Alkoxide Precursor Solution Research Articles

Crystalline structure and phase development in ZrxTi1-xO2 (x=0.9–0.2) ceramic nanofibers from electrospun precursors

Nanofibrous ZrxTi1-xO2 (x = 0.9–0.2) ceramic materials were produced using a high-yield, free surface alternating field electrospinning (AFES) process (a.k.a. AC-electrospinning) from metal alkoxide precursor solutions. Depending on the precursor composition, the production rates of 4.8–6.4 g/h in terms of the resulting ceramic nanofibers were demonstrated with a single-electrode AFES system. The average diameter of ZrxTi1-xO2 fibers varied in the range of 190–435 nm, depending on the alkoxide/polymer mass ratio in the precursor and annealing temperature. Zr/Ti molar ratio is a key factor that determines the crystallization temperature and phase composition of ZrxTi1-xO2 nanofibers after thermal processing between 600 and 1200 °C, but it has a moderate effect on textural properties of the resulting nanofibers. When the molar fraction of zirconia is > 0.7, the nanofibers are composed primarily of a nanocrystalline titania-rich TiO2–ZrO2 solid solution without the formation of separate TiO2 phase. At zirconia molar fraction of 0.5, stable orthorhombic Zr0.5Ti0.5O2 zirconium titanate structure forms above 680 °C. TiO2 (anatase or rutile) forms as a separate phase in addition to ZrxTi1-xO2 phases when Zr molar fraction is 0.2, depending on the annealing temperature. The results of this study demonstrate that a large variety of nanofibrous ZrO2–TiO2 ceramic materials with tailored compositions can be efficiently prepared for targeted applications by using free-surface AFES and appropriate thermal processing.

Robust and conductive mesoporous reduced graphene oxide-silica hybrids achieved by printing and the sol gel route

Reduced graphene oxide (rGO) scaffoldings are used as templates to create lightweight 3D rGO/silica and rGO/silico-aluminate hybrids by a simple impregnation route and the sol-gel method. The printed rGO assemblies are infiltrated by the corresponding alkoxide precursor solution and gelled by exposure to ammonia vapours, producing an hybrid replica of the rGO structure. The hybrids show a significant prevalence of mesopores, with total porosity above 94 %, density of ∼ 0.1 g⋅cm−3 and high specific surface area (≥ 190 m2⋅g−1). As a result, the 3D composite materials show enhanced water adsorption capacity and hydrophilicity, display compressive strengths in the range 0.1 – 0.4 MPa, which scale with the proportion of silica (or Al-modified silica) on the hybrid scaffold, and electrical conductivities are above 60 S⋅m−1. These properties are very attractive for applications in the removal of pollutants, water filtering, catalysis, drug delivery, or energy production and storage.

Rutile to anatase phase transition induced by N doping in highly oriented TiO2 films.

Highly oriented TiO2 thin films were deposited onto Al2O3(0001), SrTiO3(001), and LaAlO3(001) substrates by spin coating a titanium alkoxide precursor solution followed by annealing. The films were nitrogen doped by two different routes: either by adding tetramethyethylenediamine (TMEDA) to the precursor solution or alternatively by high temperature ammonolysis. Undoped TiO2 films were highly oriented and the phase was dependent on the substrate. N doping by ammonolysis led to transformation of rutile films to anatase, confirmed by XRD and by XPS valence band spectroscopy. Significant differences were observed in the spatial distribution of the nitrogen dopant depending upon which synthesis method was used. These two factors may shed light on the increased photocatalytic efficiencies reported in N doped TiO2.

Biodegradation-tunable mesoporous silica nanorods for controlled drug delivery.

Mesoporous silica in the forms of micro- or nanoparticles showed great potentials in the field of controlled drug delivery. However, for precision control of drug release from mesoporous silica-based delivery systems, it is critical to control the rate of biodegradation. Thus, in this study, we demonstrate a simple and robust method to fabricate "biodegradation-tunable" mesoporous silica nanorods based on capillary wetting of anodic aluminum oxide (AAO) template with an aqueous alkoxide precursor solution. The porosity and nanostructure of silica nanorods were conveniently controlled by adjusting the water/alkoxide molar ratio of precursor solutions, heat-treatment temperature, and Na addition. The porosity and biodegradation kinetics of the fabricated mesoporous nanorods were analyzed using N2 adsorption/desorption isotherm, TGA, DTA, and XRD. Finally, the performance of the mesoporous silica nanorods as drug delivery carrier was demonstrated with initial burst and subsequent "zero-order" release of anti-cancer drug, doxorubicin.

The effects of curing temperature on bilayer and monolayer hybrid films: mechanical and electrochemical properties

Thermal curing contributes to the formation and performance of hybrid films (HFs), because it enhances barrier properties by reticular densification, which originates from a less porous layer, and improves corrosion protection and mechanical properties. Increasing the number of deposited layers further enhances these properties. In this work, a HF formed by an alkoxide precursor solution of 3-(trimethoxysilylpropyl) methacrylate and tetraethoxysilane with cerium nitrate and polyethylene glycol was applied to the galvanized steel. The films were obtained by either monolayer or bilayer dip coating, and they were cured at different temperatures (60 and 90 °C) for 20 min. The results indicate that both the temperature and the number of layers interfere on the ability of HFs to act as effective barriers against corrosion. The bilayer system cured at 60 °C showed the best electrochemical impedance results; however, the monolayer HF cured at 90 °C presented higher wear resistance.

Improved Performance and Stability of Inverted Organic Solar Cells with Sol–Gel Processed, Amorphous Mixed Metal Oxide Electron Extraction Layers Comprising Alkaline Earth Metals

AbstractStability of organic photovoltaic devices (OPVs) is a limiting factor for their commercialization and still remains a major challenge whilst power conversion efficiencies are now approaching minimum requirements. The inverted organic solar cell (iOSC) architecture shows promising potential for improving significantly the cell's working lifetime. However, when solution processed ZnO is used as electron extraction layer, an undesirable light‐soaking step is commonly required before the device reaches a non‐permanent maximum performance. This work investigates the use of Sr and Ba doped ZnO films, ZnSrO and ZnBaO, formed by sol‐gel deposition using molecular alkoxide precursor solutions, as electron extraction layers in a model iOSCs with poly [3‐hexylthiophene] (P3HT): [6, 6]‐phenyl C60 butyl acid methyl ester (PCBM) as the active layer. We show that using these ternary oxides the light‐soaking step can be circumvented by preventing a dipole forming between the oxide and the active organic layer as supported by electroabsorption spectroscopy measurements of the device built‐in field. It is suggested that Sr or Ba doping results in suppression/reduction of the oxygen adsorption at mobile oxygen vacancy sites on the metal oxide surface. Like in thin film transistor (TFT) applications, where materials like InGaZnO are rapidly becoming an important technology, the use of amorphous, mixed metal oxides allows improving the performance and stability of interfacial charge extraction layers for organic solar cells.

BaTiO3 THIN FILM BY CSD FROM MOLECULAR-DESIGNED PRECURSOR SOLUTION

BaTiO3 (BT) thin films were deposited by the cost effective method of a chemical solution deposition (CSD). 0.3 M BT precursor solution was prepared by the partial hydrolysis method. Partially hydrolyzed Ti -alkoxide and Ba precursor solution was reacted to prepare the highly polymerized BT precursor solution. BT precursor solution was spin-coated on a Pt/Ti/SiO2/Si substrate with (100)-oriented LaNiO 3 (LNO) thin film electrode. In addition, effect of the pre-annealing at 600°C in O2 atmosphere was elucidated by measuring the electrical properties of the resulting BT thin films deposited by the different annealing process. As a result, molecular-design of the BT precursor and a LNO thin film electrode were effective to enhance the electrical properties of the resultant BT thin films, as well as 600°C pre-annealing.

Controlled synthesis of fluorescent silica nanoparticles inside microfluidic droplets

We study the droplet-based synthesis of fluorescent silica nanoparticles (50-350 nm size) in a microfluidic chip. Fluorescein-isothiocyanate (FITC) dye is first chemically linked to aminopropyl triethoxysilane (APTES) in ethanol and this reaction product is subsequently mixed with tetraethyl orthosilicate (TEOS) to yield a fluorescent silicon alkoxide precursor solution. The latter reacts with an aqueous ethanol-ammonia hydrolysing mixture inside droplets, forming fluorescent silica nanoparticles. The droplets are obtained by pinching-off side-by-side flowing streams of alkoxide solution/hydrolysing mixture on a microfluidic chip using a Fluorinert oil continuous phase flow. Synthesis in droplets leads to a faster reaction and allows drastically improved nanoparticle size uniformity (down to 3% relative standard deviation for 350 nm size particles) when compared to conventional bulk synthesis methods, thanks to the precise control of reagent concentrations and reaction times offered by the microfluidic format. Incorporating FITC inside silica nanoparticles using our method leads to reduced dye leakage and increases the dye's stability, as evidenced by a reduced photochemical bleaching compared to a pure FITC solution.

Intermediate-Temperature, Proton-Conducting Membranes of Hafnium Phosphate and Zirconium Phosphate/Borate/Sulfate

Uniform, defect-free nanofilms (around 100 nm thick) of hafnium phosphate were prepared via layer-by-layer deposition of precursor solution of metal alkoxides and were shown to give practically useful proton conductivity at as fuel cell electrolyte membrane. Annealing of the deposited precursor film at gave a lower area specific resistance than that at , and this effect was coincident with the formation of the pyrophosphate unit. The best (lowest) value of less than for hafnium phosphate membrane (annealing at , 291 nm thick, conductivity of at ) was comparable to that of a nanofilm of an yttrium-doped zirconium phosphate. The values of nanofilms of zirconium sulfate and zirconium borate were 2–3 orders higher than that of the corresponding zirconium phosphate. It is clear from these results that nanofilms of various solid acids are promising candidates for the electrolyte membrane of fuel cells operating at the intermediate temperatures of .

Sol−Gel Tungsten Oxide/Titanium Oxide Multilayer Nanoheterostructured Thin Films: Structural and Photoelectrochemical Properties

Multilayer structures of alternating thin titanium and tungsten oxide layers having dimensions of ∼20 nm have been fabricated from titanium alkoxide and various tungstate precursor solutions using the dip coating technique. Single, double, and triple layer titanate and tungstate thin films were deposited on silicon substrates, and these films were initially annealed at 400 °C. Structural and microstructural aspects of the films were investigated using a variety of techniques, including X-ray reflectometry, grazing incidence X-ray absorption spectroscopy (GIXAS), cross-sectional transmission electron microscopy (TEM), and secondary ion mass spectrometry. The dimensions of the films and the character of the interfaces were principally gauged by cross-sectional TEM and X-ray reflectometery. All films were continuous on a local scale and had relatively low surface roughness. At the treatment temperature of 400 °C, only the tungsten oxide component showed appreciable crystallinity. The multilayer films had rel...

Synthesis, Densification, and Phase Evolution Studies of Al2O3–Al2TiO5–TiO2 Nanocomposites and Measurement of Their Electrical Properties

Alumina–aluminum titanate–titania (Al2O3–Al2TiO5–TiO2) nanocomposites were synthesized using alkoxide precursor solutions. Thermal analysis provided information on phase evolution from the as‐synthesized gel with an increase in temperature. Calcination at 700°C led to the formation of an Al2O3–TiO2 nanocomposite, while at a higher temperature (1300°C) an Al2O3–Al2TiO5–TiO2 nanocomposite was formed. The nanocomposites were uniaxially compacted and sintered in a pressureless environment in air to study the densification behavior, grain growth, and phase evolution. The effects of nanosize particles on the crystal structure and densification of the nanocomposite have been discussed. The sintered nanocomposite structures were also characterized for dielectric properties.

Effect of Zr/Ti ratio on the microstructure and ferroelectric properties of lead zirconate titanate thin films

Lead zirconate titanate (PZT) thin films with Zr/Ti ratios of 30/70, 40/60, 52/48, 60/40, and 70/30 derived from metal alkoxide precursor solution were deposited on platinized silicon substrates by sol–gel technique. X-ray diffraction analysis showed that the films exhibit a single perovskite phase with mostly (1 1 1) preferred orientation. The SEM study proved that PZT films possess a dense microstructure without cracks and voids. Ferroelectric and dielectric phenomena were studied in correlation with the variation of Zr/Ti ratio and its influence on crystallographic structure and morphology of the films. It was found that, among all the investigated films, the PZT films with Zr/Ti ratio of 52/48 exhibit the most promising properties including high remanent polarization and low coercive field of ≈24 μC cm −2 and 72 kV cm −1, respectively. The films were also characterized by excellent dielectric properties (dielectric permittivity ≈1200 and loss factor ≈0.02).

Directed Mineralization on Polyelectrolyte Multilayer Films

ABSTRACTSilica formation aided by polypeptides is being actively investigated for a wide range of applications including biomaterials synthesis, ceramics and controlled release systems. We envision that biocatalyzed mineralization could have application as a dental material where in situ formation of mineral layers could provide needed wear-resistance or sealing capability. The approach would be more clinically relevant, if a polymer host could be used to carry and specifically position the biocatalyst on a surface and additionally maintain the catalyst activity.Accordingly, we studied the influence of simple catalytic polypeptides on silica formation from prehydrolyzed alkoxide precursor solutions onto a surface. The polypeptides were localized on to the surface as multilayered thin films using the layer-by-layer (LbL) assembly of polyelectrolytes. Polylysine (PLL) or another biocatalytic polycation, poly(ethyleneimine) (PEI), was adsorbed layer-by-layer up to 10 bilayers on silicon wafers in combination with a negatively charged polyelectrolyte polymer host, poly(sodium-4-styrene sulfonate) (PSS) to prepare PEI-(PLL/PSS)10, PEI-(PEI/PSS)10 and PEI-(PEI/PSS/PLL/PSS)10 multilayer films. Pre-hydrolyzed alkoxysilane solutions were placed dropwise on the catalytic films for silicification. Additionally, the effects of precursor concentration, solvent and drying were evaluated. The morphology, roughness and contact mechanical stiffness of the formed silica were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM).The resulting silica morphology was plate-like or spherical, and porous with average particle size depending on the catalyst and its positions on the surface. Without a catalyst the silica formed over longer times with a fine, gel-like appearance. The morphology of silica produced on the substrate was different from that of particles catalyzed in solution with the same polypeptide catalyst. Additionally, it was found that the homogeneity of PEI-(PLL/PSS)10 films increased with drying temperature, silica precursor concentration and the presence of ethanol. The contact mechanical stiffness of the silica particles (40 N/m) catalyzed from PEI-(PLL/PSS)10 films was lower than the non-silicified areas (48 N/m) suggesting that regions of the silica were amorphous and hydrated. These results show that a polypeptide applied to a surface as a multiple layer with an oppositely charged polymer host (PSS) maintains its activity for silicification. The generally coherent nature of the mineral coating suggests its potential for enhancing critical restorative dental interfaces; however properties like porosity, hydration and their effect on hardness and permeability will need further study.

Synthesis of mesoscopic barium titanate single crystals incorporating a cuboid-shaped hollow core

Mesoscopic barium titanate (BaTiO 3) single crystals with dimensions of 10–15 nm that incorporated a cuboid-shaped hollow core were synthesized by a sol–gel method using a highly-concentrated Ba–Ti alkoxide precursor solution combined with a surfactant templating approach. In this synthesis route, perovskite BaTiO 3 nanocrystals were formed directly by a polycondensation reaction of the gel framework during aging at room temperature. Hollow-core nanocrystals were contained in the product, which was obtained by firing the crystalline gel at 500 °C in flowing oxygen. The cuboid-shaped hollow cores of the nanocrystals were about 0.2 nm in size and had {1 0 0} inner surfaces. In addition, it was also found that some kind of ordered structure was formed on a mesoscale with an interplaner spacing of 14 nm before and after firing at 500 °C.

Porous SiO2-BaMgF4:Eu(II) Glass-Ceramic Thin Films and Their Strong Blue Photoluminescence

Oxyfluoride glass-ceramic thin films of nominal 90SiO2⋅10(Ba1−xEu x )MgF4 compositions were prepared by sol–gel method starting from mixtures of metal trifluoroacetates and silicon alkoxide precursor solutions. Films were deposited on silica glass substrates by spin-coating and heating at 750°C. Eu2+ ions were preferentially incorporated into BaMgF4 nanoparticles, which were dispersed in the silica glass matrix. The films exhibited broad-band blue photoluminescence (PL) in response to the ultraviolet light excitation. Addition of N,N-dimethylformamide to starting coating solutions resulted in a porous microstructure of the heat-treated films. Efficient UV excitation was promoted due to the Rayleigh scattering in the porous films; thereby the PL emissions could be strongly enhanced.

Piezoelectric properties of lead-free CaBi4Ti4O15 thin films

Ca Bi 4 Ti 4 O 15 (CBTi144) thin films are evaluated for use as lead-free thin-film piezoelectrics in microelectromechanical systems. CBTi144 thin films were prepared on Pt substrates by dip coating a precursor solution of metal alkoxides. We fabricated a piezoelectric bimorph actuator using those films and analyzed the displacement induced by the electric field. Young’s modulus was measured by the vibrating-reed technique and the piezoelectric constant d31 was derived by analysis of bending displacement and measurement of displacement-voltage curve. The measurements revealed that the CBTi144 films had a large piezoelectric constant d31 of 32pm∕V.

Preparation and characterization of multi-coating PZT thick films by sol–gel process

The Pb(Zr 0.5Ti 0.5)O 3 films of a few micron in thickness have been successfully deposited by sol–gel technique from nonhydrolyzed metal alkoxide precursor solutions. X-ray diffraction shows that the films exhibit a single perovskite phase with (1 0 0)-preferred orientation. SEM study indicates that PZT films possess a dense microstructure with no crack and void. A Pt/PZT/LaNiO 3 capacitor has been fabricated and showed excellent ferroelectricity, with a remnant polarization up to 53 μC/cm 2. The optical waveguide property has been examined by the prism-film coupling experiment. Multimodes are excited, indicating that the PZT thick films are potentially useful for optical waveguide devices.

Micro-patterning of Lead Zirconate Titanate Thin Films Seeded with Barium Strontium Titanate Nano-crystalline Particles by Photo-irradiation

Lead zirconate titanate (PZT) thin films seeded with barium strontium titanate (BST) nano-crystalline particles were fabricated on a Si wafer with a spin-coating technique. The BST particles synthesized with a sol-gel method were dispersed in an acetylacetone (chelating reagent) modified PZT precursor solution of complex alkoxides for the fabrication. The micro-patterns of the PZT film containing 50 mol% BST particles could be obtained by the direct photo-irradiation to the fabricated films for 40 min without any pre-heating treatments, while the PZT films in the absence of the BST particles required pre-heating treatment at 200°C for 10 s before the photo-irradiation. This suggested that the BST crystallines accelerated decomposition of the chelate compounds and subsequent polycondensation of PZT alkoxides.

Novel Ferroelectric Candidates in a Series of ABi4Ti4O15 (A: Alkaline Earth Metals) Thin Films

ABi4Ti4O15 (A: alkaline earth metals) thin films were prepared on Pt-passivated Si substrates by using the precursor solution of metal alkoxides. As-deposited thin films initiated crystallization below 550°C and enhanced the crystallinity at higher temperature via rapid thermal annealing in oxygen. The crystallinity of the ABi4Ti4O15 thin films depended on the A-site cation of the alkaline earth metals but the content of the pyrochlore phase as a second phase was independent of the cation. The phase purity of BLSFs strongly depended on the crystallinity and crystallographic orientation of the Pt bottoms. The 650°C-annealed CaBi4Ti4O15 thin films on the relatively low-crystalline Pt was a single phase of the BLSFs and exhibited better ferroelectric properties.

Preparation of PZT thick films by an interfacial polymerization method

Pb(Zr0.53Ti0.47)O3 (PZT) films of 10 to 50 μm in thickness were prepared by a new sol-gel process using an interfacial polymerization technique. The interfacial polymerization process is that an alkoxide precursor solution is poured on the surface of water in a container to form a gel film at the interface between the two immiscible liquids. The precursor solution was prepared by adding PZT alkoxide solution, PZT powders coated with Pb5Ge3O11 (PG), and a surfactant into hexane solvent. After the polymerization at the interface, the gel films were gently placed on a silicon substrate by draining the water in the container. The gel films containing PZT powders were sintered at 950°C for 10 min to obtain crystallized PZT films. The remanent polarization of a PZT thick film was 33.1 μC/cm2. The piezoelectric d33 constant measured with a Mach-Zehnder interferometer was 225 pm/V and was independent of frequency from 0.2 to 3 kHz.