The structure and photocatalytic activity of TiO2 thin films deposited by dc magnetron sputtering

This paper seeks to determine the optimal settings for the deposition parameters, for TiO₂ thin film, prepared on non-alkali glass substrates, by direct current (dc) sputtering, using a ceramic TiO₂ target in an argon gas environment. An orthogonal array, the signal-to-noise ratio and analysis of variance are used to analyze the effect of the deposition parameters. Using the Taguchi method for design of a robust experiment, the interactions between factors are also investigated. The main deposition parameters, such as dc power (W), sputtering pressure (Pa), substrate temperature (°C) and deposition time (min), were optimized, with reference to the structure and photocatalytic characteristics of TiO₂. The results of this study show that substrate temperature and deposition time have the most significant effect on photocatalytic performance. For the optimal combination of deposition parameters, the (1 1 0) and (2 0 0) peaks of the rutile structure and the (2 0 0) peak of the anatase structure were observed, at 2θ ∼ 27.4°, 39.2° and 48°, respectively. The experimental results illustrate that the Taguchi method allowed a suitable solution to the problem, with the minimum number of trials, compared to a full factorial design. The adhesion of the coatings was also measured and evaluated, via a scratch test. Superior wear behavior was observed, for the TiO₂ film, because of the increased strength of the interface of micro-blasted tools.     

Photocatalytic TiO2 thin films deposited on flexible substrates by radio frequency (RF) reactive magnetron sputtering

Titanium dioxide (TiO₂) thin films were deposited on flexible polycarbonate (PC) substrates by radio frequency (RF) reactive magnetron sputtering. The target was metallic titanium, argon was the plasma gas and oxygen was the reactive gas. Taguchi’s method, which uses an L₉ (3⁴) orthogonal array, signal-to-noise ratio and analysis of variance (ANOVA), was employed to study the performance of the deposition process. The effects of the deposition parameters on the structure, morphology and photocatalytic performance of the TiO₂ films were analyzed using scanning electron microscopy (SEM), X-ray diffraction, and UV-vis-NIR spectroscopy. Experiments varied RF power (50, 100, 150 W), deposition time (2, 3, 4 h), O₂/(Ar + O₂) argon/oxygen ratios (40, 60, 80%) and substrate temperatures (room, 80, 120 °C), to optimize the photoinduced decomposition of methylene blue (MB). The experimental results illustrate the effectiveness of this approach.     

Characterization of TiO2/Au/TiO2 films deposited by magnetron sputtering on polycarbonate substrates

Transparent and conducting TiO₂/Au/TiO₂ (TAuT) films were deposited by reactive magnetron sputtering on polycarbonate substrates to investigate the effect of the Au interlayer on the optical, electrical, and structural properties of the films. In TAuT films, the Au interlayer thickness was kept at 5 nm. Although total thickness was maintained at 100 nm, the stack structure was varied as 50/5/45, 70/5/25, and 90/5/5 nm.In XRD pattern, the intermediate Au films were crystallized, while all TAuT films did not show any diffraction peaks for TiO₂ films with regardless of stack structure. The optical and electrical properties were dependent on the stack structure of the films. The lowest sheet resistance of 23 Ω/□ and highest optical transmittance of 76% at 550 nm were obtained from TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm films. The work function was dependent on the film stack. The highest work function (4.8 eV) was observed with the TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm film stack. The TAuT film stack of TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm films is an optimized stack that may be an alternative candidate for transparent electrodes in flat panel displays.     

Optical properties of p-type CuAlO2 thin film grown by rf magnetron sputtering

We report the structural and optical properties of copper aluminium oxide (CuAlO₂) thin films, which were prepared on c-plane sapphire substrates by the radio frequency magnetron sputtering method. X-ray photoelectron spectroscopy (XPS) along with X-ray diffraction (XRD) analysis confirms that the films consist of delafossite CuAlO₂ phase only. The optical absorption studies show the indirect and direct bandgap is 1.8 eV and 3.45 eV, respectively. Room temperature photoluminescence (PL) measurements show three emission peaks at 360 nm (3.45 eV), 470 nm (2.63 eV) and 590 nm (2.1 eV). The first one is near band edge emission while the other two are originated from defects.     

Effect of RF power and sputtering pressure on the structural and optical properties of TiO2 thin films prepared by RF magnetron sputtering

TiO₂ thin films were deposited onto quartz substrates by RF magnetron sputtering. The samples deposited at various RF powers and sputtering pressures and post annealed at 873 K, were characterized using X-ray diffraction (XRD), micro Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-vis spectroscopy and photoluminescence (PL) spectroscopy. XRD spectrum indicates that the films are amorphous-like in nature. But micro-Raman analysis shows the presence of anatase phase in all the samples. At low sputtering pressure, increase in RF power favors the formation of rutile phase. Presence of oxygen defects, which can contribute to PL emission is evident in the XPS studies. Surface morphology is much affected by changes in sputtering pressure which is evident in the SEM images. A decrease in optical band gap from 3.65 to 3.58 eV is observed with increase in RF power whereas increase in sputtering pressure results in an increase in optical band gap from 3.58 to 3.75 eV. The blue shift of absorption edge in all the samples compared to that of solid anatase is attributed to quantum size effect. The very low value of extinction coefficient in the range 0.0544-0.1049 indicates the excellent optical quality of the samples. PL spectra of the films showed emissions in the UV and visible regions.     

Design and fabrication of a TiO2/nano-silicon composite visible light photocatalyst

Nano-silicon (nc-Si) was utilized as the charges generator to promote the photocatalytic and super-hydrophilic reactivity of TiO₂ film under visible light irradiation. The photocatalytic ability of TiO₂/nc-Si composite photocatalyst was evaluated by a set of experiments to photodecompose 100 ppm methylene blue (MB) in aqueous solution. And the super-hydrophilic property was characterized by measuring the water droplet contacts angle, under visible light irradiation in atmospheric air and at room temperature. Under 100 mW/cm² visible light irradiation, the droplet contact angles were reduced to 0° within 4 h with nc-Si charge generator. Additionally, the rate constant of MB photo-degradation was promoted 6.6 times.     

Room temperature ferromagnetism in vacuum-annealed TiO2 thin films

Thin films of pure TiO₂ have been prepared using both spin-coating and sputter-deposition techniques on sapphire and quartz substrates. The structural characteristics of the films have been investigated in detail using Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). When annealed in vacuum, all films demonstrate room temperature ferromagnetism, while the air-annealed samples show much smaller, often negligible, magnetic moments. The magnetization of the vacuum-annealed sputtered samples depends on film thickness, with the volume magnetization decreasing monotonically with increasing thickness. Furthermore, the magnetization per unit area also decreases slightly with increasing film thickness. These results suggest that ferromagnetism in the vacuum-annealed TiO₂ films is mediated by surface defects or interfacial effects, but does not arise from stoichiometric crystalline TiO₂.     

Crystallisation of TiO2 thin films induced by excimer laser irradiation

Titanium dioxide thin films have been deposited by reactive magnetron sputtering on glass substrate and subsequently irradiated by UV radiation using a KrF excimer laser. In this work, we have study the influence of the laser fluence (F) ranging between 0.05 and 0.40 mJ/cm² on the constitution and microstructure of the deposited films. Irradiated thin films are characterized by profilometry, scanning electron microscopy and X-ray diffraction. As deposited films are amorphous, while irradiated films present an anatase structure. The crystallinity of the films strongly varies as a function of F with maximum for F = 0.125 J/cm². In addition to the modification of their constitution, the irradiated areas present a strongly modified microstructure with appearance of nanoscale features. The physico-chemical mechanisms of these structural modifications are discussed based on the theory of nucleation.     

Investigation on properties of TiO2 thin films deposited at different oxygen pressures

TiO₂ thin films were prepared by electron beam evaporation at different oxygen partial pressures. The influences of oxygen partial pressure on optical, mechanical and structural properties of TiO₂ thin films were studied. The results showed that with the increase of oxygen partial pressure, the optical transmittance gradually increased, the transmittance edge gradually shifted to short wavelength, and the corresponding refractive index decreased. The residual stresses of all samples were tensile, and the value increased as oxygen partial pressure increasing, which corresponded to the evolutions of the packing densities. The structures of TiO₂ thin films all were amorphous because deposition particles did not possess enough energy to crystallize.     

Influence of deposition atmosphere on photocatalytic activity of TiO2/SiOx double-layers prepared by RF magnetron sputtering

TiO₂/SiO_x double-layers have been prepared at room temperature by RF magnetron sputtering. The TiO₂ top-layer was deposited in an Ar atmosphere, while the SiO_x bottom-layer was deposited in an Ar/O₂ atmosphere. Samples were characterized using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and photoluminescence techniques. The photocatalytic activity of the samples was evaluated by the photodegradation of methylene blue; the results showed that the photocatalytic activity of the TiO₂/SiO_x double-layers was superior to that of the TiO₂ single-layers. The presence of the SiO_x bottom-layer improved the photocatalytic activity of the TiO₂ layer because it may act as a trap for electrons generated in the TiO₂ layer thus preventing electron-hole recombinations.     

射频磁控溅射法制备SnO2:Sb薄膜的结构和光致发光性质研究

采用射频磁控溅射法在玻璃衬底上制备出锑掺杂的氧化锡（SnO2₂:Sb）薄膜.制 备薄膜是具有纯氧化锡四方金红石结构的多晶膜薄，晶粒生长的择优取向为［110］.室温下光致发光测量结果表明，在392nm附近存在强的紫外-紫光发射.研究了不同氧分压对薄膜结构及发光性质的影响，并对SnO2₂:Sb的光致发光机制进行了探索性研究.     

TiO2/polyaniline nanocomposite films prepared by magnetron sputtering combined with plasma polymerization process

Radiofrequency plasma polymerization in combination with direct current reactive magnetron sputtering is utilized for the synthesis of TiO₂/plasma polymerized aniline nanocomposite thin films. In the composite film, X-ray diffraction measurements reveal formation of nanocrystalline rutile TiO₂ of crystallite size 3.6 nm. Due to continuous bombardment of plasma species during simultaneous magnetron sputtering and plasma polymerization, the precursors of polymerization are broken and few functional groups are retained in the composite film. The plasma polymerized aniline has the direct optical band gap of 3.55 eV and the nanocrystalline rutile TiO₂ is wide gap semiconductor with indirect gap of 3.20 eV which suggests the existence of an energy barrier at the interface in the composite form. The ac conductivity of composite film shows significant improvement as compared to plasma polymerized aniline film and sputtered rutile TiO₂ film. The composite film may find potential application as antistatic coatings.     

Substrate effects on the oxygen gas sensing properties of SnO2/TiO2 thin films

In this study, SnO₂/TiO₂ thin films are fabricated on SiO₂/Si and Corning glass 1737 substrates using a R.F. magnetron sputtering process. The gas sensing properties of these films under an oxygen atmosphere with and without UV irradiation are carefully examined. The surface structure, morphology, optical transmission characteristics, and chemical compositions of the films are analyzed by atomic force microscopy, scanning electron microscopy and PL spectrometry. It is found that the oxygen sensitivity of the films deposited on Corning glass 1737 substrates is significantly lower than that of the films grown on SiO₂/Si substrates. Therefore, the results suggest that SiO₂/Si is an appropriate substrate material for oxygen gas sensors fabricated using thin SnO₂/TiO₂ films.     

Photocatalytic behavior of heavy La-doped TiO2 films deposited by pulsed laser deposition using non-sintered target

We have investigated the control of photocatalytic behavior under deposited conditions of non-sintered target of different molar ratios with TiO₂ and La₂O₃ from 1:0 to 1:2 for heavily La doping, and post-annealing temperature from 600 °C to 1000 °C for crystallizing by pulsed laser deposition. We have successfully crystallized heavily La-doped TiO₂ films with post-annealing temperature over 800 °C and with molar ratio of TiO₂:La₂O₃ over 1:1 on a quartz substrate. Heavily La-doped TiO₂ films are observed the decomposition of methylene blue and a water-splitting reaction in photocatalytic behavior under Xe light irradiation. When stoichiometric La-doped TiO₂ (TiO₂:La₂O₃ = 1: 1) is synthesized with heat-treatment at 900 °C, the best results are obtained under photocatalytic behavior and pure La₂Ti₂O₇ crystalline were obtained.     

Oblique angle deposition of TiO2 thin films prepared by electron-beam evaporation

Optical, structural and photocatalytic properties of TiO₂ thin films obliquely deposited on quartz glass substrate using an electron-beam evaporation method were investigated. The photocatalytic activity of the films was evaluated by photodecomposition of methylene blue. An increase in incident deposition angle increased the porosity and surface roughness of the TiO₂ films. As a result, the photocatalytic activity was enhanced with incident deposition angle up to 60°. However, a further increase in incident deposition angle to 75° reduced the photocatalytic activity due to a lack of the crystalline phase.     

Characteristics of N-doped TiO2 thin films grown on unheated glass substrate by inductively coupled plasma assisted dc reactive magnetron sputtering

N-doped TiO₂ thin films have been deposited on unheated glass substrates by an inductively coupled plasma (ICP) assisted direct current (dc) reactive magnetron sputtering. All films were produced in the metallic mode of sputtering in order to achieve a high deposition rate. The structures and properties of the N-doped TiO₂ films were studied by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, field emission scanning electron microscopy and UV–Vis spectrophotometer. Experimental results show that we can obtain well crystallized N-doped anatase phase TiO₂ thin films at low deposition temperature and at high deposition rate by using the ICP assisted dc reactive magnetron sputtering process. The doping of nitrogen into TiO₂ lattices leads to a smooth shift of the absorption band toward visible light regions.     

Morphology and natural wettability properties of sol-gel derived TiO2-SiO2 composite thin films

Previous studies suggest that granular interfaces induce a natural and persistent super-hydrophilicity in TiO₂-SiO₂ composite thin films deposited by sol-gel route. This effect enables to consider self-cleaning applications that do not require a permanent UV exposure, whereas such a permanent exposure is necessary for pure TiO₂ films. In this study, TiO₂-SiO₂ composite thin films have been deposited from a TiO₂ anatase crystalline suspension and different SiO₂ polymeric sols. Wettability studies show that a suitable control of the TiO₂-SiO₂ mixed sol formulations noticeably enhances persistence of the natural super-hydrophilicity in composite films. It is shown that, beside granular interface effects, modifications in the composite film morphologies can noticeably influence wettability properties.     

A new method to characterizing surface roughness of TiO2 thin films

Titanium dioxide (TiO₂) thin films have been widely coated in the self-cleaning glass for facade application. The benefit of these glasses is its ability to actively decompose organic compounds with the help of ultraviolet light. Understanding the surface roughness of TiO₂ thin films is important before manufacturing of self-cleaning glasses using TiO₂ thin films because surface roughness of TiO₂ thin films has highly significant influence on the photocatalytic performance. Traditional approach for measuring surface roughness of TiO₂ thin films is atomic force microscopy. The disadvantage of this approach include long lead-time and slow measurement speed. To solve this problem, an optical inspection system for rapidly measuring the surface roughness of TiO₂ thin films is developed in this study. It is found that the incident angle of 60° is a good candidate for measuring surface roughness of TiO₂ thin films and y=90.391x+0.5123 is a trend equation for predicting the surface roughness of TiO₂ thin films. Roughness average (Ra) of TiO₂ thin films (y) can be directly determined from the peak power density (x) using the optical inspection system developed. The results were verified by white-light interferometer. The measurement error rate of the optical inspection system developed can be controlled by about 8.8%. The saving in inspection time of the surface roughness of TiO₂ thin films is up to 83%.     

Substrate effects on V2O3 thin films

We apply density functional theory and the augmented spherical wave method to analyze the electronic structure of V₂O₃ in the vicinity of an interface to Al₂O₃. The interface is modeled by a heterostructure setup of alternating vanadate and aluminate slabs. We focus on the possible modifications of the V₂O₃ electronic states in this geometry, induced by the presence of the aluminate layers. In particular, we find that the tendency of the V 3d states to localize is enhanced and may even cause a metal-insulator transition.     

Effects of deposition parameters on laser-induced damage threshold of Ta2O5 films

Ta₂O₅ films were deposited on BK7 substrates by e-beam evaporation with different deposition parameters such as substrate temperature (323-623 K), oxygen pressure (0.5-3.0×10⁻² Pa) and deposition rate (0.2-0.5 nm/s). Absorption, scattering and chemical composition were investigated by surface thermal lensing (STL) technique, total integrated scattering (TIS) measurement and X-ray photoelectron spectroscopy (XPS), respectively. The laser-induced damage threshold (LIDT) was assessed using pulsed Nd:YAG 1064 nm laser at a pulse length of 12 ns. The results showed that optical properties, absorption and LIDT were influenced by the deposition parameters and annealing. However, scattering was little correlated with the deposition parameters. On the whole, the LIDT increased with increasing substrate temperature and oxygen pressure, whereas it increased firstly and then decreased upon increasing deposition rate. After annealing at 673 K for 12 h, the LIDT of films improved significantly. The dependence of possible damage mechanism on deposition parameters was discussed.