La-doped ZnO nanoparticles: Simple solution-combusting preparation and applications in the wastewater treatment

La-doped ZnO nanoparticles have been successfully synthesized by a simple solution combustion method via employing a mixture of ethanol and ethyleneglycol (v/v = 60/40) as the solvent. Zinc acetate and oxygen gas in the atmosphere were used as zinc and oxygen sources, and La(NO₃)₃ as the doping reagent. The as-obtained product was characterized by means of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. Experiments showed that La-doped ZnO nanoparticles exhibited the higher capacities for the removal of Pb²⁺ and Cu²⁺ ions in water resource than undoped ZnO nanoparticles.     

Effect of oxygen exposure on the electrical conductivity and gas sensitivity of nanostructured ZnO films

Nanostructured ZnO films (undoped and Ga, Co, Mn doped) were exposed to oxygen (1-80 vol.%) at temperature range of 300-500 °С in order to reveal the ambience-temperature effect on the electrical conductivity. The dominant effect of ambient influence via oxygen absorption was observed: the intensity of conductivity decrease was found to be proportional with temperature and tends to saturate with time. It is demonstrated that oxygen absorption occurs accordingly to diffusion law and the quantifying of oxygen diffusion was realized for different samples. It is revealed that the type of dopant affects the diffusion in ZnO and the tendency to increase the diffusion intensity with dopant content has been observed. After oxygen saturation the reversible effect of oxygen adsorption became dominant and contributed to the film's conductivity. Oxygen exposure undoped ZnO films revealed high sensitivity for oxygen content change in the ambience therefore they have been preceded further for gas sensor design and the detailed investigation of film's sensing properties has been carried out.     

Semiconductor/metal nanocomposites formed by in situ reduction method in multilayer thin films

A layer-by-layer adsorption and in situ reduction method was adopted for synthesizing semiconductor/metal nanocomposites in multilayer ultra-thin films. Alternate adsorption of ZnO nanoparticles modified with poly(ethyleneimine), hydrogentetrachloroaurate and poly(styrenesulfonate) sodium results in the formation of ZnO/AuCl₄⁻-loaded multilayer films. In situ reduction of the incorporated metal ions by heating yields ZnO/Au nanocomposites in the films. UV-vis absorption spectroscopy and X-ray photoelectron spectroscopy were used to characterize the components of the composite films. UV-vis spectra indicate regular growth of the films. The electrochemistry behavior of the multilayer films was studied in detail on indium tin oxide electrode. The combined results suggest that the layer-by-layer adsorption and subsequent reduction method used here provides an effective way to synthesize ZnO/Au nanocomposites in the polymer matrix.     

Optical and structural characteristics of ZnO thin films grown by rf magnetron sputtering

Nanostructured ZnO thin films on Pyrex glass substrates were deposited by rf magnetron sputtering at different substrate temperatures. Structural features and surface morphology were studied by X-ray diffraction and atomic force microscopy analyses. Films were found to be transparent in the visible range above 400 nm, having transparency above 90%. Sharp ultraviolet absorption edges around 370 nm were used to extract the optical band gap for samples of different particle sizes. Optical band gap energy for the films varied from 3.24 to 3.32 eV and the electronic transition was of the direct in nature. A correlation of the band gap of nanocrystalline ZnO films with particle size and strain was discussed. Photoluminescence emission in UV range, which is due to near band edge emission is more intense in comparison with the green band emission (due to defect state) was observed in all samples, indicating a good optical quality of the deposited films.     

Synthesis, characterization, UV and dielectric properties of hexagonal disklike ZnO particles embedded in polyimides

A series of novel ZnO/polyimide composite films with different ZnO contents was prepared through incorporation hexagonal disklike ZnO particles into poly(amic acid) of the pre polymer of the polyimide. The hexagonal disklike ZnO particles with a diameter of 300-500 nm were synthesized from zinc acetate and NaOH in water with citric acid. The prepared zinc oxide-polyimide composites were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy, scanning electron micrograph, X-ray diffraction and thermal analysis techniques. Thermal analyses show that the ZnO particles were successfully incorporated into the polymer matrix and these ZnO/polymer composites have a good thermal stability. Scanning electron microscopy studies indicate the ZnO particles were uniformly dispersed in the polymer and they remained at the original size (300-500 nm) before immobilization. All composite films with ZnO particle contents from 1 to 5 wt% show good transparency in the visible region and luminescent properties.     

Fabrication of room temperature H2 gas sensor using pure and La: ZnO with novel nanocorn morphology prepared by sol–gel dip coating method

Nanostructured ZnO thin films with different lanthanum concentration (0, 1, 3, 5 and 10 wt%) were fabricated by sol–gel dip coating method on glass substrates. The effect of La incorporation on structural, morphological and H₂ gas sensing (room temperature) properties of the ZnO thin films was studied. Thermal behaviour of the xerogel of pure ZnO was studied by thermo gravimetric analysis/differential thermal analysis. The structural property of the films was analyzed by powder X-ray diffraction method and which revealed the presence of hexagonal structure. It emphasized that the film became (002) textured upon the 3 wt% of La incorporation onwards. The surface morphology was examined by field emission scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (EDX) and it substantiated that all the films have uniform distribution of particles with novel corn like morphology. Obviously, the length of nanocorn increases with the increase of La. The elemental composition was studied by EDX spectroscopy. Photoluminescence (PL) spectra revealed that La: ZnO thin films showed a blue shift and an enhanced PL intensity over that of the pure ZnO. The H₂ gas sensitivity of the pure and La: ZnO thin films were studied towards the concentration of 1,000 ppm. 1 wt% of La incorporated ZnO thin film showed a high sensitivity (51 %) than the pure and the higher La concentration. The increase and decrease of H₂ gas sensitivity of pure ZnO upon La incorporation is also discussed in this paper.     

Preparation and characterization of Ba1 − xSrxTiO3 thin films deposited on Pt/SiO2/Si by sol-gel method

BST thin films have been investigated as potential candidates for use in frequency agile microwave circuit devices. Stoichiometric (Ba_1 − xSr_x)TiO₃ (BST) thin films have been prepared on Pt/SiO₂/Si substrates using sol-gel method. The BST films were characterized by X-ray fluorescence (XRF) spectroscopy analysis, X-ray diffraction (XRD), scanning electron microscope (SEM) and electrical measurements. The relationships of processing parameters, microstructures, and dielectric properties are discussed. The results show that the films exhibit pure perovskite phase through rapid thermal anneal at 700 °C and their grain sizes are about 20-40 nm. The dielectric constants of BST5, BST10, BST15 and BST20 are 323, 355, 382 and 405, respectively, at 80 kHz.     

Annealing and recrystallization of amorphous ZnO thin films deposited under cryogenic conditions by pulsed laser deposition

This article deals with the annealing of amorphous ZnO thin films prepared by pulsed laser deposition (PLD) under cryogenic conditions. The substrate holder was cooled by liquid nitrogen. X-ray diffraction analysis evidenced that as-deposited films had amorphous structures: analysis by scanning electron microscopy (SEM) revealed their fine grained surface and inner structure. Annealing at temperatures in the range of 200-800 °C resulted in a transition in the thin film crystal structure from amorphous to polycrystalline. Various properties of the ZnO films were found depending on the recrystallization temperature. In depth investigations employing SEM, X-ray diffraction, atomic force microscopy and secondary ion mass spectroscopy provided comparisons of the recrystallizations of undoped ZnO thin films during the phase transition processes from amorphous to hexagonal wurtzite structures.     

Rapid synthesis, characterization and optical properties of TiO2 coated ZnO nanocomposite particles by a novel microwave irradiation method

A novel and rapid microwave method was used to prepare TiO₂ coated ZnO nanocomposite particles. The resulted particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Results show that ZnO nanoparticles were coated with 6-10 nm amorphous TiO₂ layers. In addition, zeta potential analysis demonstrated the presence of TiO₂ layer on the surface of ZnO nanoparticles. Photoluminescence (PL) spectroscopy and UV-visible spectroscopy were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnO nanoparticles, the TiO₂ coated ZnO nanoparticles showed enhanced UV emission. The UV-visible diffuse reflectance study revealed the significant UV shielding characteristics of the nanocomposite particles. Moreover, amorphous TiO₂ coating effectively reduced the photocatalytic activity of ZnO nanoparticles as evidenced by the photodegradation of Orange G with uncoated and TiO₂ coated ZnO nanoparticles under UV radiation.     

Transparent conducting properties of Ni doped zinc oxide thin films prepared by a facile spray pyrolysis technique using perfume atomizer

Undoped and Ni doped zinc oxide (Ni–ZnO) thin films were prepared by a facile spray pyrolysis technique using perfume atomizer from aqueous solution of anhydrous zinc acetate (Zn(CH₃COOH)₂ and hexahydrated nickel chloride (NiCl₂·6H₂O) as sources of zinc and nickel, respectively. The films were deposited onto the amorphous glass substrates kept at (450 °C). The effect of the [Ni]/[Zn] ratio on the structural, morphological, optical and electrical properties of Ni doped ZnO thin film was studied. It was found from X-ray diffraction (XRD) analysis that both the undoped and Ni doped ZnO films were crystallized in the hexagonal structure with a preferred orientation of the crystallites along the [002] direction perpendicular to the substrate. The scanning electron microscopy (SEM) images showed a relatively dense surface structure composed of crystallites in the spherical form whose average size decreases when the [Ni]/[Zn] ratio increases. The optical study showed that all the films were highly transparent. The optical transmittance in the visible region varied between 75 and 85%, depending on the dopant concentrations. The variation of the band gap versus the [Ni]/[Zn] ratio showed that the energy gap decreases from 2.95 to 2.72 eV as the [Ni]/[Zn] ratio increases from 0 to 0.02 and then increases to reach 3.22 eV for [Ni]/[Zn] = 0.04. The films obtained with the [Ni]/[Zn] ratio = 0.02 showed minimum resistivity of 2 × 10⁻³ Ω cm at room temperature.     

Facile synthesis of porous ZnO microbelts and analysis of their gas-sensing property

Porous ZnO microbelts were achieved using a facile chemical solution method combined with subsequent calcination. The micro-nanostructures were characterized through X-ray diffraction, field emission scanning electron microscopy, thermogravimetric-differential thermal analysis, and Brunauer–Emmett–Teller N₂ adsorption-desorption analyses, among others. The BET surface area of the porous ZnO microbelts was calculated at 23.0 m² g⁻¹. Furthermore, the gas sensing properties of the as-prepared porous ZnO microbelts were investigated using volatile organic compounds. Compared with ZnO microflowers, the porous ZnO microbelts exhibited higher response with certain organic vapors, such as formaldehyde, acetone, and ethanol. The responses to 100 ppm formaldehyde, acetone, and ethanol were 45.7, 40.6, and 38.4, respectively, at a working temperature of 300 °C. The results showed that the porous ZnO microbelts are highly promising candidates for gas sensing applications.     

Thickness dependency of sol-gel derived ZnO thin films on gas sensing behaviors

ZnO thin films were fabricated by a sol-gel method using Zn(CH₃COO)₂·2H₂O as starting material in order to prepare an acetone gas sensor. A homogeneous and stable solution was prepared by dissolving the zinc acetate in a solution of ethanol and monoethanolamine. The sol-gel solution is coated on alumina substrates with various thicknesses by spin coating technique and heat treated to grow crystalline ZnO thin films. The effect of thickness on physical and electrical properties of as deposited ZnO thin films has been studied. The as deposited ZnO thin films were characterized by X-ray diffraction spectroscopy, field emission scanning electron microscopy and atomic force microscopy. The root mean square surface roughness factors increase with thickness of the films and found 3.9, 6.6, 9.0, and 11.28 nm for 80-, 220-, 450- and 620-nm-thin films respectively. The activation energies of the films are calculated from the resistance temperature characteristics. The sensitivities of the ZnO films towards the acetone gas were determined at an operating temperature of 200 °C. The sensitivity towards acetone vapor is strongly depending on surface morphology of the ZnO thin films.     

Preparation N-F-codoped TiO2 nanorod array by liquid phase deposition as visible light photocatalyst

An efficient method for the preparation of N-F-codoped visible light active TiO₂ nanorod arrays is reported. In the process, simultaneous nitrogen and fluorine doped TiO₂ nanorod arrays on the glass substrates were achieved by liquid phase deposition method using ZnO nanorod arrays as templates with different calcination temperature. The as-prepared samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectra measurements. It was found that calcination temperature is an important factor influencing the microstructure and the amount of N and F in TiO₂ nanorod arrays samples. The visible light photocatalytic properties were investigated using methylene blue (MB) dye as a model system. The results showed that N-F-codoped TiO₂ nanorod arrays sample calcined at 450 °C demonstrated the best visible light activity in all samples, much higher than that of TiO₂ nanoparticles and P25 particles films.     

Preparation and ethanol sensing properties of the superstructure SnO2/ZnO composite via alcohol-assisted hydrothermal route

Self-assembled superstructure of SnO₂/ZnO composite was synthesized by using alcohol-assisted hydrothermal method gas sensing properties of the material were investigated by using a static test system. The structure and morphology of the products were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM). The diameter of the SnO₂ nanorods was about 40 nm with a length of about 300 nm, SnO₂ nanorods and ZnO nanosheets interconnect each other to form a superstructure. The gas sensing properties of superstructure SnO₂/ZnO composite with different content of ZnO were investigated. Furthermore, the superstructure SnO₂/ZnO composite sensor is characterized at different operating temperatures and its long-term stability in response to ethanol vapor is tested over a period of 3 months.     

Effect of In incorporation on the structural, electrical, and gas sensing properties of ZnO films

In this paper, we report some comparative results on the structural, electrical, and gas sensing properties of undoped, In-doped ZnO, and ZnO–In₂O₃ thin films, respectively. The oxide films were obtained by thermal oxidation (flash oxidation) of metallic films, deposited by thermal evaporation under vacuum. X-ray diffraction patterns reveal that oxidized films are polycrystalline, the crystallites being preferentially oriented with (002) planes parallel with the substrate. It was observed that the films’ morphology, investigated by atomic force microscopy and scanning electron microscopy, is influenced by the In amount. The temperature dependence of electrical conductivity was studied and obtained results indicate that In-doped ZnO and ZnO–In₂O₃ films exhibit an enhancement of electrical conductivity with four orders of magnitude by comparison with undoped ZnO film. Gas sensitivity measurements were performed for four different gases (ammonia, methane, acetone, and ethanol), and it was observed that all investigated films are more sensitive to ammonia. Also, it was observed that gas sensitivity is visibly increased for In-doped ZnO and ZnO–In₂O₃ samples by comparison with undoped ZnO film.     

Improved microstructural properties of a ZnO thin film using a buffer layer in-situ annealed in argon ambient

ZnO films with improved crystallinity were grown on a Si (111) substrate by a two-step growth process using low-temperature ZnO buffer layers. The effect of the ambient gas during the temperature elevation and the in-situ thermal annealing after the growth of the low-temperature buffer layers on the optical and structural properties of the films was investigated by X-ray diffraction (XRD), photoluminescence, and transmission electron microscopy. The use of argon as the ambient gas during the thermal treatment of the buffer layer leads to the enhancement of the (0002) diffraction peak intensity at 2θ ∼ 34.4° and the reduction of the full width at half maximum value in the XRD rocking curve, which means that well-defined and c-axis oriented ZnO film was obtained. The relationship between the thickness of the SiO₂ layer between the ZnO buffer layers and Si substrates and the structural and optical properties of the ZnO films is discussed.     

Solution precursor plasma deposition of nanostructured ZnO coatings

Zinc oxide (ZnO) is a wide band gap semiconducting material that has various applications including optical, electronic, biomedical and corrosion protection. It is usually synthesized via processing routes, such as vapor deposition techniques, sol-gel, spray pyrolysis and thermal spray of pre-synthesized ZnO powders. Cheaper and faster synthesis techniques are of technological importance due to increased demand in alternative energy applications. Here, we report synthesis of nanostructured ZnO coatings directly from a solution precursor in a single step using plasma spray technique. Nanostructured ZnO coatings were deposited from the solution precursor prepared using zinc acetate and water/isopropanol. An axial liquid atomizer was employed in a DC plasma spray torch to create fine droplets of precursor for faster thermal treatment in the plasma plume to form ZnO. Microstructures of coatings revealed ultrafine particulate agglomerates. X-ray diffraction confirmed polycrystalline nature and hexagonal Wurtzite crystal structure of the coatings. Transmission electron microscopy studies showed fine grains in the range of 10-40 nm. Observed optical transmittance (∼65-80%) and reflectivity (∼65-70%) in the visible spectrum, and electrical resistivity (48.5-50.1 mΩ cm) of ZnO coatings are attributed to ultrafine particulate morphology of the coatings.     

Tin sulfide thin films and Mo/p-SnS/n-CdS/ZnO heterojunctions for photovoltaic applications

Tin sulfide (SnS) is one of the most promising materials for photovoltaics. Here we report on the preparation as well as chemical, structural and physical characterization of the Mo/p-SnS/n-CdS/ZnO heterojunctions. The SnS thin films were grown by hot wall deposition method on the Mo-coated glass substrates at 270-350 °C. The crystal structure and elemental composition were examined by X-ray diffraction and Auger electron spectroscopy methods. The CdS buffer layers were deposited onto the SnS films by chemical bath deposition. The ZnO window layers were deposited by a two step radio frequency magnetron sputtering, resulting in a ZnO bilayer structure: the first layer consists of undoped i-ZnO and the second of Al-doped n-ZnO. The best junctions have an open circuit voltage of 132 mV, a short circuit current density of 3.6 mA/cm², a fill-factor of 0.29 and efficiency up to 0.5%.     

A Raman spectroscopic study of structural evolution of electrochemically deposited ZnO films with deposition time

Zinc oxide thin films were fabricated on ITO substrates by electrodeposition method. The electrolyte used was a 0.2 M zinc nitrate aqueous solution. The substrates were maintained at room temperature and the deposition performed for different times between 10 and 30 min. X-ray diffraction measurements indicated the formation of polycrystalline ZnO film with hexagonal wurtzite structure. The structure and crystallinity of the films was also confirmed by Raman spectroscopy. Further, the degree of disorder was estimated both from the phonon correlation length calculated from the Raman spectra using the spatial correlation model and from the intensity ratios of the phonons. The variation with deposition time followed the same trend as the crystallite sizes obtained from X-ray diffraction. X-ray photoelectron spectroscopy measurements indicated oxygen deficiency in the films. A combination of annealing and optimum deposition time improves the quality of the electrodeposited ZnO films.     

Structural and optical properties of ZnO films grown on silicon and their applications in MOS devices in conjunction with ZrO<Subscript>2</Subscript> as a gate dielectric

Photoluminescence (PL) properties of undoped ZnO thin films grown by rf magnetron sputtering on silicon substrates have been investigated. ZnO/Si substrates are characterized by Rutherford backscattering (RBS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). ZrO₂ thin films have been deposited on ZnO using microwave plasma enhanced chemical vapour deposition at a low temperature (150°C). Using metal insulator semiconductor (MIS) capacitor structures, the reliability and the leakage current characteristics of ZrO₂ films have been studied both at room and high temperatures. Schottky conduction mechanism is found to dominate the current conduction at a high temperature. Good electrical and reliability properties suggest the suitability of deposited ZrO₂ thin films as an alternative as gate dielectric on ZnO/n-Si heterostructure for future device applications.