Ammonia-free method for synthesis of CdS nanocrystalline thin films through chemical bath deposition technique

The preparation of thin films of CdS by chemical bath deposition is mostly based on the utilisation of ammonia as a complexing agent for cadmium ions. Here we report on a technique based on sodium citrate dihydrate that eliminates the problems of ammonia volatility and toxicity. The crystallites with a size range of 10–20 nm in diameter with zinc blend (cubic) and wurtzite (hexagonal) crystal structures and strong photoluminescence were prepared from the mixture solutions of: cadmium chloride dihydrate as a cadmium source, thiourea as a sulfur source and sodium citrate dihydrate as a complexing agent for cadmium ions. The well-cleaned glass used as a substrate for thin film deposition. The obtained samples were characterized by the techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscope (AFM) and fluorescence spectroscopy. Also, the effect of two operating conditions, (i) pH, and (ii) the temperature of reaction on the synthesizing of CdS nanocrystals was examined. Finally, it was found that the CdS nanocrystals showed sharp excitation features and strong ”band-edge” emission.     

Optical and dielectric properties of PVA capped nanocrystalline PbS thin films synthesized by chemical bath deposition

Nanoparticles of lead sulfide (PbS) have been grown within the pores of polyvinyl alcohol (PVA) matrix on glass substrates by chemical bath deposition at and below room temperature (30 °C). Lead acetate and thiourea, dissolved in an alkaline medium, were taken as the sources of lead and sulfur. X-ray diffraction and selected area electron diffraction studies confirmed the cubic nanocrystalline PbS phase formation. Transmission electron micrograph of the films revealed the particle size lying in the range 10–20 nm. X-ray photoelectron spectroscopic studies confirmed the presence of lead and sulfur in the films, and their atomic ratios were found to be dependent on the deposition temperature. UV–vis spectrophotometric measurement showed a direct allowed band gap lying in the range 2.40–2.81 eV, which is much higher than the bulk value (0.41 eV). The band gap decreases with the increase of deposition temperature. The dielectric constant of the PVA-capped nanocrystalline PbS was in the range 155–265 at higher frequencies, which is much higher compared to only PVA and bulk PbS.     

Synthesis of CuS thin films by microwave assisted chemical bath deposition

In this study, oriented CuS nanoplates standing perpendicularly on F: SnO₂ (FTO) coated glass substrates have been prepared through a mild microwave assisted chemical bath deposition process in which copper acetate reacted with ethylenediamine tetraacetate acid disodium and thioacetamide in aqueous solution within 40 min. The effects of reaction time and microwave radiation on the treatment process were investigated. The morphology, structure, and composition of the yielded nanostructures have been confirmed by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), and scanning electron microscope (SEM). Also, the correlation between the reflectance, transmittance coefficient in the UV and the thickness of films was established. Furthermore, a two-point probe was used for resistivity measurements. We believe this simple chemical conversion technique can be further extended to the synthesis of other semiconductors with various morphologies.     

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.     

Physical properties of ZnS thin films prepared by chemical bath deposition

Zinc sulphide thin films are deposited on SnO₂/glass using the chemical bath deposition technique. X-ray diffraction and atomic force microscopy are used to characterize the structure of the films; the surface composition of the films is studied by Auger electrons spectroscopy, the work function and the photovoltage are investigated by the Kelvin method. Using these techniques, we specify the effect of pH solution and heat treatment in vacuum at 500 °C. The cubic structure corresponding to the (1 1 1) planes of β-ZnS is obtained for pH equal to 10. The work function (Φ_material − Φ_probe) for ZnS deposited at pH 10 is equal to −152 meV. Annealing at 500 °C increases Φ_m (by about 43 meV) and induces the formation of a negative surface barrier. In all cases, Auger spectra indicate that the surface composition of zinc sulphide thin films exhibits the presence of the constituent elements Zn and S as well as C and O as impurity elements.     

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.     

Controlled synthesis, characterization and optical properties of CdS nanocrystalline thin films via chemical bath deposition (CBD) route

In this study, the CdS nanocrystalline thin films obtained from an ammonia-free chemical bath deposition process. The crystallites with a size range of 10–20 nm in diameter with zinc blend (cubic) and wurtzite (hexagonal) crystal structure and strong photoluminescence were prepared from the mixture solutions of: cadmium chloride dihydrate as a cadmium source, thiourea as a sulfur source and sodium citrate dihydrate as a complexing agent for cadmium ions. The well-cleaned glass used as a substrate for thin films deposition. The obtained samples were characterized by the techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), atomic force microscopy (AFM) and fluorescence spectroscopy. Also, the effect of two parameters such as pH and temperature of reaction on the synthesis of CdS nanocrystals was studied. Finally, it was found the CdS nanocrystals showed sharp excitation features and strong “band-edge” emission.     

Lead-free ferroelectric thin films obtained by pulsed laser deposition

Na_0.5Bi_0.5TiO₃-BaTiO₃ (NBT-BT) thin films grown by pulsed laser deposition have been investigated by X-ray diffraction, scanning electron microscopy, and dielectric spectroscopy in order to clarify the role of substrate temperature on crystalline structure, grain morphology, and dielectric properties. We have shown that the structural and dielectric properties of NBT-BT thin films with composition at morphotropic phase boundary (6% BT) critically depend on the substrate temperature: small variations of this parameter induce structural changes, shifting the morphotropic phase boundary toward tetragonal or rhombohedral side. Higher deposition temperature (1000 K) favor the formation of rhombohedral phase, films deposited at 923 K and 973 K have tetragonal symmetry at room temperature. Grains morphology depends also on the deposition temperature. Atomic force micrographs show grains with square or rectangular shape in a compact structure for films grown at lower temperatures, while grains with triangular shape in a porous structure are observed for films grown at 1000 K. Dielectric spectroscopy measurements evidenced the phase transition between ferroelectric and antiferroelectric phase at 370 K. Films grown at 1000 K shown low electrical resistivity due to their porous structure. High dielectric constant values (about 800 at room temperature and 2700 at 570 K) have been obtained for films grown at temperatures up to 973 K.     

Characterization of poly (3-methyl thiophene) thin films prepared by modified chemical bath deposition

Poly (3-methyl thiophene) thin films were prepared by chemical bath deposition technique on glass substrate; the prepared thin films were characterized for structural, morphological and optical properties. The variation in the oxidant concentration has an influence on the properties of the P3MeT thin films. The increase in the oxidant concentration leads to increase in the thickness of the film. The binding energy increases due to increase in oxidation concentration. The P3MeT thin films show smooth surface morphology with increase in oxidant concentration whereas the contact angle of the thin film decreases with increase in oxidant concentration. The optical absorbance of these thin films was found to increase with decrease in the optical band gap due to increase in oxidant concentration.     

Bismuth oxide thin films prepared by chemical bath deposition (CBD) method: annealing effect

Bismuth oxide thin films have been deposited by room temperature chemical bath deposition (CBD) method and annealed at 623 K in air. They were characterized for structural, surface morphological, optical and electrical properties. From the X-ray diffraction patterns, it was found that after annealing a non-stoichiometric phase, Bi₂O_2.33, was removed and phase pure monoclinic Bi₂O₃ was obtained. Surface morphology of Bi₂O₃ film at lower magnification SEM showed rod-like structure, however, higher magnification showed a rectangular slice-like structure perpendicular to substrate, giving rise to microrods on the surface. The optical studies showed the decrease in band gap by 0.3 eV after annealing. The electrical resistivity variation showed semiconductor behavior and from thermoemf measurements, the electrical conductivity was found to be of n-type.     

Polycrystalline silicon films obtained by hot-wire chemical vapour deposition

Silicon films were deposited at moderate substrate temperatures (280–500° C) from pure silane and a silane-hydrogen mixture (10% SiH₄, 90% H₂) in a hotwire CVD reactor. The morphology, structure and composition of the samples were studied with scanning electron microscopy, transmission electron microscopy, transmission electron diffraction, X-ray diffraction, Raman spectroscopy and secondary ion mass spectrometry. The sample deposited at 500° C with pure silane has an amorphous structure, whereas the samples obtained from silane diluted in hydrogen have a polycrystalline structure, even that grown at the lowest temperature (280° C). Polycrystalline samples have a columnar structure with 0.3–1 m crystallite sizes with preferential orientation in [220] direction. Deposition rates depend on the filament-substrate distance and range from 9.5 to 37 Å/s for the polycrystalline samples. The high quality of the polycrystalline samples obtained makes the hot-wire technique very promising. Moreover, it is expected to be easily scaled up for applications to large-area optoelectronic devices and to photovoltaic solar cells.     

Interlayer interaction in three-layer films obtained by chemical deposition

The results from experimental investigations on the dependences of the displacement field of hysteresis loop H _E and the saturation field of the polar Kerr effect H _S on the thickness of nonmagnetic interlayers in three-layer films obtained by chemical deposition are presented. Possible mechanisms responsible for oscillating variations in H _S at interlayer thicknesses are presented.     

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.     

Characterization of polymer thin films obtained by pulsed laser deposition

The development of laser techniques for the deposition of polymer and biomaterial thin films on solid surfaces in a controlled manner has attracted great attention during the last few years. Here we report the deposition of thin polymer films, namely Polyepichlorhydrin by pulsed laser deposition. Polyepichlorhydrin polymer was deposited on flat substrate (i.e. silicon) using an NdYAG laser (266 nm, 5 ns pulse duration and 10 Hz repetition rate).The obtained thin films have been characterized by atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and spectroscopic ellipsometry.It was found that for laser fluences up to 1.5 J/cm² the chemical structure of the deposited polyepichlorhydrin polymer thin layers resembles to the native polymer, whilst by increasing the laser fluence above 1.5 J/cm² the polyepichlorohydrin films present deviations from the bulk polymer.Morphological investigations (atomic force microscopy and scanning electron microscopy) reveal continuous polyepichlorhydrin thin films for a relatively narrow range of fluences (1-1.5 J/cm²).The wavelength dependence of the refractive index and extinction coefficient was determined by ellipsometry studies which lead to new insights about the material.The obtained results indicate that pulsed laser deposition method is potentially useful for the fabrication of polymer thin films to be used in applications including electronics, microsensor or bioengineering industries.     

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.     

Optical and structural properties of CdS thin films grown by chemical bath deposition doped with Ag by ion exchange

In this work thin CdS films using glycine as a complexing agent were fabricated by chemical bath deposition and then doped with silver (Ag), by an ion exchange process with different concentrations of AgNO₃ solutions. The CdS films were immersed in silver solutions using different concentrations during 1 min for doping and after that the films were annealed at 200 °C during 20 min for dopant diffusion after the immersion on the AgNO₃ solutions. The aim of this research was to know the effects of different concentrations of Ag on the optical and structural properties of CdS thin films. The optical band gap of the doped films was determined by transmittance measurements, with the results of transmittance varying between 35% and 70% up to 450 nm in the electromagnetic spectra and the band gap varying between 2.31 and 2.51 eV depending of the silver content. X-ray photoelectron spectroscopy was used to study the influence of silver on the CdS:Ag films, as a function of the AgNO₃ solution concentration. The crystal structure of the thin CdS:Ag films was studied by the X-ray diffraction method and the film surface morphology was studied by atomic force microscopy. Using the ion exchange process, the CdS films’ structural, optical and electric characteristics were modified according to silver nitrate concentration used.     

Fabrication and characterization of indium sulfide thin films deposited on SAMs modified substrates surfaces by chemical bath deposition

In an effort to explore the optoelectronic properties of nanostructured indium sulfide (In₂S₃) thin films for a wide range of applications, the In₂S₃ thin films were successfully deposited on the APTS layers (-NH₂-terminated) modified ITO glass substrates using the chemical bath deposition technique. The surface morphology, structure and composition of the resultant In₂S₃ thin films were characterized by FESEM, XRD, and XPS, respectively. Also, the correlations between the optical properties, photocurrent response and the thickness of thin films were established. According to the different deposition mechanisms on the varying SAMs terminational groups, the positive and negative micropatterned In₂S₃ thin films were successfully fabricated on modified Si substrates surface combining with the ultraviolet lithography process. This offers an attractive opportunity to fabricate patterned In₂S₃ thin films for controlling the spatial positioning of functional materials in microsystems.     

化学水浴法和磁控溅射法制备硫化镉薄膜的性能研究

以氯化铵、氯化镉、氢氧化钾和硫脲为反应物采用化学水浴法制备了硫化镉薄膜,为了作对比研究,采用射频磁控溅射以硫化镉为靶材,氩气为溅射气体,制备了硫化镉薄膜。采用X射线衍射、扫描电子显微镜和紫外-可见光光谱仪分别表征了硫化镉薄膜的结构、形貌和光学吸收特性。结果表明,采用以上两种方法制备的硫化镉均具有(002)择优取向,溅射法制备的硫化镉薄膜较致密,薄膜表面较光滑,平均晶粒尺寸在20～30nm;水浴法制备的硫化镉薄膜颗粒尺寸较小,缺陷较多。除了在短波段溅射所得硫化镉薄膜的透过率略差于水浴法所得硫化镉薄膜之外,溅射法制备的硫化镉薄膜的性能整体上优于水浴法制备的薄膜。两种方法制备的硫化镉薄膜的能隙在2.3～2.5eV。     

Bioactive glass and hydroxyapatite thin films obtained by pulsed laser deposition

Bioactive glass (BG), calcium hydroxyapatite (HA), and ZrO₂ doped HA thin films were grown by pulsed laser deposition on Ti substrates. An UV KrF^* (λ = 248 nm, τ ≥ 7 ns) excimer laser was used for the multi-pulse irradiation of the targets. The substrates were kept at room temperature or heated during the film deposition at values within the (400-550 °C) range. The depositions were performed in oxygen and water vapor atmospheres, at pressure values in the range (5-40 Pa). The HA coatings were heat post-treated for 6 h in a flux of hot water vapors at the same temperature as applied during deposition. The surface morphology, chemical composition, and crystalline quality of the obtained thin films were studied by scanning electron microscopy, atomic force microscopy, and X-ray diffractometry. The films were seeded for in vitro tests with Hek293 (human embryonic kidney) cells that revealed a good adherence on the deposited layers. Biocompatibility tests showed that cell growth was better on HA than on BG thin films.     

Room-temperature deposition of nanocrystalline PbWO 4 thin films by pulsed laser ablation

Pulsed laser ablation (PLA) was applied to synthesize nanocrystalline PbWO₄ thin films onto glass substrates. The effects of Ar background gas pressure on phase evolution, microstructures and optical characteristics of PbWO₄ thin films were investigated in detail. The PLA processes were carried out at room temperature without substrate heating or post-annealing treatment. XRD and HR-TEM results revealed that the PbWO₄ thin films are composed of nanocrystalline and amorphous phases. Moreover, the films contained a high density of lattice defects such as twin boundaries and edge dislocations. The crystallite size and crystallinity increased, which were associated with a change in surface morphology as the Ar pressure increased. Reduced tungsten states W⁵⁺ or W⁴⁺ induced by oxygen vacancies were observed at 10 Pa and the atomic concentration of all constituent element was almost stoichiometric, especially the [Pb]/[W] ratio, which was nearly unity above 50 Pa. The optical energy band-gap was 3.03 eV at 50 Pa and increased to 3.35 eV at 100 Pa, which are narrower than the reported value (4.20 eV). This optical band-gap narrowing could be attributed to localized band-tail states and new energy levels induced by the amorphous structure and inherent lattice defects. PACS 81.15.Fg; 78.20.-e; 68.55.-a; 73.22.-f