Preparation of photocatalytic TiO2−SiO2 thin film by sol-gel coating

TiO₂−SiO₂ composite thin films for photocatalysis were fabricated on window glass with sol-gel technology. By measuring the contact angle of the film surface and the degradation of methylene blue, the super-hydrophilicity and photocatalytic activity of the composite thin films were studied. The results indicate that the TiO₂−SiO₂ composite thin film can yield various glass self-cleaning effects with low maintenance expenses.     

Calcination Conditions on the Properties of Porous TiO2 Film

Porous TiO₂ films were deposited on SiO₂ precoated glass-slides by sol-gel method using PEG1000 as template. The strongest XRD diffraction peak at 2θ = 25.3° is attributed to [101] plane of anatase TiO₂ in the film. The increases of calcination temperature and time lead to stronger diffraction peak intensity. High transmittance and blue shift of light absorption edge are the properties of the film prepared at high calcination temperature. The average pore size of the films increases with the increasing calcination temperature as the result of TiO₂ crystalline particles growing up and aggregation, accompanied with higher specific surface area. Photocatalytic activity of porous TiO₂ films increases with the increasing calcination temperature. The light absorption edge of the films slightly moves to longer wavelength region along with the increasing calcination time. The mesoporous film calcinated at 500 °C for 2 h has the highest transmittance, the maximum surface area, and the maximum total pore volume. Consequently, the optimum degradation activity is achieved on the porous TiO₂ film calcinated at 500 °C for 2 h.     

High transmittance and superhydrophilicity of porous TiO2/SiO2 bi-layer films without UV irradiation

In order to obtain the TiO₂ films with high transmittance and superhydrophilicity without UV irradiation, porous TiO₂/SiO₂ bi-layer films were prepared by spin coated SiO₂ sol and TiO₂ sol including polyethylene glycol 2000 (PEG 2000) onto glass and subsequent calcination at 550 °C. Meanwhile, factors that affect the TiO₂/SiO₂ bi-layer films transmittance and superhydrophilicity were investigated in details by observing their surface morphologies and measuring their water contact angles (WCAs), spreading time and transmittances. The results indicated that the as-prepared TiO₂/SiO₂ bi-layer film showed superhydrophilicity without UV irradiation when 0.5 wt.% PEG 2000 was added in TiO₂ sol. At the same time, its maximum transmittance was as high as 92.3%. The spreading time was only about 0.16 s. More importantly, the resultant film had an excellent stability of the superhydrophilic property.     

酸碱复合催化溶胶-凝胶法制备 SiO2减反膜及膜性能研究

采用酸催化法、碱催化法和酸碱复合催化法制备了SiO2溶胶,进而制得SiO2减反膜。表征了薄膜的表面形貌,测定了薄膜的透射率和硬度。结果表明,不同催化溶胶制得的膜层在表面形貌、减反效果和薄膜硬度等方面存在明显差异:酸催化得到的薄膜,孔隙率和透过率最低,但硬度和抗划伤性最好;碱催化得到的薄膜,孔隙率和透过率最高,但硬度和抗划伤性最差;酸碱复合催化得到的薄膜,孔隙率、透过率、硬度和抗划伤性能介于以上二者之间,性能与酸碱复合催化溶胶的制备工艺密切相关。     

The surface morphology and strength properties of SiO2-P2O5-Nd2O3 glassy films

The surface morphology and microstructure of undoped and neodymium-doped silicate-phosphate films, as well as the strength characteristics (Young??s modulus and the hardness) of both the films and the SiO₂-P₂O₅-Nd₂O₃/SLG and SiO₂-P₂O₅/SLG composite structures, have been studied. A specific surface microstructure composed of the basic surface with imbedded round islands with a size of a few microns to a few tens of microns has been identified. The film??s microstructure has been shown to exhibit high stability over time after the long-term resting of these structures. It has been found that the films and the composite structures have fairly high strength properties.     

Synthesis and Characterization of Hydroxyapatite/TiO<Subscript>2</Subscript> Coatings on the β-Type Titanium Alloys with Different Sintering Parameters using Sol-Gel Method

In this study, hydroxyapatite (HA) based composite films were successfully syntheses on the β-type Ti29Nb13Ta4.6Zr (TNTZ). The solutionized TNTZ substrates coated with HA and HA/Titania (TiO₂) bioactive composite coatings by sol-gel method under various sintering parameters related to sintering temperatures and heating ramp rates. Microstructural observations of the coatings revealed that apatite was formed on the substrates. The hardness values of the coatings increase with increasing both the sintering temperature and the TiO₂ concentration in the coatings layer. However, it was found that the heating ramp rate of the sintering was not affecting the hardness values so much. Also, the hardness values of the HA/TiO₂ composite coatings at all sintering temperatures were higher than only HA coated TNTZ samples due to the existence TiO₂ phases in the HA matrix. Results indicating that the doping of HA with TiO₂, improve the physical consistency between the coating layer and the substrates and provide a better inter-particle bonding due to the existence TiO₂ phases in the HA.     

Enhanced properties of nanostructured TiO<Subscript>2</Subscript>-graphene composites by rapid sintering

Despite of many attractive properties of TiO₂, the drawback of TiO₂ ceramic is low fracture toughness for widely industrial application. The method to improve the fracture toughness and hardness has been reported by addition of reinforcing phase to fabricate a nanostructured composite. In this regard, graphene has been evaluated as an ideal second phase in ceramics. Nearly full density of nanostructured TiO₂-graphene composite was achieved within one min using pulsed current activated sintering. The effect of graphene on microstructure, fracture toughness and hardness of TiO₂-graphene composite was evaluated using Vickers hardness tester and field emission scanning electron microscopy. The grain size of TiO₂ in the TiO₂-x vol% (x = 0, 1, 3, and 5) graphene composite was greatly reduced with increase in addition of graphene. Both hardness and fracture toughness of TiO₂-graphene composites simultaneously increased in the addition of graphene.     

Thermal treatment effect on structure, electrical conductivity and transient photoconductivity behavior of thiourea modified TiO2 sol-gel thin films

Thiourea modified nanocrystalline titanium dioxide (TiO₂) thin films were prepared by sol-gel route and were thermally treated at five different temperatures (400, 500, 600, 800 and 1000 °C). The films were studied using GIXRD, PIGE and UV-vis spectroscopy. It was observed that the anatase to rutile phase transformation of TiO₂ was inhibited by the thiourea modification. The transmittance of the modified films appeared reduced which was attributed both to the modification of TiO₂ with thiourea and the light scattering in the films. The dark conductivity and the transient photoconductivity of the modified TiO₂ sol-gel thin films were studied in vacuum and in air. The environment does not influence significantly the dark conductivity, because of the almost equivalent competition between oxygen and water adsorption. The photoconductivity reaches high values for all samples in both environments, with the sample treated at 500 °C to present the highest value. The larger values in vacuum can be attributed to the reduced amount of adsorbed oxygen at the surface, which acts as electron scavenger.     

Effects of defects generated in ALD TiO<Subscript>2</Subscript> films on electrical properties and interfacial reaction in TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>/Si system upon annealing in vacuum

Thin TiO₂ layers grown at 130°C on SiO₂-coated Si substrates by atomic layer deposition (ALD) using TTIP and H₂O as precursors were annealed, and the effects of the annealing temperature on the resulting electrical properties of TiO₂ and the interface properties between a Pt electrode and TiO₂ were examined using transmission line model (TLM) structures. The as-deposited TiO₂ thin film had an amorphous structure with OH groups and a high resistivity of 6×10³Ω-cm. Vacuum annealing at 700 °C transformed the amorphous film into an anatase structure and reduced its resistivity to 0.04Ω-cm. In addition, the vacuum-annealing of the TiO₂/SiO₂ structure at 700°C produced free silicon at the TiO₂-SiO₂ interface as a result of the reaction between the Ti interstitials and SiO₂. The SiO₂ formed on the TiO₂ surface caused a Schottky contact, which was characterized by the TLM method. The use of the TLM method enabled the accurate measurement of the resistivity of the vacuum-annealed TiO₂ films and the characterization of the Schottky contacts of the metal electrode to the TiO₂.     

Preparation and oxygen-sensing properties of TiO2 porous thin films on alumina substrate

The titanium dioxide sols were synthesized with tetrabutyl titanate as precursor, diethanolamine（DEA） as complexing agent , polyethylene glycol （PEG） as organic template. The porous films were prepared by sol-gel method, The structures and morphology of the titanium dioxide porous films were characterized by FE-SEM. The formation mechanism of TiO2 porous films and the relation between the porous structure and oxygen-sensing properties of TiO2 films were studied. Ordered structure was formed by assembling between TiO2 colloid particles and the template molecules. PEG molecules acted on TiO2 colloid particles by hydrogen bond and bridge oxygen. The porous structure was formed after the organic template was decomposed when calcining the films. The diameter, amount and distribution of the pores in the films are related with the content of PEG. The pore diameter increases with increasing of content of PEG and the pore density reaches the maximum at certain content. Oxygen-sensitivity and response speed of porous TiO2 films are improved compared with films without pores. Both the sensitivity and response speed increase with the increasing of pore diameter and pore density. Oxygen-sensitivity reaches 3 order of magnitude at 800 ℃. Its response time from H2/N2 to O2/N2 atmosphere and vice versa is about 0.11 s and 0.12 s respectively. Although the sensitivity and response speed increase, the resistance-temperature properties of porous films are not notably improved with the increasing of the content of PEG.     

Effects of SiO<Subscript>2</Subscript> and TiO<Subscript>2</Subscript> on resistance stabilities of flexible indium-tin-oxide films prepared by ion assisted deposition

Inorganic buffer layers such as SiO₂ or TiO₂ and transparent conductive indium-tin-oxide (ITO) films were prepared on polyethylene terephthalate (PET) substrates by ion assisted deposition (IAD) at room temperature, and the effects of SiO₂ and TiO₂ on the bending resistance performance of flexible ITO films were investigated. The results show that ITO films with SiO₂ or TiO₂ buffer layer have better resistance stabilities compared to ones without the buffer layer when the ITO films are inwards bent at a bending radius more than 1.2 cm and when the ITO films are outwards bent at a bending radius from 0.8 cm to 1.2 cm. ITO films with SiO₂ buffer layer have better resistance stabilities compared to ones with TiO₂ buffer layer after the ITO films are bent several hundreds of cycles at the same bending radius, for the adhesion of SiO₂ is stronger than that of TiO₂. The compressive stress resulted from inward bending leads to the formation of more defects in the ITO films compared with the tensile stress arising from outward bending. SiO₂ and TiO₂ buffer layers can effectively improve the crystallinity of ITO films in (400), (440) directions.     

Magnetoelectric CoFe2O4/Pb(Zr0.53Ti0.47)O3 composite thin films of 2-2 type structure derived by a sol-gel process

CoFe₂O₄/Pb(Zr_0.53Ti_0.47)O₃ (CFO/PZT) magnetoelectric composite thin films of 2-2 type structure have been prepared onto Pt/Ti/SiO₂/Si substrate by a sol-gel process and spin coating technique. The optimal annealing process of composite thin films was determined by using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It is found that the amount of the citric acid and concentration of CFO starting precursor solution have great impact on morphologies of composite thin films. Subsequent scanning electron microscopy (SEM) investigations show that the prepared thin films exhibit good morphologies and compact structure, and cross-sectional micrographs clearly display a multilayered nanostructure of multilayered thin films. The purpose of this work is to determine the optimal annealing processes of composite thin films and to prepare magnetoelectric composite thin films with good microstructure. It is shown that the films exhibit both good magnetic and ferroelectric properties, as well as a magnetoelectric effect.     

Mutifunctional arc ion plated TiO2 photocatalytic coatings with improved wear and corrosion protection

An arc ion plating (AIP) system was used to deposit anatase TiO₂ thin films with photocatalytic and antimicrobial properties. This study aims to evaluate the properties and performance of such films, including surface hardness, adhesion, abrasive wear resistance and corrosion protection. The experimental results show that film hardness and scratch adhesion reach maximum values of 679.6 HV and 21.2 N, respectively. Film quality is strongly influenced by the degree of crystallinity, which is in turn affected by both deposition time and oxygen partial pressure. The wear resistance of the TiO₂ coatings can be closely correlated to the film adhesion, however all films impart significantly higher resistance to abrasive wear than that of the uncoated surface. On the other hand, TiO₂ coatings on stainless steel give rise to an increased (less negative) corrosion potential and decreased corrosion current in a sodium chloride solution. Overall, AIP-TiO₂ film can however provide satisfactory protection for stainless steel.     

O2 plasma treatment of mesoporous and compact TiO2 photovoltaic films: Revealing and eliminating effects of Si incorporation

Radio frequency (13.56 MHz) O₂ plasmas were used to modify the surface of mesoporous and compact TiO₂ films. The effects of substrate location in the plasma, applied rf power, and plasma mode (pulsed or continuous wave) were explored. X-ray photoelectron spectroscopy, contact angle measurements, and scanning electron microscopy were used to characterize changes to the TiO₂ films. For mesoporous materials, O₂ plasma treatment was found to increase oxygen content in the films, but Si content increased with applied rf power as a result of sputtering and redeposition of Si species from the reactor walls. XPS depth profiling using ion sputtering as well as O₂ plasma treatment of dyed materials revealed that Si was deposited throughout the mesoporous network, not as a surface SiO₂ layer. Pulsing the plasma with pulse duty cycles < 40% resulted in the elimination of Si and a reduction of damage in the modified films.     

Fabrication of patterned TiO2 thin film by a wet process

Hydrophobic/hydrophilic patterned TiO₂ thin film was successfully fabricated on a glass substrate by a wet process. A micro-nano complex structure with a high roughness was fabricated by a layer-by-layer selfassembly and liquid phase deposition (LPD) method. To fabricate superhydrophobic TiO₂ thin films, TiO₂ nanoparticles were deposited on the surface of (PAH/PAA) thin film by a LPD method and the surface of TiO₂ was modified by a hydrophobic treatment using fluoroalkyltrimethoxysilane. The RMS roughness and water contact angle of the prepared TiO₂ thin film were ca. 65.6 nm and ca. 155°. The superhydrophobic surface exposed to UV light changed to a hydrophilic surface by the photocatalytic property of TiO₂ to decompose a hydrophobic group. Finally, hydrophobic/hydrophilic patterned TiO₂ thin film with a 300 ??m dot size was fabricated. The surface morphology, transmittance, surface roughness and water contact angle of the prepared thin films were measured by a field emission scanning electron microscope, an atomic force microscope, a UV-Vis spectrophotometer and a contact angle meter.     

Microstructure and optical properties of TiO2 thin films deposited at different oxygen flow rates

To research the influence of oxygen flow rate on the structural and optical properties of TiO₂ thin film, TiO₂ films on glass were deposited by reactive magnetron sputtering. The microstructure and optical properties were measured by X-ray diffractometry, AFM and UV-VIS transmittance spectroscopy, respectively. The results show that the films deposited at oxygen flow rate of 10 mL/min has the lowest roughness and the highest transmittance. The absorption angle shifts to longer wavelengths as oxygen flow rates increase from 5 to 10 mL/min, then to shorter ones as the oxygen flow rate increase from 10 to 30 mL/min. The band gap is 3.38 eV, which is nearly constant in the experiment. For the TiO₂ thin films deposited at 10 mL/min of oxyge flow rate, there are nano-crystalline structures, which are suitable for anti-reflection (AR) coating in the solar cells structure system.     

Microstructures of SiO2 and TiOX films deposited by atmospheric pressure inductively coupled micro-plasma jet

Atmospheric-pressure inductively coupled micro-plasma jet was used for deposition of SiO₂ and TiO_x thin films. Si and Ti alkoxides respectively were vaporized into Ar gas to be decomposed thermally in the Ar plasma jet, being deposited as the metal oxide films. Microstructures of the films were investigated as changing the plasma conditions such as Ar gas flow rate and concentration of the alkoxides in Ar gas. The SiO₂ and TiO_x films deposited at higher Ar gas flow rates were composed of particles of micron or submicron sizes. The SiO₂ film was composed of a single layer of the particles and the particles sometimes formed unique aggregation structures. On the other hand, the TiO_x film had a structure in which the particles were piled up randomly. The structures suggested that the SiO₂ particles grew on the substrate whereas TiO_x particles were formed in plasma gas phase.     

Capacitance performance enhancement of TiO<Subscript>2</Subscript> doped with Ni and graphite

Nano-amorphous TiO₂ was prepared by a sol-gel method. The results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the composite electrode material (TiO₂-NiO-C) is made of powder with a grain size of 36.2 nm. Doping of nickel and graphite can increase the electrical conductivity and the specific surface area of nano-amorphous TiO₂. The electrochemical properties of TiO₂-NiO-C, such as self-discharge, leakage current, and cycle life, were studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge-discharge test. With a charge-discharge current density of 500 mA/g, the specific capacity of the TiO₂-NiO-C composite material reaches 12.88 mAh/g. Also, the expense of capacity is only 3.88% after 500 cycles. The electrochemical capacitor with the electrode material of TiO₂-NiO-C shows excellent capacity and cycling performance.     

Preparation and dielectric properties of compositionally graded （Ba, Sr）TiO3 thin film by sol-gel technique

Compositional graded BaxSr1-xTiO3 （x=0.6, 0.7, 0.8, 0.9, 1.0） （BST） thin films （less than 400 nm） were fabricated on Si and Pt/Ti/SiO2/Si substrates by sol-gel technique. A special heating treatment was employed to form the uniform composition gradients at 700 ℃. The microstructures of the films were studied by means of X-ray diffraction, atomic force microscope and field emission scanning electron microscopy. The results show that the films have uniform and crack-free surface morphology with perovskite structure phase. The small signal dielectric constant （εr） and dielectric loss （tanδ） are found to be 335 and 0.045 at room temperature and 200 kHz. The dielectric properties change significantly with applied dc bias, and the graded thin film show high tunability of 42.3% at an applied field of 250 kV/cm. All the results indicate that the graded BST thin films prepared by sol-gel technique have a promising candidate for microelectronic device.     

Plasma pre-treatment and TiO2 coating of PMMA for the improvement of antibacterial properties

The antibacterial properties of polymethyl methacrylate (PMMA) are enhanced by coating with TiO₂ films. The transparent TiO₂ films on plasma-treated PMMA are prepared by sol-gel dip coating. The modified surfaces are characterized by XRD, AFM, ATR-FTIR, SEM, UV-vis spectroscopy, and contact angle measurements. Finally, the antibacterial properties are evaluated using the method of plate-counting of Staphylococcus aureus (gram positive) and Escherichia coli (gram negative). It is found that the anatase-TiO₂ film is well-conglutinated on PMMA surface with an average crystallite size of ca. 4 nm. The as-prepared TiO₂/PMMA exhibits excellent photoinduced antibacterial effect for the sterilization of bacteria under indoor natural light, and about 100% of both bacteria are inactivated within 2 h illumation. Compared to PMMA without any treatment, the superior anti-adhesion capability of the TiO₂/PMMA surface is also demonstrated.