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.     

沉积温度对硫化锌(ZnS)薄膜的结晶和光学特性影响研究

对不同温度下沉积的ZnS薄膜的结晶情况和光学特性进行了研究, 结果表明：沉积温度对ZnS薄膜的物理和光学特性有较大影响, 不同的温度沉积的ZnS薄膜具有不同的择优取向, 牢固度也大不相同; 不同沉积温度下, ZnS薄膜的光学常数也不尽相同. 温度为115 ℃和155 ℃时, ZnS薄膜的物理性能和光学性能较差, 不适合空间用光学薄膜的研制使用. 而190 ℃和230 ℃沉积温度下所得薄膜具有较好的物理和光学性能, 适合于不同要求的空间用薄膜器件的研制使用. 关键词： 硫化锌薄膜 沉积温度 表面形貌 光学常数     

A comparative study of conventional type II and inverted core–shell nanostructures based on CdSe and ZnS

The objective of this work is to investigate structural, morphological and optical properties of conventional CdSe/ZnS core–shell and inverted ZnS/CdSe core–shell nanostructures for opto-electronic device applications. For this purpose both nanostructures were synthesized using chemical bath deposition technique in thin film form. The structural properties were studied using X-ray diffraction technique with Rietveld refinement and transmission electron microscopy (TEM). The surface morphology of synthesized thin film was illustrated in the form 2D and 3D images using atomic force microscopy (AFM). The optical properties were explained using UV–Vis absorption spectroscopy and photo luminescence (PL) spectroscopy in in situ monitoring process. A comparison of estimated particle size from XRD, high resolution AFM and TEM images was resulted in good agreement as 2.1, 2.4 and 2.1 nm respectively for conventional CdSe/ZnS core–shell and as 2.5, 2.5 and 2.2 nm respectively for inverted ZnS/CdSe core–shell nanostructures.     

核壳结构CdS/ZnS纳米微粒的制备与光学特性

用微乳液法制备CdS纳米微粒 ,以ZnS对其进行表面修饰 ,得到具有核壳结构的CdS/ZnS纳米微粒 .采用X射线衍射 (XRD)、透射电镜 (TEM )表征其结构、粒度和形貌 ,紫外 可见吸收光谱 (UV)、光致发光光谱(PL)表征其光学特性 .制得的CdS近似呈球形 ,直径为 3.3nm ;以XRD和UV证实了CdS/ZnS核壳结构的实现 .研究了不同ZnS壳层厚度对CdS纳米微粒光学性能的影响 ,UV谱表明随着壳层厚度的增加纳米微粒的吸收带边有轻微的红移 ,同时短波吸收增强 ;PL谱表明壳层ZnS的包覆可减少CdS纳米微粒的表面缺陷 ,带边直接复合发光的几率增大 ,具有合适的壳层厚度时发光效率大大提高 .     

Characterization of electrodeposited Bi2S3 thin films by holographic interferometry

Optical non destructive evaluation methods, using lasers as the object illumination source, include holographic interferometry. It is widely used to measure stress, strain, and vibration in engineering structures. Double exposure holographic interferometry (DEHI) technique is used to determine thickness and stress of electrodeposited bismuth trisulphide (Bi₂S₃) thin films for various deposition times. The same is tested for other concentration of the precursors. It is observed that, increase in deposition time, increases thickness of thin film but decreases stress to the substrate. The structural, optical and surface wettability properties of the as deposited films have been studied using X-ray diffraction (XRD), optical absorption and contact angle measurement, respectively. The X-ray diffraction study reveals that the films are polycrystalline with orthorhombic crystal structure. Optical absorption study shows the presence of direct transition with band bap 1.78 eV. The water contact angle measurement shows hydrophobic nature of Bi₂S₃ thin film surface.     

Thickness dependence of optoelectrical properties of tungsten-doped indium oxide films

Pulsed laser deposition technique is used for deposition of tungsten-doped indium oxide films. The effect of film thickness on structural, optical and electrical properties was studied using X-ray diffraction (XRD), atomic force microscopy, UV-visible spectroscopy, and electrical measurements. X-ray diffraction study reveals that all the films are highly crystalline and oriented along (2 2 2) direction and the film crystallinity increases with increase in film thickness. Atomic force microscopy analysis shows that these films are very smooth with root mean square surface roughness of ∼1.0 nm. Bandgap energy of the films depends on thickness and varies from 3.71 eV to 3.94 eV. It is observed that resistivity of the films decreases with thickness, while mobility increases.     

Characteristics of sculptured Cu thin films and their optical properties as a function of deposition rate

Sculptured copper thin films were deposited on glass substrates, using different deposition rates. The nano-structure and morphology of the films were obtained, using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Their optical properties were measured by spectrophotometry in the spectral range of 340-850 nm. The real and imaginary refractive indices, film thickness and fraction of metal inclusion in the film structure were obtained from optical fitting of the spectrophotometer data.     

AFM, XPS and RBS studies of the growth process of CdS thin films on ITO/glass substrates deposited using an ammonia-free chemical process

This paper deals with a detailed study of the growth stages of CdS thin films on ITO/glass substrates by chemical bath deposition (CBD). The chemical and morphological characterization was done through X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), and atomic force microscopy (AFM) techniques. On the other hand, optical transmission and X-ray diffraction (XRD) measurements were performed in order to study the optical and structural properties of the films. The time, the chemistry, and morphology of the different stages that form the growth process by CBD were identified through these results. Furthermore, clear evidence was obtained of the formation of Cd(OH)₂ as the first chemical species adhered to the substrate surface which forms the first nucleation centers for a good CdS formation and growth. On the other hand, the ITO coating caused growth stages to occur earlier than in just glass substrates, with which we can obtain a determined thickness in a shorter deposition time. We were able to prove that CBD is a good technique for the manufacture of thin films of semiconductor materials, since the CdS film does not have any impurities. Completely formed films were transparent, uniform, with good adherence to the substrate, of a polycrystalline nature with a hexagonal structure. These results indicate that films obtained by CBD are good candidates to be applied in different optoelectronic devices.     

Substrate-target distance dependence of structural and optical properties in case of Pb(Zr,Ti)O3 films obtained by pulsed laser deposition

The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance.     

Optical inhomogeneity of ZnS films deposited by thermal evaporation

Zinc sulfide (ZnS) films with optical thickness (reference wavelength is 620 nm) ranging from 310 to 1240 nm were deposited on quartz substrates at room temperature by a thermal evaporation system. The structure and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, respectively. The optical properties of the films were determined by in situ transmittance measurements and wideband spectra photometric measurements, respectively. The experimental results show that the films exhibit cubic structure, and the intensity of the (2 2 0) diffraction peak enhances with the increase of optical thickness. Surface grain size and surface roughness increase monotonously with increasing film thickness. Refractive indices and extinction coefficients calculated by in situ transmittance measurements are well consistent with those calculated by wideband spectra photometric measurements. Both the refractive index and packing density of the film increase as the increase of film thickness, which confirms the film is positive inhomogeneous and has an expanding columnar structure. Extinction coefficients of the films increase with increasing film thickness, which results from the increase of surface roughness.     

High quality ZnS/Au/ZnS transparent conductive tri-layer films deposited by pulsed laser deposition

ZnS/Au/ZnS tri-layer films were deposited on quartz glass substrates by pulsed laser deposition. The influence of Au layer thickness on optical and electrical properties of the tri-layer ZnS/Au/ZnS was studied. X-ray diffractometer (XRD) and scanning electron microscope were employed to characterize the crystalline structure and surface morphology of the tri-layer films. Hall measurements, ultraviolet and visible spectrophotometer, four-point probe were used to explore the optoelectronic properties of the ZnS/Au/ZnS. The increase of Au layer thickness resulted in the decreased resistivity, the increased carrier concentration, and the declined transmittance in the visible light region.     

Green route fast synthesis and characterization of chemical bath deposited nanocrystalline ZnS buffer layers

Zinc sulphide (ZnS) thin films are deposited using chemical bath deposition method on the glass substrates in an aqueous alkaline reaction bath of zinc acetate and thiourea along with non-toxic complexing agent tri-sodium citrate at 95 °C. The results show noteworthy improvement in the growth rate of the deposited ZnS thin films and thickness of the film increases with the deposition time. From X-ray diffraction patterns, it is found that the ZnS thin films exhibit hexagonal polycrystalline phase reflecting from (101) and (0016) planes. The high resolution transmission electron microscopy studies confirmed the formation of hexagonal phase from the d-value calculation which was 0.3108 nm. X-ray photoelectron spectroscopy reveals that the Zn–S bonding energy is at 1022.5 and 162.1 eV for Zn 2p_3/2 and S 2p_1/2 states, respectively. Field emission scanning electron microscopy study shows that deposited thin films are highly uniform, with thin thickness and completely free from large ZnS clusters which usually form in aqueous solutions. Atomic force microscopy investigates that root mean square values of the ZnS thin films are from 3 to 4.5 nm and all the films are morphologically smooth. Energy dispersive spectroscopy shows that the ZnS thin films are relatively stoichiometric having Zn:S atomic ratio of 55:45. It is shown by ultraviolet–visible spectroscopy that ～90% transmittance and ～10% absorbance for the ZnS films in the visible region, which is significantly higher than that reported elsewhere and the band gap energy of the ZnS films is found to be 3.76, 3.74, and 3.71 eV, respectively.     

A study of the optical properties and adhesion of zinc sulfide anti-reflection thin film coated on a germanium substrate

To conduct this study, zinc sulfide (ZnS) thin films deposited on germanium (Ge) substrates were prepared by an evaporation method. The effects of deposition rate and annealing on the optical properties and adhesion of the ZnS thin films were investigated. The transmission intensity and the X-ray diffraction (XRD) pattern of the samples showed that the transmittance of the samples decreases by increasing the evaporation rates. However, with the increase of the annealing temperature, crystallinity of the thin films improves which, in turn, results in the enhancement of the transmission intensity in a far infrared region. The maximum grain size was obtained at the annealing temperature of 225 °C. Our experimental results also show that evaporation rate and annealing influences the adhesion of ZnS thin films to Ge substrates.     

Tetracene film morphology: Comparative atomic force microscopy, X-ray diffraction and ellipsometry investigations

X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry were used to study tetracene thin films as a function of deposition rate. A comparative analysis of the thickness and roughness values allows for detailed modelling of the film morphology. An interdigitated growth mode is established for the coexisting thin film and bulk phases. By comparison with the respective quinone-derivative of tetracene, we were additionally able to identify reaction products by their optical response.     

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.     

Effect of thickness on physical properties of electron beam vacuum evaporated CdZnTe thin films for tandem solar cells

The thickness and physical properties of electron beam vacuum evaporated CdZnTe thin films have been optimized in the present work. The films of thickness 300 nm and 400 nm were deposited on ITO coated glass substrates and subjected to different characterization tools like X-ray diffraction (XRD), UV‐Vis spectrophotometer, source meter and scanning electron microscopy (SEM) to investigate the structural, optical, electrical and surface morphological properties respectively. The XRD results show that the as-deposited CdZnTe thin films have zinc blende cubic structure and polycrystalline in nature with preferred orientation (111). Different structural parameters are also evaluated and discussed. The optical study reveals that the optical transition is found to be direct and energy band gap is decreased for higher thickness. The transmittance is found to increase with thickness and red shift observed which is suitable for CdZnTe films as an absorber layer in tandem solar cells. The current-voltage characteristics of deposited films show linear behavior in both forward and reverse directions as well as the conductivity is increased for higher film thickness. The SEM studies show that the as-deposited CdZnTe thin films are found to be homogeneous, uniform, small circle-shaped grains and free from crystal defects. The experimental results confirm that the film thickness plays an important role to optimize the physical properties of CdZnTe thin films for tandem solar cell applications as an absorber layer.     

Deposition of carbon films using close space sublimation

Carbon films are fabricated for the first time using an inexpensive and ecologically safe modified method of close space sublimation at atmospheric pressure. They are deposited onto quartz, glass, glass ceramic (Pyroceram), and silicon substrates. The main properties of the films (such as the growth rate, morphology and structure, optical properties, the dependences of these properties on the deposition temperature and the substrate material) are studied by X-ray diffraction, atomic force microscopy, multiangular ellipsometry, and the measurement of transmission and reflectance spectra in the visible and near ultraviolet regions. The growth rate is 5 nm/min at a film nucleation temperature of 800°C. The film thickness varies from 0.2 to 2.2 μm, and the minimum surface roughness is 0.5 nm. The refractive indices of the films range from 1.3 to 1.8 depending on the growth and subsequent heat treatment conditions. The optical energy gap is 5.4 eV.     

Structural and optical properties of monodispersed ZnS/CdS/ZnO and ZnO/ZnS/CdS nanoparticles

Excellent luminescence properties of ZnS/CdS/ZnO and ZnO/ZnS/CdS nanocrystallites synthesized through a simple chemical method at room temperature are reported. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), UV–visible absorption and photoluminescence techniques were used to characterize the undoped ZnS, CdS and ZnO and the novel ZnS/CdS/ZnO and ZnO/ZnS/CdS nanoparticles. The optical properties of ZnS/CdS/ZnO and ZnO/ZnS/CdS nanoparticles reflect a combinational effect of the photoluminescent properties of ZnS, CdS and ZnO.     

The study of structure and optoelectronic properties of ZnS and ZnO films on porous silicon substrates

ZnS and ZnO films were prepared on porous silicon (PS) substrates with the same porosity by pulsed laser deposition (PLD), and the structural, optical and electrical properties of ZnS and ZnO films on PS were investigated at room temperature by X-ray diffraction (XRD), scanning electron microscope (SEM), optical absorption measurement, photoluminescence (PL) and I–V characteristic studies. The prepared ZnS was obtained in the cubic phase along β-ZnS (1 1 1) orientation which showed a perfect match with the earlier report while ZnO films were obtained in c-axis orientation. There appeared some cracks in the surface of ZnS and ZnO films due to the roughness of PS substrates. Luminescence studies of ZnS/PS and ZnO/PS composites indicated room temperature emission in a broad, intense, visible photoluminescence band, which cover the blue emission to red emission, exhibiting intensively white light emission. Based on the I–V characteristic, ZnS/PS heterojunction exhibited the rectifying junction behavior, while the I–V characteristic of ZnO/PS heterostructure was different from that of the common diode, whose reverse current was not saturated.     

Surface structure and composition of flat titanium thin films as a function of film thickness and evaporation rate

To correlate flat titanium film surface properties with deposition parameters, titanium flat thin films were systematically deposited on glass substrates with various thicknesses and evaporation rates by electron-beam evaporation. The chemical compositions, crystal structure, surface topographies as well as wettability were investigated by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM) and water contact angle measurement, respectively. The films consisted mainly of TiO₂. Small percentages of Ti₂O₃ and metallic Ti were also found at the film surface using high-resolution XPS analysis. Quantitative XPS showed little differences regarding elemental compositions among different groups of films. The films were obtained by varying the deposition rate and the film thickness, respectively. XRD data showed consistent reflection patterns of the different titanium samples deposited using different film thicknesses. Without exception measurements of all samples exhibited contact angles of 80° ± 5°. Quantitative AFM characterization demonstrated good correlation tendency between surface roughness and film thickness or evaporation rate, respectively. It is important to notice that titanium films with different sizes of grains on their surfaces but having the same chemistry and film bulk structure can be obtained in a controllable way. By increasing the film thickness and evaporation rate, the surface roughness increased. The surface morphology and grain size growth displayed a corresponding trend. Therefore, the control of these parameters allows us to prepare titanium films with desired surface properties in a controllable and reproducible way for further biological investigations of these materials.