Low Temperature Sol-gel Technique Research Articles

Interband electronic transitions and optical phonon modes in size-dependent multiferroic BiFeO3 nanoparticles.

Bismuth ferrite (BiFeO3) multiferroic nanoparticles are synthesized using a low-temperature sol-gel auto-combustion technique. The phase purity is confirmed from X-ray diffraction (XRD) measurements and microstructural, electronic, and optical studies are correlated with the particle size of the bismuth ferrite nanostructured material. We demonstrated bandgap tunability from 2.22 to 1.93 eV with an average crystallite size from 42 to 24.42 nm following the inverse quantum confinement effect dominated by the lattice strain. The degenerate d-d electronic transitions 6A1g → 4T1g and 6A1g → 4T2g from iron dominate in these nanoparticles. The decrease in the energy band gap and the corresponding red shift in the d-d charge transfer transition energies with reduced average crystallite size are attributed to the increased lattice strain and reduced unit cell volume.

Thermogravimetric analysis, Rietveld refinement, and atomic force micrography of cobalt ferrite nanoparticles exposed to 100 kGy Co60 γ-rays

We have investigated the thermogravimetric temperature (TGA) of magnetic cobalt ferrite nanoparticles (CoFe2O4) synthesized using a low-temperature sol–gel technique and a gamma irradiation dose of up to 100 kGy in a gamma chamber to create lattice defects inside the crystalline structure. The Rietveld refinement was performed with the help of advanced graphical tools which leads to the in-depth identification of Bragg’s reflections belonging to the space group Fd3m by evaluating the profile factor (Rp), weighted profile factor (Rwp), and the expected R-factor (Rexp) parameter. Eventually, the topographic qualities of the samples were investigated using atomic force micrography (AFM), which focused on metal ion dispersion and surface roughness and was aided by scanning electron micrography (SEM images). The Raman spectra have shown the active modes Eg, 3T2g, and A1g near 250.53; 324.36; and 765.90 respectively. The UV–Vis spectroscopic absorption of CoFe2O4 nanoparticles was reported at ∼ 208.2 Å, and the bandgap was reported to be 3.82 eV with the help of Tauc’s plot; Kubelka-Munk function F(R). The current study presents a complete X-ray diffraction pattern (XRD) analysis that may aid in the investigation of intra-atomic and molecular defects generated by 100 kGy gamma irradiation.

Structural, Raman and optical investigations of barium titanate nanoparticles

Barium titanate nanoparticles were synthesized via a low temperature sol-gel technique using acetylacetone as a chelating agent. The X-ray diffraction pattern confirmed the formation of tetragonal perovskite structure of the material. The average crystallite size was found to be 49 nm using the Debye-Scherrer method. The Williamson–Hall plot was drawn for evaluating the micro-strain and crystallite size. Raman spectroscopic features typical for the tetragonal phase were identified for Barium titanate powder. In addition to these, an absorption band edge and an optical bandgap were found to be of 406 nm and 3.14 eV respectively. Barium titanate displays polychromatic luminescent peaks in UV -visible regions and it was attributed to the near-band-edge transition and defect states in the optical band gap of the perovskite structure.

Titanium content influence on the optical response characteristics of TiO2/ormosils composite films doped with azobenzene.

TiO2-based organic-inorganic composite films doped with azobenzene and photosensitive groups were prepared by combining a low-temperature solgel technique and a spin-coating method. The influence of TiO2 content on the optical and structural properties of the composite films including the film thickness, the refractive index, the transmission loss, the thermal gravity analysis, and Fourier transform infrared spectroscopy spectra was studied. Photoisomerization and optical switching characteristics of the composite film were investigated under the irradiation of 365 nm ultraviolet light and 450 nm visible light. Results indicate that several micrometer thick films can be easily obtained at room temperature and there is a proportional relationship between the refractive index value and the TiO2 content. In addition, the composite films have a low optical propagation loss of about 0.1 dB/cm. The composite films with 0.2 M TiO2 content have an obvious photoisomerization and good optical switching properties. Finally, the hexagonal microlens array was fabricated in the composite films by using an ultraviolet nanoimprint technology. All these results above indicate that the as-prepared TiO2-based organic-inorganic composite film has potential applications in optical switching devices and photonic elements.

Efficacy of Bioactive Glass Nanofibers Tested for Oral Mucosal Regeneration in Rabbits with Induced Diabetes.

The healing of oral lesions that are associated with diabetes mellitus is a matter of great concern. Bioactive glass is a highly recommended bioceramic scaffold for bone and soft tissue regeneration. In this study, we aimed to assess the efficacy of a novel formula of bioactive glass nanofibers in enhancing oral mucosal wound regeneration in diabetes mellitus. Bioactive glass nanofibres (BGnf) of composition (1–2) mol% of B2O3, (68–69) mol% of SiO2, and (29–30) mol% of CaO were synthesized via the low-temperature sol-gel technique followed by mixing with polymer solution, then electrospinning of the glass sol to produce nanofibers, which were then subjected to heat treatment. X-Ray Diffraction analysis of the prepared nanofibers confirmed its amorphous nature. Microstructure of BGnf simulated that of the fibrin clot with cross-linked nanofibers having a varying range of diameter (500–900 nm). The in-vitro degradation profile of BGnf confirmed its high dissolution rate, which proved the glass bioactivity. Following fibers preparation and characterization, 12 healthy New Zealand male rabbits were successfully subjected to type I diabetic induction using a single dose of intravenous injection of alloxan monohydrate. Two weeks after diabetes confirmation, the rabbits were randomly divided into two groups (control and experimental groups). Bilateral elliptical oral mucosal defects of 10 × 3.5 mm were created in the maxillary mucobuccal fold of both groups. The defects of the experimental group were grafted with BGnf, while the other group of defects considered as a control group. Clinical, histological, and immune-histochemical assessment of both groups of wounds were performed after one, two and three weeks’ time interval. The results of the clinical evaluation of BGnf treated defects showed complete wound closure with the absence of inflammation signs starting from one week postoperative. Control defects, on the other hand, showed an open wound with suppurative exudate. On histological and immunohistochemical level, the BGnf treated defects revealed increasing in cell activity and vascularization with the absence of inflammation signs starting from one week time interval, while the control defects showed signs of suppurative inflammation at one week time interval with diminished vascularization. The results advocated the suitability of BGnf as bioscaffold to be used in a wet environment as the oral cavity that is full of microorganisms and also for an immune-compromised condition as diabetes mellitus.

Structure Analysis and Ferroelectric Response of Bi0.5Na0.5TiO₃ Nanopowder Synthesized by Sol-Gel Method.

In this work, bismuth sodium titanate, Bi0.5±xNa0.5±yTiO₃ (BNT, x, y = -0.05-0.08) nanopowders were produced using the low-temperature sol-gel technique. The effects of deficient and excess amounts of Bi and Na on BNT structure were systemically examined through X-ray powder diffraction (XRD), energy dispersive analysis (EDS) and scanning electron microscope (SEM). The optimized composition of the BNT nanopowder was pelletized and sintered at different temperatures (950°C-1150 °C). Highly dense ceramics possessing pure perovskite phase was observed for the sample sintered at an optimum sintering temperature (1100 °C). The ferroelectric properties were found to increase with an increase in sintering temperature up to 1100 °C and then decrease. This study justifies that Bi and Na non-stoichiometry (proper excess), processing and sintering temperatures play important role in the successful synthesis of BNT ceramics.

Improved optical damage threshold graphene Oxide/SiO2 absorber fabricated by sol-gel technique for mode-locked erbium-doped fiber lasers

In this study, a mode-locked erbium-doped fiber (EDF) laser based on solid-state graphene oxide (GO)-doped sol-gel glass saturable absorber (SA) was designed and tested. The GO-based SA was fabricated for the first time using low-temperature sol-gel technique. Compared to traditional ways of fabricating SAs, the SAs-doped sol-gel glass showed outstanding advantages in terms of high optical damage threshold. The optical damage threshold of SAs-doped sol-gel glass reached as high as 50.69 GW/cm2. X-ray diffractometry (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and annex-energy spectrometry (EDS) identified the main component of prepared sol-gel glass as compact amorphous silicon dioxide. The application of GO-doped sol-gel glass to EDF laser yielded stable mode-locked fiber laser operation. The pulse duration, maximum output power and peak power were recorded as 582 fs, 17.58 mW and 1.30 kW, respectively. Overall, these data indicated that the proposed sol-gel method is promising for fabricating practical SAs for mode-locked fiber lasers.

Influence of organic pH dyes on the structural and optical characteristics of silica nanostructured matrix for fiber optic sensing

Owing to the fast responsive fiber optical pH sensing characteristics, silica porous matrix is synthesized through a low temperature sol-gel technique. Three different pH dyes namely bromophenol blue (BPB), creosol red (CR) and phenol red (PR) are encapsulated in silica matrix to observe their behavior on structural and optical characteristics of host matrix. FESEM/EDS and AFM analyses reveal that CTAB assisted silica matrix before and after dyes encapsulation has crack-free and porous morphology. The creosol red encapsulated silica matrix (SiO2-CR) has small average surface roughness (Ra) ∼1.05 nm with ultra-thin texture ∼4.06 nm compared to other dyes. FTIR analysis shows that higher content of SiOH group in SiO2-CR matrix shows more hydrophilic features than others matrices. BET analysis indicates that nano-porous structures possess extremely large surface area ∼450 m2/g, and they display specific selectivity towards each dye. UV–vis analysis shows that SiO2-CR matrix has low refractive index 1.36 and high transparency 81% at 632.8 nm with a certain extent of absorption in the visible region. The pH-responsive matrices are deposited onto the PCS (Plastic Clad Silica) optical fibers. The performance of the prepared devices is assessed by measuring their response in the pH range of 1–12. SiO2-PR matrix coated fiber sensor exhibited rapid response of time 0.51 s at pH 12 and 0.17 s at pH 1. The prepared pH sensor has linear response with coefficient of determination (R2) ∼ 0.90 at 440 nm within pH 1–12. Experimental findings suggest that SiO2-PR matrix has more sensing potential at dynamic pH range 1–12 than SiO2-CR matrix and SiO2-BPB matrix.

Sonochemical fabrication of nanocryatalline titanium dioxide (TiO2) in cotton fiber for durable ultraviolet resistance

ABSTRACTA facile approach to in situ sonosynthesis and fabrication of nanocrystalline titanium dioxide (TiO2) in cotton fiber via low temperature sol-gel technique for superior ultraviolet resistance has been studied. Tetrabutyl titanate (TBT) was used as a precursor and ultrasonic cavitation was applied to synthesis TiO2 at low temperature followed by a simultaneous deposition in cotton fibers. Functionalized cotton fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), Thermo gravimetric Analysis (TGA), UV-Visible spectroscopy (UV-Vis) and X-ray diffraction (XRD) analysis. Ultraviolet resistant property of TiO2 assembled cotton fiber and was examined by UV transmittance analyzer. The results indicate that crystal TiO2-Nps at size between 17 and 19 nm include anatase and rutile structure was successfully synthesized and deposed in mesopores, lumen and surface of the cotton fibers. Durable protection against ultraviolet radiation was obtained, which exhibit significant prospect of using low temperature sonochemical synthesis of metal oxides nanoparticles and deposition in porous textiles for a broad range of functional application.

Performance evaluation of free-silicon organic-inorganic hybrid (SiO2-TiO2-PVP) thin films as a gate dielectric

An approach to achieve the transparent thin film transistors (TTFTs) using transparent electrodes such as ITO or FTO for gate, source and drain electrodes (Free-silicon gate electrode). On the other hand, the high-k transparent metal oxides can be used for this purpose in gate dielectric by a low temperature sol-gel technique. Furthermore, not only use of high-k organic materials in gate dielectric reduces the leakage current but also it improves the device flexibility. The organic-inorganic hybrid composites of SiO2/TiO2-PVP (STP) with different TiO2 ratios are deposited on PET-ITO substrates (Free-silicon gate electrode) as gate dielectric. The thermal behavior and structural characterization of STP films are done by TGA, XRD and XPS analyses. The AFM analyze of STP films shows that they have very smooth surface. A transparent thin layer of ZnO is used as a transistor channel by sputtering technique. Evaluation on electrical performance of OFETs exhibits that they have high mobility, low threshold voltage and acceptable Ion/Ioff ratio.

Low-temperature magnetic properties of NiCrxFe2–xO4 ferrites

Nickel-chrome ferrites of general formula NiCrxFe2–xO4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were produced using low-temperature sol-gel self-combustion technique. Magnetic hysteresis loop of the samples showed that due to a low coercive field Hc, in the range of 2484–4283 A/m at 77 K, the ferrites are soft magnetic materials. The residual induction Br of the magnetic field decreases with increasing the concentration of Cr3+ ions due to a weakening of the interaction between the tetrahedral and octahedral sublattices of the ferrite with the spinel structure. The specific saturation magnetization σs of NiFe2O4 ferrite is 33.9 A m2/kg. The blocking temperature Tb was determined; its average value was found to be 157 K.

Diatom frustules decorated with zinc oxide nanoparticles for enhanced optical properties

Zinc oxide (ZnO) nanoparticles were synthesized on diatomite (DE) surface by a low temperature sol gel technique, starting from zinc acetate dihydrate (Zn(CH3COO)2 · 2H2O) solution in water/ethyl alcohol, in presence of triethanolamine (TEA) with functions of Zn2+ chelating agent, catalyst and mediator of nanoparticle growth on DE surface. Microstructural features were investigated by field emission scanning electron microscopy and x-ray diffraction. ZnO crystalline nanoparticles, well distributed both on the surface and into the porous architecture of diatomite, were obtained just after the synthesis carried out at 80 °C without the need of calcination treatments. The optical properties of ZnO/DE hybrid powders were measured for the first time by means of photoacoustic spectroscopy (PAS). A new method to retrieve both the optical absorption and scattering coefficients from PAS is here discussed for powder aggregates. The fingerprint of the zinc oxide nanoparticles has been highlighted in the Mie scattering resonance in the UV–Vis range, and in the enhancement of the optical absorption with respect to diatomite.

Luminescence properties of La2O3:Eu3+ nanophosphor prepared by sol–gel method

Undoped and Eu3+ doped La2O3 nanophosphor are synthesized by low temperature sol–gel technique. The synthesized samples are characterized by X-ray diffraction (XRD) and average crystallite size is found to be ∼18nm and ∼23nm for undoped and Eu3+ doped La2O3 respectively. Gamma ray irradiated undoped La2O3 shows high intense thermoluminescence (TL) glow peak at 640K and weak TL glow peak at 443K and the high intense peak intensity is sub linear increase with γ-dose. Whereas Eu3+ doped La2O3 nanophosphor show a prominent TL glow peak at 640K and its TL intensity linearly increases up to 1kGy. The kinetic parameters are estimated using glow curve deconvoluted (GCD) technique. TL emission of γ-ray irradiated Eu3+ doped La2O3 show peaks at 508, 586, 619 and 706nm are attributed to Eu3+ transition peaks.

Low-temperature sol–gel processed AlOx gate dielectric buffer layer for improved performance in pentacene-based OFETs

An approach to achieve improved performance in pentacene-based organic field effect transistors (OFETs) using high-k AlOx prepared by a low temperature sol–gel technique as a thin buffer layer on a SiO2 gate dielectric was demonstrated.

LDS dye-doped zirconia-organically modified silicate distributed feedback planar waveguide lasers

LDS dye-doped pure zirconia and zirconia-organically modified silicate (ORMOSIL) thin film waveguides were prepared on glass substrates by a low-temperature sol–gel technique. The absorption, fluorescence and amplified spontaneous emission properties of the waveguides were investigated. Near infrared distributed feedback laser action was induced in the LDS dye-doped zirconia-ORMOSIL waveguides. Tunable narrow linewidth lasing output from 670 up to 930 nm in a transmission grating geometry was realized in the zirconia-ORMOSIL films.

Preparation and optical properties of sol–gel derived photo-patternable organic–inorganic hybrid films for optical waveguide applications

Photo-patternable TiO 2/organically modified silane hybrid films were prepared by combining a low-temperature sol–gel technique with a spinning–coating process. A ridge waveguide pattern was fabricated by ultraviolet light irradiation through a mask placed contact with the hybrid film in direct. Optical properties and photochemical activity of the hybrid film, including refractive index, thickness, propagation mode, and propagation loss, were studied and monitored by a prism coupling technique and Fourier transform infrared spectroscopy. The change of transmittance with exposure time was also observed by ultraviolet–visible spectroscopy. These results indicate that the hybrid film is potential application for fabrication of photonic devices by ultraviolet light irradiation. The structure of ridge waveguide pattern was characterized and studied by scanning electron microscope and surface profiler. The fabrication process of the as-prepared photosensitive hybrid film as compared with traditional binary mask has a great amount of advantages of cost-effective, simple, and smooth surface over non-photosensitive material methods.

Study of Optical Properties of Macrophomina phaseolina Impregnated Sol-gel Derived Silica Matrices

In the present frame of work, Macrophomina phaseolina is encapsulated in silica matrices at various concentrations by low temperature sol-gel technique using tetraethylorthosilicate (TEOS) as precursor. The optical and photophysical properties of these samples have been studied by second harmonics of Nd:YAG laser at 532 nm. UV-visible absorption spectra of samples have been recorded and it is found that the absorption increases with increase in concentration of fungus. Further, a decrease in output transmission intensity of the laser has been observed with increase in fungus concentration. The temporal response of these samples has also been examined. The results show that the fungus concentration can be measured within approximately 15-20 min. This method of optical sensing of fungus in test sample is faster than other techniques, such as the conventional colorimetric method which takes about 1 h.

Distributed-feedback laser actions in zirconia-ORMOSIL waveguides based on energy transfer between co-doped laser dyes

Laser dyes such as pyrromethene 567 (PM567), perylene red (P-red) and coumarin 540A (C540A) were doped into zirconia-organically modified silicate (ORMOSIL) materials prepared by low temperature sol–gel technique. Narrow line-width distributed feedback (DFB) laser actions were induced in the PM567 and/or P-red doped sol–gel planar waveguide. Tuning of the output wavelength was achieved by varying the period of the gain modulation generated by a nanosecond Nd:YAG laser at 532 nm. Compared with those of PM567 and P-red solely doped thin films, tuning range of C540A, PM567 and P-red co-doped sol–gel planar waveguide was greatly extended, from 564.5 nm to 635.1 nm.

Azobenzene-containing small molecules organic–inorganic hybrid sol–gel materials for photonic applications

Azobenzene-containing germania-ormosil hybrid materials are prepared by combining a low-temperature sol–gel technique with a spin-coating process, which can be used for the simple and low cost fabrication of waveguide devices for photonic applications. The planar waveguide and structural properties of the hybrid waveguide films are characterized by a prism coupling technique and Fourier transform infrared spectroscopy. The effects of azobenzene content and heat treatment temperature on the photo-responsive properties of the hybrid films are also studied by photoirradiation with UV light. The results indicate that the azobenzene in hybrid materials can undergo trans–cis–trans photoisomerization efficiently by photoirradiation with UV light, and surface pattern structure induced due to UV light photoirradiation can be easily observed on such azobenzene-doped hybrid materials. Thus, this as-prepared organic–inorganic hybrid sol–gel material shows promising candidates for optical switch applications and allows for directly integrating on a single chip waveguide device with optical data storage and optical switching devices.

Sol-Gel Fabrication of Low Temperature Organic-Inorganic Hybrid Film Patterns for Photonic Applications

Titania/organically modified silane hybrid thin films for photonic applications were prepared by combining a low temperature sol-gel technique and a spin-coating process from an organic-inorganic hybrid system. Effects of the titanium content and heat treatment temperature on the structural and optical properties of the hybrid thin films were characterized by atomic force microscopy and UV-visible spectroscopy. It is found that the optical and microstructural properties of the hybrid thin films depend on the heat-treatment temperature and titanium molar contents. The thickness and the refractive index of the hybrid thin films were also measured and found to be related to the heat treatment temperature and titanium molar content. These results indicate that a dense and high transparent hybrid thin film can be obtained at a low heat treatment temperature. Potential photonic device structural patterns can easily fabricated from the as-prepared hybrid thin films by using etching process.