Polycrystalline Anatase Structure Research Articles

Fabrication and photocatalytic characterization of SnO2 and SnO2/Tio2 nanostructure films

Pure spherical-like SnO2 and agglomerated spherical SnO2/TiO2 nanostructures (NS) films were effectively synthesized via hydrothermal route and modest combination of pulse laser ablation besides hydrothermal (PLAL-H) methods, respectively. The as-prepared samples were deposited on glass substrates at growth temperature 100 °C and characterized by FESEM, X-ray diffraction, and UV-Vis absorption and Photoluminescence (PL) measurements. Both samples exhibit a pure tetragonal rutile and anatase polycrystalline structure. The PL spectrum of pure SnO2 Ns reveals five emission peaks in UV and visible regions. In contrast, a red shift in UV emission peak was clearly observed in SnO2/TiO2 nanocomposite spectrum and disappeared all visible emission peaks. Moreover, the samples as photocatalysts films were examined under sunlight irradiation driven photodegradation of methylene blue (MB) dye. The findings exposed that the photodegradation efficiency toward MB dye at maximum irradiation time 150 min was mostly similar around 21.5 % of both as-growth films.

Optical Properties and UV Sensing Response of Nitrogen-doped TiO2 Thin Film by CVD

This work was demonstrated a cold-wall chemical vapour deposition (CVD) setup to prepare nitrogen (N)-doped titanium dioxide (TiO2) thin film on glass substrates, which presents semi-transparent yellowish surface. The prepared N-doped TiO2 film is homogeneous and possesses polycrystalline anatase structure. The transmittance measurement was carried out in the ultraviolet-visible spectral region to evaluate the film thickness, optical constants, and the optical band gap was determined by Tauc plot. A metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector by the Pt/N-doped TiO2 film has shown a positive response towards UV illumination.

Effect of thickness on the structural, morphological, electrical and optical properties of Nb plus Ta co-doped TiO2 films deposited by RF sputtering

Transparent conductive Nb plus Ta co-doped TiO2 films with various thicknesses were deposited on quartz substrates by RF magnetron sputtering with vacuum annealing. The effect of film thickness on structural, morphological, electrical and optical properties of the films was investigated in detail. X-ray diffraction measurements indicate that the post-annealed films are polycrystalline anatase structure, which is further confirmed by Raman spectroscopy. The average crystal size and surface roughness of the annealed films gradually increase as thickness increases from 50 to 500 nm. X-ray photoelectron spectroscopy results show that the substitution of Nb5+ and Ta5+ ions in Ti4+ sites can be significantly promoted by annealing treatment. Meanwhile, Raman spectroscopy results indicate that with the increase of film thickness, the peak position of Eg (1) mode shifts to higher band frequencies, implying the increase of carrier concentration. The average visible transmittance of all these films is in the range of 75–81%. The lowest resistivity of 8.9 × 10−4 Ω cm with carrier concentration of 1.1 × 1021 cm−3 and Hall mobility of 6.2 cm2 V−1 s−1 can be obtained at the film thickness of 500 nm, indicating that the optical and electrical properties of optimized NTTO films can be compared to those of Nb or Ta single-doped anatase TiO2 films. However, co-doping with Nb and Ta provides one possibility to complement the limitations of each dopant.

Role of molar concentration in structural, optical and gas sensing performance of anatase phase TiO2 nanofilms: automated nebulizer spray pyrolysis (ANSP) technique

TiO2 nanofilms were deposited on a glass substrate at 500 °C using automated nebulizer spray pyrolysis. The anatase polycrystalline structure with increased grain size and variations of surfactant planes (T c) were influenced by molar concentration on XRD study. AFM study shows the average roughness values were increased with increase in molar concentration. A granular domain like microstructure with crack and void-free particle was examined by FESEM. The maximum transmittance ~95.5% (529.6 nm) for x = 0.05 M/L, further increment of molar concentration showed the decremented transmittance with red shift absorption edge and the calculated band gap values (E g = 3.53–3.20 eV) also noted. The gas sensing performances of films were studied with respect to various gas sensing parameters and the ammonia (NH3) gas showed better sensing response (S max = 89%) at 150 °C for 300 ppm gas concentration against other gases (C2H6O, CH4O, C3H8O and C3H6O).

Study on the chemical bond structure and chemical stability of N doped into TiO 2 film by N ion beam implantation

Titanium dioxide (TiO2) film was deposited by DC pulse magnetron sputtering technique. The surface of TiO2 film was implanted by N ion beam at room temperature and N doped TiO2 (N-TiO2) film was obtained. X-ray diffractometer result showed that with the increase of sputtering power, the crystal structure of TiO2 film changed from amorphous to anatase polycrystalline structure. Transmission electron microscopy result revealed that nanoscale clusters existed in amorphous TiO2 film. The bandgap of TiO2 film was about 3.28 ± 0.05 eV. X-ray photoelectron spectroscopy results revealed that N ion was doped into TiO2 film as Ti–N and Ti–NO bonds. With increasing TiO2 film crystallinity, N atom-percent and ratio of Ti–N to Ti–NO decreased and increased, respectively. TiO2 film deposited with 900 W in sputtering power, N atom-percent decreased to 6.6 at.% and ratio of Ti–N to Ti–NO increased to 0.81:1. The bandgap of N-TiO2 film was about 3.02 ± 0.07 eV. N atom-percent and ratio of Ti–N to Ti–NO kept at 2.73 ± 0.26 at.% and (0.87 ± 0.03):1 for all annealed N-TiO2 films. The bandgap of annealed N-TiO2 film was about 3.16 ± 0.03 eV. So, the crystallinity of TiO2 film was one of most important parameters, which influenced the chemical bond structure and chemical stability of N in TiO2 films.

An Increase in Conversion Efficiency of Dye-Sensitized Solar Cells using Bamboo-Type TiO2 Nanotube Arrays

Highly ordered, bamboo type TiO2 nanotube (NT) arrays were prepared by anodization of Ti foils in an electrolyte of 0.5 wt% NH4F in ethylene glycol using square-wave voltage. The morphology of obtained arrays consisting of closely packed TiO2 NTs with inner diameter of 90nm, wall thickness of 20nm and length of 26μm was characterized by scanning electron microscopy (SEM). Poly-crystalline anatase structure with crystallites of 28nm in average size was determined by X-ray diffraction (XRD). Intensity-modulated photocurrent spectroscopy (IMPS) was employed to study the electron transport properties of TiO2 NT arrays used in dye-sensitized solar cells (DSSCs). Dye molecules were found to cover both the inner and outer surface of the bamboo type TiO2 NT arrays. Electrochemical impedance spectroscopy (EIS) showed reduced interfacial resistance and increased interfacial capacitance for the bamboo type TiO2 NT arrays compared with the smooth type arrays, indicating an increase in surface area of the bamboo type TiO2 NT arrays, which resulted in the higher dye loading. An increased conversion efficiency of 7.36% was achieved for the DSSCs based on the bamboo type TiO2 NT arrays attributing to the significant increase of dye loading resulted from the bamboo structure.

Correlation between bioactivity and structural properties of titanium dioxide coatings grown by atomic layer deposition

TiO2 coatings were grown on Ti and Si by Atomic Layer Deposition (ALD) from titanium ethoxide and water at 300°C in a wide range of the reaction cycles number N=100–2000. TiO2 coatings were found to be amorphous at low value of N<300 while the coatings grown at N≥300 revealed anatase polycrystalline structure. The TiO2 coatings bioactivity was evaluated by hydroxyapatite forming ability by the technique of soaking in Simulated Body Fluid (SBF). Correlation between bioactivity and structural properties of TiO2 was determined. X-ray diffraction and scanning electron microscopy with electron probe microanalysis showed that amorphous TiO2 coating did not induce the hydroxyapatite growth whereas anatase resulted in the hydroxyapatite forming on the samples surfaces which confirmed TiO2 anatase bioactivity.

Preparation and photocatalytic properties of nanometer TiO2 thin films by improved ultrasonic spray pyrolysis

The nitrogen-doped TiO2 thin films were prepared on glass substrate by an improved ultrasonic spray pyrolysis device with butyl titanate as the titanium source and ammonia as the nitrogen source. The surface morphology, crystal structure and optical properties of the resulting films were characterized by SEM, XRD and UV-VIS spectroscopy, respectively. The results show that N-doped TiO2 films have a more uniform and compact surface, the particle size trends to become smaller and then larger with the increasing amount of doping nitrogen. All the thin films belong to polycrystalline anatase structure and have a well visible light responsiveness with N doped. The photocatalytic activity and hydrophilic properties were investigated under ultraviolet irradiation. The degradation rate for methylene blue solution can reach 94.0% after 3 h under ultraviolet irradiation. The hydrophilic test shows that the hydrophilicity of TiO2 thin films can be improved by doping nitrogen to some extent.

Optical properties of TiO2 thin films prepared by chemical spray pyrolysis from aqueous solutions

AbstractTitanium dioxide (TiO2) is known to have three different kinds of polymorphous crystalline forms: rutile, anatase, and brookite. The rutile phase is always formed at higher temperatures, while the anatase phase is formed at lower temperatures and transformed into rutile phase above 800 ºC. Various deposition techniques have been developed for depositing TiO2 thin films, including evaporation, sputtering, chemical vapour deposition and thermal oxidation of titanium. Among them, the Chemical Spray Pyrolysis (CSP) technique has many advantages, such as good conformal coverage, the possibility of epitaxial growth and the application to large area deposition. Also, this method is low cost and it is easy to control the deposition growth parameters. In the present work, TiO2 thin films have been deposited on p‐Si (001) and fused silica substrates by Chemical Spray Pyrolysis (CSP) method from aqueous solution containing titanium (IV) isopropoxide (Ti[OCH(CH3)2]4. As‐deposited thin films show anatase polycrystalline structure, and rutile phase formed for films annealed at 750ºC. SEM images have confirmed a smooth and crack‐free surface with low surface roughness. X‐ray photoelectron spectroscopy (XPS) combined with 4 keV Ar+ depth profiling has shown that crystallized films correspond to TiO2. Residual carbon coming from the organic precursor solution is only detected at the surface of the film. Thin films deposited on fused silica were highly transparent (more than 85%), with an indirect optical band gap of 3,43 and 3,33 eV for as‐deposited and annealed films, respectively, and refractive indexes in the range between 2.01–2.29. Spectroscopic Ellipsometry (SE) also has been used to extract optical parameters. SE data fitted to triple‐layer physical model revealed the same tendency to increase refractive index in annealed films. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Influences of underlayers on structure of TiO2 thin films prepared by radio frequency magnetron sputtering

In this study, the effects of several underlayers (Cu, Co, Ag and Fe) on the thin structure of TiO2 by RF magnetron sputtering were studied and compared. The results of X-ray diffraction (XRD) revealed that the Cu and Ag underlayer worsened the crystal quality of the TiO2 films. When the Fe underlayer was used, fabricated TiO2 film showed a mixture of rutile and anatase. The Co underlayer, on the other hand, induced TiO2 anatase polycrystalline structure. This study also compared the surfactant effect of a Ag layer on the TiO2 film structure. The results of XRD, X-ray photoelectron spectroscopy, and atomic force microscopy revealed that the Ag layer works as an effective surfactant for reducing the surface roughness and the rutile growth of TiO2 film on the Fe underlayer.

Pulsed plasma-enhanced chemical vapor deposition of Al 2O 3–TiO 2 nanolaminates

Self-limiting synthesis of alumina–titania nanolaminates (ATO, Al 2O 3/TiO 2) was accomplished via pulsed plasma-enhanced chemical vapor deposition. At the synthesis temperature of 150 °C the alumina layers were amorphous, while TiO 2 layers displayed a polycrystalline anatase structure. Digital control over nanolaminate structure was demonstrated through elemental analysis and transmission electron microscopy imaging. The dielectric performance of the ATO structures was examined as a function of composition and bilayer thickness. Capacitance–voltage measurements showed that the effective dielectric constant was consistent with treating the nanolaminates as individual capacitors in series. Current–voltage measurements showed that leakage current deteriorated with TiO 2 content, though low leakage was restored through interfacial engineering.

Implantation of anatase thin film with 100 keV 56Fe ions: Damage formation and magnetic behaviour

We have investigated the damage morphology and magnetic properties of titanium dioxide thin films following implantation with Fe ions. The titanium dioxide films, having a polycrystalline anatase structure, were implanted with 100 keV 56Fe + ions to a total fluence of 1.3 × 10 16 ions/cm 2. The ion bombardment leads to an amorphized surface with no indication of the presence of secondary phases or Fe clusters. The ion-beam induced damage manifested itself by a marked change in surface morphology and film thickness. A room temperature ferromagnetic behaviour was observed by SQUID in the implanted sample. It is believed that the ion-beam induced damage and defects in the polycrystalline anatase film were partly responsible for the observed magnetic response.

Fabrication of anatase titania inverse opal films using polystyrene templates

Abstract High-performance titania inverse opal films have been derived from a sol–gel procedure using polystyrene colloidal crystals as templates. By carefully controlling the synthetic procedures, the titania inverse opal films display a uniform color over centimeter dimensions. Scanning electron microscopy is employed to characterize the qualities of the titania inverse opal films. Electron diffraction pattern shows a polycrystalline anatase structure of TiO2.

Optimization and deposition of CdS thin films as applicable to TiO2∕CdS composite catalysis

Methanol decomposition has been studied by in situ Fourier transform infrared spectroscopy on a CdS∕TiO2 bilayer deposited on glass substrates. First CdS thin films were deposited by chemical bath deposition method using the CdSO4 and thiourea as the precursors and ammonia as the complexing agent and have the optical band gap of 2.2–2.29 eV for the different CdSO4 solution concentrations. The structure of the CdS films was found to have mixed cubic and hexagonal phases, while the TiO2 films were polycrystalline anatase structure with an optical band-gap energy of 3.2 eV deposited at a total sputtering pressure of 0.1 Pa in an argon and oxygen gas mixture (Ar:O2=80:20) at 200 W sputtering power. The visible light active photocatalytic degradation efficiency of methanol over a TiO2∕CdS double layer is four times higher than that of a TiO2 single layer. The decomposition of methanol pathway proceeds via formaldehyde as the intermediate product.

The influence of annealing temperature on the structure and properties of TiO2 films prepared by sputtering

The TiO2 films were prepared on slides by dc reactive magnetron sputtering, then the samples were annealed at 300°C, 350°C, 400°C, 450°C, 500°C and 550°C, respectively. X-ray diffraction (XRD) was used to obtain the TiO2 film crystalline structure; X-ray photoelectron spectroscopy (XPS) was used to study the film surface stoichiometries; surface morphologies were studied by scanning electron microscopy (SEM); the contact angle was tested to indicate the TiO2 film wettability; and the photocatalytic activity testing was conducted to evaluate the photocatalysis properties. The photocatalytic activity and contact angle testing results were correlated with the crystallinity, surface morphologies and surface ·OH concentration of TiO2 films. The samples with a higher polycrystalline anatase structure, rough surface and high ·OH concentration displayed a better photoinduced hydrophilicity and a stronger photocatalysis.

Photocatalytic TiO 2 films deposited by reactive magnetron sputtering with unipolar pulsing and plasma emission control systems

TiO 2 films with thickness of about 500 nm were deposited on unheated non-alkali glass substrates by reactive magnetron sputtering using one Ti metal target with unipolar pulsed powering of 50 kHz and the plasma emission feedback system (PCU). In order to keep the very high deposition rate, the depositions were carried out in the “transition region” between the metallic and the reactive (oxide) sputter mode where the target surface was metallic and oxidized, respectively. Stable deposition was successfully carried out in the whole “transition region” with PCU at total gas pressure of 3.0 Pa. All the as-deposited films deposited in the “transition region” showed amorphous structure, which performed very low photocatalytic activity. After the post-annealing in air at higher than 300 °C, all the films crystallized to anatase polycrystalline structure. They performed both photoinduced decomposition of acetaldehyde and photoinduced hydrophilicity under UV light illumination. The highest deposition rate in this study to deposit the photocatalytic TiO 2 films in the “transition region” was 90 nm/min, which was over twenty times higher than that for conventional sputter deposition processes.

Effect of silica addition on crystallinity and photo-induced hydrophilicity of titania–silica mixed films prepared by sol–gel process

Effect of silicon dioxide (silica) addition into titanium oxide (titania) films on crystallinity and photo-induced hydrophilicity was investigated. Titania films and titania–silica mixed films with 20% or 50% silica were prepared by spin-coating deposition. For the titania films, photo-induced hydrophilicity is only observed in the films with anatase polycrystalline structure. For the titania–silica mixed films, however, despite these films showing no obvious anatase polycrystalline structure, very strong photo-induced hydrophilicity is observed. Particularly, even super-hydrophilicity where the contact angle shows 0° is easily observed for the titania–silica mixed films with 20% silica. The hydrophilicity of the titania films correlates closely with anatase crystalline structure. In the titania–silica mixed films, the synergistic effects of anatase polycrystalline structure of titania and water-trapping effect of silica are important for their strong photo-induced hydrophilicity.

Photocatalytic Properties of TiO2 Films Deposited by Reactive Sputtering in Mid-Frequency Mode with Dual Cathodes

Titanium dioxide (TiO2) films were deposited on unheated nonalkali glass substrates by reactive midfrequency (mf) magnetron sputtering using dual cathodes with two Ti metal targets. In order to maintain the very high deposition rate, the depositions were successfully carried out stably in the “transition region” between the metallic and reactive (oxide) sputter modes using plasma control units (PCU). Very high-rate depositions of 12–70 nm/min were successfully achieved in the deposition of TiO2 films throughout the whole “transition region”. The as-deposited films deposited in the “oxide mode” had a polycrystalline anatase structure and exhibited both photoinduced hydrophilicity and photodecomposition of acetaldehyde. Whereas, all the as-deposited TiO2 films deposited in the “transition region” had amorphous structure, which did not exhibit photocatalytic activity. Such amorphous films deposited in the transition region were crystallized by postannealing in air at 200°C or 300°C and were then shown to have photocatalytic activity. Very thin TiO2 films with a thickness of 25 nm deposited in the transition region and postannealed at 300°C exhibited photoinduced hydrophilicity, whereas there was a clear thickness dependence of photodecomposition and the rather thick films of 300 nm exhibited pronounced photodecomposition.

Relationship between the Photocatalytic Characteristics and the Oxygen Partial Pressure of TiO2 Thin Films Prepared by a DC Reactive Sputtering Method

It was confirmed that the oxygen partial pressure that is used during DC reactive sputtering can influence the generation of oxygen defects on TiO2 thin films and/or the surface structure, which then affects the photocatalytic characteristics. TiO2 films were deposited by DC reactive magnetron sputtering on a Si wafer at 250°C under oxygen partial pressures of 0.1 Pa, 0.5 Pa and 0.8 Pa. Structural analysis of the TiO2 thin films was conducted using X-ray diffraction (XRD), field-effect scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), the photo luminescence method (PL). Characterization of the photocatalytic properties was performed by measuring the concentration change of methylene blue (wet methylene blue method) and the change of the contact angle with pure water. All films showed a polycrystalline anatase structure. TiO2 thin films deposited under reducing conditions (an oxygen partial pressure of 0.1 Pa) exhibited peaks that are characteristic of Ti3+ and can also contain a number of oxygen defects. The domain size was about 150–300 nm, and the domain boundaries were unclear. On the other hand, for TiO2 thin films deposited in oxidizing mode (oxygen partial pressures of 0.5 Pa and 0.8 Pa), the peak corresponding to Ti3+ was not observed. The domain size was between 300–1000 nm and the boundaries were clear. TiO2 thin films exhibit better photocatalytic properties when the domain size is large and there are fewer oxygen defects in the film. It has been suggested that the decreasing proportion of domain boundaries, which act as trapping centers for electrons, and the lower concentration of oxygen defects, which act as recombination centers for electron-hole pairs, improved the photocatalytic characteristics.

Studies on evaporated titanium oxide thin films for oxygen gas detection

Present work deals with the preparation of TiO2 thin films of different thicknesses by PVD technique using an electron beam and to characterize the films for oxygen gas detection. The films were characterized using optical transmission measurements, XRD and atomic force microscopy. From the spectral data, the extinction, absorption coefficient and refractive index of the films are evaluated and reported. The optical band gap energy varies between 3 and 3.68 eV. The XRD pattern confirms the formation of polycrystalline anatase structure of Titanium with preferred orientation of (110) plane. The AFM images indicate the presence of coarse and fine grains with uniform as well as smooth surfaces over the entire range of the analyzed surface. Response characteristics of TiO2 thin films for oxygen gas detection are studied, which indicate a low response time of 120 seconds and high sensitivity of 16 at the operating temperature 450 °C.