Characterization and antibacterial capabilities of nanocrystalline CdS thin films prepared by chemical bath deposition

Antibacterial capabilities of nanocrystalline cadmium sulfide (CdS) thin films have been developed against Gram-positive and Gram-negative bacteria in dark and sunlight at 60 °C. For this purpose, a strain of Gram-positive Staphylococcus aureus, and two strains of Gram-negative bacteria (Pseudomonas aeruginosa, and Escherichia coli) were used. The nanocrystalline CdS thin films have been prepared using a chemical bath deposition (CBD) method at different thicknesses (50, 80 and 100 nm). The different deposition parameters including the speed of rotation of substrate, temperature of chemical bath, pH of solution and time of the deposition were optimized. The Polyvinylpyrrollidone (PVP) was successfully used as capping agent in order to stop the agglomeration in the CdS thin films. It was found that, CdS thin films have remarkable antibacterial activity in dark and sunlight and it could be applied as antimicrobial agent in medical field. In order to confirm the crystalline structure of CdS thin films, the polycrystalline nature of the deposited CdS thin films with hexagonal structure was obtained. Furthermore, the structural parameters including lattice parameters, cell volume, the space group, average grain size, dislocation density and the strain have been calculated. The topography and surface roughness of the CdS thin films have been studied before and after the bacteriostatic effect using Scanning Electron Microscopy (SEM). Furthermore, the compositions of nanocrystalline CdS thin films have been evaluated using Energy Dispersive X-ray emission (EDX) and a Transmission Electron Microscope (TEM). Based on the optical measurements in the range of 300–2500 nm, the band gap energy of the prepared CdS thin films was found to be 2.4 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.     

Preparation and characterization of ZnS thin films prepared by chemical bath deposition

Zinc sulfide thin films were prepared by chemical bath deposition technique using zinc sulfate (ZnSO₄·7H₂O) and thiourea [SC(NH₂)₂] as sources of Zn²⁺ and S^2– ions, and ammonia (NH₃) and hydrazine hydrate (N₂H₄) as complexing agents. The structural, stoichiometric proportion, morphology and optical properties of the ZnS thin films were investigated as a function of thiourea and ammonia concentrations using X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and UV-visible spectrophotometry measurements. The deposition mechanism is discussed. The results reveal that the ZnS films exhibit poor crystallinity. The ammonia concentration had an obvious effect on the surface morphology, optical properties and deposition mechanism. The S/Zn atomic ratio and optical bandgap of the ZnS thin films first increased and then decreased with increasing ammonia or thiourea concentration.     

Synthesis and characterization of CdSe nanocrystalline thin films deposited by chemical bath deposition

Cadmium selenide (CdSe) nanocrystalline thin films were prepared by chemical bath deposition (CBD) using ammonia and triethanolamine (TEA) as complexing agents, cadmium chloride and sodium selenosulphate as the sources of Cd²⁺ and Se^2? ions, respectively. The structural and optical properties of CdSe nanocrystalline thin films were investigated as a function of the sodium selenosulphate concentrations or ammonia concentrations in precursors using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) measurements, transmission electron microscopy (TEM) and UV–visible spectrophotometer measurements. The results reveal that the CdSe thin films are in the pure cubic phase, which composed of a large number of uniform spherical particles. Each spherical particle contains many nanocrystals 3–10 nm in crystallite size. An increase in both the average diameter of the spherical particles and the crystallite size of the nanocrystals occurs with an increase in ammonia concentrations. The Se/Cd atom ratios of CdSe thin films firstly increase and then decrease with an increase in ammonia concentration or sodium selenosulphate concentration. The optical band gap of CdSe thin films decrease with an increase in ammonia concentrations. The kinetics and reaction mechanism of the CdSe nanocrystalline thin films during deposition are discussed.     

Resistive switching behavior of Sb2S3 thin film prepared by chemical bath deposition

The chalcogenides are the excellent memristor materials. Here we report the resistive switching properties of an amorphous Sb₂S₃ thin film. Sb₂S₃ films were deposited on FTO glass using a low-temperature (10 °C) chemical bath deposition technique. SEM and XRD results indicate that the as-grown Sb₂S₃ film is dense and amorphous with uniform thickness and smooth surface. The Ag/Sb₂S₃/FTO memristor shows typical bipolar switching behavior with low operating voltage, high resistance ratio, long retention time, and good endurance. The electrical tests demonstrate that the switching behavior of the amorphous Sb₂S₃ film is based on electrochemical metallization mechanisms.     

Effects of ammonia concentration on property of Cd1−xZnxS films by chemical bath deposition

Cd_1−xZn_xS thin films were grown on soda–lime glass substrates by chemical-bath deposition (CBD) at 80 °C with stirring. All the samples were annealed at 200 °C for 60 min in the air. The crystal structure, surface morphology, thickness and optical properties of the films were studied with transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), step height measurement instrument and spectrophotometer respectively. The results revealed that Cd_1−xZn_xS thin films had cubic crystal structure and the intensity of the diffraction peak increased gradually as ammonia concentration rose and the grain size varied from 5.1 to 8.3 nm. All of Cd_1−xZn_xS thin films had a granular surface with some smaller pores and the average granule sizes increased from 92 to 163 nm with an increase in ammonia concentration. The Cd_1−xZn_xS thin films had the highest transmittance with ammonia concentration of 0.5 M L⁻¹, whose thickness was 50 nm and band gap was 2.62 eV.     

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 deposition time on lead selenide thermoelectric thin films prepared by chemical bath deposition technique

A series of lead selenide (PbSe) films was deposited at constant bath temperature with various deposition time (3–5 h) using simple chemical bath deposition techniques, to study the effect of deposition time on its structural and thermoelectric properties. The as-deposited film was analyzed through X-ray diffraction, SEM, Energy dispersive X-ray analysis, Raman spectroscopy and Seebeck coefficient measurement. The improvement of crystallinity of the PbSe films was studied using X-ray diffraction and Raman scattering. The structural parameters, such as the lattice constant (a), crystallite size (D), dislocation density (δ) and microstrain (ε) were evaluated from the XRD spectra. Average crystallite size was calculated from Scherrer׳s formula and it was found to be increased from 19.65 to 23.97 nm as the deposition time was varied from 3 h to 5 h. The dislocation density and microstrain were found to vary inversely with the crystallite size, whereas the lattice constant increases with an increase in crystallite size. SEM images show that the morphology of particles strongly depends on the deposition time. The possible growth mechanism for the variation in the morphology is discussed. The thermoelectric measurements have shown n-type conductivity in “as deposited films” and the magnitude of Seebeck coefficient is found to be increasing with an increase in deposition time.     

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 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.     

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.     

Comparative studies on the structural,morphological, optical,and electrical properties of nanocrystalline PbS thin films grown by chemical bath deposition using two different bath compositions

High-quality lead sulfide (PbS) thin films were synthesized by chemical bath deposition from two baths with different compositions. One of them (bath-І) contained an aqueous solution of lead acetate, thiourea, sodium hydroxide, and the second (bath-ІІ) had additional triethanolamine. The introduction of triethanolamine reduced the grain size and increased the optical band gap of the PbS nanoparticles. The structure, morphology, and optical properties of the obtained films were investigated and compared with respect to the deposition time. X-ray diffraction data were used to obtain the crystallite size, lattice constant, and strain of the films. Atomic force microscopy results show that the roughness and rms-surface slope of the samples obtained from bath-I (PbS-I) were higher than those of bath-II (PbS-II) samples. PbS thin films with high reflectance (~61%) in the near-infrared region, which is important in our solar system, were obtained. The band gap, extinction coefficient, and refractive index of the samples were calculated. Furthermore, Raman analysis was performed and electrical properties of the samples were studied.     

SnS thin films deposited by chemical bath deposition, dip coating and SILAR techniques

The SnS thin films were synthesized by chemical bath deposition (CBD), dip coating and successive ionic layer adsorption and reaction (SILAR) techniques. In them, the CBD thin films were deposited at two temperatures: ambient and 70 ℃. The energy dispersive analysis of X-rays (EDAX), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and optical spectroscopy techniques were used to characterize the thin films. The electrical transport properties studies on the as-deposited thin films were done by measuring the I-V characteristics, DC electrical resistivity variation with temperature and the room temperature Hall effect. The obtained results are deliberated in this paper.     

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.     

Optical properties of chemical bath deposited CdS thin films

CdS thin films have been prepared by chemical bath deposition. As-deposited films are cubic and show a sulfur deficiency. From the transmittance and reflectance data analysis direct band gaps (E_g) ranging from 2.180 to 2.448 eV have been obtained. Air and vacuum annealed samples show a decrease in the band gap. The refractive index (n) lies in the range 1.61–2.34. A dependence of band gap on composition has been observed and the possible reasons are discussed.     

溶液PH值对CdS薄膜结构特性的影响

采用化学水浴沉积(CBD)工艺在玻璃衬底上制 备CdS薄膜,研究溶液PH值对CdS 薄膜结构特性的影响。薄膜的厚度、组份、晶相结构和表观形貌分别由台阶仪、X射线荧光 光谱(XRF)、X射线衍射(XRD)和场发射扫描电子显微镜(FESEM)来表征。溶液的 PH值为11.26、 11.37和11.48时,CdS薄膜的晶相以六方相为主,薄膜的厚度先增大后减小; PH值为11.62、11.66时,薄膜的晶相以立方相为主,薄 膜的厚度进一步减小。同时,随着溶液PH值 增大,CdS薄膜的晶格常数也逐渐增大。两种晶相的CdS薄膜缓冲层与CIGS薄膜分别构成异 质 对形成异质结时的晶格失配分别为32.297%和1.419%,界面态密度分别为2.792×10¹⁴和8.507×10¹²,因此高效CIGS薄 膜太阳电池更需要立方相的CdS薄膜。     

沉积温度对多元醇法制备硫化镉薄膜的影响

CdS thin films were successfully deposited onto glass substrates for the first time by the polyol method using cadmium acetate, thiourea and diethylene glycol as the raw materials. The effects of the deposition tempera- ture from 120 to 200 ℃ in steps of 20 ℃on the structure, morphology and optical properties of the resultant films were investigated. It was found that the crystallinity was improved and the value of the surface average roughness was decreased with increasing the deposition temperature. The average grain sizes of the CdS thin films were 77.16 and 76.61 nm at 140 and 180 ℃, respectively. All samples showed excellent transmittance and the band gaps were found to reduce from 2.55 to 2.45 eV with the increase of the deposition temperature, which was attributed to the improvement of crystallinity.     

Low-cost TiO2/Sb2(S,Se)3 heterojunction thin film solar cell fabricated by sol-gel and chemical bath deposition

Low cost TiO₂/ Sb₂(S, Se)₃ heterojunction thin film solar cell are prepared successfully by using sol-gel and chemical bath deposition. At first, TiO₂ thin film is prepared on the ITO-coated glass substrate by a simple sol-gel and dip-coating method. Subsequently, Sb₂(S, Se)₃ film is fabricated on TiO₂ by selenizing the Sb₂S₃ film prepared by chemical bath deposition (CBD). The heat-treated process of TiO₂ and Sb₂(S, Se)₃ films has been discussed, respectively. After being heat-treated at 550 °C for TiO₂ and 290 °C for Sb₂(S, Se)₃ films, the photovoltaic devices are completed with the conductive graphite as electrode. The J-V characteristics of TiO₂/ Sb₂(S, Se)₃ solar cell are measured and the open circuit voltage (V_oc) of this cell is about 350 mV.     

Optimising conditions for the growth of nanocrystalline ZnS thin films from acidic chemical baths

The growth of nanocrystalline zinc sulfide thin films onto glass substrates by chemical bath deposition has been optimized at acidic pH. Powder X-ray diffraction (p-XRD) confirms the deposition of sphalerite, the cubic phase of ZnS. The crystallite size calculated by Scherrer equation was found to be 4.0 nm. Scanning Electron Microscopy (SEM) show clusters of spherical nanoparticles uniformly distributed over the surface of the glass substrates. Energy Dispersive X-ray (EDX) analysis of the deposited thin films show the zinc to sulfur ratio close to 1:1. The observed band gap (3.78 eV) of the deposited thin films is higher than that reported for cubic phase of bulk ZnS (3.54 eV) as expected due to nano-size crystallites. Binding energies calculated by X-ray Photoelectron Spectroscopy (XPS) confirm the material as ZnS and the photoluminescence measurements show the blue shift in emission maximum.     

Structural and optical studies on PVA capped SnS films grown by chemical bath deposition for solar cell application

Tin monosulphide (SnS) thin films capped by PVA have been successfully deposited on glass substrates for cost effective photovoltaic device applications by a simple and low-cost wet chemical process, chemical bath deposition (CBD) at different bath temperatures varying in the range, 50–80 °C. X–ray diffraction analysis showed that the deposited films were polycrystalline in nature, showing orthorhombic structure with an intense peak corresponding to (040) plane of SnS. These observations were further confirmed by Raman analysis. FTIR spectra showed the absorption bands which corresponds to PVA in addition to SnS. The scanning electron microscopy and atomic force microscopy studies revealed that the deposited SnS films were uniform and nanostructured with an average particle size of 4.9 to 7.6 nm. The optical investigations showed that the layers were highly absorbing with the optical absorption coefficient ~10⁵ cm^–1. A decrease in optical band gap from 1.92 to 1.55 eV with an increase of bath temperature was observed. The observed band gap values were higher than the bulk value of 1.3 eV, which might be due to quantum confinement effect. The optical band gap values were also used to calculate particle size and the results are discussed.