Doped Titania Films Research Articles

Thin film transistor based on epitaxial Ta doped titanium dioxide film

Ta doped titanium dioxide (TiO2:Ta) films were deposited by a metalorganic chemical vapor deposition (MOCVD) system. X-ray diffraction (XRD) measurement revealed the TiO2:Ta films with low Ta contents (≤4.0 at.%) to be epitaxial films of anatase phase. X-ray photoelectron spectroscopy (XPS) measurement showed that Ta element only existed as Ta5+ in TiO2 lattice without other valence states. The electrical characteristics of the films could be modified through Ta doping. The minimum resistivity was obtained at Ta content of 2.0%. As Ta content increased, the carrier concentration increased from 4.9 × 1017 to 1.3 × 1019cm−3 while the Hall mobility decreased from 20.4 to 3.07 cm2V−1s−1. The deposited TiO2:Ta films all presented high visible transparency over 93.0%. A thin-film transistor based on 1.0% Ta-doped TiO2 film was fabricated, which exhibited high performances with a ION/IOFF ratio of 7.5 × 107, a subthreshold swing of 0.55 V/decade, and a saturation mobility of 3.4 cm2V−1s−1.

Electrochromic properties of nitrogen doped titanium dioxide films

Nitrogen doping is an effective way to improve the electrochromic performance of inorganic materials. However, there is still a lack of systematic studies on the electrochromic properties of nitrogen-doped TiO2 materials. In this work, the N-doped titanium dioxide films (N-TiO2) with different N content were prepared by an ion exchange method combined with hydrothermal approach. The effects of different N doping concentrations on the morphology and electrochromic properties of samples were studied by XRD, XPS, FESEM, HR-TEM and electrochemical methods. It was found that the nitrogen doping has a great influence on the crystal structure of the TiO2, leading to an obvious light transmittance difference in bleaching/coloring states for all the films. The N1-TiO2 film (nitrogen doping concentration was 1 mol/L) shows the best electrochromic performance. The ion diffusion coefficient of N1-TiO2 composite film was 2.28 × 10−9 cm2/s, and the coloring efficiency is 10.61 cm2/C, the coloring and bleaching switching time was 31.13 s and 3.79 s, and the optical modulation amplitude retention rate after 100 cycles can reach 65.43 %, indicating that nitrogen doping with proper amount is indeed an effective method to tune electrochromic properties of TiO2.

Influence of Fe3+ ions on the optical properties and photocatalytic ability of spin coated Fe3+ doped brookite TiO2 thin films

The spin coating process has been used to deposit pure and Fe3+ doped brookite titania films onto glass substrates. In essence, such as films annealed at 500 °C are found to be orthorhombic crystal structure with brookite phase. X-ray diffractometer measurements revealed that Fe ions are incorporated into cation sites of TiO2. The crystallite size reduces with the doping of Fe3+ ions. The scanning electron microscope images show highly uniform, crack free films and the particles size is found to be within the range of 150–200 nm. Energy-dispersive x-ray spectroscopy analysis Fe3+ doped TiO2 films confirmed good stoichiometry of chemical compositions. The Raman spectra of brookite TiO2 exhibit a very strong characteristic band at 153cm−1. The optical band gap was found to be declined from 3.08 eV to 2.54 eV with adding the Fe ions into TiO2 matrix. The EPR studies approve incorporation of Fe3+ in the crystal lattice of brookite by substituting Ti4+ and generation of defects, and Ti3+ states. Photocatalytic ability of films has been studied by degradation of methyl orange solution under illumination of visible light. The 7% Fe doped brookite film was exhibited high catalytic activity compared to other pure and doped films.

Photoluminescence and photocatalytic activity of rare earth ions doped anatase TiO2 thin films

TiO2 thin films doped with 1% rare earth (RE) ions (Sm3+, Eu3+, and Dy3+) have been deposited by the sol-gel spin coating technique. The X-ray diffraction, confocal Raman, optical transmittance, and photoluminescence spectra of resultant films were recorded at room temperature (RT). As revealed by X-ray diffraction, RE ions doped TiO2 films were found to have a tetragonal crystal structure with anatase phase TiO2. The crystallite size gets declined with RE (III) ions doping. TEM analysis of 1% Sm3+ ions doped TiO2 and 1% Dy3+ ions doped TiO2 films endorsed the particles have spherical shape structure with an average size of about 10.9 nm and 10.5 nm, respectively. The characteristic vibrational Raman modes also revealed that the RE ions doped TiO2 films founded to anatase phase. The RE ions doped TiO2 nanostructures have high refractive indices and narrow band gaps. Under UV (375 nm, 388 nm, and 393 nm) excitations, the RE ions doped TiO2 nanophosphor thin films show characteristic photoluminescence in the visible spectral range. The PL decay spectra were recorded by time-correlated single photon counting (TCSPC) and the decay times of phosphors were obtained by bi-exponential curve fitting. The RE ions doped Titania films possessing significant color coordinate (x, y) values might have potential uses in solid-state display devices. The photocatalytic ability of RE ions doped TiO2 showed that the excellent photocatalytic activity (PCA) response for the degradation of methyl orange (MO) under visible light irradiation.

Investigation on structural, optical and electrical properties of Nd doped titania films and application of optical model

The effect of dopant concentration and temperature on the structural, optical and electrical properties of TiO2 (Titania) thin films deposited through sol-gel spin coating was investigated. The X-Ray Diffractometer was used for phase analysis, UV–Vis spectrometer and Ellipsometer techniques were used for the optical measurements and Hall effect was used for the electrical characterization. Annealing temperature and dopant concentration were chosen as the parameters in the present study. The optical band gap marginally increased from 3.40 eV to 3.43 eV with increase in dopant concentration for the films annealed at 350 ֯C. The increasing trend was also observed for the films annealed at 450 °C with the optical band gap in the range 3.34 eV–3.39 eV. Using ellipsometric measurement, thickness and optical constants were obtained and we compared the refractive index values with those obtained from PARAV software. For Nd doped films, a single oscillator model was tested by using the refractive index values from ellipsometric measurement. The carrier density and plasma frequency were calculated using the Wemple Di Domenico (W-D) model. The electrical properties indicate decreased resistivity from 103 Ωcm to 101 Ωcm and increased carrier density from 1015 cm-3 to 1017 cm-3 with increase in annealing temperature. Similarly, with increase in dopant concentration at a given annealing temperature, we have observed a decreased resistivity compared to the prestine samples. However, the carrier density increased marginally with increase in dopant concentration.

Tuning mixed-phase Nb-doped titania films for high-performance photocatalysts with enhanced whole-spectrum light absorption

Heterojunction of rutile and anatase phase enhanced photocatalytic performance of mixed-phase Nb doped titania films to degrade pollutants under visible (vis) light.

Fluorine doped titanium dioxide films manufactured with the help of plasma enhanced chemical vapor deposition technique

In this work, a manufacture of TiO2 coatings doped with fluorine, in a concentration range of 0.6 to 6.7 at.%, is presented. The coatings were deposited onto silicon and quartz substrates with the help of radio frequency plasma enhanced chemical vapor deposition technique. They were characterized with regard to their elemental composition, chemical structure, phase composition, surface topography, optical properties, photo-wettability and bactericidal properties. For that purpose, such analytical techniques as X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy, atomic force microscopy, ultraviolet–visible absorption spectroscopy and variable angle spectroscopic ellipsometry were used.GIXRD analysis of the coatings doped with fluorine shows their amorphous structure. Apart from TiO2 bonding, FTIR and XPS analyses of the films reveal a presence of TiF and OF bonds. Surface morphology studies indicate an increasing number of surface defects along with growing fluorine content. The coatings exhibit promising optical properties with some of them showing a super-hydrophilic effect as well. On the other hand, the bactericidal effect of fluorine doped TiO2 coatings is weaker than that of plain TiO2.

Development of Silver Doped Titanium Oxide Thin films for Gas Sensor Applications

Gas sensors find numerous applications in fields of automotives, medical, industries and others. A number of studies focused on synthesis of silver doped titanium dioxide films with various doping concentrations of silver. The objective of the research work is to optimize gas sensing properties of Ag-TiO2 thin films using orthogonal array experimentation with different dopants, concentration, annealing temperatures and gas concentrations exposure time. Synthesis of Ag-TiO2 thin films on quartz substrates was carried out by sol-gel spin coating. TiO2 films were characterized optical, chemical and mechanical and sensing properties. Surface roughness of TiO2 Thin films are RSM 11 to 45 nm and decrease of transmittance from 74% to 45% and energy bad gap from 3.44 to 3.29 eV for variation of annealing temperature from 400 to 600 °C. Surface roughness in RSM of 15 to 67 nm and decrease in transmittance from 85 to 63 % and band gap from 3.40 to 3.28 eV from 3 to 7 layers of coating was found. Ag-TiO2 thin films showed highest sensor response of 1.247 for 300 °C annealing temperature, 0.025 atomic ratio, 5 ppm CO gas exposure. Analysis of variance showed CO gas exposure influenced sensor response by 72.95%, and annealing temperature influenced sensor response by 18.39 %. Response surface methodology showed desirability of 70.7% with maximum response value to be 1.2346.

In English

The simple and fast route of the synthesis of platinum ions doped titania thin films is designed where platinum(II) acetylacetonate is used as a perspective doping agent due to the possibility of platinum incorporation in the form of the different valence states. Additionally, the multilayered films showing the varied properties are obtained. The increase in Pt content as well as the number of layers leads to the higher absorbance and the band edge shift to the red part of the spectrum. The indirect electronic transition is suggested and the calculated band gap values are depended on the film compositions as well as the number of layers. The significant decrease in the band gap value of titania is noted for 0.5 % Pt/TiO 2 films. Pure titania and doped titania films contain anatase phase only with the average crystallite size near 14 nm. The conversion percentage of photocatalytic dichromate ions reduction is increased in the presence of three-layered 0.5 % Pt/TiO 2 films under both UV and visible light. The activity of three-layered films is higher compare to the single layered samples. The film contained 0.1 % Pt exhibited the similar activity to titania one.

Deposition of Visible Light-Active C-Doped Titania Films via Magnetron Sputtering Using CO₂ as a Source of Carbon.

Doping of titanium dioxide with p-block elements is typically described as an efficient pathway for the enhancement of photocatalytic activity. However, the properties of the doped titania films depend greatly on the production method, source of doping, type of substrate, etc. The present work describes the use of pulsed direct current (pDC) magnetron sputtering for the deposition of carbon-doped titania coatings, using CO2 as the source of carbon; ratios of O2/CO2 were varied through variations of CO2 flow rates and oxygen flow control setpoints. Additionally, undoped Titanium dioxide (TiO2) coatings were prepared under identical deposition conditions for comparison purposes. Coatings were post-deposition annealed at 873 K and analysed with scanning electron microscopy (SEM), X-ray diffreaction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic properties of the thin films were evaluated under ultraviolet (UV) and visible light irradiation using methylene blue and stearic acid decomposition tests. Photoinduced hydrophilicity was assessed through measurements of the water contact angle under UV and visible light irradiation. It was found that, though C-doping resulted in improved dye degradation compared to undoped TiO2, the UV-induced photoactivity of Carbon-doped (C-doped) photocatalysts was lower for both model pollutants used.

Sulfur-Doped Cubic Mesostructured Titania Films for Use as a Solar Photocatalyst

Sulfur-doped titania thin films with cubic mesostructures were prepared by dip coating via the evaporation induced self-assembly route. The effect of sulfur doping on structure, morphology, porosity, optical properties, and photocatalytic activity of the mesoporous films was studied. Compared to undoped titania films, the S-doped films showed better long-range ordering, bigger pore size, higher porosity, less shrinkage of the structure during calcination, a red-shift of the band gap, and a more hydrophilic surface. These characteristics led to an improved photocatalytic activity when the S-doped and undoped titania films were tested for degradation of methylene blue in aqueous solutions under the irradiation of 1 sun from a solar simulator. The photocatalytic activity of the sulfur doped titania film was stable during three consecutive experiments under solar light irradiation, confirming the mechanical stability and reusability of the doped nanostructured thin film photocatalysts.

In English

The metal (Zn 2+ or Zr 4+ ) and non-metal (nitrogen) doped titania films are synthesized by sol-gel method. High absorption in the visible region is observed and the band gap values are estimated for indirect electron transition. The decrease in the intensity and broadening of the anatase peaks in XRD spectra for TiO 2 /N films with increasing urea contents are observed. Anatase formation in the films with double doping agents is proven by Raman measurements. XPS clarified the chemical state of the elements, their surface ratios and the incorporation of nitrogen in the matrix of the synthesized films. XPS results show that the substitutional nitrogen is only registered for TiO 2 /Zr 4+ /N. Photocatalytic properties are estimated in the process of tetracycline destruction reaction. The increase of the film activity by factor three is noted for TiO 2 /N. Modification TiO 2 /N by metal ions has no influence on the photocatalytic properties under UV and visible light.

Photocatalytic characteristics of boron and nitrogen doped titania film synthesized by micro-arc oxidation

A boron and nitrogen co-doped titania catalyst was synthesized by micro-arc oxidation to obtain high efficiency and wide application through the extension of photocatalytic activity into the visible-light region. During micro-arc oxidation process, which is known as an energy saving and environmentally friendly method, boron and nitrogen ions in the electrolyte were incorporated into the interstitial site of TiO2. The presence of B and N as doping elements was confirmed by XPS analysis. The surface characteristics of the synthesized B,N co-doped titania film were investigated by SEM and XRD. The synthesized TiO2 film showed an excellent adherence to the titanium substrate. For estimation of photocatalytic activity, photocurrent response and dye decomposition tests were performed, and the B, N co-doped TiO2 exhibited much higher dye degradation rate, rate constant, and photocurrent response.

Tungsten Doped TiO2 with Enhanced Photocatalytic and Optoelectrical Properties via Aerosol Assisted Chemical Vapor Deposition.

Tungsten doped titanium dioxide films with both transparent conducting oxide (TCO) and photocatalytic properties were produced via aerosol-assisted chemical vapor deposition of titanium ethoxide and dopant concentrations of tungsten ethoxide at 500 °C from a toluene solution. The films were anatase TiO2, with good n-type electrical conductivities as determined via Hall effect measurements. The film doped with 2.25 at.% W showed the lowest resistivity at 0.034 Ω.cm and respectable charge carrier mobility (14.9 cm3/V.s) and concentration (×1019 cm−3). XPS indicated the presence of both W6+ and W4+ in the TiO2 matrix, with the substitutional doping of W4+ inducing an expansion of the anatase unit cell as determined by XRD. The films also showed good photocatalytic activity under UV-light illumination, with degradation of resazurin redox dye at a higher rate than with undoped TiO2.

Aerosol assisted chemical vapor deposition of conductive and photocatalytically active tantalum doped titanium dioxide films

This paper shows the aerosol assisted chemical vapour deposition of transparent, blue coloured and conductive tantalum doped titanium dioxide films from the CVD reaction of Ti(OEt)4 and Ta(OEt)5. Hall effect measurements showed the doped films to have excellent n-type electrical conductivity showing, to the best of our knowledge, the lowest reported sheet resistance ever recorded for Ta-doped TiO2 of 14 Ω sq−1. The Ta 6 atom% doped TiO2 film also showed the best electrical results with a charge carrier concentration of 1.60 × 1021 cm−3 and mobility of 1.44 cm2 V−1 s−1 making it a suitable electrode in photovoltaic devices. The doped films were multifunctional, showing good photocatalytic activity under UV-light illumination. XPS and XRD studies gave strong evidence that the Ta was entering the TiO2 lattice as Ta5+ and that a reduction of some Ti4+ to Ti3+ was observed.

Preparation of Sn4+-Doped Titanium Dioxide Photocatalytic Films on 304 Stainless Steel by Duplex Treatment

Sn4+-doped titanium dioxide photocatalytic films were synthesized on 304 stainless steel (SS) by a duplex treatment. The SS substrates were alloyed with titanium (Ti) through cathodic-arc ion plating followed by a microarc oxidation (MAO) treatment in different electrolytes. Field-emission scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy were used to characterize the films surface morphology, crystalline phase, and composition, respectively. Photocatalytic activity was measured using an UV-Vis spectrophotometer. It was found that the films with a porous structure are mainly composed of TiO2, which exists in an anatase and rutile state. Furthermore, small quantities of SnO2 have been found in the Sn4+-doped titanium dioxide films. The fraction of anatase varies with the MAO time and electrolytes, whereas the pore size remains the similar with the same MAO current intensity and density and the surface roughness increases slightly with increasing MAO time. It was also found that the photocatalytic activity of the Sn4+-doped porous film improved, and the film synthesized with a shorter MAO time in a lower Na2SnO3-containing electrolyte is superior to the films with longer MAO times and higher Na2SnO3 concentrations.

CVD Production of Doped Titanium Dioxide Thin Films

AbstractThis review focuses on the formation of doped titanium dioxide films by CVD. It describes a number of the functional applications of titanium dioxide films, and illustrates how these properties can be improved or modified by the introduction of anion and cation dopants. It details some of the underlying theory and looks at how density of states diagrams can be used to explain the doped film properties.

Microstructures and Photocatalytic Properties of S Doped Nanocrystalline TiO2 Films

The nanocrystalline S doped titanium dioxide films were successfully prepared by the improved sol-gel process. Here TiO(C4H9O)4 and CS(NH2)2 were used as precursors of titania and sulfur, respectively. The as-prepared specimens were characterized using x-ray diffraction (XRD), x-ray energy dispersive spectroscopy (EDS), high-resolution field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) surface area, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of organic dyes in aqueous solution. The results of XRD, FE-SEM, and BET analyses indicated that the TiO2 films were composed of nanoparticles. S doping could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Compared with pure TiO2 film, S doped TiO2 film exhibited excellent photocatalytic activity. It is believed that the surface microstructure of the modified films is responsible for improving the photocatalytic activity.

Doped Titanium Dioxide Films Prepared by Pulsed Laser Deposition Method

TiO2was intensively researched especially for photocatalystic applications. The nitrogen-doped TiO2films prepared by pulsed laser deposition (PLD) method were reviewed, and some recent new experimental results were also presented in this paper. A new optical transmission method for evaluating the photocatalystic activity was presented. The main results are (1) PLD method is versatile for preparing oxide material or complex component films with excellent controllability and high reproducibility. (2) Anatase nitrogen-doped TiO2films were prepared at room temperature, 200°C, and 400°C by PLD method using novel ceramic target of mixture of TiN and TiO2. UV/Vis spectra, AFM, Raman spectra, and photocatalystic activity for decomposition of methyl orange (MO) tests showed that visible light response was improved at higher temperature. (3) The automatic, continuous optical transmission autorecorder method is suitable for detecting the photodecomposition dynamic process of organic compound.

Nitrogen and europium doped TiO 2 anodized films with applications in photocatalysis

Micro-arc oxidation method is a useful process for mesoporous titanium dioxide films. In order to improve the photocatalytic activity of the TiO 2 film, N–Eu co-doped titania catalyst was synthesized by micro-arc oxidation in the H 2SO 4/Eu(NO 3) 3 mixture solution. The specific surface area and the roughness of the anodic titania film fabricated in the H 2SO 4/Eu(NO 3) 3 electrolyte, were increased compared to that of the anodic TiO 2 film prepared in H 2SO 4 solution. The absorbance response of N–Eu titania film shows a higher adsorption onset toward visible light region, and the incorporated N and Eu ions during anodization as a dopant in the anodic TiO 2 film significantly enhanced the photocatalytic activity for dye degradation. After dye decomposition test for 3 h, dye removal rates for the anodic TiO 2 film were 60.7% and 90.1% for the N–Eu doped titania film. The improvement of the photocatalytic activity was ascribed to the synergistic effects of the surface enlargement and the new electronic state of the TiO 2 band gap by N and Eu co-doping.