Mesostructured Dye‐Doped Titanium Dioxide for Micro‐Optoelectronic Applications

Optically transparent, mesostructured titanium dioxide thin films were fabricated using an amphiphilic poly(alkylene oxide) block copolymer template in combination with retarded hydrolysis of a titanium isopropoxide precursor. Prior to calcination, the films displayed a stable hexagonal mesophase and high refractive indices (1.5 to 1.6) relative to mesostructured silica (1.43). After calcination, the hexagonal mesophase was retained with surface areas >300 m² g^?1. The dye Rhodamine 6G (commonly used as a laser dye) was incorporated into the copolymer micelle during the templating process. In this way, novel dye‐doped mesostructured titanium dioxide films were synthesised. The copolymer not only directs the film structure, but also provides a solubilizing environment suitable for sustaining a high monomer‐to‐aggregate ratio at elevated dye concentrations. The dye‐doped films displayed optical thresholdlike behaviour characteristic of amplified spontaneous emission. Soft lithography was successfully applied to micropattern the dye‐doped films. These results pave the way for the fabrication and demonstration of novel microlaser structures and other active optical structures. This new, high‐refractive index, mesostructured, dye‐doped material could also find applications in areas such as optical coatings, displays and integrated photonic devices.     

The formation of MoS<Subscript>2</Subscript> secondary phase at the Cu—Zn—Sn—S/Mo interface during the sulfurization process of Cu—Zn—Sn precursor films

We report on the influence of the sulfurization conditions on the MoS₂ secondary phase formation in Cu—Zn—Sn—S thin films synthesized by thermal evaporation method of metals and intermetallics that can be used for the formation of absorbing layers of solar cells. The dependence between photoconductivity and the intensity of the base line of MoS₂ was found in Raman spectra, which is described by a curve with characteristic maximum. It was found that the secondary phase formation on the Cu—Zn—Sn—S/Mo boundary and photoconductivity of sulfurized films are strongly dependent on the applied temperature conditions. Specifically, films without MoS₂ phase have a low photoconductivity, whereas a high photoconductivity was observed for the films with significant content of secondary phase.     

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.     

Controlled Synthesis of Highly Crystallized Mesoporous Mn2O3 and Mn3O4 by Using Anionic Surfactants

Mesostructured manganese oxide (Mn₃O₄) is prepared by a soft‐templating method employing sodium dodecyl sulfate (SDS) as a structure‐directing agent. By removing the template from the as‐prepared mesostructured Mn₃O₄ by extraction or calcination, we successfully synthesized highly crystallized mesoporous Mn₃O₄ or Mn₂O₃, respectively, with different crystalline structures.     

Ordered micro/mesoporous composite prepared as thin films

A new synthesis method for preparation of thin films and powders consisting of zeolite beta nanocrystals embedded in ordered mesoporous silica matrix is described. The final structures possessing bimodal porosity, i.e., high degree of mesophase order and spatially defined microporous zeolite nanocrystals are obtained via simultaneous solvent evaporation of preformed silica/surfactant/ethanol/nanosized zeolite beta assemblies. The films were characterized with grazing-incident diffraction (GID), nitrogen sorption based on gravimetric measurements with quartz crystal microbalance (QCM) devices, and transmission electron microscopy (TEM). It is shown that the incorporation of beta nanocrystals in the mesoporous silica matrix and the mesophase order itself can be controlled through the variation of the fractional amounts of the zeolite nanoparticles and silica/surfactant solutions. The HR-TEM measurements showed that the nanosized Beta microporous crystals are separated and at the same time connected through an ordered mesostructured matrix.     

Graphitic mesostructured carbon prepared from aromatic precursors

Mesostructured carbons with graphitic framework walls are conveniently prepared at ambient pressures through the replication of a mesostructured silica template using an aromatic hydrocarbon as the carbon precursor and a catalyst.     

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.     

Preparation of transparent thin films of silica-surfactant mesostructured materials

Our recent studies on the simple synthetic route to the thin films of the periodic silica-surfactant mesostructured materials are summarized. By depositing the mixtures of the prehydrolyzed tetramethoxysilane and alkyltrimethylammonium salts under anacidic condition on solid supports, transparent thin films of the periodic silica-surfactant mesostructured materials formed. The resulting transparent films have been used as a precursor of the porous silica films and a support for organic photoactive species. Compared with other reported reactions for the silica-surfactant mesostructured materials, this method possesses advantages such as the ease of operation and the possibility to control microstructure and macroscopic morphology.     

Charge transport properties of MDMO PPV thin films cast in different solvents

Charge transport properties in thin films of Poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (MDMO PPV) cast using either chloroform (CF), toluene (TOL), or chlorobenzene (CB) as solvent were investigated. Hole mobility (μ) in these thin films measured using time‐of‐flight transient photoconductivity showed an increasing trend with respect to the solvent used in the same order, that is, μ_CF (2.4 × 10^?7 cm²/Vs) < μ_TOL (6.9 × 10^?7 cm²/Vs) < μ_CB (2.3 × 10^?6 cm²/Vs). Observed variations in mobilities were attributed to different morphologies of MDMO PPV chains in thin films cast using the aforesaid solvents. Nature of the interchain interactions and aggregate formation were obtained using photoluminescence (PL), Raman spectroscopy, and AFM studies. Ratio of PL peak intensities of 0–0 and 0–1 transitions, which is a direct measure of interchain interaction, was the highest in CB and lowest in CF. Variation in the relative intensities of out‐of‐plane wagging of vinylene group (～963 cm^?1 mode) in Raman spectra suggested different extent of coiling of polymer chains in these thin films. From these observations, it was elicited that aggregate size and interchain interactions are highest in CB and least in CF. AFM‐based topographic images of thin films further supported these variations in the size of aggregates. Variation in the aggregate sizes and interchain interactions explained the corresponding variation in the mobility. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1431–1439     

Specific features of the photoconductivity of polymer film composites containing a heterometallic iron(II)/zinc(II) complex

The specific features of electric conductivity and photoconductivity in films of composites based on poly(vinyl alcohol) doped with the complex [Fe(bipy)₃][Zn(NCS)₄] (where bipy is 2,2′-bipyridyl) and the effect of magnetic field on these properties were studied. It was found that photocurrent decreases with an increase in the magnetic field strength up to 5.5 kOe. It was assumed that the photoconductivity of these composites and its dependence on magnetic field are affected by paramagnetic iron(III) complex particles produced as a result of internal photoelectric effect. The effect of magnetic field on the photoconductivity is associated with the spin-dependent recombination of photogenerated charge pairs.     

Nanoporous silica films containing aluminum and titanium

By utilizing surfactant aggregates as supramolecular templates, mesoporous and mesostructured silicas with highly ordered structures became available. The resulting mesoporous silicas are promising candidates to host various photo- and electro-active species along with catalytically active species, due to their large and controllable pore sizes, highly ordered pore arrangements with low dimensional geometries, and reactive surfaces. We have developed the rapid solvent evaporation method, which is a modified sol-gel process, for synthesizing the mesostructured silica-surfactant films as well as the mesoporous silica films. Supported thin films, self-standing films and bubbles of mesoporous silicas have been synthesized by the rapid solvent evaporation method. The microstructures of the films have also been successfully controlled by changing the synthetic conditions. Taking advantage of the ease of synthetic operation and the transparency and homogeneity of the resulting materials, we have been interested in the introduction of functional units into the mesostructured materials. This paper reports the synthesis of transparent films of titanium- and aluminum-containing nanoporous silicas to modify the surface properties (such as adsorptive and catalytic) of nanoporous silicas. The incorporation of Al led to the formation of cation exchange or acidic sites on the mesopore surface, as revealed by the cationic dye adsorption experiments. The photocatalytic reactions of the Ti-containing nanoporous silica films were also examined.     

Mesostructured silica tubes and rods by templating porous membranes

Mesostructured silica tubes and rods were prepared by deposition of a prehydrolysed silica sol with surfactant onto the cylindrical pores of a polycarbonate (PC) membrane template, followed by calcination to remove the surfactant and membrane template. The tubular and rodlike morphologies of mesostructured silica were demonstrated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The tubes and rods show ordered hexagonal mesostructures, which were demonstrated by small angle X-ray diffraction (XRD) patterns and TEM measurements.     

Fabrication and properties of xBiFeO3-(1 − x)Bi4Ti3O12 system by sol–gel process

The thin films of mixture of xBiFeO₃-(1 − x)Bi₄Ti₃O₁₂ (x = 0.4, 0.5, and 0.6) system were prepared by a sol–gel process. The thicknesses of the thin films were 540, 500, and 570 nm, respectively. The crystal structure of all thin films annealed at 650 °C was analyzed by X-ray diffraction. It was found that the thin films at x = 0.4 and 0.5 mainly consisted of a Bi₄Ti₃O₁₂ phase while Bi₅Ti₃FeO₁₅ was the major phase of the thin film at x = 0.6. The thin film (x = 0.6) showed better ferroelectric properties in remnant polarization and polarization fatigue than those observed in the thin films (x = 0.4 and 0.5). The values of remnant polarization 2P _r and coercive field 2E c of the thin film at x = 0.6 were 36 μC/cm² and 192 kV/cm at an applied electric field of 260 kV/cm, respectively. There was almost no polarization fatigue up to 10¹⁰ switching cycles. Also weak ferromagnetism was observed in the thin film at x = 0.6.     

Macroscopic, mesostructured cationic surfactant/neutral polymer films: structure and cross-linking

Mesostructured films of alkyltrimethylammonium bromides or cetylpyridinium bromide and polyethylenimines that spontaneously self-assemble at the air/water interface have been examined using a range of surface sensitive techniques. These films are unusual in that they can be micrometers thick and are relatively robust. Here we show that the films can be cross-linked and thus removed from the liquid surface where they form, as solid, mesostructured polymer-surfactant membranes. Cross-linking causes little change in the structure of the films but freezes in the metastable mesostructures, enhancing the potential of these films for future applications. Cross-linked films, dried after removal from the solution surface, retain the ordered nanoscale structure within the film. We also report grazing incidence X-ray diffraction (GID), which shows that most films display scattering consistent with 2D-hexagonal phase crystallites of rodlike surfactant micelles encased in polymer. Polymer branching makes little difference to the film structures; however, polymer molecular weight has a significant effect. Films with lower polymer MW are generally thinner and more ordered, while higher polymer MW films were thicker and less ordered. Increased pH causes formation of thicker films and improves the ordering in low MW films, while high MW films lose order. To rationalize these results, we propose a model for the film formation process that relates the kinetic and thermodynamic limits of phase separation and mesophase ordering to the structures observed.     

Porphyrin-doped mesoporous silica films for rapid TNT detection

Two kinds of porphyrin-doped silica films with mesoporous structures were fabricated using evaporation-introduced self-assembly approach and examined for chemosensor applications to detect explosive compounds such as 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), and nitrobenzene (NB). All synthesized silica films showed high fluorescence quenching sensitivity toward the vapors of TNT, DNT, and NB but is strongly dependent on pore structure. The silica film with three dimensional pore structure exhibits the highest quenching efficiency close to the quenching efficiency reported for emissive conjugated polymers, indicating these kinds of mesostructured composites are potentially useful chemosensory materials for rapidly detecting trace explosives. The preparation conditions, the structures of the resulting films, their sensing performances, and the fluorescence quenching mechanism were discussed in this paper.     

Chemical solution processing and characterization of Ba(Zr,Ti)O<Subscript>3</Subscript>/LaNiO<Subscript>3</Subscript> layered thin films

Ba(Zr,Ti)O₃/LaNiO₃ layered thin films have been synthesized by chemical solution deposition (CSD) using metal-organic precursor solutions. Ba(Zr,Ti)O₃ thin films with smooth surface morphology and excellent dielectric properties were prepared on Pt/TiO _x /SiO₂/Si substrates by controlling the Zr/Ti ratios in Ba(Zr,Ti)O₃. Chemically derived LaNiO₃ thin films crystallized into the perovskite single phase and their conductivity was sufficiently high as a thin-film electrode. Ba(Zr,Ti)O₃/LaNiO₃ layered thin films of single phase perovskite were fabricated on SiO₂/Si and fused silica substrates. The dielectric constant of a Ba(Zr_0.2Ti_0.8)O₃ thin film prepared at 700°C on a LaNiO₃/fused silica substrate was found to be approximately 830 with a dielectric loss of 5% at 1 kHz and room temperature. Although the Ba(Zr_0.2Ti_0.8)O₃ thin film on the LaNiO₃/fused silica substrate showed a smaller dielectric constant than the Ba(Zr_0.2Ti_0.8)O₃ thin film on Pt/TiO _x /SiO₂/Si, small temperature dependence of dielectric constant was achieved over a wide temperature range. Furthermore, the fabrication of the Ba(Zr,Ti)O₃/LaNiO₃ films in alternate thin layers similar to a multilayer capacitor structure was performed by the same solution deposition process.     

Ferroelectric and dielectric behaviour of Bi0.92La0.08FeO3 multiferroic thin films prepared by soft chemistry route

Bi_0.92La_0.08FeO₃ (BLFO) thin films were grown on platine substrates by the soft chemical route. Ferroelectric and dielectric behaviors of BLFO films deposited by spin-coating technique and annealed at 773 K for 2 h in air atmosphere were explained. BLFO thin films obtained presents a rhombohedral structure. The BLFO films present dielectric and ferroelectric behaviors with dielectric permittivity and dielectric loss of approximately 81 and 0.0144 at 1 kHz. The Au/BLFO/Pt capacitor shows a hysteresis loop with remnant polarization of 20.6 μC/cm² and coercive field of 53.88 kV/cm. The polarization switching and the fatigue behavior of the BLFO films were significantly enhanced.     

In situ fluorescence probing of the chemical and structural changes during formation of hexagonal phase cetyltrimethylammonium bromide and lamellar phase CTAB/Poly(dodecylmethacrylate) sol–gel silica thin films

Surfactant-templated mesostructured sol–gel films formed by evaporation induced self assembly (EISA) exhibit highly-ordered hexagonal, lamellar, and cubic structures. The steady-state dip-coating configuration allows both the chemistry and the dynamics of the EISA process to be traced in real time because the steps involved in the formation of the mesostructured material are separated both spatially and temporally in the dip-coating direction. The dynamic processes occurring during film formation can be conveniently monitored by the combination of interferometry and fluorescence spectroscopy of incorporated molecular probes. The selected probes respond to changes in their rotational mobility and the surrounding solvent composition and report these changes through their fluorescence characteristics. By taking in situ fluorescence spectra at various positions within the progressively thinning film, changes in the solvent composition, onset of micelle formation and further organization to the final mesophase structure can be followed. The luminescence of the probe molecule is measured with a spatial resolution of 100 μm. Two categories of surfactant-templated mesostructured sol–gel films were examined. Cetyltrimethylammonium bromide (CTAB) systems assemble into a 2-D hexagonal surfactant/silica mesophase with the surfactant concentration used in this study. CTAB dodecylmethacrylate systems assemble into a lamellar mesophase, which can be further polymerized to form a poly(dodecylmethacrylate)/silica hybrid nanocomposite that mimics nacre. X-ray diffraction patterns, transmission electron microscopy images, and other techniques are used to characterize the final films.     

Electrorheology of suspensions of mesostructured and mesoporous silica in poly(dimethylsiloxane)

The effect of electric fields on the viscosity and shear stress of dispersions of mesostructured silicon dioxide powders and the products of their thermal treatment, that is, mesoporous silicas, in silicone oil is investigated. Mesostructured silicon dioxide powders are prepared using different structuring reagents, namely, octylamine, dodecylamine, and polyethylenimine. It is shown that the shear stresses developing in systems containing mesostructured powders as dispersed phases under the action of electric fields are several times higher than those in dispersions of mesoporous materials. The shear stresses developing in the systems containing powders of mesostructured materials as dispersed phases under the effect of electric fields depend on the nature of organic substrates present in pores and the conductivity of the systems. Electrorheological effect in dispersions of mesoporous silicas slightly depends on the structure of the materials. The observed synergism may be related to the interactions between the components of a mesostructured material, which manifest themselves as a rise in interfacial polarization. The stress-strain curves were measured upon tensile and compression in electric fields of different strengths.     

Sol–gel derived silver-incorporated titania thin films on glass: bactericidal and photocatalytic activity

Titanium dioxide (TiO₂) and silver-containing TiO₂ (Ag-TiO₂) thin films were prepared on silica pre-coated float glass substrates by a sol–gel spin coating method. The bactericidal activity of the films was determined against Staphylococcus epidermidis under natural and ultraviolet (UV) illumination by four complementary methods; (1) the disk diffusion assay, (2) UV-induced bactericidal test, (3) qualitative Ag ion release in bacteria inoculated agar media and (4) surface topographical examination by laserscan profilometry. Photocatalytic activity of the films was measured through the degradation of stearic acid under UV, solar and visible light conditions. The chemical state and distribution of Ag nanoparticles, as well as the structure of the TiO₂ matrix, and hence the bactericidal and photocatalytic activity, is controlled by post-coating calcination treatment (100–650 °C). Additionally, under any given illumination condition the Ag-incorporated films were found to have superior bactericidal and photocataltyic activity performance compared to TiO₂ thin films. It is shown that with optimized thin film processing parameters, both TiO₂ and Ag-TiO₂ thin films calcined at 450 °C were bactericidal and photocatalytically active.