ZnO Hybrid Films Research Articles

Morphology Transformation Pathway of Block Copolymer‐Directed Cooperative Self‐Assembly of ZnO Hybrid Films Monitored In Situ during Slot‐Die Coating

AbstractCooperative self‐assembly (co‐assembly) of diblock copolymers (DBCs) and inorganic precursors that takes inspiration from the rich phase separation behavior of DBCs can enable the realization of a broad spectrum of functional nanostructures with the desired sizes. In a DBC assisted sol–gel chemistry approach with polystyrene‐block‐poly(ethylene oxide) and ZnO, hybrid films are formed with slot‐die coating. Pure DBC films are printed as control. In situ grazing‐incidence small‐angle X‐ray scattering measurements are performed to investigate the self‐assembly and co‐assembly process during the film formation. Combining complementary ex situ characterizations, several distinct regimes are differentiated to describe the morphological transformations from the initially solvent‐dispersed to the ultimately solidified films. The comparison of the assembly pathway evidences that the key step in the establishment of the pure DBC film is the coalescence of spherical micelles toward cylindrical domains. Due to the presence of the phase‐selective precursor, the formation of cylindrical aggregates in the solution is crucial for the structural development of the hybrid film. The pre‐existing cylinders in the ink impede the domain growth of the hybrid film during the subsequent drying process. The precursor reduces the degree of order, prevents crystallization of the PEO block, and introduces additional length scales in the hybrid films.

A facile surfactant assisted hydrothermal synthesis of ZnO and graphene loaded ZnO for efficient photocatalytic self-cleaning

Superhydrophilicity and photocatalysis are of great importance for self-cleaning applications. We report the synthesis of ZnO and ZnO loaded graphene nanostructures at different pH values with exposed polar facets by a simple hydrothermal method. Cetyltrimethylammonium bromide is used as surfactant and the synthesis is carried out without the aid of high temperature and demonstrated to have a superior photocatalytic activity. We observed a reduction in band gap for graphene loaded ZnO samples. Further, a one-step spin coating method is used for the preparation of optically transparent and photoinduced superhydrophilic ZnO hybrid films. We investigated the effect of cetyltrimethylammonium bromide capping agent on crystal growth and morphology of as synthesised samples. An effective improvement in photocatalytic activity of the nanohybrid (∼100%) compared to pure ZnO (85%) is observed within 150 min. This can be attributed to the synergetic interaction of the components of the hybrid. Also, the hybrid samples coated on the glass substrate exhibits good transparency and superhydrophilicity upon UV irradiation. An unexpected transmittance as high as 84%–97% throughout most of the visible light region of the spectrum of the hybrid samples along with good photocatalytic efficiency and photoinduced superhydrophilicity makes the samples more suitable for self-cleaning applications.

Films of Reduced Graphene Oxide with Metal Oxide Nanoparticles Formed at a Liquid/Liquid Interface as Reusable Surface Enhanced Raman Scattering Substrates for Dyes.

Free standing, thin films of reduced graphene oxide (rGO) with ZnO, CuO and SnO(2) nanostructures are prepared at a water/toluene interface utilizing simple interfacial reaction and self-assembly. rGO-ZnO, rGO-CuO and rGO-SnO(2) films exhibit unique morphologies such as hexagonal cylinders, elongated splinters, and balls, respectively, wrapped by rGO layers. The hybrid films exhibit surface enhanced Raman scattering (SERS) of rhodamine 6G dye with enhancement factors one order higher than bare metal oxide caused by a synergic effect of charge transfer between the dye, metal oxide and rGO. Doping with Ag+ ions improves SERS enhancement in rGO-Ag–ZnO hybrid films, exploiting the electromagnetic effect of metal surface plasmons. Detection sensitivity up to 10 μM dye with an enhancement factor of 104 is shown. The enhanced photodegradation rate by the hybrid films is utilized for UV induced regeneration of the used SERS substrate and is demonstrated for successive use of different analytes.

Synthesis, characterization and optical properties of hybrid PVA–ZnO nanocomposite: A composition dependent study

Nanocomposites of poly vinyl alcohol (PVA) and ZnO have been synthesized using the solution casting technique for different concentrations of nano ZnO powder prepared by low temperature solution combustion method. The formation of polymer nanocomposite and changes in the structural and micro structural properties of the materials were investigated by X-ray diffraction, Energy dispersive X ray spectroscopy and optical microscopy techniques (FTIR and UV–Visible). The surface morphology of PVA–ZnO nanocomposite films were elucidated using Scanning Electron Microscopy. The optical absorption spectrum of nano ZnO shows blue shift in the optical band gap energy with respect to characteristic bulk ZnO at room temperature, whereas PVA–ZnO hybrid films show red shift with respect to nano ZnO. The photoluminescence studies show that the intensity of the blue emission (470nm) varies with change in concentration of ZnO with an optimum intensity observed at 10mol% of ZnO.

VLS Growth of Highly Oriented SnO2 Nanorods and ZnO Hybrid Films for Gas Sensing Measurements

Tin Oxide (SnO2) nanorods have been successfully grown on a p-type Si substrate by a low-temperature vapor-liquid-solid (VLS) technique. Tin chloride and zinc chloride powders were used as starting materials. Surface morphologies and structural properties of the SnO2 nanorods were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The SEM images shows distinct hierarchical growth of SnO2 as well as the mixture with ZnO microstructures. The structural studies demonstrated rutile crystal structure SnO2 nanorods with square-shaped facets of 40–60 nm in cross section size and 2 μm in length approximately and ZnO microrods of 10 μm diameter and 50 μm length. The fabrication of a gas sensor for acetone and ethanol vapors is also reported and its properties are discussed.

Polypyrrole–ZnO hybrid sensor: Effect of camphor sulfonic acid doping on physical and gas sensing properties

The polypyrrole–zinc oxide (PPy–ZnO) hybrid sensor doped with different weight ratios of camphor sulfonic acid (CSA) were prepared by spin coating technique. These CSA doped PPy–ZnO hybrids were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transform infrared (FTIR) and UV–vis techniques which proved the formation of polypyrrole, PPy–ZnO and the interaction between polypyrrole–ZnO (PPy–ZnO) hybrid with CSA doping. The gas sensing properties of the PPy–ZnO hybrid films doped with CSA have been studied for oxidizing (NO2) as well as reducing (H2S, NH3, C2H5OH and CH3OH) gases at room temperature. We demonstrate that CSA (30wt.%) doped PPy–ZnO hybrid films are highly selective to NO2 along with high-sensitivity at low concentration (80% to 100ppm), fast-response time (120s) and better stability, which suggested that the CSA (30%) doped PPy–ZnO hybrid films are potential candidate for NO2 detection at room temperature.

Dielectric studies on hybridised PVDF–ZnO nanocomposites

Nanocomposites of polyvinylidene fluoride (PVDF) and nano-ZnO were prepared using the solution casting method for different concentrations of nano-ZnO and were characterised by X-ray diffraction and atomic force microscopy. Optical properties of these nanocomposites were determined by using UV-Vis absorption spectroscopy and Fourier transform infrared analysis. The variation of dielectric properties such as dielectric constant, dielectric loss and electric modulus of the hybrid films based on the content of ZnO studied for various microwave frequencies at room temperature showed that the dielectric constant of PVDF–ZnO hybrid films increased with increasing ZnO content at room temperature.

Solution-processed polyfluorene–ZnO nanoparticles ambipolar light-emitting field-effect transistor

We report on a solution-processed polyfluorene (PFO)–ZnO nanoparticles composite light-emitting organic field-effect transistor (LE-OFET). The behavior of absorption, photoluminescence spectra and electroluminescence intensity of the PFO:ZnO hybrid films with different concentration of ZnO nanoparticles is analyzed. By changing the PFO/ZnO nanoparticles concentration ratio the PFO:ZnO OFET shows either unipolar or ambipolar behavior of current–voltage characteristics and operates in the hole/electron accumulation mode with current saturation behavior. The field effect mobility of charge carriers depends on the ZnO concentration. For the ambipolar PFO:ZnO OFET with modest PFO/ZnO nanoparticles ratio (1:0.2), well balanced electron and hole mobility values at 300 K are ∼0021 and ∼0029 cm 2/Vs, respectively, whereas for films with high ZnO concentration (1:1) the mobility (∼2 cm 2/Vs) is close to that of polycrystalline ZnO. The ambipolar PFO:ZnO LE-OFET emits light at both positive and negative gate bias. The working mechanism of the PFO:ZnO LE-OFET is investigated.

A light-emitting field-effect transistor based on a polyfluorene–ZnO nanoparticles film

We report on a light-emitting organic field-effect transistor (LE-OFET) based on a polyfluorene (PFO)–ZnO nanoparticles film. We have analysed the behaviour of absorption, photoluminescence spectra and electroluminescence (EL) intensity of the PFO : ZnO hybrid films with different ZnO concentrations prepared in the FET configuration. We have found that the PFO : ZnO LE-OFET exhibits the current–voltage characteristics of a unipolar FET with saturation behaviour and operates in the hole accumulation mode. The FET mobility values in the PFO : ZnO films with a high ZnO concentration are close to the mobility of polycrystalline ZnO. A significant increase in the EL intensity of the hybrid films has been observed with an increase in the concentration of ZnO nanoparticles and with the application of gate voltages. The working mechanism of the LE-OFET device is discussed.

Low-temperature fabrication of porous and transparent ZnO films with hybrid structure by self-hydrolysis method

Porous, transparent and controllable ZnO nanoparticulate films were fabricated by self-hydrolysis of zinc salts in its crystalline water without any additions at 65 °C by an evaporating acetone solvent. The crystallite size of ZnO nanoparticles was about 30 nm, and the thickness of the nanoparticle film was controllable by simply changing the coating times. ZnO nanoparticulate films in thickness of 500 nm showed a high transmittance (>90%) in the visible range and widen bandgap (3.35 eV). The c-axis oriented ZnO nanoarray film was fabricated by a subsequent heterogeneous nucleation and growth in an aqueous solution. As-grown ZnO hybrid films showed a good transmittance (>85%) in the visible range.

Study on luminescence characteristic of the ZnO/polymer hybrid films

The cyclohexane solution of PS (polystyrene) and the ethyl acetate solution of PMMA (polymethyl methacrylate) were used as flowing liquid; the ZnO/polymer hybrid colloids were successively produced by focused pulsed laser ablation of ZnO target in interface of solid and flowing liquid. As solvent in the hybrid colloids has volatized, the ZnO/polymer hybrid films were obtained. The hybrid colloids were characterized by high-resolution transmission electron microscopy (HRTEM) and select-area electron diffraction (SEAD). The results show a good dispersion of the ZnO nanoparticles in the polymer matrix. The hybrid films were characterized by fluorescence spectrum, Fourier transform infrared spectroscopy (FTIR) spectroscopy, thermogravimetry with FTIR (TG/FTIR), and X-ray photoelectron spectrum. The results show the ZnO/polymer hybrid films can radiate strong blue light under ultraviolet. Meanwhile, the ZnO/polymer hybrid films have higher chemical stability than ZnO nanoparticles because nano-ZnO nanoparticles were enwrapped by polymers. In addition, the ZnO hybrid films have higher thermal stability then the related pure polymers because of strong interaction among ZnO nanoparticles and polymers.

Incorporation of carbon nanotube into direct-patternable ZnO thin film formed by photochemical solution deposition

Abstract Direct-patterning of ZnO hybrid films containing MWNT was realized without using photoresist and dry etching. Photosensitive 2-nitrobenzaldehyde was introduced into the solution precursors as a stabilizer and contributed to form a cross-linked network structure during photochemical reaction. According to the incorporation of multi-walled nanotube (MWNT) into ZnO films, the transmittance of ZnO hybrid film containing MWNT did not change but the sheet resistance was improved due to the enhancement of charge mobility due to π-bonding nature of MWNT. These results suggested a possibility that a micro-patterned system can be fabricated relatively easily and without high-cost processes, for example, by conventional etching procedure.

Electromagnetic shielder compatible ZnO transparent conducting oxides hybridized with various sizes of Ag metal nanoparticles

In this paper, the effect of different sizes of Ag-nanoparticles dispersed in ZnO matrix using sol–gel method has been focused. Low-temperature crystallized ZnO thin films was achieved by sol–gel process, using zinc acetate dihydrate and 2-methoxyethanol as starting precursor and solvent, respectively. Various sizes of Ag-nanoparticles could be prepared by the spontaneous reduction method with changing the preparation temperatures and mole concentrations of Ag 2-ethylhexanoate in dimethyl sulfoxide solvent. The crystallographic structure of the Ag–ZnO hybrid film was analyzed by X-ray diffraction. Ag-nanoparticle size and optical property of Ag–ZnO hybrid films were measured by UV–vis spectrophotometer.

Growth by Electrochemistry of Zinc Oxide Films with Controlled (nano)Structure and Properties

Electrodeposition is a versatile method for the preparation of ZnO films with controlled nanostructures and properties. In the present paper we describe two approaches for the preparation of ZnO hybrid films with red/green adjustable luminescence. ZnO is imparted with luminescence properties by bipyridine (dcbpy)- lanthanide complexes. In the first route, ZnO/ dcbpy hybrid films are prepared and subsequently chelated with Ln3+ ions (with Ln being Eu or Tb) to form the luminescent complex. In the second proposed route, highly porous ZnO matrices are prepared by electrodeposition with help of eosin Y molecules. The matrices are loaded with in- situ assembled Ln3+:dcbpy luminescent complexes. In both cases, the ligand is anchored to ZnO by its carboxylic acid groups. The film emission and excitation characteristics show UV absorption by the ligand bipyridine group and an efficient energy transfer to Ln3+.

Persistent photoconductivity in highly porous ZnO films

ZnO and ZnO-dye hybrid films prepared by electrochemical deposition are highly porous if fabricated in the presence of structure directing agents and they can easily be sensitized by various molecules. If the material is sensitized with the appropriate molecules, it becomes interesting for various sensor applications, i.e., gas sensors and biosensors, or as an electrode material for solar energy conversion in dye sensitized solar cells. In the present work, the focus is on dye sensitized ZnO as a model system. The long term photoconductivity transients have been investigated in such kind of material. Upon excitation with different wavelengths, the conductivity increases already under sub-band-gap illumination due to widely distributed trap states within the band gap. The slow photoconductivity transients follow a stretched exponential law if the illumination is rapidly changing in a dry atmosphere. The underlying mechanism of persistent photoconductivity can be attributed to a lattice relaxation process of surface states, immediately after electrons have been photoexcited into distributed surface states located inside the band gap of the ZnO thin film.

Effect of the Polyimide Structure and ZnO Concentration on the Morphology and Characteristics of Polyimide/ZnO Nanohybrid Films

AbstractSummary: A series of polyimide/ZnO nanohybrid films with different ZnO content were prepared from a rigid pyromellitic dianhydride‐4,4′‐diaminodiphenyl ether (PMDA‐ODA) polyimide (PI) and a flexible 3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride‐4,4′‐diaminodiphenyl ether (BTDA‐ODA) PI with ZnO nanoparticles (3–4 nm). Fourier‐transform infrared (FT‐IR) and X‐ray photoelectron spectroscopy (XPS) depict that the ZnO nanoparticles function as a physical cross‐linking agent with PI through hydrogen bonding between the OH on the ZnO nanoparticles and the CO of the imide groups. ZnO nanoparticles in the rigid PMDA‐ODA matrix cause a larger percentage decrease in the coefficient of linear thermal expansion (CTE) than in the flexible BTDA‐ODA matrix. The BTDA‐ODA/ZnO hybrid films have two transition peaks in dynamic mechanical tan δ curves, but PMDA‐ODA/ZnO hybrid films only have one transition peak. Thermogravimetric analysis reveals that ZnO decreases the thermal degradation temperature (Td) in both hybrid films, but less so in PMDA‐ODA/ZnO films. Transmission electron microscopy (TEM) images reveal that the rigid matrix induces larger particle size (30–40 nm) compared to the flexible matrix (10–15 nm).Illustration of the interaction between ZnO nanoparticles and PI.magnified imageIllustration of the interaction between ZnO nanoparticles and PI.