One-dimensional Zinc Oxide Nanostructures Research Articles

Low-Temperature Vapor-Solid Growth of ZnO Nanowhiskers for Electron Field Emission

One-dimensional zinc oxide nanostructures have aroused interest from scientists and engineers for electron field emission applications because of their experimentally accessible high aspect ratio in combination with their low work function. A comprehensive study of the vapor-solid growth of zinc oxide (ZnO) nanowhiskers by utilizing zinc acetylacetonate hydrate and oxygen at low temperature (580 °C) is reported herein. The nanowhiskers morphology was investigated by varying different growth parameters, such as temperature, substrate type and position, gas flow, precursor amount, and growth time. According to the obtained parameter dependences, the process was optimized to achieve homogenous crystalline nanowhiskers with high aspect ratios and clearly defined surface facets and tips. We show electron field emission measurements from tailor-made ZnO nanowhiskers grown on n-doped silicon, titanium thin films, and free-standing silicon nitride membranes, revealing field emission turn-on fields significantly lower compared to a perfect flat ZnO thin film. Especially the latter devices—ZnO nanowhiskers on a free-standing membrane—might pave the way into a novel nanomembrane detector unit in proteomics, which can significantly extend the mass range of current time-of-flight mass spectrometers.

Manufacturing process, characterization and optical investigation of amorphous 1D zinc oxide nanostructures

The purpose of this article was to produce amorphous ZnO nanowires via the electrospinning process from a polyvinylpyrrolidone (PVP)/zinc acetate dihydrate (Zn(COOH)2)/dimethylformamide (DMF) and ethanol (EtOH) solution. The as obtained nanofibers were calcined at temperatures ranging from 400 to 600 °C to remove the organic phase. The one-dimensional zinc oxide nanostructures were studied using a scanning electron microscope (SEM) and a transmission electron microscope (TEM) to analyse the influence of the used temperature on the morphology and structures of the obtained ceramic nanomaterials. In order to examine the chemical structure of nanowires, the energy dispersive spectrometry (EDX) was used. Besides, a thermogravimetric analysis (TGA) was performed to show the polymer concentration loss in a function of temperature in order to obtain pure zinc oxide nanowires. The optical property analysis was performed on the basis of UV–vis spectra of absorbance as a function of the wavelength. Using the modified Swanepoel method, which the authors proposed, and the recorded absorbance spectra determined the banded refractive index n, real n′ and imaginary k part of the refractive index as a function of the wavelength, complex dielectric permeability ɛ, real and imaginary part εr and εi of the dielectric permeability as a function of the radiation energy of the produced ZnO nanowires.

Electrochemical synthesis of one-dimensional ZnO nanostructures on ZnO seed layer for DSSC applications

Abstract Electrochemical deposition of vertically aligned zinc oxide (ZnO) nanorods were prepared on ZnO seeded fluorine doped tin oxide (FTO) substrate in the solutions consisting of different concentrations of hexamethylenetetramine (HMTA). The electrochemical, structural, morphological, vibrational and optical properties were characterized by cyclic voltammetry (CV), X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectroscopy and photoluminescence (PL) spectroscopy, respectively. CV curves confirm that metallic zinc phase is not deposited as the HMTA concentration is about 9 mM in a deposition solution. XRD patterns of the as-prepared films show that the increasing HMTA concentrations from 0 mM to 9 mM not only increase the formation of zinc hydrate chloride (Zn 5 (OH) 8 Cl 2 ·H 2 O) but also decrease and finally disappear the metallic Zn deposition. After the as-prepared films annealed at 450 ° C, the crystalline phases of Zn and Zn 5 (OH) 8 Cl 2 ·H 2 O are completely converted to ZnO hexagonal wurtzite phase with high intense growth (002) plane orientation. SEM images support that the vertical growth of ZnO nanostructures (nanorods and petals) with a few flowers is found to be in the cordillera structure as the films are deposited in the solutions consisting of 3 mM, 6 mM and 9 mM HMTA respectively. Raman and PL spectra confirm that the ZnO film deposited in the solution consisting of 9 mM HMTA has a higher crystalline nature with lesser atomic defects and is also higher c-axis growth than that of other films deposited in the solutions consisting of 0 mM, 3 mM and 6 mM, respectively. UV–vis absorbance spectra corroborate that the ZnO film deposited in the solution consisting of 9 mM HMTA shows a high dye absorbance as compared with other films. The efficiency of DSSCs based on ZnO photoanodes deposited in the solutions consisting of 0 mM and 9 mM HMTA was 1.79 and 3.75%, respectively. Electrochemical impedance spectra revealed that DSSC based on ZnO photoanode deposited in the solution consisting of 9 mM HMTA has a higher charge recombination resistance (Rrec) than that of another DSSC.

One-dimensional ZnO nanostructures: fabrication, optoelectronic properties, and device applications

One-dimensional (1D) zinc oxide (ZnO) nanostructures have been extensively and intensively studied for several decades not only for their extraordinary chemical and physical properties, but also for their current and future different electronic and optoelectronic device applications. This review provides a brief overview of the progress of different synthesis methods and applications of 1D-ZnO nanostructures. Morphology of ZnO nanostructures grown by various methods and progress in the optical properties are briefly described. Using low-temperature photoluminescence (LTPL) study, detailed informations about the defect states and impurity of such nanostructures are reported. Improvement of field emission properties by modifying the edge of 1D-ZnO nanostructures is briefly discussed. Applications such as different sensors, field effect transistor, light-emitting diodes (LEDs), and photodetector are briefly reviewed. ZnO has large exciton binding energy (60 meV) and wide band gap (3.37 eV), which could lead to lasing action based on exciton recombination. As semiconductor devices are being aggressively scaled down, ZnO 1D nanostructures based resistive switching (RS) memory (resistance random access memory) is very attractive for nonvolatile memory applications. Switching properties and mechanisms of Ga-doped and undoped ZnO nanorods/NWs are briefly discussed. The present paper reviews the recent activities of the growth and applications of various 1D-ZnO nanostructures for sensor, LED, photodetector, laser, and RS memory devices.

Scalable synthesis and device integration of self-registered one-dimensional zinc oxide nanostructures and related materials

On integrating one-dimensional (1D) nanocrystals (nanowires) to useful devices, in this review article, we provide a background on vapor-based growth processes and how they impact device integration strategies. Successful integration of nanowires to devices and their scalability simply rely on where and how nanowires are formed, how they are interfaced to other device components and how they function. In this direction, we will provide a discussion on developed growth strategies for lateral and standing growth of semiconductor nanostructures and assess their success in addressing current challenges of nanotechnology such as mass integration of nanowires, and the necessary accuracy in their positioning and alignment. In this regard, we highlight some of our recent work on formation of two-dimensional (2D)- and three-dimensional (3D)- nanowire and nanowall arrays and provide an overview of their structural and electro-optical properties. This will be followed by discussing potential applications of such hierarchical assemblies in light generation, photocatalysis and conversion of motion to electricity.

Controlled Growth of one-dimensional zinc oxide nanostructures in the pulsed electrodeposition mode

Zinc oxide nanostructures are objects of study in the field of optoelectronics, solar power engineering, nanosensorics, and catalysis. For the purpose of the controlled growth of one-dimensional submicrometer zinc oxide structures in the pulsed electrodeposition mode, the effect of the pulse electrolysis parameters on the morphology of ZnO layers, their optical properties, and structural and substructural characteristics is determined using X-ray diffraction, optical spectrophotometry, and atomic-force microscopy. The possibility of fabricating arrays of ZnO nanowires with different geometrical shapes, perpendicular to the substrate surface, by varying the frequency of cathode-substrate potential pulses is shown.

Synthesis and Properties of One-dimensional ZnO Nanostructures and their Integration into Dye-sensitive Solar Cells

Zinc oxide (ZnO) is a wide-band gap IIb-I compound with wurtzite crystal structure, and possesses semiconducting, pyroelectric, piezoelectric, biosafe and biocompatible properties. With these unique characteristics, ZnO becomes one of the most important nanomaterials in scientific research and applications nowadays. The diversity of ZnO nanostructures gives the promising solution to many fields of nanotechnology research, such as dye-sensitized solar cells (DSSCs). As a low-cost alternative to conventional silicon-based or TiO2-based photovoltaic, one-dimensional (1D) ZnO nanomaterials exhibit remarkable potentials and meet the clean energy demand. The aim of this review is to present a brief overview for the preparation methods and properties of 1D ZnO nanotructures and describe their integration into the DSSCs field. In the end, the perspectives of the 1D ZnO nanostructures applied in DSSCs field are introduced. Keywords: Zinc Oxide (ZnO), One-dimension (1D), Nanostructure dye-sensitive solar cell (DSSC).

Zinc Oxide Nanostructures by Solvothermal Synthesis

The synthesis, characterization, and properties of three types of one-dimensional zinc oxide nanostructures are described. They were obtained by solvothermal treatment of nanometric zinc oxide as zinc ion source (i.e., starting from pure oxide), from a mixture of the oxide with stearic acid, and from intercalated oxide in the layered nanocomposite ZnO(stearic acid)0.38. The reactions were performed at 180°C in a (1:1) ethanol/water mixture. Depending on the precursor and reaction times, morphologically homogenous phases corresponding to ZnO nanoneedles, nanorods or nanowires were obtained. Photoluminescence emissions were observed and are attributed to exciton transitions and to the presence of intrinsic defects such as oxygen and zinc interstitials. The band gap energies (Eg) were comparable to the values of bulk ZnO. The prepared nanostructures showed photocatalytic activities with respect to the degradation of methylene blue which were comparable to that of bulk zinc oxide.

Size- and Surface-dependent Stability, Electronic Properties, and Potential as Chemical Sensors: Computational Studies on One-dimensional ZnO Nanostructures

The structures and electronic properties of zinc oxide (ZnO) one-dimensional (1D) nanostructures, including nanowires with hexagonal or triangular cross sections, faceted nanotubes, and conventional single-walled nanotubes, were investigated using density functional theory. The binding energies and band gaps of ZnO 1D nanostructures are determined by surface atom ratios and sizes. Hydrogen passivation preserves semiconducting characteristics and further enhances the band gap of ZnO nanowires. ZnO nanowires are potential chemical sensors for dioxin.

Quasi One-dimensional ZnO Nanostructures Fabricated without Catalyst at Lower Temperature

One- or quasi one-dimensional zinc oxide nanostructures possess plenty of morphologies. Only by controlling the gas flow rates, and partial pressures of argon, oxygen and zinc vapor, can various types of high-quality ZnO nanomaterials (such as wires, belts, arrays, saws or combs, tetraleg rods, nails, and pins) be synthesized through pure zinc powder evaporation without a catalyst at the temperature range of 600–700°C. In this study, deposited nanostructures were characterized by means of scanning electron microscopy, X-ray diffraction and high-resolution transmission electron microscopy. The authors propose and discuss the growth mechanisms of various ZnO. In addition, properties of room temperature photoluminescence and field emission of several typical ZnO nanostructures are measured and investigated.

Deposition and characterization of a novel integrated ZnO nanorods/thin film structure

One-dimensional (1-D) ZnO (zinc oxide) nanostructures have received a lot of attention due to their superior properties. Various techniques have been developed to synthesize ZnO nanorods at high-temperature process using vapor–liquid–solid (VLS) mechanism. In this paper, we report a novel process to synthesize integrated ZnO nanorods/thin film structures using an RF magnetron sputter deposition under different deposition parameters and substrate conditions. The substrate used was glass plated with electroless Cu prepared using various conditions. The resulting specimens are analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The effect of the copper surface roughness was found to be significant. ZnO nanorods were found only when the copper layer is rough enough. The roughness of the copper in general increases with the plating time and/or the ratio of V HCHO/ V Cu used in the plating bath. Post-plating annealing of the copper was also found to increase the surface roughness of the copper.

Field emission from one-dimensional nanostructured zinc oxide

In this paper, the field emission characteristics of one-dimensional zinc oxide nanostructures are reviewed based on our works. The cold electron emission behaviours of zinc oxide nanowires, nanopins and vertical aligned nanofibres are studied. The factors that influence the electron emission process such as the geometry and the energy level structure of nanostructured zinc oxide are discussed in theory and experiment. Good field emission performances have been obtained from the vertical aligned nanofibre with sharp tips and gallium doping.