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Highly transparent and preferential c-axis oriented nanocrystalline undoped and Al doped zinc oxide (AZO) thin films have been deposited onto amorphous glass substrate by spray pyrolysis. The XRD studies reveal that AZO with a hexagonal (wurtzite) crystal structure having (002) preferred orientation is formed. The atomic force microscope (AFM) shows uniform surface topography. The optical band gap values of undoped and AZO thin films were changed from 3.34 to 3.35 eV. The band gap energy and photoluminescence are found to depend on the Al doping. Thermoelectric power measurement shows film having n-type in nature. Dielectric constant and loss (tan δ) were found to be frequency dependent. Interparticle interactions in the deposited films are studied by complex impendence spectroscopy.

Thin films of zinc oxide have been deposited onto glass/FTO substrates at optimized 400 °C by using a chemical spray pyrolysis technique. Deposited films are character photocatalytic activity by using XRD, an SEM, a UV-vis spectrophotometer, and a PEC single-cell reactor. Films are polycrystalline and have a hexagonal (wurtzite) crystal structure with c-axis (002) orientation growth perpendicular to the substrate surface. The observed direct band gap is about 3.22 eV for typical films prepared at 400 °C. The photocatalytic activity of starch with a ZnO photocatalyst has been studied by using a novel photoelectrocatalytic process.

The photocatalytic decomposition of an eco-persistent AO7 dye with sunlight in an oxygenated aqueous suspension has been studied under a nano-crystalline hexagonal ZnO photocatalyst. The effect of substrate temperature on the structural, morphological and photoactive properties has been investigated. The degradation of the AO7 dye is achieved using a photoelectrochemical reactor module equipped with ZnO synthesized electrodes. Kinetic parameters have been investigated in terms of a first order rate equation. The rate constant for this heterogeneous photocatalysis was evaluated as a function of the initial concentration of original species. A substantial reduction in AO7 dye is achieved as analyzed from COD and TOC studies. The mechanism for the degradation could be explained on the basis of the Langmuir-Hinshelwood mechanism.

The influence of substrate temperature and nozzle-to-substrate distance (NSD) on the structural, morphological, optical and electrical properties of Sb:SnO2 thin films prepared by chemical spray pyrolysis has been analyzed. The structural, morphological, optical and electrical properties were characterized by using XRD, SEM, UV-visible spectrophotometry and Hall effect measurement techniques. It was seen that the films are polycrystalline, having a tetragonal crystal structure with strong orientation along the (200) reflection. The pyramidal crystallites formed due to coalescence were observed from SEM images. The values of highest conductivity, optical transmittance and figure of merit of about 1449(Ω·cm)−1, 70 %and 5.2 × 10−3 □/Ω, respectively, were observed for a typical film deposited using optimal conditions (substrate temperature = 500 °C and NSD = 30 cm).

Transparent conducting antimony doped tin oxide (Sb:SnO2) thin films have been deposited onto preheated glass substrates using a spray pyrolysis technique by varying the quantity of spraying solution. The structural, morphological, X-ray photoelectron spectroscopy, optical, photoluminescence and electrical properties of these films have been studied. It is found that the films are polycrystalline in nature with a tetragonal crystal structure having orientation along the (211) and (112) planes. Polyhedrons like grains appear in the FE-SEM images. The average grain size increases with increasing spraying quantity. The compositional analysis and electronic behaviour of Sb:SnO2 thin films were studied using X-ray photoelectron spectroscopy. The binding energy of Sn3d5/2 for all samples shows the Sn4+ bonding state from SnO2. An intensive violet luminescence peak near 395 nm is observed at room temperature due to oxygen vacancies or donor levels formed by Sb5+ ions. The film deposited with 20 cc solution shows 70 % transmittance at 550 nm leading to the highest figure of merit (2.11 × 10−3Ω−1). The resistivity and carrier concentration vary over 1.22 × 10−3 to 0.89 × 10−3Ωcm and 5.19 × 1020 to 8.52 × 1020 cm−3, respectively.

p-CdTe thin films were prepared by spray pyrolysis under different ambient conditions and character- ized using photoelectrochemical (PEC), X-ray diffraction (XRD), scanning electron microscopy, energy-dispersive analysis by X-ray (EDAX), and optical transmission studies. The different preparative parameters viz solution pH, solution quantity, substrate temperature and solution concentration have been optimized by the PEC technique in order to get good-quality photosensitive material. XRD analysis shows the polycrystalline nature of the film, hav- ing cubic structure with strong (111) orientation. Micrographs reveal that grains are uniformly distributed over the surface of the substrate indicating the well-defined growth of polycrystalline CdTe thin film. The EDAX study for the sample deposited at optimized preparative parameters shows the nearly stoichiometric Cd : Te ratio. Optical absorption shows the presence of direct transition with band gap energy of 1.5 eV. Deposited films exhibit the highest photocurrent of 2.3 mA, a photovoltage of 462 mV, a 0.48 fill factor and 3.4% efficiency for the optimized preparative parameters.

The physical properties and photoelectrochemical characterization of aluminium doped hematite α-Fe2O3, synthesized by spray pyrolysis, have been investigated in regard to solar energy conversion. Stable Al-doped iron (III) oxide thin films synthesized by a spray pyrolysis technique reveals an oxygen deficiency, and the oxide exhibits n-type conductivity confirmed by anodic photocurrent generation. The preparative parameters have been optimized to obtain good quality thin films which are uniform and well adherent to the substrate. The deposited iron oxide thin films show the single hematite phase with polycrystalline rhombohedral crystal structure with crystallite size 20–40 nm. Optical analysis enabled to point out the increase in direct band-gap energy from 2.2 to 2.25 eV with doping concentration which is attributed to a blue shift. The dielectric constant and dielectric loss are studied as a function of frequency. To understand the conduction mechanism in the films, AC conductivity is measured. The conduction occurs by small polaron hopping through mixed valences Fe2+/3+ with an electron mobility 300 K of 1.08 cm2/(Vs). The α-Fe2O3 exhibits long term chemical stability in neutral solution and has been characterized photoelectrochemically to assess its activity as a photoanode for various electrolytes using white light to obtain I — V characteristics. The Al-doped hematite exhibited a higher photocurrent response when compared with undoped films achieving a power conversion efficiency of 2.37% at 10 at % Al:Fe2O3 thin films along with fill factor 0.38 in NaOH electrolyte. The flat band potential Vfb (−0.87 VSCE) is determined by extrapolating the linear part to C−2 = 0 and the slope of the Mott-Schottky plot.

Co1.2−xMnxFe1.8O4 (0≤x≤0.4) compositions were synthesized by the autocombustion route by keeping the oxidizer to fuel ratio (Φe) at 1. Thermogravimetric analysis (TGA) shows the stable phase formation takes place at a temperature above 600 °C. Structural characterization of all the samples was carried out by the x-ray diffraction technique. Room temperature magnetization measurements showed that, for the substitution of Co by Mn, there is an initial increase in the saturation magnetization (Ms) for lower concentrations (i.e. x = 0.1 and 0.2); and then the magnetization decreases for higher concentrations (i.e. x = 0.3 and 0.4). Also, it is observed that the coercivity (Hc) goes on decreasing with the substitution of Mn content, except for x = 0.3 which shows a slight increase in coercivity as compared to x = 0.4. Room temperature dielectric properties, namely relative dielectric permittivity (e'), dielectric loss (tanδ) and ac conductivity (σac), for all the samples were studied as a function of applied frequency in the range from 20 Hz to 1 MHz. These studies indicate that the relative dielectric permittivity goes on increasing with the increase of Mn content in Co ferrite and also all the samples show the usual dielectric dispersion which is due to the Maxwell–Wagner-type interfacial polarization. The ac conductivity measurement suggests that the conduction is due to small polaron hopping.

Ferrites with general formula Ni(1−x)CoxFe2O4 (where x = 0.0,0.2,0.4,0.6 and 0.8) were prepared by the conventional double sintering ceramic method. The microstructural features were observed by scanning electron microscopy. An infrared spectroscopy study shows the presence of absorption bands in the higher frequency range around 578 cm−1 (ν1) and in the lower frequency range around 396 cm−1 (ν2); these indicate the presence of tetrahedral and octahedral group complexes, respectively, within the spinel phase. In an effort to understand the conduction mechanism, complex impedance measurements were carried out. The results of complex impedance measurements show that as the cobalt concentration increases, the total impedances (Z' and Z'') decrease. The dielectric permittivity (e') was measured at room temperature (300 K) as a function of frequency from 20 Hz to 1 MHz; it shows the usual dielectric dispersion due to the Maxwell–Wagner type of interfacial polarization. Increase of the dielectric permittivity is observed with increase of the cobalt concentration in the nickel ferrite matrix. AC conductivity (σAC) measurements made in the frequency range 100 Hz–1 MHz suggest that the conduction is due to small polaron hopping.

This communication is a response to the comments made by Tiburcio-Silver and Castaneda on our recently published paper entitled 'Optoelectronic properties of sprayed transparent and conducting indium doped zinc oxide thin films'. Each one of the points questioned is clarified in order to give the respective reasons, and additional information is given that supports the content of our paper.

Zinc oxide (ZnO) and ZnO : Ga films have been deposited by the spray pyrolysis method onto preheated glass substrates using zinc acetate and gallium nitrate as precursors for Zn and Ga ions, respectively. The effect of Ga doping on the structural, morphological, optical and electrical properties of sprayed ZnO thin films were investigated using x-ray diffraction (XRD), scanning electron microscopy, optical absorption, photoluminescence (PL) and Hall effect techniques. XRD studies reveal that films are polycrystalline with hexagonal (wurtzite) crystal structure. The thin films were oriented along the (0 0 2) plane. Room temperature PL measurements indicate that the deposited films exhibit proper doping of Ga in ZnO lattice. The average transparency in the visible range was around ~85–95% for typical thin film deposited using 2 at% gallium doping. The optical band gap increased from 3.31 to 3.34 eV with Ga doping of 2 at%. The addition of gallium induces a decrease in electrical resistivity of the ZnO : Ga films up to 2 at% gallium doping. The highest figure of merit observed in this present study was 3.09 × 10−3 cm2 Ω−1.

Indium doped zinc oxide (IZO) thin films are grown onto Corning glass substrates using the spray pyrolysis technique. The effect of doping concentration on the structural, electrical and optical properties of IZO thin films is studied. X-ray diffraction studies show a change in preferential orientation from the (0 0 2) to the (1 0 1) crystal planes with increase in indium doping concentration. Scanning electron microscopy studies show polycrystalline morphology of the films. Based on the Hall-effect measurements and analysis, impurity scattering is found to be the dominant mechanism determining the diminished mobility in ZnO thin films having higher indium concentration. The addition of indium also induces a drastic decrease in the electrical resistivity of films; the lowest resistivity (4.03 × 10−5 Ω cm) being observed for the film deposited with 3 at% indium doping. The effect of annealing on the film properties has been reported. Films deposited with 3 at% In concentration have relatively low resistivity with 90% transmittance at 550 nm and the highest value of figure of merit 7.9 × 10−2 Ω−1.