Investigation of structural properties of ITO thin films deposited on different substrates

The influence of the substrate nature on the structure and morphology of ITO thin films grown by thermal evaporation in vacuum is investigated. The as-prepared metal films with Sn/In molar ratio of 0.1 were subsequently annealed for 2 h at 723 K in air (to obtain tin doped indium oxide), then annealed in vacuum at 523 K, followed by UV irradiation (to reduce the electrical resistivity). Irrespective of substrate nature, XRD data evidence a (222) preferential orientation in films. Substrate nature, annealing in vacuum and UV irradiation influence the structure, morphology, optical, electrical and surface wetting properties of the films' surface.     

Structure and gas sensing properties of nanocrystalline Fe-doped ZnO films prepared by spin coating method

Nanocrystalline Fe-doped ZnO films were obtained by spin coating, using zinc acetate and iron acetate as starting materials and N,N-dimethylformamide as solvent. Characteristic XRD patterns indicate that the films under study are single phase with the ZnO-like wurtzite structure. There are not any secondary phases and Fe²⁺ as well as Fe³⁺ substitutes for Zn²⁺ of ZnO host. Atomic force microscopy analysis revealed that the studied films are characterized by high-density columnar structure and the incorporation of Fe atoms into the ZnO lattice modified the surface morphology. The sensitivity, at three different gases, was investigated and it was observed that acetone is the test gas that produces the most significant changes in the electrical resistance of all studied samples. Experimental results indicate that the optimum operating temperature increases for Fe-doped ZnO films by comparison with the undoped one. Also, the values of sensitivity were found to depend on the dopant concentration in ZnO films.     

Structural studies on some doped CdS thin films deposited by thermal evaporation

The influence of the Mn, Se and Sb impurities on the structure and morphology of CdS thin films grown on p⁺ Si wafers was studied. The starting powders were mixed in the same molar ratios (0.3%) and deposited in the same conditions by vacuum thermal evaporation. X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and reflectance studies made on thermal treated thin films (573 K, 2 h in air) evidenced that thin films have a hexagonal oriented structure, and that dopants enter into the CdS lattice merely by substitution. The dopant nature influences the thin film thickness and chemical composition. The doped CdS thin films have roughness in nanometer region and a reflectivity lower than 40%. Silicon substrate acts as a template and favors the retention of Mn and scatters the Sb dopants. The CdS:Se thin film is thicker than CdS:Mn and CdS:Sb ones and is a mixture of doped and undoped nanocrystals.     

Studies on the structure and gas sensing properties of nickel–cobalt ferrite thin films prepared by spin coating

The influence of Co²⁺ ions content on structure and sensing properties of Ni_1−xCo_xFe₂O₄ (x = 0.25, 0.5, 0.75) thin films deposited on glass substrates by spin coating is presented. Structural characterization evidenced thin films with cubic spinel structures and morphologies dependent on cobalt content. Repartition of cations in spinel tetrahedral and octahedral sites was determined and was found that the presence of Co²⁺ ions in octahedral sites favor the formation of Fe²⁺ species. The sensitivity to some reducing vapor gases (acetone, liquefied petroleum gas LPG, ethyl alcohol and methyl alcohol) was investigated and was found that thin films with x = 0.75 exhibit high sensitivity to ethyl alcohol and thin films with x = 0.25 have high sensitivity to acetone. This sensitivity largely depends on the temperature and test gas concentration and was related to the Fe²⁺ species formed in octahedral sites.     

Electrical conduction properties of Co-doped ZnO nanocrystalline thin films

The temperature dependent conductivity behavior of 15% Co and 25% Co-doped ZnO nanocrystalline thin films prepared by spin-coating method was examined. It was found that the conductivity shows a change when the Co concentration varies from 15 to 25%. The observed increase of conductivity with increasing Co concentration was interpreted through the grain boundary conduction model. The temperature dependent conductivity of the films was analyzed in term of formulas in consistence with grain boundary conduction model. With rising temperature for 25% Co doped ZnO, a transition from the region in which crystallites are only partially depleted to the region in which the crystallites are entirely depleted was observed around 375 K. Some improtant electrical parameters were determined for the films.     

Substrate and Fe-doping effects on the hydrophilic properties of TiO2 thin films

Titanium dioxide films are known for their hydrophilic and photocatalytic characteristics. Increasing specific surface area and doping can enhance their photocatalytic activity and hydrophilicity. We report here results regarding the enhancement of the photocatalytic properties of titania by both controlling surface morphology and the anatase/rutile ratio. The samples were deposited on glass, indium tin oxide covered glass, and SrTiO₃ by sputtering and laser ablation techniques. Film structure and surface morphology were investigated by X-ray diffraction and atomic force microscopy. Film hydrophilicity was assessed from contact angle measurements during- and post-irradiation with UV light. The contact angle data are discussed in terms of the synergic effects of surface morphology, structure and composition of the films.     

Undoped and Cr-doped TiO2 thin films obtained by spray pyrolysis

Undoped and chromium doped titanium oxide thin films were fabricated by spray pyrolysis by using a solution of titanium tetrachloride and ethyl alcohol. The films have been deposited on heated glass substrates at 373 K. After annealing for 90 min at 723 K, the initially amorphous films became polycrystalline with a predominant anatase structure and average crystallite sizes depending on dopant (Cr) concentration. The repartition of chromium impurities in the matrix of titanium oxide films, analyzed by electron paramagnetic resonance and X-ray photoelectron spectroscopy showed that the entrance of chromium into the anatase structure is mainly achieved by substitution. A decrease in unit cell parameters ratio (c/a) with the increase of chromium content sustains this assertion. The wetting properties of the titanium oxide films were evaluated from contact angle measurements between de-ionized water and films surface during- and post-irradiation with UV light. The correlation between the concentration of the dopant, film structure, surface morphology and wettability characteristics is discussed.     

The Meyer‐Neldel rule in layered silicone‐silver nanocomposites

X‐Ray diffraction and X‐ray photoelectron spectroscopy studies, applied on some silicone‐silver nanocomposites, revealed the influence of the solvent used in preparation on the morphology of the resulted materials. It has been emphasized that dimethylformamide solvent favors the formation of silver nanoparticles and their migration at the surface, while water solvent favors the formation of a homogeneous composite with small silver nanoparticles. The places occupied by Ag nanoparticles (some prevent their oxidation and others that favor the oxidation process) are dependent on the mixture used in sol‐gel technique and have influence on the nanocomposite electrical conductivity. The temperature dependence of the electrical conductivity is investigated. A linear relationship between the pre‐exponential factor (σ₀) and activation energy (E_a) was observed, in the high temperature range (T > 315 K), for all the samples, indicating that the conductivity data obey Meyer‐Neldel rule. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Polydimethyldiphenylsiloxanes/silica interconnected networks: preparation and properties evaluation

A series of copolymers, polydimethyldiphenylsiloxane-α,ω-diols, differing by compositions and molecular masses has been prepared by equilibrium anionic ring-opening copolymerization of octamethylcyclotetrasiloxane with octaphenylcyclotetrasiloxane in presence of tetramethylammonium hydroxide as a catalyst. These copolymers were used as matrix for the in situ developing silica networks. The crosslinking of the copolymers concomitantly occurs by reaction between the ending silanol groups and tetraethoxysilane, thus the polydiorganosiloxane network interconnects with the silica one. The resulted materials processed as films (thickness 0.25–1.50 mm) were investigated by various techniques in order to evaluate morphology, optical properties, and thermal behavior. The results were compared with those obtained by model samples based on polydimethylsiloxanes/silica.