Fabrication Of TiO2 Films Research Articles

Effect of TiO2 Film Thickness on the Stability of Au9 Clusters with a CrOx Layer.

Radio frequency (RF) magnetron sputtering allows the fabrication of TiO2 films with high purity, reliable control of film thickness, and uniform morphology. In the present study, the change in surface roughness upon heating two different thicknesses of RF sputter-deposited TiO2 films was investigated. As a measure of the process of the change in surface morphology, chemically -synthesised phosphine-protected Au9 clusters covered by a photodeposited CrOx layer were used as a probe. Subsequent to the deposition of the Au9 clusters and the CrOx layer, samples were heated to 200 ℃ to remove the triphenylphosphine ligands from the Au9 cluster. After heating, the thick TiO2 film was found to be mobile, in contrast to the thin TiO2 film. The influence of the mobility of the TiO2 films on the Au9 clusters was investigated with X-ray photoelectron spectroscopy. It was found that the high mobility of the thick TiO2 film after heating leads to a significant agglomeration of the Au9 clusters, even when protected by the CrOx layer. The thin TiO2 film has a much lower mobility when being heated, resulting in only minor agglomeration of the Au9 clusters covered with the CrOx layer.

Controlling microstructure and electrochemical performance of TiO2 film by defect engineering

TiO2 film structure has a significant impact on its electrochemical performance. Improving the film structure has become an important means to promote the electrochemical performance of TiO2. Growth of high quality TiO2 film is extremely important for corrosion resistance or optoelectronics applications; however, it is considerable challenging using conventional methods. Herein, we report on a novel control method based on the defect engineering. The results show that the defect concentration is controlled by adjusting the mechanical activation time with tunable film thickness from 155 nm to 998 nm. Moreover, the pure titanium with high activity anodized display the best high crystallinity and corrosion resistance probably due to the Gibbs free energy educed by mechanical activation, which increased the defect concentration and reaction rate constant, and promoted the transition of unstable Ti3+ and Ti2+ to stable Ti4+. Our findings provide an effective method for the fabrication of TiO2 films, which can pave the way to further provide theoretical support for surface interfacial reactions.

Semi-automatic spray pyrolysis deposition of thin, transparent, titania films as blocking layers for dye-sensitized and perovskite solar cells.

For proper function of the negative electrode of dye-sensitized and perovskite solar cells, the deposition of a nonporous blocking film is required on the surface of F-doped SnO2 (FTO) glass substrates. Such a blocking film can minimise undesirable parasitic processes, for example, the back reaction of photoinjected electrons with the oxidized form of the redox mediator or with the hole-transporting medium can be avoided. In the present work, thin, transparent, blocking TiO2 films are prepared by semi-automatic spray pyrolysis of precursors consisting of titanium diisopropoxide bis(acetylacetonate) as the main component. The variation in the layer thickness of the sprayed films is achieved by varying the number of spray cycles. The parameters investigated in this work were deposition temperature (150, 300 and 450 °C), number of spray cycles (20–200), precursor composition (with/without deliberately added acetylacetone), concentration (0.05 and 0.2 M) and subsequent post-calcination at 500 °C. The photo-electrochemical properties were evaluated in aqueous electrolyte solution under UV irradiation. The blocking properties were tested by cyclic voltammetry with a model redox probe with a simple one-electron-transfer reaction. Semi-automatic spraying resulted in the formation of transparent, homogeneous, TiO2 films, and the technique allows for easy upscaling to large electrode areas. The deposition temperature of 450 °C was necessary for the fabrication of highly photoactive TiO2 films. The blocking properties of the as-deposited TiO2 films (at 450 °C) were impaired by post-calcination at 500 °C, but this problem could be addressed by increasing the number of spray cycles. The modification of the precursor by adding acetylacetone resulted in the fabrication of TiO2 films exhibiting perfect blocking properties that were not influenced by post-calcination. These results will surely find use in the fabrication of large-scale dye-sensitized and perovskite solar cells.

Low-temperature fabrication of TiO2 film on flexible substrate by atmospheric roll-to-roll CVD

Titanium dioxide (TiO2) thin film was fabricated using titanium isopropoxide as a precursor through an atmospheric low-temperature roll-to-roll chemical vapor deposition method. TiO2 was deposited on the PET substrate in the temperature range of room temperature to 100°C, and the working pressure was 740 Torr. The surface morphology of TiO2 thin film was analyzed by field emission scanning electron microscopy and a 2D surface profiler. The results revealed that the growth rate of TiO2 film was 31 nm/min at 100°C, and it also showed that the surface is uniform and smooth. Moreover, the lowest root mean square roughness (R q) value of 1.87 nm was obtained for TiO2 film prepared at 100°C. The composition of TiO2 film was confirmed by X-ray photoelectron spectroscopy (XPS) analysis. The film showed very good chemical and optical properties while increasing the substrate deposition temperature. The UV–Vis spectroscopy analysis revealed that TiO2 films exhibited excellent optical transmittance, more than 91% observed in the visible region.

Role of Sodium Ion on TiO2 Photocatalyst: Influencing Crystallographic Properties or Serving as the Recombination Center of Charge Carriers?

There have been continuing debates about the role of Na+ on TiO2 photocatalyst in the past decades. Most researchers accepted that Na+ served as the recombination center of photogenerated electrons and holes. Nevertheless, other opinions also existed, such as Na+ increased the crystallite size of TiO2, Na+ hampered the crystallization of anatase TiO2, and Na+ promoted the formation of brookite TiO2 or titanate sodium. In this research, we have systematically investigated the role of Na+ during the fabrication of TiO2 film and powder through the sol–gel method and studied the influences of crystallinity and the content of Na+ on the photocatalytic activities of TiO2 film and powder. It has been found that the existence of Na+ in TiO2 film and powder should influence their crystallographic properties, in detail, inhibiting the crystallization and growth of anatase phase in TiO2 film and powder, promoting the formation of brookite phase in TiO2 film, and increasing the transformation temperature of anatase t...

MOCVD of TiO2 thin films from a modified titanium alkoxide precursor

A new titanium precursor, [Ti(OPri)2(deacam)2] (deacam = N,N-diethylacetoacetamide), was developed by the reaction of the parent Ti alkoxide with the β-ketoamide. The compound, obtained as a monomeric six-coordinated complex, was used in metal organic chemical vapor deposition (MOCVD) of TiO2 both as a single source precursor (SSP) and in the presence of oxygen. The high thermal stability of [Ti(OPri)2(deacam)2] enabled the fabrication of TiO2 films over a wide temperature range, with steady growth rates between 500 and 800 °C. The microstructure of the obtained systems was analyzed by X-ray diffraction (XRD) and Raman spectroscopy, whereas atomic force microscopy (AFM) and field emission-scanning electron microscopy (FE-SEM) measurements were performed to investigate the surface morphology and nanoorganization. Film composition was investigated by complementary techniques like Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). The electrical properties of the layers were investigated by performing capacitance voltage (C–V) and leakage current measurements.

Fabrication of TiO2 film with different morphologies on Ni anode and application in photoassisted water electrolysis

The anode of an alkaline electrolytic cell for water electrolysis was modified by TiO2 photocatalysts with different morphologies. The water electrolysis was coupled with photocatalytic decomposition of water by irradiation of UV light on the modified anode. And a feasible process for the hydrogen production of water electrolysis assisted by photocatalysis (WEAP) was proposed and experimentally confirmed. The results show that the highly ordered, vertically oriented tubular arrays structure on Ni anode surface has better hydrogen production performance than random TiO2. In WEAP process, the maximum rate of hydrogen production is 2.77ml/(h*cm2) when the anode modified by ordered TiO2 nanotube arrays, compared to traditional alkaline electrolytic cell for water electrolysis with Ni anode, H2-production rate increased by 139%.

Fabrication and photocatalytic characteristics of TiO2 films on silicon substrates

Silicon (111) and Silicon (100) have been employed for fabrication of TiO2 films by metal organic chemical vapor deposition (MOCVD). Titanium (IV) isopropoxide (Ti[O(C3H7)4]) was used as a precursor. The as-deposited TiO2 films have been characterized with Field emission scanning electron microscopy (FE-SEM), X ray diffraction (XRD) and atomic force microscopy (AFM). The photocatalytic properties were investigated by decomposition of aqueous orange II. The crystalline and structural properties of TiO2 film had crucial influences on the photodegradation efficiency. For MOCVDin-situ deposited films on Si substrates, the photoactivities varied following a shape of “M”: At lower (350°C) middle (500 °C) and higher (800 °C) temperature of deposition, relative lower photodegradation activities have been observed. At 400 °C and 700 °C of deposition, relative higher efficiencies of degradation have been obtained, because one predominant crystallite orientation could be obtained as deposition at those two temperatures, especially a single anatase crystalline TiO2 film could be obtained at 700 °C growth.