Influence of vacuum annealing on the structural and photoelectrochemical properties of nanocrystalline MoBi2S5 thin films

In the present paper we report structural, optical, morphological and electrical properties of thin films of MoBi₂S₅ prepared by facile self organized arrested precipitation technique (APT) from aqueous alkaline bath. X-ray diffraction study on thin films suggests orthorhombic and rhombohedral mixed phase structure. The samples are further annealed under vacuum at 373 and 473 K. The EDS pattern shows minor loss of sulphur upto 473 K. The optical absorption in visible region shows direct allowed transition with band gap variation over 1.2–1.1 eV. Post-heat treated samples exhibit n-type electrical conductivity. SEM images show uniform distribution of spherical grains with diameter ∼200 nm for as-synthesized MoBi₂S₅ thin film. The grain size increases with annealing temperature and morphology becomes more compact due to crystallization of thin film. The surface roughness deduced from AFM, was in the range of 1.29–1.92 nm. The MoBi₂S₅ thin films are employed for the fabrication of photoelectrochemical solar cells as all the samples exhibit strong absorption in visible to near IR region. Due to vacuum annealing it gives a significant enhancement of power conversion efficiency (η) upto 0.14% as compared to as-synthesized MoBi₂S₅ thin film.     

Optical and transport properties of chemical bath deposited CdS: Al films

Aluminium doped and undoped CdS films are deposited on the glass substrates by chemical bath deposition technique. Their optical and transport properties are studied and the effect of dopant concentration on these properties is discussed at length.     

Effect of complexing agent on the properties of electrochemically deposited Cu2ZnSnS4 (CZTS) thin films

The Cu₂ZnSnS₄ (CZTS) thin films have been electrochemically deposited on Mo-coated glass substrate from weak acidic medium (pH 4.5-5) at room temperature. The effect of complexing agent (tri-sodium citrate) on the structural, morphological and compositional properties of CZTS thin films has been investigated. The as-deposited and annealed thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM),EDAX and X-ray photoelectron spectroscopy (XPS) techniques for their structural, morphological, compositional and chemical properties, respectively. XRD studies reveal that the amorphous nature of as-deposited thin film changes into polycrystalline with kesterite crystal structure after annealing in Ar atmosphere. The film prepared without complexing agent showed well-covered surface morphology on the substrate with some cracks on the surface of the film whereas those prepared using complexing agent, exhibited uneven and slightly porous and some overgrown particles on the surface of the films. After annealing, morphology changes into the flat grains, uniformly distributed over the entire surface of the substrate. The EDAX and XPS study reveals that the films deposited using 0.2 M tri-sodium citrate are nearly stoichiometric.     

Effect of Mg/Co on the properties of CdS thin films deposited by spray pyrolysis technique

Mg, Co doped and (Mg, Co) co-doped CdS thin films were prepared using chemical spray pyrolysis method. It is observed from the X-ray diffraction study that the deposited film exhibit cubic phase of CdS with preferred orientation along the (111) plane and incorporation of Mg and Co has been confirmed form energy dispersive analysis and XPS analysis as well. The doped and codoped CdS thin films exhibit 1LO and 2LO vibrations as confirmed by Raman spectrum. The core level XPS spectra ensures the incorporation of doping elements precisely. The morphological variations due to the incorporation of Co and Mg in CdS thin films have been observed by FE-SEM. The particle sizes and crystalline nature have been revealed from HRTEM images and corresponding SAED patterns. The co-doped CdS thin films show a significant shift blue in absorption spectrum. Improved magnetic properties have been observed for the co-doped CdS thin films.     

Characterization of chemical bath deposited CdS thin films doped with methylene blue and Er3+

The optical, electrical, and structural properties of CdS thin films grown by chemical bath deposition and simultaneously doped with methylene blue (MB) and Er³⁺ were studied. Doping was achieved by adding a constant volume of an MB aqueous solution to the chemical bath while the relative volume (V_R) of the Er aqueous solution varied within the range 0–10% of the total growing solution. X-ray diffractograms displayed the zincblende crystalline structure for all the CdS samples, with a remarked preferred orientation along the (111) direction. The interplanar distance among the (111) planes decreased for low doping leves of Er³⁺, while for high doping concentrations such distance increased to saturation. Measurements on the carriers density indicated that the CdS thin films doped with Er³⁺ at 6% V_R presented the maximum value. In addition, the band gap energy (Eg) resulted higher for CdS:MB films with low Er³⁺ doping levels than for undoped films; however, Eg decreased until stabilization for increasing Er³⁺ concentrations.     

Effect of precursor concentration and bath temperature on the growth of chemical bath deposited tin sulphide thin films

SnS is a promising candidate for a low-cost, non-toxic solar cell absorber layer. Tin sulphide thin films have been deposited by chemical bath deposition technique from a solution containing stannous chloride, thioacetamide, ammonia and triethanolamine (TEA). The effects of concentration of tin salt, triethanolamine and bath temperature on the growth of tin sulphide films have been investigated in order to optimize the growth conditions to obtain tin monosulphide (SnS) films. SnS films obtained under optimized conditions were found to be polycrystalline in nature with orthorhombic structure. The optical band gap of these films was found to be 1.5 eV.     

Modeling the effects of oxidizer, complexing agent and inhibitor on material removal for copper chemical mechanical polishing

The paper presents a novel mathematical model that systematically describes the role of oxidizer, complexing agent and inhibitor on the material removal in chemical mechanical polishing (CMP) of copper. The physical basis of the model is the steady-state oxidation reaction and etched removal in additional to mechanical removal. It is shown that the complexing agent concentration-removal relation follows a trend similar to that observed from the effects of oxidizer on Cu removal in CMP. In addition, the removal rate and the coupled effects of the chemical additives are determined from a close-form equation, making use of the concepts of chemical-mechanical equilibrium and chemical kinetics. The model prediction trends show qualitatively good agreement with the published experimental data. The governing equation of copper removal reveals some insights into the polishing process in addition to its underlying theoretical foundation.     

Influence of complexing agent on the electrodeposited Co-Pt-W magnetic thin films

Complexing agents are often used to improve the quality of electrodeposited alloys. Influence of different complexing agents with hydroxycarboxylic acid group on the electrodeposited Co-Pt-W thin films has been investigated. Cathodic polarization curves show that the polarization behaviors of electroplating bath with different complexing agents are very different. Surface morphology, phase composition and magnetic properties are observed by means of FESEM, XRD and vibrating sample magnetometer (VSM), respectively. It has been found out that, if citrate was used as complexing agent, the Co-Pt-W thin films were homogeneous and the granular crystals with the average grain size of 2 μm have been observed. Co-Pt-W thin films exhibited hexagonal close packed (hcp) lattice and strong perpendicular anisotropic magnetic behavior (H_c⊥ = 215.5 kA/m; H_c∥ = 55.4 kA/m). In the presence of gluconate, needle-like deposits were obtained and a strong face centered cubic (fcc(1 1 1)) texture was measured. The Co-Pt-W thin films showed isotropic magnetic behavior. In the case of tartate and malate, the coexistence of needle-like deposits and cellular deposits appeared. The XRD patterns showed that the mixed fcc and hcp phase formed. Perpendicular anisotropic magnetic behaviors of thin films, from malate or tartate baths, were not obvious.     

Effect of [Zn]/[S] ratios on the properties of chemical bath deposited zinc sulfide thin films

ZnS thin films have been prepared by chemical bath deposition (CBD) technique onto glass substrates deposited at about 80 °C using aqueous solution of zinc sulfate hepta-hydrate, ammonium sulfate, thiourea, ammonia and hydrazine hydrate. Ammonia and hydrazine hydrate were used as complexing agents. The influence of the ratio of [Zn]/[S] on formation and properties of ZnS thin films has been investigated. The ratio of [Zn]/[S] was changed from 3:1 to 1:9 by varying volumes and/or concentrations of zinc sulfate hepta-hydrate and thiourea in the deposition solution. The structural and morphological characteristics of films have been investigated by X-ray diffraction (XRD), scanning electron microscope and UV-vis spectroscopic analysis. ZnS films were obtained with the [Zn]/[S] ratio ranged from1:1 to 1:6. In the cases of [Zn]/[S] ratio ≥ 3:1 or ≤1:9, no deposition was found. Transparent and polycrystalline ZnS film was obtained with pure-wurtzite structure at the [S]/[Zn] ratio of 1:6. The related formation mechanisms of CBD ZnS are discussed. The deposited ZnS films show good optical transmission (80-90%) in the visible region and the band gap is found to be in the range of 3.65-3.74 eV. The result is useful to further develop the CBD ZnS technology.     

FT-IR, XPS and PEC characterization of spray deposited hematite thin films

Hematite thin films were prepared by spraying ethanolic solution of ferric trichloride and have been characterized by using Fourier transform infra-red (FT-IR) and X-ray photoelectron spectroscopic (XPS) techniques. The film prepared by spray consists of a single phase of α-Fe₂O₃. The XPS studies confirm that chemical states of Fe³⁺ and O²⁻ in the film; thereby confirming the formation of the hematite thin films. The photoelectrochemical (PEC) studies have been carried out by forming a three-electrode system using 1 M NaOH electrolyte. The junction is illuminated with white light to obtain I-V characteristics in chopped light. The studies indicate the films exhibit n-type conductivity.     

Effect of annealing on properties of electrochemically deposited CdTe thin films

Thin films of CdTe have been deposited onto stainless steel and fluorine-doped tin oxide (FTO)-coated glass substrates from aqueous acidic bath using electrodeposition technique. The different preparative parameters, such as deposition time, bath temperature and pH of the bath have been optimized by photoelectrochemical (PEC) technique to get good quality photosensitive material. The deposited films are annealed at different temperature in presence of air. Annealing temperature is also optimized by PEC technique. The film annealed at 200 °C showed maximum photosensitivity. Different techniques have been used to characterize as deposited and also as annealed (at 200 °C) CdTe thin film. The X-ray diffraction (XRD) analysis showed the polycrystalline nature, and a significant increase in the XRD peak intensities is observed for the CdTe films after annealing. Optical absorption shows the presence of direct transition with band gap energy 1.64 eV and after annealing it decreases to 1.50 eV. Energy dispersive analysis by X-ray (EDAX) study for the as-deposited and annealed films showed nearly stoichiometric compound formation. Scanning electron microscopy (SEM) reveals that spherically shaped grains are more uniformly distributed over the surface of the substrate for the CdTe film.     

Effects of processing on the electrical and structural properties of spray deposited CdS:In thin films

Polycrystalline CdS:In thin films were prepared by the Spray pyrolysis technique (SP) at a substrate temperature T_s=490 °C. The effects of annealing in nitrogen atmosphere at 400 °C and HCl-etching on the electrical and structural properties of the films were investigated. The electrical properties were studied through the analysis of the I-V curves, while the structural properties were studied through the analysis of the X-ray diffraction (XRD) patterns and the scanning electron microscope (SEM) images. An increase in the films’ resistivity was occurred after annealing and/or HCl-etching, which was accompanied by changes in the XRD patterns and SEM images. These changes were related to a phase change from the mixed (cubic and hexagonal) phase to the hexagonal phase which was expected to occur during the aforementioned processes. The X-ray diffraction (XRD) patterns and the scanning electron microscope images confirm this expectation.     

Characterization of gallium-doped CdS thin films grown by chemical bath deposition

Ga-doped CdS thin films, with different [Ga]/[Cd] ratios, were grown using chemical bath deposition. The effect of Ga-doping on optical properties and bandgap of CdS films is investigated. Resistivity, carrier density, and mobility of doped films were acquired using Hall effect measurements. Crystal structure as well as crystal quality and phase transition were determined using X-ray diffraction (XRD) and Micro-Raman spectroscopy. Film morphology was studied using scanning electron microscopy, while film chemistry and binding states were studied using X-ray photoelectron spectroscopy (XPS). A minimum bandgap of 2.26 eV was obtained at [Ga]/[Cd] ratio of 1.7 × 10⁻². XRD studies showed Ga³⁺ ions entering the lattice substitutionally at low concentration, and interstitially at high concentration. Phase transition, due to annealing, as well as induced lattice defects, due to doping, were detected by Micro-Raman spectroscopy. The highest carrier density and lowest resistivity were obtained at [Ga]/[Cd] ratio of 3.4 × 10⁻². XPS measurements detect an increase in sulfur deficiency in doped films.     

Effect of deposition time on structural, electrical, and optical properties of SnS thin films deposited by chemical bath deposition

The effect of deposition time on the structural, electrical and optical properties of SnS thin films deposited by chemical bath deposition onto glass substrates with different deposition times (2, 4, 6, 8 and 10 h) at 60 °C were investigated. The obtained films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and optical absorption spectra. All deposited films were polycrystalline and had orthorhombic structure with small crystal grains. Their microstructures had changed with deposition time, and their compositions were nearly stoichiometric. Electrical parameters such as resistivity and type of electrical conduction were determined from the Hall Effect measurements. Hall Effect measurements show that obtained films have p-type conductivity and resistivity values of SnS films have changed with deposition time. For allowed direct, allowed indirect, forbidden direct and forbidden indirect transitions, band gap values varied in the range 1.30-1.97 eV, 0.83-1.36 eV, 0.93-1.49 eV and 0.62-1.23 eV, respectively.     

Investigation of chemical bath deposition of CdO thin films using three different complexing agents

Chemical bath deposition of CdO thin films using three different complexing agents, namely ammonia, ethanolamine, and methylamine is investigated. CdSO₄ is used as Cd precursor, while H₂O₂ is used as an oxidation agent. As-grown films are mainly cubic CdO₂, with some Cd(OH)₂ as well as CdO phases being detected. Annealing at 400 °C in air for 1 h transforms films into cubic CdO. The calculated optical band gap of as-grown films is in the range of 3.37-4.64 eV. Annealed films have a band gap of about 2.53 eV. Rutherford backscattering spectroscopy of as-grown films reveals cadmium to oxygen ratio of 1.00:1.74 ± 0.01 while much better stoichiometry is obtained after annealing, in accordance with the X-ray diffraction results. A carrier density as high as 1.89 × 10²⁰ cm⁻³ and a resistivity as low as 1.04 × 10⁻² Ω-cm are obtained.     

Preparation of chemically deposited thin films of CdS/PbS solar cell

The present paper reports the preparation of a solar cell which has a cross-sectional scheme: ITO/CdS/PbS, containing a commercially transparent conductive ITO; chemically deposited n-type CdS (340 nm) and absorbed layer of p-type PbS (1400 nm). The structural and optical properties of the constituent films are presented. X-ray diffraction showed that all of the thin films are polycrystalline. Using scanning electron microscopy, the present study revealed that the films have uniform surface morphology over the substrate. The solar cell was characterized by determining the open circuit voltage, short-circuit current density, and J–V under 40 mW/cm² solar radiation. The efficiency of the solar cells was 1.35%, which is much higher (0.041, 0.5 and 0.1–0.4%) and slightly smaller (1.65%) than some solar cells reported in the literature.     

Effect of Fe-ion implantation doping on structural and optical properties of CdS thin films

We report on effects of Fe implantation doping-induced changes in structural, optical, morphological, and vibrational properties of cadmium sulfide thin films. Films were implanted with 90 keV Fe⁺ ions at room temperature for a wide range of fluences from 0.1×10¹⁶ to 3.6×10¹⁶ ions cm⁻² (corresponding to 0.38–12.03 at.% of Fe). Glancing angle X-ray diffraction analysis revealed that the implanted Fe atoms tend to supersaturate by occupying the substitutional cationic sites rather than forming metallic clusters or secondary phase precipitates. In addition, Fe doping does not lead to any structural phase transformation although it induces structural disorder and lattice contraction. Optical absorption studies show a reduction in the optical band gap from 2.39 to 2.17 eV with increasing Fe concentration. This is attributed to disorder-induced band tailing in semiconductors and ion-beam-induced grain growth. The strain associated with a lattice contraction is deduced from micro-Raman scattering measurements and is found that size and shape fluctuations of grains, at higher fluences, give rise to inhomogeneity in strain.     

Synthesis, characterization and photoelectrochemical properties of n-CdS thin films

Cadmium sulfide thin films have been deposited on glass substrates by simple and cost effective chemical bath deposition technique. Triethanolamine was used as a complexing agent. The preparative parameters like ion concentration, temperature, pH, speed of substrate rotation and deposition time have been optimized for good quality thin films. The ‘as-grown’ films are characterized for structural, electrical, optical and photoelectrochemical (PEC) properties. The X-ray diffraction (XRD) studies reveal that the films are polycrystalline in nature. Energy-dispersive analysis by X-ray (EDAX) shows that films are cadmium rich. Uniform deposition of CdS thin films on glass substrate is observed from scanning electron microscopy (SEM) and atomic force microscopy (AFM) micrographs. Optical studies reveal a high absorption coefficient (10⁴ cm⁻¹) with a direct type of transition. The band gap is estimated to be 2.47 eV. The film shows n-type conduction mechanism. The photoelectrochemical (PEC) cell with CdS thin film as a photoanode and sulfide/polysulfide (1 M) solution as an electrolyte have been constructed and investigated for various cell parameters. The solar to electrical conversion efficiency (η) and fill factor (ff) are found to be 0.049% and 0.36, respectively.     

The effect of various complexing agents on the morphology and optoelectronic properties of chemically deposited ZnS thin films: A comparative study

Thin films of ZnS were synthesized on glass substrates by chemical bath deposition technique. The effect of three different complexing agents, viz. hydrazine hydrate (HH), triethanolamine (TEA) and trisodiumcitrate (TSC) on the growth and physical properties of ZnS films has been investigated. The experimental results indicated that the complexing agents affect the structure, lattice strain, surface morphology and optoelectronic properties of ZnS films significantly. X-ray diffraction studies disclosed that all the ZnS layers crystallized in hexagonal form and the predominant orientations of the crystallites differed with complexing agents. Thickness of the films profoundly varied with the complexing agents though the deposition parameters like time, temperature and pH of reaction baths were kept constant. Atomic Force Microscopy revealed the variation in surface topography and roughness of the films. The film with HH as complexing agent exhibited maximum transmittance (87%) in the visible region of electromagnetic spectrum whereas those synthesized using TEA and TSC had a lower transmittance of approximately 60% and 50% respectively. The corresponding values of optical band gap were found to be 3.73, 3.64 and 3.57 eV respectively. The room temperature photoluminescence emission spectra consisted of bright blue emission peaks for all the samples. The intensity of emission peak was found to be maximum for TSC film and minimum for HH film.