Metal Zinc Oxide Research Articles

Transparent Zinc Oxide Gate Metal–Oxide–Semiconductor Field-Effect Transistor for High-Responsivity Photodetector

We report a new structure of high-responsivity photodetectors that utilizes the transparent and metallic zinc oxide (ZnO) gate in bulk silicon metal-oxide-semiconductor field-effect-transistor photodetectors. The device has a small optical window only in the channel region, and all other regions (depletion) are protected from external light. Whereas the amplification of photocurrent by external light was not significant at the floated or positively biased substrate, the photocurrent was enhanced at the grounded or negatively biased substrate due to the decrement of the recombination rate in the n-channel MOSFET. Responsivity was in excess of 1500 A/W under white-light illumination, which is higher than that of conventional photodetectors with the semitransparent polycrystalline-silicon gate.

Ultra fast synthesis of zinc oxide nanostructures by microwaves

We describe a novel route for the synthesis of nanostructured zinc oxide powder using a modified kitchen microwave. A SiC-based composite showing a very strong absorption of microwaves was used as a microwave heater. Tests showed that high temperatures exceeding 1700 ∘C can be reached in less than hundred second exposure of the composite material of microwaves. Zinc oxide nanopowder was obtained by evaporation and oxidation of metallic zinc in the ambient atmosphere of the microwave oven. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques revealed the prepared powder includes a wide variety of nanostructures including nanoparticles, nanosheets and tetrapods.

Electroluminescent Characteristics of DBPPV–ZnO Nanocomposite Polymer Light Emitting Devices

We have demonstrated that fabrication and characterization of nanocomposite polymer light emitting devices with metal Zinc Oxide (ZnO) nanoparticles and 2,3-dibutoxy-1,4-poly(phenylenevinylene) (DBPPV). The current and luminance characteristics of devices with ZnO nanoparticles are much better than those of device with pure DBPPV. Optimized maximum luminance efficiencies of DBPPV–ZnO (3:1 wt%) before annealing (1.78 cd/A) and after annealing (2.45 cd/A) having a brightness 643 and 776 cd/m2at a current density of 36.16 and 31.67 mA/cm2are observed, respectively. Current density–voltage and brightness–voltage characteristics indicate that addition of ZnO nanoparticles can facilitate electrical injection and charge transport. The thermal annealing is thought to result in the formation of an interfacial layer between emissive polymer film and cathode.

Novel Low Temperature Chemical Synthesis and Characterization of Zinc Oxide Nanostructures

We report a new and highly efficient method to synthesize zinc oxide (ZnO) nanostructures having a variety of sizes and shapes. A simple chemical reaction is followed that utilizes the oxidation of metallic zinc in the presence of an appropriate catalyst. This one-step method has advantages such as low temperature and atmospheric pressure synthesis, high yield of more than 90% and excellent optical and crystalline properties of the product. X-ray diffraction pattern of the samples shows hexagonal phase of ZnO with particles size in the range of 60-75 nm. Scanning electron microscope and transmission electron microscope images of the ZnO show hexagonal and rod-shaped nanoparticles. UV-visible spectra of the dispersed samples show strong absorption peaks at approximately 378 nm. The photoluminescence spectra show a strong emission peak at approximately 388 nm indicating good optical characteristics. The product formed is found to be dependent on the ratio of the starting materials and on other reaction conditions such as temperature, time etc. This method is suitable for large-scale production of nanosized ZnO and could be extended for the synthesis of other metal oxides, such as MgO etc.

Second and third order nonlinear optical properties of microrod ZnO films deposited on sapphire substrates by thermal oxidation of metallic zinc

We report the preparation of microcrystalline ZnO thin films on sapphire substrates using a simple method based on the thermal evaporation of metallic Zn in vacuum with further annealing process. The aim of annealing in the oxygen atmosphere in the range of 800–850°C was to obtain the high quality ZnO films. The surface morphology was studied by scanning electron microscopy and atomic force microscopy. The polycrystalline films with ZnO microrods at different stages of their growth were investigated. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064nm in picosecond regime. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications of the investigated materials in the optical switching devices based on refractive index changes.

Radio frequency sputtered zinc oxide thin films with application to metal–semiconductor–metal photodetectors

Zinc oxide (ZnO) films were successfully deposited on silicon, silicon dioxide, and glass substrates by radio frequency magnetron sputtering at different deposition conditions. Field emission scanning electron microscopy, X-ray photoelectron spectroscopy, transmission and photoluminescence measurements were employed to analyze the effect of the deposition conditions and the postdeposition annealing treatment on the surface morphology, structure, chemical deposition and optical properties of ZnO thin films. It was found that the thickness of ZnO films decreased with increased ratio of oxygen/argon and increased temperature. The crystalline and stoichiometric quality of the film was improved by depositing at high temperature and low pressure. Crystals formed more tightly and uniformly with heat treatment under air ambient. The dark current of the ZnO metal–semiconductor–metal photodetector was reduced from 3.06 μA to 96.5 nA at 5 V after postdeposition annealing when compared with that of as-deposited ZnO. Its magnitude was found to be at least two orders lower than that of the as-deposited sample.

GROWTH OF ZnO NANOSTRUCTURES ON ZINC AND Pt SUBSTRATES

Nanocrystalline ZnO of various shapes was obtained without the use of catalysts by dry oxidation of metallic zinc. Oxidation treatments performed below the melting point of Zn (T m = 419°C) led to the formation of flakes-type structure. At 500°C, long nanofibers of circular and uniform cross section covering the surface of the oxidized samples were observed. At 600°C, large density of cone-shape needles covered the oxidized surface. High quality nanocrystals of hexagonal shape were obtained by vapor deposition on Pt substrate. XRD results showed that the lattice parameters of the needles are 1% smaller than those of microcrystalline ZnO .

Properties of ZnO varistor blocks under multiple lightning impulse voltages

Abstract This paper presents the effect of multiple impulse voltages on the electrical and physical properties of a zinc oxide (ZnO) varistor. To investigate the dynamic characteristics of a ZnO varistor subjected to multiple impulse voltages, we designed and fabricated the multiple combination wave generator. The multiple combination wave generator can produce quintuple 1.2/50 μs impulse voltages of 100 kV and quintuple 8/20 μs impulse currents of 12 kA. Applying these voltages and currents, the electrical and physical properties of the ZnO varistor were evaluated. The multiple impulse failures of a ZnO varistor are mainly caused by the surface flashover. When multiple impulse voltages are injected, the charge enhancement near the joined edges of a ZnO varistor and metal electrodes plays a decisive role on the surface flashover or breakdown initiation and developments. Also, after the injection of the quintuple 8/20 μs impulse currents of 10 kA, the residual voltage and quiescent current of the ZnO varistor were changed markedly.

ZnO nanoparticle films prepared by oxidation of metallic zinc in H 2O 2 solution and subsequent process

An efficient and size-controllable three-step method for fabricating ZnO nanoparticle films was described in this paper, which consists of: (1) oxidation of metallic zinc (Zn) in hydrogen peroxide (H 2O 2) solution, (2) spraying of the solution formed in step 1 onto substrates to form precursor films, and (3) annealing of the precursor films in the air to form ZnO nanoparticle films. The crystalline structure and the microstructure of the nanoparticle films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), which indicated that ZnO nanoparticles are in wurzite structure with particle size in the range of 5–25 nm. The size of the ZnO nanoparticles in the films can be controlled by controlling the annealing temperature. In additon, the optical properties of ZnO nanoparticle films, including both UV–vis absorption and photoluminescence (PL), showed typical blue-shift as the gain-size decreased.

Characteristics of surface acoustic wave convolver in the monolithic metal–zinc oxide–silicon nitride–silicon dioxide–silicon structure

The nonlinear analysis of the metal–insulator semiconductor shows that the ac currents charging the interface traps lead to large dc operating voltage and an inefficient operation of the monolithic convolvers. These interface traps are annihilated during a low temperature anneal, which utilizes hydrogen atoms implanted underneath the SiO2–Si interface. The overlay piezoelectric ZnO film in the metal–ZnO–Si3N4–SiO2–Sistructure is protected from the influx of hydrogen atoms by an interposed silicon nitride layer. Hydrogen implantation and rapid thermal annealing steps are integrated in the process sequence of realizing an efficient metal–ZnO–Si3N4–SiO2–Si monolithic surface acoustic wave convolver.

Structure of ZnO films prepared by oxidation of metallic Zinc

ZnO is an n-type, wide band gap semiconductor that exhibits electrooptic and piezoelectric properties and it has a gamut of applications. In this paper, ZnO films were prepared by oxidizing the Zn film deposited by thermal evaporation on glass substrates. The oxidation of Zn films was carried out at different temperatures in two different atmospheres namely oxygen and ozone. The oxidized samples were characterized with regard to their microstructure, phase(s) present, and transmittance in the wavelength range of 200–1000 nm. Zn films have hexagonal phase and flake like structure. After oxidation, wurtzite phase of ZnO is formed. Texture and structure of ZnO films are shown to be dependent on the temperature, time for oxidation and type of the oxidant. The XRD pattern of these films shows the peaks corresponding to both Zn and ZnO phases that indicate incomplete oxidation of the Zn films. Transmittance of these films is low due to incomplete oxidation and impurities present in the starting material.

Electrochemical Synthesis and Characterization of Complexes of Zn and Cd with 2-Pyridinone and 2-Pyrddinemethanethiol-l-Oxide

Abstract The electrochemical oxidation of metallic zinc and cadmium in acetonitrile solutions of 2-pyridinone (HOpy) and 2-pyridinemethanethiol-l-oxide (HPMTO) or its disulphide, 2,2′-dithiodimethyldipyridine-l, l-dioxide (DPMTO), gave the simple complexes Zn(Opy)2.H2O, Cd(Opy)2.H2O, Zn(PMTO)2 and Cd(PMTO)2.3H2O. The mixed complexes Zn(Opy)2bipy.3H2O, Zn(Opy)2phen.4H2O and Cd(Opy)2phen were obtained when the neutral ligands 2,2′-bipyridyl (bipy) or 1,10-phenanthroline (phen) were added to the electrolytic phase. These complexes were characterized by elemental analysis and IR, 1H and 13C NMR spectrometry.

Optical Determination of Cuprous Oxide at Zinc Oxide—Metal Interface of an Oxidized α-Brass

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Interstitial zinc in zinc oxide

Methods of introducing interstitial zinc into single crystals of zinc oxide are described which involve heating the crystals in zinc vapor followed by rapid quenching. The interstitial zinc atoms act as donors with a low ionization energy and they are observed by the extra conductivity which they impart to the crystals. The solubility in atoms/cm 3 from saturated zinc vapor is : n=3.4 × 10 20exp(−0.65 e kT ) . This solubility leads to a reasonable value for the vibrational entropy of the interstitial atom. In the range 180–350°C the diffusion coefficient of the donor obeys: 2 D i= 5.3 × 10 −4exp(−0.55 e kT ) . From these results the parabolic rate constant for the oxidation of metallic zinc may be calculated and the results are in good agreement with previous observations. The results of the high temperature diffusion of radioactive zinc into zinc oxide are less easy to understand and it may be that interstitial zinc is not involved in this process. Evidence is advanced that the defects are interstitial zinc atoms and not oxygen vacancies. The donors normally present in zinc oxide are not interstitial zinc atoms, but may be chemical impurities.