Structure and magnetic properties of La0.67Sr0.33MnO3 thin films prepared by sol–gel method

La_1?xSr_xMnO₃ (x = 0.33) (LSMO) thin films have been fabricated successfully by sol–gel method on two different types of substrates, Si (111) and SrTiO₃ (STO) (001). Microstructure and magnetic properties of LSMO thin films have been investigated. The X-ray diffraction studies of the films confirm the pure phase of the LSMO thin films. In contrast with LSMO thin films on Si substrate, the performances of LSMO on STO substrate are superior both from structural and magnetic properties. For the samples deposited on STO substrate, highly preferred orientation as well as less strain and grain defects was found; in other aspect, the magnetization, the residual and saturation moment value, tended greater while a decreased coercive field required merely (saturation moment value was about five times and coercive field was only about 13 % of those on Si substrate). The Curie temperature of LSMO thin films on Si and STO substrates is estimated to be about 349.7 and 359 K, respectively.     

Microstructure and performance of AZO thin films prepared by sol–gel processing

Al-doped zinc oxide (AZO) films were prepared by a wet-chemical coating technique, their microstructure and crystal growth were characterized as a function of the single layer thickness. When similar final thicknesses are attained by more multiple subsequent coating-firing cycles, film porosity is reduced from over 14 to 2 %. Simultaneously the AZO crystallite size is increased from approximately 23 to 60 nm, a preferential c-axis oriented growth is observed. Different substrates (soda-lime glass, soda-lime glass with a SiO₂ barrier coating, borosilicate glass and alkali-free display glass) were used and the resulting AZO films were compared. It is found that the substrate composition primarily affects grain growth and subsequently the electrical performance of the AZO films.     

Deposition of silica thin films formed by sol–gel method

Deposition of silica thin films on silicon wafer was investigated by in situ mass measurements with a microbalance configured for dip coating. Mass change was recorded with respect to deposition time when the substrate was fully immersed in the silica sol. Mass gain during deposition was higher than predicted from monolayer coverage of silica nano particles. This implied that deposition was facilitated by gelling of the nanoparticles on the substrate. The rate of deposition was enhanced by increasing the particle concentration in the sol and by decreasing the particle size from 12 to 5 nm. Increasing the salt concentration of the silica sol at constant pH enhanced the deposition of the silica particles. Reducing the pH of the sol from 10 to 6 decreased the deposition rate due to aggregation of the primary silica particles.     

The influence of annealing on electrochromic properties of Al–B–NiO thin films prepared by sol–gel

Al–B–NiO thin films were prepared using the sol–gel process and deposited on Indium tin oxide (ITO)-coated glass substrates via the dip-coating technique for the purpose of developing high performance electrochromic materials. The influence of the anneal on the structural and electrochromic properties of Al–B–NiO films is reported. Thermogravimetry (TG) and differential thermal analysis (DTA), cyclic voltammetry measurements (CV), UV spectrophotometer, atomic force microscopy (AFM) and X-ray diffraction (XRD) have been used to investigate the structural and electrochromic properties. The thickness of the films was determined by spectrophotometric analysis in 350–1,000 nm wavelength. Results showed that the Al–B–NiO thin films treated at high temperature have both the excellent electrochromic properties and good reversibility. The transmittance change (ΔT) of the film treated at 500 °C reaches still ~50% at the wavelength of 550 nm. The microstructure and the surface morphology were considered to play an important role in the electrochromic properties with different temperatures.     

SnO2 thin films doped indium prepared by the sol–gel method: structure, electrical and photoluminescence properties

This paper reports on the preparation, characterization, electrical and optical properties of tin oxide (SnO₂) thin films doped indium prepared by the sol–gel method and deposited on glass substrates with dip coating technique. X-ray diffraction patterns showed an increase in the crystallinity of the films with increase in annealing temperatures. Atomic force microscopy analyses revealed an increase of grain growth with raise in annealing temperature. The film surface revealed positive skewness and kurtosis values less than 3 which make them favorable for OLEDs applications. The lowest resistivity (about 10^?7) was obtained for the ITO films annealed at 500 °C. These films acquire n-type conductivity due to the non-stoichiometric in the films like (interstitial tin atoms) and also due to low indium doping concentration. The optical properties of the films have been studied from transmission spectra. An average transmittance of >80 % in ultraviolet–visible region was observed for all the films. Optical band gap energy (E _gap) of ITO films was found to vary in the range of 3.69–3.81 eV with the increase in annealing temperature. This slight shift of E _gap to higher photon energies could be related to the crystalline nature of the films associated with the decrease in the defect concentration caused by annealing. Photoluminescence spectra of the films exhibited an increase in the emission intensity with increase in annealing temperature. The high temperature annealing would be expected to decrease the density of defects, improve the crystal orientation and reduce the traps for non-radiative transition and also increase the oxidation processes.     

Photocatalytic and antibacterial activities of Ag-doped ZnO thin films prepared by a sol–gel dip-coating method

Silver-doped ZnO thin films with various loadings of Ag in the range of 0–10 mol% were prepared by the sol–gel dip-coating method. All prepared films show X-ray powder diffraction patterns that matched with ZnO in its würtzite structure. The grain size decreased as the Ag loading increased. The prepared films, under UV blacklight illumination, produced a photocatalytic degradation of methylene blue, rhodamine B and reactive orange solutions. Furthermore, they inhibited the growth of Escherichia coli bacteria under UV blacklight irradiation and to a lesser extent in dark conditions. The photocatalytic and antibacterial activities of the prepared films increased with Ag loading, presumably because Ag enhanced the efficiency of generation of superoxide anion radicals (^•O₂ ⁻) and hydroxyl radicals (^•OH).     

Preparation and properties of VO2 thin films by a novel sol–gel process

Vanadium dioxide (VO₂) thin films were fabricated using a simple and novel sol–gel process in which V₂O₅ was used as the vanadium source; oxalic acid was used as the reducing agent; and polyvinyl alcohol was used as the film former to control the viscosity of the VO₂ precursor solution and bond vanadium ions. The microstructure and surface morphology of VO₂ films were studied by X-ray diffraction and scanning electron microscopy, respectively. The results showed that using polyvinyl alcohol forms porous nanostructure of VO₂ films with a uniform grain size of ~25 nm. The measured optical reflectance shows well-defined phase transition as observed by an increase of reflectance upon heating above the transition temperature from ~11 to ~30 % at 1,100 nm. Upon cooling, the expected hysteresis is observed.     

The effect of heat treatment in the reducing atmosphere on the physical properties of TiO2 thin films prepared by sol–gel method

Multilayered nanostructured TiO₂ thin films were prepared by sol–gel and dipping deposition on quartz substrate followed by thermal treatment under reducing atmosphere (20 %H₂–80 %Ar). Heat treatment at progressively higher temperatures caused structural, morphological, and optical changes, which were investigated by X-ray diffraction (XRD), atomic force microscopy, scanning electron microscopy, and UV–Vis spectroscopy. The conductivities of the thin films were also measured by 4-point probe method. The XRD results showed that the calcined TiO₂ thin films consist of single anatase phase which was completely transformed into rutile phase after heat treatment at 1,000 °C. The grains of films grew by intra-agglomerate densification after heat treatment at higher temperatures. The root mean square roughness of the samples was found to be in the range of 0.58–3.36 nm. The partially reduced TiO₂ samples have red-shifted transmittance bands due to new energy band formed by oxygen vacancies. The electrical conductivity of the films was also enhanced after heat treatment in reducing atmosphere.     

Synthesis and characterization of tellurium-doped CdO nanoparticles thin films by sol–gel method

In this work, tellurium (Te) doped CdO nanoparticles thin films with different Te concentrations (1, 3, 5, 7 and 10 %) were prepared by sol–gel method. The effects of Te doping on the structural, morphological and optical properties of the CdO thin films were systematically studied. From X-ray diffraction spectra, it has seen that all of thin films were formed polycrystalline and cubic structure having (111), (200) and (311) orientations. The structure of CdO thin films with Te-dopant was formed the unstable CdTeO₃ monoclinic structure crystal plane ( $ {\bar{\text{1}}\text{22}} $ 1 ¯ 22 ), however, the intensity of this unstable peak of the crystalline phase decreased with the increase of Te-doping ratio. The strain in the structure is also studied by using Williamson-Hall method. From FE-SEM images, it has seen that particles have homogeneously distributed and well hold onto the substrate surface. Additionally, grain size increases from 27 to 121 nm with the increase of Te-doping ratio. Optical results indicate that 1 % Te-doped CdO thin film has the maximum transmittance of about 87 %, and the values of optical energy band gap increases from 2.50 to 2.64 eV with the increase of Te-doping ratio. These results make Te-doped CdO thin films an attractive candidate for thin film material applications.