Rare earth element (i.e.) europium co-doped aluminum zinc oxide (Eu:AZO) thin films were deposited on microscope glass slides by nebulizer spray pyrolysis with different Eu-doping concentrations (0, 0.5, 1, and 1.5%). The deposited films were investigated using X-ray diffraction, AFM, EDAX, FT-Raman, UV–visible, PL, and Hall effect measurements. X-ray confirmed the incorporation of aluminum and europium ions into the ZnO structure. All films have polycrystalline nature with hexagonal wurtzite structure at (002) direction. Topological depictions exhibited minimum surface roughness and low film thickness for pristine AZO thin film. EDAX study authorizes the existence of Zn, O, Al, and Eu in Eu: AZO thin films. Raman spectra exhibited the characteristic of ZnO-wurtzite structure (E2-high) mode at 447?cm?1. The deposited film showed high optical transmittance of ~90% in visible region, and the direct energy gap was around 3.30?eV for pristine AZO thin film. The PL spectra emitted a powerful UV emission situated at 388?nm, and it indicates that the film has good optical quality. The obtained large carrier concentration and less resistivity values are 4.42?×?1021?cm?3 and 3.95?×?10?4?Ω?cm, respectively, for 1.5% Eu-doped AZO thin film. The calculated figure of merit value is 17.29?×?10?3 (Ω/sq)?1, which is more suitable for the optoelectronic device.
A novel approach based on sol–gel spin coating method to deposit Zn(O,S) thin film using thiourea(TU) as a sulfur source replacing CdS as buffer layer was developed and the influence of TU concentration on the properties of Zn(O,S) thin films and Cu(In,Ga)Se2(CIGS) solar cells were investigated in this paper. It was found by X-ray diffraction and X-ray photoelectron spectroscopy that sol–gel derived Zn(O,S) thin films were amorphous and composed of ZnS, ZnO as well as Zn(OH)2. The variation of the optical band gap as a function of the S/(S+O) ratio was determined by energy-dispersive spectroscopy and UV-VIS-NIR. The results indicated that the minimum value for band gap of approximate 3.72?eV was obtained when the S/(S+O)?=?0.44. Efficiency of up to 7.28% was achieved for a CIGS solar cell with Zn(O,S) buffer layer from 0.2M TU, which was attributed to the optimized conduction band offset (CBO) of +0.45?eV at the CIGS/Zn(O,S) interface.
Zn(O,S) thin films prepared in sol–gel route was used to replace traditional CdS buffer layer deposited by chemical bath deposition method in Cu(In,Ga)Se2 solar cells. The best efficiency was achieved for CIGS/Zn(O,S)/i-ZnO/ITO heterostructure solar cell with S/(S+O)?=?0.18, which was attributed to the optimized conduction band offset (CBO) of +0.45?eV at the CIGS/Zn(O,S) interface.
Nano noble metal coating on surface patterned mesoporous semiconductor thin film can play an important role in enhancing visible light harvesting efficiency (LHE) towards improvement in photoelectrochemical (PEC) activity of the material. In this work, one-dimensional (1D) and two-dimensional (2D) mesoscale surface patterns have been created on sol–gel-based titanium tin oxide (TSO) nanostructured thin film on pure silica/indium tin oxide-coated glass by soft lithography. The TSO film matrix is observed to be mesoporous and semicrystalline as evidenced from the structural characterization by transmission electron microscopy and measurement of atmospheric ellipso-porosimetry, respectively. The 2D patterned film exhibits maximum LHE value in visible wavelength region. Further film surface modification has been carried out by depositing nano Au coating onto the bare patterned TSO films by a low temperature solution technique. Under visible light, a significant improvement in PEC activity is found and the gold-coated patterned 2D film shows higher visible LHE as well as >2.7 times higher photocurrent density than bare 2D film. This facile fabrication strategy can create an avenue toward improvement in LHE vis-à-vis the PEC activity of mesoporous mixed metal oxide semiconductor thin film.
The behaviour of alginate gel film in response to the tensile load is analysed in this paper. The bubbles of 0.5?mm diameter were embedded in the film by the fluidic method prior to gelation, thus providing uniform voidage over the entire film. Further, the intrinsic porosity of the gel matrix around the voids was varied by removing water through either evaporation under vacuum, or employing lyophilisation. The Poisson’s ratio and the modulus of elasticity were estimated from direct measurements. The viscoelasticity of the gel matrix was characterized from stress-relaxation measurement. The transient response to tensile loading and the evolution of stress contours were studied through numerical simulation in ANSYS. The ultimate strength was studied for the gel films with embedded voids of different sizes. The numerical simulations were validated by experimental measurements.
Barium zirconium titanate (Ba(ZrxTi1?x)O3, BZT) super smooth thin films are synthesized through modified sol-gel dip coating route on fluorine-doped tin oxide substrates with a suitably low calcination temperature. The Fourier tranformed infrared spectroscopy proves that impurities and starting materials are completely removed in the calcination process. Crystallographic phases of the samples are identified by the X-ray diffractometry and confirms that all samples are crystallized into a single perovskite phase. Introducing zirconium into the structure causes a reduction in dielectric constant of barium titanate. The optical properties of the films are also investigated. The results indicate that all samples are highly transparent and zirconium reduces the absorption coefficient. Moreover, the band gap energy of barium titanate increases when doped with zirconium and the highest band gap energy of about 3.71?eV along with the lowest dielectric constant of 850 at frequency of 100?kHz are obtained in 15 at.% zirconium-doped sample.
MgF2 coating solutions were solvothermally treated at 160?°C for different time periods, this procedure induced crystallization and particle growth. Antireflection coatings prepared on glass from these solutions were compared to films derived from untreated precursor material. Ellipsometric porosimetry (EP) was employed to characterize structural features of coatings on glass as function of annealing temperature. Based on precursor solutions that had undergone solvothermal treatment antireflective coatings with a peak transparency exceeding 99% were prepared on PMMA substrates.
Solvothermal treatment of MgF2 precursor solutions results in crystallization of particles that can directly be applied to PMMA substrates for λ/4 antireflective films.
Two series of TiO2 thin films were prepared based on soluble precursor powders: The first run originated directly from an alcohol-based coating solution whereas for the second batch the aqueous precursor powder sol had previously undergone a hydrothermal treatment. The respective microstructures were characterized by electron microscopy, the phase evolution was monitored by X-ray diffraction. Ellipsometric porosimetry (EP) was employed to reveal changes of porosity and pore size induced by thermal treatment of the films.
Soluble TiO2 precursor powders were hydrothermally treated to yield coating solutions. Films from these sols were compared with those directly obtained by dissolving the precursor powders. Results indicate that crystallization to anatase is induced under hydrothermal conditions and the resulting films mostly maintain their porosity throughout thermal treatment. In contrast to that coatings processed from as-dissolved precursor powders undergo more extensive densification
Since the late 1960s, ceric hydrogen phosphates have attracted the attention of scientists due to remarkable ion exchange, sorption, proton-conduction and catalytic properties. In this work, through the application of various solvents, we, for the first time, have obtained monolithic aerogels based on ceric hydrogen phosphates with high porosity (~99%) and extremely low density (~10?μg/cm3). The composition and structure of aerogels were thoroughly studied with XRD, TEM, SEM, XPS, low temperature nitrogen adsorption methods, TGA/DSC, Fourier-transform infrared spectroscopy (FTIR) and small-angle neutron scattering (SANS). The aerogels were found to belong to the fibrous macroporous aerogels family.
Pure and Ag-doped zinc oxide sol–gel thin films were prepared by spin-coating process. Pure and Ag–ZnO films, containing 2–8% Ag, were annealed at 500?°C for 2?h. All thin films were prepared and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–visible spectroscopy. X-ray diffraction studies show the polycrystalline nature with hexagonal wurtzite structure of ZnO and Ag:ZnO thin films. The crystallite size of the prepared samples reduced with increasing Ag doping concentrations. AFM and SEM results indicated that the average crystallite size decreased as Ag doping concentration increased. The transmittance spectra were then recorded at wavelengths ranging from 300 to 1000?nm. The films produced yielded high transmission at visible regions. The optical band gap energy of spin-coated films also decreased as Ag doping concentration increased. In particular, their optical band gap energies were 3.75, 3.55, 3.4, 3.3, and 3.23?eV at 0%, 2%, 4%, 6%, and 8%, respectively. Antibacterial activity of pure and Ag-doped zinc oxide against Escherichia coli and Staphylococcus aureus was evaluated by international recognized test (JIS Z 2801). The results showed that pure and Ag-doped ZnO thin film has an antibacterial inhibition zone against E. coli and S. aureus. Gram-positive bacteria seemed to be more resistant to pure and Ag-doped ZnO thin film than gram-negative bacteria. The test shows incrementally increasing in antibacterial activity of the thin films when dopant ratio increased under UV light.
Nuclear magnetic resonance (NMR) spectroscopy offers an element-selective, inherently quantitative and experimentally very flexible approach for the structural elucidation of non-crystalline materials. The present review introduces the basic concepts of this technique, highlighting the use of advanced NMR methodology for characterizing short- and intermediate range order in bioactive glass systems. The current state of the literature in this field is summarized in a comprehensive manner. NMR can give clear-cut and quantitative answers about the extent of network polymerization, the spatial distribution of the network former and network modifier species, and the structural roles of Group III elements introduced into these networks. These results facilitate our understanding of the influence of bioglass compositions upon the dissolution kinetics and bioactivities of these glasses. A particular mission of this review is to highlight the utility of non-routine, more advanced experimentation, in the hope of their increased usage and circulation in future applications.
The main six nuclear isotopes used in obtaining high-resolution magic-angle spinning NMR spectra for the structural characterization of bioactive glasses
Powders of Sm0.6Sr0.4CoO3-δ and La0.6Sr0.4CoO3-δ were synthesized using wet chemical technique. Structural and surface properties of synthesized materials were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The influence of pH on the phase state, chemical composition, morphology, and fractal dimension of the synthesized powders were investigated. It was found that the change of pH has the influence on phase composition of synthesized powders. The increase of solution pH allows one to obtain homogeneous samples at lower temperatures down to 900–950?°C.
In this report, we have primarily studied the influence of nickel (Ni) incorporation on ac electrical conductivity, dielectric relaxation mechanism and impedance spectroscopy characteristics of copper oxide (CuO) thin films synthesized by successive ion layer adsorption and reaction (SILAR) technique. The materials has been characterized using X-ray diffraction and UV–VIS spectrophotometric measurements. Reduction in grain size in doped films up to a certain extent of doping (tentatively 6%) were confirmed from XRD analysis, beyond which there is a reverse tendency. Increase in band gap in doped films were observed up to 6% doping level which could be associated with enhanced carrier density in doped films. Impedance spectroscopy analysis confirmed enhancement of ac conductivity and dielectric constant for doped samples. The results are useful for capacitive application of the films. Beyond 6% doping level, AC conductivity and dielectric constant shows a reverse tendency indicating reduced density of charge carriers. Nyquist plot shows contribution of both grain and grain boundary towards total resistance and capacitance. Imaginary part of complex modulus and imaginary part of complex impedance was used to find the migration/activation energy to electrical conduction process. Nearly identical result was obtained from relaxation frequency/relaxation time approach suggesting hopping mechanism of charge carriers.
Cuprous oxide (Cu2O) thin films have been deposited onto fluorine doped tin oxide (FTO) glass substrates by using electrochemical route. The structural, morphological, and chemical composition of the deposited films have been studied by using X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive x-ray spectroscopy (EDAX) techniques respectively. The optical studies have been carried out by using UV-Vis spectroscopy. The effect of potential, pH and bath temperature onto absorption and band gap of Cu2O thin films have been studied. The highest sensitivity 6.25 mA·mM·cm-2 is observed for the thin films which shows glucose concentration 7 mM in 0.1 M NaOH solution. The results indicates Cu2O is promising material for glucose sensor with high sensitivity, high stability, and repeatability.
Graphical abstract The surface morphology of Cu2O thin films was found to be tip-truncated octahedral. The films were prepared by electrodeposition. The Cu2O thin films were used to construct low cost, highly sensitive and stable glucose sensor.
The aim of this work was an investigation of structural and electrical properties of ZnO/Zn2-xFexTiO4 (x?=?0.7, 1, 1.4) powders. The compounds obtained by sol-gel method are characterized by several techniques: X-ray diffraction (XRD), N2 adsorption–desorption isotherms, scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), electrical and dielectrical measurements. The XRD, SEM and XPS analysis confirmed the formation of ZnFeTiO4 inverse spinel structure. The electrical and dielectrical properties of ZnO/Zn2-xFexTiO4 (x?=?0.7, 1, 1.4) were measured by impedance spectroscopy, revealing a decrease in the electrical conductivity and the dielectric constant with Fe content.
TiO2/WO3 nanocomposite with nanodisk morphology was prepared and successfully used as a photocatalyst. The nanocomposite was obtained via sonochemical and hydrothermal methods, using pomegranate juice as a capping agent. The products were characterized by FE-SEM imaging, BET, EDAX spectroscopy, X-ray diffraction, DRS, and FT-IR spectroscopy. TiO2/WO3 nanocomposite showed high sensitivity to absorb visible light in compared to TiO2. In an optimized condition, the yield of the aerobic photocatalytic oxidation of benzyl alcohol derivatives reached to 65% for the TiO2/WO3 nanocomposite, while the conversion percent of the derivatives was less than 8% and 50% on the TiO2 and WO3 nanoparticles, respectively. Experimental results were supported by density functional theory (DFT) calculations. The DFT results in several solvents of different dielectric constants, confirmed the strong dependence of light absorption and photocatalytic activity to adsorption energy of the substrates on the surface of the nanoparticles (Ead). In addition, the theoretical results showed an inverse correlation between the adsorption energy of benzyl alcohol and its conversion percent, accordance to the experimental trend.
Natural dyes, namely, indigo carmine, cochineal carmine, curcumin and annatto, were encapsulated in silica by a sol-gel method and applied in the dyeing of different textile fibers by exhaustion. For comparative reasons, dyeing using the free (non-encapsulated) bare dyes was also carried out. The hybrid materials were analyzed by a set of techniques to investigate their elemental, structural, textural and morphological properties, and the results showed that it was possible to obtain stable natural dyes for applications in textile dyeing. The silica-structured dyes showed better affinities with the fibers (WO, PA, PAC and PET) in dyeing with cochineal carmine, while cotton (CO) showed better affinities with the encapsulated curcumin and annatto dyes. The performances of the encapsulated dyes were evaluated by color and washing fastness measurements and resulted in improved dye absorption and wash fastness properties. The color change and color transfer measurements of the encapsulated dyes were better (rated at 4–5 on a scale of 1–5) compared to the bare dyes.
Undoped and transition metal (TM: Ni, Mn, Co)-doped CeO2–SnO2 nanocomposite thin films were prepared by sol-gel dip coating (SGDC) technique. The grazing incidence X-ray diffraction (GIXRD) patterns indicated that CeO2–SnO2 film has a cubic structure of CeO2 and the crystallinity deteriorated with incorporation of dopant. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed that the surface morphology of the films was affected by TM incorporation. The surface roughness and fractal dimensions of CeO2–SnO2 films increased with doping. The average transmittance of CeO2–SnO2 thin film is found nearly 80% in the visible region and increased with doping. The absorption edge revealed a blue shift toward shorter wavelengths after incorporation of TM ions. The compositional dependence of optical parameters such as refractive index, extinction coefficient, and optical conductivity were also investigated. Cyclic voltammetry measurements showed that ion storage capacity was decreased significantly with increasing scan rate. The undoped and doped CeO2–SnO2 films showed good reversible cycle of intercalation/deintercalation of Li+ ions. The ion storage capacity and electrochemical stability were enhanced with transition metal doping. The Mn-doped CeO2–SnO2 composite thin film had better ion storage capacity rather than other samples due to its special porous morphology. The Li diffusion toward electrode surface was described in terms of self-similar fractal dimension. A quenching in blue-green photoluminescence (PL) intensity of CeO2–SnO2 films was occurred by transition metal doping.
Aluminum-doped ZnO thin films with pebble-like structures have been successfully deposited on glass substrates by successive ionic layer adsorption reaction method. The effect of percentage composition of the aluminum dopant on the flower-like clusters of the ZnO nanostructures on the structure, morphology, and optical properties was investigated. The ZnO thin films which were crystallized in hexagonal wurtzite structures with crystallite sizes of 44, 51, 56, and 43 nm for the intrinsic and 1, 3, and 5% Al-doped ZnO thin films, respectively. Preferred orientation of crystallites is in all cases in [001] direction perpendicular to the sample surface The Raman spectroscopy revealed decrease in the intensity of the ZnO characteristic peak due to the substitution of the Zn2+ atoms by the Al3+ and attributed to potential fluctuations of the alloy disorder. The introduction of the Al3+ dopant significantly increased the optical band gap.
An optical biosensor for the determination of catechol, a widely used yet toxic and carcinogenic molecule, is proposed using a crude extract of desert truffle (Terfezia leonis Tul.) as an enzymatic source of tyrosinase. The biosensor is constructed by the immobilization of tyrosinase crude extract in a bi-layered silica gel film prepared by dip-coating of an alkoxide/colloidal silica solution containing the enzyme on glass slide. Encapsulation has a moderate effect of the enzyme optimal pH stability but largely increases its thermal stability. Immobilized enzymes have a higher substrate affinity towards catechol but smaller maximum conversion velocity. The optical biosensor provides a linear response for catechol in the concentration range of 50–400?µM and a limit of detection was 52?µM. AFM studies show that the enzymes impact on the silica gel structure, preventing further deposition of additional layers. Comparison with similar dopamine biosensors points out that the impact of encapsulation on enzymatic activity may depend on the considered substrate.
Bismuth ferrite (BiFeO3) nanopowder have been successfully synthesized for the first time via a microwave-assisted sol-gel combustion method by using citric acid as fuel. The resulting nanopowder was characterized using FT-IR, TG-DTA, XRD, EDX, VSM, SEM, and UV-Vis DRS. A ferromagnetic hysteresis loop with a saturation magnetization (MS) of 0.66?emu?g?1 has been observed at room temperature in the sample. The optical properties of the nanosized BiFeO3 showed its small band gap (=2.08?eV) indicates a possibility of utilizing much visible light for photocatalysis.
