Structural analysis of hybrid titania-based mesostructured composites

High-optical-quality titania-based mesostructured films with cubic or 2D-hexagonal symmetry were fabricated by combining trifluoroacetate (TFA)-modified titanium precursors with amphiphilic triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) copolymers. The distribution, dynamics, and local environments of the TFA-modified titania, PEO, and PPO components of the hybrid were investigated. IR/Raman spectroscopy, in situ small-angle X-ray scattering, and transmission electron microscopy studies indicate that TFA coordinates the titanium center and forms a stable complex that is subsequently organized by the block copolymer species into ordered mesostructures. Solid-state NMR (19)F-->(1)H cross-polarization, (13)C{(1)H} two-dimensional heteronuclear correlation, and (1)H relaxation techniques were used to determine that PEO is predominantly incorporated within the TFA-modified titania, and that PPO environments encompass both microphase separated regions and interfacial regions composed of mixed PPO and TFA-modified titania. NMR (19)F multiple-quantum spin counting measurements suggest that -CF(3) groups of the trifluoroacetate ligands do not form clusters but instead randomly distribute within the inorganic component of the hybrid.     

Preparation,characterization and luminescence of transparent thin film of ionogels

The sol–gel fabrication of luminescent and transparent thin film of ionogels containing trivalent lanthanide complexes have been obtained from the silylated ionic liquid in the presence of lanthanide salts (Ln³⁺, Ln=Tb and Eu) and organic ligands. The resulting thin films were investigated by FT-IR spectroscopy, scanning electron microscopy and luminescence spectroscopy. FT-IR spectra reveal the hydrolysis and condensation of the silylated ionic liquid as well as the formation of luminescent lanthanide complexes in the thin films. Scanning electronic microscope images show the homogeneous characteristic of the thin films.     

Evaporated thin films of insulating poly-(tetrabromo-p-phenylenediselenide)

It has been shown that thin insulating film at the interface transparent conductive oxide/organic electroluminescent film could improve the performance of organic electroluminescent diodes (OLED). Such insulating film can be inorganic or organic. Poly-(tetrabromo-p-phenylenediselenide) (PBrPDSe) has been proved to be an efficient insulating film in OLED. The properties of these evaporated PBrPDSe thin films have been systematically studied by IR absorption, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electron spin resonance and optical transmission measurements. It is shown that, when the deposition temperature is kept below the decomposition temperature of the polymer, tetrabromo-p-phenylenediselenide molecule is preserved during the deposition process. However the polymer, which is insoluble in powder form, becomes soluble after deposition. It can be concluded that films are mainly composed of oligomers of tetrabromo-p-phenylenediselenide.The electrical properties of SnO₂/PBrPDSe/Al thin films structures have been studied. The current-voltage characteristics exhibit a rectifying behaviour with a forward direction corresponding to a positive bias of the transparent conductive oxide film, the SnO₂.     

Deviations from bulk morphologies in thin films of block copolymer/additive binary blends

Deviations from bulk morphologies in thin films of binary blends of alkyne-functionalized diblock copolymer poly(ethylene oxide)-block-poly(n-butyl methacrylate-random-propargyl methacrylate) (PEO-b-P(nBMA-r-PgMA)) and Rhodamine B azide are reported, where thermal click reaction between the two components leads to microphase separated morphologies. Both in the bulk and in thin films, increasing the azide loading ratio resulted in the transition from a lamellar microdomain morphology to a hexagonally packed cylindrical mircodomain morphology. However, in thin films the lamellae-cylinder transition was observed at a different azide loading ratio, which was determined by film thickness. As a result, significant deviations from the bulk morphology were observed. These results indicate that surface interactions and confined geometry can play an important role in dictating the morphology in thin films of BCP/additive binary blends.     

Silica-Titania Mesostructured Films

Mesostructured silica-titania mixed oxide films in which the titania is well accessible on the silicate pore wall have been synthesized by a ligand-assisted templating (LAT) approach in combination with sol-gel processing. Control over the different hydrolysis and condensation rates of silicon and titanium alkoxides was achieved by complexation of the titanium species to the poly(ethylene oxide) part of an amphiphilic surfactant molecule (Brij56®). This modified precursor was used as structure-directing agent in the formation of thin mesostructured films. The structure and composition of the resulting material was characterized by X-ray diffraction, UV-vis spectroscopy and transmission electron microscopy.     

Sol–gel titania coating on unmodified and surface-modified polyimide films

Sol–gel coating of metal oxides on polymer substrates is a useful process to fabricate various organic–inorganic hybrid materials under mild conditions. However, this process is hardly applicable to pristine polyimide (PI) films because their surfaces do not display effective functional groups for metal oxide coatings. In this study, we firstly examined direct sol–gel coating of titania thin layers on unmodified PI film surfaces. The results confirmed homogeneous, ultrathin titania layer coating and showed that the thickness and microscopic morphology of the titania layers were affected by titanium alkoxide concentrations in the spin coating solutions. We next investigated titania layer coating on surface-modified PI films that prepared using alkaline hydrolysis, which generated carboxylic acid groups on the film surfaces. Optimal hydrolysis time was determined using FT-IR spectroscopy and contact angle measurements. After sol–gel titania coating on the hydrolyzed PI film surfaces, the Scotch tape test was conducted to evaluate adhesion strength between the titania layers and PI film surfaces. Morphological observations of the sample surfaces after the tests clearly showed that surface modification of PI films increased titania layer adhesions. Effect of hydrothermal treatments on film formability and adhesion strength between titania-PI film interfaces was also evaluated.     

Morphology and photoluminescence study of titania nanoparticles

Titania nanoparticles are prepared by sol–gel chemistry with a poly(ethylene oxide) methyl ether methacrylate-block-poly(dimethylsiloxane)-block-poly(ethylene oxide) methyl ether methacrylate triblock copolymer acting as the templating agent. The sol–gel components—hydrochloric acid, titanium tetraisopropoxide, and triblock copolymer—are varied to investigate their effect on the resulting titania morphology. An increased titania precursor or polymer content yields smaller primary titania structures. Microbeam grazing incidence small-angle X-ray scattering measurements, which are analyzed with a unified fit model, reveal information about the titania structure sizes. These small structures could not be observed via the used microscopy techniques. The interplay among the sol–gel components via our triblock copolymer results in different sized titania nanoparticles with higher packing densities. Smaller sized titania particles, (∼13–20 nm in diameter) in the range of exciton diffusion length, are formed by 2% by weight polymer and show good crystallinity with less surface defects and high oxygen vacancies.     

Electrochromic and photoelectrochromic properties of sol–gel derived tungsten trioxide/titania composite thin films

Tungsten trixoide/titania (WO₃-titania) composite thin films with W/Ti molar ratios of 100/0, 98/2, 96/4, 94/6 92/8 and 90/10 were prepared on fluorine-doped tin oxide conducting glass, and their electrochromic (EC) and photoelectrochromic (PEC) performances were investigated in this study. The composite thin films were synthesized by sol–gel process using peroxotungstic acid and titanium (IV) n-butoxide as the precursors. The surface morphology and composition of the composite thin films were characterized using scanning electron microscope with energy dispersive spectrometer. Electrochemical experiments with in situ spectroscopic measurement were employed to study the EC properties of the composite thin films. It was found that the presence of titania in the WO₃ matrix might slightly decreases its EC performance. PEC cells using the composite thin films as the working electrode and a sputtered semitransparent platinum thin film on ITO as the counter electrode were fabricated and their PEC performances were investigated. The device using composite thin film prepared from sol solution with a W/Ti molar ratio of 96/4 exhibited the best PEC performance.     

Efficient preparation of nanocrystalline anatase TiO2 and V/TiO2 thin layers using microwave drying and/or microwave calcination technique

This study has demonstrated that the synthesis of TiO₂ and V/TiO₂ thin layers may be significantly improved and extended if microwave energy is employed during the drying and/or calcination step. Thin nanoparticulate titania layers were prepared via the sol-gel method using titanium n-butoxide as a precursor. As prepared films were then analyzed by means of various characterization techniques (Raman spectroscopy, UV/Vis, AFM, XPS) in order to determine their functional properties. The photocatalytic activities of prepared layers were quantified by the decoloring rate of Rhodamine B. All thermal treatments in microwave field were done in the same manner, by using an IR pyrometer in the microwave oven and monitoring the temperature of the heating. Nevertheless the microwave and thermally prepared materials were different. This in turn may lead to differences in their functional and also photocatalytic properties.     

Precise Control of Metal Oxide Thin Films Deposition in Magnetron Sputtering Plasmas for High Performance Sensing Devices Fabrication

Magnetron sputtering deposition is a widely used technique to deposit thin film precisely at nanoscale level. During the deposition of metal oxide thin films, reactive oxygen gas is introduced into the deposition chamber. Pure metal and metal oxide materials can be used as sputter target, although the simplest way is by using a pure metal target. In such reactive process, the effect of target poisoning significantly influence the deposition process and the growth mechanisms of metal oxide thin films became very complex. In general, external parameters such as discharge power, working pressure, reactive gases ratio and substrate temperature are used to optimize the properties of deposited thin films. Then, ex-situ analyses such as scanning electron microscope and X-ray diffraction analysis are performed to obtain the optimized parameter. Sample depositions and ex-situ analyses consume time to achieve the goal through try and error. In this article, in-situ plasma diagnostics are reviewed focusing on an optical emission spectroscopy to precisely control and investigate the sputter target poisoning effect during the deposition of metal oxide thin films. The emission of atomic lines from several metal and oxygen atoms were used to discuss the deposition mechanisms and their correlation with the deposited thin films was observed. Finally, the deposited metal oxide thin films were proposed and tested for several applications such as gas sensor and frequency selective surface glass.     

Nanoporous thin films from ionically connected diblock copolymers

An ionically connected polystyrene-block-poly(ethylene oxide) diblock copolymer (PS^?+PEO) has been prepared by blending a PEO block functionalized by a dimethylamino group at one extremity with a sulfonic acid terminated PS block. Proton transfer occurs from the sulfonic acid to the dimethylamino group, resulting in the formation of an ion pair acting as a junction between the two polymer blocks. This copolymer was further used to prepare thin films with a cylindrical morphology consisting of PEO cylinders embedded in a PS matrix and oriented perpendicularly to the film surface. Nanoporous thin films with sulfonate groups on the pore walls have been finally obtained after solvent extraction of the PEO microphases. The presence of those sulfonate groups was evidenced by grafting a positively charged fluorescent dye on the pore walls.     

Nano-architectural silica thin films with two-dimensionally connected cagelike pores synthesized from vapor phase

Novel mesostructured silica thin films were prepared on a Si substrate by a vapor-phase synthesis. Vapor of tetraethoxysilane (TEOS) was infiltrated into a surfactant film consisting of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer. Nanophase transition from a lamellar structure to a two-dimensional cage structure of a silica-surfactant nanocomposite was found under vapor infiltration. The rearrangement into the cage structure implies high mobility of the silica-surfactant composites in solid phase. The silica thin films have two-dimensionally connected cagelike mesopores and are isotropic parallel to the film surface. The structure of pores of the films is advantageous for next-generation low-k films. The mesoporous structure has a large lattice parameter d of approximately 102 A, silica layer thickness of approximately 58 A, pillar diameter in the middle of approximately 60 A, pore size of approximately 72 A, BET surface area of approximately 729 m(2)/g, and pore volume of approximately 1.19 cm(3)/g. The films synthesized by the vapor infiltration show a lower concentration of residual Si-OH groups compared to the films prepared by a conventional sol-gel method. The films show high thermal stability up to 900 degrees C and high hydrothermal stability. This method is a simpler process than conventional sol-gel techniques and attractive for mass production of a variety of organic-inorganic composite materials and inorganic porous films.     

PM IRRAS investigation of thin silica films deposited on gold. Part 1. Theory and proof of concept

Polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) was successfully used for the first time to characterize an optically transparent thin oxide film. SiO2 layers of 7 nm thickness were synthesized by plasma enhanced chemical vapor deposition (PECVD) on 200 nm thick gold covered glass slides. Despite the fact that silica is transparent and absorptive to IR radiation when deposited in the form of thin films on a gold surface, it preserves the high metallic reflectivity for the IR light. At grazing angles of incidence of the IR beam, the enhancement of the normal component of the electric field at the interface is comparable to that of Au alone. In addition, the analysis of the structure of a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid monolayer deposited using the Langmuir-Blodgett technique is demonstrated.     

Structural and optical properties of TiO2 thin films prepared by spin coating

Transparent semiconducting thin films of titanium oxide (TiO₂) were deposited on glass substrates by the sol–gel method and spin-coating technique. The physical properties of the prepared films were studied as a function of the number of spun-cast layers. The microstructure and surface morphology of the TiO₂ films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), with respect to the film thickness. The XRD analysis reveals that the films are polycrystalline with an anatase crystal structure and a preferred grain orientation in the (101) direction. The morphological properties were investigated by AFM, which shows a porous morphology structure for the films. The optical properties of the films were characterized by UV–Visible spectrophotometry, which shows that the films are highly transparent in the visible region and their transparency is slightly influenced by the film thickness, with an average value above 80 %. The dependence of the refractive index (n), extinction coefficient (k), and absorption coefficient (α) of the films on the wavelength was investigated. A shift in the optical band gap energy of the films from 3.75 to 3.54 eV, as a function of the film thickness, has been observed.     

Functionalized nanoporous thin films from metallo-supramolecular diblock copolymers

A polystyrene-[Ni(2+)]-poly(ethylene oxide) metallo-supramolecular block copolymer (PS-[Ni(2+)]-PEO), where -[ is a terpyridine, is used to create nanoporous thin films with free terpyridine ligands homogenously distributed on the pore walls. The PS-[Ni(2+)]-PEO block copolymer is synthesized by a two step assembly process, and is then self-assembled into a thin film in order to obtain PEO cylinders oriented perpendicularly to the film surface. The supramolecular junction is opened by exposing the film to an excess of a competing ligand, and the free PEO block is then rinsed away by a selective solvent. The presence of the terpyridines on the pore walls is evidenced by fluorescence spectroscopy after formation of a fluorescent complex with an europium salt.     

Preparation of nitrogen doped zinc oxide nanoparticles and thin films by colloidal route and low temperature nitridation process

Nitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO₂ substrate from a ZnO colloidal solution. Zinc peroxide (ZnO₂) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H₂O₂ solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250 °C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV–Visible transmittance spectroscopy.     

Nanostructured latex films from poly(butyl methacrylate) latex cross-linked with poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock macro-cross-linker

Biphasic polymer latexes were synthesized by a seeded swelling and polymerization method. The latexes were composed of a poly(butyl methacrylate) core and a poly(ethylene oxide) rich shell cross-linked with poly(ethylene oxide)-poly (propylene oxide)-poly(ethylene oxide) triblock diol diacrylate macro-cross-linker. Nanostructured films were obtained by annealing the biphasic polymer latexes at a temperature between the glass-transition temperatures of the core latex and the cross-linked poly(ethylene oxide) based shell. Atomic force microscope images of the latex film revealed that the poly(butyl methacrylate) core phase is confined in the poly(ethylene oxide)-rich continuous phase with the form of separate nanosized spheres.     

Electrodeposition of Dye-Doped Titania Thin Films

We extend our novel low-voltage electrochemical method for oxide thin film formation from sol-gel monomers to include entrapment of organic molecules within the films. We also describe an extension of the method to titania thin films, which are obtained from titanium tetra-n-propoxide in alcoholic solutions by applying potentials in the range of +2.0 to ?1.4 V to indium tin oxide electrodes. The film thickness (ranging between 20–1000 nm) is controllable by changing either the potential or the duration of its application. We demonstrate that this electrochemical method provides a convenient way for entrapment of organic dopants within the film. Four dyes were used for that purpose: Basic Blue 41, methylene-blue, tris(2,2′-bipyridine)iron(II) and tris(2,2′-bipyridine)ruthenium(II).     

Oxynitride perovskite LaTiOxNy thin films deposited by reactive sputtering

This paper reports on the first study of structural and optical properties of reactively RF-sputtered lanthanum titanium oxynitride thin films using an original oxynitride LaTiO₂N target and an argon–nitrogen mixture as reactive plasma. The depositions were carried out by varying the process parameters such as RF power, total pressure, argon and nitrogen rates and substrate temperature. Wavelength dispersive spectrometry (WDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–visible spectroscopy show that titanate lanthanum oxynitride compounds can exist as a domain composition, LaTiO_xN_y. Films prepared in pure argon are oxide films, transparent, amorphous and insulating. Polycrystalline and [001]-textured oxynitride thin films, with different nitrogen contents, can be deposited on SrTiO₃ substrates, depending on the sputtering conditions. As expected, the introduction of nitrogen in the coatings leads to a band gap narrowing. Oxynitrides' thin films are thus coloured and semiconductive.     

Synthesis and characterization of metal substituted AlxCr1−x(acetylacetonate)3 single-source precursors for their application to MOCVD of thin films

A detailed study, involving the synthesis of a single-source precursor containing two metal ions sharing the same crystallographic site, has been undertaken to elucidate the use of such a single-source precursor in a CVD process for growing thin films of oxides comprising these two metals, ensuring a uniform composition and distribution of metal ions. The substituted complexes Cr_1−xAl_x(acac)₃, where acac = acetylacetonate, have been prepared by a co-synthesis method, and characterized using UV–Vis spectroscopy, TGA/DTA measurements, and single crystal X-ray diffraction at low temperature. All the studied compositions crystallize in the monoclinic space group P2₁/c with Z = 4 in the unit cell. It was observed that the ratio (Al:Cr) of the site occupancy for the metal ions, obtained from single crystal refinement, is in agreement with the results obtained from complexometric titrations. All the solid state structures have the metal in an octahedral environment forming six-membered chelate rings. M–O acac bond lengths and disorder in the terminal carbon have been studied in detail for these substituted metal–organic complexes. One composition among these was chosen to evaluate their suitability as a single-source precursor in a LPMOCVD process (low-pressure metal–organic chemical vapour deposition) for the deposition of a substituted binary metal oxide thin film. The resulting thin films were characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy.