Formation of nanoporous and nanocrystalline anatase films by pyrolysis of PEO–TiO2 hybrid films

Poly(ethylene oxide)–titania (PEO–TiO₂) organic–inorganic hybrid films were synthesized through a sol–gel process and spin coating. The mixed precursor sols were aged for 6 and 12 h, respectively, prior to the spin coating. Hybrid films were crystallized to the anatase phase first and then further heat treated at elevated temperatures for different time periods to analyze the anatase-to-rutile phase transformation. Quantitative X-ray diffraction (Q-XRD) results were employed for Johnson–Mehl–Avrami (JMA) kinetic analyses and the Avrami exponent (n) was determined for each film. The Arrhenius plots were created based on the JMA plots and the activation energy (Q) values for the phase transformation were determined for each film. The difference in the phase transformation kinetics in the films was discussed based upon the difference in the activation energy values and thus the molecular structures of each hybrid film. Nanoporous and nanocrystalline anatase films were successfully achieved through the retarded phase transformation during the pyrolysis of the organic–inorganic hybrid films. Owing to the maximized surface area these nano-structured anatase films are highly expected to show the enhanced photocatalytic efficiency compared to common TiO₂ films as well as sintered bulk forms.     

Optical constants of DC magnetron sputtered titanium dioxide thin films measured by spectroscopic ellipsometry

Optical constants of DC magnetron sputtered TiO₂ thin film have been determined by Spectroscopic Ellipsometry in the photon energy range 1.2 to 5.5 eV at room temperature. The measured dielectric‐function spectra reveal distinct structures at energies of the E1, E1 + Δ1 and E2 critical points are due to interband transitions. The root mean square roughness of the magnetron sputtered TiO₂ thin films evaluated by ex‐situ atomic force microscopy is 5.8 nm. The Dielectric constant values were found to be substantially lower than those for the bulk TiO₂. The dielectric related Optical constants, such as the refractive index, extinction coefficient, absorption coefficient and normal incidence of reflectivity determined from the spectroscopic ellipsometry data are presented and analyzed. The optical constants of the films were also determined using the optical transmittance measurements and the results were discussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polymer dye-containing nanocomposites as photocatalysts

A significant improvement of photocatalytic efficiency is achieved by the synthesis of TiO₂/SiO₂ nanocomposites where silica matrix provides the transport of reagents to TiO₂ nanoparticles via porous structure, generation of the new active sites and thermal stability. The semiconductive films contained 10 or 30% of TiO₂ in silica matrix are synthesized by sol-gel method using concentrated anatase titania colloid. The complex composites consisted of i) the Acridine Yellow dye molecules and the polyepoxypropyl carbazole; ii) the azobenzene containing polymer covered onto the titania/silica films are obtained as photocatalytic materials. Photocatalytic activity of the composites is tested via the reduction of dichromate ions.     

Wide viewing optically clear adhesives using PMMA/TiO2 core-shell micro/nanoparticles

Abstract

Optically clear adhesives (OCAs) are widely used in optoelectronic displays because of their high outdoor visibility. Here, we develop new transparent adhesive films with wide-viewing-angle characteristics using poly(methyl methacrylate) (PMMA)/TiO₂ core–shell micro/nanoparticles. TiO₂ nanoparticles are embedded in the shell of PMMA microparticles, forming an organic–inorganic hybrid structure. To examine the optical transmittance of the films in the visible wavelength region, ultraviolet-visible spectroscopy is performed and light diffusion is evaluated. The TiO₂ nanoparticles in the shell of the PMMA microparticles exhibit improved light scattering, and the new functional OCAs are expected to provide wide-viewing-angle characteristics for future flexible displays.     

Preparation and characterization of monolithic methylsilicone xerogels doped with liquid-phase synthesized TiO2

The xerogels of methylsilicone doped with TiO₂ were prepared by incorporation of liquid-phase prepared TiO₂ in methylsilicone matrix. The microstructure and properties of the composite xerogels were investigated by Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), N₂ sorption, and wide-angle X-ray powder diffraction (XRD). The results indicated that the as-prepared TiO₂ particles could be well dispersed in methylsilicone matrix. The different amounts of TiO₂ doped in methylsilicone oligomer solution resulted in different reaction process and microstructure. The thermal stability of the composite monolith was enhanced after doping TiO₂ particles.     

Structural and optical properties of TiO2:SnO2 thin films prepared by sol gel method

ABSTRACT

TiO₂:SnO₂ thin films were deposited on glass substrates, by using sol gel spin coating method with different ratio (3%, 5% and 7%) at 3200 rpm, to study their effect on different properties of TiO₂: SnO₂ thin films. The structural and optical properties of films have studied for different ratio. These deposited films have been characterized by various methods such as X-Ray Diffraction (XRD), Ultra Visible spectroscopy. The (XRD) can be used to identify crystal structure of as deposited films. The Transmission spectra have shown the transparent and opaque parts in the visible and UV wavelengths.     

EXAFS study of the Er3+ ion coordination in SiO2–TiO2–HfO2 sol–gel films

The local order around ion-implanted Er³⁺ ions in SiO₂–TiO₂–HfO₂ thin films prepared by sol–gel, was studied by extended X-ray absorption fine structure at the Er-L_III edge. Both the first and second coordination shells of Er³⁺ were analyzed for different heat-treatments. While the first coordination shell always consisted of ～6–7 oxygen atoms at distances varying between 2.23 and 2.27 Å, the structure of the second shell was found to vary with the film composition and heat-treatment. Namely, whereas Si was found to be the only second neighbor of erbium in binary SiO₂–TiO₂ films, the addition of HfO₂ caused a preferential replacement of Si by Hf. The post-implantation thermal treatments also played a fundamental role in determining the final environment of the erbium ions.     

Development of multifunctional photoactive self-cleaning glasses

Glasses for architecture must have many functions in addition to their transparency. For example, the glasses with the functions, of self-cleaning, light control, UV reduction, anti-bacterial, energy conversion, and so on, will be used in buildings in the near future. This paper reviews some results on multifunctional photoactive glasses based on multi-layer coatings containing TiO₂ film and other functional coatings developed by us recently. The self-cleaning of glasses can be realized by coating the photoinduced super-hydrophilic nanoporous thin films based on TiO₂ photocatalysts via sol–gel route. A new method to enhance the photocatalytic activity of TiO₂ thin films direct coated on soda-lime glass was developed by treating the films in acidic solutions. The films also have good photoinduced anti-bacterial properties. The doping of a small amount of silver into the TiO₂ porous film can enhance its anti-bacteria effect without UV light irradiation. The TiO₂ thin films by appropriate heat-treatment can operate as self-cleaning glass in the visible light region. The UV reduction self-cleaning glasses are prepared by magnetron sputtering two layers of TiO₂–CeO₂ and TiO₂ thin films on soda-lime glasses. The TiO₂–CeO₂ thin films can cut all of UV light through adjusting the ratio of TiO₂ and CeO₂. The TiO₂/TiN/TiO₂ type multi-layer coated on glass substrate can act as low-E self-cleaning glass. The potential water-repellent coating based on TiO₂ is discussed finally.     

Microstructure and percolation threshold characteristics of reactive sputtered Au-TiO2 granular composite films

The Au/TiO₂ composite films were prepared by using reactive co-sputtering technique. The size and shape of the embedded Au particles and the absorption spectra of the composite films were investigated by using SEM, XRD, and UV-VIS-NIR spectrophotometer, respectively. The average size of Au particles and the electrical conductivity decrease as the sputtering pressure increases. The normalized conductivity of the films deposited at five different pressures with the Au concentration in the range of 0.15-0.91 were measured. The percolation threshold increases from 0.21 to 0.90 as the sputtering pressure increases from 2 × 10⁻² Torr to 9.5 × 10⁻² Torr.     

Fabrication of two-dimensional lattices by using photosensitive sol-gel and four-beam laser interference

This work demonstrates a promising method to fabricate 2D lattices by using photosensitive sol-gel method combining with four-beam of a 350.7 nm Kr ion laser interference. Photosensitive TiO₂ gel films with chelate complexes as precursors are fabricated. The characteristics of UV and IR spectra of the films and their variations in the process of laser irradiation are investigated. The results show that the gel films had an absorption peak at about 358 nm due to the formation of chelate complex. This peak gradually decreases with irradiation in time, which indicates the photosensitive properties of the TiO₂ films. A flexible four-beam interference system is proposed. Given incident angles 20.5° and 44.5°, the lattices with pitch of 700 nm and 326 nm are fabricated, respectively. The diffraction phenomenon of the 700 nm lattices is investigated by inverse method. The results are fully consistent with the 2D crystal diffraction theory.     

Photocatalytic properties of TiO2/ZnO thin film

ABSTRACT

TiO₂, ZnO and ZnO/TiO₂ thin films have been prepared by radio frequency magnetron sputtering method under different temperatures. Their photo catalytic activities have been investigated. The structural of the thin films were characterized by X-ray diffraction and Raman spectroscopy. The photo catalytic activities of TiO₂ and ZnO/TiO₂ samples were evaluated by the photo decomposition of methylene blue. We note that the structural proprieties of the thin films showed a perfect crystallization along the (002) for ZnO, Rutile (110) for TiO₂ and Anatase (101) for TiO₂. The experimental results show that the bilayer ZnO/TiO₂ were the most efficient photo catalysts compared to the layer of TiO₂. This increased catalytic effect can attributed to the interface between the ZnO layer and the TiO₂ one, which modify significantly the chemical potential of the bilayer.     

Surface enhanced Raman scattering in an amorphous matrix for Raman amplification

In order to improve the efficiency of Raman Amplifiers, the Surface Enhanced Raman Scattering (SERS) effect of an amorphous matrix of TiO₂ was studied. First, optimisation of the amorphous layer quality was performed by depositing thin films on glass substrates at different temperatures. Then, thin films of amorphous TiO₂ were deposited on silicon commercial gold SERS substrates (Klarite®) by a dip-coating process. The SERS effect was demonstrated by the great difference of Raman intensities of the amorphous TiO₂ matrix dip-coated on active and inactive parts of Klarite® substrate under 633 nm and 780 nm laser excitations in the tail of the Surface Plasmon Resonance band of gold nanoparticles.     

Urbach absorption edge and disordering processes in As2S3 thin films

The temperature studies of transmission spectra for as-deposited and annealed amorphous As₂S₃ thin films are carried out. The optical absorption spectra in the range of their exponential behaviour are analysed, and the dispersion dependences of refractive index as well as their temperature variation are investigated. The Urbach behaviour of optical absorption edge is revealed, the Urbach absorption edge parameters are determined, and their temperature dependences are studied. The effect of different type of disordering on the optical absorption processes in As₂S₃ thin films is studied. A comparative analysis of Urbach absorption edge parameters of As₂S₃ bulk glasses and thin films is performed.     

Far-infrared spectra of amorphous titanium dioxide films

The amorphous TiO₂ film structure on an aluminum substrate was studied by far infrared reflection-absorption spectroscopic (IRAS) analysis. The transverse (TO) and longitudinal (LO) optical modes of the amorphous oxide films were studied experimentally and through simulation. These optical modes were compared to those of the corresponding crystal. While TO modes of the films correspond to those of the crystal, the LO modes do not. The best agreement between the experimental and the simulated IRAS spectra is obtained when an appropriate dielectric function ε_film(ν) is chosen. ε_film(ν) must be related to the amorphous character of the films e.g. by averaging the anisotropic crystal properties. As a consequence of our findings, the Berreman effect does apply in amorphous films to absorption bands at frequencies of the peaks of the loss function Im[−1/ε_film(ν)], which does not correspond to frequencies of the LO modes of the crystal.     

Studies on a possible growth mechanism of silver nanoparticles loaded on TiO2 thin films by photoinduced deposition method

The TiO₂ thin films loaded with silver nanoparticles were prepared on soda-lime glass substrates by a photoinduced deposition method. The TiO₂ films immersed in AgNO₃ solution were vertically irradiated by UV light with center wavelength of 365 nm for 60 h. The as-produced films were characterized by X-ray diffraction (XRD), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The studies show that the film after UV excitation is composed of anatase phase TiO₂ and metallic silver with face centered cubic structure. A possible growth mechanism of silver nanoparticles on TiO₂ thin films under UV irradiation was proposed. The charge carriers of TiO₂ semiconductor are generated by photoexcitation. Owing to the conduction band position of TiO₂ which is above the standard potential of Ag⁺/Ag, the generated electrons could transfer from the conduction band to Ag⁺ adsorbed on the surface of the TiO₂ films. Therefore, the Ag⁺ was finally reduced into a Ag atom, which could preferentially localize in the grain boundaries of TiO₂ particles due to high surface free energy there. With the irradiation time extended, silver nanoparticles were shaped into certain morphologies on the surface of the TiO₂ films.     

Structure and optical properties of amorphous GeSx films prepared by PLD

Amorphous GeS_x (x = 2, 4, 6) films were prepared by the pulsed laser deposition (PLD) technique. The optical band gaps (E_g^opt) and refractive indices of the films were obtained from the optical absorption spectra and transmission spectra, respectively. The short-wave absorption edges of the films were described using the ‘non-direct transition’ model proposed by Tauc. The dispersion of the refractive index was analyzed in terms of the single-oscillator Wemple–Di Domenico model. The structural units of the films were characterized using Raman spectroscopy. In addition to the basic structural units of edge-sharing and corner-sharing [GeS₄] tetrahedra, there are S–S homopolar bonds in S-rich GeS₄ and GeS₆ films while Ge–Ge bonds exist in stoichiometric GeS₂ film. The results show that the index of refraction decreases while E_g^opt increases with the sulphur content in the GeS_x films. The changes of E_g^opt were discussed in relation to the structure of GeS_x films, which were confirmed by the Raman spectra analysis.     

Optical spectra of borate glasses containing Ti and Co in relation to their structure

The optical absorption spectra of borate glasses of the base composition (mol%) 35 (Na₂O+BaO)·65 B₂O₃, to which Ti and Co ions were introduced, have been measured in the range 190–900 nm. The addition of increasing amounts of TiO₂ up to 16 g/100 g glass, introduces an intense charge transfer band in the UV region that shifts towards longer wavelengths without imparting any coloration to the glass samples.Titanium ions are present as the Ti⁴ state and its addition produces glass of more coherent structure. The cobalt ions are found to be present in two symmetries; as CoO₆ units with absorption bands (denoted here as bands a and b) around 525–530 nm and 580–595 nm (respectively), and as CoO₄ units with absorption bands (denoted here as band-c) around 620–635 nm. Replacing Na ions by Ba ions or increasing the TiO₂ content favours the conversion of CoO₄ units into the CoO₆ ones.     

Synthesis and optical properties of MPTMS-capped CdS quantum dots embedded in TiO2 thin films for photonic applications

CdS nanoparticles have been prepared via a colloidal route using 3-mercatopropyltrimethoxysilane as a capping agent. The stability of the particles in solution and embedded in TiO₂ matrices has been followed by optical absorption. Both the size and the size distribution of the particles are well controlled, thus allowing a tunable emission. Raman and photoluminescence spectroscopies have been used to characterize colloidal CdS, TiO₂:CdS solutions and thin films deposited on soda-lime slides. The Z-scan technique has been used to measure the non-linear refractive indices of the solutions and the non-linear absorption coefficients of the thin films.     

Nanocrystalline properties of chemically deposited (Cd0.95‐Pb0.05)S:CdCl2, Gd/Dy films

Results of SEM and XRD studies, optical absorption spectra and photoluminescence emission spectra are presented for the films of (Cd_0.95‐Pb_0.05)S:CdCl₂, Gd/Dy prepared by chemical bath deposition technique and using thiophenol and methanol as capping agents. The deposition of films is based on precipitation followed by condensation on the substrates. SEM studies show existence of irregular distribution of particles alongwith presence of rod/tube type structure. The XRD studies show diffraction lines of CdS, PbS and CdCl₂. Blue shift has been observed in absorption spectra showing quantum confinement. Particle sizes determined from XRD studies and absorption spectral studies are found to lie in the nano range. Photoluminescence emission spectra consist of emissions in blue and green‐yellow regions. The observed emissions are related to the combination of defect levels and levels due to rare earths. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and characterization of ZnO-TiO2 films obtained by sol-gel method

The sol-gel route has been applied to obtain ZnO-TiO₂ thin films. For comparison, pure TiO₂ and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400-750 °C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400 °C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn₂TiO₄, anatase TiO₂ and amorphous fraction. The XRD analysis presumes that Zn₂TiO₄ becomes a favored phase at the highest annealing temperature of 750 °C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO-TiO₂ films have been compared with those of single component films (ZnO and TiO₂). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature.