ZnO Composite Films Research Articles

Polyoctanediol citrate–ZnO composite films: Preparation, characterization and release kinetics of nanoparticles from polymer matrix

In this paper we describe a novel composite material consistent of citric acid-based polyester elastomer and zinc oxide nanoparticles (ZnO NPs). Produced material was characterised by field emission electron microscopy, Fourier-transform infra-red spectroscopy and mechanical tests. Release kinetics of NPs from the polymer matrix and anti-bacterial properties of the composite are also reported. We demonstrate that the composite morphology, mechanical integrity and the relative amount of NPs released under physiological conditions are strongly affected by variation of the initial concentration of NPs in the composite mixture during the fabrication process.

Temperature and concentration dependences of the photoluminescence of MEH-PPV polymer composite films with ZnO nanoparticles

The absorption and photoluminescence (PL) spectra of MEH-PPV: ZnO composite films have been investigated at different concentrations of ZnO nanoparticles and at different temperatures (in the case of PL). It has been shown that, at 297 K, with increasing concentration of ZnO nanoparticles in the composite, the intensity of the PL lines of MEH-PPV decreases, whereas the intensity of the PL lines of ZnO increases. At a relatively low concentration of ZnO nanoparticles, a decrease in the temperature leads to an increase in the intensity of PL lines associated with MEH-PPV and ZnO, whereas at higher concentrations of ZnO nanoparticles, the intensity of these lines decreases. This is accompanied by a slight shift in the maximum of the PL toward the infrared (IR) region and a narrowing of the PL line of MEH-PPV with a decrease in the temperature and with an increase in the ZnO concentration. The mechanism of energy transfer in composite systems consisting of a polymer and inorganic nanoparticles that can be responsible for the observed effects has been discussed.

Synthesis of ZnO nanorod–nanosheet composite via facile hydrothermal method and their photocatalytic activities under visible-light irradiation

ZnO composite films consisting of ZnO nanorods and nanosheets were prepared by low-temperature hydrothermal processing at 80°C on seeded glass substrates. The seed layer was coated on glass substrates by sol–gel dip-coating and pre-heated at 300°C for 10min prior to hydrothermal growth. The size of the grain formed after pre-heat treatment was ~40nm. A preferred orientation seed layer at the c-axis was obtained, which promoted vertical growth of the ZnO nanorod arrays and formation of the ZnO nanosheets. X-ray diffraction patterns and high-resolution transmission electron microscope (HR-TEM) images confirmed that the ZnO nanorods and nanosheets consist of single crystalline and polycrystalline structures, respectively. Room temperature photoluminescence spectra of the ZnO nanorod–nanosheet composite films exhibited band-edge ultraviolet (UV) and visible emission (blue and green) indicating the formation of ZnO crystals with good crystallinity and are supported by Raman scattering results. The formation of one-dimensional (1D) ZnO nanorod arrays and two-dimensional (2D) ZnO nanosheet films using seeded substrates in a single low-temperature hydrothermal step would be beneficial for realization of device applications that utilize substrates with limited temperature stability. The ZnO nanorods and nanosheets composite structure demonstrated higher photocatalytic activity during degradation of aqueous methylene blue under visible-light irradiation.

The effects of Ta2O5–ZnO films as cathodic buffer layers in inverted polymer solar cells

Ta2O5–ZnO composite films with varied composition were fabricated by sol–gel processing and applied as cathodic buffer layers (CBLs) for inverted polymer solar cells, and demonstrated enhanced power conversion efficiency with excellent stability.

Titanium dioxide composite films for enhanced photocatalytic activity

In order to extend light response of TiO2 into the visible region and enhance its photocatalytic activity, W and S codoped TiO2–SiO2–ZnO composite film was successfully prepared. The Brunauer–Emmett–Teller (BET) results showed that the surface area of the modified TiO2 was 424.5m2g−1, while that of the pure TiO2 was 103.4m2g−1. The high-resolution field emission scanning electron microscopy (FE-SEM) results revealed that the surface of the modified TiO2 film was more uniform and smooth with smaller particles compared to pure TiO2 film. The diffuse reflectance measurements exhibited that the modified TiO2 film had obvious red-shift. The photoluminescence (PL) analysis indicated that the electron–hole recombination rate was effectively inhibited in the modified TiO2 systems. The photocatalytic activities of the TiO2 films were evaluated by the photocatalytic decomposition of organic dyes in aqueous solution. Compared with pure TiO2 film, the modified TiO2 film exhibited excellent photocatalytic activity.

Effect of Zn and Ti mole ratio on microstructure and photocatalytic properties of magnetron sputtered TiO2–ZnO heterogeneous composite film

Series of TiO2–ZnO heterojunction composite films with different n(Zn)/n(Ti) ratios were prepared by UDP450 magnetron sputter ion plating equipment, and the mole ratio of Zn to Ti was controlled by adjusting the current values of sputtering target. The effects of n(Zn)/n(Ti) on the microstructures of TiO2–ZnO films were investigated by SEM, AFM, Raman and XPS, and their photocatalytic decomposition of methyl orange solutions was evaluated. The results show that an increase in n(Zn)/n(Ti) typically results in a decrease in the grain size of composite films firstly and then an increase of grain size, while an increase in n(Zn)/n(Ti) leads to an increase in film roughness firstly and then a decrease in film roughness. Both grain size and roughness of TiO2–ZnO films reach the maximum and minimum at n(Zn)/n(Ti) of 1/9.3, respectively. The n(Zn)/n(Ti) shows little effect on the valences of Zn and Ti elements, which mainly exist in the form of TiO2 and ZnO phases. The n(Zn)/n(Ti) has influence on the amount of anatase/rutile TiO2 heterojunction in the film. With increase of the n(Zn)/n(Ti), the absorption intensity of the composite film increases and the absorption region extends to 450 nm, which is redshifted as much as 150 nm in comparison with the pure TiO2 films. However, the photocatalytic abilities of heterogeneous composite films do not depend on the n(Zn)/n(Ti) but rather on the microstructures of the TiO2–ZnO composite films. Degradation rate of the film reaches the maximum and the photocatalytic decomposition of pollutants works best when n(Zn)/n(Ti)=1:9.3.

Field Electron Emission from Carbon Nanotube/ZnO Composite Films Prepared by Electrodeposition

Multi-walled carbon nanotube (MWNT)/ZnO composite films were fabricated by electrodeposition using water-soluble MWNTs prepared by a high-speed vibration milling (HSVM) technique. Raman scattering spectroscopy and scanning electron microscopy revealed that the MWNTs were incorporated into the ZnO films in different manners depending on the deposition temperature. Field emission (FE) of electrons from the MWNT/ZnO films was investigated with a conventional FE device and a side-electron emission device (SEED). The MWNTs embedded horizontally in the ZnO films exhibited superior FE characteristics with luminance beyond 4000 cd/m2 for the SEED.

The fabrication and optimization of OTFT formaldehyde sensors based on Poly(3-hexythiophene)/ZnO composite films

Formaldehyde (HCHO), a colorless and pungent-smelling gas, is confirmed be a huge threat to human health. The detection of formaldehyde is necessary and important. The Poly(3-hexythiophene) (P3HT)/ZnO organic-inorganic composite thin film was fabricated and used as the sensitive layer of organic thin film transistors (OTFT) by spray-deposited method to detect HCHO at room temperature. The process parameters such as P3HT/ZnO weight ratios and airbrushed masses were optimized. The results showed that P3HT/ZnO OTFT exhibited good sensing response to HCHO. Airbrushed mass of 1ml was the optimal mass, and the 1:1 and 1:5 weight ratios of P3HT/ZnO exhibited better sensing properties compared with others. OTFT gas sensors based on P3HT/ZnO composite film provides a novel promising approach to the detection of HCHO.

Wear resistant electrically conductive Au–ZnO nanocomposite coatings synthesized by e-beam evaporation

The tribological and electrical behavior of e-beam codeposited Au–ZnO nanocomposite films were investigated for compositions in the range 0.1–28.0vol% of ZnO. A 2.0vol% ZnO film did not exhibit measurable wear sliding against a commercial gold alloy rider. Electron backscatter diffraction (EBSD) analysis on film surfaces of varying composition revealed a significant reduction in grain size for a 0.1vol% ZnO film contrasting with a pure Au film. Electrical resistivity measurements of films in the range 0.0–28.0vol% ZnO exhibited a linear increase in resistivity from 2.73μΩcm to 39.88μΩcm. The friction, wear, and electrical contact resistance of 2.0 and 28.0vol% ZnO films sliding against commercially available hardened Au riders (72Au–14Cu–8Pt–5Ag by weight) were investigated. Friction coefficient and electrical contact resistance data were in the range μ=0.3–0.5 and ECR=40mΩ and 500–2000mΩ, respectively, for 2μm thick films deposited on conductive substrates in unidirectional sliding at 1mm/s under a 185MPa maximum Hertzian contact pressure (100mN contact force). The presence of ZnO transfer to the rider was observed via energy-dispersive X-ray spectroscopy (EDS). Significant improvements in wear resistance and friction behavior were observed for Au–ZnO composite films with volume fractions of ZnO commensurate with the metal species codeposited in traditional hardened gold coatings.

Producing CuO and ZnO composite thin films using the spin coating method on microscope glasses

In this work, we have presented a new route to produce pure ZnO and composite ZnO-CuO thin films. In the process we have started with pure ZnO thin films and ended up with CuO by doping Cu in various percentages, ranging from 0% to 100%. We have managed to attain crystal phases in all doping concentrations. All the produced thin films have been crystallized at the annealing temperatures of 600 and 700 °C for 6 h. The X-ray diffraction (XRD) spectra have been performed to see the formation of crystal phases of all pure ZnO and composite ZnO-CuO thin films. These give insight that the two crystal phases related to ZnO and CuO stayed together within the thin film matrices, which were produced in different doping concentrations, i.e. nZnO + mCuO (0 ≤ n, m ≤ 100%). The scanning electron microscopy (SEM) micrographs and UV–vis absorption spectra have also been taken to elucidate the structure and composition of the all films.

Spectral response of nanocrystalline ZnO films embedded with Au nanoparticles

The optical response of a two-phase composite consisting of Au nanoparticles (AuNPs) in a nanocrystalline ZnO thin film matrix has been systematically studied and analyzed by the Bergman–Milton spectral density formalism. The real and imaginary parts of the effective dielectric function exhibited anomalous dispersion and absorption, respectively, at the characteristic localized surface plasmon resonance (LSPR) wavelength. A multilayer structure consisting of two AuNP–ZnO composite films separated by a thin ZnO film displayed a twofold increase in the absorption at LSPR (with negligible change in FWHM), which is attributed to the increase in the number density of the AuNPs resulting from the nanocrystalline nature of the ZnO film. The results have been used to correlate the spectral density function to the morphology of AuNPs in a ZnO matrix.

Flexible dye-sensitized solar cells with one-dimensional ZnO nanorods as electron collection centers in photoanodes

A ZnO composite film with an electron-collection center of ZnO nanorods (ZnNRs) embedded in a ZnO nanoparticle (ZnNP) film was fabricated on flexible photoanodes of back-illuminated dye-sensitized solar cells (DSSCs). Different lengths of the ZnNRs in ZnNP films were compared by considering their electron-collection and -scattering abilities. The morphologies and structures of the ZnO films were observed by examining their X-ray diffraction (XRD) patterns and scanning electron micrographs. The highest light-to-electricity conversion efficiency (η) of 2.17% was obtained for DSSCs, the ZnO composite film of which had about the same thickness of ZnNPs as the length of ZnNRs on its photoanode. At a thickness of only 7μm of ZnNPs, the highest η was achieved with the composite film, leading to a 66.9% enhancement in efficiency compared to that obtained with only ZnNPs (1.30%). When the ZnNR length was shorter than the thickness of the ZnNP film, electrons in the ZnNPs film were not effectively transferred. On the other hand, if the ZnNRs were too long and stuck out of the ZnNP film, the incident light was scattered, resulting in less light utilization. These explanations were substantiated by electrochemical impedance spectra, laser-induced photo-voltage transients, and incident photon-to-electron conversion efficiency curves.

Crack free and spherical shape copper–zinc composite oxide thin films fabrications by AACVD

Crack free, mesoporous and crystalline 3CuO–ZnO composite oxide thin films have been prepared by aerosol assisted chemical vapor deposition (AACVD) using the tetranuclear heterobimetallic complex [Zn(TFA)3(μ-O)Cu3(dmap)3Cl]·THF (1) (where dmap=N,N-dimethylamino-1-propanolato, TFA=trifluoroacetate and THF=tetrahydrofuran). The designed precursor 1 has been synthesized by a simple chemical reaction in high yield and characterized by its melting point, elemental analysis, FT-IR, mass spectrometry, single crystal X-ray analysis and thermal analysis (TGA/DTA). The single crystal X-ray analysis of complex 1 shows that it crystallizes in the triclinic space group P1¯ with cell dimensions a=10.617, b=10.952, c=18.713Ǻ. The TGA/DTA analysis proved that the thermal decomposition of precursor 1 at 723K gives the 3CuO–ZnO composite oxide residue. Crystalline thin films of 3CuO–ZnO composite have been fabricated by using AACVD on a glass substrate at 723K in a single step without pre or post annealing. The material properties of the deposited thin films have been characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and Rutherford back scattering (RBS) analysis, and the results proved that the deposited thin films are of the crystalline 3CuO–ZnO composite oxide, free from other impurities. Further exploration of the XRD data of the films proved the formation of the crystalline 3CuO–ZnO composite with an average crystallite size of 45nm, calculated from broadening by the Debye–Scherrer formula. Scanning electron microscopy (SEM) showed that the spherical-like particles have a diameter in the range of 0.2–0.5μm, sintered together to form a compact 3CuO–ZnO composite oxide thin film, and qualify the scotch tape test.

Characterization of ZnO–SnO 2 thin film composites prepared by pulsed laser deposition

Thin films of ZnO–SnO 2 composites have been deposited on Si(1 0 0) and glass substrates at 500 °C by pulsed laser ablation using different composite targets with ZnO amount varying between 1 and 50 wt%. The effect of increasing ZnO-content on electrical, optical and structural properties of the ZnO–SnO 2 films has been investigated. X-ray diffraction analysis indicates that the as-deposited ZnO–SnO 2 films can be both crystalline (for ZnO <1 wt%) and amorphous (for ZnO ≥ 10 wt%) in nature. Atomic force microscopy studies of the as-prepared composite films indicate that the surfaces are fairly smooth with rms roughness varying between 3.07 and 2.04 nm. The average optical transmittance of the as-deposited films in the visible range (400–800 nm), decreases from 90% to 72% for increasing ZnO concentration in the film. The band gap energy ( E g) seems to depend on the amount of ZnO addition, with the maximum obtained at 1 wt% ZnO. Assuming that the interband electron transition is direct, the optical band gap has been found to be in the range 3.24–3.69 eV for as-deposited composite films. The lowest electrical resistivity of 7.6 × 10 −3 Ω cm has been achieved with the 25 wt% ZnO composite film deposited at 500 °C. The photoluminescence spectrum of the composite films shows a decrease in PL intensity with increasing ZnO concentration.

Optoelectronic studies of sol–gel derived nanostructured CdO–ZnO composite films

Compositional dependence of the optoelectronic properties of sol–gel derived CdO–ZnO composite films with volume ratio of Cd:Zn ranging from 1:0 to 0:1 (with a step of 1/4) has been studied. After heat treatments in air the prepared thin films were investigated by studying their structural, morphological, d.c. electrical and optical properties. X-ray diffraction (XRD) results suggest that the samples are polycrystalline and the crystallinity of them increased with Cd ratio. The average grain size is in the range of 20–34 nm. As composition and structure changed due to the Cd volume ratio, the order of the carrier concentration was varied from 10 16 to 10 20 cm −3 with Cd ratio and the mobility increased from less than 2 to 45 cm 2 V −1 s −1. It was found that the transmittance and the band gap decreased as Cd ratio increased. The optical constants of the film were studied and the dispersion of the refractive index was discussed in terms of the Wemple–DiDomenico single oscillator model. The real and imaginary parts of the dielectric constant of the films were also determined. The volume energy loss (VELF) increases more than the surface energy loss (SELF) at their particular peaks. The third-order nonlinear polarizability parameter is higher for CdO–ZnO thin films with higher concentration of cadmium oxide.

Preparation and properties of poly(propylene carbonate) and nanosized ZnO composite films for packaging applications

AbstractA series of polypropylene carbonate (PPC)/ZnO nanocomposite films with different ZnO contents were prepared via a solution blending method. The morphological structures, thermal properties, oxygen permeability, water sorption, and antibacterial properties of the films were investigated as a function of ZnO concentration. While all of the composite films with less than 5 wt % ZnO exhibited good dispersion of ZnO in the PPC matrix, FTIR and SEM results revealed that solution blending did not lead to a strong interaction between PPC and unmodified ZnO. As such, poor dispersion was induced in the composite films with a high ZnO content. By incorporating inorganic ZnO filler nanoparticles, the diffusion coefficient, water uptake in equilibrium, and oxygen permeability decreased as the content of ZnO increased. The PPC/ZnO nanocomposite films also displayed a good inhibitory effect on the growth of bacteria in the antimicrobial analysis. The enhancement in the physical properties achieved by incorporating ZnO is advantageous in packaging applications, where antimicrobial and environmental‐friendly properties, as well as good water and oxygen barrier characteristics are required. Furthermore, UV light below ∼ 350 nm can be efficiently absorbed by incorporating ZnO nanoparticles into a PPC matrix. ZnO nanoparticles can also improve the weatherability of a PPC film. In future research, the compatibility and dispersion of the PPC matrix polymer and the inorganic ZnO filler nanoparticles should be increased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Synthesis of cauliflower-like ZnO–TiO 2 composite porous film and photoelectrical properties

A series of cauliflower-like TiO 2–ZnO composite porous films with various molar ratios of Zn/Ti were prepared by the screen printing technique on the fluorine-doped SnO 2 (FTO) conducting glasses. The composite films were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray energy-dispersive spectrometry (EDS) and UV–vis transmittance spectrum. The results showed composite film electrode had a novel cauliflower-like morphology, which could effectively increase the dye absorption. The corresponding dye-sensitized solar cells (DSCs) were made by the composite film, and effects of ZnO incorporation on the photovoltaic performances of the DSCs were studied. With the Zn/Ti molar ratio not more than 3% in ZnO–TiO 2 composite film of about 5 μm-thickness, the photocurrent density ( J sc) and the solar-to-electricity conversion efficiency ( η) were greatly improved compared with those of the DSC based on bare TiO 2 film of same thickness. This increases in efficiency and J sc were attributed to high electron conductivity of ZnO, the improved dye adsorption and large light transmittance of composite film.

INVESTIGATIONS ON THE ELECTRICAL PROPERTIES OF ZnO NANORODS AND COMPOSITES FOR PHOTOVOLTAIC AND ELECTROCHEMICAL APPLICATIONS

ZnO nanorods grown by hydrothermal technique on glass, Zinc, and Indium tin oxide (ITO) substrates exhibit both open and closed hexagonal structures. On the nanoscale, closed ZnO nanostructures exhibit two types of ion conduction regions as revealed by AC-impedance spectra collected through the tip of an atomic force microscope (AFM). One region has higher impedance values (apparent values of approximately 107 ohms) with two semicircles. Two semicircles are indicative of a ZnO structure composed of bulk and grain boundary conduction. Other regions were found to have impedance values that were two orders of magnitude lower (apparent values of 105 ohms). This indicates that these ZnO films have two conduction pathways. The polyethylene oxide ( PEO )– ZnO nanorod composite was made by spin-coating the ZnO rods growing from the ITO substrate with PEO. In the PEO – ZnO composite film, only the AC impedance values of 105 ohms were observed. This is higher than PEO electrolyte without ZnO nanorods. Since regions of higher impedance were not seen in the PEO – ZnO nanorod composites, the polymer electrolyte either dominated the conduction of the system or suppressed the first pathway of higher impedance in the ZnO rods.

Photocatalytic behavior of ZnO and Pt-incorporated ZnO nanoparticles in phenol degradation

Nanostructured Pt–ZnO composite thick films were prepared using the composite nanoparticles synthesized through Triton X-100 polymer assisted thermolysis of zinc acetate. It has been observed that only a fraction of added Pt incorporates into the ZnO lattice and the rest segregates over the ZnO nanoparticle surface to form metallic nanoclusters. Morphology, crystallinity, and optical properties of the ZnO and Pt–ZnO nanostructures have been studied. Photocatalytic behavior of the samples for phenol degradation process has been studied in a high performance liquid chromatography system. It has been observed that though the phenol degradation rate is higher for pure ZnO nanostructures, Pt–ZnO nanostructures act as selective catalyst, producing only one intermediate product and dissociating it faster than ZnO.

Isostructural copper–zinc mixed metal complexes for single source deposition of Cu–ZnO composite thin films

The mixed metal complex [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Br]·THF (1) and its isostructural analogues ([Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Cl]·THF (2) and [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Cl/Br]·THF (3)) have been prepared by a simple metal ligand assembly method and were characterized by their melting points, elemental analysis, IR spectroscopy, thermogravimetry and single crystal X-ray structures. The compounds are distinguished only by the nature of the halide ions and are made up of the same [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)X]·THF molecular building block with Cu(3)ZnO(4) cubane moieties as the central core in which the four metal ions and four oxygen atoms are joined together in alternate positions of the cuboid. All the complexes crystallize with similar packing and crystallographically related symmetry settings, distinguished mainly by the degree of disorder within the complexes and the ordering of the complexes in the structures. The triclinic cell of (1) emulates the monoclinic cell of (2) and is pseudomerohedrally twinned by a symmetry operation of the monoclinic cell. The molecules in (2) are 1:1 disordered around a crystallographic mirror plane. The structure of the mixed halogen compound (3) in turn is a superstructure of the less symmetric structures of (1) and (2) formed by ordering of the complexes along the longest axis of (3). Aerosol-assisted chemical vapour deposition (AACVD) experiments showed that they are promising precursors to deposit thin films of crystalline Cu/ZnO composites. The surface morphology, microstructure, chemical composition and crystallinity of the resulting Cu/ZnO composite thin films were analysed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX), which suggest that the films are thin, crystalline, uniform, smooth and tightly adherent to the substrates with average crystallite sizes in a range between 40.2 and 80.0 nm. Particle sizes, shapes and film morphology were investigated as a function of precursor and decomposition temperature.