Effect of four different zinc salts and annealing treatment on growth,structural, mechanical and optical properties of nanocrystalline ZnS thin films by chemical bath deposition

ZnS thin films were deposited from four different zinc salts on glass substrates by chemical bath deposition method. Different anions of zinc salts affect the deposition mechanism and growth rate, which influence the properties of the films significantly. The ZnS thin film deposited from ZnSO₄ is smoother, thicker, more homogeneous and compact, nearly stoichiometric, comparing with the films deposited from Zn(CH₃COO)₂ and Zn(NO₃)₂, and ZnCl₂. The scratch test of bonding force between ZnS film and substrate shows that the ZnS film deposited from ZnSO₄ has the most excellent adhesion with the substrate. The presence of SO₄²⁻ promotes heterogeneous ZnS thin film growth via ions by ions deposition, and the films deposited from Zn(CH₃COO)₂ and Zn(NO₃)₂ are formed via clusters by clusters deposition. XRD and HRTEM results show that cubic ZnS films are obtained after single deposition, and the grain size of ZnS thin film deposited from ZnSO₄ for 2.5 h is 10 nm. The average transmission of all films is greater than 85% in the wavelength ranging from 600 to 1100 nm, and the transmission of films deposited from ZnSO₄ or Zn(NO₃)₂ for 1.5, 2 and 2.5 h is greater than 85% in the wavelength varying from 340 to 600 nm, which can enhance the blue response. The band gaps of all ZnS thin films are in the range of 3.88–3.99 eV. After annealing treatment, the mechanical and optical properties of the ZnS thin film deposited from ZnSO₄ are improved significantly.     

Effect of deposition temperature on structural,optical properties and configuration of CdSe nanocrystalline thin films deposited by chemical bath deposition

CdSe nanoparticle thin films were deposited on glass substrates by the chemical bath deposition (CBD) method at low deposition temperature ranging from room temperature up to 50 °C while the pH of the bath was kept constant at 12.1. The structural and morphological variation were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) technique. The energy band gap and optical properties were characterized by the absorbance spectra. Rutherford backscattering spectroscopy (RBS) analysis reveals the excess of Cd rather than Se in depth profile along the thin film thickness. The prepared CdSe nanoparticles have cubic structure and by increasing the temperature the deposited films become continues, homogeneous and tightly adherent. The results also revealed that by increasing the deposition temperature from room temperature up to 50 °C, the band gap decreases from 3.52 eV up to 1.84 eV.     

Effect of temperature on structural and optical properties of ZnS thin films by chemical bath deposition without stirring the reaction bath

ZnS thin films were deposited at different temperatures on glass substrates by chemical bath deposition method without stirring the deposition bath. With deposition temperature increasing from 50 °C to 90 °C, pH decreases rapidly, homogeneous precipitation of ZnS, instead of Zn(OH)₂ easily forms in the bath. It means that higher temperature is favorable for the formation of relatively high stoichiometric film, due to the lower concentration of OH⁻. The thickness of the films deposited at 90 °C is much higher than that of the films deposited at 50 °C and 70 °C. Combining the film thickness with the change of pH, the growth of film, especially deposited at 90 °C mainly comes from the fluctuation region of pH. At the same time, with the increase of deposition temperature, the obtained films are transparent, homogeneous, reflecting, compact, and tightly adherent. The ZnS films deposited for 1.5 h, 2 h and 2.5 h at 70 °C and 90 °C have the cubic structure only after single deposition. The average transmission of all films, especially the thicker films deposited at 90 °C, is greater than 90% for wavelength values in the visible region. Comparing with the condition of stirring, the structural and optical properties of films are improved significantly. The direct band gaps range from 3.93 to 4.06 eV.     

Deposition of morphology-tailored PbS thin films by surfactant-enhanced aerosol assisted chemical vapor deposition

In this work, we report the results of deposition of PbS thin films using single molecular precursor, bis(O-isobutylxanthato)lead(II), in the presence of additives namely: sodium dodecyl sulfate (SDS), Tween and Triton x-100, via aerosol assisted chemical vapor deposition (AACVD). The as-deposited PbS thin films are highly crystalline and exhibited superior adhesion to glass substrates. Powder X-ray diffraction (XRD) analysis confirmed the formation of pure cubic phase of PbS. Thin films deposited using 0.4 mM Triton X-100 as additive resulted in wire like structures while 0.8 mM Triton X-100 deposited thin films comprised of predominantly shoe shaped structures. Further, increase in concentration (1.2 mM) of Triton X-100 deposited films having rod like morphology. The scanning electron microscopy (SEM) confirmed that in the presence of SDS, thin films consist of spherical shaped crystallites. Energy dispersive X-ray spectroscopy (EDX) and X-ray photon electron microscopy (XPS) of as-deposited PbS thin films was used to study chemical composition of thin films.     

Detection of zinc blende phase by the pulsed laser photoacoustic technique in ZnO thin films deposited via pulsed laser deposition

Pulsed laser deposition (PLD) was used to grow ZnO thin films on corning glass and silicon substrates at different oxygen pressures (1 y 10 mTorr). The structural analysis of the films was performed by X-ray diffraction and pulsed laser photoacoustic (PLPA) techniques. Both methods were employed to identify the minority zinc blende phase in the films. The relative difference between the structural changes detected in the films with the temperature increases was statistically analyzed. It was found that regardless of the substrate and the oxygen pressure used for the growth, the films exhibit a phase transition at 310 °C, which corresponds to the transformation of zinc blende structure to hexagonal wurtzite. The results demonstrate that the zinc blende phase in the films is present not only on cubic substrates but also on glass, and confirm that PLPA technique is a very sensitive method for the detection of minority phase changes.     

Chemical bath deposition of nanocrystalline ZnS thin films: Influence of pH on the reaction solution

Zinc sulfide (ZnS) thin films were deposited onto glass substrates using chemical bath deposition technique (CBD). The deposition were carried out in a bath solution with pH ranged from 9 to 11. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to characterize the films structure and morphology respectively. The amorphous structure of as-deposited films is converted to a nanocrystalline one after a thermal annealing at 550 °C. The deposited ZnS films exhibit a high optical transmission in the UV–visible range (≥80%). They have a direct band gap. Using a solution with pH equal to 10 yields to films with larger optical band gap, smoother surface and lower electrical conductivity.     

Effect of the deposition rate on the phase transition in silver telluride thin films

Silver telluride thin films of thickness 50 nm have been deposited at different deposition rates on glass substrates at room temperature and at a pressure of 2×10⁻⁵ mbar. The electrical resistivity was measured in the temperature range 300–430 K. The temperature dependence of the electrical resistance of Ag₂Te thin films shows structural phase transition and coexistence of low temperature monoclinic phase and high temperature cubic phase. The effect of deposition rate on the phase transition and the electrical resistivity of silver telluride thin films in relation to carrier concentration and mobility are discussed.     

Effects of deposition pressure on the properties of transparent conductive ZnO:Ga films prepared by DC reactive magnetron sputtering

Gallium (Ga)-doped zinc oxide (ZnO:Ga) transparent conductive films were deposited on glass substrates by DC reactive magnetron sputtering. Effects of deposition pressure on the structural, electrical and optical properties of ZnO:Ga films were investigated. X-ray diffraction (XRD) studies show that the films are highly oriented with their crystallographic c-axis perpendicular to the substrate almost independent of the deposition pressure. The morphology of the film is sensitive to the deposition pressure. The transmittance of the ZnO:Ga thin films is over 90% in the visible range and the lowest resistivity of ZnO:Ga films is 4.48×10⁻⁴ Ω cm.     

Synthesis of mackinawite FeS thin films from acidic chemical baths

The growth of monophasic iron sulfide thin films onto glass substrates has been achieved by chemical bath deposition at acidic values of pH. Powder X-ray diffraction (p-XRD) confirms the deposition of tetragonal FeS (mackinawite) with preferred orientation along (001) plane. The crystallite size estimated by Scherrer equation was found to be 14 nm. Scanning electron microscopy (SEM) shows the formation of nanoflakes as base layer and nanoflowers as top layer. Energy Dispersive X-ray (EDX) analysis of the deposited iron sulfide thin films shows the iron to sulfur ratio close to 1:1 confirming the deposition of FeS. UV–vis absorption spectroscopy showed a blueshift due to the nanosize crystallites FeS with a band gap of 1.87 eV.     

Study of some physical properties of ultrasonically spray deposited silver doped lead sulphide thin films

In this study, undoped and Ag doped PbS thin films at different concentrations were deposited onto glass substrates at 225 °C by using ultrasonic spray pyrolysis technique, in order to investigate the effect of Ag doping on the physical properties of PbS thin films. Structural investigations revealed that all doped PbS:Ag thin films have cubic structure and Ag doping enhances crystalline level of PbS thin films. It was determined that average crystallite size of PbS:Ag thin films increased from 24 nm to 49 nm by increasing Ag doping concentration. Morphological studies showed that surfaces of the films become denser after Ag doping. Optical transmittance and absorption spectra revealed that all deposited thin films have low transmission and high absorbance within the visible region and band gap energy of the PbS:Ag thin films were determined to be in the range of 1.37 eV and 1.28 eV by means of optical method. Electrical conductivity type of PbS:Ag films was determined to be p-type and calculated electrical resistivity was found to be lowest for Ag-doped PbS thin films at 2%.     

Investigations on the structural and optical properties of Li,N and (Li,N) co-doped ZnO thin films prepared by sol–gel technique

Pure and doped zinc oxide thin films have been deposited on sapphire substrates by using the sol–gel method and spin coating technique. The X-ray diffraction pattern showed that the deposited films exhibit hexagonal zinc oxide structure. Room temperature photoluminescence measurements show the presence of two emission bands. The predominant near band edge ultraviolet emission is at 3.28 eV and a suppressed broad band of deep level emission in the range of 2.1–2.5 eV. The incorporation of nitrogen is indicative of p-type behavior as observed from X-ray photoelectron spectrum of nitrogen in the doped samples. The p-type conduction of Li, N:ZnO may be attributed to the formation of a LiZn–N complex acceptor.     

Properties of cobalt-doped zinc oxide thin films grown by pulsed laser deposition on glass substrates

Undoped and cobalt-doped zinc oxide (CZO) polycrystalline piezoelectric thin films (Co: 3, 5 at.%) using a series of high quality ceramic targets have been deposited at 450 °C onto glass substrates using a pulsed laser deposition method. The used source was a KrF excimer laser (248 nm, 25 ns, 2 J∕cm²). X-ray diffraction patterns showed that the Co-doped ZnO films crystallize in a hexagonal wurtzite type structure with a strong (0 orientation, and the grain sizes calculated from these patterns decrease from 37 to 31 nm by increasing Co doping. The optical waveguiding properties of the films were characterized by using a prism-coupling method. The distinct M-lines of the guided transverse magnetic (TM) and transverse electric (TE) modes of the ZnO films waveguide have been observed. With the aim of study the optical properties of the ZnO films, an accurate refractive index and thickness measurement apparatus was set up, which is called M-lines device. An evaluation of experimental uncertainty and calculation of the precision of the refractive index and thickness were developed on ZnO films. The optical transmittance spectra showed a good transparency in the visible region. Calculated optical band gap varying from 3.23 to 3.37 eV when the content of Co doping increases from 0 to 5 at.%.     

Characterization of CdSe thin films deposited by chemical bath solutions containing triethanolamine

Cadmium selenide (CdSe) thin films were prepared by chemical bath deposition on glass substrates at different temperatures beginning at room temperature (25 °C) upto 80 °C from an aqueous alkaline medium using a precursor solution containing cadmium acetate, 2,2′,2′′-nitrilotriethanol (triethanolamine), ammonia and sodium selenosulphate. The pH of bath was kept constant around 10.50±0.10. Energy dispersive analysis of X-rays confirmed that the films are nearly stoichiometric in composition. The structural and surface morphological properties have been studied by X-ray diffraction, Scanning electron microscopy and Atomic force microscope techniques. X-ray diffraction study reveals a cubic structure with preferential orientation along (111) direction. The dependency of structural parameters such as crystallite size, strain and dislocation density with different bath temperatures for CdSe thin films are calculated. X-ray peak broadening was used to evaluate the crystallite size and lattice strain by the Williamson–Hall plots. Optical properties are studied by photoluminescence spectra which shows blue shift in peak position and reduction in luminescence intensity were observed for films deposited at different bath temperatures.     

Spray pyrolysis deposition of Cu–Zn–In–S solid-solution thin films with tunable compositions and band gaps

Cu–Zn–In–S solid solution thin films with tunable compositions and band gaps were deposited on glass substrates using a chemical spray pyrolysis approach. XRD results reveal the cubic-structured Cu–Zn–In–S films without detectable impurities. The successive shift of XRD patterns toward high-angle side of ZnS with increasing ZnS molar fraction in products proves a formation of Cu–Zn–In–S solid solutions. SEM images and EDAX analyses demonstrate homogeneous surface morphologies and adjustable compositions of Cu–Zn–In–S films, which results in film band gaps broadly tunable from 1.54 eV to 3.61 eV. These sprayed Cu–Zn–In–S solid solution thin films may find potential uses in photovoltaics and photocatalysis.     

Variation of the structural,optical and electrical properties of CBD CdO with processing temperature

Nanostructures of CdO thin films are prepared by chemical bath deposition (CBD) technique. The synthesized film is annealed in static air by using the hotplate at 373, 473, 573 and 673 K for 10 min. The effect of annealing temperature on structural, morphological, optical and electrical properties of CdO thin films has been investigated. The prepared thin films are characterised by X-ray diffraction (XRD), atomic force microscope (AFM), optical reflection microscope (ORM), UV–Visible Spectrophotometer and electrical resistivity. XRD shows the emergence of the cubic phase of CdO film in a preferred orientation (111) plane at 573 K. The AFM and ORM show that CdO films have smooth homogeneous surface in the formula with the emergence of nanoclusters gathering as nanoparticles with the average of grain size about 100 nm at 573 K. The optical properties prove that deposited films have high transparency within the visible range of the spectrum that reaches to more than 85% with a wide band gap that extends from 2.42 eV to 2.7 eV. The electrical properties of the CdO films show that resistivity decreases with increased annealing temperatures. In addition, it is proved that more than one activation energy appears and they change according to the temperature of annealing and this comes as a result of the polycrystalline structure. This study indicates that the properties of CdO thin films could be improved with annealing temperature and these films can be used in many technological applications.     

Behavior of chemically deposited PbS thin films subjected to two different routes of post deposition annealing

Lead sulfide (PbS) thin films were prepared on soda lime glass substrates at room temperature by Chemical Bath Deposition (CBD) technique. This paper reports a comparative study of characteristic properties of as-prepared PbS thin films after thermal treatment through two different routes. Studies were carried out for as-prepared as well as rapidly and gradually annealed samples at 100, 200 and 300 °C. The characterizations of the films were carried out using X-ray diffraction, scanning electron microscopy and optical measurement techniques. The structural studies confirmed the polycrystalline nature and the cubic structure of the films. As-deposited films partly transformed to Pb₂O₃ when gradually annealed to 300 °C. The presence of nano crystallites was revealed by structural and optical absorption measurements. The values of average crystallite size were found to be in the range 18–20 nm. The variation in the microstructure, thickness, grain size, micro strain and optical band gap on two types of annealing were compared and analyzed. Data showed that post deposition parameters and thermal treatment strongly influence the optical properties of PbS films. Optical band gap of the film gets modified remarkably on annealing. Direct band gap energy values for rapidly and gradually annealed samples varied in the range of 1.68–2.01 eV and 1.68–2.12 eV respectively. Thus we were succeeded in tailoring direct band gap energies by post deposition annealing method.     

Effect of Pb:S molar ratio in precursor solution on the properties of lead sulphide thin films by ultrasonic spray pyrolysis

In this work, PbS thin films were deposited onto glass substrate at 225 °C by spraying precursor solution prepared with different molar ratio of lead acetate and thiourea as a source of Pb²⁺ and S^2- respectively in order to investigate the effect of Pb:S molar ratio in the precursor solution on the physical properties of PbS thin films. Structural investigations carried out by X-ray diffractometer have shown that all films have fcc cubic structure and the average crystal size increased from 11 nm to 25 nm with the increasing the thiourea ratio in the precursor solution. In order to analyze the surface morphology of PbS thin films, AFM and SEM images were taken and elemental analysis of the films was performed by EDS. Optical transmittance and absorption spectra show that all deposited films have fairly low transmittance and high absorbance in the visible region. Additionally, it was determined that optical band gap of the deposited films were varied between 1.18 eV and 1.37 eV. As a consequence of electrical investigations, it was seen that all films have p-type conductivity and electrical resistivity decreased by increasing thiourea molar ratio in the precursor solution. All examinations have revealed that the molar ratio of lead acetate and thiourea has a significant effect on the physical properties of PbS thin films.     

Effects of the substrate temperature and solution molarity on the structural opto-electric properties of ZnO thin films deposited by spray pyrolysis

Zinc oxide (ZnO) was largely studied in various applications such as photovoltaic conversion, optoelectronics and piezoelectric, because of its interesting physical properties (morphological, structural, optical and electrical). The present work deals with the preparation of zinc oxide thin films (ZnO) deposited by the spray pyrolysis method. The starting solution was zinc chloride (ZnCl₂). Effects of solution molarity and substrate temperature on films properties were investigated. All films deposited were characterized by various techniques such as X-ray diffraction for structural characterizations, profilometry for thickness measurements, UV–vis transmission spectrophotometry for optical properties and the four probes conductivity measurements for electrical characterization. The X-ray diffraction (XRD) patterns show that the films deposited are polycrystalline with (0 0 2) plan as preferential orientation. The UV–vis spectroscopy confirms the possibility of good transparent ZnO thin films deposition with an average transmission of about ∼85% in the visible region. However, the measured electrical resistivities of the deposited films were in the order of 10⁴ Ω cm     

Investigation on post annealed copper sulfide thin films from photochemical deposition technique

Cu_xS thin films were deposited on glass substrates at room temperature by photochemical deposition after 1 h photo irradiation using the precursor solution containing copper sulphate pentahydrate (CuSO₄·5H₂O), sodium thiosulphate (Na₂S₂O₃) as a source material for Copper and Sulphur respectively and Di Sodium salt of EDTA as a chelating agent in acidic medium (pH~3.0). The as deposited and annealed Cu_xS thin films were investigated using XRD, UV–vis, AFM, SEM and Hall measurements. The deposited thin films were annealed at temperature up to 400 °C for 1 h. Above 200 °C the deposited film of Cu_xS changes from anilite phase (Cu_1.75S) to digenite (Cu_1.8S) phase. The reduction in sulphur content of the films is evident in the EDX analysis. From the Hall Effect results as deposited and annealed films show p-type conductivity with increasing bulk concentration. Analyses of the optical bandgap of the films indicate an indirect bandgap between 1.75 and 2.35 eV.     

Effects of Sb,Zn doping on structural,electrical and optical properties of SnO2 thin films

Highly transparent, low resistive pure and Sb, Zn doped nanostructured SnO₂ thin films have been successfully prepared on glass substrates at 400° C by spray pyrolysis method. Structural, electrical and optical properties of pure and Sb, Zn doped SnO₂ thin films are studied in detail. Powder X-ray diffraction confirms the phase purity, increase in crystallinity, size of the grains (90–45 nm), polycrystalline nature and tetragonal rutile structure of thin films. The scanning electron microscopy reveals the continuous change in surface morphology of thin films and size of the grains decrease due to Sb, Zn doping in to SnO₂. The optical transmission spectra of SnO₂ films as a function of wavelength confirm that the optical transmission increases with Sb, Zn doping remarkably. The optical band gap of undoped film is found to be 4.27 eV and decreases with Sb, Zn doping to 4.19 eV, 4.07 eV respectively. The results of electrical measurements indicate that the sheet resistance of the deposited films improves with Sb, Zn doping. The Hall measurements confirm that the films are degenerate n-type semiconductors.