Effect of stabilizer on optical and structural properties of MgO thin films prepared by sol–gel method

The effects of monoethanolamine (MEA) and acetylacetone (ACAC) addition as stabilizer on the crystallization behaviour, morphology and optical properties of magnesium oxide were investigated using thermogravimetry (TG/DTG), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Visible, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. Stabilizer addition reduces transparency of the films. MgO films prepared at 500 °C showed weak orientation of (200). However, the films prepared by addition of stabilizer are amorphous. MgO powders were prepared for exhibiting the structural properties. The patterns of MgO powders showed a preferred orientation of (200). The addition of stabilizer causes a reduction in grain size. SEM micrographs show that a homogenous and crack-free film can be prepared at 500 °C and addition of stabilizer causes an increase in packing density.     

Influence of Fe dopant concentration and annealing temperature on the structural and optical properties of ZnO thin films deposited by sol–gel method

Nanostructured Fe doped ZnO thin films were deposited onto glass substrates by sol–gel spin coating method. Influence of Fe doping concentration and annealing temperature on the structural, compositional, morphological and optical properties were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–Vis spectroscopy and photoluminescence (PL) measurements. XRD analysis showed that all the films prepared in this work possessed a hexagonal wurtzite structure and were preferentially oriented along the c-axis. Pure ZnO thin films possessed extensive strain, whereas Fe doped films possessed compressive strain. In the doped films, least value of stress and strain was observed in the 0.5 at.% Fe doped thin film, annealed at 873 K. Average crystallite size was not significantly affected by Fe doping, but it increased from 15.57 to 17.79 nm with increase in annealing temperature from 673 to 873 K. Fe ions are present in +3 oxidation state as revealed by XPS analysis of the 0.5 at.% Fe doped film. Surface morphology is greatly affected by changes in Fe doping concentration and annealing temperature which is evident in the SEM images. The increase in optical band gap from 3.21 to 3.25 eV, with increase in dopant concentration was attributed to Moss–Burstein shift. But increase in annealing temperature from 673 to 873 K caused a decrease in band gap from 3.22 to 3.20 eV. PL spectra showed emissions due to excitonic combinations in the UV region and defect related emissions in the visible region in all the investigated films.     

Post annealing effect on structural and optical properties of ZnO thin films derived by sol–gel route

Zinc oxide thin films have been spun coated on p-Si (100) substrates by sol–gel route. These films were annealed at different annealing temperatures from 300 to 1,000 °C in the oxygen ambient. In this way a suitable annealing temperature window for the sol–gel derived ZnO films exhibiting minimum defects (points and dislocations) and better quality (crystal and optical) was investigated. The structural and optical features of ZnO thin films have been examined by X-ray diffraction, atomic force microscopy, UV–Vis spectroscopy, and photoluminescence spectra. The results revealed that the crystallization in the films initiated at 300 °C, improved further with annealing. All the deposited films exhibited wurtzite phase with c-axis orientations. The variations in the position of characteristic (002) peak, stress, strain and lattice parameters are investigated as a function of annealing temperature. The optical band gap is not significantly affected with annealing as observed by UV–Vis transmission spectroscopy. The Photoluminescence spectra exhibited three luminescence centers. The near band edge esmission was observed in UV region which enhanced with the heat treatment, is an indication of improvement in the optical quality of films. The other two visible emissions are related to native defects in ZnO lattice were appeared only for higher annealing (≥700 °C).     

Influence of annealing temperature on the structural,topographical and optical properties of sol–gel derived ZnO thin films

This investigation deals with the effect of annealing temperature on the structural, topographical and optical properties of Zinc Oxide thin films prepared by sol–gel method. The structural properties were studied using X-ray diffraction and the recorded patterns indicated that all the films had a preferred orientation along (002) plane and the crystallinity along with the grain size were augmented with annealing temperature. The topographical modification of the films due to heat treatment was probed by atomic force microscopy which revealed that annealing roughened the surface of the film. The optical properties were examined by a UV–visible spectrophotometer which exhibited that maximum transmittance reached nearly 90% and it diminished with increasing annealing temperature.     

Structural,morphological and optical properties of undoped and Co-doped ZnO thin films prepared by sol–gel process

Undoped and Co-doped ZnO thin films with different amounts of Co have been deposited onto glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, cobalt acetate tetrahydrate, isopropanol and monoethanolamine (MEA) were used as a precursor, doping source, solvent and stabilizer, respectively. The molar ratio of MEA to metal ions was maintained at 1.0 and a concentration of metal ions is 0.6 mol L^?1. The Co dopant level was defined by the Co/(Co + Zn) ratio it varied from 0 to 7 % mol. The structure, morphology and optical properties of the thin films thus obtained were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis), photoluminescence (PL) and Raman. The XRD results showed that all films crystallized under hexagonal wurtzite structure and presented a preferential orientation along the c-axis with the maximum crystallite size was found is 23.5 nm for undoped film. The results of SEM indicate that the undoped ZnO thin film has smooth and uniform surface with small ZnO grains, and the doped ZnO films shows irregular fiber-like stripes and wrinkle network structure. The average transmittance of all films is about 72–97 % in the visible range and the band gap energy decreased from 3.28 to 3.02 eV with increase of Co concentration. DRX, EDX and optical transmission confirm the substitution of Co²⁺ for Zn²⁺ at the tetrahedral sites of ZnO. In addition to the vibrational modes from ZnO, the Raman spectra show prominent mode representative of Zn_yCo_3?yO₄ secondary phase at larger values of Co concentration. PL of the films showed a UV and defect related visible emissions like violet, blue and green, and indicated that cobalt doping resulted in red shifting of UV emission and the reduction in the UV and visible emissions intensity.     

Effect of Zn doping on structure and ferroelectric properties of PST thin films prepared by sol–gel method

(Pb _y Sr_1−y )Zn _x Ti_1−x O_3−x thin films were prepared on ITO/glass substrate by sol–gel process using dip-coating method. The phase structure, morphology and ferroelectric property of the thin film were studied. All the thin films show the typical perovskite phase structure. Both the crystallinity and c/a ratio of the perovskite phase increases initially and then decreases gradually with doping Zn in the thin film. Ferroelectric properties of the Zn-doped PST thin films, including ferroelectric hysteresis-loop, remnant polarization and coercive force, decrease gradually with increasing Zn. And the effect of Zn on ferroelectric properties is more obvious in PST thin film with high content of Pb than that with low Pb although the high lead thin film exhibits high intrinsic ferroelectric properties.     

Influence of Yttrium on optical,structural and photoluminescence properties of ZnO nanopowders by sol–gel method

Undoped and Yttrium doped ZnO nanopowders (Zn_1−xY_xO, 0 ⩽ x ⩽ 0.05) were prepared by sol–gel method and annealed at 500 °C for 4 h under air atmosphere. The prepared nanopowders were characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV–Visible spectrophotometer and Fourier transform infrared spectroscopy. The EDS analysis confirmed the presence of Y in the ZnO system. Both atomic and weight percentages were nearly equal to their nominal stoichiometry within the experimental error. XRD measurement revealed the prepared nanoparticles have different microstructures without changing a hexagonal wurtzite structure. The calculated average crystallite size decreased from 26.1 to 23.2 nm for x = 0–0.02 then reached 24.1 nm for x = 0.05. The change in lattice parameters was demonstrated by the crystal size, bond length, micro-strain and the quantum confinement effect. The observed blue shift of energy gap from 3.36 eV (Y = 0) to 3. 76 eV (Y = 0.05) (ΔE_g = 0.4 eV) revealed the substitution of Y³⁺ ions into ZnO lattice. The presence of functional groups and the chemical bonding are confirmed by FTIR spectra. The appreciable enhancement of PL intensity with slight blue shift in near band edge (NBE) emission from 396 to 387 nm and a red shift of green band (GB) emission from 513 to 527 nm with large reduction in intensity confirm the substitution of Y into the ZnO lattice. Y-doped ZnO is useful to tune the emission wavelength and hence is appreciable for the development of supersensitive UV detector.     

Influence of pH on ZnO nanocrystalline thin films prepared by sol–gel dip coating method

ZnO nanocrystalline thin films have been prepared on glass substrates by sol?Cgel dip coating method. ZnO thin films have been coated at room temperature and at four different pH values of 4, 6, 8 and 10. The X-ray diffraction pattern showed that ZnO nanocrystalline thin films are of hexagonal structure and the grain size was found to be in the range of 25?C45?nm. Scanning electron microscopic images show that the surface morphology improves with increase of pH values. TEM analysis reveals formation of ZnO nanocrystalline with an average grain size of 44?nm. The compositional analysis results show that Zn and O are present in the sample. Optical band studies show that the films are highly transparent and exhibit a direct bandgap. The bandgap has been found to lie in the range of 3 $\boldsymbol\cdot$ 14?C3 $\boldsymbol\cdot$ 32?eV depending on pH suggesting the formation of ZnO nanocrystalline thin films.     

Red luminescent and structural properties of Mg-doped ZnO phosphors prepared by sol–gel method

Magnesium-doped zinc oxide phosphors with the formula of Mg_xZn_1?xO were synthesized by sol–gel method, and the crystal structure and luminescent properties were investigated by means of XRD, SEM, FTIR, Raman spectrum, EPR, DRS and PL. The results indicated that the materials consisting of Mg_xZn_1?xO particles exhibit good crystallinity and the particle size varies with the calcining temperature. An obvious blue shift of excitation band was observed in samples as the doping concentration was increased from 5 at% to 10 at%. The optimal concentration for obtaining the highest photoluminescent intensity for Mg_xZn_1?xO phosphors was 10 at% (calcined at 875 °C for 3 h). Raman and EPR results suggested that the red emission of Mg-doped ZnO phosphors was attributed to zinc vacancies and oxygen vacancies.     

Effect of monovalent dopant ionic radius and concentration on the growth orientation and optical properties of the sol–gel-derived ZnO thin films

Journal of Materials Science: Materials in Electronics - Pure and doped ZnO thin films with different monovalent elements (Li+, Na+, Ag+ and Cs+) are deposited onto glass substrates using a...     

Influence of annealing temperature and oxygen atmosphere on the optical and photoluminescence properties of BaTiO3 amorphous thin films prepared by sol–gel method

Homogeneous and transparent BaTiO₃ thin films were prepared by sol–gel dip coating method. The prepared BaTiO₃ thin films were annealed in air and O₂ atmosphere at different temperatures. The annealed BaTiO₃ thin films were amorphous in nature. Scanning electron microscopy (SEM) revealed the nucleation and particle growth on the films. Energy-dispersive X-ray (EDX) analysis data revealed the adsorption of oxygen atoms in the BaTiO₃ film. The direct energy band gap was found to vary (3.84–3.58 eV) as functions of annealing atmosphere and temperature. Photoluminescence (PL) revealed intense emission peaks at 393 and 675 nm. Quenching of PL intensity was observed in films annealed at high temperature and in O₂ atmosphere. This is due to reduction in the oxygen vacancy by the adsorption of oxygen in the film. Luminescence spectra also have been related to the results obtained by SEM and EDX analysis. The change in luminescence intensity of BaTiO₃ thin films makes it suitable for optoelectronic temperature sensor applications.     

Low-temperature preparation of transparent conductive Al-doped ZnO thin films by a novel sol–gel method

We developed a novel sol–gel method to prepare transparent conductive Al-doped ZnO (AZO) thin film at low temperature. The AZO nanocrystals were prepared by a solvothermal method and then they were dispersed in the monoethanolamine and methanol to form AZO colloids. A (002)-oriented ZnO thin film was used as a nucleation layer to induce the (002)-oriented growth of AZO thin films. The AZO thin films were prepared on Si(100) and fused quartz glass substrates with the (002)-oriented ZnO nucleation layer and annealed at 400 °C for 60 min. All AZO thin films showed (002) orientation. For electrical and optical measurements, the films deposited on glass substrates were post-annealed at 400 °C for 30 min in forming gas (100 % H₂) to improve their conductivity. These samples had high transparency in the visible wavelength range, and also showed good conductivity. A 0.2 mol L^?1 AZO solution with 3 at.% Al content was heated in a Teflon autoclave at 160 °C for 30 min to form AZO nanocrystals, and then the AZO nanocrystals were suspended in the MEA and methanol to obtain the stable AZO colloid. The Al content in the AZO nanocrystals was 2.7 at.%, and the high Al doping coefficient was mainly attributed to the formation of AZO nanocrystals in the autoclave. The AZO thin film using this colloid had the lowest resistivity of 3.89 × 10^?3 Ω cm due to its high carrier concentration of 3.29 × 10²⁰ cm^?3.     

Structure,morphology, photocatalytic and antibacterial activities of ZnO thin films prepared by sol–gel dip-coating method

ZnO thin films were deposited on soda lime glass substrates by the sol–gel dip-coating method with variations of the initial Zn²⁺ concentrations. Various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) were used to investigate the effects of the initial Zn²⁺ concentrations on the structure, and surface morphology and topography of the prepared films. All prepared ZnO thin films showed a high transparency of over 88% in the visible region. The particle size increased with an increased initial Zn²⁺ concentration. This also reduced the surface denseness and the energy band gap of the ZnO thin films. All the prepared films showed photocatalytic properties through photodegradation of the methylene blue (MB) dye. The ZnO thin film prepared from the 0.1 M Zn²⁺ concentration showed the greatest efficiency as it had the highest surface area because of its greatest surface roughness. Furthermore, the prepared ZnO thin film showed antibacterial activities against the Escherichia coli bacterium.     

Investigation of the iron doping on the structural,optical, and magnetic properties of Fe-doped ZnO nanoparticles synthesized by sol–gel method

Journal of Materials Science: Materials in Electronics - In this work, the compatibility of zinc oxide for spintronic applications motivated the development of single-phase Fe/ZnO nanostructures by...     

Effect of annealing temperature on electrical and nano-structural properties of sol–gel derived ZnO thin films

Zinc oxide (ZnO) thin films have been prepared on silicon substrates by sol–gel spin coating technique with spinning speed of 3,000 rpm. The films were annealed at different temperatures from 200 to 500 °C and found that ZnO films exhibit different nanostructures at different annealing temperatures. The X-ray diffraction (XRD) results showed that the ZnO films convert from amorphous to polycrystalline phase after annealing at 400 °C. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on pre-cleaned silicon (100) substrates and electrical properties such as current versus voltage (I–V) and capacitance versus voltage (C–V) characteristics were studied. The electrical resistivity decreased with increasing annealing temperature. The oxide capacitance was measured at different annealing temperatures and different signal frequencies. The dielectric constant and the loss factor (tanδ) were increased with increase of annealing temperature.