value decomposition and multiexponential decay analysis, the luminescence is found to originate from two distinct and parallel channels: band-edge excitonic emission and trapping state emission. With increasing amount of Te, the emission peaks of the QDs show an obvious red shift. Our experimental results suggest that CdS:Te quantum dots have tunable emission spectra and luminescence lifetimes which may have applications in chemical sensing, high throughput screening and other biotechnological applications.
Solvothermal technique has been used for the synthesis of Fe-doped CdS nanorods (Cd1−xFexS) with (x = 0.0, 0.3, 0.5, 1.0, 1.5). Structural analysis carried out using X-ray diffraction reveals the formation of defect-free hexagonal phase of the CdS nanorods. Energy dispersive X-ray analysis confirms the presence of elements Cd, Fe and S in their stoichiometric ratio. Blue shift in the band gap, as compared to the bulk CdS, has been observed in UV–visible spectra. The decrease in the intensity of the photoluminescence peaks confirms the quenching of spectra upon Fe doping. Transmission electron microscopy, high-resolution transmission electron microscopy and selected area diffraction studies confirm the polycrystalline nature as well as growth of CdS nanorods along (112) plane. Magnetic study confirms the ferromagnetic nature of the synthesized nanorods. Magnetic saturation has been found to be 0.187, 0.300, 0.450, 0.675, 0.600 emu g−1, respectively, for undoped, 3, 5, 10, and 15 % Fe-doped CdS.
Polycrystalline indium doped cadmium sulfide (CdS:In) thin films are prepared by the spray pyrolysis technique on glass substrates at a substrate temperature of 490 °C. The photoluminescence (PL) spectra of the films showed a broad peak in the visible region and another smaller one in the infrared. The first peak is deconvoluted to two Gaussian peaks corresponding to the yellow and red bands, and the second one is deconvoluted to one Gaussian peak corresponding to the infrared band. The influence of the probing laser power on the intensity, position and width at half maximum of these bands is investigated. It is found that the PL intensity of the observed bands increases with laser power until a critical value, after which it slightly decreases then slightly increases again. These variations are interpreted in terms of a band filling mechanism and a laser-induced local heating, where the increase is due to the first effect and the decrease to the second one. A competition between these two effects occurs and the stronger one predominates. The increase before the critical value is explored by plotting the logarithm of the PL integrated intensity against that of the laser power for the three aforementioned bands. Linear fits are performed and the slopes for the three bands are found to be close to 2, which mean that the relation between the PL intensity and laser power is quadratic. Variations in the positions of the peaks and their widths at half maximum with laser power are explained in terms of these two competing effects too.
CdSe films have been deposited on glass substrates at different substrate temperatures between room temperature and 300 °C. The films exhibited hexagonal structure with preferential orientation in the (002) direction. The crystallinity improved and the grain size increased with temperature. Band gap values are found decreasing from about 1.92 eV to 1.77 eV with increase of the substrate temperature. It is observed that the resistivity decreases continuously with temperature. Laser Raman studies show the presence of 2 LO and 3 LO peaks at 416 cm-1 and 625 cm-1respectively. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Fe doped CdS quantum dots have been prepared using simple precursors by chemical precipitation technique. Fe doped CdS quantum dots have been synthesized by mixing cadmium nitrate, sodium sulfide and adding Fe under suitable conditions. X-ray diffraction analysis reveals that undoped and Fe doped CdS crystallizes in hexagonal structure. The lattice constants of Fe doped CdS nanoparticles decreased slightly with incorporation of Fe and no secondary phase was observed. The average grain size of the nanoparticles is found to lie in the range of 2.8–4.2 nm. HRTEM results show that undoped and 3.75% Fe doped CdS nanoparticles exhibit a uniform size distribution and average size of the nanoparticles is about 2–3 nm. Raman spectra show that 1LO and 2LO peaks of the Fe doped CdS samples are slightly red shifted compared with those of undoped CdS. Optical absorption spectra of Fe doped CdS nanoparticles exhibited red shift.
c-axis oriented ZnO thin films have been deposited on fused silica by pulsed laser reactive ablation using a Zn target. The films are polycrystalline, transparent, smooth, dense and crackfree. The influence of the deposition parameters on film quality has been discussed. The fwhm of the (002) X-ray reflection peak reaches its minimum of 0.320 ° at substrate temperatures of 375–425 °C. The refractive index of the film versus wavelength has been determined. Favorable optical waveguiding property has been demonstrated by observation of sharp m-lines from the TE mode.
A quantum system which can tunnel, at T=0, out of a metastable state and whose interaction with its environment is adequately described in the classically accessible region by a phenomenological friction coefficient eta, is considered. By only assuming that the environment response is linear, it is found that dissipation multiplies the tunneling probability by the factor exp[-Aeta(Deltaq)2ℏ], where Deltaq is the "distance under the barrier" and A is a numerical factor which is generally of order unity.
Cadmium chalcogenides with appropriate band gap energy have been attracting a great deal of attention because of their potential applications in optoelectronic devices. CdS in the form of thin film is prepared at different substrate temperatures by a simple and inexpensive chemical spray pyrolysis technique. The as-deposited thin films have been characterized by XRD, SEM, EDAX and electrical resistivity measurement techniques. The XRD patterns show that the films are polycrystalline with hexagonal crystal structure irrespective of substrate temperature. SEM studies reveal that the grains are uniform with uneven spherically shaped, distributed over the entire surface of the substrates. Compositional analysis reveals that the material formed is stoichiometric at the optimized substrate temperature. The optical band gap energy is found to be 2.44 eV with direct allowed band-to-band transition for film deposited at 300°C. The electrical resistivity measurement shows that the films are semiconducting with a minimum resistivity for film deposited at 300°C. The thermoelectric power measurement shows that films exhibit n-type of conductivity.
Cobalt oxyhydroxide thin films were grown by anodic electroprecipitation on a ITO/glass substrate from a cobalt nitrate solution. The electrochromic characteristics of the material, such as electrochromic efficiency, optical contrast, durability, optical memory, and response time are presented in this work. The total optical contrast between fully bleached and fully coloured states was 40%, and the electrochromic efficiency in the visible range was 20 cm2 °C−1. The film can withstand more than 104 coloration/bleaching cycles, without significant decrease of the optical contrast. Results indicate that this anodic electrochromic material has properties suitable for a smart window or rearview mirror application.
CdS and CdS:In films (at the In percentages of 25, 35 and 45) were deposited onto glass substrates at the substrate temperature of 300±5°C by ultrasonic spray pyrolysis technique and the effect of In concentration on some physical properties of the films were presented. The deposited films were characterized for their electrical, structural, morphological and elemental properties using current–voltage measurements, X-ray diffraction patterns, scanning electron microscopy micrographs and energy dispersive X-ray spectroscopy analyses, respectively. It was determined from the results of these investigations that the electrical, structural, morphological and elemental properties of CdS films considerably changed with In doping and CdS:In films are more desirable than CdS for window layer applications in photovoltaic solar cells.
Sm-doped CdO thin films (0.4, 1.1, 3, 7.5, and 9.3%) have been prepared by a vacuum evaporation method on glass and Si wafer substrates. The prepared films were characterised by X-ray fluorescence, X-ray diffraction, UV–VIS–NIR absorption spectroscopy, and dc-electrical measurements. Experimental results indicate that Sm3+ doping creates a slight compressive stress in the CdO crystalline structure and changes (and controls) the optical and electrical properties. The bandgap of CdO was suddenly narrowed by about 17% due to a light (0.4%) doping with Sm3+ ions. Then, as the Sm doping level was increased, the energygap was slightly increasing reaching a steady state (2.17eV). This variation was explained by the available bandgap narrowing (BGN) models. The electrical behaviour of Sm-doped CdO films shows that they are degenerate semiconductors of energygaps 1.87–2.17eV. The 0.4% Sm-doped CdO film shows increase in its mobility by about 6 times, conductivity by 36 times, and carrier concentration by 6 times, relative to undoped CdO film. From transparent-conducting-oxide point of view, Sm is sufficiently effective for CdO doping like other metallic dopants such as In, Sn, Sc, and Y.
Undoped and Cr (2 and 4 at.%) doped CdS nanoparticles were synthesized in aqueous solution by simple chemical co-precipitation method using polyvinylpyrrolidone (PVP) as stabilizer. The prepared nanoparticles were examined using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDAX), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). XRD pattern of the nanoparticles showed cubic zincblende phase with the particle size of the order of 3–4 nm, which was in good agreement with the results obtained from TEM studies. The EDAX analysis confirmed that Cd, Cr and S elements were present in the samples and the variations between the target and actual compositions were microscopic. UV–vis DRS spectra of the samples exhibited decrease in the band gap which further attests the incorporation of Cr into CdS nanoparticles. FTIR studies revealed that the undoped as well as Cr doped CdS nanoparticles were capped by polyvinylpyrrolidone.Highlights► Cr doped CdS nanoparticles were synthesized by chemical co-precipitation method using PVP as surfactant. ► The influence of Cr content on the physical properties of Cr doped CdS nanoparticles were investigated. ► The synthetic route could be adopted for producing high-quality gram scale synthesis of doped semiconductor nanoparticles.
CdS nanoparticles doped with Tb 3+ were synthesized by sol–gel technique. The influence of CdS on the Tb 3+ glass was studied by UV-Visible and luminescence spectroscopy. The luminescence intensity of the glasses increased significantly in the presence of CdS nanoparticles. Terbium ions excited into the 5 D 3 level have a rich emission spectrum in the 400–700 nm range decaying to different 7 F J levels. The intensity of violet and blue lumi-nescence from 5 D 3 level is highly dependent on Tb 3+ concentration, on presence of CdS co-dopant and annealing conditions.
In this work, CdS and Cu doped CdS films (at the Cu percentages of 1, 3 and 5) have been deposited onto glass substrates at 350 ± 5 °C by ultrasonic spray pyrolysis technique and their application potential for photovoltaic solar cells have been investigated. Optical properties and thicknesses of the films have been investigated by spectroscopic ellipsometry (SE). Ellipsometric angle ψ was used as the source point for optical characterizations. The optical constants (n and k) and the thicknesses of the films have been fitted according to Cauchy model. Also, optical properties of the produced films have been analyzed by transmittance and reflectance spectra. Refractive index (n), extinction coefficient (k) and reflectance (R) spectra have been taken by spectroscopic ellipsometer, while transmittance spectra have been taken by UV/vis spectrophotometer. The optical method has been used to determine the band gap type and value of the films. Mott-Schottky (M-S) measurements have been made to determine the conductivity type and carrier concentration of the films. Samples showed n-type conductivity and carrier concentration of undoped CdS sample was found to be 1.19 × 1019 cm−3. Also, it was concluded that Cu doping has an acceptor effect in CdS samples. From the results of these investigations, the application potential of CdS:Cu films for photovoltaic solar cells as window layer was searched.
The Cu–CdSe–Cu nanowire heterojunctions were fabricated by sequential electrochemical deposition of layers of Cu metal and
CdSe semiconductor within the nano-pores of anodic alumina membrane templates. X-ray diffraction reveals the cubic phase for
Cu and hexagonal phase for CdSe in the electrodeposited Cu–CdSe–Cu nanowire heterojunctions. The composition of the nanowire
heterojunction segments is characterized by energy dispersive X-ray spectroscopy. The morphological study of nanowire heterojunctions
has been made using scanning electron microscope and high resolution transmission microscopy. The nanowire heterojunctions
grown in 100 and 300nm nano-pore size templates have been found to have optical band gaps of 1.92 and 1.75eV, respectively.
The absorption spectra of 100nm nanowire heterojunctions show a blue shift of 0.18eV. The collective nonlinear current–voltage
(I–V) characteristics of the 300 and 100nm nanowire heterojunctions show their rectifying and asymmetric behaviour, respectively.
KeywordsElectrodeposition–Nanowire heterojunctions–Template–
I–V characteristics
Green and blue photoluminescence has been observed below 100°K in vacuum‐deposited low‐resistivity CdS films given no post‐deposition treatment. The films were deposited on fused quartz substrates in a heated chamber inside the bell jar on substrates held at temperatures between 140° and 180°C. The CdS evaporant containing a trace of residual chlorine gave polycrystalline films that had resistivities at 300°K in the range of 1–10<sup>2</sup> Ω cm parallel to the substrate. The green luminescence in the films at 77°K was similar to the emission reported in the literature for donor‐doped CdS. The doped‐CdS emission differs from the phonon‐assisted ``edge emission'' starting at 5140 Å when observed in pure CdS in that the emission peak at 5220 Å, corresponding to the emission of one k=0 LO phonon, is more intense than the zero phonon peak. The relative peak intensities of the zero phonon and phonon replicas in pure CdS can be described by a Poisson distribution in N¯ where N¯ is the mean number of phonons emitted in the transition. These Gaussian‐shaped component peaks also have equal halfwidths H. For pure CdS at 77°K values found in the literature are N¯≅0.8-1.0 and H≅0.03 eV. For the CdS films good fits could be obtained with N¯=1.1-1.5 and H=0.04-0.06 eV. However, it is also possible that the film luminescence is the superposition of two emission series. The peak position of the green emission spectrum observed at 10°K was close to that at 77°K, and an additional peak at 5040 Å was observed. The decay time of the green emission was less than 1.5 μsec at 77°K, and thermal quenching of the luminescence began around 100°K, with an activation energy of 0.15–0.17 eV. Baking in saturated cadmium vapor at 500°C quenched the green emission, and for films baked in H-
2 S or H 2 S+HCl+H 2 at 600°C, emission similar to that observed in pure CdS was obtained. Optical absorption measurements indicated that the band edge was sharpened by the baking processes. The blue emission peak observed in the films was at 4892 Å at 77°K, which is in the fundamental absorption edge. It shifted to 4875 Å and became more intense and narrower at 10°K. This emission persists to 300°K with the peak position decreasing in energy as the bandgap. The peak is quenched by baking in H 2 S but not by baking in saturated Cd vapor. The blue emission is probably associated with a shallow donor or Cd excess in the films.
Cobalt oxide coatings with an integrated solar absorptance of 0.93 and a hemispherical emittance at 100°C of 0.14 were prepared by spray pyrolysis on stainless steel substrates kept at 300°C. The coatings are strongly adherent and stable up to temperatures of about 600°C. Auger electron spectroscopy, X-ray photoelectron spectroscopy and X-ray and electron diffraction investigations revealed the coatings to be composed of an upper layer of Co3O4 and subsequent layers of CoO down to the substrate. The absorption mechanism is primarily intrinsic. Lower substrate temperatures (about 150°C) can be used for preparing coatings from equimolar aqueous solutions of cobaltous acetate and thiourea. Such coatings, containing both cobalt oxide and cobalt sulphide, have a comparable absorptance but a higher emittance and are stable only up to about 300°C.
Co3O4 nanoparticles of 35 nm with a cauliflower-like morphology were obtained when a monolayer colloidal dispersion of dodecyl sulfate intercalated alpha-cobalt hydroxide in butanol was subjected to solvothermal hydrolytic decomposition. The nanogranular particles exhibit weakly ferromagnetic properties in contrast with both bulk and dispersed nanoparticulate Co3O4.
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