Sprayed Films Research Articles

Photoelectrocatalytic degradation of methyl blue using sprayed WO3 thin films

WO3 thin films have been deposited using simple chemical spray pyrolysis technique and successfully applied as photoanode for photoelectrocatalytic degradation of methylene blue. The films were deposited on bare glass and fluorine doped tin oxide coated glass substrates to study photoelectrochemical (PEC) properties, crystal structure, surface morphology, chemical composition and optical studies. The PEC results indicate that, the films deposited at 300 °C show the improved the photocurrent response relative to other deposited thin films. The monoclinic crystal structure of WO3 has been confirmed from X-ray diffraction studies. The Raman spectra of optimized films show two strong peaks at 271.34 and 327.27 cm−1 can be assigned to the bending δ (O\W\O) vibrations in the monoclinic WO3 structure. Field emission scanning electron microscopy showed that the film surface constituted of aggregates of very small seed like nanoparticles. UV–vis spectrophotometry shows that the WO3 film deposited at the 300 °C shows a band gap of ~2.66 eV and has emerged as one of the visible light photocatalysts, which can absorb light below 520 nm wavelength. The photocatalytic degradation of methyl blue has been investigated in aqueous solution. The removal of the color and decrease of UV–Visible absorbance was simultaneously able to show the oxidation of methylene blue dye.

Gram‐scale carbon nanotubes as semiconducting material for highly versatile route of integration in plastic electronics

A versatile chemical functionalization of single‐walled carbon nanotubes (SWNT) is developed to eliminate the conductivity of metallic SWNTs in pristine SWNT mixtures, without sorting. Thanks to the high selectivity of the diazoether reagent, metallic SWNTs can be functionalized while preserving the transport properties of semiconducting SWNTs, even in nonindividually dispersed SWNT solutions. In this way, liters of aqueous semiconducting ink for printing or spray can be prepared at the laboratory scale and used for the fabrication of thin‐film transistors (TFT) by spraying. Diazoether grafting also improved SWNT dispersion by preventing rebundling. Consequently, while less conductive than pristine SWNTs, diazoether‐treated SWNTs provided higher TFT transconductance thanks to a more homogeneous percolation in the film. SWNT TFTs made on wafer and plastic with pristine and diazoether‐treated SWNTs were compared. Sprayed films of diazoether treated, unsorted SWNTs provided TFTs with ION/IOFF around 500, about 2 orders of magnitude higher than pristine SWNT TFTs. Mobilities were similar, up to 1 cm2/V s. Interestingly, diazoether‐treated SWNT TFTs kept a high ION/IOFF in a wide range of SWNT density and channel length, where pristine SWNT films became metallic.

Physical investigations on perovskite LaMnO3-δ sprayed thin films for spintronic applications

Oxygen deficient LaMnO3 thin films were successfully grown on glass substrate by spray pyrolysis at 460°C. XRD studies show oxygen vacancies corresponding to the orthorhombic La4Mn4O11 with (040) preferential orientation. Optical properties were investigated through optical band gap and Urbach energy. The dispersion of the refractive index was discussed in terms of both Cauchy and Wemple & Di-domenico models. Raman spectroscopy shows the band positions corresponding to LaMnO3 with a shift related to oxygen deficiency. Electrical properties were quantified using impedance spectroscopy technique within frequency range of 5Hz–13MHz at various temperatures. Both the DC conductivity and relaxation frequency were thermally activated with activation energy around 0.9eV. Also, AC conductivity was investigated through Jonscher law. Finally, magnetic measurements at room temperature using vibrating sample magnetometer (VSM) technique show ferromagnetic behavior of these ternary sprayed thin films.

Photoelectrocatalytic degradation of methyl red using sprayed WO3 thin films under visible light irradiation

WO3 thin films have been deposited onto glass and FTO coated glass substrates using simple chemical spray pyrolysis technique. The effect of solution concentration on the photoelectrochemical (PEC), structural, morphological and photoelectrocatalytic properties has been investigated. The structure and morphology of WO3 photoelectrodes are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The PEC study shows that both open circuit voltage (Voc) and short circuit current (Isc) at the optimized solution concentration (0.125 M) are relatively maximum (Isc = 0.62 mA and Voc = 0.58 V). XRD study reveals that the films are polycrystalline in nature with monoclinic crystal structure. SEM images show that the substrate surface is well covered with uniform, compact and fine grain like morphology. The AFM image shows the rough nature of the film. Photoelectrocatalytic degradation of methyl red dye in aqueous solutions is studied. The end result shows that the degradation percentage of methyl red using WO3 photoelectrode has reached 97 % under visible light illumination after 160 min. The amount of mineralization is confirmed by COD and TOC analysis.

The sprayed ZnO films: nanostructures and physical parameters

We synthesized the pure and indium-doped (IZO) ZnO films with a facile composition control spray pyrolysis route. The substrate temperature (Ts) and In-doping effects on the properties of as-grown films are investigated. The X-ray pattern confirms that the as-synthesized ZnO phase is grown along a (002) preferential plane. It is revealed that the crystalline structure is improved with a substrate temperature of 350 °C. Moreover, the morphology of as-grown films, analyzed by AFM, shows nanostructures that have grown along the c-axis. The (3 × 3 μm2) area scanned AFM surface studies give the smooth film surface RMS < 40 nm. The UV–VIS–IR measurements reveal that the sprayed films are highly transparent in the visible and IR bands. The photoluminescence analysis shows that the strong blue and yellow luminescences of 2.11 and 2.81 eV are emitted from ZnO and IZO films with a slight shift in photon energy caused by In-doping. The band gap is a bit widened by In-doping, 3.21 eV (ZnO) and 3.31 eV (IZO) and the resistivity is reduced from 385 to 8 Ω·m. An interesting result is the resistivity linear dependence on the substrate temperature of pure ZnO films.

Effect of deposition rate on the structural, optical and electrical properties of Zinc oxide (ZnO) thin films prepared by spray pyrolysis technique

Zinc oxide (ZnO) thin films were deposited on glass substrates by spray pyrolysis technique decomposition of Zinc acetate dihydrate in an ethanol solution with various deposition rates, the ZnO thin films were deposited at 350°C, the substrates were heated by using the solar cells method. The substrate was R217102 glass in a size of 30cm×7.5cm×0.1cm. Nanocrystalline films with a hexagonal wurtzite structure with a strong (002) preferred orientation were observed at all sprayed films. The maximum value of grain size (21.91nm) is attained of sprayed films with 30ml. The decrease of the strain of ZnO films is probably due to an improvement of the crystallinity of the films. The average transmittance of all films is about 90 – 95% measured by UV – vis analyzer. The band gap energy varies from 3.265 to 3.286eV was affected by deposition rates lying between 10 and 35ml. The electrical resistivity of the films decreased from 0.394 to 0.266 (Ω cm). The best results are achieved in sprayed films between 25 and 30ml.

Comparison of tin‐doped indium oxide films fabricated by spray pyrolysis and magnetron sputtering

A comparison of the properties between Tin‐doped Indium Oxide (ITO) films fabricated by sputtering and spray pyrolysis is presented. This analysis shows that the ITO films fabricated by DC magnetron sputtering in pure argon gas requires of a subsequent annealing for the improvement of their structural, electrical and optical properties, when they are compared to films fabricated by single‐stage spray pyrolysis process that includes a new approach. The optimum annealing temperature for ITO films sputtered at room temperature lies in the 300‐350 °C range. Under such conditions, the ITO sputtered films are slightly more resistive than the resistivity (2 × 10‐4 Ω‐cm) shown by films sprayed at 480 °C using a solution with a 5 % of tin to indium ratio, and almost four times the worst value of the combination of transparency and conductivity determined by the value of the figure of merit (FOM). The sprayed films have a high value of the FOM, 2.9×10‐2 Ω‐1, which is comparable with the best published results.

Effect of Mn content on structural, optical, opto-thermal and electrical properties of ZnO:Mn sprayed thin films compounds

Manganese-doped zinc oxide thin films (ZnO:Mn) at different percentages (0–3%) were deposited on glass substrates using a chemical spray technique. The effects of manganese element content on structural, optical, opto-thermal and electrical conductivity of ZnO:Mn thin films were investigated by means of X-ray diffraction, optical measurement, Photoluminescence spectroscopy and impedance spectroscopy. XRD analysis revealed that all films consist of single phase ZnO and were well crystallized in würtzite phase with the crystallites preferentially oriented towards (002) direction parallel to c-axis. Doping manganese resulted in a slight decrease in the optical band gap energy of the films and a noticeably change in optical constants. The UV peak positions for ZnO:Mn samples slightly red shift to the longer wavelength in comparison with the pure ZnO which can be attributed to the change in the acceptor level induced by the substitutional Mn2+ and the band-gap narrowing of ZnO with the Mn dopant. We have performed original AC and DC conductivity studies inspired from Jonscher and small polaron models. These studies helped establishing significant correlation between temperature and activation energy and Mn content. From the spectroscopy impedance analysis we investigated the frequency relaxation phenomenon and the circuit equivalent circuit of such thin films. Finally, all results have been discussed, as an objective of the actual work, in terms of the manganese doping concentration.

Experimental and numerical assessment of impingement and mixing of urea–water sprays for nitric oxide reduction in diesel exhaust

This study presents a joint experimental and numerical investigation of a spray used in selective catalytic NOx reduction (SCR) after-treatment systems for Diesel engine exhaust gases. The focus lies on the impingement conditions and distribution and mixing mechanisms of the spray in cross-flowing exhaust gases. These aspects are vital to system performance but still not well described.A pressure-driven SCR injector is characterized in an optically accessible flow test rig at different temperatures and mass flow rates representative of Diesel engine exhaust gas conditions by means of Mie scattering and Phase Doppler Anemometry (PDA). The effects of cross-flow velocity and temperature on spray structure, droplet size and velocity distributions are assessed resulting in a comprehensive characterization of the spray. Results show that the dense spray core, with droplets up to 200μm, only moderately reduces in density as smaller droplets are entrained at high exhaust flows. Wall impingement conditions however vary substantially as impingement angles are shallower at higher cross-flow velocities.A detailed assessment of the numerical model is presented and validation is carried out at different measurement locations of interest. The predicted droplet size distributions and velocities follow the observed trends and impingement angles as well as spray film areas on the channel floor are also in agreement with the experimental data. The validated model is subsequently used to numerically study the mixing dynamics.The findings suggest that at low cross-flow conditions two counter-rotating kidney vortices are formed which entrain reflected droplets of the spray impinging on the channel floor, which leads to improved mixing. Vapor concentrations increase close to the side walls and reflected droplets lead to film-formation on the side walls. At higher cross-flow velocities, vortex formation is not evident and spray-wall interaction is less pronounced – impairing mixing and leading to a reduction in concentration uniformity at down-stream locations. Film formation and high vapor concentrations are restricted to the bottom channel centerline.

Effect of Acetic Acid Adding on Structural, Optical and Electrical Properties of Sprayed ZnO Thin Films

Effect of Acetic Acid Adding on Structural, Optical and Electrical Properties of Sprayed ZnO Thin Films

Effect of Substrate Temperature on the Properties of Sprayed WO3 Thin Films Using Peroxotungstic Acid and Ammonium Tungstate: A Comparative Study

A comparative study on the physicochemical properties of tungsten oxide (WO3) thin films synthesized using peroxotungstic acid (PTA) and ammonium tungstate (AT) by simple spray pyrolysis technique is reported. X-ray diffraction patterns show that the films deposited using both the precursors are polycrystalline with monoclinic crystal structure. The x-ray photoelectron spectroscopy studies confirm that the films are sub-stoichiometric with O/W ratios of 2.93 and 2.87, respectively, for typical PTA and AT films. Tungsten (W) exists in two chemical states, 5+ and 6+. Scanning electron microscopy images show the uniform and dense network of wires in PTA films, while the films deposited using AT possess a porous structure with small grains. Electrical and dielectric studies show that films are highly resistive and possess high dielectric constant. The near ultra-violet, blue, green and weak red emissions due to defects were observed in the photoluminescence studies. Properties of the WO3 thin films reported here are suitable for gas sensor applications. Films deposited using PTA are more functional than those deposited using AT.

Evaluation of Drug–Polymer Solubility Curves Through Formal Statistical Analysis: Comparison of Preparation Techniques

In this study, the influence of the preparation technique (ball milling, spray drying, and film casting) of a supersaturated amorphous dispersion on the quality of solubility determinations of indomethacin in polyvinylpyrrolidone was investigated by means of statistical analysis. After annealing of the amorphous dispersions above the crystallization temperature for 2 h, the solubility curve was derived from the glass transition temperature of the demixed material using the Gordon-Taylor relationship and fitting with the Flory-Huggins model. The study showed that the predicted solubility from the ball-milled mixtures was not consistent with those from spray drying and film casting, indicating fundamental differences between the preparation techniques. Through formal statistical analysis, the best combination of fit to the Flory-Huggins model and reproducibility of the measurements was analyzed. Ball milling provided the best reproducibility of the three preparation techniques; however, an analysis of residuals revealed a systematic error. In contrast, film casting demonstrated a good fit to the model but poor reproducibility of the measurements. Therefore, this study recommends that techniques such as spray drying or potentially film casting (if experimental reproducibility can be improved) should be used to prepare the amorphous dispersions when performing solubility measurements of this kind.

Structural, optical and electrical properties of zinc oxide thin films deposited by a spray pyrolysis technique

Zinc oxide (ZnO) thin films were deposited on glass substrates by spray pyrolysis technique decomposition of zinc acetate dihydrate in an ethanol solution with 30 mL of deposition rate, the ZnO thin films were deposited at two different temperatures: 300 and 350 °C. The substrates were heated using the solar cells method. The substrate was R217102 glass, whose size was 30 × 17.5 × 1 mm3. The films exhibit a hexagonal wurtzite structure with a strong (002) preferred orientation. The higher value of crystallite size is attained for sprayed films at 350 °C, which is probably due to an improvement of the crystallinity of the films at this point. The average transmittance of obtain films is about 90%–95%, as measured by a UV—vis analyzer. The band gap energy varies from 3.265 to 3.294 eV for the deposited ZnO thin film at 300 and 350 °C, respectively. The electrical resistivity measured of our films are in the order 0.36 Ω·cm.

Influence of Spray Rate on Structural and Optical Properties of Sprayed ZnO Films

Influence of Spray Rate on Structural and Optical Properties of Sprayed ZnO Films

Influence of Spray Rate on Structural and Optical Properties of Sprayed ZnO Films

In this report, the ZnO nanostructure films have been deposited by ultrasonic spray pyrolysis technique (USP) on fluorine doped tinoxide~(FTO) substrate using zinc acetate and aqueous 2-propanol as reactants. The effects of solution spray rate on structural, morphological and optical properties of ZnO nanostructure films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and UV-Vis measurements. ZnO films were crystallized in the hexagonal wurtzite phase and preferential orientation changed with changing of spray rate. Grain size and roughness of films depended on spray rate. Increasing spray rate made the films grown with bigger grain size and higher roughness. Band gap energy was determined from the UV-Vis. Its value was found to be of 3.25 eV and was almost independent on the spray rate.

Bandedge emission in sprayed ZnO thin films

ZnO thin films were grown by spraying aqueous solutions of zinc acetate on quartz and silicon substrates heated to 500°C. X-ray diffraction (XRD) studies show that the ZnO films crystallize in the hexagonal phase and are highly oriented along the [002] direction. SEM micrographs show that the surface of the films is uniformly covered with worm shaped particles. EDAX results together with XRD studies confirm that the synthesized films are single phase ZnO with good stoichiometry. The sharp absorption occurring near the band edge indicates high quality growth of the material. Room temperature photoluminescence (PL) studies of the sprayed films show a strong near band edge (NBE) emission. PL spectra obtained at low temperature (20 K) exhibit better resolved peaks of the NBE emission caused by the radiative recombination of free and bound excitons. The dominant free exciton emission observed in the PL spectra confirms the high quality of the sprayed ZnO layers. Open image in new window

Dye-sensitized solar cell using sprayed ZnO nanocrystalline thin films on ITO as photoanode

ZnO thin films had been successfully prepared by spray pyrolysis (SP) technique on ITO/Glass substrates at different substrate temperature in the range 250–400°C using Zinc acetylacetonate as precursor. The X-ray diffraction studies confirmed the hexagonal wurtzite structure with preferred orientation along (002) plane at substrate temperature 350°C and the crystallite size was found to vary from 18 to 47nm. The morphology of the films revealed the porous nature with the roughness value of 8–13nm. The transmittance value was found to vary from 60% to 85% in the visible region depending upon the substrate temperature and the band gap value for the film deposited at 350°C was 3.2eV. The obtained results revealed that the structures and properties of the films were greatly affected by substrate temperature. The near band edge emission observed at 398nm in PL spectra showed better crystallinity. The measured electrical resistivity for ZnO film was ∼3.5×10−4Ωcm at the optimized temperature 350°C and was of n-type semiconductor. The obtained porous nature with increased surface roughness of the film and good light absorbing nature of the dye paved way for implementation of quality ZnO in DSSCs fabrication. DSSC were assembled using the prepared ZnO film on ITO coated glass substrate as photoanode and its photocurrent – voltage performance was investigated.

Photoelectrocatalytic degradation of benzoic acid using sprayed TiO2 thin films

Transparent TiO2 thin films have been sucessfully synthesized by chemical spray pyrolysis technique. The effect of substrate temperature on the photoelectrochemical (PEC), structural, morphological, optical and photoelectrocatalytic properties has been investigated. The PEC study shows that both short circuit current (Isc) and open circuit voltage (Voc) at the optimized substrate temperature (450°C) are relatively maximum (Isc=1.7mA and Voc=770mV). The tetragonal crystal structure has been confirmed from X-ray diffraction patterns. FE-SEM study reveals that the film surface is changed from nanogranular to nanorod like morphology. The films exhibit a transmittance of about 80% in the visible region and a sharp absorption edge at 375nm corresponding to the fundamental absorption edge in UV region. Band gap energy varies from 3.33 to 3.43eV with substrate temperature. Electron-phonon coupling present in TiO2 films has been analyzed using Raman spectroscopy. The elemental composition and valence states of TiO2 film are studied by using X-ray photoelectron spectroscopy. The effect on the photoelectrocatalytic behavior of the large surface area (64cm2) TiO2 photocatalyst samples were studied by using photoelectrocatalytic degradation of benzoic acid under UV light illumination.

Investigation of structural, optical, electrical and dielectric properties of catalytic sprayed hausmannite thin film

Hausmannite Mn3O4 thin film have been synthesized using spray pyrolysis method. These films are characterized using X-ray diffraction (XRD), atomic force microscope AFM, UV–vis–NIR spectroscopy and impedance spectroscopy. XRD study confirms the tetragonal structure of the as-deposited films with lattice parameters, a=5.1822Å and c=9.4563Å and a grain size of about 56nm. UV–vis–NIR spectroscopy was further used to estimate optical constants such as extinction coefficient, refractive index, band gap and Urbach energy. Moreover, impedance spectroscopy analysis was employed to estimate electrical and dielectrical properties of the sprayed thin films. The activation energy values deduced from DC conductivity and relaxation frequency were almost the same, revealing that the transport phenomena is thermally activated by hopping between localized states. The AC conductivity is found to be proportional to ωs. The temperature dependence of the AC conductivity and the frequency exponent, s was reasonably well interpreted in terms of the correlated barrier-hopping CBH model. The dielectric properties were sensitive to temperature and frequency. The study of the electrical modulus indicated that the charge carrier was localized. Experimental results concerning optical constants as Urbach energy, dielectric constant, electric modulus and AC and DC conductivity were discussed in terms of the hopping model as suggested by Elliott.

Sprayed films of europium complexes toward light conversion devices

Rare-earth complexes have become subject of intensive research due to the high quantum efficiency of their emission, very narrow bands, and excellent fluorescence monochromaticity. The chemical design and characterization of Eu complexes based on β-diketone ligands hexafluoroacetylacetate (hfac) and dibenzoylmetanate (dbm) is reported here. K[Eu(dbm)4] and K[Eu(hfac)4] complexes were immobilized as thin films by using the spray technique, a promising methodology for practical applications. The latter provides not only a faster layer deposition but also larger coated areas compared to conventional methods, such as layer-by-layer (LbL) and Langmuir–Blodgett (LB). The growth of the sprayed films was monitored through microbalance (QCM) and ultraviolet–visible (UV–Vis) absorption spectroscopy, which reveal a higher mass and absorbance per deposited layer of K[Eu(dbm)4] film. Micro-Raman images display a more homogeneous spatial distribution of the K[Eu(dbm)4] complex throughout the film, when compared to K[Eu(hfac)4] film. At nanometer scale, atomic force microscopy (AFM) images indicate that the roughness of the K[Eu(hfac)4] film is approximately one order of magnitude higher than that for the K[Eu(dbm)4] film, which pattern is kept at micrometer scale according to micro-Raman measurements. The photoluminescence data show that the complexes remain as pure red emitters upon spray immobilization. Besides, the quantum efficiency for the sprayed films are found equivalent to the values achieved for the powders, highlighting the potential of the films for application in light conversion devices.