The gas sensitivity of nano TiO2-SnO2 film doped with Cd(II) ion

The nanocomposite oxide (0.2TiO₂-0.8SnO₂) doped with Cd²⁺ powder have been prepared and characterized by XRD and their gas-sensing sensitivity were characterized using gas sensing measurement. Experimental results show that, bicomponent nano anatase TiO₂ and rutile SnO₂ particulate thick film doped with Cd²⁺ behaves with good sensitivity to formaldehyde gas of 200 ppm in the air, and the optimum sensing temperature was reduced from 360 °C to 320 °C compared with the undoped Cd²⁺ thick film. The gas sensing thick films doped with Cd²⁺ also show good selectivity to formaldehyde among benzene, toluene, xylene and ammonia as disturbed gas and could be effectively used as an indoor formaldehyde sensor.     

Fast response detection of H2S by CuO-doped SnO2 films prepared by electrodeposition and oxidization at low temperature

Fast response detection of H₂S by CuO-doped SnO₂ films prepared was prepared by a simple two-step process: electrodeposition from aqueous solutions of SnCl₂ and CuCl₂, and oxidization at 600 °C. The phase constitution and morphology of the CuO-doped SnO₂ films were characterized by X-ray diffraction and scanning electron microscopy. In all cases, a polycrystalline porous film of SnO₂ was the product, with the CuO deposited on the individual SnO₂ particles. Two types of CuO-doped SnO₂ films with different microstructures were obtained via control of oxidation time: nanosized CuO dotted island doped SnO₂ and ultra-uniform, porous, and thin CuO film coated SnO₂. The sensor response of the CuO doped SnO₂ films to H₂S gas at 50–300 ppm was investigated within the temperature range of 25–125 °C. Both of the CuO-doped SnO₂ films show fast response and recovery properties. The response time of the ultra-uniform, porous, and thin CuO coated SnO₂ to H₂S gas at 50 ppm was 34 s at 100 °C, and its corresponding recovery time was about 1/3 of the response time.     

Synthesis and characterization of beta barium borate thin films obtained from the BaO-B2O3-TiO2 ternary system

This work reports on the synthesis and the structural and optical characterization of beta barium borate (β-BBO) thin films containing 4, 8 and 16 mol% of titanium oxide (TiO₂) deposited on fused silica and silicon (0 0 1) substrates using the polymeric precursor method. The thin films were characterized by X-ray diffraction, Raman spectroscopy, atomic force microscopy and scanning electron microscopy techniques. The optical transmission spectra of the thin films were measured over a wavelength range of 800-200 nm. A decrease was observed in the band gap energy as the TiO₂ content was raised to 16 mol%. Only the β-BBO phase with a preferential orientation in the (0 0 l) direction was obtained in the sample containing 4 mol% of TiO₂ and crystallized at 650 °C for 2 h.     

Structural, thermal and optical characterization of TiO2:ZrO2 thin films prepared by sol-gel method

We have studied the structural and optical properties of thin films of TiO₂, doped with 5% ZrO₂ and deposited on glass substrate (by the sol-gel method). The dip-coated thin films have been examined at different annealing temperatures (350 to 450 °C) and for various layer thicknesses (63-286 nm). Refractive index and porosity were calculated from the measured transmittance spectrum. The values of the index of refraction are in the range of 1.62-2.29 and the porosity is in the range of 0.21-0.70. The coefficient of transmission varies from 50 to 90%. In the case of the powder of TiO₂, doped with 5% ZrO₂, and aged for 3 months in ambient temperature, we have noticed the formation of the anatase phase (tetragonal structure with 14.8 nm grains). However, the undoped TiO₂ exhibits an amorphous phase. After heat treatments of thin films, titanium oxide starts to crystallize at the annealing temperature 350 °C. The obtained structures are anatase and brookite. The calculated grain size, depending on the annealing temperature and the layer thickness, is in the range (8.58-20.56 nm).     

Nanostructured leaf like hydroxyapatite/TiO2 composite coatings by simple sol-gel method

We demonstrate an approach for the coating of nanostructured leaf like hydroxyapatite (HAp)/TiO₂ composite on glass substrate by sol-gel dip coating process. HAp/TiO₂ nanocomposite thin film was obtained by controlling the dipping rate and the dipping cycle. It was observed from Scanning Electron Microscope that leaf like nanostructured film was deposited on the glass substrate. However, the structure of the film was changed with the dipping cycle and dipping rate. Transmission Electron Microscopic analysis further confirms the morphology of the nanostructured coatings. The presence of Ti, O, Ca and P was detected by Energy Dispersive X-ray Analysis. We further confirmed the composite by X-ray diffraction analysis. Atomic Force Microscope analysis indicates that the films are composed of nanoparticles ranging from 100 to 200 nm and the films were observed to present well-defined grain boundaries. It has been shown that nanocomposite coatings are dependent on the sol concentration, dipping parameters, and the composition of HAp and TiO₂.     

Photocatalytic properties of porous TiO2/Ag thin films

In this study, nanocrystalline TiO₂/Ag composite thin films were prepared by a sol-gel spin-coating technique. By introducing polystyrene (PS) spheres into the precursor solution, porous TiO₂/Ag thin films were prepared after calcination at a temperature of 500 °C for 4 h. Three different sizes (50, 200, and 400 nm) of PS spheres were used to prepare porous TiO₂ films. The as-prepared TiO₂ and TiO₂/Ag thin films were characterized by X-ray diffractometry (XRD) and by scanning electron microscopy to reveal structural and morphological differences. In addition, the photocatalytic properties of these films were investigated by degrading methylene blue under UV irradiation.When PS spheres of different sizes were introduced after calcination, the as-prepared TiO₂ films exhibited different porous structures. XRD results showed that all TiO₂/Ag films exhibited a major anatase phase. The photodegradation of porous TiO₂ thin films prepared with 200 nm PS spheres and doped with 1 mol% Ag exhibited the best photocatalytic efficiency where ∼ 100% methylene blue was decomposed within 8 h under UV exposure.     

One-pot synthesis of intestine-like SnO2/TiO2 hollow nanostructures

In the present study the intestine-like binary SnO₂/TiO₂ hollow nanostructures are one-pot synthesized in aqueous phase at room temperature via a colloid seeded deposition process in which the intestine-like hollow SnO₂ spheres and Ti(SO₄)₂ are used as colloid seeds and Ti-source, respectively. The novel core (SnO₂ hollow sphere)-shell (TiO₂) nanostructures possess a large surface area of 122 m²/g (calcined at 350 °C) and a high exposure of TiO₂ surface. The structural change of TiO₂ shell at different temperatures was investigated by means of X-ray diffraction and Raman spectroscopy. It was observed that the rutile TiO₂ could form even at room temperature due to the presence of SnO₂ core and the unique core-shell interaction.     

In-situ preparation of TiO2/SnO2 nanocrystalline sol for photocatalysis

A novel preparation method to synthesize TiO₂/SnO₂ nanocrystalline sol under mild conditions was presented. Ti(OC₄H₉)₄ used as a precursor was hydrolyzed in the rutile SnO₂ nanocrystalline sol, and in-situ formed TiO₂/SnO₂ nanocrystalline sol. The crystal structure, morphology and photocatalysis performance of samples were investigated. The results show that the additional rutile SnO₂ nano grains serve as heterogeneous crystal nucleus and exhibite the inducing effect on TiO₂ grains growth, thus leading to the changes in crystalline phase and particle morphology. In addition, the photoluminescence (PL) spectra analysis indicates that TiO₂/SnO₂ composite structure induces a better charge separation, and thus the photocatalytic activity of TiO₂/SnO₂ sol is increased significantly compared with TiO₂ sol.     

Photocatalytic properties of Au/TiO2 thin films prepared by RF magnetron co-sputtering

Au/TiO₂ thin films with various Au doping contents were deposited on quartz substrates by radio frequency (RF) magnetron co-sputtering. The as-deposited Au/TiO₂ films were characterized by energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), XRD, and UV-vis techniques. Au doping and UV treatment enhanced the photocatalytic efficiency of TiO₂ thin films. The optimal RF power of the Au target and UV treatment time were 5 W and 1 h, respectively. The enhanced photoactivity of Au(5 W)/TiO₂ thin films with UV treatment is found to result from the increased hydroxyl concentration.     

Preparation and super-hydrophilic properties of TiO2/SnO2 composite thin films

SnO₂-TiO₂ composite thin films were fabricated on soda-lime glass with sol-gel technology. By measuring the contact angle of the film surface and the degradation of methyl orange, we studied the influence of SnO₂ doping concentration, heat-treatment temperature and film thickness on the super-hydrophilicity and photocatalytic activity of the composite films. The results indicate that the doping of SnO₂ into TiO₂ can improve their hydrophilicity and photocatalytic activity, and the composite film with 1-5 mol% SnO₂ and heat-treated at 450°C is of super-hydrophilicity. The optimal SnO₂ concentration for the photocatalytic activity is 10 mol% and larger film thickness is helpful to reduce the contact angle of the composite films.     

Phase transformation in semi-transparent TiO2 films irradiated with CO2 laser

Anatase (TiO₂) thin films were obtained by immersion of glass plates into a titanium sol-gel precursor followed by calcination at 450 °C for 3 h. The Raman results for the CO₂ laser irradiated TiO₂ films show that laser radiation is able to promote favorable changes of anatase phase in anatase/rutile mixtures. Nevertheless, the transformation process level depends on laser characteristics and scan speed of the radiation treatment.     

Preparation and properties of Ti/SnO2-Sb2O5 electrodes by electrodeposition

Sb and Sn coatings were deposited on Ti substrate by the method of cathode deposition, and the Ti/SnO₂-Sb₂O₅ electrodes were obtained by annealing at different temperatures for 3 h. Ti/SnO₂-Sb₂O₅ coating was characterized using technique such as X-ray diffraction (XRD), and scanning electron microscopy (SEM). Ti/SnO₂-Sb₂O₅ electrode calcined at 550 °C exhibits the best catalytic capacity. Ti/SnO₂-Sb₂O₅ electrode obtained by electrodeposition had longer service life and faster degradation capacity compared with that obtained by dip-coating. Accelerated service life tests were carried out in 0.5 mol L^− 1 H₂SO₄ solution with the current density of 100 mA cm^− 2. Service life of Ti/SnO₂-Sb₂O₅ electrode prepared in present study was 15 h, and it was only 0.14 h for Ti/SnO₂-Sb₂O₅ electrode obtained by dip-coating.     

Effects of post-deposition surface treatment on the optical, structural and hydrogen sensing properties of TiO2 thin films

TiO₂ thin films were prepared by DC reactive magnetron sputtering in a mixture of oxygen and argon on glass and oxidized silicon substrates. The effect of post-deposition annealing (300 °C, 500 °C and 700 °C for 8 h in air) on the structural and morphological properties of TiO₂ thin films is presented. In addition, the effect of Pt surface modification (1, 3 and 5 nm) on hydrogen sensing was studied. XRD patterns have shown that in the range of annealing temperatures from 300 °C to 500 °C crystallization starts and the thin film structure changes from amorphous to polycrystalline (anatase phase). In the case of samples on glass substrate, optical transmittance spectra were recorded. TiO₂ thin films were tested as sensors of hydrogen at concentrations 10,000-1000 ppm and operating temperatures within the 180-200 °C range. The samples with 1 nm and in particular with 3 nm of Pt on the surface responded to hydrogen fast and with high sensitivity.     

Gas sensing mechanism of TiO2-based thin films

Two classes of thin film gas sensors have been studied: TiO₂ doped with Cr or Nb and TiO₂-SnO₂ mixed systems. Thin films have been prepared by the reactive sputtering from mosaic targets. It is demonstrated that titanium dioxide doped with Nb and Cr should be considered as a bulk sensor. Its performance is governed by the diffusion of point defects, i.e. very slow diffusion of Ti vacancies for TiO₂: 9.5 at% of Nb and fast diffusion of oxygen vacancies in the case of TiO₂: 2.5 at% Cr sensor. The corresponding response times are 55 min for TiO₂: 9.5 at% of Nb and 20 s for TiO₂: 2.5 at% Cr. In turn, sensors based on TiO₂-SnO₂, particularly those of the SnO₂-rich composition, belong to the group of surface sensors.     

Optical properties of TiO2 thin films after Ag ion implantation

Metal plasma ion implantation has being successfully developed for improving the electronic and optical properties of semiconductor materials. Prior to deposition, a TiO₂ colloidal suspension was synthesized by microwave-induced thermal hydrolysis of the titanium tetrachloride aqueous solution. The TiO₂ thin film was optimized to obtain a high-purity crystalline anatase phase by calcinations at 550 °C. The TiO₂ coating was uniform without aggregation, which provided good photo conversion efficiency. Ag ion implantation into the as-calcined TiO₂ thin films was conducted with 1 × 10¹⁵ ~ 1 × 10¹⁶ ions/cm² at 40 keV. The peak position and intensity of the photoluminescence and UV-Vis absorption spectra are quite sensitive to Ag doping. The optical characterization showed a shift in optical absorption wavelength towards infrared ray side, which was correlated with the structure variation of the Ag⁺ implanted TiO₂. Due to the strong capability of forming compounds between the energetic silver ions and TiO₂, the photoluminescence emission and UV-Vis absorption efficiencies were improved.     

Synthesis of SnO2/Pd composite films by PVD route for a liquid petroleum gas sensor

Synthesis of SnO₂/Pd composite films was carried out by depositing antimony doped SnO₂ films by magnetron sputtering technique and evaporating a thin layer of palladium on the top of it. This bi-layer structure was subjected to rapid thermal annealing for the incorporation of Pd in SnO₂. The films thus obtained were characterized by measuring electrical, optical and microstructural properties. Liquid petroleum gas-sensing properties were also investigated.     

Influence of annealing treatments for ZnO-doped Zr0.8Sn0.2TiO4 thin films by RF magnetron sputtering

Zirconium tin titanium oxide doped 1 wt.% ZnO thin films on n-type Si substrate were deposited by rf magnetron sputtering at a fixed rf power of 300 W, a substrate temperature of 450 °C, a deposition pressure of 5 mTorr and an Ar/O₂ ratio of 100/0 with various annealing temperatures and annealing times. Electrical properties and microstructures of 1 wt.% ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films prepared by rf magnetron sputtering on n-type Si(100) substrates at different annealing temperatures (500 °C-700 °C) and annealing times (2 h-6 h) have been investigated. The structural and morphological characteristics analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM) were sensitive to the treatment conditions such as annealing temperature and annealing time. At an annealing temperature of 600 °C and an annealing time of 6 h, the ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films possess a dielectric constant of 46 (at f = 10 MHz), a dissipation factor of 0.059 (at f = 10 MHz), and a low leakage current density of 3.8 × 10^− 9 A/cm² at an electrical field of 1 kV/cm.     

Fabrication of highly conductive Ta-doped SnO2 polycrystalline films on glass using seed-layer technique by pulse laser deposition

We discuss the fabrication of highly conductive Ta-doped SnO₂ (Sn_1 − xTa_xO₂; TTO) thin films on glass by pulse laser deposition. On the basis of the comparison of X-ray diffraction patterns and resistivity (ρ) values between epitaxial films and polycrystalline films deposited on bare glass, we proposed the use of seed-layers for improving the conductivity of the TTO polycrystalline films. We investigated the use of rutile TiO₂ and NbO₂ as seed-layers; these are isostructural materials of SnO_2, which are expected to promote epitaxial-like growth of the TTO films. The films prepared on the 10-nm-thick seed-layers exhibited preferential growth of the TTO (110) plane. The TTO film with x = 0.05 on rutile TiO₂ exhibited ρ  = 3.5 × 10^− 4 Ω cm, which is similar to those of the epitaxial films grown on Al₂O₃ (0001).     

Spray-pyrolysis Cd2SnO4 films for electrochemical applications

Conductive cadmium stannate (Cd₂SnO₄,) films were grown by a simple spray-pyrolysis technique using aerosols ultrasonically generated from solutions containing Cd(thd)₂(TMEDA) and ⁿBu₂Sn(AcAc)₂, and monoglyme as solvent (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate, TMEDA = N,N,N′,N′-tetramethylethylenediamine, AcAc = acethylacetonate). The overall film growing procedure was carried out at or below 400 °C thus allowing low-melting temperature materials like glass to be used as film substrates. Typical resistivity values of Cd₂SnO₄ films were found to be ∼ 2 · 10 ⁻³ Ωcm. The films exhibit excellent electrochemical activity with comparable or higher electron transfer rates than cadmium stannate films obtained via sol-gel methods at high annealing temperature.     

Tribological behaviour of MoS2/Au coatings

This study aims to enhance the endurance of MoS₂ coating by applying a thin layer of Au (∼ 80 nm) on MoS₂ surface. Experimental results show that the addition of Au film increases the endurance of MoS₂/Au over equivalent coatings without Au. The friction coefficient rapidly decreases to a stable value (μ ∼ 0.045) after about 100 cycles sliding. After more than 15,000 cycles, the friction coefficient gradually increased to a second stable value (μ ∼ 0.15). An average endurance of over 50,000 cycles was measured in this case. The Au or Au-MoS₂ composite layer can effectively prevent oxygen or moisture reaction with MoS₂ and hence significantly increases the wear life.