Preparation and characterization of nanocomposite ZnO–Ag thin film containing nano-sized Ag particles: influence of preheating,annealing temperature and silver content on characteristics

Nanocomposite ZnO–Ag thin film containing nano-sized Ag particles have been grown on glass substrate by spin-coating technique using zinc acetate dihydrate as starting precursor in 2-propanol as solvent and monoethanolamine as stabilizer. Silver nanoparticles were added in the ZnO sol using silver nitrate dissolved in ethanol-acetonitrile. Their structural, electrical, crystalline size and optical properties were investigated as a function of preheating, annealing temperature and silver content. The results indicated that the crystalline phase was increased with increase of annealing temperature up to 550 °C at optimum preheating temperature of 275 °C. Thermal gravimetric differential thermal analysis results indicated that the decomposition of pure ZnO and nanocomposite ZnO–Ag precursors occurred at 225 and 234 °C, respectively with formation of ZnO wurtzite crystals. The scanning electron microscopy and atomic force microscopy revealed that the surface structure (the porosity and grain size) of the ZnO–Ag thin film (the film thickness is about 379 nm) was changed compared to pure ZnO thin film. The result of transmission electron microscopy showed that Ag particles were about 5 nm and ZnO particles 58 nm with uniform silver nanoclusters. Optical absorption results indicated that optical absorption of ZnO–Ag thin films decreased with increase of annealing temperature. Nanocomposite ZnO–Ag thin films with [Ag] = 0.068 M and [Ag] = 0.110 M showed an intense absorption band, whose maximum signals appear at 430 nm which is not present in pure ZnO thin films. The result of X-ray photoelectron spectroscopy revealed that the binding energy of Ag 3d_5/2 for ZnO–Ag shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between Ag and ZnO.     

The effects of oxygen concentration on ultraviolet luminescence of ZnO films by sol–gel technology and annealing

ZnO thin films were successfully deposited on SiO₂/Si substrate using the sol–gel technique and annealed in various annealing atmospheres at 900 °C by rapid thermal annealing (RTA). X-ray diffraction revealed the (002) texture of ZnO thin films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the grains of the ZnO thin film were enlarged and its surface was smoothed upon annealing in oxygen. PL measurement revealed two ultraviolet (UV) luminescence bands at 375 and 380 nm. The intensity of the emission peak at 380 nm became stronger as the concentration of oxygen in the annealing atmosphere increased. The X-ray photoelectron spectrum (XPS) demonstrated that a more stoichiometric ZnO thin film was obtained upon annealing in oxygen and more excitons were generated from the radiative recombination carriers consistently. Additionally, the UV intensity increased with the thickness of ZnO thin film.     

Preparation of nitrogen doped zinc oxide nanoparticles and thin films by colloidal route and low temperature nitridation process

Nitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO₂ substrate from a ZnO colloidal solution. Zinc peroxide (ZnO₂) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H₂O₂ solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250 °C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV–Visible transmittance spectroscopy.     

Various shaped-ZnO nanocrystals via low temperature synthetic methods: Surfactant and pH dependence

ZnO nanocrystals, rod-, carnation-, and flower-like structures, have been synthesized in a high yield through low-temperature synthetic methods. Well-aligned ZnO nanorods having hexagonal wurtzite structure were grown on the ZnO thin films assembled by a spin-coating method. The morphologies of ZnO seed films are affected by pHs of sol–gel solutions, resulting smaller sizes and homogeneous roughness at higher pHs and higher number of spin-coating times. The carnation-like structures, average size of about 2–3 μm, were assembled by tens of uniform ZnO nanosheet petals of ∼50 nm in thickness when a different volume ratio of the precursory solution was used. ZnO nanocrystals on the facets of the compact ZnO nanorods have grown to linear nanorods having an average diameter of ∼500 nm and length of ∼2 μm. Furthermore, a noticeable difference in the growth of ZnO nanocrystals in the presence of various surfactants, polyvinylpyrrolidone, polyvinylsulphonic acid, and polyethyleneimine, has been observed and discussed.     

Structural and optical properties of ZnO thin films by the spin coating Sol-Gel method

ZnO thin films were deposited onto glass subsrates by a Sol-gel spin coating method. The structural and optical properties of ZnO thin films were investigated. The molar ratios of the zinc acetate dihydrate to Monoethanolamine were maintained 1:1. The as-grown film was sintered 250 °C for 10 min, then annealed in air at 500 °C for 30 min. The XRD results indicate that ZnO films were strongly oriented to the c-axis of the hexagonal nature. Absorption measurements were carried out as a function of temperature with 10 K steps in the range 10–320 K. The band gap energy was measured 3.275 and 3.267 eV for 0.5 and 1.0 molarity (M) ZnO thin films at 300 K. The steepness parameters were observed between 10 and 320 K and their extrapolations converged at (E₀, α₀) = 3.65 eV, 172,819 cm⁻¹ and 3.70 eV, 653,436 cm⁻¹ for 0.5 and 1.0 M ZnO thin films, respectively.     

White light emission from nano-fibrous ZnO thin films/porous silicon nanocomposite

Nanocomposites composed of nano-fibrous ZnO thin films and porous silicon (PS) were prepared and examined by atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) to investigate their structural and optical properties. PS, consisting of irregular and random nanosized-pores, was prepared by electrochemical anodization. The nano-fibrous ZnO thin films were grown on PS by the sol-gel spin-coating method. The texture coefficient (TC _(hkl)) of the nano-fibrous ZnO thin films was calculated to determine the preferred orientation. The nano-fibrous ZnO thin films were grown with a c-axis preferred orientation. The residual stress in the films was reduced in the case of PS. The observed broad PL emission peak from 460 to 598 nm was attributed to coupled emission from ZnO to PS. The results show that white light luminescence with blue, green, and red emission peaks having highly uniform intensities can be obtained from the nanocomposite via a relatively simple and low-cost sol-gel spin-coating method.     

Effect of electron radiation on electrical parameters of Zn/n-Si/Au–Sb and Zn/ZnO/n-Si/Au–Sb diodes

In this study, RF-magnetron sputtered ZnO thin film as an interlayer was used to improve radiation tolerance of the Schottky diodes. The structural and optical measurements showed that the ZnO thin films have hexagonal crystal structure with preferential c-axis orientation, 20.39 nm grain sizes and 3.15 eV bandgap. The electrical parameters such as ideality factor, barrier height and series resistance of Zn/n-Si/Au–Sb and Zn/ZnO/n-Si/Au–Sb diodes were calculated before and after electron radiation at 25, 50 and 75 gray doses. Deviation values of the parameters showed that the ZnO as an interlayer caused to improved radiation tolerance of the diodes.

     

Luminescence properties of Cu‐ion‐implanted and annealed ZnO thin films deposited by chemical vapor deposition and pulsed laser deposition

Ion implantation techniques were used to study the effect of an MgO additive on the luminescence properties induced by Cu in ZnO thin films. Cu ions (accelerating voltage of 75 keV, dose of 4.5 × 10¹⁴ ions/cm²) were implanted at room temperature in nondoped and Mg‐doped ZnO thin films. After annealing, emissions in the visible region originating from Cu phosphor were observed at 510 nm in CVD‐ZnO and at 450 nm in Mg‐doped ZnO (MZO) thin films. The Cu depth profile shows distortion in the low‐concentration region of CVD‐ZnO. After the annealing, the Cu implant was homogenized in thin films, and then the Cu concentration was determined to be 1.5 × 10¹⁹ ions/cm³ in CVD‐ZnO and 5.6 × 10¹⁸ ions/cm³ in MZO thin films. Copyright © 2005 John Wiley & Sons, Ltd.     

Indium and aluminium-doped ZnO thin films deposited onto FTO substrates: nanostructure,optical, photoluminescence and electrical properties

The microstructure, optical, photoluminescence and electrical properties of ZnO based films deposited onto FTO glass substrates by ultrasonic spray pyrolysis have been investigated. For comparison and a better understanding of physical properties of indium- and aluminum-doped ZnO and undoped ZnO thin films, X-ray diffraction analysis, photoluminescence spectra, optical, SEM texture and electrical conductivity analyses were performed. The AZO and IZO films exhibit the nanofiber structure with diameters 260 and 400 nm. X-ray diffraction showed all samples to be polycrystalline with hexagonal ZnO. The optical band gaps of the films were varied by Al and In dopants. The photoluminescence spectra of the films show a weak broad in the visible range and shifted to green emission for indium doping and to the green blue emission for aluminum as dopant. The width of the PL spectra for aluminum-doped films is too large compared to those of the indium-doped ones. The electrical conductivity of the ZnO film changes with Al and In dopants. The position of donor levels changes with In and Al dopants and approaches the conduction band level with the metal dopants. The obtained results suggest that the metal doping has a clear effect upon the growth, optical, photoluminescence and electrical conductivity properties of the ZnO films.     

旋涂水溶液前驱体制备氧化锌薄膜及其性质

通过旋涂法, 采用Zn(OAc)2·2H2O和聚环氧乙烷(PEO)的水溶液为前驱体在不同的热处理温度下制备了ZnO薄膜. PEO的加入增加了溶液的成膜性, 其较低的热分解温度有利于制得纯净的ZnO薄膜. 文中考察了在不同热处理温度下制备的ZnO薄膜的形貌、结晶性、带隙(Eg)以及电导性. 原子力显微镜(AFM)测试表明在热处理温度为400、450和500 ℃制备的ZnO薄膜的粗糙度均方根值分别为3.3、2.7和3.6 nm. 采用透射电子显微镜(TEM)测试发现ZnO薄膜中含有大量纳晶粒子. 通过测试ZnO薄膜的UV-Vis吸收光谱, 根据薄膜位于373 nm处的吸收带边计算得到ZnO的带隙为3.3 eV. 通过对薄膜的电流-电压(I-V)曲线的测试计算得到在热处理温度为400、450和500 ℃制备的ZnO薄膜的电阻率分别为3.3×109、2.7×109和6.6×109 Ω·cm. 450 ℃时制备的ZnO薄膜的电阻率最小, 主要是由于较高的热处理温度有利于提高薄膜的纯度、密度和吸附氧. 而纯度较高、密度较大的薄膜电阻率比较小; 吸附氧含量增加, 晶界势垒增大, 电阻率增大. 因此在纯度和吸附氧的双重作用下450 ℃时制备的ZnO薄膜的电阻率最小, 而500 ℃时制备的ZnO薄膜的电阻率最大.     

Correlation between structural and optical properties of TiO<Subscript>2</Subscript>:ZnO thin films prepared by sol–gel method

We have studied structural and optical properties of thin films of TiO₂, doped with 5% ZnO and deposited on glass substrate (by the sol–gel method). Dip-coated thin films have been examined at different annealing temperatures (350–450 °C) and for various layer thicknesses (89–289 nm). Refractive index, porosity and energy band gap were calculated from the measured transmittance spectrum. The values of the index of refraction are in the range of 1.97–2.44, the porosity is in the range of 0.07–0.46 and the energy band gap is in the range of 3.32–3.43. The coefficient of transmission varies from 50 to 90%. In the case of the powder of TiO₂, doped with 5% ZnO, and aged for 3 months in ambient temperature, we have noticed the formation of the anatase phase (tetragonal structure with 20.23 nm grains). However, the undoped TiO₂ exhibits an amorphous phase. After heat treatments of thin films, titanium oxide starts to crystallize at the annealing temperature 350 °C. The obtained structures are anatase and brookite. The calculated grain size, depending on the annealing temperature and the layer thickness, is in the range of 8.61–29.48 nm.     

Ordered porous ZnO thin films formed by dip-coating method using PS templates

Monolayer polystyrene spheres (∼400 nm) array templates were assembled orderly on clean glass substrates by dip-coating method from emulsion of polystyrene (PS). Porous ZnO thin films were also prepared by dip-coating method to fill the interstices among the close-packed PS templates with ZnO and annealing to remove the PS templates. Results showed that ZnO sol concentration and dipping time of PS templates in sol had great influences on the morphology of ordered porous ZnO thin films. There was a shrinkage ratio of about 30% from pore to PS. SEM observation showed that the PS array templates had face-centered cubic close-packing. X-ray diffraction (XRD) spectra showed the porous ZnO thin film was wurtzite structure. The optical transmittance decreased with decreasing wavelength of lights, but was kept above 80% beyond the wavelength of 550 nm. Optical band-gap of the porous ZnO thin film annealed at 500°C was 3.22 eV.     

The effect of different gas atmospheres on the structure,morphology and photoluminescence properties of pulsed laser deposited Y3(Al,Ga)5O12:Ce3+ nano thin films

Luminescent properties of Y₃(Al,Ga)₅O₁₂:Ce³⁺ phosphor powder and thin films were obtained. The phosphor powder was used as target material for Pulsed Laser Deposition (PLD) of the thin films in the presence of different background gases. Excitation peaks for the powder were obtained at 439, 349, 225 and 189 nm and emission peaks at 512 and 565 nm. X-ray diffraction indicated that better crystallization took place for films deposited in a 20 mTorr O₂ atmosphere. Atomic force microscope revealed an RMS value of 0.7 nm, 2.5 nm and 4.8 nm for the films deposited in vacuum, O₂ and Ar atmospheres, respectively. The highest PL intensity was observed for films deposited in the O₂ atmosphere. A slight shift in the wavelength of the PL spectra was obtained for the thin films due to a change in the crystal field. The thickness of the films varied from 120 nm to 270 nm with films deposited in vacuum having the thin layer and those in Ar having the thick layer. The stoichiometry of the powder was maintained in the film during the deposition as confirmed by Rutherford backscattering spectroscopy.     

Physical properties of suspension ZnO nanoparticles prepared by wet chemical method: Comparison study

In this work a suspension of Nano-crystalline of ZnO particle is prepared by wet chemical at different temperature and concentration. From FTIR spectral exhibit present of Zn–O bond which indicate to formation ZnO particles. While all suspension and nano films exhibit a high transmittance in visible region about 90% which falls sharply in the UV region. The particle size is measured by using effective mass approximation (EMA), which was approximation (1.7–1.96 nm), and the band gap changes from 3.95 to 4.52eV for nanoparticles in suspension, and change from 3.76 to 3.94 eV for nanoparticles in ZnO film, which is change as function of concentration, temperature and aging time. Hall Effect measurements for ZnO films exhibit n-type conductivity for films deposited with activation energy 0.742eV at high temperature and 0.178eV at low temperature which is different as prepared sample conditions. Also the nanoparticle suspension and nanoparticle film could be implemented as a filter with variable cut off (8.9 × 10¹⁴–1.28 × 10¹⁵) H_Z.     

Synthesis and suspension rheology of titania nanoparticles grafted with zwitterionic polymer brushes

Thin films of polydimethylsiloxane (PDMS) and ZnO quantum dots (QDs) were built up as multilayers by spin-coating. The films are characterized by a UV-blocking ability that increases with increasing number of bilayers. Photoluminescence (PL) emission spectra of the thin films occur at 522 nm, which is the PL wavelength of the ZnO QDs dispersion, but with a lower intensity and a quantum yield (QY) less than 1% that of the dispersion. Cross-linking has introduced new features to the absorption spectra in that the absorption peak was absent. These changes were attributed to the morphological and structural changes revealed by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR), respectively. TEM showed that the ZnO particle size in the film increased from 7 (±2.7) nm to 16 (±7.8) upon cross-linking. The FTIR spectra suggest that ZnO QDs are involved in the cross-linking of PDMS and that the surface of the ZnO QDs has been chemically modified.     

Room temperature ferromagnetism in sol–gel deposited un-doped ZnO films

Dilute magnetic semiconductors are fast emerging spintronic materials where advantage of magnetic properties of semiconductor materials (usually doped with small quantities of magnetic ions) is being explored. Sol–gel technique, being low-cost simple and application oriented method, has been used in the present case. ZnO films of <150 nm thickness have been deposited by spin coating onto single crystal p-type Si substrates. The optimized sol is of paramagnetic nature, whereas, mixed para- dia-magnetic phase is observed for the as-prepared films. A complete ferromagnetic phase transition has been observed after heating the films in vacuum at a temperature of 300 °C. These sol–gel prepared films exhibit hexagonal wurtzite structure as observed by X-ray diffraction. After the magnetic field annealing in vacuum the films showed strengthened magnetic as well as structural properties. This work presents a clear evidence of ferromagnetic behavior of the un-doped ZnO films deposited by sol–gel at room temperature. It is also pointed out that Zn vacancies rather than oxygen deficiency are responsible for ferromagnetism in these sol–gel deposited ZnO thin films, whereas, the experimental evidence has been substantiated with the theoretical calculations using density functional theory.     

Structure and morphology of nanostructured zinc oxide thin films Prepared by dip-vs. spin-coating methods

In this study, we use dipping and spinning methods to coat glass slides with sol-gel ZnO thin films, composed of zinc acetate dihydrate, monoethanolamine (MEA), de-ionized water and isopropanol. The effect of the annealing temperature on the structural morphology and optical properties of these films is investigated. These ZnO films were preheated at 275 °C for 10 min and annealed either at 350, 450 or 550 °C for 60 min. As-deposited films, formed by amorphous zinc oxide-acetate submicron particles, are transformed into a highly-oriented ZnO after thermal treatment. The surface morphology, phase structure and optical properties of the thin films were investigated by scanning electron microscopy, X-ray diffraction (XRD) and optical transmittance. Both techniques produced nanostructured ZnO thin films with well-defined orientation. The annealed films were transparent in the visible range with an absorption edge at about 375 nm and a transmittance of ca 85–90% with an average diameter of 40 nm. XRD results show the film was composed of polycrystalline wurtzite, with a preferential c-axis orientation of (002) and a single sharp XRD peak at 34.40, corresponding to the hexagonal ZnO. The grain size is increased by the annealing temperature. Both coating techniques create sol-gel ZnO films with the potential for application as transparent electrodes in optic and electronic devices.     

Preparation and photoelectric properties of mesoporous ZnO films

Mesoporous ZnO films doped with Ti⁴⁺ (M-ZnO) have been prepared by doping process and sol–gel method. The films have mesoporous structures and consist of nano-crystalline phase, as evidenced from small angle X-ray diffraction and high resolution transmission electron microscopy. The wide angle X-ray diffraction of M-ZnO films confirms that M-ZnO has hexagonal wurtzite structure and ternary ZnTiO₃ phases. Ultraviolet–visible transmittance spectra, absorbance spectra and energy gaps of the films were measured. The Eg of M-ZnO is 3.25 eV. Photoluminescence intensity of M-ZnO centered at 380 nm increases obviously with the excitation power, which is due to the doping process and enhanced emission efficiency. M-ZnO thin films display a positive photovoltaic effect compared to mesoporous TiO₂ (M-TiO₂) films.     

Zein films with ZnO and ZnO:Mg quantum dots as functional nanofillers: New nanocomposites for food package with UV-blocker and antimicrobial properties

The preparation of a new nanocomposite by combining zein and quantum dots (QDs) was the main interest of the present work. By the sol-gel method, colloidal ethanolic dispersions of zinc oxide (ZnO) particles and ZnO particles doped with magnesium (II) (ZnO:Mg) were obtained, sized 4.26 and 3.65 nm, respectively, as determined by UV–Vis spectroscopy. The prepared QDs were used as nanofillers in order to obtain zein-based nanocomposite films, which displayed good visual appearance, homogeneity, and transparency. The presence of QDs increased the hydrophobicity and reduced, up to three times, the amount of water uptake of the composite films when compared to pure zein. Those effects were more pronounced for ZnO:Mg QDs. TEM, FTIR, and fluorescence microscopy analysis indicated that zein interacts more effectively with ZnO:Mg than with ZnO. In addition, and most importantly, the presence of QDs in the films showed an important advantage when compared to those of pure zein: the extended UV-blocking in the absorbance spectra. The antimicrobial assays demonstrated that the ZnO NPs, loaded into zein films, are promising antibacterial materials since the inhibition of growth of S. aureus reached (96.5 ± 4.9)% at 44.8 wt% of ZnO NPs. Therefore, the nanocomposites show promising features for the development of food packaging, UV protective films, and for the development of new and sustainable materials.     

Synthesis of ZnO nanobundles via Sol–Gel route and application to glucose biosensor

ZnO nanobundles were fabricated by Sol–Gel route. The as-prepared ZnO nanobundles were characterized by XRD, FE-SEM, TEM and PL. ZnO nanobundles structure are composed of many nanorods of about 80 nm in diameter and 0.6 μm in length. It showed weaker UV emission and stronger green emission. A glucose biosensor was constructed using these ZnO nanobundles as supporting materials for glucose oxidase (GO_X) loading by chitosan-assisted cross-linking technique. The biosensor exhibits a high affinity, high sensitivity, and fast response for glucose detection. These results demonstrate that zinc oxide nanostructures have potential applications in biosensors.