Effects of pH and polyethylene glycol on surface morphology of TiO2 thin film

In this investigation, a sol gel procedure for preparation of TiO₂ thin films was developed using polyethylene glycol (PEG). Effect of pH on the structure of the films was also investigated. The morphology and surface structure of the films were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was found that the films from the base sols had a porous structure and the surface was considerably rough. However, the films made by the acid sols were very dense and had a relatively smoother surface. It was also found that by using PEG, the surface area of the film became larger as a result of the increase in the film porosity. BET analysis confirmed the increase in the surface area which enhanced the photocatalytic activity of TiO₂ thin film in degradation of Malachite Oxalate Green.     

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.     

Composite cerium oxide/titanium oxide thin films for corrosion protection of AZ91D magnesium alloy via sol–gel process

Anti‐corrosive composite cerium oxide/titanium oxide (CeO₂/TiO₂) thin films were successfully prepared on an AZ91D magnesium alloy substrate by applying cerium oxide (CeO₂) thin films as the inner layer with a sol–gel process. Composition and surface morphology of the thin films were analyzed using X‐ray diffraction (XRD) and scanning electron microscope (SEM). XRD showed that the composite films consisted of cerianite and anatase phases. The wettability of the thin films was evaluated by water contact angles measurements. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) tests were used to evaluate the corrosion behavior of the bare substrate and coated samples in 3.5 wt% sodium chloride solution (3.5 wt% NaCl). The results demonstrated that titanium oxide (TiO₂) thin film mainly dominated the corrosion resistance of samples and the composite films with excellent hydrophilicity could significantly improve the corrosion resistance of AZ91D magnesium alloy.     

Dehydroxylation action on surface of TiO2 films restrained by nitrogen carrier gas during atomic layer deposition process

A strong influence of nitrogen gas on the content of surface hydroxyl groups of TiO2 films by atomic layer deposition（ALD） was investigated by X-ray photoelectron spectroscopy（XPS）, contact angle measuring system, and UV–Vis spectrophotometer. XPS spectra of O 1s indicate that the content of surface hydroxyl groups is varied when using N2 as carrier gas. The results of water contact angles and optical reflection spectra show that the content variation of surface hydroxyl groups influences the wetting properties and optical reflectivity of TiO2 films. A surface reaction model is suggested to explain the ALD reaction process using N2 as carrier gas.     

Plasma Spray Physical Vapor Deposition of La1−x Sr x Co y Fe1−y O3−δ Thin-Film Oxygen Transport Membrane on Porous Metallic Supports

Plasma spray physical vapor deposition (PS-PVD) is a very promising route to manufacture ceramic coatings, combining the efficiency of thermal spray processes and characteristic features of thin PVD coatings. Recently, this technique has been investigated to effectively deposit dense thin films of perovskites particularly with the composition of La_0.58Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) for application in gas separation membranes. Furthermore, asymmetric type of membranes with porous metallic supports has also attracted research attention due to the advantage of good mechanical properties suitable for use at high temperatures and high permeation rates. In this work, both approaches are combined to manufacture oxygen transport membranes made of gastight LSCF thin film by PS-PVD on porous NiCoCrAlY metallic supports. The deposition of homogenous dense thin film is challenged by the tendency of LSCF to decompose during thermal spray processes, irregular surface profile of the porous metallic substrate and crack and pore-formation in typical ceramic thermal spray coatings. Microstructure formation and coating build-up during PS-PVD as well as the annealing behavior at different temperatures of LSCF thin films were investigated. Finally, measurements of leak rates and oxygen permeation rates at elevated temperatures show promising results for the optimized membranes.     

Friction and wear mechanisms of thermally sprayed ceramic and cermet coatings

The tribological behavior of Al₂O₃/TiO₂ and WC/Co plasma-sprayed coatings was studied under dry sliding conditions. X-ray photoelectron spectroscopic analyses have shown the presence of graphite in WC/17 wt% Co coatings and a thin WO₃ layer in the contact. These phases could explain the improvement in the friction behavior of the cermet/ceramic couples versus the ceramic/ceramic couples.     

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.     

Chemically synthesized hydrous RuO2 thin films for supercapacitor application

The hydrous RuO₂ thin films have been successfully synthesized at low temperature on glass and stainless steel substrates using lucrative chemical bath deposition (CBD) method. Their structural, morphological, optical, electrical and wettability properties were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), UV-vis-NIR spectrophotometer, two point probe method and water contact angle measurement techniques. The results showed that, the CBD method allows to formation of amorphous, porous, superhydrophilic, semiconducting, hydrous RuO₂ thin films with optical band gap of 2.7 eV. The supercapacitive behavior of hydrous RuO₂ in 0.5 M H₂SO₄ electrolyte examined by cyclic voltammetric (CV) measurements showed maximum specific capacitance of 73 F g⁻¹.     

Highly Ordered Good Crystalline ZnO-Doped WO3 Thin Films Suitable for Optoelectronic Applications

Highly ordered ZnO-doped WO₃ thin films with good crystalline quality are prepared using radio frequency magnetron sputtering technique, and its morphological and structural properties are studied using various characterization tools such as field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction technique, micro-Raman spectroscopy, and x-ray photoelectron spectroscopy. Morphological analysis shows a smooth surface for pure film, whereas the ZnO-doped films presents a dense distribution of grains of larger sizes with well-defined grain boundary. X-ray diffraction studies reveal the enhancement of crystalline quality of the films with increase in ZnO doping concentration up to 5 wt.%, beyond which the crystalline quality gets deteriorated. A phase modification from a single monoclinic WO₃ phase to mixed monoclinic WO₃ and W₁₈O₄₉ phases is observed for films with higher ZnO doping concentrations.

     

Microstructure and apatite-forming ability of the MAO-treated porous titanium

Porous titanium was treated by micro-arc oxidation (MAO) in the aqueous electrolytes containing 0.1 and 0.2 M NaOH. The microstructure (including morphology, phase component, element composition and chemical species) and in vitro apatite-forming ability of the oxidized films formed on the inner-pore walls of porous titanium were investigated. It is found that continuous thin films with pore sizes of 20-60 nm are formed in both electrolytes. The films consist of an amorphous TiO₂ outmost layer, a coexisted intermediate layer of amorphous TiO₂ and rutile, and a Ti₂O₃ bottom layer, and tightly bond to the titanium substrate without any cracks. In vitro bioactivity assessment shows that both MAO films possess high apatite-forming abilities. It is also found that, compared with the film formed in the 0.1 M NaOH-containing electrolyte, the film formed in the 0.2 M NaOH-containing electrolyte has a higher roughness and more nanopores which help shorten apatite induction time. It is expected the MAO-formed bioactive porous titanium will not only be beneficial to bone ingrowth into the porous structure, but also be beneficial to achieve a tough chemical bonding at the bone/implant interface.     

Corrosion performance of anodic films containing polyaniline and TiO2 nanoparticles on AA3105 aluminium alloy

The corrosion protection afforded to an AA3105 aluminium alloy supporting an anodic film with incorporated polyaniline and TiO₂ nanoparticles has been examined. The films were synthesised by simultaneous anodizing and electropolymerisation of aniline in the presence of nanoparticles. The morphology and composition of the films were probed by TEM, SEM, rf-GDOES and XPS. The resultant coatings comprised a thin porous anodic film of 2-3 µm thickness, with an outer hybrid polyaniline/TiO₂ layer of several tens nanometres thickness, with the dimensions of TiO₂ nanoparticles being below 10 nm. Electrochemical impedance spectroscopy analysis and salt spray testing revealed that TiO₂ containing films provide improved corrosion protection to the AA3105 aluminium alloy compared with the film without nanoparticles. The improved protection provided by the coatings containing TiO₂ nanoparticles is attributed to the TiO₂ particle-rich thin film layer formed on the outer part of the coating that acts as a blocking barrier layer for the anodic porous aluminium oxide film.     

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.     

The effect of oxygen concentration on the low temperature deposition of TiO2 thin films

The aim of this study was to investigate the influence of oxygen concentration in Ar/O₂ gas mixture on the crystalline properties of TiO₂ thin films obtained at low temperature by reactive magnetron sputtering technique. Mass spectrometry of plasma medium provides, in conjunction with XRD and AFM measurements, a guide for attainment of good quality anatase TiO₂ films.     

Passivation and oxygen ion implantation double surface treatment on porous NiTi shape memory alloys and its Ni suppression performance

The surfaces of porous NiTi shape memory alloys (SMAs) were modified by double treatment of passivation (PA) in HNO₃ solution and oxygen plasma immersion ion implantation (O-PIII) methods. SEM and XPS were used to characterize the modified surface. It has been found that a protective film consists of three layers formed on the surface after modification. From the outmost surface towards inside, they are a 10 nm thick layer consisting of rutile and anatase TiO₂ with pure rutile TiO₂ on the surface and their ratio varying in gradient, a 45 nm thick layer containing anatase TiO₂ and NiTi with constant ratios and a 40 nm thick layer of TiO₂, TiO and NiTi with their ratio varying in gradient. The immersion tests in simulated human body fluid demonstrated that the modified porous NiTi samples exhibit a good Ni suppression performance, approaching to that of the untreated dense NiTi samples. The Ni ion content released from the porous NiTi SMAs double treated by PA and O-PIII is one magnitude lower than that from the untreated porous samples. Moreover, the released Ni ion content after 8 weeks can be reduced into the safe range acceptable to the human body.     

Controlling the particle size of nanobrookite TiO2 thin films

In this study, pure nanobrookite TiO₂ thin films were successfully deposited on glass substrates with the spin-coating method using titanium butoxide and acetic acid. The particle size of TiO₂ films was controlled by the water:AcAc volume ratio. This study shows that it is possible to obtain single oriented pure brookite films. The structural and optical properties of the nanobrookite TiO₂ thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), spectrophotometer (NKD), and Fourier transform infrared spectrometer (FTIR).     

Wettability of pure Ti by molten pure Mg droplets

The wetting behavior of molten pure Mg droplets on pure Ti substrate, a crucial phenomenon in the design of Mg matrix composites reinforced with Ti particles, was investigated by the sessile drop method. The contact angle was measured in high-purity argon (99.999%) at 1073 K. In particular, the effects of two important parameters on the contact angle were evaluated: Mg evaporation during the wetting test; and surface oxide film of the substrate. The calculation method to estimate the modified contact angle involved taking the morphological changes of the droplet outline due to the evaporation into consideration. By changing the thickness of the surface oxide films on the Ti substrate, it was possible to examine the wettability and the chemical reactions at the interface between the solidified Mg drop and the substrate were investigated by scanning electron microscopy–energy dispersive X-ray spectrometry analysis. At the initial wetting stage, a large contact angle with 95–110° was obtained, which depended on the reduction of TiO₂ surface films by Mg droplets. When the molten Mg contacts an area of pure Ti after reduction, the contact angle suddenly decreased. The equilibrium value at the stable state strongly depended on the surface roughness of the Ti plate.     

Effect of annealing and O2 pressure on structural and optical properties of pulsed laser deposited TiO2 thin films

In this paper, effect of annealing and O₂ pressure on the structural and optical properties of pulsed laser deposited thin films of TiO₂ is reported. XRD, FTIR spectra and SEM images confirm that at high annealing temperatures, the rutile phase and crystalline quality of thin films increases. Higher pressure of O₂ during deposition improves the rutile phase and favors the rod like growth of TiO₂ thin film. The red shift in photoluminescence (PL) spectra of TiO₂ thin films with annealing temperature is reported. Contact angle measurement data for the thin films reveals the hydrophobic nature of the films. The very low reflectivity (～10%) reported in this paper may be promising for anti-reflection coating applications of pulsed laser deposited TiO₂ thin films.     

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.     

Wetting characteristics of CaO−SiO2−Al2O3 ternary slag on refractory oxides, Al2O3, SiO2 and TiO2

The wettabilities of the metallurgical slag, CaO−55.2 wt.%SiO₂−15 wt.%Al₂O₃ on refractory oxides, Al₂O₃, SiO₂ and TiO₂ were investigated at temperatures of 1350, 1400 and 1470°C. Contact angle measurements were performed using a combination of the sessile drop method and the X-ray fluoroscopic technique. The contact angle was obtained from the numerical solution of the Young-Laplace equation. The steady contact angles obtained were 31°, 24°, and 15° for SiO₂, Al₂O₃ and TiO₂ at 1470°C, respectively. The spreading rate of the liquid slag was characterized by the formation of cognate interface between the liquid slag and solid oxide, and further enhanced by the formation of a diffuse layer around the slag drop at higher temperatures.     

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.