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.     

New modified filler obtained by silica formed by sol–gel method on calcium carbonate

This study focus on the modification of the particles of precipitated calcium carbonate (PCC) with silica formed in situ by sol–gel method. The new materials were characterized by several spectroscopic, analytical and microscopic techniques. A dense film of highly branched silica was formed at the surface of the scalenohedral PCC crystals. The amount of silica deposited at the PCC surface, as determined by thermogravimetric analysis, reached up to 25 wt% under appropriate experimental conditions. Particle size distributions obtained by laser diffraction spectroscopy of the new modified PCC’s were close to the distribution of the original PCC, even considering that some variation in the average size of the particles was noted. This result is of great interest regarding the application of these materials, for instance, as fillers in the paper industry since the coating of silica may contribute to the fibre-to-fibre bonding, thus improving paper strength.     

Preparation of nanostructured titania thin films by sol–gel technology

This study is concerned with the preparation of hydrolytically active heteroligand complex [Ti(OC₄H₉)_3.61(O₂C₅H₇)_0.39] from titanium butoxide and acetylacetone and with the gel formation kinetics in a solution of this complex upon hydrolysis and polycondensation. Single-layer and double-layer thin films of a solution of this precursor were coated on polished silicon substrates using the dip-coating method. The crystallization of nanostructured titania films during the heat treatment of these xerogel coatings was studied using various protocols; the anatase–rutile phase transition temperature was found to depend on the film thickness. The effects of the precursor solution viscosity on the film thickness and crystallite size were determined.     

Effect of annealing temperature on the quality of Al-doped ZnO thin films prepared by sol–gel method

The different thermal expansion coefficients and lattice mismatch between ZnO and Al may produce residual stress in Al-ZnO (AZO) thin films. Annealing processes can be applied to modulate this residual stress. In this study, three different rapid thermal annealing (RTA) temperatures (350, 450, and 600 °C) were applied to an AZO thin film, prepared using sol–gel method. The mechanical properties, optical properties, and structure of the AZO thin film were investigated experimentally. The results show that increasing the RTA temperature increased the Young’s modulus and hardness of the films. The grain size of the films also increased with increasing RTA temperature. However, the film thickness and shear stress component decreased with increasing RTA temperature. Both compressive and tensile stress decreased gradually with increasing film thickness after RTA treatment. It was demonstrated that the use of a relatively high RTA temperature can effectively relax the residual stress in AZO thin films.     

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).     

Facile preparation of vanadium oxide thin films on sapphire(0001) by sol–gel method

The Ba_0.6Sr_0.4TiO₃ (BST60) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method. The thickness of CeO₂, serving as a buffer layer, was varied from 0 to 75 nm, in order to optimize the dielectric tunable property. X-ray patterns analysis indicates that all the thin films exhibit good crystalline quality with a pure perovskite phase and insertion of the CeO₂ buffer layer does not change the crystal structure of BST60. Dielectric properties of the thin films were investigated as a function of both temperature and direct current electric field. The results show that dielectric constant and loss are modified by insertion of the CeO₂ buffer layer. The BST60 thin films with 25 nm thickness CeO₂ buffer layer have the highest figure of merit, low dielectric loss, and suitable dielectric constant, which render them attractive for the tunable microwave device applications.     

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.     

Crystallization of inorganic silica based on interaction between polyimide and silica by sol–gel method

Crystalline silica in cristobalite phase was successfully prepared at a relatively low temperature of 800 °C by calcinating polyimide/silica hybrid films under ambient air. X-ray photoelectron spectroscopy measurements show that the product is silica after calcination. It is found that the crystallinity is dependent on the removing rate and the strength of the interaction between polyimide and silica. The presence of polyimide plays an important role in the growth of silica. Calcination to remove polyimide with rapid heating results in lower crystallinity compared with calcination with slow heating. For samples with the same content of silica, the crystallinity changes with the strength of the interaction between polyimide and silica molecules.     

Orientation of tungsten trioxide thin films fabricated by sol–gel method using aqueous sols of colloidal layered tungstates

Oriented monoclinic WO₃ thin films were fabricated by sol–gel method using aqueous sols of colloidal layered tungstates. The colloidal tungstate sols were prepared by reacting different alkylamines with layered tungstic acid H₂WO₄ in water. With decreasing the alkyl chain length of the alkylamines, the colloidal layered tungstate became smaller. Alkylamines with a short alkyl chain provided transparent aqueous sols. Furthermore, the WO₃ thin films fabricated from the obtained aqueous sols had a high (100)-orientation. However, upon annealing H₂WO₄ crystals applied on a glass substrate with the tungstate layers parallel to the substrate, highly (001)-oriented WO₃ layers were obtained. Since both of the A- and C-planes of WO₃ have a similar structure to the layers of H₂WO₄, the orientation of the WO₃ thin films and layers probably resulted from the topotactic structural conversion of the tungstates. Interestingly, the preferential orientation of the thin films was dependent on the presence or absence of interlayer alkylamines in the tungstates.     

Surface sol–gel synthesis of silica films on polyimide substrate

Silica films were grown on polyimide substrate using surface sol–gel reaction, and the film growth process was characterized by ellipsometry, atomic force microscopy, and X-ray photoelectron spectroscopy. On the activated polyimide surface, silica film was grown by sequential immersion in SiCl₄ solution and H₂O. The thickness of silica films is linear with the depositing cycle, about 5.0 nm per cycle. The silica films present an island-like growth type and are not a strict equilibrium SiO₂ structure. Moreover, the result of the tensile test suggests that the silica films have a good adhesion to the polyimide substrate.     

Nanostructures of surfaces of silica films obtained by sol—gel method in the presence of organic additives

The dependence of the antireflection properties of film coatings deposited on the silicate glass obtained by sol—gel method in the presence of organic additives on the dimensions of nanostructures of the silica films was studied.     

The morphologies and optoelectronic properties of delafossite CuFeO2 thin films prepared by PEG assisted sol–gel method

Single phase delafossite CuFeO₂ thin films were synthesized by a simple sol–gel method. The influence of polyethylene glycol (PEG) on the morphology and optoelectronic properties of the films was studied by addition of 1.0 g PEG in 10 ml precursor solution. The crystal sizes of the derived CuFeO₂ films with and without addition of PEG were 49 nm, but the sample with addition of PEG (labeled as CFO-PEG) showed weaker c-axis orientation growth. The sample without addition of PEG (labeled as CFO) showed a compact surface without detectable pores and had a thickness around 50 nm. However, the sample CFO-PEG exhibited a porous surface with worm-like grains in nanometric scale and had a thickness around 310 nm. Enhanced absorbance in UV–vis region was observed for the sample CFO-PEG which might ascribe to both the thickness and porous surface. The optical direct bandgaps at near-UV were estimated to be ~3.0 and 3.38 eV for the sample CFO-PEG and CFO, respectively. Though the porous surface of CFO-PEG has improved the absorbance in UV–vis region, the resistivity has also been increased due to the homogeneous distribution of interspaces between the worm-like grains, which makes the incident photon to current efficiency of CFO-PEG lower than that of CFO.     

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.