Substrate temperature influence on ZnS thin films prepared by ultrasonic spray

ZnS thin films were deposited by ultrasonic spray technique. The starting solution is a mixture of 0.1 M zinc chloride as source of Zn and 0.05 M thiourea as source of S. The glass substrate temperature was varied in the range of 250 °C-400 °C to investigate the influence of substrate temperature on the structure, chemical composition and optical properties of ZnS films. The DRX analyses indicated that ZnS films have nanocrystalline hexagonal structure with (002) preferential orientation and grain size varied from 20 to 50 nm, increasing with substrate temperature. The optical films characterization was carried out by the UV-visible transmission. The optical gap and films disorder were deduced from the absorption spectra and the refractive indices of the films were determined by ellipsometric measurements. It is shown that the obtained films are generally composed of ZnO and ZnS phases with varied proportion, while at deposition temperature of 400 °C, they are near stoichiometric ZnS.     

Optical constants of CdS thin films prepared by spray pyrolysis

CdS thin films were prepared by spray pyrolysis techniques. Variable angle spectroscopic ellipsometry was used for optical constant calculations. Multiple angle measurements were taken in the most sensitive angle of incidence region. The sensitive regions of angle of incidence were obtained theoretically using 3-dimensional graph ofδψ andδΔ. Real partn and imaginary partk of the complex refractive index of the samples were calculated in the wavelength range 470–650 nm, taking into account surface roughness. Bruggeman’s effective medium approximation is used for analysis of the surface rough layer of the thin films.     

Growth and properties of ZnS thin films by sulfidation of sputter deposited Zn

ZnS thin films with the hexagonal structure have been produced by sulfurizing sputter deposited Zn in sulfur vapor for 1 h. These films have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), synchrotron radiation photoelectron spectroscopy (SR-PES), Auger electron spectroscopy (AES) and UV-VIS transmission spectra. It is found that at the sulfidation temperature (T_S) of 400 °C a little and partial Zn can be transformed to ZnS. At T_S = 500 °C, the total conversion of Zn in sulfur vapor can take place and form ZnS with a c-axis preferred orientation. The Zn-to-ZnS conversion is kinetically a reactive diffusion process. Also the ZnS thin film has much greater size of grains than the as-deposited Zn film, due to ZnS recrystallization and growth in sulfur vapor. Residual sulfur existing on the surface of ZnS grains leads to the poor optical transparency and great broadening of absorbing edge in the optical transmittance. However, ZnS thin film prepared by gradient sulfidation exhibits the improved optical transmittance, with a band-gap energy of 3.64 eV.     

化学水浴法制备ZnS薄膜光学性能

利用薄膜分析系统测量不同沉积时间制备的ZnS薄膜透射谱,通过分析薄膜透射谱,来确定ZnS薄膜光学常数和禁带宽度.实验结果表明,在线性生长阶段,薄膜的沉积速率大约为1 nm/min,具有很好的线性关系,沉积0.5 h的ZnS薄膜在可见光范围内光透过率为82%左右.     

Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200–600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1·56–5·72×10⁻³ Ω-cm, 128–189 Ω/□, 1·6–3·9×10²¹ cm⁻³ and 0·3–3 cm²/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2·20–2·42 eV. These films have transmittance around 77% and average reflectance is below 2·6% in the spectral range 350–850 nm. The films aren-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K.     

Self diffusion studies on cobalt thin films

The study of lateral diffusion in thin metallic films is important from the application point of view, especially in electromigration reliability studies. Lateral self diffusion in cobalt thin films is studied using a non-destructive tracer scanning method. Neutron irradiation is employed to make a well-defined radioactive (⁶⁰Co) region in the middle of a continuous cobalt thin film stripe of width 3 mm. The experimental data are fitted to the appropriate solution of the diffusion equations by means of a non-linear least square fitting procedure using a computer. The diffusion experiments are conducted in the temperature range 300–600°C in argon atmosphere. This thin film data are compared with the diffusion data available on bulk cobalt. The activation energy for surface diffusion obtained (0·14 eV) is very much smaller than the reported activation energy for grain boundary diffusion in cobalt.     

Sulfidation growth and characterization of nanocrystalline ZnS thin films

Nanocrystalline ZnS thin films are prepared on glass and quartz substrates by sulfurizing ZnO thin films in the H₂S-containing mixture at 500 °C. These films are investigated by X-ray diffraction, scanning electron morphology, optical transmittance and photoluminescence spectra. The results show that the ZnS thin films have the hexagonal structure with a c-axis preferred orientation. Also, these nanostructure ZnS thin films with the grain size of ∼50 nm along the c-axis, exhibit the optical transparency as high as ∼80% in the visible region. It is found that sulfur replacement of oxygen sites in crystal lattices and recrystallization can take place during sulfidation, resulting in an evident increase of the grain size for the sulfurized films. Under the optimum sulfidation time of 2 h, the resultant ZnS thin films have a high crystallinity, low defect concentration and good optical properties with the band gap of 3.66 eV.     

Optical properties of silver sulphide thin films formed on evaporated Ag by a simple sulphurization method

Silver sulphide (Ag₂S) thin films were grown on the surface of silver films (Ag) deposited on glass substrate by using a simple chemical sulphurization method. According to X-ray diffraction analysis, the Ag₂S thin films display low intensity peaks at 34.48°, 36.56°, and 44.28°, corresponding to diffraction from (100), (112) and (103) planes of the acanthite phase (monoclinic). A model of the type Ag₂S/Ag/glass was deduced from spectroscopic ellipsometric measurements. Also, the optical constants (n, k) of the system were determined. Furthermore, the optical properties as solar selective absorber for collector applications were assessed. The optical reflectance of the Ag₂S/Ag thin film systems exhibits the expected behavior for an ideal selective absorber, showing a low reflectance in the wavelength range below 2 µm and a high reflectance for wavelengths higher than that value. An absorptance about 70% and an emittance about 3% or less were calculated for several samples.     

Investigation of the effect of temperature on growth mechanism of nanocrystalline ZnS thin films

In this paper the temperature effect on the growth mechanism of ZnS thin films prepared in a chemical bath containing zinc acetate, ethylenediamine, and thioacetamide aqueous solutions has been studied in the temperature range between 25 and 75 °C. These ZnS thin films possess a nanocrystalline structure, exhibit quantum size effects due to the small crystal size and produce a blue shift in the optical spectra. This blue shift was attributed to a decrease in crystal size by using X-ray diffraction and scanning electron microscopy. The growth mechanism of the thin films is suggested to proceed by two fundamental steps: in the first step, the ZnS nanocrystallites coalesce into small grains through homogeneous nucleation in the solution phase. In the second step, eventually, these small grains or large-sized clusters diffuse and stick to the surface of the substrate to form the ZnS thin film, in a way called a cluster-by-cluster manner, resulting in particulate thin film.     

Optical and electrical properties of zinc oxide films prepared by spray pyrolysis

Zinc oxide thin films were prepared on glass substrates from an aqueous solution of zinc acetate by spray pyrolysis. These films were characterized using X-ray diffraction, scanning electron microscopy and optical transmission. The films were highly transparent to the visible radiation and electrically conductive. Films deposited at optimum conditions exhibited a resistivity of 3·15×10⁻³ Ωm along with a transmittance of 98% at 550 nm.     

Role of precursors on morphology and optical properties of ZnS thin films prepared by chemical spray pyrolysis

This study investigates the effect of different growth parameters on the structural and optical properties of ZnS thin films, prepared using spray pyrolysis. The films were prepared using different Zn:S ratios (between 1:1 and 1:6) and in different growth solutions: (A), zinc chloride and thiourea and (B) dehydrated zinc acetate and thiourea, both in distilled water.By varying the Zn:S ratio in the films, the optical properties (absorption and photoluminescence) show that different species are created during film growth. This was deduced from the wide emission band appearing in the green region of the photoluminescence spectra, and from the change in band gap, which varies between 3.2 and 3.5 eV. Films formed from solution (A) with a Zn:S ratio of 1:3 or 1:4 show the best morphology and transmission. ZnS has a wider band gap than other conventional II-VI semiconductors utilized in various electronic and optical devices and can be expected to provide a useful window layer of solar cells which leads to an improvement in overall efficiency by decreasing absorption loss.     

Synthesis and characterization of nanostructured nickel oxide thin films prepared with chemical spray pyrolysis

Nickel oxide thin films have been deposited in an open atmosphere onto glass substrates by chemical spray pyrolysis using aqueous nickel acetate solutions and air as driving gas. The films show a strong variation in the surface morphology depending on the substrate temperature and the precursor solution flux. At 350 °C substrate temperature, a reticular tissue-like film morphology is obtained, becoming the reticular nickel oxide fibres of the film thicker with increasing precursor solution flux. At 450 °C substrate temperature, the film growth rate is 4 times slower and a highly symmetric self-ordering of the material at nanometer length scale occurs. These films consist of interconnected grains separated by pores, both of about 100 nm in size. XRD and TEM revealed that the films are cubic NiO, being the crystallite size around 10 nm. The optical band gap of the films decreases strongly for increasing film thickness from 4.3 eV to 3.65 eV.     

ZnS薄膜的制备及性能研究

用射频溅射法在Si基片和石英基片上分别制备了490nm厚的ZnS薄膜,并在不同温度下进行退火处理.微结构分析表明:退火后的ZnS薄膜均呈多晶状态,晶体结构为立方闪锌矿结构的β-ZnS;随着退火温度的升高,薄膜的平均晶粒尺寸逐渐增大,由20℃的10.91nm增大到500℃的15.59nm,晶格常数在不同退火温度下均比标准值0.5414nm稍小.应力分析表明:退火后的ZnS薄膜应力减小,400℃时分布较均匀,平均应力为1.481×108Pa,应力差为1.939×108Pa.且400℃前为张应力,400℃以后转变为压应力.光学分析表明,随着退火温度的升高,ZnS薄膜的透过率增强,吸光度减弱.     

Microstructure and superconducting properties of Y-Ba-Cu-O films prepared by chemical spray pyrolysis

Y-Ba-Cu oxide superconducting films were prepared by spray pyrolysis on (100) MgO substrates and alumina coated with a silver buffer layer. Acetate, nitrate, and oxide precursors were used as starting materials. The optimum starting compounds have been assessed and the effectiveness of rapid thermal processing as a fabrication tool for annealing of highT _c superconducting films has been established. The superconducting behavior was found to be strongly dependent on the type of the precursor used, on the method of heat treatment, and on the substrate material. The films show preferred orientation and good adherence to the substrate. Transport measurements indicated that the films exhibited a superconducting transition with an onset temperature between 83–93 K and ending between 52–74 K. The critical current density was found to be strongly dependent on film processing.     

Investigations on Tl-2223 thin films fabricated through ultrasonic spray pyrolysis under oxygen deficient conditions

In this paper we have shown that polycrystalline films corresponding to Tl-2223 phase can be grown by employing high thalliation temperatures and short thalliation times. Ultrasonically deposited precursor films corresponding to Ba₂Ca_2.2Cu_3.3O_x(Ag_y) have been thalliated under high vacuum (∼ 10^-5 torr) at 890°C to obtain single phase Tl-2223 films. An off-stoichiometric and unreacted pellet of composition Tl_2.05Ba₂Ca₂Cu₃O_z has been used as source of Tl. We have shown that oxygen ambient is not necessary for the growth of Tl-2223 phase. The as-thalliated films have T_c’s in the range 123 K ±0.70 K. TheT _c has been found to be independent of the addition of AgNO₃ to the precursor. The zero field transportJ _c has been observed to be > 1.2 X 10⁵ A/cm² at 77 K. NearT _c (110 K-122 K),J _c has been observed to follow the power lawJ _c ∞ (1-T/T _c )_p,p 2. A power law withp tt 1.4 has been observed for the temperature range 70 K-110 K. An optimum doping of Ag has been observed to induce about 25% increase inJ _c and it also leads to uniform and enlarged grain growth. The surface morphology of Ag free samples contains plate like grains having arbitrary shapes. In contrast to this 0.35 Ag doped sample exhibits nearly rectangular plate like grains     

Characterization of CuInS2 thin films for solar cells prepared by spray pyrolysis

We have made a study of the chemical composition, the electrical, the optical and the structural properties of polycrystalline CuInS₂ thin films prepared by spray pyrolysis to be used for thin film solar cells. These films were deposited starting from aqueous solutions with different chemical compositions ([Cu]/[In] and [S]/[Cu] ratios) and at different substrate temperatures. In all cases, the material is p-type with grains preferentially oriented in the (112) direction of the sphalerite structure. The electro-optical properties show a very strong dependence on the [Cu]/[In] ratio in the solution. Films with copper excess have smaller resistivity and better crystallinity than those which are stoichiometric or have indium excess. The results obtained in this work show the possibility of having CuInS₂ thin films with a wide range of resistivity, a fact that could be important for making solar cells based on this material.     

热氧化法制备纳米ZnO薄膜及其发光特性的研究

用热氧化ZnS薄膜方法制备纳米ZnO薄膜．并用X射线衍射谱．光致发光谱表征和研究纳米ZnO薄膜结构特征及热氧化温度对薄膜质量的影响。X射线衍射结果表明纳米ZnO薄膜具有六角纤锌矿结构．且随热氧化温度升高．薄膜晶粒尺寸逐渐增大。光致发光谱是由紫外激子发光和与氧空位有关的深能级缺陷发光组成的．且随热氧化温度升高，激子发光峰发生红移．激子发光和深能级缺陷发光强度之比逐渐增大．在热氧化温度为800℃时，其比值为10。     

Al-Mg-B thin films prepared by magnetron sputtering

Hard, nanocomposite aluminum magnesium boride thin films were prepared on Si (100) substrates with a three target magnetron sputtering system. The films were characterized by X-ray diffraction, atomic force microscope, electron micro-probe, Fourier transform infrared spectroscopy and nanoindentation. The results show that the maximum hardness of the as-deposited films is about 30.7 GPa and these films are all X-ray amorphous with smooth surfaces. The influences of substrate temperature and boron sputtering power on the quality of the films are discussed. From the results of this work, magnetron sputtering is a promising method to deposit Al-Mg-B thin films.     

Structural and electrical properties of the Y-Ba-Cu-O superconducting films prepared by spray pyrolysis

High-T _c , superconducting YBa₂Cu₃O_7– thin films have been grown on (100) MgO substrates by a chemical spray pyrolysis method. The crystal structure and surface morphology have been studied by X-ray diffraction and scanning electron microscopy, respectively. The assprayed films were amorphous and insulating, but upon annealing the films became superconducting and show a textured surface morphology with an average grain size of the order of 5–15m. The films were highly oriented with thec-axis being perpendicular to the substrate surface. Three different microstructures were recorded: long rod-shaped grains, platelet or rounded-shape grains, and a melting-like growth. Electrical measurements were carried out in a low-temperature cryostat using a standard d.c. four-probe technique. The onset transition temperature was around 83–86 K, and the completion of the transition to zero resistance was in the range 73–78 K. The magnitude of the measured critical current density was in the range 750–3750 A/cm² at 30 K. A correlation between the resistance of the tunnelling junctions and the critical current density was found from the theoretical models.