Zinc Oxide Precursor Research Articles

Structural, optical and photoelectron spectroscopic studies of nano/micro ZnO:Cd rods synthesized via sol-gel route

Thin films of cadmium doped zinc oxide rod like microstructure have been synthesized by a very simple sol-gel dip coating technique. Sols were prepared from hydrated zinc oxide precursor and 2-methoxyethanol solvent with monoethanolamine as a sol stabilizer. XRD pattern confirmed the hexagonal wurtzite structure of the deposited ZnO films. Surface morphologies of the films have been studied by a scanning electron microscope and an atomic force microscope, which confirmed that the films are composed of densely packed randomly oriented nano/submicron rods with diameter in the range 300–400 nm having various lengths. We proposed a possible growth mechanism for this rodlike structure. X-ray photoelectron spectroscopic study was used to determine the binding energies and the Zn 2p3/2, Cd 3d5 and O 1s peaks in the XPS spectra were located at 1021.08 eV, 404.6 eV and 529.8 eV respectively, which confirmed the Cd doping in ZnO. Cadmium content in the film was estimated both from energy dispersive X-ray analysis and XPS measurement. Band gap energy determined from optical transmittance spectra systematically varied from 3.28 eV to 3.15 eV for 0% to 5.6% of Cd doping. Urbach parameter determined from the band tail of the transmittance spectra showed that it increased with doping percentage and this parameter for a fixed cadmium doping level decreased with increase of temperature.

Fabrication of high aspect ratio nanostructures using capillary force lithography

A new ultraviolet (UV) curable mold consisting of functionalized polyurethane with acrylate group (MINS101m, Minuta Tech.) has recently been introduced as an alternative to replace polydimethylsiloxane (PDMS) mold for sub-100-nm lithography. Here, we demonstrate that this mold allows for fabrication of various high aspect ratio nanostructures with an aspect ratio as high as 4.4 for 80 nm nanopillars. For the patterning method, we used capillary force lithography (CFL) involving direct placement of a polyurethane acrylate mold onto a spin-coated polymer film followed by raising the temperature above the glass transition temperature of the polymer (Tg). For the patterning materials, thermoplastic resins such as polystyrene (PS) and poly(methyl methacrylate) (PMMA) and a zinc oxide (ZnO) precursor were used. For the polymer, micro/nanoscale hierarchical structures were fabricated by using sequential application of the same method, which is potentially useful for mimicking functional surfaces such as lotus leaf.

Preparation and characterization of transparent ZnO/epoxy nanocomposites with high-UV shielding efficiency

Transparent ZnO/epoxy nanocomposites with high-UV shielding efficiency were reported in this paper. First, zinc oxide (ZnO) precursor was synthesized via the homogeneous precipitation method and ZnO nanoparticles were then made by calcination of the precursor at different temperature. The structural properties of the as-prepared ZnO nanoparticles were studied in detail using thermogravimetry (TGA), differential thermal analysis (DTA), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR) and transmission electron microscopy (TEM), respectively. Transparent ZnO/epoxy nanocomposites were subsequently prepared from transparent epoxy (EP-400) and as-prepared ZnO nanoparticles via in situ polymerization. Optical properties of ZnO/epoxy nanocomposites, namely visible light transparency and UV light shielding efficiency, were studied using an ultraviolet–visible (UV–vis) spectrophotometer. The optical properties of the as-obtained nanocomposites were shown to depend on ZnO particle size and content. The nanocomposite containing a very low content (0.07% in weight) of ZnO nanoparticles with an average particle size of 26.7 nm after calcination at 350 °C possessed the most optimal optical properties, namely high-visible light transparency and high-UV light shielding efficiency, that are desirable for many important applications.

Hybrid Solar Cells Using a Zinc Oxide Precursor and a Conjugated Polymer

AbstractWe describe a new method towards bulk‐heterojunction hybrid polymer solar cells based on composite films of zinc oxide (ZnO) and a conjugated polymer poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylene vinylene] (MDMO‐PPV). Spin‐coating diethylzinc as a ZnO precursor and MDMO‐PPV from a common solvent at 40 % humidity and annealing at 110 °C provides films in which crystalline ZnO is found to be intimately mixed with MDMO‐PPV. Photoluminescence and photoinduced spectroscopy demonstrate that photoexcitation of these hybrid composite films results in a fast and long‐lived charge transfer from the polymer as a donor to ZnO as ato be obtained n acceptor. Using the ZnO‐precursor method, hybrid polymer solar cells have been made with an estimated air‐mass of 1.5 (AM 1.5) energy conversion efficiency of 1.1 %. This new method represents a fivefold improved performance compared to similar hybrid polymer solar cells based on amorphous TiO2.

Theoretical analysis of growth of ZnO nanorods on the amorphous surfaces

Semiconductor nanorod arrays on a substrate have a preferential alignment orientation that minimizes the excessive free energy of the system. In the case of wet chemically synthesized zinc oxide (ZnO) nanorod on the amorphous surfaces, the thermodynamic driving force determines the orientation to be normal to the surface. Among the various kinds of amorphous surfaces, the spherical seed layer composed of ZnO precursors gives isotropic radially aligned arrays. For other surfaces, such as wrinkled and planar ZnO precursor thin film, nanorod arrays are aligned to be perpendicular to the tangential line of the surface. The maximum value of the aspect ratio of the nanorod is determined by the thermodynamic relationship. The number density of nanorods per unit precursor particles decreases with increasing contact angle of the seed particles.

Nanostructured zinc oxide films grown from microwave activated aqueous solutions

ZnO films have been obtained by a modification of the chemical bath deposition (CBD) procedure in which crystal growth is activated using microwave (MW) radiation. ZnO films has been grown on F-doped SnO 2-covered glass substrates immersed in an aqueous solution which contains a soluble zinc oxide precursor (zinc nitrate or zinc acetate) and urea or hexamethylenetetraamine to promote the formation of the oxide. This new method, MW-CBD, produces well-adhered films at low temperatures, in an open atmosphere and in short times. The deposited material is crystalline and, thus, no additional heat treatment is necessary. The degree of coverage and the shape of the ZnO nanocrystallites are determined by the composition of the chemical bath and by the MW radiation power and irradiation time. A suitable selection of these parameters allows attaining complete substrate coverage with ZnO nanorods, mainly oriented perpendicularly to the substrate, in only 12 min.

Microstructure of Varistors Prepared with Zinc Oxide Nanoparticles Coated with Bi2O3

Zinc oxide (ZnO) nanoparticles coated with 1–5 wt% Bi2O3 were prepared by precipitating a Bi(NO3)3 solution onto a ZnO precursor. Transmission electron microscopy showed that a homogeneous Bi2O3 layer coated the surface of the ZnO nanoparticles and that the ZnO particle size was ∼30–50 nm. Scanning electron microscopy showed that ZnO grains sintered at 1150°C were homogeneous in size and surrounded by a uniform Bi2O3 layer. When the ZnO grains were surrounded fully by Bi2O3 liquid phases, further increases in the ZnO grain size were not affected by the Bi2O3 content. This predesigned ZnO nanoparticle structure was shown to promote homogeneous ZnO grains with perfect crystal growth.