Preparation and photocatalytic activity of CeO2/TiO2 interface composite film

The CeO₂/TiO₂ and TiO₂/CeO₂ interface composite films were prepared on glass substrates by the sol-gel process via dip-coating and calcining technique. The scanning electron microscopy (SEM) revealed that the TiO₂ layer has a compact and uniformity glasslike surface with 200 nm in thickness, and the CeO₂ layer has a coarse surface with 240 nm in thickness. The X-ray diffractometer (XRD) analysis showed that the TiO₂ layer is made up of anatase phase, and the CeO₂ layer is structured by cubic fluorite phase. Through a series of photo-degradation experiments, the relationship of the photocatalytic activity with the constituents of the films was studied. In virtue of the efficient interfacial charge separation via the process of electron transfer from TiO₂ to CeO₂, the photocatalytic activity of the CeO₂/TiO₂ composite film is high. Contrarily, the photocatalytic activity of the TiO₂/CeO₂ composite film is low, due to its inert surface made up of CeO₂ with broad bandwidth. Apart from the effect of the film structure, the effect of film thickness on photocatalytic activity was also discussed.     

Growth of highly-oriented CaCu3Ti4O12 thin films on SrTiO3 (1 0 0) substrates by a chemical solution route

Highly-oriented CaCu₃Ti₄O₁₂ (CCTO) thin films deposited directly on SrTiO₃ (1 0 0) substrates have been developed successfully using a chemical solution coating method. X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were employed to characterize the structure and the morphology. It was observed that the CCTO thin films had the 1 μm × 1 μm domain-like microstructure that consists of compact grains of about 0.1 μm in size. The cross sectional SEM image shows that the CCTO grains grow regularly close to the clear interface between the CCTO film and the SrTiO₃ substrate. The result was discussed in terms of lattice mismatch between CCTO and SrTiO₃.     

On the spray-drying deposition of TiO2 photocatalytic films

The photocatalytic activity of TiO₂ films deposited on different substrates by the spray-drying method using suspensions of commercially available TiO₂ (Degussa P25 or Tronox) as starting material was studied. The influence of the type of the initial TiO₂, preparation conditions (temperature of the substrate during the film deposition, temperature of the post-deposition annealing), substrate material (glass, fused silica, stainless steel and graphite), the presence of additives in the spraying suspension (polyethylene glycol, ethylene glycol and acetylacetone) and its sonication before spraying on the morphology, size of crystallites and phase composition (rutile/anatase ratio) was studied. Optimal conditions for spray deposition of the films are suggested.     

Effect of calcination temperature on the morphology and surface properties of TiO2 nanotube arrays

Well-ordered TiO₂ nanotube arrays were prepared by electrochemical anodization of titanium in aqueous electrolyte solution of H₃PO₄ + NH₄F at a constant voltage of 20 V for 3 h, followed by calcined at various temperatures. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and Photoluminescence (PL) were used to characterize the samples. The results showed that the as-prepared nanotube arrays before being calcined were amorphous and could transform to anatase phase at a heat treatment temperature higher than 400 °C. As the calcination temperatures increased, crystallization of anatase phase enhanced and rutile phase appeared at 600 °C. However, further increasing the calcination temperature would cause the collapse of nanotube arrays. PL intensity of the nanotube arrays annealed at 500 °C was the lowest, which was probably ascribed to better crystallization together with fewer surface defects of the nanotube arrays.     

Structure and electrical properties of CdIn2O4 thin films prepared by DC reactive magnetron sputtering

CdIn₂O₄ thin films were prepared by direct-current (DC) reactive magnetron sputtering. The structure, surface morphology and the chemical composition of the thin films were analyzed by X-ray diffraction (XRD), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. The electrical properties of the films prepared in different oxygen concentration and annealing treatment were determined, and the effects of the preparing conditions on the structure and electrical properties were also explored. It indicates that the CdIn₂O₄ thin films with uniform and dense surface morphology contain mainly CdIn₂O₄, In₂O₃ phases, and CdO phase is also observed. The XPS analysis confirms the films are in oxygen-deficient state. The electrical properties of these films significantly depend on the preparing conditions, the resistivity of the films with the oxygen concentration of 4.29% is 2.95 × 10⁻⁴ Ω cm and the Hall mobility is as high as 60.32 cm²/V s. Annealing treatment can improve the electrical performance of the films.     

Structure, magnetic and electrical transport properties of cosputtered Fe0.5Ge0.5 nanocomposite films

Fe_0.5Ge_0.5 nanocomposite films with different film thicknesses were fabricated using cosputtering. The films are composed of Ge, Fe and Fe₃Ge₂, and are ferromagnetic at room temperature. The saturation magnetization and magnetic interaction including dipolar interaction and exchange coupling increase with the increasing film thickness. The electrical conductance mechanism turns from metallic to semiconducting and the saturation Hall resistivity ρ_xys increases with the decreasing film thickness. At 28 nm, ρ_xys is ∼137 μΩ cm at 2 K, about 150 times larger than that of pure Fe film (0.9 μΩ cm) and four orders larger than that of bulk Fe. The ρ_xy-H curves of all the films show the same linearity character in low-field range even though the temperature-independent slope is different at different film thicknesses. At high temperatures, the skew scattering mechanism is dominant. At low temperatures, side-jump effect should be dominant at large resistivity ρ_xx regime for the thin films, and the skew scattering is dominant at small ρ_xx regime for the thick films.     

Structure, magnetic and optical properties of polycrystalline Co-doped TiO2 films

Co-doped TiO₂ films were fabricated under different conditions using reactive facing-target magnetron sputtering. Co doping improves the transformation of TiO₂ from anatase phase to rutile phase. The chemical valence of doped Co in the films is +2. All the films are ferromagnetic with a Curie temperature above 340 K. The average room-temperature moment per Co of the Co-doped TiO₂ films fabricated at 1.86 Pa decreases from 0.74 μ_B at x=0.03 to 0.02 μ_B at x=0.312, and decreases from 0.54 to 0.04 μ_B as x increases from 0.026 to 0.169 for the Co-doped TiO₂ films fabricated at 0.27 Pa. The ferromagnetism originates from the oxygen vacancies created by Co²⁺ dopants at Ti⁴⁺ cations. The optical band gaps value (E_g) of the Co-doped TiO₂ films fabricated at 1.86 Pa decreases linearly from 3.35 to 2.62 eV with the increasing x from 0 to 0.312. For the Co-doped TiO₂ films fabricated at 1.86 Pa, the E_g decreases linearly from 3.26 to 2.53 eV with increasing x from 0 to 0.350.     

Characteristics of SrBi2Ta2O9 ferroelectric films in an in situ applied low electric field prepared by metalorganic decomposition

SrBi₂Ta₂O₉ (SBT) films were prepared on Pt/TiO₂/SiO₂/Si substrates at 750 °C in oxygen by metalorganic decomposition method. A low electric field was in situ applied during the film crystallization. It was first found that a low electric field and its direction have significant influence on the microstructures and ferroelectric properties of SBT films. Under a positive electric field (assuming that the bottom electrode is electrically grounded), the films show stronger c-axis-preferred orientation than without electric field and under a negative electric field. As a possible origin is proposed that the interface-induced nucleation growth between SBT and Pt coated substrate with application of low electric field plays a key role. Above all, an in situ applied low electric field during the film crystallization is a promising technique controlling film orientation for film preparation by wet chemical method.     

Magnetic,structural and electrical properties of ordered and disordered Co50Fe50 films

Co₅₀Fe₅₀ films with thickness varying from 100 to 500 Å were deposited on a glass substrate by sputtering process, respectively. Two kinds of CoFe films were studied: one was the as-deposited film, and the other the annealed film. The annealing procedure was to keep the films at 400 °C for 5 h in a vacuum of 5×10⁻⁶ mbar. From the X-ray study, we find that the as-deposited film prefers the CoFe(1 1 0) orientation. Moreover, the body-centered cubic (bcc) CoFe(1 1 0) line is split into two peaks: one corresponding to the ordered body-centered tetragonal (bct) phase, and the other, the disordered bcc phase. After annealing, the peak intensity of the ordered bct phase becomes much stronger, while that of the disordered bcc phase disappears. The annealing has also caused the ordered CoFe(2 0 0) line to appear. When the amount of the ordered bct phase in Co₅₀Fe₅₀ is increased, the saturation magnetization (M_s) and coercivity (H_c) become larger, but the electrical resistivity (ρ) decreases. From the temperature coefficient of resistance (TCR) measurement, we learn that the bct grains in the CoFe film start to grow at temperature 82 °C.     

Structural and optical characterization of Ce-doped Gd2SiO5 films by sol-gel technique

Cerium-doped Gd₂SiO₅ (GSO:Ce) films have been prepared on (1 1 1) silicon substrates by the sol-gel technique. Annealing was performed in the temperature range from 400 to 1000 °C. X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to investigate the structure and morphology of GSO:Ce films. Results showed that GSO:Ce film starts to crystallize at about 600 °C, GSO:Ce films have a preferential (0 2 1) orientation, as the annealing temperature increase, the (0 2 1) peak intensity increases, the full width of half maximum (FWHM) decreases, and the grain size of GSO:Ce films increases. Emission spectra of GSO:Ce films were measured, results exhibit the characteristic blue emission peak at 427 nm.     

Mg substitutions in ZnO-Al2O3 thin films and its effect on the optical absorption spectra of the nanocomposite

ZnO-Al₂O₃ nanocomposite thin films were prepared by sol-gel technique. The room temperature synthesis was mainly based on the successful peptization of boehmite (AlO(OH)) and Al(OH)₃ compounds, so as to use it as matrix to confine ZnO nanoparticles. The relative molar concentrations of xZnO to (1 − x) Al₂O₃ were varied as x = 0.1, 0.2 and 0.5. The optical absorption spectra of the thin films showed intense UV absorption peaks with long tails of variable absorption in the visible region of the spectra. The ZnO-Al₂O₃ nanocomposites thin films were doped with MgO by varying its molar concentrations as y = 0.05, 0.75, 0.1, 0.125, 0.15 and 0.2 with respect to the ZnO present in the composite. The MgO doped thin films showed suppression of the intense absorption peaks that was previously attained for undoped samples. The disappearance of the absorption peaks was analyzed in terms of the crystalline features and lattice defects in the nanocomposite system. The bulk absorption edge, which is reportedly found at 3.37 eV, was shifted to 5.44 eV (for y = 0.05), 5.63 eV (for y = 0.075) and maximum to 5.77 eV (for y = 0.1). In contrast, beyond the concentration, y = 0.1 the absorption edges were moved to 5.67 eV (for y = 0.125), 5.61 eV (for y = 0.15) and to 5.49 eV (for y = 0.2). This trend was explained in terms of the Burstein-Moss shift of the absorption edges.     

Studies on the structural and electrical properties of spray deposited SnO2:Sb thin films as a function of substrate temperature

Thin films of antimony doped tin oxide (SnO₂:Sb) were prepared by spray pyrolysis technique using SnCl₂ as precursor with the various antimony doping levels ranging from 1 to 4 wt%. The XRD analysis showed that the undoped SnO₂ films grow in (211) preferred orientation whereas the Sb doped films grow in (200) plane. Scanning electron microscopy studies indicated that the surface of the films prepared with lower doping level (1 wt%) consists of larger grains whereas those prepared with higher doping levels (>1 wt%) consist of smaller grains. The sheet resistance has been found to be reduced considerably (2.17 Ω/□) for Sb doped films. To the best of our knowledge this is the lowest sheet resistance obtained for Sb doped SnO₂ thin films.     

Optical properties of GdTaO4:Eu thick films prepared from a PVP-containing solution

Transparent GdTaO₄:Eu³⁺ thick films were prepared from the inorganic salt and 2-methoxyethanol solution containing polyvinylpyrrolidone (PVP) via sol-gel technique. The critical thickness of the film, i.e. the maximum thickness achievable without crack formation via non-repetitive deposition, was 0.8 μm. The effect of PVP on the morphology, crystallization behavior and optical property of the GdTaO₄:Eu³⁺ thick film was investigated. The results indicated that PVP could play an important role in the formation of transparent GdTaO₄:Eu³⁺ thick films, suppressing the stress evolution, adjusting the sol viscosity, ameliorating the crystallinity, and strengthening the covalency of Eu-O bonds. The GdTaO₄:Eu³⁺ thick films prepared with PVP exhibited a superior photoluminescence and X-ray exited luminescence, which implies that it will have promising applications in high-spatial-resolution X-ray imaging and flat panel display devices.     

Effects of substrates on the structure and dielectric properties of Ba(Sn0.15Ti0.85)O3 thin films

Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films were grown on Pt(1 1 1)/Ti/SiO₂/Si and LaNiO₃(LNO)/Pt(1 1 1)/Ti/SiO₂/Si substrates by a sol-gel processing technique, respectively. The BTS thin films deposited on annealed Pt(1 1 1)/Ti/SiO₂/Si and annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrates exhibited strong (1 1 1) and perfect (1 0 0) orientations, respectively. The BTS thin films grown on un-annealed Pt(1 1 1)/Ti/SiO₂/Si substrates showed random orientation with intense (1 1 0) peak, while the films deposited on un-annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrate exhibited random orientation with intense (1 0 0) peak, respectively. The dielectric constant of the BTS films deposited on annealed Pt(1 1 1)/Ti/SiO₂/Si, annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si, un-annealed Pt(1 1 1)/Ti/SiO₂/Si and un-annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrates was 512, 565, 386 and 437, respectively, measured at a frequency of 100 kHz. A high tunability of 49.7% was obtained for the films deposited on annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrate, measured at the frequency of 100 kHz with an applied electric field of 200 kV/cm. The high tunability has been attributed to the (1 0 0) texture of the films and larger grain sizes.     

Optical and structural properties of nanosized ZnGa2O4:Cr phosphor

Nanosized ZnGa₂O₄:Cr³⁺ powder is synthesized through hydrothermal method. The average particle size is 20 nm and they are spherical in shape. The excitation band from the charge transfer between Cr³⁺-O²⁻ shows a blueshift behavior due to quantum confinement effect. X-ray diffraction pattern, Fourier transform-infrared spectrum, and electron paramagnetic resonance signal indicate that nanosized ZnGa₂O₄:Cr³⁺ phosphor shows many defect-related energy states and heavy lattice distortion in comparison with bulk ZnGa₂O₄:Cr³⁺ phosphor. Many defect states result in more nonradiative loss and shorter decay time.     

Structural, optical and electrical properties of Al-N codoped ZnO films by RF-assisted MOCVD method

N-doped ZnO films were produced using N₂ as N source by metal-organic chemical vapor deposition (MOCVD) system which has been improved with radio-frequency (RF)-assisted equipments. The data of secondary ion mass spectroscopy (SIMS) indicate that the concentration of N in N-doped ZnO films is around 5 × 10²⁰ cm⁻³, implying that sufficient incorporation of N into ZnO can be obtained by RF-assisted equipment. On this basis, the structural, optical and electrical properties of Al-N codoped ZnO films were studied. Then, the effect of RF power on crystal quality, surface morphologies, optical properties was analyzed using X-ray diffraction, atomic force microscopy and photo-luminescence methods. The results illustrate that the RF plasma is the key factor for the improvement of crystal quality. Then the observation of A⁰X recombination associated with N_O acceptor in low-temperature PL spectrum proved that some N atoms have occupied the positions of O atoms in ZnO films. Hall measurements shown that p-type ZnO film deposited on quartz glasses was obtained when RF power was 150 W for the Al-N codoped ZnO films, while the resistivity of N-doped ZnO films was rather high. Compared with the Al-doped ZnO film, the obviously increased resistivity of codoped films indicates that the formation of N_O acceptors compensate some donors in ZnO films effectively.     

Structural and morphological characterization of TiO2 nanostructured films grown by nanosecond pulsed laser deposition

TiO₂ has attracted a lot of attention due to its photocatalytic properties and its potential applications in environmental purification and self cleaning coatings, as well as for its high optical transmittance in the visible-IR spectral range, high chemical stability and mechanical resistance. In this paper, we report on the growth of TiO₂ nanocrystalline films on Si (1 0 0) substrates by pulsed laser deposition (PLD). Rutile sintered targets were irradiated by KrF excimer laser (λ = 248 nm, pulse duration ∼30 ns) in a controlled oxygen environment and at constant substrate temperature of 650 °C. The structural and morphological properties of the films have been studied for different deposition parameters, such as oxygen partial pressure (0.05-5 Pa) and laser fluence (2- 4 J/cm²). X-ray diffraction (XRD) shows the formation of both rutile and anatase phases; however, it is observed that the anatase phase is suppressed at the highest laser fluences. X-ray photoelectron spectroscopy (XPS) measurements were performed to determine the stoichiometry of the grown films. The surface morphology of the deposits, studied by scanning electron (SEM) and atomic force (AFM) microscopies, has revealed nanostructured films. The dimensions and density of the nanoparticles observed at the surface depend on the partial pressure of oxygen during growth. The smallest particles of about 40 nm diameter were obtained for the highest pressures of inlet gas.     

Photoluminescence studies in sol-gel derived Zno films

The photoluminescence (PL) properties of high quality ZnO thin films grown on Si (1 0 0) substrates using spin coating technique are investigated as a function of temperature in the range 10-300 K. The PL spectra shows dominant donor bound excitonic emission along with free exciton related emission in the UV region. The corresponding activation energy of thermal quenching is found to be . The parameters that describe the temperature dependent red shift of the band-edge transition energy are evaluated using different models. The broadening of the PL peak due to increase in temperature is mainly attributed to the exciton-LO phonon coupling.     

Switching phenomenon and optical properties of Se85Te10Bi5 films

Se₈₅Te₁₀Bi₅ films of different thicknesses ranging from 126 to 512 nm have been prepared. Energy-dispersive X-ray (EDX) spectroscopy technique showed that films are nearly stoichiometric. X-ray diffraction (XRD) measurements have showed that the Se₈₅Te₁₀Bi₅ films were amorphous. Electrical conduction activation energy (ΔE_σ) for the obtained films is found to be 0.662 eV independent of thickness in the investigated range. Investigation of the current voltage (I-V) characteristics in amorphous Se₈₅Te₁₀Bi₅ films reveals that it is typical for a memory switch. The switching voltage V_th increases with the increase of the thickness and decreases exponentially with temperature in the range from 298 to 383 K. The switching voltage activation energy (ε) calculated from the temperature dependence of V_th is found to be 0.325 eV. The switching phenomenon in amorphous Se₈₅Te₁₀Bi₅ films is explained according to an electrothermal model for the switching process. The optical constants, the refractive index (n) and the absorption index (k) have been determined from transmittance (T) and reflectance (R) of Se₈₅Te₁₀Bi₅ films. Allowed non-direct transitions with an optical energy gap (E_g^opt) of 1.33 eV have been obtained. ΔE_σ is almost half the obtained value of E_g^opt, which suggested band to band conduction as indicated by Davis and Mott.     

Fabrication and characterization of TS-1 films on α-Al2O3 substrates using TiCl3 as titanium source

The continuous and highly intergrown anatase-free TS-1 film was fabricated with TiCl₃ as the titanium source for the first time. The in situ nucleation and secondary growth method was employed to synthesize the TS-1 film. By means of scanning electron microscopy (SEM) images, X-ray diffraction (XRD) patterns, and FT-IR and UV-vis spectra measurements, the resulting film was observed to be anatase-free, continuous and highly intergrown with the MFI-type structure, and the Ti atoms existed only in tetrahedral coordination.