Fabrication of sol–gel derived ZrO2 thin film for HR coatings via rapid thermal annealing process

The properties of sol–gel derived ZrO₂ thin films heated via a novel method of rapid thermal annealing process were studied. We investigated the effects of heat-treatment schedules with different ramp rates on the refractive index and thickness of ZrO₂ thin films as well. By controlling the heating treatment parameter, the refractive index of the ZrO₂ coatings can be adjusted from 1.69 up to 1.9 continuously, which can meet different requirement for high reflectance well. The thickness of crack-free ZrO₂ coatings can be easily controlled by employing different experimental parameters. The result of X-ray diffraction shows that as-deposited film is amorphous, and it remains stable up to the heating temperature of 400 °C. However, it begins to crystallize as the temperature increases further attaining 500 °C. Meanwhile, the surface morphology was evaluated by atomic force microscopy and the result shows that the surface of the ZrO₂ coating is smooth and uniform with root means square of 0.63 nm for the measured area of 5 × 5 μm. As a typical example, ZrO₂ thin films with refractive index of 1.9 are chosen for highly reflective coatings. Nearly full reflective mirror at 1,064 nm was fabricated on fused silica substrate. The laser induced damage thresholds of 22 J/cm² (1,064 nm, 10 ns) and 14.6 J/cm² (1,064 nm, 10 ns) are obtained for ZrO₂ coating and ZrO₂/SiO₂ multilayer coatings respectively.     

The effects of the nanostructure of mesoporous TiO<Subscript>2</Subscript> on optical band gap energy

Mesoporous TiO₂ is prepared by sol–gel process with a triblock copolymer as an organic template and aqueous TiOCl₂ solution as inorganic precursor. The XRD patterns reveal that only the anatase phase can be observed in mesoporous TiO₂, regardless of the different calcining temperatures, and with increasing calcining temperature the grain size gradually increases. The grain sizes of TiO₂ increased from 4.7 to 11.9 nm with calcining temperature increasing from 300 to 400 °C. The pore size and the surface area evaluated from the Barrett–Joyner–Halenda model and Brunauer–Emmett–Teller method indicated that the average pore sizes increased from 87 to 153 Å and specific surface areas decreased from 179.71 to 74.31 m²/g for 300–400 °C calcination. The relationship between the optical band gap (E _g) and microstructure of anatase has been determined and discussed. The quantum confinement effect is observed at grain sizes lower than 10 nm, and the estimated E _g shifts from 3.32 to 3.46 eV. These results suggest that there are potential applications of mesostructured TiO₂ with nanocrystals in the design of optical devices and photocatalysts.     

Photocatalytic Activity for Water Decomposition to Hydrogen over Nitrogen‐doped TiO2 Nanoparticle

Nitrogen-doped TiO2 nanoparticle photocatalysts were obtained by an annealing method with gaseous ammonia and nitrogen. The influence of dopant N on the crystal structure was characterized by XRD, XPS, BET, TEM and UV-Vis spectra. The results of XRD indicate that, the crystal phase transforms from anatase to rutile structure gradually with increase of annealing temperature from 300 to 700 ℃. XPS studies indicate that the nitrogen atom enters the TiO2 lattice and occupies the position of oxygen atom. Agglomeration of particles is found in TEM images after annealing. BET results show that the specific surface areas of N-doped samples from 44.61 to 38.27 m2/g are smaller than that of Degussa TiO2. UV-Vis spectra indicate that the absorption threshold shifts gradually with increase of annealing temperature, which shows absorption in the visible region. The influence of annealing condition on the photocatalytic property has been researched over water decomposition to hydrogen, indicating that nitrogen raises the photocatalytic activity for hydrogen evolution, and the modified TiO2 annealed for 2 h at 400 ℃ under gas of NH3/N2 (V/V＝1/2) mixture shows better efficiency of hydrogen evolution. Furthermore, the N-doped TiO2 nanoparticle catalysts have obvious visible light activity, evidenced by hydrogen evolution under visible light (λ＞400 nm) irradiation. However, the catalytic activity under visible light irradiation is absent for Degussa as reference and the N-doped TiO2 annealed at 700 ℃.     

Sensor Performance of Nanostructured TiO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript> Films Prepared by an Aqueous Sol–Gel Process

Nanostructured TiO₂–SnO₂ thin films and powders were prepared by a facile aqueous particulate sol–gel route. The prepared sols showed a narrow particle size distribution with hydrodynamic diameter in the range 17.2–19.3 nm. Moreover, the sols were stable over 5 months, since the constant zeta potential was measured during this period. The effect of Sn:Ti molar ratio was studied on the crystallisation behaviour of the products. X-ray diffraction analysis revealed that the powders were crystallised at the low temperature of 400 °C containing anatase-TiO₂, rutile-TiO₂ and cassiterite-SnO₂ phases, depending on annealing temperature and Sn:Ti molar ratio. Furthermore, it was found that SnO₂ retarded the anatase to rutile transformation up to 800 °C. The activation energy of crystallite growth was calculated in the range 0.96–6.87 kJ/mol. Transmission electron microscope image showed that one of the smallest crystallite sizes was obtained for TiO₂–SnO₂ binary mixed oxide, being 3 nm at 600 °C. Field emission scanning electron microscope analysis revealed that the deposited thin films had nanostructured morphology with the average grain size in the range 20–40 nm at 600 °C. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at low operating temperature of 200 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption.     

Sol-enhanced triple-layered Ni–P–TiO2 composite coatings

A novel coating process, TiO₂ sol enhanced Ni–P electroless composite coatings on carbon steel, is presented in this paper. Transparent TiO₂ sol was added into the electroless plating Ni–P solution at a controlled rate, leading to in situ synthesis of a triple-layered Ni–P–TiO₂ composite coating, i.e. the inner, transition and outer layers. The inner layer has a thickness of ~3 μm, mainly composed of Ni and P elements. The transition layer of the coating has a relatively high content of TiO₂ with a thickness of ~500 nm and a columnar-structure. The thickness of the outer layer was ~7 μm, with almost evenly distributed Ni, P and TiO₂. The hardness and Young’s modulus of the composite coating were greatly improved to ~10 and ~200 GPa, respectively, compared to ~6 and ~110 GPa of the traditional Ni–P coating.     

Low temperature nanostructured lithium titanates: controlling the phase composition, crystal structure and surface area

Low temperature lithium titanate compounds (i.e., Li₄Ti₅O₁₂ and Li₂TiO₃) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol–gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was in the range 2–4 nm and a gradual increase occurred up to 10 nm by heat treatment at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 21–28 nm at 600 °C and 49–62 nm at 800 °C depending upon the Li:Ti molar ratio. Moreover, atomic force microscope (AFM) images confirmed that the lithium titanate films had columnar like morphology at 600 °C, whereas they showed hill-valley like morphology at 800 °C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate shapes. The surface area of the powders was enhanced by increasing Li:Ti molar ratio and reached as high as 77 m²/g for the ratio of Li:Ti = 75:25 at 500 °C. This is one of the smallest crystallite size and the highest surface areas reported in the literature, and the materials could be used in many applications such as rechargeable lithium batteries and tritium breeding materials.     

Effect of synthesis conditions on the preparation of titanium dioxides from peroxotitanate solution and their photocatalytic activity

Nanosized TiO₂ particles were prepared by the hydrothermal method from the amorphous powders which were precipitated in an aqueous peroxotitanate solution. The physical properties of the nanosized TiO₂ particles prepared were investigated. We also examined the activity of TiO₂ particles as a photocatalyst on the decomposition of orange II. The titania sol can be successfully crystallized to the anatase phase through hydrothermal aging at temperatures higher than 160°C. The particle size increases from 18 to 26 nm as the synthesis temperature increases from 140 to 200°C. Titania particles prepared at 180°C show the highest activity, and titania particles calcined at 400°C show also the highest activity on the photocatalytic decomposition of orange II.     

Influence of surfactant and annealing temperature on optical properties of sol–gel derived nano-crystalline TiO2 thin films

Titanium dioxide thin films have been synthesized by sol–gel spin coating technique on glass and silicon substrates with and without surfactant polyethylene glycol (PEG). XRD and SEM results confirm the presence of nano-crystalline (anatase) phase at an annealing temperature of 300 °C. The influence of surfactant and annealing temperature on optical properties of TiO₂ thin films has been studied. Optical constants and film thickness were estimated by Swanepoel's (envelope) method and by ellipsometric measurements in the visible spectral range. The optical transmittance and reflectance were found to decrease with an increase in PEG percentage. Refractive index of the films decreased and film thickness increased with the increase in percentage of surfactant. The refractive index of the un-doped TiO₂ films was estimated at different annealing temperatures and it has increased with the increasing annealing temperature. The optical band gap of pure TiO₂ films was estimated by Tauc's method at different annealing temperature.     

The structural, morphological, and surface properties of tungsten-doped TiO2 nanopowders and their contribution to the photocatalytic activity

Tungsten-doped TiO₂ nanopowders (W-TiO₂) were prepared by chemical vapor synthesis and the effects of a post-heat treatment on their physical, surface, and photocatalytic properties were investigated. The W-TiO₂ nanopowders containing about 1.0 mol % of tungsten were obtained and annealed from 400 to 700 °C. The as-synthesized and annealed W-TiO₂ nanopowders were carefully examined for their crystalline and opto-electronic structure and morphology by means of X-ray diffraction, UV–Vis spectroscopy, and transmission electron microscopy. In addition, the surface condition was investigated by X-ray photoelectron spectroscopy. The photocatalytic activities were studied by the oxidative degradation of 2-propanol under UV light irradiation. We found that the photocatalytic activity of W-TiO₂ varied significantly with the temperature of the heat treatment, exceeding the performance of P25 after annealing at 600 °C. Interestingly, the chemical composition of titanium and tungsten of W-TiO₂ played a crucial role to its photocatalytic activity as the mixed valence states, Ti ⁿ⁺ (n = 4, 3, 2, 0) and W ⁿ⁺ (n = 6, 5, 4), were found in accordance with altering the annealing temperature.     

Low-temperature versus oxygen plasma treatment of water-based TiO2 paste for dye-sensitized solar cells

High-temperature treatment steps in fabrication process of dye sensitized solar cell (DSSC) significantly contribute to the manufacturing costs and limit the use of temperature sensitive substrates. Therefore our aim was to develop a simple method for the preparation of water-based TiO₂ paste. The paste is based on peroxotitanic acid (PTA) sol–gel matrix and commercial TiO₂ nanoparticles (P25). Two fabrication processes to decompose/transform the PTA matrix in the printed TiO₂ layer are explored and combined: annealing at temperatures up to 250 °C and/or oxygen plasma treatment. The results show that the PTA matrix in the paste converts to anatase phase and to some extent also attaches to the TiO₂ nanoparticles P25 acting as an interconnecting network within TiO₂ layer. The transformation of the PTA matrix occurs around 250 °C, but in the presence of TiO₂ nanoparticles P25 it starts already at 120 °C. In addition the results reveal that the crystallization is achievable also solely with the oxygen plasma treatment. The efficiency of the TiO₂ layers, exposed to different post-deposition treatments, is evaluated in DSSCs. The results show that oxygen plasma treatment of the TiO₂ layers could efficiently replace temperature curing at 250 °C. Within this study the DSSCs with the efficiency up to 4.2 % measured under standard test conditions (1,000 W/m², AM1.5, 25 °C) were realized.     

Evolution of water vapor from indium-tin-oxide transparent conducting films fabricated by dip coating process

Tin-doped indium oxide In₂O₃ (indium-tin-oxide) transparent conducting films were fabricated on silicon substrates by a dip coating process. The thermal analysis of the ITO films was executed by temperature-programmed desorption (TPD) or thermal desorption spectroscopy (TDS) in high vacuum. Gas evolution from the ITO film mainly consisted of water vapor. The total amount of evolved water vapor increased on increasing the film thickness from approx. 25 to 250 nm and decreased by increasing the preparation temperature from 365 to 600°C and by annealing at the same temperature for extra 10 h. The evolution occurred via two steps; the peak temperatures for 250 nm thick films were approx. 100-120 and 205-215°C. The 25 nm thick films evolved water vapor at much higher temperatures; a shoulder at approx. 150-165°C and a peak at approx. 242°C were observed. The evolution temperatures increased by increasing the preparation and the annealing temperatures except in case of the second peak of the 25 nm thick films. The evolution of water vapor at high temperature was tentatively attributed to thermal decomposition of indium hydroxide, In(OH)₃, formed on the surface of the nm-sized ITO particles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal treatment of (TiZr)N coatings on CO2‐controlled atmosphere

Currently, studies about the CO₂ gas injection improve the production efficiency of crude oil. The surface interaction between CO₂ and thin films is a large area of research in the scientific community. In this work, we are showing that The TiZrN (coating) + Si (substrate) system immersed on environments of fully CO₂ can interact to below 400°C temperature, because the TiZrN (coating) + Si (substrate) system is broken to temperatures above of the 400°C. The Ti2p, Zr3d, N1s, O1s, and C1s narrow spectra are shown, which illustrate the evolution of TiZrN to TiN_x, TiO_x, and TiON_x compounds and afterwards to TiO₂ and ZrO₂ phases. TiN_x, TiO_x, and TiON_x compounds are responsible for the increase of the micro‐hardness (measured through Vickers Hardness Testing) of the system (TiZrN [coating] + Si [substrate]) due to that are found at 400°C thermal treatment. Topographical images obtained by atomic force microscopy showed an increase of the surface roughness due to the thermal treatment. Scanning electron microscopy demonstrated that sample submit to 600°C temperature suffered fracture with small indentations.     

Synthesis of highly pure nanocrystalline and mesoporous CaTiO3 by a particulate sol–gel route at the low temperature

The low temperature perovskite-type calcium titanate (CaTiO₃) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol–gel route. The prepared sol had a narrow particle size distribution about 17 nm. X-ray diffraction and Fourier transform infrared spectroscopy revealed that, the synthesized powders had highly pure and crystallized CaTiO₃ structure with preferable orientation growth along (1 2 1) direction at 400–800 °C. The activation energy of crystal growth was calculated 5.73 kJ/mol. Furthermore, transmission electron microscope images showed that the average crystallite size of the powders annealed at 400 °C was around 3.5 nm. Field emission scanning electron microscope analysis and atomic force microscope images revealed that, the deposited thin films had uniform, mesoporous and nanocrystalline structure with the average grain size in the range 33–39 nm depending on annealing temperature. Based on Brunauer–Emmett–Teller (BET) analysis, the synthesized powders showed mesoporous structure with BET surface area in the range 51–21 m²/g at 400–800 °C. One of the smallest crystallite size and one of the highest surface areas reported in the literature is obtained which can be used in many applications, such as photocatalysts.     

The influence of film thickness and process temperature on <Emphasis Type="Italic">c</Emphasis>-axis orientation of Bi<Subscript>3</Subscript>TiTaO<Subscript>9</Subscript> thin films

Bi-layered ferroelectric Bi₃TiTaO₉ (BTT) thin films with different thickness (ranging from 100 to 400 nm) were successfully fabricated on Pt(111)/TiO₂/SiO₂/(100)Si substrates using chemical solution deposition (CSD) technique at different annealing temperatures. The c-axis orientation of the films was affected by film thickness and process temperature. The thinner the film and the higher the process temperature, the higher the c-axis orientation. With the increase of film thickness, the stress decreased but the film roughness increased, which led to the decrease of c-axis orientation of films. BTT films annealed at 800°C were found to have much improved remament polarization (P _r ) than that of films annealed at 650 and 750°C. The P _r and coercive field (E _c ) values were measured to be 2 μC/cm² and 100 kV/cm, respectively. BTT films showed well-defined ferroelectric properties with grain size larger than 100 nm.     

The formation mechanism and distribution of micro-aluminum oxide layer

It is of great significance to study the thermal oxidation process to understand the reaction mechanism of aluminum particle and further its applications in propellants. The physical and chemical properties of micron-aluminum particle were evaluated by scanning electron microscopy, laser particle size analyzer, X-ray diffractometer and inductively coupled plasma atomic emission spectrometer. The thermal oxidation characteristics of the sample were studied by thermal analyzer. The experimental results showed that the initial oxide thickness of the sample was about 3.96 nm, and the calculated values of the specific surface area and the active aluminum content obtained by the established mathematical model were in good agreement with the measured values. The thermal oxidation process of the sample was divided into three stages. When the temperature rose to 1100 °C, the thermal oxidation efficiency of the sample reached 98.55%. With the increase in treatment temperature, dramatic crystalline changes occurred on the surface of the sample: amorphous alumina—γ-Al₂O₃, α-Al₂O₃, and the oxide layer thickness increased from 3.96 to 5.72 nm and 31.56 nm up to 320.15 nm. When the temperature reached 700 °C, the outer surface of the oxide layer contained a small amount of α-Al₂O₃, while the interior consisted of a large amount of γ-Al₂O₃, indicating that the conversion of γ-Al₂O₃ to α-Al₂O₃ occurred from the inside out.     

Inkjet-Printed TiO2/Fullerene Composite Films for Planar Perovskite Solar Cells

Perovskite solar cells have garnered and held international research interest, due to ever-climbing power conversion efficiency values, now >25 %. Some high efficiency configurations utilize a compact TiO₂ layer underneath a mesoporous TiO₂ layer, both of which require high temperature annealing steps that could hinder perovskite commercialization. To address the high thermal budget, we chose to use inkjet-printing to combine the two layers into a single TiO₂ film, which incorporates both nanoparticle and molecular precursor as well as organic fullerene additives. We printed the ink on fluorine-doped tin oxide, and after annealing at various temperatures, we found that 400 °C was the optimum annealing temperature for the inkjet-printed electron transport layers, which is significantly lower than the 500 °C required to anneal typical mesoporous TiO₂ films.     

Effect of pore size/distribution in TiO2 films on agarose gel electrolyte-based dye-sensitized solar cells

This study develops a simple method to change the distribution of the pore size in a TiO₂ layer, using polyethylene glycol (PEG), while maintaining nearly the same surface area and porosity to clarify how large pores affect the performance of dye-sensitized solar cells (DSSCs). Specifically, a heating step at 100 °C for a specific duration is added prior to PEG removal and TiO₂ sintering at 400 °C. This process transforms the role of the PEG from a surfactant to a pore generator (porogen) and forms larger pores, depending on the loading and aggregation time for the PEG to gain larger pores. The effect of larger pores in TiO₂ films under 30 % PEG loading, on the performance of an agarose gel electrolyte-based DSSC, was further investigated using the ionic liquid, 1-allyl-3-ethylimidazolium iodide (AEII). The I–V characteristic and the electrochemical impedance spectroscopy analysis show that larger pores readily improve redox couple diffusion in a TiO₂ porous electrode and modify the interface between electrolyte and TiO₂. Using the optimized TiO₂ film with larger pores (30 % PEG loading, 100 °C/60 min), an efficiency of 7.43 % is achieved for the agarose gel electrolyte-based DSSC, which represents a 26.1 % improvement over TiO₂ without the addition of PEG.     

Evaluation of in vitro bioactivity and MG63 Oesteoblast cell response for TiO2 coated magnesium alloys

The present investigation reports TiO₂ coating on magnesium alloy AZ31 by sol–gel method via dip coating technique. TiO₂ coated surface was characterized by thin film X-ray diffraction (TF-XRD), Fourier transform infrared red (FT-IR) spectroscopy, scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM) techniques. From TF-XRD results, the peaks at 2θ values of 25.14, 32.12, 68.73 and 70.11 confirm the presence of TiO₂. The TiO₂ is crystalline in nature and the crystallite size is about 32.4 nm. SEM-EDX, TEM and AFM show that the coated surface is uniform and nanoporous. FT-IR analysis shows that the peak in the range of 692 cm^?1 is assigned to Ti–O–Ti stretching vibration. Contact angle measurements show that the coating is hydrophilic in nature. Bioactivity of the coating in simulated body fluid (SBF) was also examined, the hydroxyl functionalized surface greatly enhances the hydroxyapatite growth. The potentiodynamic polarization studies prove that the corrosion resistance of the TiO₂ coated surface after immersion in SBF for 7 days is improved dramatically. Cell adhesion studies confirm the increased cell attachment on TiO₂ coated surface when compared to uncoated alloy, due to less amount of Mg ion release from the substrate in the culture medium.     

Correlation between structural and optical properties of TiO<Subscript>2</Subscript>:ZnO thin films prepared by sol–gel method

We have studied structural and optical properties of thin films of TiO₂, doped with 5% ZnO and deposited on glass substrate (by the sol–gel method). Dip-coated thin films have been examined at different annealing temperatures (350–450 °C) and for various layer thicknesses (89–289 nm). Refractive index, porosity and energy band gap were calculated from the measured transmittance spectrum. The values of the index of refraction are in the range of 1.97–2.44, the porosity is in the range of 0.07–0.46 and the energy band gap is in the range of 3.32–3.43. The coefficient of transmission varies from 50 to 90%. In the case of the powder of TiO₂, doped with 5% ZnO, and aged for 3 months in ambient temperature, we have noticed the formation of the anatase phase (tetragonal structure with 20.23 nm grains). However, the undoped TiO₂ exhibits an amorphous phase. After heat treatments of thin films, titanium oxide starts to crystallize at the annealing temperature 350 °C. The obtained structures are anatase and brookite. The calculated grain size, depending on the annealing temperature and the layer thickness, is in the range of 8.61–29.48 nm.     

Influence of annealing temperature on the electrochemical and surface properties of the 5-V spinel cathode material LiCr0.2Ni0.4Mn1.4O4 synthesized by a sol–gel technique

LiCr_0.2Ni_0.4Mn_1.4O₄ was synthesized by a sol–gel technique in which tartaric acid was used as oxide precursor. The synthesized powder was annealed at five different temperatures from 600 to 1,000 °C and tested as a 5-V cathode material in Li-ion batteries. The study shows that annealing at higher temperatures resulted in improved electrochemical performance, increased particle size, and a differentiated surface composition. Spinel powders synthesized at 900 °C had initial discharge capacities close to 130 mAh g^?1 at C and C/2 discharge rates. Powders synthesized at 1,000 °C showed capacity retention values higher than 85 % at C/2, C, and 2C rates at 25 °C after 50 cycles. Annealing at 600–800 °C resulted in formation of spinel particles smaller than 200 nm, while almost micron-sized particles were obtained at 900–1,000 °C. Chromium deficiency was detected at the surface of the active materials annealed at low temperatures. The XPS results indicate presence of Cr⁶⁺ impurity when the annealing temperature was not high enough. The study revealed that increased annealing temperature is beneficial for both improved electrochemical performance of LiCr_0.2Ni_0.4Mn_1.4O₄ and for avoiding formation of Cr⁶⁺ impurity on its surface.