Sol-gel Thin Films Research Articles

Structure evolution of mesoporous silica under heavy ion irradiations of intermediate energies

Mesoporous sol-gel silica thin films were irradiated with gold ions of medium energies from 0.5 MeV to 12 MeV. In all cases these porous materials are compacted as a result of mesopore collapse and deformation. X-ray reflectivity and SEM measurement show that the total compaction (densification) is achieved for a fluence of about 2 × 1014 cm−2 (∼5 × 1021 keV cm−3). The process of mesoporosity collapse seems different according to the irradiation regime (nuclear versus electronic). This effect results in a U-shaped evolution of the curve of the damage cross section as a function of the energy of ions Au. Infrared measurement of Au 0.5 MeV irradiated samples show a shift of TO3 band towards lower wavenumber, related to Si-O-Si bond angle and Si-O bond length change. The sol-gel mesoporous and nonporous samples exhibit a delayed shift compared to thermal nonporous ones, which indicates that sol-gel materials are more radiation tolerant from this point of view. The sensitivity of these mesoporous structures to the damage caused by irradiation opens interesting prospects for obtaining self-conditioning materials.

Effects of aging time and annealing temperature on structural and optical properties of sol-gel ZnO thin films

The ZnO thin films have been prepared by sol-gel method at different annealing temperatures and aging time. The structural properties of ZnO thin films were investigated by X-ray diffraction (XRD) patterns and atomic force microscope (AFM) images. The results indicated that the film possess a hexagonal wurtzite structure with preferred orientation along the (002) direction. The crystalline quality of films improved with increasing post-annealing temperature, while gradually worsened with prolonging aging time. The optical properties of ZnO thin films were studied by the ultra-violet transmittance (UV-Vis) and photoluminescence (PL) spectra. The variations of UV-Vis transmittance and energy gap accorded well with the tendency presented in XRD patterns and AFM images. The PL spectra appeared the apparent ultraviolet emission and visible emissions. As the annealing temperature increased, the ultraviolet and visible emissions of films enhanced and decreased respectively. However, as the sol aging time prolonged, the PL emission presented an opposite tendency.

Multi-wavelength spectrophotometric determination of pH using phenol red–doped sol–gel film sensors

ABSTRACTDye leakage and the nonlinear relationship between absorbance and pH affect the pH measurement precision of absorption-based optic sensors and limit their application. Based on the preparation of a transparent sol–gel thin film with a phenol red indicator, this work assumed that the absorbancies had an exponential relationship to the concentrations of the indicator, and the multi-wavelength equation for the pH was derived as follows:where n is the exponential coefficient, e1, e2, and e3 are the extinction coefficient ratios, and R is the ratio of the absorbancies. The calculation parameters for an immobilized phenol red film were pKa = 8.577, e1 = 0.0191, e2 = 1.530, e3 = 0.2992, and n = 0.6322, while those for an immobilized phenol red/Triton X-100 film were pKa = 8.612, e1 = 0.0507, e2 = 1.501, e3 = 0.3687, and n = 0.3931. The correspondence between the calculated pKa and the pKa from the calibration curve verifies the equation. The calculation parameters remain stable as the indicator content is increased, but change with an increase in the Triton X-100 content. Using the equation, the calculated pH shows stable behavior over a long duration regardless of dye leakage, and the calculated precision is 0.0053. The method provides drift-free and precise water pH measurements for R that is not dependent on the total concentration of the indicator, and can be applied to online monitoring.

Synthesis and characterization of pure and Fe doped TiO2 thin films for antimicrobial activity

Pure and Fe-doped titanium dioxide sol-gel thin films were prepared by spin coating process. Pure and Fe-TiO2 films, containing 3–6% Fe, were annealed at 450 °C for 1h. All thin films were prepared and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV–vis spectroscopy. From XRD data, the dominant crystalline phase of titanium dioxide was anatase, and the range of the crystal size for the films was 19–26nm. On the other hand, antibacterial activity of pure and Fe-doped titanium dioxide against E. coli and S. aureus was evaluated by international recognized test (JIS Z 2801). The test shows incrementally increasing in antibacterial activity of the thin films when dopant ratio increased under UV light.

Reduction of ∙Si≡Si3 defect density at the Si/SiO2 interface by sol-gel SiO2 thin film passivation

The effect of SiO2 thin film passivation by sol-gel processes with various acid catalysts, ethanol (EtOH): tetraethyl orthosilicate (TEOS) volume ratios and baking temperatures on the carrier lifetime of the Si surface and Si/SiO2 interface properties was studied. SiO2 thin film passivation prepared by H2SO4 catalyst with a EtOH:TEOS volume ratio of 10:1 at a baking temperature of 50°C greatly increased the carrier lifetime on the various Si wafers regardless of dopant type, wafer resistivity and crystal orientation. For example, the carrier lifetime increased from 28 to 316μs before and after the sol-gel SiO2 passivation on the Si (100) surface with resistivity higher than 1000Ωcm. It was confirmed that the increase of carrier lifetime resulted from the significant decrease in the defect density related to the ∙Si≡Si3 dangling bond at the Si/SiO2 interface. In the current study, proper sol-gel SiO2 film passivation increased the carrier lifetime on the Si surface by controlling the formation of ∙Si≡Si3 defects at the Si/SiO2 interface.

Effect of Li codoping on highly oriented sol-gel Ce-doped ZnO thin films properties

Ce-doped and (Ce, Li) codoped ZnO thin films have been deposited onto glass substrates by sol–gel dip coating method. The effects of Ce–Li co-doping for 0.1at.% Ce and 0–20at.% Li on structural, morphological and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), UV–Vis–NIR spectrophotometry and photoluminescence spectroscopy (PL). XRD analysis revealed that all the films were highly c-axis oriented and had a hexagonal wurtzite structure. AFM images showed that film morphology and surface roughness were influenced by Li doping concentration. UV–Vis–NIR measurements indicated that the film transmission decreases with increasing Li content and the optical band gap was dependent on the Li concentration. Room temperature PL spectra put into evidence that emission is significantly influenced by Li content. In particular, it was found that the visible emission intensity of the film with 20at.% Li codoping in 0.1at.% Ce-doped ZnO is approximately 30 times greater than that of the undoped film.

Effect of Isothermal Oxidation and Sol-Gel Thin Film Formation on Corrosion Behaviour of AZ31 and AZ61 Commercial Magnesium Alloys

The authors review their recent research work in an endeavour to interpret the influence of native oxide films on the corrosion behaviour of commercial AZ31 and AZ61 magnesium alloys and the oxidation kinetics of these alloys in air at 200ºC. The tendency of some of these thin films to be sufficiently protective in mild or weak corrosive environments was examined. For obtaining oxide films with different protective properties, some of the specimens were tested with the surface in the as-received condition, while others were tested immediately after mechanical polishing. The techniques applied to characterise thin oxide films of a thickness of just a few nanometres present on the surface of alloys has mainly been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Oxidation resistance of the alloys was quantified by thermogravimetric (TG) curves. Their corrosion rate was evaluated by Electrochemical Impedance Spectroscopy (EIS) and hydrogen evolution measurement in chloride solutions with different concentrations. Emphasis was placed on the possible effects of: (a) the different thickness of the native oxide films formed on the polished surfaces on the corrosion behaviour of the alloys; and (b) the different film homogeneity and uniformity on the oxidation results [1-5]. In parallel studies, an attempt was made to learn more about the influence of the native oxide films that covers the substrate on the subsequent growth and protective behaviour of the sol-gel coatings. In this way, the influence of heat treatment of magnesium alloy substrates on corrosion resistance of a sol-gel coating has been assessed during immersion tests in 0.6M NaCl aqueous solution. Relative differences in the chemical nature of the layers were quantified by scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX). Long-term immersion testing showed that the sol-gel/heat treated AZ61 substrate exhibited a superior anti-corrosion property in comparison with the sol-gel/non-heated substrate. In contrast, no significant changes have been observed between the heated and non-heated samples in the case of the sol-gel coated AZ31 substrates. A link was found between lower O/Si atomic ratios observed by EDX analysis on the sol-gel coatings after the preparation process and reduced corrosion upon the coated substrates. The thermal treatment increases the protective properties of the passive film on the surface of the AZ61 substrate and hence inhibited magnesium dissolution and hydrophilic groups formation during coating preparation [5-7]. Finally, some preliminary results are shown on our studies in progress about the modification of these sol-gel coatings with different inhibitor (L-cysteine, benzotriazole and 8-hydroxyquinoline) in an attempt to improve the corrosion performance of the AZ31 and AZ61 magnesium alloys. Acknowledges: This work was supported by the Ministry of Economy and Competitiveness of Spain (Project MAT2015-65445-C2-1-R). References Feliu Jr., S., Maffiotte, C., Samaniego, A., Galván, J.C., Barranco, V., Effect of naturally formed oxide films and other variables in the early stages of Mg-alloy corrosion in NaCl solution, Electrochimica Acta, 56 (12), pp. 4554-4565 (2011).Feliu Jr., S., Maffiotte, C., Samaniego, A., Galván, J.C., Barranco, V., Effect of the chemistry and structure of the native oxide surface film on the corrosion properties of commercial AZ31 and AZ61 alloys, Applied Surface Science, 257 (20), pp. 8558-8568 (2011).Feliu, S., Maffiotte, C., Galván, J.C., Barranco, V., Atmospheric corrosion of magnesium alloys AZ31 and AZ61 under continuous condensation conditions, Corrosion Science, 53 (5), pp. 1865-1872 (2011). Feliu S. Jr, Samaniego A., Barranco V., El- Hadad A.A., LLorente I., Serra C., Galván J.C., A study on the relationships between corrosion properties and chemistry of thermally oxidised surface films formed on polished commercial magnesium alloys AZ31 and AZ61, Applied Surface Science, 295, pp 219-230 (2014).Feliu S. Jr., El hadad A.A, Barranco V., Llorente I., García-Galván F.R., Jiménez-Morales A., Galván J.C., Native Oxide Films on AZ31 and AZ61 Commercial Magnesium Alloys: Corrosion Behaviour Resistance, Effect on Conversion Coating Growth and Sol-gel Thin Film Formation. In “New Trends in Alloy Development, Characterization and Applications”. Editor: Zaki Ahmad. Publisher: InTechOpen, September 2015.El hadad A.A., Barranco V., Samaniego A., Llorente I., García-Galván F.R., Jiménez-Morales A., Galván J.C., Feliu Jr. S., Influence of substrate composition on corrosion protection of sol-gel thin films on magnesium alloys in 0.6 M NaCl aqueous solution, Progress in Organic Coatings 77 (11) 1642–1652 (2014).Diaz, L., García-Galván, F.R., Llorente, I., Jiménez-Morales, A., Galván, J.C., Feliu Jr, S., Effect of heat treatment of magnesium alloy substrates on corrosion resistance of a hybrid organic-inorganic sol-gel film, RSC Adv., 5, 105735-105746 (2015).

Optimization of NiO Thin Films By Sol-Gel for Electrochromic Properties

Among electrochromic materials, nickel oxide, NiO, has received significant attention due to its anodic coloration leading to neutral color devices when combined with WO3 [1]. In the past few years, few authors pointed out the key role plays by the film stoichiometry on its electrochromic (EC) properties [2, 3]. In particular in our group, we reported a strong correlation between electrohromic properties and the nickel/oxygen content in Ni1-xO thin films deposited by RF Sputtering [4]. Especially a departure from the stoichiometry leads to unexpected EC properties in electrolytes with no small cations. Such non stoichiometry, leading to unusual properties can also be induced by dopant addition. Herein, NiO based thin films were fabricated by sol-gel method combined with spin coating technique onto ITO/Glass substrate. The influence of molarity, solvents, stabilizing and the nature of the final treatment on the structural, morphological, electrical and optical properties of NiO based thin films was studied and correlated to their EC behavior. Overall films are poorly crystallized. The films synthesized by methanol as solvent, triton 100X as stabilizer and treated by UV light thin film exhibit the highest capacity in KOH based electrolyte and the highest optical contrast. Lithium addition was investigated for improved p-type conductivity. Finally, the integration of sol-gel NiO thin films in full devices (WO3/Li-based electrolyte/NiO) will be discussed. [1] H. Moulki, D.H. Park, B.K. Min, H. Kwon, S.J. Hwang, J.H. Choy, T. Toupance, G. Campet, A. Rougier, Electrochimica Acta, 2012, 74, 46 [2] R.T. Wen, C.G Granqvist, G.A. Niklasson, ChemElectroChem 2016, 3(2) 266. [3] X. Song, G. Dong, F. Gao, Y. Xiao, Q. Liu, X. Diao, Vacuum 2015, 111, 48. [4] M. Da Rocha, A. Rougier, Electrochromism of nonstoichiometric NiO thin film: as single layer and in full device, Applied Physics A, 2016, 122(4), art. n° 370, 7.

Thermomechanical Characteristics of Low Carbon Magnesia-Based Monolithic Refractory Containing Nanostructured Surface-Modified Graphites in Matrix

ABSTRACTThis study has been carried out on castable and matrix of a magnesia-based unshaped refractory system containing respectively 5.0% and 20.0% graphites. The graphite has been incorporated either as uncoated or surface-modified form, the latter containing a thin sol-gel calcium aluminate film over graphite surface. Surface modification of graphite has been confirmed by scanning electron microscopy, X-ray diffraction, Raman spectra, Fourier transformed infrared study and some other experiments. The sol-gel coating improved hydrophilicity and oxidation resistance of graphite. Sinterability, thermal and thermomechanical properties of castable matrices have been elaborately documented. From this work it is apparent that presence of coated graphite in matrix part of basic castable is not that encouraging as observed in alumina-carbon system. However, the castable properties as a whole are satisfactory due to protection of graphite and its less water demand for casting.

High-resistivity sol-gel ITO thin film as an interfacial buffer layer for bulk heterojunction organic solar cells

Bulk heterojunction organic solar cells have been fabricated by inserting a high-resistivity sol-gel ITO buffer layer between an ITO anode and a PEDOT:PSS hole injection layer. The performance of the devices with the sol-gel ITO atop the ITO anodes treated by conventional annealing at 500 °C for 1 h and rapid thermal process (RTP) at 800 °C for 20 and 30 s was compared. The best power conversion efficiency of 3.5% was achieved for the device with the 15-nm-thick sol-gel ITO treated with RTP at 800 °C for 30 s, as compared with 2.7% of the standard device under an illumination of AM 1.5. In addition, the short circuit current of the device was significantly increased by 42.7%. The observed enhancement of the short circuit current can be attributed an interfacial energy step created by the high-resistivity sol-gel ITO between the ITO anode and the PEDOT:PSS.

Uncharacteristic effect on the ultraviolet and visible photoluminescence properties of ZnO:Cl films: A physical insight

Study on the photoluminescence (PL) properties of cation or anion doped sol-gel ZnO thin films can lead to new insights into its defects. In this work, an in-depth knowledge on defect formation in phase pure Cl doped ZnO films has been acquired through comprehensive studies on their PL properties supported by the electrical and X-ray photoelectron spectroscopy (XPS) results. Here, we demonstrate an uncharacteristic enhancement in the ultraviolet (UV)/visible (VIS) peak intensity ratio from 2.7 to 9.5 with an increase in the doping content from 0–10 at% Cl, signifying a large change in the defect chemistry. Also an atypical change in the green (GE) and orange emission (OE) with a gradual decrease in the GE/OE intensity ratio as Cl dopant increases has been observed which is not reported earlier. Critical analyses of the UV and VIS PL emissions and electrical results supported by XPS data indicate that Cl occupies oxygen vacancy site forming ClO and forms Cl interstitial defects (Cli) besides a small fraction of the Cl is being substituted in the O site. Therefore, we propose that ClO and Cli defects act as nonradiative recombination paths for the trapped electrons and holes resulting in reduced GE and OE.

Ultrasound assisted sol-gel TiO2 powders and thin films for photocatalytic removal of toxic pollutants

The paper presents a study on the structural, surface and photocatalytic properties of the ultrasound assisted sol-gel titanium dioxide particles, as part of stable photocatalytic ink formulations deposited on fabrics. The photocatalytic activity was validated using methylene blue as reference pollutant, under UV, VIS and combined UV+VIS radiation and allowed selecting the optimum TiO2 samples for inks preparation. To minimize the particles agglomeration stabilizing agents were added and the stability was quantitatively evaluated considering the relative increase in the VIS transmittance for a pre-set period of 30min. Further on, the ink(s) were deposited by cold spraying on cotton woven fabrics and a removal efficiency higher than 95% was observed in the degradation of the highly toxic mustard gas, after 30min of UV irradiation.

Thermal-frequency dependence study of the sub-band localized states effect in Sb-doped SnO2 based sol-gel thin films

Films of transparent conducting antimony-doped tin oxide have been deposited by sol-gel based Dip-coating technique. The morphological analysis revealed that the deposited films are homogenous, smooth and the roughness depends on the Sb-doping. The Raman scattering showed that the vibrational modes are sensitive to oxygen deficiency, structural disorder and were red-shifted compared to the rutile SnO2 single crystal. The FTIR study depicted the presence of SnO (610cm−1) and SnOSn (740cm−1) bonds in the films. Optical measurements revealed high transparency (~85%) over the visible region. The optical band gap varies from 3.87 to 3.79eV with increasing the width of tail states and corresponds to direct allowed transition in the bulk. The AC-conductivity (σac) exhibits a semiconductor temperature-dependence behavior and varies from extrinsic to intrinsic conduction. The thermal energy promotes the polarization involving electrons localized at randomly oriented oxygen vacancies of the inhomogeneous dielectric structure grain/grain boundary and induces high dielectric constant. σac was found to follow the power law: σac=A. f0.49 at high frequencies and the experimental results showed that the correlated barrier hopping mechanism is appropriate for the charge transfer between localized states.

Silica Sol-Gel Optical Biosensors: Ultrahigh Enzyme Loading Capacity on Thin Films via Kinetic Doping.

Easy to use and easy to produce biosensors would have a huge range of applications. To reach this goal many see the incorporation of a protein into a sol-gel network as one of the most viable options. The current most prevalent technique of predoping presents inherent limits on the concentration possible for the resulting thin film. In this study we demonstrate a new process utilizing the newly developed kinetic doping method to load silica sol-gel thin films with cytochrome C (CytC) and horseradish peroxidase (HRP). Both enzymes are shown to successfully load and have a concentration increase over their original loading solution by factors of 1300× and 2600×, respectively. Furthermore, each enzyme once loaded retained the ability to act as a catalyst for the detection of hydrogen peroxide. Ultimately the CytC- and HRP-loaded thin films were found to have enzyme concentrations of 11 ± 1 mM and 6.0 ± 0.4 mM, respectively, a considerable step up from any doping method reported in the past.

Ilmenite type nano-crystalline Co–Ti–O ternary oxides: sol–gel thin film on borosilicate glass, characterization and photocatalytic activity in mineralization of reactive red 198

The sol–gel preparation of cobalt titanium oxide nano-crystals using the reaction between cobalt chloride (CoCl2·6H2O) and tetraisopropyl orthotitanate (Ti[OCH(CH3)2]4) with 1:1 molar ratio was studied. The nano-crystals were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDAX), fourier transform infrared spectroscopy (FTIR), thermogravimetric (TG-DTG) analysis and UV–Vis diffuse reflectance spectra (UV–Vis DRS) spectroscopy. TG-DTG results revealed that the weight loss with peak temperatures of 189, 267 and 692 °C. The XRD results showed that the sample calcinated at 550 and 750 °C were mixtures of CoTiO3, Co3O4, and TiO2 phases while at 650 °C a single crystalline phase of CoTiO3 was formed. FESEM results of the cobalt titanium oxide nanocrystalles demonstrate that CoTiO3 is nano-particles with an average size of 70 nm. FTIR results showed the formation of cobalt–oxygen, titanium–oxygen, and titanium–oxygen–cobalt bonds. DRS spectroscopy results of the sample calcinated at 650 °C showed band gap of 1.734 eV (715 nm) and 2.389 eV (519 nm) well in the visible portion of sun light. The cobalt titanium oxide nano crystales thin films on borosilicate glass showed an excellent photocatalytic activity on mineralization of Reactive Red 198 textille dye as environmental pollutant of industrial wastewater. An excellent photocatalytic activity in mineralization of Reactive Red 198 is related to the efficient separation of cobalt titanium oxide nano-crystals and visible-light absorption.

Hierarchically Structured Macro with Nested Mesoporous Zinc Indium Oxide Conducting Film.

Fabrication of homogeneously distributed (HD) macropores by breath figure process is an active research area. Adopting the process, for the first time, we report the fabrication of HD macro with nested meso (hierarchical) porous nanocrystalline zinc indium oxide conducting sol-gel thin film on glass by dip-coating at 45-50% room relative humidity (RH) from a solution in ethanol-2-butanol (1:1, w/w) medium with a 1:1, Zn:In ratio. In this process, solution composition and RH are found to play key roles on HD macropore generation. The film is highly promising toward visible-light-driven photoelectrochemical water splitting.

Effect of Pt Concentration on the Grain Growth of TiO2sol-gel Films

Pt metallic has been supported on TiO2 surface using different methods, Here, Pt doped TiO2 (Pt-TiO2) sol gel thin film were successfully produced by reducing chloroplatinc acid (H2PtCl6). The structures of prepared composites were investigated using X-ray diffraction (XRD). The physical morphologies of the composites were examined using transmission electron microscope (TEM). The grain size of Pt-TiO2 thin film after annealing was also measured by atomic force microscope (AFM) images.

On the mechanical and electrical properties of self-assembly-based organosilicate porous films

The effect of the replacement of Si–O–Si by Si–CH2–Si groups on the mechanical and electrical properties of silica-based hybrid sol–gel thin films is reported.

High Mobility Flexible Amorphous IGZO Thin-Film Transistors with a Low Thermal Budget Ultra-Violet Pulsed Light Process.

Amorphous, sol-gel processed, indium gallium zinc oxide (IGZO) transistors on plastic substrate with a printable gate dielectric and an electron mobility of 4.5 cm2/(V s), as well as a mobility of 7 cm2/(V s) on solid substrate (Si/SiO2) are reported. These performances are obtained using a low temperature pulsed light annealing technique. Ultraviolet (UV) pulsed light system is an innovative technique compared to conventional (furnace or hot-plate) annealing process that we successfully implemented on sol-gel IGZO thin film transistors (TFTs) made on plastic substrate. The photonic annealing treatment has been optimized to obtain IGZO TFTs with significant electrical properties. Organic gate dielectric layers deposited on this pulsed UV light annealed films have also been optimized. This technique is very promising for the development of amorphous IGZO TFTs on plastic substrates.

Converting Water Adsorption and Capillary Condensation in Usable Forces with Simple Porous Inorganic Thin Films.

This work reports an innovative humidity-driven actuation concept based on conversion of chemical energy of adsorption/desorption using simple nanoporous sol-gel silica thin films as humidity-responsive materials. Bilayer-shaped actuators, consisting of a humidity-sensitive active nanostructured silica film deposited on a polymeric substrate (Kapton), were demonstrated as an original mean to convert water molecule adsorption and capillary condensation in usable mechanical work. Reversible solvation stress changes in silica micropores by water adsorption and energy produced by the rigid silica film contraction, induced by water capillary condensation in mesopores, were finely controlled and used as energy sources. The influence of the film nanostructure (microporosity, mesoporosity) and thickness and the polymeric substrate thickness on actuation force, on movement speed and on displacement amplitude are clearly evidenced and discussed. We show that the global mechanical response of such silica-based actuators can easily be adjusted to fabricate tailor-made actuation systems triggered by humidity variation. This study provides insight into hard ceramic stimulus-responsive materials that seem to be a promising alternative to traditional soft organic materials for surface-chemistry-driven actuation systems.