Sol-gel Films Research Articles

The Study of Graphene Oxide on the Regulations and Controls of the Sol-Gel Film Structure and Its Performance

A facile strategy to boost anticorrosion potency of graphene oxide/silica hybrid sol-gel coating is developed through fully exploiting the capabilities of graphene oxide (GO). Together with a barrier to corrosives and crack inhibitor, GO was further explored herein as a regulator to regulate the gelation process and provide robust coating films with stratified microstructures and ultimately extended diffusion paths. The sol-gel coating with stratified microstructure achieved on AA5052 aluminum alloy surface afforded greatly enhanced corrosion protection capability as assessed by electrochemical measurements and immersion tests. The corrosion current density of the sample of a hybrid GO sol-gel film was about 30 times less than that of sample of pure sol-gel film sample. The regulation mechanism of GO during the film formation process and the anticorrosive protection properties of the film were discussed.

One-step electrochemical modification of pencil graphite electrode with reduced graphene oxide/phosphotungstic acid/sol–gel, and its application to the trace analysis of lead(II)

To determine lead ions, the reduced graphene oxide/phosphotungstic acid (rGO/PWA) composite was used to modify the pencil graphite electrode (PGE). To enhance the efficiency of the sensor, sol–gel was used for the modification, which had a favorable effect of stabilizing, dispersing and increasing the effective sites produced by rGO/PWA. Instead of the traditional sol–gel film preparation method, the modifier composite (rGO/PWA/Sol-Gel) was deposited on the electrode surface electrochemically in a single step in a suitable solution by applying a constant potential. During the sol–gel film formation process, film mesoporous channels were used as a model for the growth of rGO/PWA conductor modifier arrays. The whole process of electrodeposition on the electrode surface took place in a short time (120 s). The modifier was evaluated by SEM and EIS. The effective surface of the modified electrode was calculated, and it was shown that the conductivity of the electrode was increased after using the sol–gel substrate. The modified electrode was used to measure Pb(II) using the differential pulse anodic stripping voltammetry (DPASV) method. Several influential factors were optimized in the designing sensor and measurement of Pb(II). A linear range of 5.0 × 10-10–5.0 × 10-7 M and a detection limit of 2.2 × 10-11 can be accessed by the modified electrode. The measurement of Pb(II) was performed successfully in real samples of drinking water and urine.

Hybrid Sol-Gel Surface-Enhanced Raman Sensor for Xylene Detection in Solution.

This paper reports on the fabrication and characterization of a plasmonic/sol-gel sensor for the detection of aromatic molecules. The sol-gel film was engineered using polysilsesquioxanes groups to capture the analyte, through π-π interaction, and to concentrate it close to the plasmonic surface, where Raman amplification occurs. Xylene was chosen as an analyte to test the sensor. It belongs to the general class of volatile organic compounds and can be found in water or in the atmosphere as pollutants released from a variety of processes; its detection with SERS is typically challenging, due to its low affinity toward metallic surfaces. The identification of xylene was verified in comparison with that of other aromatic molecules, such as benzene and toluene. Investigations were carried out on solutions of xylene in cyclohexane, using concentrations in the range from 0 to 800 mM, to evaluate the limit of detection (LOD) of about 40 mM.

Amorphous CdO-In2O3 alloy thin films with high conductivity and transparency synthesized by sol-gel method

The growth of CdO-In2O3 amorphous oxide semiconductor alloys with high mobility in a wide composition range, suitable for many optoelectronic applications, has been previously reported using room temperature sputtering. In the present work, we synthesized Cd1−xInxO1+δ alloy thin films across the entire composition range using the non-vacuum, low-cost sol-gel spin coating method. Structural, electrical and optical properties of these alloy films were studied using a variety of analytical tools. We find that the alloy films become amorphous within the In composition range of 0.2 <x < 0.7, while films with x < 0.2 and x > 0.7 have the rocksalt CdO and bixbyite In2O3 structure, respectively. As-grown amorphous alloys have resistivity in the ranging from high 10−3 to low 10−2 Ω-cm due to their relatively low mobility of<10 cm2/Vs. Electrical properties of these amorphous films are improved after annealing at ~400 °C with a mobility of ~10 cm2/Vs and a low resistivity in the low 10−3 Ω-cm range. The optical gap varies from 2.54 to 3.52 eV with increasing In mole fraction, so that transmittance> 85% over a wide transmission window of ~400–1600 nm can be achieved. The low temperature, low-cost non-vacuum processing, wide bandgap tunability, and low resistivity, make these sol-gel alloy films promising materials for optoelectronic applications, especially on organic layers and/or flexible substrates.

Impact of γ-rays Irradiation on Hybrid TiO2-SiO2 Sol-Gel Films Doped with RHODAMINE 6G.

In the present paper, we investigate how the optical and structural properties, in particular the observed photoluminescence (PL) of photocurable and organic-inorganic TiO2-SiO2 sol-gel films doped with Rhodamine 6G (R6G) are affected by γ-rays. For this, four luminescent films, firstly polymerized with UV photons (365 nm), were submitted to different accumulated doses of 50 kGy, 200 kGy, 500 kGy and 1 MGy while one sample was kept as a reference and unirradiated. The PL, recorded under excitations at 365 nm, 442 nm and 488 nm clearly evidences that a strong signal peaking at 564 nm is still largely present in the γ-irradiated samples. In addition, M-lines and Fourier-transform infrared (FTIR) spectroscopies are used to quantify the radiation induced refractive index variation and the chemical changes, respectively. Results show that a refractive index decrease of 7 × 10−3 at 633 nm is achieved at a 1 MGy accumulated dose while a photo-induced polymerization occurs, related to the consumption of CH=C, Si-OH and Si-O-CH3 groups to form Ti-O and Si-O bonds. All these results confirm that the host matrix (TiO2-SiO2) and R6G fluorophores successfully withstand the hard γ-ray exposure, opening the way to the use of this material for sensing applications in radiation-rich environments.

Low-energy intense pulsed light annealing of InZnO sol-gel films via employment of a resonant absorber

A resonant absorber enables low-temperature sintering of InZnO sol–gel films with low-energy-density intense pulse light (IPL) irradiation (1 J/pulse). A back-gate structure, incorporated with a resonant absorber, exhibits effective light absorption. A device fabricated based on such a gate structure and sintered with irradiation of 50 pulses (∼50 J/cm2) demonstrates good electrical properties with a mobility of 0.34 cm2/V s and an on–off ratio of 106 and a substrate temperature under 210 °C, showcasing that employing a resonant absorber could enable low-temperature sintering of sol–gel films with low-energy-density irradiation. Further x-ray photoelectron spectroscopy analysis of the oxygen and nitrogen peaks indicates that IPL irradiation facilitated sol–gel reactions in films.

Improvement of Properties of Stainless Steel Orthodontic Archwire Using TiO2:Ag Coating

Orthodontic treatment carries the risk of major complications such as enamel demineralization, tooth decay, gingivitis, and periodontal damage. A large number of elements of fixed orthodontic appliance results in the creation of additional plaque retention sites which increase the risk of biofilm creation. Modification of the surface of orthodontic elements may prevent the formation of bacterial biofilm. In this paper, surface modification of stainless steel orthodontic wires with TiO2: Ag was carried out by the sol-gel thin film dip-coating method. To obtain the anatase crystal structure, substrates were calcined for 2 h at 500 °C. The properties of the obtained coatings were investigated using scanning electron microscopy, X-ray diffraction, and electrochemical tests. Corrosion studies were performed in a Ringer’s solution, which simulated physiological solution. SEM and XRD analyses of the coated surface confirmed the presence of Ag nanoparticles which may have antimicrobial potential.

Optical Detection of VOC Vapors Using Nb2O5 Bragg Stack in Transmission Mode

In this study, an emphasis is put on vapor-sensitive Bragg stacks as an important class of optical sensors. All-niobia Bragg stacks were deposited by spin-coating of sol-gel Nb2O5 thin films alternated with mesoporous layers after proper design through optimization of operating wavelength and number of layers in the stack. Mesoporous Nb2O5 films with different morphology and identical structure were obtained using organic templates (Pluronics PE6200 and PE6800) and subsequent annealing. Transmittance measurements were performed as a detection method that offers technological simplicity and accuracy. It was demonstrated that stacks including PE6200 templated films exhibit higher sensitivity than stacks templated with PE6800. It was assumed and verified by computer-aided modelling of experimental data that mesoporous films prepared with addition of PE6200, although less porous, were more stable compared to those templated with PE6800, and did not collapse during the thermal treatment of the stacks. Furthermore, the reproducibility of optical response was studied by sorption and desorption cycles of acetone vapors. The suitability of all-niobia Bragg stacks for optical sensing of VOCs was discussed.

All-Fiber Magneto-Optical Effect Using Nanoparticles Doped Sol-Gel Thin Film Deposited Within Microstructured Fibers

An innovative functionalization method allowing to greatly increase the Faraday effect of microstructured silica-based optical fibers is described. This method relies on the coating of a sol-gel thin film doped with magnetic field sensitive cobalt ferrite nanoparticles around the suspended core of the fiber. By varying the functionalization process parameters, both the film thickness and nanoparticle concentrations can be tailored to optimize the fiber magneto-optical response by a proper adjustment the interaction between the guided mode and the composite film. Experimental measurements in an all-fiber configuration on several samples diversely functionalized show a significant polar magneto-optical effect. A polarization rotation as large as 10° has been measured at 1550 nm when the most efficiently functionalized fiber is located inside a 0.7 cm air gap electromagnet at 1 Tesla. The present method and the developed all-fiber components are very promising candidates for the design of fiber-based sensors of magnetic fields.

Synthesis and fluorescent thermal response of sol-gel SiO2 composite film containing nanodiamonds

Fluorescence of negatively charged nitrogen-vacancy color centers in nanodiamond is applied in nanoscale sensing. Here, we generated a stable transparent composite ND-SiO2 film by introducing well-dispersed nanodiamonds into silica sol with sol-gel method and spin coating. The transmission electron microscope, X-ray diffraction and Raman curves all can demonstrate homogeneous dispersion of nanodiamond particles in the silicon dioxide film. The hybrid coating displayed significant temperature dependence by studying the fluorescence behavior from liquid nitrogen temperature to room temperature. With rising temperature, the red shift in zero phonon line position, reduction in intensity, extension in the full width at half maximum and decrease in amplitude were obviously typical characteristics. In addition, the sensitivity was 19 K Hz−1/2 at 80K, while it increased to 28 K Hz−1/2 at 300K.

Modified solar cells with antireflection coatings

Designing a solar cell that can harvest energy with a high level of efficiency is an important research topic. For improving the performance of solar cells, this paper introduces four proposed structures for solar cells and examines their efficiencies for potential production with low cost and high efficiency. In each model, the absorbent material is Borofloat glass and the antireflection coatings used are SiNx and sol-gel -based materials. The four proposed solar cell structures are as follows: (i) a three-layer solar cell in which a sol-gel film is used to match the refractive index between the glass substrate and air cladding; (ii) a four-layer solar cell in which a sol-gel film is used to match the refractive index between SiN x laid on top of a glass substrate and air cladding; (iii) a four-layer structure in which a sol-gel film topped with air cladding is used as a match between the glass and SiN x ; and (iv) a four-layer solar cell in which two layers of SiN x are stacked between the glass and the air. A transfer-matrix method is used to solve for the total transmission and total reflection for all structures, and the effects of the film thicknesses and incidence angles are considered in each case. An analysis is carried out using Maple 17, and the results show that using a sol-gel material between glass and air gives almost zero reflection for a wide range of wavelengths, meaning that this can be used as a perfect absorbent and can therefore be recommended for high-efficiency solar cells. Using two layers of SiN x between the air and glass gives almost zero reflection at 600 nm, making this approach an outstanding candidate for solar cells with a maximum absorption of around 600 nm. The other two structures have lower values of transmission, meaning that they are good candidates for low-efficiency solar cells. However, further techno-economic studies of the proposed structures should be carried out, and that solar cell manufacturers should consider these structures.

Effects of atmosphere composition during direct ultraviolet-light patterning of solution-deposited In2O3 thin film transistors

Sol-gel synthesis is widely used to fabricate metal oxide thin films by solution, but it requires high-temperature thermal annealing to fully convert precursors to metal oxides. Exposure to Ultraviolet (UV) light before thermal annealing of precursor films has been shown to reduce the conversion temperature, with the added benefits of film patterning when done through a shadow mask and improved device performance. However, the mechanism by which UV exposure under different atmospheric compositions affects the properties of metal oxide films after thermal annealing has not been investigated. Here, we control the atmospheric composition during UV-patterning—prior to high-temperature thermal annealing—of In2O3 sol-gel films which serve as the semiconductor in thin-film transistors. Despite all films being annealed at 250°C in air after UV patterning, films exposed to UV under oxygen-containing atmospheres have higher metal-oxygen-metal bonding and exhibit higher transistor mobility compared to the films exposed to UV under N2 atmosphere. The origin of the effect of atmospheric composition on mobility is studied through X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy and is revealed to be the result of the reformation of the nitrate species in the films under more oxidizing atmospheres during UV exposure. These nitrates can be completely removed by thermal annealing, facilitating more complete metal-oxygen-metal bond formation, which is reflected in higher OI XPS signal and transistor mobility. In contrast, films processed under N2 atmosphere during UV exposure contain nitrite species that cannot be removed by thermal annealing, resulting in less metal-oxygen-metal bond formation and lower mobility.

Photonic Curing of Solution-Processed Oxide Semiconductors with Efficient Gate Absorbers and Minimal Substrate Heating for High-Performance Thin-Film Transistors.

In this study, photonic curing is used to rapidly and effectively convert metal-oxide sol–gels to realize high-quality thin-film transistors (TFTs). Photonic curing offers advantages over conventional thermal processing methods such as ultrashort processing time and compatibility with low-temperature substrates. However, previous work on photonically cured TFTs often results in significant heating of the entire substrate rather than just the thin film at the surface. Here, sol–gel indium zinc oxide (IZO)-based TFTs are photonically cured with efficient gate absorbers requiring as few as five pulses using intense white light delivering radiant energy up to 6 J cm–2. Simulations indicate that the IZO film reaches a peak temperature of ∼590 °C while the back of the substrate stays below 30 °C. The requirements and design guidelines for photonic curing metal-oxide semiconductors for high-performance TFT applications are discussed, focusing on the importance of effective gate absorbers and optimized pulse designs to efficiently and effectively cure sol–gel films. This process yields TFTs with a field-effect mobility of 21.8 cm2 V–1 s–1 and an Ion/Ioff ratio approaching 108, which exceeds the performance of samples annealed at 500 °C for 1 h. This is the best performance and highest metal-oxide conversion for photonically cured oxide TFTs achieved to date that does not significantly heat the entire thickness of the substrate. Importantly, the conversion from sol–gel precursors to the semiconducting metal-oxide phase during photonic curing is on par with thermal annealing, which is a significant improvement over previous pulsed-light processing work. The use of efficient gate absorbers also allows for the reduction in the number of pulses and efficient sol–gel conversion.

Influence of weathering and temperature on the electrochemical and microscopical characteristics of CeO2 and CeO2:V2O5 sol-gel thin films

Thin films of cerium dioxide (CeO2) and cerium dioxide doped with vanadium pentoxide (CeO2:V2O5) were prepared through sol-gel route and spin coating deposition, for use as smart materials. This work evaluated films that underwent a weathering process in an accelerated weathering test chamber and the changes in their properties. The influence of the temperature was also studied electrochemically. Regarding the weathering process, there were variations in the charge insertion capacity during the investigated period. However, at the end of the 900 simulated days, the CeO2:V2O5 presented interesting values. For the EIS analyses, the curve (Nyquist plot) remained about 45° inclination, suggesting a diffusional process. The morphological and structural analyses demonstrated that by doping the film, occurs a reduction on the degradation, although the structure showed no changes. For different temperatures, the film becomes more resistive as the temperature increases. The chronocoulometry showed that the charge insertion capacity increases with temperature.

EVALUATION ON THE EGFET PH SENSING PERFORMANCE OF SOL-GEL SPIN COATED TITANIUM DIOXIDE THIN FILM

For this study, TiO2 thin film was fabricated using the sol-gel spin coating method. The fabricated film was then applied as a sensing membrane in an extended gate field effect transistor (EGFET) pH sensor system. The pH sensing performance of the sol-gel spin-coated TiO2 was evaluated in terms of sensitivity, linearity, and hysteresis where the value obtained was 58.70 mV/pH, 0.9922, and 86.17 mV respectively. The drift rate of the sample when being measured for 12 consecutive hours was also determined where measurement in pH 4, pH 7, and pH 10 yield drift rate of 1.72 mV/h, 4.14 mV/h, and 6.05 mV/h respectively. Besides that, the TiO2 was characterized for its thickness (24.32 nm) and surface roughness (5.129 nm). From the results obtained, it was found that sol-gel spin-coated TiO2 thin film with thickness between 20 - 29 nm will have high pH sensitivity (more than 50 mV/pH).

A recycling strategy of ion beam removal and recoating of sol-gel film on fused silica surface

A recycling strategy is presented on ion beam removal and recoating of sol-gel film on fused silica surface, which is based on non-contact inert ion beam etching to remove sol-gel films followed by recoating on the surface of fused silica to realize the recycling of the anti-reflection films on optical components. Through the characterization and analysis of optical properties of the samples before and after etching, the influence of ion energy on the film removal is studied and further optimized. The results indicate that the ion beam removal method does not degrade the performance of the fused silica substrate. After recoating of sol-gel porous silica film, the surface contact angle, surface roughness, optical transmittance, and laser damage threshold are characterized and compared with that of the original coated samples. The results show that the performance is as good as or even better than that of the original coated fused silica, which verifies the effectiveness of the recycling method presented in this work.

Impact of electrode materials on microstructure, leakage current and dielectric tunable properties of lead-free BSZT thin films

Lead-free ferroelectric sol-gel thin films derived from barium strontium titanate (Ba0.85Sr0.15Zr0.1Ti0.9O3, BSZT) were deposited onto two types of electrode: (i) noble metallic Pt- and (ii) conductive oxides LaNiO3- and SrRuO3-coated silicon substrates. The present studies demonstrate that electrode materials impact significantly on morphology, crystallographic orientation, lattice mismatch-induced microstrains and electrical properties of BSZT thin films. Highly (100)-textured BSZT thin films with the highest crystallinity and lowest microstrain were found on conductive oxide electrodes, whereas Pt electrodes showed polycrystalline. Capacitors with oxide LaNiO3 electrode display predominated Schottky emission with a rather low leakage current density ~4.68 × 10−8 A/cm2, while Pt electrode capacitors indicate space-charge limited conduction. Dielectric characterizations in the frequency range of 103–5 × 106 Hz and the dc electric field up to ±800 kV/cm show that the permittivity, loss tangent, and tunability of BSZT films also strongly depend on the electrode materials used. The optimal dielectric tunability with a large figure of merit (FOM ≈ 22.53) and low dielectric loss (tanδ ≈ 2.9%), was found to be 66% for BSZT thin films on the conductive LaNiO3 electrode, suggesting that the as-deposited ferroelectric films are promising candidates for applications in tunable microwave elements and related electronic devices.

Sol-gel coating filled with SDS-stabilized fullerene nanoparticles for active corrosion protection of the magnesium alloy

Sodium Dodecyl Sulfate (SDS) surfactant was stabilized on the fullerene C60 nanoparticles. The raw, aminated (F-NH 2 ), and SDS-stabilized (F-SDS) fullerene nanoparticles were characterized by Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-ray Spectroscopy (EDS), and Thermal Gravimetric Analysis (TGA). Then, the functionalized nanoparticles were dispersed inside the sol-gel coating for active corrosion protection of AM60B magnesium alloy . Suitable dispersion of the F-SDS nanoparticles inside the sol-gel coating was confirmed by Transmission Electron Microscopy (TEM). After addition of the F-NH 2 and F-SDS nanoparticles, micrometric defects in the sol-gel coating disappeared. A relative increment in the surface roughness of the coating was observed by Atomic Force Microscopy (AFM) after incorporation of the F-NH 2 and F-SDS nanoparticles. Also, a considerable improvement in the corrosion protection of the sol-gel coating after addition of the F-NH 2 and F-SDS nanoparticles (500 ppm) was shown by Electrochemical Impedance Spectroscopy (EIS) in 3.5 wt% NaCl. Based on the SEM and EDS-mapping analyses at the end of the corrosion tests , the corrosion damages of the F-SDS containing sol-gel coating has been considerably reduced. • SDS molecules were successfully stabilized on the fullerene C60 nanoparticles. • SDS grafted nanoparticles (F-SDS) showed suitable dispersion in sol-gel coating. • The F-SDS containing coating was crack-free, uniform, and thermally resistive. • The F-SDS containing sol-gel film showed the best corrosion protection performance.

Effect of storage and surface roughness on the SiO2 thin films adhesion behavior

The thin film elaboration and use, commonly related by the substrate properties and quality, are of great interest in the optical field. Indeed, storage conditions and duration, in addition to the surface quality, can have an effect on the materials and their performances, especially if they are functioning as optical materials. For this purpose, this study aims to contemplate both the storage duration of optical glasses and their surface quality, as well as the adhesion behavior of silica thin film deposition. Therefore, optical glasses were developed and stored for 3 years in the same solution (colloidal silica premixed [CMP] slurry), then they were characterized before the study of their sol-gel thin films adhesion behavior. Furthermore, surfaces were treated with several techniques and their surface quality was measured. The adhesion phenomenon was studied via droplet technique. The results show the influence of the storage duration on the optical properties of the optical glasses (refraction index, Abbe number) and the surface roughness. Moreover, the surface roughness has a great influence on the adhesion of the thin films. In addition to that, sol-gel prepared with 20% TEOS has the highest adhesion of the optical glass when the surface roughness is low.

Effect of heat treatment temperature on the properties of silicon dioxide films derived from film-forming solutions

The effect of the heat treatment temperature on the physical properties of sol-gel silicon dioxide films derived from film-forming solutions is investigated experimentally. The dependencies of the thickness of the films, their refractive index, electrical strength, resistivity, etching rate, and the level of internal mechanical stresses on the treatment temperatures in the range from 700 to 1150 °C are obtained. It was found that the dependencies of the electrical strength, the etching rate, and the level of internal mechanical stresses have the sections with the different characters. The transition region between these sections corresponds to the heat treatment temperature equal to 900-950 °C.