纳米二氧化钛粉体及薄膜制备的研究进展

本文对近几年有关纳米二氧化钛粉体及薄膜的制备研究进行综述。重点介绍及评述了以无机钛盐和有机钛盐为前驱体制备纳米二氧化钛粉体及利用自组装方法制备二氧钛薄膜的最新研究成果。对今后研究工作的趋势进行了探讨。     

Atomic-layer deposition of thin titanium dioxide films from tetramethoxytitanium and water

Comparative analysis of atomic-layer deposition of titanium dioxide in precursor systems Ti(OCH₃)₄-H₂O and Ti(OC₂H₅)₄-H₂O demonstrated that the growth rate of titanium dioxide produced by atomic-layer deposition in the Ti(OCH₃)₄-H₂O system can be adequately estimated using a model taking into account the number and size of ligands in the metal-containing precursor. Studies in simulated body fluids demonstrated that polycrystalline anatase TiO₂ coatings are capable of accelerated osteointegration, which makes this precursor promising for development of new biomedical articles.     

Atomic layer deposition of thin films of titanium dioxide from titanium tetramethoxide and water

The atomic layer deposition of titanium oxide in the precursor systems Ti(OCH₃)₄-H₂O and Ti(OC₂H₅)₄-H₂O was compared. The growth rate of titanium oxide formed by the atomic layer deposition in the Ti(OCH₃)₄-H₂O system can be adequately estimated with due to regard for the number and size of ligands of a metal-containing precursor. The study in simulated body fluid solutions showed that polycrystallin TiO₂ coatings with anatase structure are prone to accelerated osseointegration and, consequently, promising for the development of new biomedical products.     

Photocatalytic lithography based on thin films of amorphous hydrated titanium dioxide

The mechanism of photoactivation of amorphous hydrated titanium dioxide thin films containing palladium ions toward the reaction of electroless deposition of nickel was studied. It was shown that the photocatalytic reduction of palladium ions during UV irradiation results in the formation of intermediate Pd(I) states that subsequently disproportionate, yielding a Pd nanophase. The palladium nanoparticle-catalyzed electroless deposition of nickel on exposed areas of the titanium dioxide photolayer makes it possible to fabricate metal patterns having a 5-μm resolution, with the fast and irreversible capture of photoelectrons at the latent image formation step preventing the image from blurring, including the process on conducting substrates.     

Kinetic rules of precipitation of thin films of titanium dioxide from the gas phase containing titanium tetraisopropylate

Precipitation of titanium dioxide layers from the gas phase in the reaction system containing titanium tetraisopropylate and oxygen at the total pressure 1 kPa is studied. It is shown that in the range of 300–500°C the precipitation proceeds in the kinetic regime and is accompanied by the formation of layers of monotonous thickness containing nanocrystalline phases of anatase and rutile. In the temperature range 300–350°C the activation energy value was 92.7 kJ mol^?1, and at higher temperatures (up to 500°C) it decreased to 17.5 kJ mol^?1. The increase in the precipitation temperature caused the increase in relative amount of rutile in the precipitated layers.     

Thick titanium dioxide films for semiconductor photocatalysis

Thick paste TiO₂ films are prepared and tested for photocatalytic and photoinduced superhydrophilic (PSH) activity. The films are effective photocatalysts for the destruction of stearic acid using near or far UV and all the sol–gel films tested exhibited a quantum yield for this process of typically 0.15%. These quantum yields are significantly greater (4–8-fold) than those for titania films produced by an APCVD technique, including the commercial self-cleaning glass product Activ™. The films are mechanically robust and optically clear and, as photocatalysts for stearic acid removal, are photochemically stable and reproducible. The kinetics of stearic acid photomineralisation are zero order with an activation energy of ca. 2.5 kJ mol⁻¹. All titania films tested, including those produced by APCVD, exhibit PSH. The light-induced fall, and dark recovery, in the water droplet contact angle made with titania paste films are similar in profile shape to those described by others for thin titania films produced by a traditional sol–gel route.     

Sol-gel made titanium dioxide nanostructured thin films as gas-sensing materials for the detection of oxygen

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Effect of the substrate nature on the formation of thin titanium dioxide films by molecular layering

Results of structural studies of titanium dioxide films synthesized on glass, silicon, and mica substrates by molecular layering are presented. An analysis of data furnished by electron and X-ray diffraction analyses and atomic-force microscopy of the samples in different growth stages revealed the effect of the substrate nature on the structure of the titanium oxide coatings synthesized.     

Visible-light induced hydrophilicity on nitrogen-substituted titanium dioxide films

Nitrogen-substituted titanium dioxide thin films were found to undergo hydrophilic conversion under irradiation with visible light. The hydrophilicity was enhanced by increasing the degree of nitrogen substitution at oxygen sites. The water contact angle for the thin film with the greatest hydrophilicity, TiO1.9884N0.0116, changed from 20 degrees to 6 degrees following irradiation.     

Photocatalytic activity and biodegradation of polyhydroxybutyrate films containing titanium dioxide

This study aims to evaluate the photocatalytic activity and biodegradation of polyhydroxybutyrate (PHB) films containing titanium dioxide (TiO₂). Nanosized TiO₂ photocatalysts were immobilized onto PHB film to overcome the difficulty of the recovery process. PHB is a suitable base material as it is naturally biodegradable and is produced from renewable resources. The photocatalytic degradation of organic compounds, photocatalytic sterilization activity and biodegradation rate in garden soil of PHB-TiO₂ composite films were investigated. After an hour under solar illumination, 96% of methylene blue solution was decolorized. The antibacterial activity against Escherichia coli (E. coli) using PHB-TiO₂ composite film exhibited enhanced photocatalytic sterilization activity over time. As for the ability to biodegrade, PHB-TiO₂ composite films placed on soil surface with no direct solar illumination showed slower degradation rate compared to those receiving direct solar illumination. Interestingly, the latter composite films showed faster degradation rates compared to pure PHB films indicating that the degradation is mainly due to photocatalytic activity. PHB-TiO₂ composite films buried in soil generally showed slower degradation rates compared to pure PHB films and were dependent on the soil microbial activity.     

Photo-electrochemical and photocatalytic properties of chemically-treated and thermally-annealed titanium dioxide films

Chemical treatment followed by thermal annealing of titanium dioxide nanoparticle film surfaces with urea or ammonium acetate were found to exert a profound influence on their photoelectrochemical or photocatalytic activity. These films were dip-coated over conducting substrates, then dipped in urea or ammonium acetate aqueo us solutions, and finally baked at 300 or 500°C to yield two sets of chemically-treated TiO₂ (CT-TiO₂) films. The incident photon to electron conversion efficiency (IPCE) of the CT-TiO₂ films in the near-UV region was significantly higher compared to the pristine (untreated) TiO₂ samples baked similarly at 300 or 500°C. Higher photocurrents for formate photo-oxidation were also observed for the CT-TiO₂ samples relative to their untreated TiO₂ counterparts. All the CT-TiO₂ films showed better photocatalytic activity toward Cr(VI) reduction with respect to their untreated TiO₂ counterparts. The enhanced performance of the CT-TiO₂ films was attributed to morphological changes as seen in scanning electron microscopy images. Possible reasons for the performance improvement in terms of better charge carrier separation properties of the CT-TiO₂ films are finally discussed.     

Atomic layer deposition of the titanium dioxide thin film from tetraethoxytitanium and water

Using the methods of Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction in the geometry of the grazing beam, and Fourier transform infrared spectroscopy, we studied the chemical composition and structure of thin films of titanium dioxide formed by atomic layer deposition from tetraethoxytitanium and water. It is shown that the films obtained are characterized by a high stoichiometry of composition and by amorphous or polycrystalline structure of the anatase modification, depending on the number of reaction cycles. Using a model of the process of atomic layer deposition that takes into account the size and number of ligands of the reacting molecules, we calculated the amount of titanium dioxide deposited in a single reaction cycle.     

Fe-doped SnO2 transparent semi-conducting thin films deposited by spray pyrolysis technique: Thermoelectric and p-type conductivity properties

In this paper, we report structural, electrical, optical, and especially thermoelectrical characterization of iron (Fe) doped tin oxide films, which have been deposited by spray pyrolysis technique. The doping level has changed from 0 to 10 wt% in solution ([Fe]/[Sn] = 0–40 at% in solution). The thermoelectric response versus temperature difference has exhibited a nonlinear behavior, and the Seebeck coefficient has been calculated from its slope in temperature range of 300–500 K. The Hall effect and thermoelectric measurements have shown p-type conductivity in SnO₂:Fe films with [Fe]/[Sn] ≥ 7.8 at%. In doping levels lower than 7.8 at%, SnO₂:Fe films have been n-type with a negative thermoelectric coefficient. The Seebeck coefficient for SnO₂:Fe films with 7.8 at% doping level has been obtained to be as high as +1850 μV/K. The analysis of as-deposited samples with thicknesses ～350 nm by X-ray diffraction (XRD) and scanning electron microscopy (SEM) has shown polycrystalline structure with clear characteristic peak of SnO₂ cassiterite phase in all films. The optical transparency (T%) of SnO₂:Fe films in visible spectra decreases from 90% to 75% and electrical resistivity (ρ) increases from 1.2 × 10^?2 to 3 × 10³ Ω cm for Fe-doping in the range 0–40 at%.     

Photocatalytic degradation of polyhydroxybutyrate films using titanium dioxide nanoparticles as a photocatalyst

Photocatalytic degradation of polyhydroxybutyrate (PHB) polymeric films (30 μm thickness) containing different concentrations of titanium dioxide (TiO₂) nanoparticles under ultraviolet (UV) irradiation (λ_max = 313 nm) has been studied. The activity of TiO₂ (0.001-0.005%) as a photocatalyst was determined by monitoring various functional group indices, weight loss in polymeric films and photodegradation rate constant (k _d) with irradiation time. Photodegradation was found to be highly dependent on the TiO₂ nanoparticles concentration and the UV irradiation time. The rate of PHB sample photodegradation was highest when the concentration of TiO₂ was 0.005% (by weight) and lowest when its concentration was 0.001%.

     

Partial dewetting of polyethylene thin films on rough silicon dioxide surfaces

The effect of roughness on the dewetting behavior of polyethylene thin films on silicon dioxide substrates is presented. Smooth and rough silicon dioxide substrates of 0.3 and 3.2-3.9 nm root-mean-square roughness were prepared by thermal oxidation of silicon wafers and plasma-enhanced chemical vapor deposition on silicon wafers, respectively. Polymer thin films of approximately 80 nm thickness were deposited by spin-coating on these substrates. Subsequent dewetting and crystallization of the polyethylene were observed by hot-stage optical microscopy in reflection mode. During heating, the polymer films melt and dewet on both substrates. Further observations after cooling indicate that, whereas complete dewetting occurs on the smooth substrate surface, partial dewetting occurs for the polymer film on the rough surface. The average thickness of the residual film on the rough surface was determined by ellipsometry to be a few nanometers, and the spatial distribution of the polymer in the cavities of the rough surface could be obtained by X-ray reflectometry. The residual film originates from the impregnation of the porous surface by the polymer fluid, leading to the observed partial dewetting behavior. This new type of partial dewetting should have important practical consequences, as most real surfaces exhibit significant roughness.     

Quantification of antimony depth profiles in Sb-doped tin dioxide thin films

Sb-doped SnO(2) thin films, deposited by atomic layer epitaxy (ALE) for gas sensor applications, have been characterized by secondary ion mass spectrometry (SIMS). Quantification of the depth profile data has been carried out by preparing a series of ion implanted standards. Average concentrations determined by SIMS have been compared with Sb/Sn ratios obtained by X-ray fluorescence (XRF) spectrometry and proton induced X-ray emission (PIXE) spectrometry and have been found to be in good agreement. However, a detection limit of 5x10(18) at cm(-3) could only be obtained because of mass interferences. SIMS data show that the ALE technique can be used to produce a controllable growth and doping of thin films.     

Quantification of antimony depth profiles in Sb-doped tin dioxide thin films

Sb-doped SnO₂ thin films, deposited by atomic layer epitaxy (ALE) for gas sensor applications, have been characterized by secondary ion mass spectrometry (SIMS). Quantification of the depth profile data has been carried out by preparing a series of ion implanted standards. Average concentrations determined by SIMS have been compared with Sb/Sn ratios obtained by X-ray fluorescence (XRF) spectrometry and proton induced X-ray emission (PIXE) spectrometry and have been found to be in good agreement. However, a detection limit of 5×10¹⁸ at cm^-3 could only be obtained because of mass interferences. SIMS data show that the ALE technique can be used to produce a controllable growth and doping of thin films.     

Novel titanium compounds for metal-organic chemical vapor deposition of titanium dioxide films with an ultrahigh deposition rate

A new titanium diolate compound Ti(mpd)(mdop)(2) (1) containing a beta-ketoester and a dimeric derivative [Ti(mpd)(mdop)(mu-OMe)](2) [2; mpd = 2-methyl-2,4-pentanediolate, mdop = (CH(3))(3)CC(O)C(-)HCOOCH(3)] have been synthesized and characterized by FT-IR, (1)H NMR, (13)C NMR, mass spectroscopy, and elemental analysis. Complex 2 was further characterized by X-ray structural analysis. Both 1 and 2 are fairly stable in air and in solvents such as tetrahydrofuran and toluene. They are also thermally stable and do not leave any residue during flash evaporation at around 280 degrees C. The new titanium complexes were used as precursors for the deposition of TiO(2) thin films by liquid-source metal-organic chemical vapor deposition. Compared with commercial Ti precursors, such as Ti(mpd)(tmhd)(2) (tmhd = 2,2,6,6-tetramethylheptanedionate) and Ti(OPr(i)())(2)(tmhd)(2), the new titanium complexes demonstrated a much higher deposition rate of TiO(2) film growth (3-6 times) at 400-475 degrees C. The deposited TiO(2) film from complex 2 was found to be in a crystalline anatase phase with a smooth surface morphology and low carbon content. Crystal data for 2: 233(2) K, a = 12.570(4) A, b = 13.817(4) A, c = 11.157(3) A, beta = 101.059(5) degrees, monoclinic, space group P2(1)/c, Z = 2.     

Surface functionalized titanium thin films: zeta-potential, protein adsorption and cell proliferation

The relationship between electric charge at a material surface and protein adsorption is essential to understand the mechanism of biological integration of materials with tissues. This study investigated the influence of titanium thin films' surface chemistry and surface electric charge (zeta-potential) properties on protein adsorption and cell proliferation. Titanium thin films were surface functionalized with different functional end groups, such as -CH=CH2, -NH2 and -COOH groups in order to produce surfaces with a variety of electric charge properties. The chemical compositions, electric charges and wettability were investigated by using X-ray photoelectron spectroscopy (XPS), zeta-potential measurements and water contact angle measurements, respectively. XPS revealed the surface functionalization of titanium films with -CH=CH2, -NH2, and -COOH groups, which were converted from -CH=CH2 groups. Ti-COOH samples showed the lowest water contact angles and zeta-potential compared to all other samples investigated in this study. NH2-terminated titanium films displayed intermediate contact angles of 70.3+/-2.5 degrees . Fibrinogen adsorption on titanium films and surface functionalized titanium films were investigated in this study. Ti-COOH samples displayed a lower protein adsorption than all other groups, such as NH2-, -CH=CH2-terminated titanium thin films. A tendency that the lower zeta-potential of the samples, the lower the protein adsorption at their surfaces was observed. In vitro cell proliferation tests were also performed on the different surface functionalized titanium films. NH2-terminated titanium films displayed good cell proliferation and cell viability tendency. However, a lower cell proliferation on COOH-terminated titanium films was observed compared with NH2-terminated titanium films. This effect was attributed to the difference in protein adsorption of these samples.     

In situ monitoring of electrostriction in anodic and thermal silicon dioxide thin films

Stresses due to electric fields in thermal and anodic silica thin layers can impact the devices using these films as dielectrics. Accurately quantifying the internal stress as a function of the electric field is thus of technological importance. In this work, electrostrictive stresses are monitored during cyclic polarization of silica thin films on silicon and during the growth of anodic silica. These are obtained by combining curvature and ellipsometry measurements in situ. In silica films grown by thermal oxidation of silicon, the electric field can generate either tensile or compressive stresses depending on its magnitude and on the silica polarization history. The electromechanical coupling in thermal silica is assumed to be controlled by a reversible change of the dipole organization. For anodic silica films, the stress generated by the electric field is tensile and varies linearly with the square of the electric field above 0.26 V²/nm² under both cyclic polarization and oxidation conditions.