Sol-Gel Preparation and Characterization of Ag-TiO2 Nanocomposite Thin Films

Ag-TiO₂ thin films were prepared with a sol-gel route, using titanium isopropoxide and silver nitrate as precursors, at 0.03 and 0.06 Ag/Ti nominal atomic ratios. After drying at 80°C, the films were fired at 300°C and 500°C for 30 min. The films were analysed by X-ray diffraction (XRD) with glancing angle, and X-ray photoelectron spectroscopy (XPS), with depth profiling of the concentration. XPS analysis showed the presence of C and N as impurities in the nanocomposite films. Their concentration decreased with increasing the firing temperature. Chemical state analysis showed that Ag was present in metallic state, except for the very outer layer where it was present as Ag⁺. For the films prepared with a Ag/Ti concentration of 0.06, depth profiling measurements of the film fired at 300°C showed a strong Ag enrichment at the outer surface, while composition remained almost constant within the rest of the film, at 0.019. For the films heated to 500°C, two layers were found, where the Ag/Ti ratios were 0.015 near the surface and 0.026 near the substrate.     

Photocatalytic performance of silver-modified TiO2 embedded in poly(ethyl-acrylate-co-methyl metacrylate) matrix

The plasmonic Ag-TiO₂ (with 0.5 wt% Ag) photocatalyst was prepared on P25 TiO₂ surface. The presence of AgNPs on the titania was indicated by the UV–vis spectrum, which showed a plasmonic absorbance band in the visible range (λ _max?=?455 nm). XPS measurements suggested that Ag was in metallic (Ag) and in oxide forms on TiO₂. Ag-TiO₂ photocatalyst and TiO₂ were embedded in [poly(ethyl acrylate-co-methyl methacrylate; p(EA-co-MMA)] copolymer to attain mechanically stable, photocatalytically active nanocomposite films. The photooxidation of ethanol was slower on the photocatalyst/polymer nanocomposites, but it could be significantly improved by irradiating them with UV light. The photoaging was applied as a post-preparation treatment to improve the photocatalytic activity of the nanocomposite films. Changed surface morphology and the partial destruction of the polymer were supported by AFM and FTIR results. Contact angle measurements were used to determine the surface free energies of the prepared and the photoaged nanocomposite films.     

Preparation and Characterization of Titania Thin Films from Aqueous Solutions

Dip- or spin-coating and characterization of titania (TiO₂) thin films from various aqueous solutions have been studied. The aqueous titanium solutions mainly used in this study were halogen- and chelate-free solutions with the concentrations up to 1.4 M derived from titanium isopropoxide (TIP) with tetramethylammonium hydroxide (TMAOH) or some alkylamines, while aqueous and alcoholic solutions containing titanium atoms stabilized chelating ligands were examined for comparison. The TiO₂ films prepared from the TIP-TMAOH solution were already crystallized at 350°C to anatase form and those formed at 600°C had high transparency and refractive indices of 2.40. No carbon residue in the film prepared at 400°C was detected by XPS. The pure anatase form was sustained up to 850°C. Interestingly, it was found that the (004) preferentially oriented anatase films were obtained from TIP-lactic acid (LA) system until 700°C. The solutions containing citric acid (CA) or alkanolamines yielded anatase and rutile form fired at the temperatures equal to or higher than 600°C. Carbon residue was detected in the film fired at 400°C. The film thickness monotonically decreased from the upper to the bottom ends of the substrate. However, it was found that the thickness uniformity was drastically improved by an addition of sucrose to the aqueous solutions. The effects of the solution composition and polyhydroxy compounds on the crystal modifications of formed films and the film uniformity are discussed.     

Effect of silver incorporation on crystallization and microstructural properties of sol–gel derived titania thin films on glass

Titanium dioxide (TiO₂) thin films, with and without silver (Ag), were prepared on float glass via sol–gel processing. The float glass substrates were pre-coated with a silica-barrier layer prior to the deposition of TiO₂-based thin films. Silver nanoparticle incorporation into the TiO₂ matrix was achieved by thermal reduction of Ag ions dissolved in a titanium-n-butoxide (Ti[O(CH₂)₃CH₃]₄) based sol during calcination in air at 250, 450 and 650 °C. Thin films were characterized using glancing incidence X-ray diffraction, UV–visible spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The effects of Ag concentration and calcination temperature on microstructure and on chemical and physical properties of the thin films have been reported. The size and chemical state of Ag particles, as well as the phase characteristics of the titania matrix were strongly influenced by Ag concentration and calcination temperature. Results from this study can be utilized in both processing and structure-functional property optimization of sol–gel based Ag-TiO₂ thin films by aqueous routes.     

Ag掺杂TiO2纳米管阵列的制备及光电催化降解氨氮废水

采用光化学沉积法、光还原法以及光电沉积法3种不同的掺杂方法 ,通过控制掺杂时间来控制Ag的担载量制备出Ag-TiO2纳米管阵列。采用场发射扫描电镜(FE-SEM)、X-射线衍射(XRD)、X-射线光电子能谱(XPS)、X-射线荧光光谱(PL)对样品进行表征。用氨氮废水的光电催化降解反应评价其催化活性,研究不同的掺杂方法以及不同的Ag担载量对TiO2纳米管阵列光催化性能的影响。结果表明:适量的Ag的引入有利于光催化效率的提高,即Ag的掺杂量存在一个最佳值,光电沉积60 s制备的样品具有最佳的光电催化效率。     

Influence of O2 Plasma on Surface Properties of PC-TiO2 Nanocomposite Film

In this work, polycarbonate-TiO₂ nanocomposite films were prepared with different percentages. The aim was to consider the effect of O₂ LF plasma (50 Hz) on the hydrophilicity, surface energy, and surface morphology of polycarbonate and polycarbonate-TiO₂ nanocomposite. Structure of samples was determined by using X-ray diffraction analysis. In comparison with the reference sample, the samples’ structure did not change after plasma treatment. Surface properties of polycarbonate and polycarbonate-TiO₂ nanocomposite films were studied by X-ray photoelectron spectroscopy (XPS), contact angle measurement, atomic force microscopy (AFM), and Vickers microhardness tester. XPS analysis showed that the surface of samples became more oxidized due to plasma treatment. The water contact angle significantly decreased from 88° to 15° after plasma treatment. It was observed that the hardness of the nanocomposite films was not modified after plasma treatment.     

Cr2O3-modified ZnO thick film resistors as LPG sensors

Thick films of pure ZnO were obtained by screen-printing technique. Surface functionalized ZnO thick films by Cr₂O₃ were obtained by dipping pure ZnO thick films into 0.01 M aqueous solution of chromium trioxide (CrO₃). The dipped films were fired at 500 °C for 30 min. Upon firing, the CrO₃ would reduce to Cr₂O₃. Cr₂O₃-activated (0.47 mass%) ZnO thick films resulted in LPG sensor. Upon exposure to 100 ppm LPG, the barrier height between Cr₂O₃ and ZnO grains decreases markedly, leading to a drastic decrease in resistance. The sensor was found to sense LPG at 350 °C and no cross sensitivity was observed to other hazardous, polluting and inflammable gases. The quick response (∼18 s) and fast recovery (∼42 s) are the main features of this sensor. The effects of microstructures and dopant concentrations on the gas sensing performance of the sensor were studied and discussed.     

Silver Nanoparticles Filling in TiO2 Hollow Nanofibers by Coaxial Electrospinning

This study investigated the coaxial electrospinning process of silver filling in TiO₂ ultrafine hollow fibers using polyvinyl pyrrolidone (PVP) sol/titanium n-butyloxide (Ti(OC₄H₉)₄) and PVP sol/silver nanoparticles as pore-directing agents. The bicomponent fibers were heat treated at 200 °C and calcined at 600 °C. Silver particles having diameters of 5 to 40 nm were deposited on the inner surface of the long hollow TiO₂ nanofibers (outer diameter of 150.300 nm) with mesoporous walls (thickness of 10.20 nm). The morphological structure of the filled ultrafine hollow fibers has been studied by means of infrared (IR) spectrum, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The diameters and wall thicknesses of the hollow fibers could be tuned by adjusting the electrospinning parameters. Compared with other nanostructured TiO₂ materials, such as mesoporous Ag-TiO₂ blending fibers, TiO₂ hollow nanofibers, TiO₂ nanofibers, and TiO₂ powders, the silver filled TiO₂ hollow fibers exhibited a higher photocatalytic activity toward the degradation of methylene blue.     

MoS x Thin Films by Thermolysis of a Single-Source Precursor

Thin films of MoS _x have been prepared on silicon substrates by spin coating and thermolysis of 0.5 M solutions of alkyldiammonium tetrathiomolybdates in 1,2-ethanediamine (EDA) and 1,2-propanediamine (12PDA). The films have been heat treated in air at temperatures between 80 and 250°C and under N₂ atmosphere at temperatures between 300 and 800°C. X-ray diffraction shows a restricted crystallisation and amorphous residues in both kind of films. EDA-based films exhibit a high tendency to crystallise whereas 12PDA-based films form associated structures with the solvent preventing precursor crystallisation. An insight into the processes occurring in film formation is gained by infrared spectroscopy which indicates a beginning of the decomposition of the 12PDA-based film at temperatures as low as 80°C with incorporation of the diamine solvent. In contrast, the EDA-based films show first signs of a decomposition at 150°C. The decomposition of the intermediate MoS₃ in both cases starts between 250 and 300°C. By means of SNMS depth profiles carbon contents up to 21 and 32 atom-% were found in EDA- and 12PDA-based films, respectively. The films show a significant deficit of sulphur which is compensated by the carbon. Near the surface of the coatings a loss of carbon is observed.     

Spectroellipsometric Characterization of Multilayer Sol-Gel Fe2O3 Films

Multilayer Fe₂O₃ films were deposited by the sol-gel method on glass substrates using three successive deposition procedures. The films were thermally treated for 1 h at 300°C.The optical and microstructural properties of these films were investigated by spectroscopic ellipsometry (SE) in the 500–1000 nm range. The optical gap was found by fitting the dispersion of the film refractive index (n) with the Wemple-DiDomenico (WDD) formula.The ellipsometric measurements showed also that the Fe₂O₃ films are anisotropic. The birefringence values (n) of the sol-gel films (0.05–0.08) are smaller than the large values of the Fe₂O₃ (which are around 0.28) but increase with the crystalization of the films. AFM mesurements showed that the films treated at 300°C start to crystallize.     

UV-Visible and IR Spectroelectrochemical Properties of V2O5 Crystalline Films Charged/Discharged in Extended Potential Range

Electrochemical properties of amorphous and crystalline V₂O₅ films, dip-coated from V-oxoisopropoxide sols and thermally treated at various temperatures (100, 150, 200 and 300°C), have been studied in extended potential range, i.e. from 1.4 to –1.6 V vs. Ag/AgCl in 1M LiClO₄/propylen carbonate (PC) electrolyte. The formation of various lithiated (-, -, - and -Li _x V₂O₅) phases was correlated with the values of insertion coefficient x obtained from cyclic voltammograms (CV) of crystalline V₂O₅ films (300°C). Reversible charging was observed when films were cycled up to –1.0 V vs. Ag/AgCl, while the extension of the potential to –1.3 V vs. Ag/AgCl change the CV of films irreversibly. Charging of crystalline V₂O₅ films was followed by the help of in-situ UV-visible spectroscopy, that revealed the intensity variations of the polaron absorption above 600 nm and the presence of the absorbing V³⁺ species between 550 and 650 nm. Ex-situ IR spectra of the crystalline films charged/discharged at –1.6V/1.4V vs. Ag/AgCl confirmed the amorphisation of the films' structure.     

Optimization of the photocatalytic activity of CdO + CdTiO3 coupled oxide thin films obtained by sol-gel technique

In the preparation of CdO + CdTiO₃ polycrystalline thin films by the sol-gel method, the optical, structural and crystalline properties, as well as the photocatalytic activity (PA) depends strongly on the sintering temperature (Ts) of the films and of the Ti/Cd ratio used in the precursor solution. In this work, CdO + CdTiO₃ thin films were prepared using a Ti/Cd constant ratio in the precursor solution. The films were sintered at six different Ts in the 450-550 °C range, in an open atmosphere. The structure of the films was characterized by X-ray diffraction and the PA was evaluated by the photobleaching of methylene blue in an aqueous solution using a UV-vis spectrometer. The relative intensity of the diffraction peaks associated with CdO and CdTiO₃, change with the Ts. The better photocatalytic activities were obtained for the films sintered at 490 °C and 550 °C. When the CdO was removed from the films by chemical etching the PA decreased, showing the importance of coupling both oxides.     

Neo-Pentoxide Precursor Synthesis,Solution Preparation,and Electronic Properties of (Ba,Sr)TiO3 Thin Films Derived from a Solution Route

We have recently isolated the neo-pentoxide (HOCH₂CMe₃, ONp) derivatives of Ba, Sr, and Ti as Ba₄(ONp)₈(HONp)₆(py)₂, Sr₅(O)(ONp)₈(Solv)₅ (Solv = solvent), and Ti₂(ONp)₈, respectively. The combination of these precursors were found to be readily soluble in a wide range of solvents and thus were excellent candidates for preparation of barium strontium titanate ((Ba,Sr)TiO₃ or BST) thin films using spin-cast deposition techniques. The highest quality BST films for this system were generated from ternary mixtures dissolved in either pyridine or pyridine/toluene. By in situ VT-GIXRD analysis it was determined that the perovskite phase of BST was readily formed at 650°C. The electronic properties of films crystallized at 700°C indicated that the thin films (300 nm) possessed a dielectric constant of 120 (tan = 0.03) with a tunability of 29% at ±10 V. 300 nm films (700°C) which had been generated from a standard BST solution modified with a novel tridentate ligand, had a higher dielectric constant of 180 and a tunability of 35% at ±10 V. The collective characteristics of these precursors offer an attractive alternative to the more complex, less stable sol-gel precursors currently in use.     

The influence of A-site rare-earth for barium substitution on the chemical structure and ferroelectric properties of BZT thin films

Rare-earth (RE) doped Ba(Zr,Ti)O₃ (BZT) thin films were prepared by rf-magnetron sputtering from a Ba_0.90Ln_0.067Zr_0.09Ti_0.91O₃ (Ln=La, Nd) target. The films were deposited at a substrate temperature of 600 °C in a high oxygen pressure atmosphere. X-ray diffraction (XRD) patterns of RE-BZT films revealed a 〈001〉 epitaxial crystal growth on Nb-doped SrTiO₃, 〈001〉 and 〈011〉 growth on single-crystal Si, and a 〈111〉-preferred orientation on Pt-coated Si substrates. Scanning electron microscopy (SEM) showed uniform growth of the films deposited, along with the presence of crystals of about half-micron size on the film's surface. Transmission electron microscopy (TEM) evidenced high crystalline films with thicknesses of about 100 nm for 30 min of sputtering. Electron-probe microanalysis (EPMA) corroborated the growth rate (3.0-3.5 nm/min) of films deposited on Pt-coated Si substrates. X-ray photoelectron spectroscopy (XPS), in depth profile mode, showed variations in photoelectron Ti 2p doublet positions at lower energies with spin-orbital distances characteristic of BaTiO₃-based compounds. The XPS analysis revealed that lanthanide ions positioned onto the A-site of the BZT-perovskite structure increasing the MO₆-octahedra distortion (M=Ti, Zr) and, thereby, modifying the Ti-O binding length. Polarization-electric field hysteresis loops on Ag/RE-doped BZT/Pt capacitor showed good ferroelectric behavior and higher remanent polarization values than corresponding non-doped system.     

Sol–gel derived silver-incorporated titania thin films on glass: bactericidal and photocatalytic activity

Titanium dioxide (TiO₂) and silver-containing TiO₂ (Ag-TiO₂) thin films were prepared on silica pre-coated float glass substrates by a sol–gel spin coating method. The bactericidal activity of the films was determined against Staphylococcus epidermidis under natural and ultraviolet (UV) illumination by four complementary methods; (1) the disk diffusion assay, (2) UV-induced bactericidal test, (3) qualitative Ag ion release in bacteria inoculated agar media and (4) surface topographical examination by laserscan profilometry. Photocatalytic activity of the films was measured through the degradation of stearic acid under UV, solar and visible light conditions. The chemical state and distribution of Ag nanoparticles, as well as the structure of the TiO₂ matrix, and hence the bactericidal and photocatalytic activity, is controlled by post-coating calcination treatment (100–650 °C). Additionally, under any given illumination condition the Ag-incorporated films were found to have superior bactericidal and photocataltyic activity performance compared to TiO₂ thin films. It is shown that with optimized thin film processing parameters, both TiO₂ and Ag-TiO₂ thin films calcined at 450 °C were bactericidal and photocatalytically active.     

Photoluminescence properties of BaMoO4 amorphous thin films

BaMoO₄ amorphous and crystalline thin films were prepared from polymeric precursors. The BaMoO₄ was deposited onto Si wafers by means of the spinning technique. The structure and optical properties of the resulting films were characterized by FTIR reflectance spectra, X-ray diffraction (XRD), atomic force microscopy (AFM) and optical reflectance. The bond Mo-O present in BaMoO₄ was confirmed by FTIR reflectance spectra. XRD characterization showed that thin films heat-treated at 600 and 200 °C presented the scheelite-type crystalline phase and amorphous, respectively. AFM analyses showed a considerable variation in surface morphology by comparing samples heat-treated at 200 and 600 °C. The reflectivity spectra showed two bands, positioned at 3.38 and 4.37 eV that were attributed to the excitonic state of Ba²⁺ and electronic transitions within MoO²⁻₄, respectively. The optical band gaps of BaMoO₄ were 3.38 and 2.19 eV, for crystalline (600 °C/2 h) and amorphous (200 °C/8 h) films, respectively. The room-temperature luminescence spectra revealed an intense single-emission band in the visible region. The PL intensity of these materials was increased upon heat-treatment. The excellent optical properties observed for BaMoO₄ amorphous thin films suggested that this material is a highly promising candidate for photoluminescent applications.     

ZnO thin films prepared on titanium substrate by PLD technique at different substrate temperatures

ZnO thin films were grown by pulsed laser deposition on titanium substrates at different substrate temperatures ranging from 300 to 700 °C. X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS),photoluminescence, and Raman spectroscopy are employed to investigate the change of properties. XRD, XPS, and Raman data showed that the films consisted of TiO₂ at high substrate temperature, which will deteriorate the crystallization quality of ZnO films. The optimum temperature for the growth of ZnO films on the Ti substrate is about 500 °C in this paper. The ZnO films grown on titanium substrate can be used in direct current, microwave, and medical applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Application of surface science techniques to study a gilded Egyptian funerary mask: A multi-analytical approach

A wide range of analytical techniques has been used to study an Egyptian funerary mask of the Ptolemaic period (305-30 bc ). Secondary electron (SE) and back-scattering (BS) images, recorded by a scanning electron microscope (SEM), provided a detailed representation of the metallurgical techniques used to construct the gilded mask. It is confirmed, that the golden leaf used to cover the mask is the product of an antique refinery practice, so called, cementation process of naturally occurring alloy of gold and silver, namely electrum. Complementary results of SEM-electron dispersion spectroscopy (EDS) and electron probe microanalysis (EPMA)–wavelength dispersion spectroscopy (WDS) provided chemical compositions of the golden leaf as well as in the plaster base of the mask. X-ray photoemission spectroscopy (XPS) revealed the presence of Au, Ag, Si, S, Cl, Ca, and N, in addition to O and C. Relative concentration of Au/Ag at the surface has been measured by XPS to be 70% to 30%. XPS depth profiling verified silver-enrichment at the surface, as ratio of gold to silver is measured to be 80% to 20% at the depth of 15 nm. XPS chemical mapping images of gold and silver confirmed a rather inhomogeneous character of Au/Ag relative concentration at the surface. The main diffraction peaks in the X-ray diffraction (XRD) spectrum coincide with diffraction peaks of pure gold, silver metals, and magnesium calcite Mg_0.03Ca_0.97CO₃. Whereas, Raman spectroscopy results implied the existence of Ag₂S, a tarnishing compound, on the golden area of the mask.     

Orientation and Surface Properties of Sol-Gel Derived Y2O3 Films

The orientation, surface and optical properties of sol-gel derived Y₂O₃ films have been investigated. Transparent Y₂O₃ films were prepared on quartz glass substrates by sol-gel processes using YCl₃·6H₂O as a starting material. The water droplet contact angles of the films reached constant values between 79° and 90° after the films were left for 8 to 10 days in air at ambient temperature, indicating that the film surface exhibited hydrophobicity. When 2-(2-methoxyethoxy)ethanol (MEE) was added to the sol, yttria in the films crystallized to a strongly oriented cubic phase at firing temperatures between 400°C and 500°C. The intensity of the XRD peaks increased as the firing temperature was increased to 900°C. However, yttria crystallized to a non-oriented cubic phase when MEE was not used. The refractive index and packing density of the Y₂O₃ films increased from 1.55 to 1.68 and from 0.67 to 0.79, respectively, as the firing temperature was raised from 400°C to 900°C, indicating that sol-gel derived Y₂O₃ films are lower in density than evaporated ones.     

Degradation of C<Emphasis Type="Italic">andida albicans</Emphasis> on TiO<Subscript>2</Subscript> and Ag-TiO<Subscript>2</Subscript> thin films prepared by sol–gel and nanosuspensions

In this study, both suspensions and thin films of TiO₂ and silver loaded TiO₂ (Ag-TiO₂) were used in the photocatalytic degradation/disinfection of C. albicans. In the case of thin films coated materials, both microscope slides and steel pieces of similar dimensions were dip coated using sol–gel solutions prepared from titanium isopropoxide. Surface analysis of the materials confirmed that thin film formation had been succesful. After set periods of irradiation in the presence of suspension or thin film coated material, 10 μL aliquots of the solution were withdrawn and directly cultivated on sabouraud dextrose agar for 24 h at 37 °C. The number of living colonies was counted. The results show that both the suspensions and the thin films displayed superior antimicrobial properties towards C. albicans. In particular the Ag-TiO₂ catalyst was extremely active even in the dark, for disinfection of C. albicans. The degradation percentage over TiO₂ and Ag-TiO₂ thin films coated on the steel substrate was higher than those coated on glass achieving 80 and 97.9%, respectively, using the 365 nm, near visible region light source.