ZnO Sol Research Articles

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 3d5/2 for ZnO–Ag shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between Ag and ZnO.

Reliability analysis of transparent conductive tracks embossed in ZnO and Al-ZnO sol–gel materials

In this paper, we present a low-cost rapid replication approach to fabricate ZnO and Al-doped ZnO Transparent Conductive Oxide electrode structures using both hard UV curable polyurethane acrylate and soft thermal curable polydimethylsiloxane moulds. The thin films of the ZnO and Al-ZnO sol–gel precursor solution prepared from zinc acetate monoethanolamine and isopropanol were cast into a polydimethylsiloxane or polyurethane acrylate mould containing the electrode design. For soft mould embossing, the sol–gel coated substrate and polydimethylsiloxane mould were dried under vacuum at 70 °C for 3h. While for hard mould embossing, the system was heated at 150 °C for 30 min with 100 N applying force and then demoulded at 80 °C. The formed electrode patterns can be further densified or annealed giving a stable film that retains the embossed shape. The difference of surface profile obtained by soft and hard moulding is detailed and the hard mould is shown to be more suitable for low aspect ratio conductors. And the reliability study on embossed ZnO and Al-ZnO conductive tracks prepared with hard moulds shows that the embossed structure still retains good quality.

Thin film chemical sensors based on p-CuO/ n-ZnO heterocontacts

Previous work on bulk ceramic heterocontacts ( n-ZnO/ p-CuO) has indicated significant sensitivity to the presence of specific adsorbed chemical species. Here, these results are extended to thin film heterostructures fabricated via chemical solution methods. It is expected that thin film sensor architectures will possess significant advantages over their bulk counterparts. In this study, the desired properties of porosity and crystallinity have been optimized with respect to pyrolysis temperature for each ZnO and CuO sol–gel process . The results of microscopy and X-ray diffraction (XRD) indicated that an optimal balance of these two properties is achieved at a pyrolysis temperature of 250 °C. The CuO films were seen to possess a level of porosity significantly higher than that seen in the ZnO films, making them an ideal candidate for the top layer in a planar thin film heterostructure. Results of current–voltage measurements conducted in 4000 ppm hydrogen have confirmed that the inherent porosity of the CuO films led to an enhanced sensor response in CuO on ZnO heterostructures. Lastly, the fabrication and structural characterization of a mixed solution type heterostructure has been detailed. Atomic force microscopy and XRD data indicated the presence of ZnO pillars dispersed among a matrix of CuO.

EFFECT OF SUBSTRATE TEMPERATURE ON THE MICROSTRUCTURE AND OPTICAL PROPERTIES OF ZnO NANOCRYSTALLINE THIN FILMS

In this work, ZnO nanocrystalline thin films were prepared by sol–gel dip-coating method on glass substrates and the effect of substrate temperature on the microstructure and optical properties of these films was investigated. The structural properties were analyzed by X-ray diffraction (XRD) and scanning probe microscope. The optical properties were studied by UV-visible spectrophotometer and fluorophotometer. The experimental results showed that if substrate temperature was relatively high, once the substrate was dipped into ZnO sol, some aggregated colloidal particles would be absorbed on it. After the ZnO gel film was annealed, the poor quality ZnO thin film was formed, which had a weak ultraviolet emission and a relatively strong defect-related visible emission.

Preparation of ZnO nanoparticles localized on SiC@SiO 2 nanocables by a physical templating method

Impregnation of interlaced SiC@SiO 2 nanocables (SiC NWs sheathed by SiO 2 coatings) into a ZnO sol at 0 °C yielded, after thermal treatment up to 600 °C under argon, SiC@SiO 2@ZnO nanostructures. These novel nanostructures consist in SiC@SiO 2 nanocables covered by numerous agglomerated ZnO nanoparticles. The latter are less than 5 nm in diameter. This result is to our knowledge the first example of a physical templating technique involving SiC-based nanowires. Moreover, we have obtained localized ZnO nanoparticles. This localization can be of interests for a further study of their physical properties. When a similar experiment was conducted with pure SiC nanowires, there was no interaction between the nanowires (NWs) and the solution, resulting in the formation of agglomerated ZnO NPs embedded into the 3D NWs network.

Patterned transparent zinc oxide films produced by sol–gel embossing

AbstractA low cost zinc oxide embossing technique is reported as a method of fabricating structures relevant to a variety of applications. A zinc based sol–gel material was prepared from zinc acetate [Zn(C2H3O2)2], monoethanolamine [H2NC2H4OH] and isopropanol. The sol–gel was cast into a polydimethylsiloxane (PDMS) mould a track design, placed in contact with the substrate and dried under vacuum at 70 °C for 3 hours. The formed track pattern was further densified to provide a stable conductor film that retained the embossed shape. An optimum Zn sol–gel content of 0.6 M was identified. The embossed films had a transparency of greater than 83% in the visible region. The optical bandgap energy was evaluated to be 3.306 eV. The influence of ZnO sol–gel film synthesis and embossing parameters on the microstructure, morphology and optical transparency of fabricated structures is described. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sol–gel process of ZnO and ZnAl2O4 coated aluminum borate whiskers

Zinc nitrate and citric acid were used to prepare ZnO sol. ZnO and ZnAl2O4 coated aluminum borate whiskers were separately prepared by a sol–gel process. The results show that ZnO forms when ZnO xerogel is calcined at 500 °C and it does not undergo any phase transformation in the range of 500 and 1000 °C during calcinations. In ZnO xerogel coated aluminum borate whiskers system, a large amount of heat, gas and pores are produced during the heating process. When ZnO xerogel coated aluminum borate whiskers are calcined at 500 °C, ZnO can be uniformly coated on the surface of the whikers and the coated whiskers can be easily dispersed in distilled water through an ultrasonic vibration apparatus. During the calcination of ZnO coated whiskers at 1000 °C, ZnO reacts with the whiskers and ZnAl2O4 forms on the surface of aluminum borate whiskers.

Sol–gel derived zinc oxide buffer layer for use in random laser media

In this study ZnO thin nanofilm has been prepared by dip coating method. A novel sol–gel system consisting of zinc acetate dihydrate, triethanolamine and ethanol has been employed for fabricating ZnO sols. Their different thin films have been prepared and annealed at different temperatures and characterized by photospectroscopy, scanning electron microscopy and AFM. Experimental results have shown that high quality nanostructured ZnO thin film can be obtained by control of the sol preparation method. It is clear from absorption spectra and AFM image that ZnO thin film with the best optical properties is formed from nanoparticles with spherical shape and high uniformity distributed nanoparticles.

Synthesis of alcoholic ZnO nanocolloids in the presence of piperidine organic base: Nucleation-growth evidence of Zn 5(OH) 8Ac 2⋅2H 2O fine particles and ZnO nanocrystals

Piperidine as a new free OH − organic base has been successfully used to prepare Zn 5(OH) 8(Ac) 2⋅2H 2O particles (named Zn-HDS) or concentrated alcoholic ZnO sols. Considering the applications of Zn-HDS and ZnO compounds, as well as interests of these synthesis mechanisms for fundamental chemistry, such investigations are of importance. This strategy not only allows preparing Zn-HDS compounds at room temperature but also brings evidence of some new nucleation-growth, and permits the preparation of well crystalline ZnO nanocrystals at low temperature (maximum 60 °C). It was possible to convincingly prove that the formation of Zn-HDS phase is concomitant to the ZnO nanocrystals formation and that Zn-HDS could be considered as an intermediate initiator of ZnO nanocrystals. A parallel approach was used for the fast screening of the synthesis progress.

Excimer laser processing of ZnO thin films prepared by the sol–gel process

ZnO thin films were prepared on soda-lime glass from a single spin-coating deposition of a sol–gel prepared with anhydrous zinc acetate [Zn(C 2H 3O 2) 2], monoethanolamine [H 2NC 2H 4OH] and isopropanol. The deposited films were dried at 50 and 300 °C. X-ray analysis showed that the films were amorphous. Laser annealing was performed using an excimer laser. The laser pulse repetition rate was 25 Hz with a pulse energy of 5.9 mJ, giving a fluence of 225 mJ cm −2 on the ZnO film. Typically, five laser pulses per unit area of the film were used. After laser processing, the hexagonal wurtzite phase of zinc oxide was observed from X-ray diffraction pattern analysis. The thin films had a transparency of greater than 70% in the visible region. The optical band-gap energy was 3.454 eV. Scanning electron microscopy and profilometry analysis highlighted the change in morphology that occurred as a result of laser processing. This comparative study shows that our sol–gel processing route differs significantly from ZnO sol–gel films prepared by conventional furnace annealing which requires temperatures above 450 °C for the formation of crystalline ZnO.

Controllable growth of ZnO nanoarrays in aqueous solution and their opticalproperties

ZnO sheet arrays were vertically aligned onto an aluminium flake after pyrolysis ofZn5(OH)8Cl2H2O sheets which were fabricated in aqueous zinc chloride andhexamethylenetetraamine solution. The ZnO sheets, with diameter of0.5–1 µm and thickness of 30–50 nm, incline to have satisfactory configuration of verticalalignment on the aluminium flake. Vertically aligned ZnO rod arrays withdiameters of 50 nm were successfully grown on a silicon wafer coated with ZnO sol(Sicoated) inthe same aqueous solution. Furthermore, from the photoluminescence (PL) and the energy dispersivex-ray (EDX) analysis, the dominant intrinsic defect of the ZnO sheet arrays was vacancies of zinc(VZn). As-synthesized ZnO nanostructures have potential applications in fabricatingnext-generation nanodevices.

Growth and optical properties of ZnO nanorods by introducing ZnO sols prior to hydrothermal process

ZnO nanorods of 25 nm with quite homogeneous size and shape have been fabricated by introducing ZnO sols as nucleation centers prior to the hydrothermal reaction. The samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, photoluminescence and resonant Raman spectra. After ZnO sols are introduced, the width of the resulting nanorods decreases above an order of magnitude and the aspect ratio increases 5 times. The increase of the intensity ratio of ultraviolet to visible emissions in room-temperature photoluminescence spectrum and the decrease of the Raman linewidths show the improvement in the quality of ZnO nanorods. Influences of the number of seed nuclei and the aging time of ZnO sols on the morphology of ZnO nanorods are discussed.

Luminescent polyvinylpyrrolidone/ZnO hybrid nanofibers membrane prepared by electrospinning

AbstractPolyvinylpyrrolidone (PVP)/ZnO composite nanofibers were successfully prepared by a facile method called electrospinning technique. The synthetic strategy involved two steps: (1) Preparation of ZnO sol in ethanol solution. PVP molecules then added into the above sol and achieved the appropriate rheology for electrospinning; (2) Electrospun the above solution to obtain fibers of PVP/ZnO composites. Scanning electron microscopic (SEM) analysis of the composite nanofibers revealed network structures like a spider’s web. Transmission electron microscopy (TEM) showed small nanoparticles of the ZnO component with an average particle size in the range of 3 - 4 nm and a good dispersion. X-Ray diffraction results showed that a pure wurtzite phase was obtained in PVP fibers. XPS spectra proved that the Zn and O elements existed in PVP/ZnO composite nanofibers. FTIR and UV-vis spectroscopy were used to characterize the structure of PVP/ZnO composite nanofibers. The photoluminescence properties of the PVP/ZnO composite nanofibers were also investigated.

Synthesis of nanocrystalline ZnO at low temperatures using inorganic sols as precursors

ZnO nanocrystals were synthesized as a case study of a novel, general method for the preparation of nanocrystalline oxides. ZnO sols were injected into a solution of diphenyl ether and dodecylamine heated at 160 °C, followed by heating for 1 h and further extraction and purification of the product. The key point in the preparation of the ZnO sol was the hindering of the condensation reactions, by complexing the Zn ions by acetylacetone before adding an ammonia solution. The ZnO grain size could be controlled by changing the amine concentration and the sol processing. Evidence is presented for a double role of dodecylamine, as an inorganic condensation catalyst and also as a growth regulator.

Fabrication of TiO 2 nanotube film by well-aligned ZnO nanorod array film and sol–gel process

High density TiO 2 nanotube film with hexagonal shape and narrow size distribution was fabricated by templating ZnO nanorod array film and sol–gel process. Well-aligned ZnO nanorod array films obtained by aqueous solution method were used as template to synthesize ZnO/TiO 2 core–shell structure through sol–gel process. Subsequently, TiO 2 nanotube array films survived by removing the ZnO nanorod cores using wet-chemical etching. Polycrystalline anatase TiO 2 nanotube films were ∼ 1.5 μm long and ∼ 100 nm in inter diameter with a wall thickness of ∼ 10 nm.

The selective detection of C 2H 5OH using SnO 2–ZnO thin film gas sensors prepared by combinatorial solution deposition

Sensing materials for selective detection of C 2H 5OH were designed using combinatorial solution deposition of SnO 2–ZnO thin films. The SnO 2–ZnO composite sensor prepared by alternate deposition of 10 droplets of SnO 2 and ZnO sols (S50Z50 sensor) showed a high response to 200 ppm C 2H 5OH (S(ethanol) = R a/ R g = 4.69, R a: resistance in air, R g: resistance in gas) at 300 °C, while the gas responses to 100 ppm C 3H 8, 100 ppm CO, 200 ppm H 2, and 5 ppm NO 2 ranged from 1.11 to 1.19. The S(ethanol) value of the S50Z50 sensor was twice that to 200 ppm CH 3COCH 3 (S(acetone)). In contrast, the S(ethanol) and S(acetone) of pure SnO 2 and ZnO thin films were similar to each other. The heterostructure between SnO 2 and ZnO was suggested as one of the probable reasons for the successful discrimination between C 2H 5OH and CH 3COCH 3.

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.

Blue-emitting ZnO sol and film obtained by sol-gel process

In this paper, bright blue-emitting ZnO sol and film were prepared by sol-gel process and the luminescent properties were investigated. The absorption spectrum of the sol consists of a wide band with two steps in the long wavelength region. The sol and film show a single wide blue-emission band under excitation of UV light, while the excitation spectra are composed by multiple bands. The quantum yield of the ZnO sol is 0.52 when the excitation wavelength is 348 nm. The particle size of the film is smaller than 10 nm, which results in the fine structure of the absorption and excitation spectra.

Luminescent properties of ZnO sol and film doped with Tb 3+ ion

In this paper, ZnO sol and nanosized film were prepared at low temperature, and effect of Tb 3+ doping on the luminescent properties was investigated. ZnO sol and film show yellow emission with peak at about 533 nm under excitation of UV light. If Tb 3+ is doped in ZnO sol and film, energy transfer from ZnO to Tb 3+ ion takes place, and the emission of Tb 3+ can be obviously detected. Energy diagram was schematically drawn to illustrate the luminescent mechanism of ZnO:Tb.

Luminescence of nanosized ZnO/polyaniline films prepared by self-assembly

ZnO sol was prepared and ZnO monolayer film and nanosized ZnO/polyaniline (PAN) multylayer films were coated on polished Al foil using the layer-by-layer self-assembly method. UV–vis absorbance, reflection and photoluminescence spectroscopy were obtained to investigate the luminescent properties of the samples. The ZnO sol has a single excitation peak in the UV (ultraviolet) region and a single emission peak in the green region. The excitation spectra of ZnO monolayer film and ZnO/PAN multylayer films show a continuous wide band without evident peak, and the emission spectra consist of three parts with peaks in UV, blue and green region, respectively.