Anatase-rutile transformation through high-temperature annealing of titania films produced by ultrasonic spray pyrolysis

Titanium dioxide films were prepared by ultrasonic spray pyrolysis on (0001) α-quartz substrates at 400 °C and/or annealed in air at 600°, 800°, or 1000 °C. The as-deposited films at 400 °C (50 nm grains) and annealed at 600 °C (100 nm grains) showed single-phase anatase of high transparency in the visible region. Films annealed at 800 °C and 1000 °C showed mixed-phase anatase (100 nm grains) plus rutile (700 nm agglomerates) and pure rutile, (700 nm grains), respectively. Raman and X-ray data indicate the presence of residual stress in the films, which may arise from contamination, silicon diffusion into the films, and/or oxygen deficiency.     

Characterization of ultrasonic spray pyrolysed ruthenium oxide thin films

The ultrasonic spray pyrolysis (USP) technique was employed to deposit ruthenium oxide thin films. The films were prepared at 190°C substrate temperature and further annealed at 350°C for 30 min in air. The films were 0.22 μ thick and black grey in color. The structural, compositional and optical properties of ruthenium oxide thin films are reported. Contactless transient photoconductivity measurement was carried out to calculate the decay time of excess charge carriers in ruthenium oxide thin films.     

Synthesis and characterization of carbon nanotubes via ultrasonic spray pyrolysis method on zeolite

Ultrasonic spray pyrolysis method for the synthesis of carbon nanotubes (CNTs) has been investigated with zeolite supporting material. Single wall carbon nanotubes (SWCNTs) were obtained at 850 °C in nitrogen environment. Such deposition system makes it possible to grow CNTs without reducing agent at atmospheric pressure in a simple setup. Iron and cobalt acetate were used as catalyst and ethanol as carbon source for the synthesis of CNTs. Results show that nature of zeolite and cobalt concentration play important roles for SWCNTs production. Interestingly, we notice that in catalyst particles of sharp shape, nucleation of a nanotubes cap occurs dominantly in the forward direction.     

Preparation of AgInS2 chalcopyrite thin films by chemical spray pyrolysis

AgInS₂ thin films were prepared by the spray pyrolysis technique using a water/ethanol solution containing silver acetate, indium chloride and thiourea. We reported our results on the characterization of tetragonal AgInS₂ (chalcopyrite type) films, which were grown from indium deficient spraying solution. The films displayed a n-type conductivity with room temperature resistivities in the range between 10³ and 10⁴ Ω cm. The absorption spectra of sprayed films revealed two direct band-gaps with characteristic energies around 1.87 and 2.01 eV, which are in good agreement with the reported energy values for interband transitions from the split p-like valence band to the s-like conduction band in tetragonal AgInS₂ single crystals.     

Low cost synthesis of high-Tc superconducting films on metallic substrates via ultrasonic spray pyrolysis

Ultrasonic spray pyrolysis technique has been used to deposit both in situ and ex situ high temperature superconducting films (HTSC) of Y₁Ba₂Cu₃O_x(YBCO) and Bi₂Sr₂CaCu₂O_x (BSCCO) compounds over various substrates. Nitrate precursor solutions are used to deposit films of ∼10 μm thickness. Both low temperature spray with substrate temperature T_s < 500 °C and high temperature deposition with T_s = 550-900 °C are carried out. Superconducting properties of these films are observed to vary with various parameters such as concentration of spray solution, deposition temperature and nature of substrate and annealing process. Best quality films show T_c (R = 0) of 89 K and J_c of ∼4 × 10⁴ A/cm² at 77 K and ∼ 10⁵ A/cm² at 20 K. X-ray diffraction pattern reveals that the films are textured along c-axis. Successful attempt has been made to deposit in situ superconducting films over polycrystalline Ag for coated conductor applications. Various deposition and annealing conditions are optimized to control the diffusion of Ag from substrate to film, which otherwise can segregate into the grain boundaries and make the films non-superconducting.     

超声喷雾热解法制备ZnO薄膜及性能研究

以醋酸锌水溶液为前驱体溶液,使用自制的超声喷雾热解系统在玻璃基板上制备得到了ZnO薄膜.经X射线衍射(XRD),扫描电镜(SEM)分析得到ZnO薄膜的晶体结构和微观形貌.测试结果表明,ZnO薄膜为六角纤锌矿结构,在450～500℃下制备的薄膜显示出良好的结晶性能,并且沿(002)晶面择优取向生长,薄膜具有优良的均匀性和致密性.同时,制备得到的薄膜在可见光区也表现出80%以上的高透过率.     

喷雾热分解法制备SnO2·F薄膜与导电性能研究

以SnCl4·5H2O和NH4F为原料,采用喷雾热分解的方法在片状日用玻璃基材和石英玻璃基材上制得了掺氟氧化锡透明导电薄膜.采用X射线衍射仪(XRD)和扫描电镜(SEM)分别对薄膜的内部结构和表面形貌进行了表征.研究了F-的掺杂量、喷涂温度、沉积时间和热处理对薄膜方阻R□的影响.实验结果表明,当[NH4F]/[SnCl4·5H2O]=32wt%、成膜温度为450℃、喷涂时间为15s时,可使所得薄膜的方阻R□达最低,为10Ω/□.     

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.     

Gas-chromism in ultrasonic spray pyrolyzed tungsten oxide thin films

A simple and inexpensive ultrasonic spray pyrolysis (USP) technique has been employed to deposit tungsten oxide (WO₃) thin films by spraying 2.0 mM aqueous ammonium metatungstate solution onto the amorphous glass substrates kept at 250°C. The films were further annealed at 400°C for 4 h in air. X-ray diffraction (XRD) technique was used to determine the crystallinity and to identify the WO₃ phases. It was found that the films were sub-stoichiometric, WO_3-z. To study gas-induced properties, a catalyzing layer of platinum (Pt) was sputtered onto it. The gas-induced electrical and optical properties of Pt/WO₃/glass samples were studied and results reported. It was found that electrical resistivity decreased by a factor of 10 within 2 min and stabilized after 15 min, after H₂ gas exposure. Similarly the optical transmittance of the samples attenuated from 55% to 10% within 15–20 min. The reversible changes in electrical resistivity and optical transmittance were observed when the samples were exposed to oxygen. The response times and sensitivity of the samples were estimated.     

Comparison of structural and photoluminescence properties of ZnO thin films grown by pulsed laser deposition and ultrasonic spray pyrolysis

ZnO thin films have been deposited by pulsed laser deposition (PLD) and ultrasonic spray pyrolysis (USP) method, respectively. X-ray diffraction and transmission electron microscopy characterizations indicate that ZnO film grown by PLD exhibits better crystallinity than that grown by USP. Photoluminescence spectra show that the near-band edge ultraviolet emission of film grown by PLD is narrower and shifts to higher energy, compared with that of film grown by USP. In the visible range, ZnO film grown by PLD exhibits four local level emission centered at 470 nm, 486 nm, 544 nm, and 613 nm, respectively, while the film grown by USP only presents a weak broad band emission centered at 502 nm. Hall measurement shows higher carrier density and lower hall mobility in ZnO film grown by PLD than that in film grown by USP. The higher density of intrinsic defects as well as higher crystallintiy is considered to account for the difference of photoluminescence in ZnO film grown by PLD with that in film grown by USP.     

Low substrate temperature synthesis of carbon nanowalls by ultrasonic spray pyrolysis

In this paper, we report the synthesis of two-dimensional wall like carbon nanostructures (i.e. carbon nanowalls) by ultrasonic spray pyrolysis of ethanol and fullerene mixture. At higher temperature carbon nanofibers were formed on the substrate placed at the center of the reactor tube, whereas carbon nanowalls were observed on the substrate placed downstream of the tube below 100 °C. Spaces between the nanowalls changed with distance of the substrates from the furnace. Qualitative analysis of materials was performed using scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.     

Photocatalytic degradation of selected dyes by titania thin films with various nanostructures

Titania thin films with various nanostructures of quasi-aligned nanorods, well-aligned nanotubes and nanoparticle aggregates were fabricated and utilized to assist photodegradation of three typical dye derivatives in water, i. e., rhodamine B (RB), methylene blue (MB) and methyl orange (MO). The thin films were characterized by X-ray diffraction, scanning electron microscope and UV-Vis diffuse reflectance spectra. It is found that the bandgap of most lab-fabricated thin films can be estimated more appropriately assuming a direct transition between the valance band and the conduction band of titania. The so-called natural ageing phenomenon was evidence for all the films to assist photodegradation of RB and MB in water; but not discernible for MO, which was much reluctant to photodegradation. MB decomposed much quickly than RB when assisted by titania with predominantly anatase; on the other hand, rutile favored the photodegradation of RB than that of MB. Titania thin films with top morphologies of quasi-aligned nanorods or nanotubes were found to possess advantageous turnover frequency and photonic efficiency over commercial P25 titania and sol-gel derived titania to assist photodegradation of RB and MB in water.     

Crystalline alumina films prepared by nebulized spray pyrolysis

Crystalline alumina films have been successfully deposited on Si(100) and amorphous silica substrates by the nebulized spray pyrolysis technique. The surface morphology of the films has been studied by various microscopic techniques. The films exhibit satisfactory microhardness and frequency independent capacitance.     

Effect of acetic acid on ZnO:In transparent conductive oxide prepared by ultrasonic spray pyrolysis

Undoped and indium doped zinc oxide (ZnO) transparent conductive oxide were prepared by a low-cost Ultrasonic Spray Pyrolysis. The influence of acetic acid on properties of the ZnO thin films was investigated. The complex formed by [CH₃COO⁻] and [Zn²⁺] in precursor solution was better for the growth of ZnO film. The acetic acid added in precursor solution can supply [CH₃COO⁻] for both [Zn²⁺] and [In³⁺] to form complexes. That made the [Zn²⁺] and [In³⁺] have similar statement, which can promote the indium doping in the ZnO films. The surface morphology, structural and electrical properties of the ZnO thin films were influenced by the acetic acid adding. The total transmittance of the ZnO thin films is above 80% in the wide wavelength region from 400 nm to 2000 nm.     

Structure and magnetic characterizations of cobalt ferrite films prepared by spray pyrolysis

Cobalt ferrite films were prepared by spray pyrolysis with post-annealing. For the as-deposited film, the differential scanning calorimetry measurement shows a crystallization peak at around 375 °C during the isochronal heating at 20 °C/min, and the X-ray diffraction pattern shows its amorphous-like characteristic. The isothermal post-annealings were performed for 2 h at various temperatures from 400 to 700 °C, leading to the crystallization of films, forming the spinel structure. The cross-sectional analysis with scanning electron microscopy shows that the film's thickness keeps almost constant after annealing, and the layered granular structure appears when the annealing temperature is high. The magnetic hysteresis loops of as-deposited and annealed films show that both the saturation magnetization and coercivity increase with the annealing temperature, due to the crystallization of CoFe₂O₄ phase.     

Effect of chloride ion on crystalline phase transition of iron oxide produced by ultrasonic spray pyrolysis

Ultrafine spherical Fe₂O₃ powders with controllable morphology and crystal phase were synthesized by ultrasonic spray pyrolysis. In this experiment, we chose three common ferric salts (Fe(NO₃)₃·9H₂O, FeSO₄·7H₂O or FeCl₂·4H₂O) as precursor solution and regulated the concentration of chlorine ion (Cl^?) in precursor solution to produce Fe₂O₃ particles. The morphology, crystal structure and magnetic property of prepared Fe₂O₃ particles were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vibrating sample magnetometer (VSM). The diameter of the obtained Fe₂O₃ products ranged from 0.2 to 2?μm. And the product obtained from FeCl₂ precursor solution was magnetic, which was composed of hexagonal α-Fe₂O₃ and cubic γ-Fe₂O₃ from XRD results. We also calculated the weight percent of α-Fe₂O₃ and γ-Fe₂O₃ in the product through XRD quantitative analysis. However, with the addition of Cl^? in Fe(NO₃)₃ or FeSO₄ precursor solution, the products turned from non-magnetic to magnetic, whose pure α-Fe₂O₃ phase became to α-Fe₂O₃ and γ-Fe₂O₃ multi-phase. Besides, the weight percent of γ-Fe₂O₃ and the amount of M_s increased with the Cl^? concentration in precursor solution improving. According to the research, it can be inferred that the presence of Cl^? inhibits the phase transition of γ-Fe₂O₃ to α-Fe₂O₃ at high temperature.     

One-pot synthesis of hematite-alumina hollow sphere composite by ultrasonic spray pyrolysis technique with high adsorption capacity toward PAHs

A hybrid nanocomposite of alumina and hematite was synthesized by ultrasonic spray pyrolysis technique. The study of microscopic images, mapping analysis, and XRD patterns revealed that the Al₂O₃ – Fe₂O₃ nanocomposite was composed of separated spherical particles with a thin layer ball-shaped structure that metal oxides are uniformly distributed in the wall of hollow sphere particles, led to a coherent and monotonous construction. A series of coefficients of equilibrium sorption of polycyclic aromatic hydrocarbons (PAHs) as hazardous materials were measured on the prepared composite material in a batch technique. The free or pure Al₂O₃ or Fe₂O₃ showed negligible removal efficiency for the mentioned analytes. The various significant variables, such as initial analyte concentration, solution pH, adsorbent dose, and contact time to remove analyte, were studied in the aqueous solutions. Adsorption data were modeled to Langmuir, Freundlich, and Temkin isotherms, and a good correlation found in the case of Langmuir isotherm and adsorption capacity for anthracene, phenanthrene, and naphthalene were 370, 333, and 322 mg g^?1, respectively. Investigation of the kinetic models proved a pseudo-second-order, and the prepared adsorbent can be reused more than 7 times without a significant decrease of adsorption performance.     

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.     

Stoichiometry and superconductive properties of YBaCuO films deposited by spray pyrolysis

The dependence of the stoichiometry and the superconducting characteristics of YBaCuO films deposited by spray pyrolysis on the spraying solution composition and the deposition conditions is reported. It has been found that a proper optimization of the starting materials concentration in the spraying solution results in superconducting films with zero resistance temperature of 91 K and a transition to superconducting state within a 3 K range. X-ray diffraction and resistance vs temperature measurements have been used to monitor the crystal composition and the conductive characteristics of the films as a function of the spraying solution composition and the deposition parameters.     

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.