Synthesis and characterization of CeO<Subscript>2</Subscript> thin films deposited by spray pyrolysis

Cerium dioxide (CeO₂) thin films were deposited on glass substrates by spray pyrolysis using a solution of alcohol–water and CeCl₃ · 7H₂O as precursor. The structural, morphological, optical and electrical properties of these films were investigated. SEM images reveal the presence of cracks in the films that depend on substrate temperature and deposition time. Films deposited in temperatures between 400 and 500 °C during up to 10 min are crack free and also present high optical transmittance, reaching up to 90% in the visible range and close to infrared. X-ray diffraction shows that all films are polycrystalline and the growth preferential direction is altered from (111) to (200) with the increase of the deposition temperature. The activation energy of the electrical conduction process is 0.67 ± 0.03 eV.     

Structural,morphological, optical and gas sensing properties of pure and Ce doped SnO<Subscript>2</Subscript> thin films prepared by jet nebulizer spray pyrolysis (JNSP) technique

Pure and cerium (Ce) doped tin oxide (SnO₂) thin films are prepared on glass substrates by jet nebulizer spray pyrolysis technique at 450 °C. The synthesized films are characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive analysis X-ray, ultra violet visible spectrometer (UV–Vis) and stylus profilometer. Crystalline structure, crystallite size, lattice parameters, texture coefficient and stacking fault of the SnO₂ thin films have been determined using X-ray diffractometer. The XRD results indicate that the films are grown with (110) plane preferred orientation. The surface morphology, elemental analysis and film thickness of the SnO₂ films are analyzed and discussed. Optical band gap energy are calculated with transmittance data obtained from UV–Visible spectra. Optical characterization reveals that the band gap energy is found decreased from 3.49 to 2.68 eV. Pure and Ce doped SnO₂ thin film gas sensors are fabricated and their gas sensing properties are tested for various gases maintained at different temperature between 150 and 250 °C. The 10 wt% Ce doped SnO₂ sensor shows good selectivity towards ethanol (at operating temperature 250 °C). The influence of Ce concentration and operating temperature on the sensor performance is discussed. The better sensing ability for ethanol is observed compared with methanol, acetone, ammonia, and 2-methoxy ethanol gases.     

Evaluation of the physical,optical, and electrical properties of SnO<Subscript>2</Subscript>: F thin films prepared by nebulized spray pyrolysis for optoelectronics

Fluorine-doped tin oxide (SnO₂:F, FTO) thin films were prepared by the nebulized spray pyrolysis technique on glass substrates using tin(IV) chloride pentahydrate (SnCl₂·5H₂O) and ammonium fluoride (NH₄F) as source materials. Different volumes of solvent were used to prepare the spray solution, and their effects on structural, optical, morphological, and electrical properties were investigated. X-ray diffraction patterns revealed the polycrystalline tetragonal structure of FTO films. FESEM images demonstrated well-aligned trigonal-shaped nano-grains. Optical band gap values were estimated to be in the range of 3.71–3.66 eV by Tauc’s plot. The effects of solvent volume on the resistivity, conductivity, carrier concentration, mobility, and figure of merit of FTO films were examined. The lowest electrical resistivity and sheet resistance values were 1.90?×?10^?4 Ω cm and 4.96 Ω/cm, respectively.     

SnO<Subscript>2</Subscript>-based thin films with excellent photocatalytic performance

SnO₂ semiconductor is a new-typed promising photocatalyst, but wide application of SnO₂-based photocatalytic technology has been restricted by low visible light utilization efficiency and rapid recombination of photogenerated electrons–holes. To overcome these drawbacks, we prepared B/Fe codoped SnO₂–ZnO thin films on glass substrates through a simple sol–gel method. The photocatalytic activities of the films were evaluated by degradation of organic pollutants including acid naphthol red (ANR) and formaldehyde. UV–Vis absorption spectroscopy and photoluminescence (PL) spectra results revealed that the B/Fe codoped SnO₂–ZnO film not only enhanced optical absorption properties but also improved lifetime of the charge carriers. X-ray diffraction (XRD) results indicated that the nanocrystalline SnO₂ was a single crystal type of rutile. Field emission scanning electron microscopy (FE-SEM) results showed that the B/Fe codoped SnO2–ZnO film without cracks was composed of smaller nanoparticles or aggregates compared to pure SnO2 film. Brunauer–Emmett–Teller (BET) surface area results showed that the specific surface area of the B/Fe codoped SnO₂–ZnO was 85.2 m² g^?1, while that of the pure SnO₂ was 20.7 m² g^?1. Experimental results exhibited that the B/Fe codoped SnO₂–ZnO film had the best photocatalytic activity compared to a pure SnO₂ or singly-modified SnO₂ film.     

Substrate dependent morphological and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films prepared by spray pyrolysis

A scheme of substrate dependent self-organization of vanadium oxide has been used to create unique supercapacitor electrodes. In present work, thin films of V₂O₅ were prepared on different substrates by using well known spray pyrolysis technique.The sample depositions were carried out at 673 K, by spraying 0.05 M, 40 ml solution of ammonium metavanadate at the spray rate 10 ml/min. V₂O₅ thin films grown on aluminum (Al), copper (Cu) and stainless steel (SS) substrates shows porous valley and mountains, rough and dense morphology with overgrown agglomeration of nano grains. In electrochemical characterizations, by using standard electrode configurations, specific capacitance values were evaluated from cyclic voltammetry in 1 M KCl, these are 18.43, 1500.0, 439.60 and 250.58 F/g at 5 mV/s for the electrodes deposited on Al, Cu, SS substrates and two electrode cell respectively. Charge discharge behavior of the SS electrode and two electrode cell was observed using chronopotentiometry. This exhibits specific energy, specific power, and coulombic efficiency (η) 84.91 Wh/kg, 120.00 kW/kg and 89.51 % for SS electrode and 19.92 Wh/kg, 65.00 kW/kg and 99.90 % for two electrode cell respectively. Impedance study was carried out in the frequency range 1 mHz–1 MHz depicts less internal resistance of SS electrode ~2.69 Ω and two electrode cell ~3.04 Ω.     

Structural,optical and electrical properties of SnO<Subscript>2</Subscript>:F thin films deposited by spray pyrolysis for application in thin film solar cells

Fluorine doped tin oxide (FTO) thin films with adequate properties to be used as transparent electrical contact for PV solar cells were synthesised using the spray pyrolysis technique, which provides a low cost operation. The deposition temperature and the fluorine doping have been optimized for achieving a minimum resistivity and maximum optical transmittance. No post-deposition annealing treatments were carried out. The X-ray diffraction study showed that all the FTO films were polycrystalline with a tetragonal crystal structure and preferentially oriented along the (200) direction. The grain size ameliorates with the increase in substrate temperature. The samples deposited with the substrate temperature at 440 °C and fluorine content of 20 wt % exhibited the lowest electrical resistivity (1.8 × 10^?4 Ω cm), as measured by four-point probe. Room-temperature Hall measurements revealed that the 20 wt% films are degenerate and exhibit n-type electrical conductivity with carrier concentration of ~4.6 × 10²⁰ cm^?3, sheet resistance of 6.6 Ω/□ and a mobility of ~25 cm² V^?1 s^?1. In addition, the optimized growth conditions resulted in thin films (~500 nm thickness) with average visible transmittance of 89 % and optical band-gap of 3.90 eV. The electrical and optical characteristics of the deposited films revealed their excellent quality as a TCO material.     

Structural,morphological and optical properties of SnS<Subscript>2</Subscript> thin films by nebulized spray pyrolysis technique

The thin films of Nano crystalline tin disulfide (SnS₂) have been prepared by nebulized spray pyrolysis technique (NSP) with different molar concentrations (0.3, 0.4 and 0.5 M). Cleaned glass substrates were used and the substrate temperature was maintained at 300?°C. The films were deposited using tin tetrachloride monohydrate (SnCl₄·H₂O) and thiourea in de-ionized water and Isopropyl alcohol (1:3 ratio). The prepared films structural, morphological and optical properties were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), UV–Vis spectrophotometer. The structure of the films were found to be face centered cubic with preferential orientation along (002) plane. X-ray line profile analysis was used to evaluate the micro structural parameters such as crystallite size, micro strain, dislocation density and texture coefficient. The average crystallite size values are 60 nm. Morphological results of the SnS₂ thin films are small needle shaped particles and the average grain size was 400 nm. The optical studies revealed that the band gap between 2.65 and 2.72 eV and high optical transmittance 98%. EDAX spectrum of tin disulfide result showed some amount of excess tin was present in the sample. This is the method with very low cost of producing tin disulfide (SnS₂) thin films, which is very important for many applications in industry.     

Synthesis and characterization of zinc stannate thin films prepared by spray pyrolysis technique

The zinc stannate thin films were synthesized by simple and inexpensive spray pyrolysis technique on the glass and fluorine doped tin oxide coated conducting glass substrates. The as deposited films were further annealed at 500 °C temperature for 12 h. The structural optical and morphological characterization of as prepared and annealed films was carried out by XRD, UV–Vis spectroscopy, SEM and AFM techniques respectively. The structural analysis shows that films are polycrystalline and crystallized in cubic inverse spinel crystal structure. SEM studies show that grain size increases after annealing and exhibits spherical morphology. AFM study shows that roughness is higher for the post annealed film. Further the samples were tested for testing their applicability for dye sensitized solar cells. The as prepared, annealed and CNT doped samples exhibits photoconversion efficiencies 2.7, 2.8 and 3.1 % respectively.     

AC conduction in amorphous thin films of SnO<Subscript>2</Subscript>

Alternating current (a.c.) electrical properties of thermally evaporated amorphous thin films of SnO₂ sandwiched between aluminium electrodes have been investigated for temperature during electrical measurements, film thickness, substrate temperature and post-deposition annealing. The a.c. conductivity, σ(ω), is found to vary with frequency according to the relation σ(ω) ∝ ω^s, indicating a hopping process at low temperature. The conduction is explained by single polaron hopping process as proposed by Elliott. The increase in electrical conductivity with increase in temperature during electrical measurements is ascribed to the increase in the formation and high mobility of doubly ionized oxygen vacancies. The increase in conductivity with increase in film thickness is caused by the increase in interstitial tin, oxygen vacancies and defects produced due to deviation from stoichiometry. The increase in conductivity with increase in substrate and annealing temperature may be due to the formation of singly or doubly ionized oxygen vacancies and tin species of lower oxidation state. Measurements of capacitance C as a function of frequency and temperature show a decrease in C with increasing frequency and increase in C with increasing temperature. The increase in capacitance in the high-temperature low-frequency region is probably due to space charge polarization induced by the increasing number of free carriers as a result of increasing temperature.     

Properties of nickel doped In<Subscript>2</Subscript>S<Subscript>3</Subscript> thin films deposited by spray pyrolysis technique

In this work, nickel (Ni) doped indium sulfide (In₂S₃) films have been prepared by the spray pyrolysis (CSP) technique on glass substrates at 350 °C. The Ni doping level was changed with Ni:In (0, 2 and 4% in solution). The structural studies reveal that the deposited films are polycrystalline in nature exhibiting cubic structure. The crystallite size decreases from 27.5 to 23 nm and the root mean square roughness values increase from 13 to 18 nm. The transmission coefficient is about 70–55% in the visible region and 85–75% in near-infrared region. The band gap energy increases with nickel content from 2.74 to 2.82 eV for direct transitions. The refractive index values of In₂S₃:Ni thin films decrease from 2.43 to 2.40 and the extinction coefficient values are in the range 0.01–0.20. Besides, the AC conductivity contribution is interpreted using the universal Jonscher’s power law and it is found thermally activated and it can be described by the correlated barrier-hopping models. These studies help to form significant correlation between temperature and activation energy. Nyquist plots show that the electrical response is accurately fitted by the Cole–Cole model and represented by an equivalent electrical circuit which consists of a parallel combination of a resistance and a constant phase element. From this analysis, the evidence of grain boundary conduction has been observed.     

Synthesis and characterization of nanostructured SnO<Subscript>2</Subscript> film

Nanostructured tin dioxide (SnO₂) film was deposited on glass substrate by thermal evaporation of tin metal followed by thermal oxidation at 600 °C for 2 h. XRD investigation confirms that grown film is crystalline tetragonal rutile. The average optical transmittance of the film was as high as 90%. The optical band gap of the nanostructured SnO₂ was estimated from transmittance data and found to be 3.4 eV. The variation of electrical conductivity with temperature was investigated. The root mean square (RMS) roughness and topography of the film were investigated by atomic force microscopy and found to be 2 nm with grain size of 17 nm.     

Synthesis and characterization of nanocrystalline TiO<Subscript>2</Subscript> thin films

Nanocrystalline thin films of TiO₂ have been synthesized by sol gel spin coating technique Thin films of TiO₂ annealed at 700 °C were characterized by X-ray diffraction(XRD), Atomic Force Microscopy, High resolution TEM and Scanning Electron Microscopy (SEM), The XRD shows formation of tetragonal anatase and rutile phases with lattice parameters a = 3.7837 Å and c = 9.5087 Å. The surface morphology of the TiO₂ films showed that the nanoparticles are fine with an average grain size of about 60 nm. Optical studies revealed a high absorption coefficient (10⁴ cm^?1) with a direct band gap of 3.24 eV. The films are of the n type conduction with room temperature electrical conductivity of 10^?6 (Ω cm)^?1.     

Morphological and humidity sensing characteristics of SnO<Subscript>2</Subscript>-CuO,SnO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and SnO<Subscript>2</Subscript>-SbO<Subscript>2</Subscript> nanocooxides

This paper reports the synthesis of SnO₂-CuO, SnO₂-Fe₂O₃ and SnO₂-SbO₂ composites of nano oxides and comparative study of humidity sensing on their electrical resistances. CuO, Fe₂O₃ and SbO₂ were added within base material SnO₂ in the ratio 1: 0.25, 1: 0.50 and 1: 1. Characterizations of materials were done using SEM and XRD. SEM images show the surface morphology and X-ray diffraction reveals the nanostructure of sensing materials. The pellets were annealed at 200, 400 and 600°C respectively for 3 h and after each step of annealing, observations were carried out. It was observed that as relative humidity (%RH) increases, there was decrease in the resistance of pellet for the entire range of RH. Results were found reproducible. SnO₂-SbO₂ shows maximum sensitivity for humidity (12 MΩ/%RH) among other composites.     

Effect of very low to high Sb-doping on the structural,electrical, photo-conductive and thermoelectric properties of fluorine-doped SnO<Subscript>2</Subscript> (FTO) thin films prepared by spray pyrolysis technique

Transparent conducting fluorine and Sb-doped [SnO₂: (F, Sb)] thin films have been deposited onto preheated glass substrates using the spray pyrolysis technique by the various dopant quantity of spray solution. The effect of antimony impurities on the structural, morphological, electrical, Thermo-electrical, optical and photoconductive properties of films has been investigated. The [F/Sn] atomic concentration ratio (x) in the spray solution is kept at value of 0.7 and the [Sb/Sn] atomic ratio (y) varied at values of 0, 0.0005, 0.001, 0.002, 0.01, 0.03, 0.05, 0.07 and 0.10. It is found that the films are polycrystalline in nature with a tetragonal crystal structure corresponding to SnO₂ phase having orientation along the (110) and (200) planes. SEM images indicated that nanostructure of the films has a particle type growth. The average grain size increases with increasing spraying quantity of Sb-dopant. The compositional analysis of SnO₂: (F, Sb) thin films were studied using EDAX. SEM and AFM study reveals the surface of SnO₂: (F, Sb) to be made of nanocrystalline particles. The Hall Effect measurements have shown n-type conductivity in all deposited films. The lowest sheet resistance and highest the carrier concentration about 7.7 Ω/□ and 6.6 × 10²², respectively, were obtained for the film deposited with y = [Sb/Sn] = 0.001 and x = [F/Sn] = 0.7. The maximum of the Seebeck coefficient equal to 12.8 μV K^?1 was obtained at 400 K for the film deposited with y = [Sb/Sn] = 0.10. The average transmittance of films varied over the range 10–80 % with change of Sb-concentration. The band gap values of samples were obtained in the range of 3.19–3.8 eV. From the photoconductive studies, the Sb-doped films exhibited sensitivity to incident light especially in y = 0.001. The electrical resistivity and carrier concentration vary in range 5.44 × 10^?4 to 1.02 × 10^?2Ω cm and 2.6 × 10²²–6.6 × 10²² cm^?3, respectively.     

Decay of photo-excited conductivity of Er-doped SnO<Subscript>2</Subscript> thin films

Er-doped SnO₂ thin films, obtained by sol-gel-dip-coating technique, were submitted to excitation with the 4th harmonic of a Nd:YAG laser (266 nm), at low temperature, and a conductivity decay is observed when the illumination is removed. This decay is modeled by considering a thermally activated cross section of an Er-related trapping center. Besides, grain boundary scattering is considered as dominant for electronic mobility. X-ray diffraction data show a characteristic profile of nanoscopic crystallite material (grain average size ≈5 nm) in agreement with this model. Temperature dependent and concentration dependent decays are measured and the capture barrier is evaluated from the model, yielding 100 meV for SnO₂:0.1% Er and 148 meV for SnO₂:4% Er.     

Microstructure and gas-sensing properties of nanocrystalline NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared by spray pyrolysis

Nanocrystalline nickel ferrite with a crystallite size from 3 to 40 nm has been prepared by spray pyrolysis. The ⁵⁷Fe Mössbauer spectrum of NiFe₂O₄ samples has been found to vary systematically with crystallite size. The sensing response of the nanocrystalline nickel ferrite to 50 ppm NH₃ has been studied using in situ conductance measurements. NiFe₂O₄ offers a strong sensing response to ammonia at the level of its maximum concentration limit. The optimum nickel ferrite crystallite size and temperature for ammonia detection are determined.     

Investigation of ethanol gas sensing properties of Dy-doped SnO<Subscript>2</Subscript> nanostructures

In this paper we report doping induced enhanced sensor response of SnO₂ based sensor towards ethanol at a working temperature of 200 °C. Undoped and dysprosium-doped (Dy-doped) SnO₂ nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD and Raman results verified tetragonal rutile structure of the prepared samples. It has been observed that crystallite size reduced with increase in dopant concentration. In addition, the particle size has been calculated from Raman spectroscopy using phonon confinement model and the values match very well with results obtained from TEM and X-ray diffraction investigations. Dy-doped SnO₂ sensors exhibited significantly enhanced response towards ethanol as compared to undoped sensor. The optimum operating temperature of doped sensor reduced to 200 °C as compared to 320 °C for that of undoped sensor. Moreover, sensor fabricated from Dy-doped SnO₂ nanostructures was highly selective toward ethanol which signifies its potential use for commercial applications. The gas sensing mechanism of SnO₂ and possible origin of enhanced sensor response has been discussed.     

Influence of Ag concentration on the structure,optical and electrical properties of SnS<Subscript>2</Subscript>:Ag thin films prepared by spray pyrolysis deposition

Ag-doped tin-sulfide thin films were deposited with in spray pyrolysis method at T = 425 °C on soda lime glass substrates. The effects of Ag doping were investigated on the structural, optical, and electrical properties of thin films. Double deionized water was used as a precursor solution in which tin chloride (SnCl₄5H₂O) and thiourea (CS(NH₃)₂) in addition to silver acetate (AgC₂H₃O₂) were dissolved. All in all resulted to preparation of SnS₂:Ag thin films with \(\frac{{\left[ {\text{Ag}} \right]}}{{\left[ {\text{Sn}} \right]}}\% = 0, \,1, \,2, \,3\, {\text{and}} \,4\,{\text{at}}.\%\). The (001) plane is the preferred orientation of the SnS₂ phase which is analyzed by X-ray diffraction (XRD). The intensity of mentioned peak has an increasing trend, generally, with increasing Ag doping concentration. Thin films have spherical grains as is shown in SEM images. Increasing doping concentration from 1 to 4%, causes decrease in: single-crystal grains from 14.68 to 6.31 nm, optical band gap from 2.75 to 2.62 eV, carrier concentration from 3.11 × 10¹⁷ to 2.58 × 10¹⁷ cm^?3, and Hall mobility from 1.81 to 0.13 cm²/v s, as well as increase in: average grain size, generally, from 70 to 79 nm and electrical resistance from 11.11 to 181.26 Ω cm, respectively. The majority carriers are electrons for these films as is concluded from Hall Effect measurements.     

Synthesis and enhanced ethanol sensing performance of nanostructured Sr doped SnO<Subscript>2</Subscript> thick film sensor

In the present paper we have synthesized pristine and Sr doped SnO₂ in order to prepare a selective ethanol sensor with rapid response–recovery time and good repeatability. Pristine as well as Sr (2, 4 and 6 mol%) doped SnO₂ nanostructured powder was synthesized by using a facile co-precipitation method. The samples were characterized by TG–DTA, XRD, HR-TEM, SAED, FEG-SEM, SEM–EDAX, XPS, UV–Vis and FTIR spectroscopy techniques. The gas response performance of sensor towards ethanol, acetone, liquid petroleum gas and ammonia has been carried out. The results demonstrate that Sr doping in SnO₂ systematically decreases crystallite size, increases the porosity and hence enhances the gas response properties of pristine SnO₂ viz. lower operating temperature, higher ethanol response and better selectivity towards ethanol. The response and recovery time for 4 mol% Sr doped SnO₂ thick film sensor at the operating temperature of 300 °C were 2 and 7 s, respectively.     

LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> particles prepared by spray pyrolysis from spray solution with citric acid and ethylene glycol

Spinel LiMn₂O₄ particles with fine sizes and regular morphologies were successfully synthesized by ultrasonic spray pyrolysis at the severe preparation conditions from a spray solution with citric acid and ethylene glycol. The as-prepared particles with spherical shapes, porous structures and micron sizes turned into LiMn₂O₄ particles with submicron size and narrow size distribution at the post-treatment temperature of 800 °C. The discharge capacities of the particles prepared from the spray solution with citric acid and ethylene glycol changed from 90 to 127 mAh/g when the post-treatment temperature was changed from 700 to 1,000 °C. The LiMn₂O₄ particles had maximum discharge capacities at the post-treatment temperature of 800 °C. The discharge capacity of the LiMn₂O₄ particles dropped from 127 to 108 mAh/g by the 30th cycle.