Formation Of Zinc Oxide Films Research Articles

Low-temperature solution-processed zinc oxide field effect transistor by blending zinc hydroxide and zinc oxide nanoparticle in aqueous solutions

We present a novel methods of fabricating low-temperature (180 °C), solution-processed zinc oxide (ZnO) transistors using a ZnO precursor that is blended with zinc hydroxide [Zn(OH)2] and zinc oxide hydrate (ZnO ∙ H2O) in an ammonium solution. By using the proposed method, we successfully improved the electrical performance of the transistor in terms of the mobility (μ), on/off current ratio (Ion/Ioff), sub-threshold swing (SS), and operational stability. Our new approach to forming a ZnO film was systematically compared with previously proposed methods. An atomic forced microscopic (AFM) image and an X-ray photoelectron spectroscopy (XPS) analysis showed that our method increases the ZnO crystallite size with less OH− impurities. Thus, we attribute the improved electrical performance to the better ZnO film formation using the blending methods.

Morphology control of zinc oxide films via polysaccharide-mediated, low temperature, chemical bath deposition.

In this study we present a three-step process for the low-temperature chemical bath deposition of crystalline ZnO films on glass substrates. The process consists of a seeding step followed by two chemical bath deposition steps. In the second step (the first of the two bath deposition steps), a natural polysaccharide, namely hyaluronic acid, is used to manipulate the morphology of the films. Previous experiments revealed a strong influence of this polysaccharide on the formation of zinc oxide crystallites. The present work aims to transfer this gained knowledge to the formation of zinc oxide films. The influence of hyaluronic acid and the time of its addition on the morphology of the resulting ZnO film were investigated. By meticulous adjustment of the parameters in this step, the film morphology can be tailored to provide an optimal growth platform for the third step (a subsequent chemical bath deposition step). In this step, the film is covered by a dense layer of ZnO. This optimized procedure leads to ZnO films with a very high electrical conductivity, opening up interesting possibilities for applications of such films. The films were characterized by means of electron microscopy, X-ray diffraction and measurements of the electrical conductivity.

Effect of ammonia solution on properties of sprayed ZnO thin films consisting of nano-pyramids

Hexagonal wurtzite zinc oxide (ZnO) thin films were deposited at substrate temperatures from 300 to 500 °C with surfactant of ammonia solution. The effect of ammonia on the structural, surface morphology, compositional, optical and electrical properties of ZnO thin films was studied. X-ray diffraction shows that the all films are polycrystalline in nature and have a hexagonal wurtzite structure with a high preferential orientation (002) plane for ammonia solution. High-resolution SEM studies reveal the formation of ZnO films consisting of nano-pyramids with uniformly distributed grains over the entire surface of the substrates. Photoluminescence studies indicate the presence of two emission peaks: (a) a sharp ultra-violet near band edge ∼392 nm, (b) a sharp visible deep-level green emission peak ∼564 nm. The optical properties show that the direct band gap energy values increase with increasing substrate temperatures.

Formation of zinc oxide films using submicron zinc particle dispersions

The thermal oxidation of submicron metallic Zn particles was studied as a method to form nanostructured ZnO films. The particles used for this work were characterized by electron microscopy, x ray diffraction, and thermal analysis to evaluate the Zn-ZnO core shell structure, surface morphology, and oxidation characteristics. Significant nanostructural changes were observed for films annealed to 400 °C or higher, where nanoflakes, nanoribbons, nanoneedles, and nanorods were formed as a result of stress induced fractures arising in the ZnO outer shell due to differential thermal expansion between the metallic Zn core and the ZnO shell. Mass transport occurs through these defects due to the high vapor pressure for metallic Zn at temperatures above 230 °C, whereupon the Zn vapor rapidly oxidizes in air to form the ZnO nanostructures. The Zn particles were also incorporated into zinc indium oxide precursor solutions to form thin film transistor test structures to evaluate the potential of forming nanostructure...

G060015 高周波酸素プラズマを用いたマグネシウム合金表面の高機能皮膜形成([G06001]熱工学部門一般セッション(1):電気・化学過程を伴う熱流体,およびプラズマ・放電)

Mg alloy has a lot of useful properties and its application has been enlarged to various industrial products. However, it has poor corrosion resistance and therefore surface treatment is necessary. In this study, zinc oxide film formation is tried on magnesium alloy surface with RF oxygen plasma in order to improve corrosion resistance preserving good electrical conductivity. Ar gas in addition to oxygen is used to assist an easy plasma production, and the influence of argon on coating film characteristic is investigated.

Preparation of Patterned Zinc Oxide Films by Breath Figure Templating

A large variety of microporous polymer films can be prepared by the breath figure technique. Here, we report on its use for the formation of microporous zinc oxide films. Zinc acetylacetonate, a zinc oxide precursor, is either dissolved in a polymer solution that is cast at high humidity to form microporous films or is vacuum evaporated onto a preformed microporous polymer film. Annealing leads to the pyrolysis of the organic material and the formation of zinc oxide films, which show increased photocatalytic activity as compared to unstructured films.

Formation of zinc oxide film by boiling metallic zinc film in ultrapure water

A simple method for forming zinc oxide (ZnO) films has been discovered. Radio-frequency (rf) sputtered metallic zinc (Zn) film is boiled in ultrapure water at 368 K. The opaque Zn film changes into a transparent film. It is confirmed by transmission electron microscopy and X-ray diffraction that the transparent film is hexagonal ZnO. Optical and morphological properties of the ZnO film are discussed.

Growth mechanism of ZnO nanowires via direct Zn evaporation

Zinc oxide (ZnO) nanowire synthesized from direct Zinc (Zn) vapor transport in O2 environment has been studied. The results show that the first step is the formation of ZnO film on the substrate. Then anisotropic abnormal grain growth in the form of ZnO platelets takes place. Subsequently, single-crystalline ZnO platelets grow in [0001] direction to form whiskers. During whisker growth, transformation from layer-by-layer growth to simultaneous multilayer growth occurs when the two-dimensional (2D) Ehrlich–Schwoebel (ES) barrier at the ZnO island edge is sufficiently large and the monolayer island diameter is smaller than the island spacing. As multilayered islands grows far away from the base, isotropic mass diffusion (spherical diffusion) will gradually displace anisotropic diffusion (linear diffusion), which contributes to the formation of pyramid on the top plane of the whisker. When the pyramid contains enough atomic layers, the 2D ES barrier transits to 3-dimensional ES barrier, which contributes to repeated nucleation and growth of multilayered islands or pyramids on the old pyramids. The pyramids play a critical role to taper the whisker to nanorod with a diameter less than 100 nm. The nanorod then grows to nanowire via repeated growth of epitaxial hexagonal-pyramid shape-like islands on the (0001)-plane with $$ \left\{ {11\overline{2} 3} \right\} $$ facets as the slope planes. During coarsening, the breakage of step motion of $$ \left\{ {11\overline{2} 3} \right\} $$ facets and the appearance of $$ \left\{ {11\overline{2} 0} \right\} $$ facets on the base of pyramids may result from the step bunching of {0001} facets, which is consistent with the existence of “2D” Ehrlich–Schwoebel barrier on the edge of (0001) facets.

Electrodeposition and characterization of transparent ZnO thin films

Abstract Thin films of zinc oxide (ZnO) have been grown by potentiostatic cathodic deposition onto tin oxide-coated glass from a simple aqueous zinc nitrate electrolyte. Cyclic voltammetry (CV) experiments were performed to determine the reaction kinetics of the species. The various optimum deposition parameters like potential, pH and bath temperature are found to be −1.1 V (SCE), 5±0.1 and 80 °C, respectively. Structural characterization by X-ray diffraction indicates the formation of ZnO film with a preferred c -axis orientation and exhibits the wurtzite structure. Optical studies revealed a band gap energy 3.32 eV which is characteristic of ZnO films. SEM micrographs show a compact structure with nodular appearance, which is in agreement with the reported value of ZnO and the results are discussed.

ZnO film formation using a steered and shielded reactive vacuum arc deposition

Zinc oxide (ZnO) thin films were prepared on a borosilicate glass substrate by a steered and shielded reactive vacuum arc deposition method. The cathode spot was driven on a cathode surface using weak and strong permanent magnets, placed behind the cathode. The radial magnetic flux densities at the bottom of cathode shoulder were 1.0 mT and 5.5 mT, respectively. The arc was operated at DC 30 A and the in-process pressure was varied from 0.1 to 5.0 Pa. No bias was applied to the substrate. The substrate temperature was below 75°C after 20-min deposition. The deposition rate increased with the in-process pressure until 1.0 Pa with both weak and strong magnets. X-Ray diffraction analysis revealed that all films had a strong ZnO (200) peak, indicating c-axis orientation. In particular, the films strongly oriented to (200) were obtained at 0.5–3.0 Pa for the strong magnet. Highly transparent films in visual region were obtained at 0.5 and 3.0 Pa with both weak and strong magnets. A refractive index at 600 nm varied from 1.75 to 1.95. With the strong magnet, electric resistivity varied from 10 −3 to 15 Ω cm as the pressure increased. However, with the weak magnet, resistivity of the order of 10 −3 Ω cm was obtained over a wide pressure range of 0.1–1.0 Pa.

Chemically deposited zinc oxide thin film gas sensor

Zinc oxide (ZnO) thin films were prepared by a low cost chemical deposition technique using sodium zincate bath. Structural characterizations by X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) indicate the formation of ZnO films, containing 0.05–0.50 μm size crystallites, with preferred c-axis orientation. The electrical conductance of the ZnO films became stable and reproducible in the 300–450 K temperature range after repeated thermal cyclings in air. Palladium sensitised ZnO films were exposed to toxic and combustible gases e.g., hydrogen (H2), liquid petroleum gas (LPG), methane (CH4) and hydrogen sulphide (H2S) at a minimum operating temperature of 150 °C; which was well below the normal operating temperature range of 200–400 °C, typically reported in literature for ceramic gas sensors. The response of the ZnO thin film sensors at 150 °C, was found to be significant, even for parts per million level concentrations of CH4 (50 ppm) and H2S (15 ppm).

Chemical deposition of ZnO films for gas sensors

Zinc oxide (ZnO) thin films were prepared following a chemical, deposition technique using a sodium zincate bath. Structural characterizations by scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicate the formation of ZnO film with a preferred c-axis orientation. The electrical conductance of the ZnO films became stable and reproducible in the 300–500 K temperature range with two activation energy barrier values of 0.3 eV and 0.8 eV in the low temperature (300–420 K) and high temperature (430–500 K) ranges, respectively. The ZnO films prepared by this method are highly resistive, indicating the presence of a large density of oxygen adsorbed acceptor-like trap states (O2-, O-, etc.). Palladium sensitized ZnO films were exposed to hydrogen (H2) with air as a carrier gas at different operating temperatures ranging between 150–375°C and the response is evaluated.

Rapid Formation of Zinc Oxide Films by an Atmospheric‐Pressure Chemical Vapor Deposition Method

Zinc oxide films were prepared by an atmospheric‐pressure chemical vapor deposition method using (acetylacetonato)‐zinc as a source material. Transparent and uniform ZnO films of considerable area (20 × 70 mm, ∼0.3 μm thick) could be obtained easily on a crown glass (CGW #200) with a high deposition rate. The deposition rate first remained constant with increasing substrate temperature (Ts), then increased abruptly from 120 nm/min at Ts= 550°C to 220 nm/min at Ts= 600°C, and finally stopped increasing above Ts= 600°C. The maximum preferred orientation and best crystallinity of the films were obtained at Ts= 550°C.

Formation of ZnO films by CO2 laser ablation at atmospheric pressure

Laser ab la t ion has often been used to obtain high-quality thin ceramic films such as A120 3 [1], Si3N 4 [1], TiN [1], CdTe [2], SnO2 [3], BN [4] and high-T0 superconductor films [5, 6]. A laser ablation system usually consists of a clean vacuum chamber in order to rea l i ze a long mean free path of the atoms in the gas phase. However, certain oxide films can be prepared without a vacuum chamber by chemical vapour deposition (CVD). For example, TiO2 films can be prepared by the traditional method of thermal CVD at atmospheric pressure [7]. This observation has led us to an attempt to produce thin ceramic films by a laser ablation method at atmospheric pressure . Zinc oxide (ZnO) provides a wide range of scientific and technological applications because of its semiconducting, photoconducting and piezoelectric characteristics [8]. This letter reports the preparation of ZnO films by CO2 laser ablation at atmospheric pressure . ZnO targets w e r e prepared by pressing 99.99% purity ZnO powder into circular discs (about 1.3 cm in diameter and 1.0 cm thick). A schematic diagram of the experiment is shown in Fig. 1. A glass substrate was heated to 200-600 °C by an infrared lamp. A c.w. CO2 laser was operated at 75 W and focused on the surface of a ZnO target through a ZnSe lens ( f = 30 cm). The ZnO vapour formed by laser i rradiat ion was brought to the surface of the substrate in a stream of nitrogen gas admitted through a nozzle with a slit size of 1 mm × 8 mm. The distance between the nozzle head and the substrate was 2.3 cm. When the snbstrate was not h e a t e d by the lamp, the substrate t e m p e r a t u r e was raised to about 200 °C by the blowing gas containing the high-temperature ZnO vapour formed by the laser irradiation. The growth rate of the ZnO film