Effect of calcination temperature on phase transformation,structural and optical properties of sol–gel derived ZrO2 nanostructures

Zirconia (ZrO₂) nanostructures of various sizes have been synthesized using sol–gel method followed by calcination of the samples from 500 to 700 °C. The calcined ZrO₂ powder samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infra-red spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis.), Raman spectroscopy (RS) and thermogravimetric analysis (TGA). The phase transformation from tetragonal (t) to monoclinic (m) was observed. The average diameter of the ZrO₂ nanostructures calcined at 500, 600 and 700 °C was calculated to be 8, 17 and 10 nm, respectively. The ZrO₂ sample calcined at 500 °C with tetragonal phase shows a direct optical band gap of 5.1 eV. The value of optical band gap is decreased to 4.3 eV for the ZrO₂ calcined at 600 °C, which contains both tetragonal (73%) and monoclinic (27%) phases. On further calcination at 700 °C, where the ZrO₂ nanostructures have 36% tetragonal and 64% monoclinic phases, the optical band gap is calculated to be 4.8 eV. The enhancement in optical band gap for ZrO₂ calcined at 700 °C may be due to the rod like shape of ZrO₂ nanostructures. The tetragonal to monoclinic phase transformation was also confirmed by analyzing Raman spectroscopic data. The TG analysis revealed that the ZrO₂ nanostructure with dominance of monoclinic phase is found to be more stable over the tetragonal phase. In order to confirm the phase stability of the two phases of ZrO₂, single point energy is calculated corresponding to its monoclinic and tetragonal structures using density functional theory (DFT) calculations. The results obtained by theoretical calculations are in good agreement with the experimental findings.     

Influence of Ag doping on structural and optical properties of ZnO thin films synthesized by the sol–gel technique

Thin films of Ag–ZnO samples deposited on glass substrates with a different percentage of Ag content (1, 2, and 3 at%) were synthesized, at room temperature, by a dip-coating sol-gel method. The obtained samples are hexagonal wurtzite structure. The average grain size of deposits is about 5 nm. Up to 3 at%, c-axis lattice parameter shifts toward a higher value, which indicates that silver atoms replace Zn atoms in the crystal lattice. As shown by the DRX spectra, growth rate in the (101) direction is favored by the presence of silver ions in the ZnO. The layers present a homogeneous crystallites distribution, as we can remark it on SEM micrographs and exhibit a very low roughness according to AFM images. The entire samples exhibit a transmission value greater than 80 %, in the visible region, while the maximum is obtained for those doped at 2 at%. Energy band varies between 3.15 eV and 3.25 eV. The wider gap obtained is that of the ZnO layer doped with 2 at%. It is worth noting a strong UV emission observed on PL spectrum, performed at very low temperature (liquid nitrogen temperature), for silver doped ZnO compared to that of pure ZnO.     

Acoustic and optical phonons in EVOH–TiO2 nanocomposite films: Effect of aggregation

Films of an organic–inorganic nanocomposite material formed by a polymeric matrix (ethylene–vinyl alcohol copolymer—EVOH) and nanometric TiO₂ particles (ca. 10 nm) have been obtained with photo-catalytic properties in the elimination of pathogens. Optical spectroscopy experiments have been performed in order to characterize the films and evaluate their properties as a function of TiO₂ doping in the range between 0.25 and 13 wt%. Anatase TiO₂ nanoparticles seem to be well-dispersed up to 2% but aggregation for higher doping originates the two different regimes observed in the acoustic modes as well as in the optical absorption in the visible spectral range.     

Investigation of the crystallinity,structural, and optical properties in hydrotreating of Li–W co-doped ZnO thin films

The hydrotreated Li–W co-doped ZnO (LWZO:H) thin films was prepared on quartz glass substrates by RF magnetron sputtering at substrate temperature 100 °C with varied hydrogen flow ratios. The X-ray diffraction spectra indicated that the hydrotreating Li–W co-doped ZnO films showed a preferred orientation toward the c-axis. The chemical compositions of all samples were confirmed by X-ray photoelectron spectroscopy, which clearly showed the existence of W as a doping element into ZnO crystal lattice. The surface morphology of LWZO:H thin films changed with the increasing R value can clearly be seen. The average transmittance of the films was found to be almost 85 % for the wavelength range of 400–1,200 nm. Meanwhile, the optical band gap increase of the films may be attributed to the band Burstein–Moss effect.     

Grain boundary effect on structural,optical, and electrical properties of sol–gel synthesized Fe-doped SnO_2 nanoparticles

Tin oxide(SnO_2) and iron-doped tin oxide(Sn_(1-x)Fe_xO_2,x=0.05 wt%,0.10 wt%) nanoparticles are synthesized by the simple sol-gel method.The structural characterization using x-ray diffraction(XRD) confirms tetragonal rutile phases of the nanoparticles.The variations in lattice parameters and relative intensity with Fe-doping concentration validate the incorporation of iron into the lattice.The compressive strain present in the lattice estimated by using peak profile analysis through using Williamson-Hall plot also exhibits the influence of grain boundary formation in the lattice.The radiative recombination and quenching observed in optical characterization by using photoluminescence spectrum(PL) and the shift in the band gap estimated from UV-visible diffused reflectance spectrum corroborate the grain boundary influence.Raman spectrum and the morphological analysis by using a field emission scanning electron microscope(FESEM) also indicate the formation of grain boundaries.The compositional analysis by using energy dispersive x-ray spectrum(EDAX) confirms Fe in the SnO_2 lattice.The conductivity studies exhibit that the impendence increases with doping concentration increasing and the loss factor decreases at high frequencies with doping concentration increasing,which makes the Sn_(1-x)Fe_xO_2 a potential candidate for device applications.     

Effect of manganese ions concentration on the anatase–rutile phase transformation of TiO2 films

The phase structures of Ti_1?xMn_xO₂ (0?x<0.08) films synthesized by sol–gel spin coating have been investigated. The effect of Mn dopants on the stability of titanium dioxide (TiO₂) was studied by X-ray diffraction and Raman spectra for isochronally annealed samples. The increased Mn dopant concentration decreased the onset temperature of anatase–rutile (A–R) phase transformation. The calculated activation energy for the phase transformation decreased from 173.6 to 89.4 kJ/mol with Mn dopants concentration increasing from 0% to 7.51%. The Mn ions incorporated into the TiO₂ lattice reduce the rutile nucleation barrier and promote the nucleation rate.     

Influence of drying conditions on the optical and structural properties of sol–gel-derived ZnO nanocrystalline films

Zinc oxide nanothin films were prepared on glass substrate by sol–gel dip-coating method using zinc acetate dihydrate, methanol, and monoethanolamine as precursor, solvent, and stabilizer, respectively. The relationship between drying conditions and the characteristics of ZnO nanocrystalline films (c-axis orientation, grain size, roughness and optical properties) was studied. The films were dried in an oven at different temperatures and by IR radiation. Then, the films were annealed at 500°C in a furnace. The chemical composition, transmission spectra, structure, and morphology of the samples were studied using infrared (IR) and UV–visible spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM), respectively. The XRD results show that the drying conditions affect the orientation of crystallization along the (0 0 2) plane. AFM images show that the thicknesses of the films decrease from 128 to 93 nm by changing the drying conditions. The photoluminescence (PL) of ZnO nanothin films shows the UV emission at near band edge and broad green radiation at about 465 nm wavelength.     

Effect of dopants on the structural,optical and electrical properties of sol–gel derived ZnO semiconductor thin films

Undoped, Ga-, In-, Zr-, and Sn-doped ZnO transparent semiconductor thin films were deposited on alkali-free glasses by sol–gel method. 2-methoxyethanol (2-ME) and diethanolamine (DEA) were chosen as a solvent and a stabilizer, respectively. The doping concentration was maintained at 2 at.% in the impurity doping precursor solutions. The effects of different dopants on the structural, optical, and electrical properties of ZnO thin films were investigated. XRD results show that all annealed ZnO-based thin films had a hexagonal (wurtzite) structure. ZnO thin films doped with impurity elements obviously improved the surface flatness and enhanced the optical transmittance. All impurity doped ZnO thin films showed high transparency in the visible range (>91%). The Ga- and In- doped ZnO thin films exhibited higher Hall mobility and lower resistivity than did the undoped ZnO thin film.     

Study on the optical properties of PPV／TiO2 nanocomposites

The optical properties of poly(Phenylenevinylene)(PPV)/TiO2 nanocomposites,prepared via the sol-gel process,were investigated by UV-VIS,FT-IR,FL spectroscopy and TEM.TEM images indicated that the surfaces of TiO2 nanoparticles became rough,and finally formed the connected network as the TiO2 content increased.FT-IR spectra showed the titanium butoxide hydrolyzed to from Ti organic compound,which can result in the connected network of TiO2 nanoarticles.The conjugation of PPV polymer chains can be interrupted by the TiO2 network structure,as evdenced in UV-VIS spectra.The investigation of the PL spectra revealed that the emitted light of the PPV/TiO2 nanocoposites blue shifted wihout fine structure,and the PL intensity enhanced,when the TiO2 net work fromed.These phenomena suggested that the optical properties of the PPV/TiO2 nanocomposites were dependent on the interfacial structure between PPV and TiO2 nanoparticles.2001 Elsevier Science B.V.All rights reserved.     

Influences of Co doping on the structural and optical properties of ZnO nanostructured

Pure and Co-doped ZnO nanostructured samples have been synthesized by a chemical route. We have studied the structural and optical properties of the samples by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), field-emission transmission electron microscope (FETEM), energy-dispersive X-ray (EDX) analysis and UV–VIS spectroscopy. The XRD patterns show that all the samples are hexagonal wurtzite structures. Changes in crystallite size due to mechanical activation were also determined from X-ray measurements. These results were correlated with changes in particle size followed by SEM and TEM. The average crystallite sizes obtained from XRD were between 20 to 25 nm. The TEM images showed the average particle size of undoped ZnO nanostructure was about 20 nm whereas the smallest average grain size at 3% Co was about 15 nm. Optical parameters such as absorption coefficient (α), energy band gap (E _g ), the refractive index (n), and dielectric constants (σ) have been determined using different methods.     

Effect of gamma irradiation on the structural,thermal and optical properties of Makrofol BL 2–4

Makrofol BL 2–4 is an extrusion film based on Makrolon polycarbonate. It comprises excellent die-cutting performance combined with high light transmission and moderate light scattering properties. It is a class of polymeric solid state nuclear track detectors which has many applications in various radiation detection fields. In the present work, Makrofol samples were irradiated using different gamma doses ranging from 10 to 350 kGy. The structural modifications in the gamma-irradiated Makrofol samples have been studied as a function of dose using different characterization techniques such as X-ray diffraction, intrinsic viscosity, Fourier transform infrared spectroscopy, thermogravimetric analysis, refractive index and color difference studies. The gamma irradiation in the dose range 20–200 kGy led to a more compact structure of Makrofol polymer, which resulted in an improvement in its thermal stability with an enhancement in its structural and optical properties.     

First-principles calculations of the structural,electronic, optical and thermal properties of the BNxAs1–x alloys

The present paper aims to study the structural, electronic, optical and thermal properties of the boron nitride (BN) and BAs bulk materials as well as the BN_xAs_1–x ternary alloys by employing the full-potential-linearised augmented plane wave method within the density functional theory. The structural properties are determined using the Wu–Cohen generalised gradient approximation that is based on the optimisation of the total energy. For band structure calculations, both the Wu–Cohen generalised gradient approximation and the modified Becke–Johnson of the exchange-correlation energy and potential, respectively, are used. We investigated the effect of composition on the lattice constants, bulk modulus and band gap. Deviations of the lattice constants and the bulk modulus from the Vegard’s law and the linear concentration dependence, respectively, were observed for the alloys where this result allows us to explain some specific behaviours in the electronic properties of the alloys. For the optical properties, the calculated refractive indices and the optical dielectric constants were found to vary nonlinearly with the N composition. Finally, the thermal effect on some of the macroscopic properties was predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account.     

Electrical and optical properties of Sb-doped ZnO thin films synthesized by sol–gel method

Sb-doped ZnO thin films with different values of Sb content （from 0 to 1.1 at.%） are deposited by the sol-gel dip- coating method under different sol concentrations. The effects of Sb-doping content, sol concentration, and annealing ambient on the structural, optical, and electrical properties of ZnO films are investigated. The results of the X-ray diffraction and ultraviolet-visible spectroscopy （UV-VIS） spectrophotometer indicate that each of all the films retains the wurtzite ZnO structure and possesses a preferred orientation along the c axis, with high transmittance （〉 90%） in the visible range. The Hall effect measurements show that the vacuum annealed thin films synthesized in the sol concentration of 0.75 mol/L each have an adjustable n-type electrical conductivity by varying Sb-doping density, and the photoluminescence （PL） spectra revealed that the defect emission （around 450 nm） is predominant. However, the thin films prepared by the sol with a concentration of 0.25 mol/L, despite their poor conductivity, have priority in ultraviolet emission, and the PL peak position shows first a blue-shift and then a red-shift with the increase of the Sb doping content.     

Rapid thermal annealing effects on the structural and optical properties of Na–N codoped ZnO films

Polycrystalline ZnO thin films codoped with Na and N were obtained by chemical bath deposition. The structural characteristic and the optical properties of the rapid thermal annealed ZnO:(Na,N) films were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer (EDS), Raman spectrum and room-temperature photoluminescence. After RTA treatment, the XRD spectra showed a continuous decrease of the full- width at half-maximum (FWHM) of the (0 0 2) diffraction peak of the ZnO:(Na,N) film. The Raman spectra revealed that the intensity of the mode around 582 cm⁻¹ increased with the increase of the RTA temperature. The PL spectra showed different trends in the UV luminescence of ZnO:(Na,N) films after RTA treatments.     

Influence of post-deposition annealing on the structural and optical properties of ZnO thin films prepared by sol–gel and spin-coating method

Thin films of zinc oxide have been deposited onto (0001) sapphire substrate by sol–gel and spin-coating methods. The XRD pattern showed that the crystallinity of the annealed ZnO films had improved in comparison with that of the as-grown films. Photoluminescence spectra revealed a two-line structure, which is identified in terms of UV emission and defect-related emission. The emission intensity was found to be greatly dependent on heat treatment. Host phonons of ZnO and a shift of the _E2$E_2$ (high) peak from its position have been observed from Raman spectra. The surface morphologies of the film had been improved after annealing was observed from AFM images.     

Facile synthesis and photocatalytic activity of ZnO–CuO nanocomposite

Nanostructured ZnO–CuO composite with an open and porous surface was successfully prepared through a simple one-step homogeneous coprecipitation method under low temperature (80 °C), without using any organic solvent or surfactant. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV–vis spectroscopy. The results demonstrated that the ZnO–CuO nanocomposite presented a hierarchical 3D morphology composed of flower-like ZnO microstructures adorned with leaf-like CuO nanopatches. The photocatalytic activity of ZnO–CuO nanocomposite was evaluated by the photodegradation of rhodamine B under the simulated sunlight irradiation, and compared with those of the monocomponent oxides synthesized by the identical synthetic route and their physical mixture in the approximate molar ratio as that of the nanocomposite. The results indicated that the ZnO–CuO nanocomposite exhibited an appreciable photocatalytic activity, which was mainly attributed to the extended photo-responding range and the increased charge separation rate in the nanocomposite.     

Anomalous behavior and phase transformation of α-GaOOH nanocrystals under static compression

The structural compression mechanism and compressibility of gallium oxyhydroxide, α-GaOOH, are investigated by in situ synchrotron radiation x-ray diffraction at pressures up to 31.0 GPa by using the diamond anvil cell technique. Theα-GaOOH sustains its orthorhombic structure when the pressure is lower than 23.8 GPa. The compression is anisotropic under hydrostatic conditions, with the a-axis being most compressible. The compression proceeds mainly by shrinkage of the void channels formed by the coordination GaO_3(OH)_3 octahedra of the crystal structure. Anomaly is found in the compression behavior to occur at 14.6GPa, which is concomitant with the equatorial distortion of the GaO_3(OH)_3 octahedra. A kink occurs at 14.6 GPa in the plot of finite strain f versus normalized stress F, indicating the change in the bulk compression behavior. The fittings of a second order Birch–Murnaghan equation of state to the P–V data in different pressure ranges result in the bulk moduli B_0= 199(1) GPa for P 14.6 GPa and B_0= 167(2) GPa for P 14.6 GPa. As the pressure is increased to about 25.8 GPa, a first-order phase transformation takes place, which is evidenced by the abrupt decrease in the unit cell volume and b and c lattice parameters.     

Synthesis of Photoactive ZnO–SnO2–Ag(AgCl) Nanomaterials for Medical and Ecological Applications and Study of Their Structure and Properties

Optics and Spectroscopy - Photoactive ZnO–SnO2–Ag(AgCl) nanomaterials capable of generating chemically active single oxygen under action of UV and blue light are synthesized using a...     

Influence of post-deposition annealing on the structural,optical and electrical properties of Li and Mg co-doped ZnO thin films deposited by sol–gel technique

Lithium (Li) and magnesium (Mg) co-doped zinc oxide (ZnO) thin films were deposited by sol–gel method using spin coating technique. The films were deposited on glass substrates and annealed at different temperatures. The effects of annealing temperature on the structural, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), Ultraviolet–Visible absorption spectra (UV–VIS), photoluminescence spectra (PL), X-ray photo electron spectroscopy (XPS) and Hall measurements. XRD patterns indicated that the deposited films had a polycrystalline hexagonal wurtzite structure with preferred (0 0 0 2) orientation. All films were found to exhibit a good transparency in the visible range. Analysis of the absorption edge revealed that the optical band gap energies of the films annealed at different temperatures varies between 3.49 eV and 3.69 eV. Room temperature PL spectra of the deposited films annealed at various temperatures consist of a near band edge emission and visible emission due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O_Zn), interstitial zinc (Zn_i), interstitial oxygen (O_i) and zinc vacancy (V_Zn) which are generated during annealing process. The influence of annealing temperature on the chemical state of the dopants in the film was analysed by XPS spectra. Ion beam analysis (Rutherford back scattering) experiments were performed to evaluate the content of Li and Mg in the films. Hall measurements confirmed the p-type nature of the deposited films.     

Structural,thermal and optical behavior of laser irradiation-induced PVA–PEG–Ag nanocomposites

Polyvinyl alcohol?polyethylene glycol?silver (PVA–PEG–Ag) nanocomposites were prepared by adding Ag nanoparticles with 5?wt.% to the (PVA–PEG) blend. The films of 0.05?mm thickness were prepared by the casting method. Samples from these films were irradiated with infrared (IR) laser fluences ranging from 1.7 to 15?J/cm². The effect of IR laser radiation on the structural properties of PVA–PEG–Ag has been investigated using X-ray diffraction and Fourier transform infrared spectroscopy. The results indicate that the crosslinking dominates due to laser exposure at the fluence range 1.7–15?J/cm², reducing the ordering character of the nanocomposite samples. Also, the variation of transition temperatures with the laser fluence has been determined using differential thermal analysis. The nanocomposite thermograms were characterized by the appearance of an endothermic peak due to melting, and were found to be dependent on the laser fluence. In addition, the color changes due to laser irradiation were computed using the transmission data. It is found that the color difference is largely dependent on the proportions of the red color component.