Growth and electron field-emission of single-crystalline ZnO nanowires (original) (raw)
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Field emission studies on electrochemically synthesized ZnO nanowires
Ultramicroscopy, 2009
Nanocrystalline zinc oxide (ZnO) films were synthesized using cathodic reduction of Zn foil in aqueous electrolyte of different molar concentrations containing ZnCl 2 and H 2 O 2 , followed by annealing at 400 1C in air. An X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were used for characterization. The XRD patterns exhibited a set of well-defined diffraction peaks corresponding to the wurtzite phase of ZnO. SEM and TEM images clearly revealed the formation of randomly oriented ZnO nanowires having lengths of several microns and diameters less than 100 nm. From the field emission studies, the threshold field values, required to draw emission current density of 1mA/cm2werefoundtobe1.44,1.36and1.5V/mmfornanowiressynthesizedusing0.002,0.004and0.016Melectrolyteconcentrations,respectively.AllFolwer−Nordheim(F−N)plotsshowednon−linearbehaviorindicatingsemiconductingnatureoftheemitters.TheZnOnanowiresexhibitedgoodemissioncurrentstabilityatthepre−setvalueof1 mA/cm 2 were found to be 1.44, 1.36 and 1.5 V/mm for nanowires synthesized using 0.002, 0.004 and 0.016 M electrolyte concentrations, respectively. All Folwer-Nordheim (F-N) plots showed non-linear behavior indicating semiconducting nature of the emitters. The ZnO nanowires exhibited good emission current stability at the pre-set value of 1mA/cm2werefoundtobe1.44,1.36and1.5V/mmfornanowiressynthesizedusing0.002,0.004and0.016Melectrolyteconcentrations,respectively.AllFolwer−Nordheim(F−N)plotsshowednon−linearbehaviorindicatingsemiconductingnatureoftheemitters.TheZnOnanowiresexhibitedgoodemissioncurrentstabilityatthepre−setvalueof10 mA over a duration of 6 h. The simplicity of the synthesis route coupled with the promising emission properties made the electrochemically synthesized ZnO nanowires a suitable candidate for high-current density applications.
Journal of Nanoengineering and Nanomanufacturing, 2012
Crystalline hexagonal wurtzite nanowires of ZnO were prepared by thermal evaporation method from zinc foil with zinc microparticles in air atmosphere. The nanowires have been characterized by a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), energy dispersive X-ray spectrometer (EDS), Raman spectroscopy, UV-Vis absorption and room temperature photoluminescence (PL). SEM and STEM images show that as-obtained ZnO nanowires have diameters in the range between 40 nm and 60 nm and length up to 30 m. The Raman spectrum of the ZnO nanowires were obtained and compared with the corresponding spectrum of the bulk ZnO. The optical band gap is found to be 3.34 eV. PL measurements show that the nanowires present a strong UV emission peak at 487 nm (2.54 eV) accompanied by other peaks of relatively lower intensities. This emission is due to the existence of various defects in the fabricated nanowires. These nanowires have potential in applications such as optoelectronics.
Optical Investigation of ZnO Nanowires
Acta Physica Polonica A, 2010
In this study we report the application of synchrotron X-ray fluorescence, photoluminescence and Raman scattering techniques to the analysis of the incorporation of impurities in unintentionally doped ZnO nanowires. Highly ordered one-dimensional ZnO arrays were fabricated by an oxidation process of Zn metal electrodeposited in nanoporous anodic alumina template. X-ray fluorescence data show the contribution of residual elements into the ZnO nanowires growth. A rough analytical quantification of the main light and heavy chemical contents derives impurity concentrations below 1%. The optical efficiency of ZnO nanowires is strongly affected by non-radiative centers up to temperatures as low as 100 K. The photoluminescence was found to be totally dominated by optical transitions associated with the anodic alumina template. Finally, the Raman scattering provides no evidence of local vibrational modes or secondary phases, but it shows the unambiguous signature of the ZnO hexagonal phase.
Growth and characterization of ZnO nanowires for optical applications
Laser Physics, 2013
In the present work, cerium oxide CeO 2 nanoparticles were synthesized by the sol-gel method and used for the growth of ZnO nanorods. The synthesized nanoparticles were studied by x-ray diffraction (XRD) and Raman spectroscopic techniques. Furthermore, these nanoparticles were used as the seed layer for the growth of ZnO nanorods by following the hydrothermal growth method. The structural study of ZnO nanorods was carried out by means of field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and XRD techniques. This study demonstrated that the grown ZnO nanorods are well aligned, uniform, of good crystal quality and have diameters of less than 200 nm. Energy dispersive x-ray (EDX) analysis revealed that the ZnO nanorods are composed only of zinc, cerium as the seed atom, and oxygen atoms, with no other impurities in the grown nanorods. Moreover, a photoluminescence (PL) approach was applied for the optical characterization, and it was observed that the near-band-edge (NBE) emission was the same as that of the zinc acetate seed layer, however the green and orange/red emission peaks were slightly raised due to possibly higher levels of defects in the cerium oxide seeded ZnO nanorods. This study provides an alternative approach for the controlled synthesis of ZnO nanorods using cerium oxide nanoparticles as the seed nucleation layer, improving both the morphology of the nanorods and the performance of devices based upon them.
The vibration and photoluminescence properties of one-dimensional ZnO nanowires
Journal of Crystal Growth, 2005
Under argon-and oxygen-mixed atmosphere, the vapor-liquid-solid method was introduced to fabricate the ZnO nanowires at 700-1000 1C. As grown on Au-coated Si substrate, the single-crystalline ZnO one-dimensional structure was obtained. From XRD patterns, the growth orientation of nanowires was /0 0 2S along the c-axis. Two emission bands were observed in PL spectra, one is UV emission at 380nmandtheotherisagreenemissionat380 nm and the other is a green emission at 380nmandtheotherisagreenemissionat500 nm. The oxygen vacancies were assigned to result in green emission and influenced the vibration energy. By means of annealing at oxygen atmosphere, the vacancies and residual stress were eliminated effectively. This phenomenon was evidenced by XRD patterns and Raman spectrum. Through this easy, rapid and low-cost method, the high-quality ZnO nanowires were obtained. r
Current Applied Physics, 2011
In this paper the effect of source temperature on the morphological and optical properties of ZnO nanowires using a thermal evaporation set-up was investigated. A simple horizontal double-tube system was used to grow the ZnO nanowires. The nanowires with different morphology were obtained by the same substrate temperature and different source temperatures. Vertical and aligned nanowires with hexagonal shape were grown at the source temperature of 950 C, while the nanowires with spear shape were grown at the source temperature of 1050 C. The diameters of nanowires were the same for the both set of nanowires, approximately. In addition, characterizations showed that the growth direction of the both set of nanowires was [0001]. Room temperature photoluminescence and Raman spectroscopy studies demonstrated that the ZnO nanowires were grown in lower source temperature zone had better crystalline quality and optical properties than those were grown by higher source temperature.
ZnO nanowires formed on tungsten substrates and their electron field emission properties
Applied Physics Letters, 2003
Using a vapor transport method, ZnO nanowires were selectively synthesized both on tungsten tips as electron field emitters and on tungsten plates with designed patterns. Control of the growth locations of the nanowires was accomplished by selectively positioning a thin film of Au catalyst. The angular intensity and fluctuation of the field emission current from the ZnO nanowires synthesized on tungsten tips have been demonstrated to be similar to those of carbon nanotubes. A self-destruction limit of ∼0.1 mA/sr for angular intensity was observed, and the power spectra showed a 1/f3/2 characteristic from 1 Hz to 6 kHz.
Low temperature growth of aligned ZnO nanowires and their application as field emission cathodes
Materials Chemistry and Physics, 2010
Aligned ZnO nanowires have been synthesized by annealing gold deposited zinc foil in air at 400 • C. The X-ray diffraction pattern indicates formation of ZnO possessing hexagonal wurtzite structure along with binary phases like Au 3 Zn and AuZn 3 . The scanning electron microscope images depict presence of densely distributed aligned ZnO nanowires, having length of several microns and diameter in the range of 40-80 nm. The transmission electron microscope and selected area electron diffraction analysis confirms the nanocrystalline nature of the ZnO wires exhibiting preferential growth along the [0 0 1] direction. Based on the microscopic analysis a possible growth mechanism of the ZnO nanowires is presented. From the field emission studies, the value of the turn-on field corresponding to an emission current density of 0.1 A cm −2 is found to be 2.4 V m −1 and a current density of 100 A cm −2 is obtained at an applied field of 3.4 V m −1 . The field emission current stability investigated over a period of 3 h at the preset value of 1 A is found to be promising. The simplicity of the synthesis rout coupled with the promising field emission properties offer unprecedented advantage for the use of ZnO field emitters for high current density applications.
Influence of geometrical properties on light emission of ZnO nanowires
Optical Materials, 2007
The present paper deals with the preparation and study of optical properties of ZnO nanowires. Nanoporous ion track polycarbonate foils were used as templates for ZnO nanowires growth by electrochemical deposition. The growth was performed using an aqueous electrochemical bath at a temperature of 70°C. SEM and TEM were employed to study the morphological properties of the nanowires. Electron diffraction was employed for structural characterization. Reflection and photoluminescence spectroscopy were used for optical characterization. A comparison between the properties of electrodeposited thin films and nanowires of ZnO was made from the point of view of photoluminescence properties.
Vertical single-crystal ZnO nanowires grown on ZnO:Ga/glass templates
IEEE Transactions on Nanotechnology, 2005
Vertical single-crystal ZnO nanowires with uniform diameter and uniform length were selectively grown on ZnO : Ga/glass templates at 600 C by a self-catalyzed vapor-liquid-solid process without any metal catalyst. It was found that the ZnO nanowires are grown preferred oriented in the (002) direction with a small X-ray diffraction full-width half-maximum. Photoluminescence, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy measurements also confirmed good crystal quality of our ZnO nanowires. Field emitters using these ZnO nanowires were also fabricated. It was found that threshold field of the fabricated field emitters was 14 V/ m. With an applied electric field of 24 V/ m, it was found that the emission current density was around 0.1 mA/cm 2 Index Terms-Field emission, field-emission scanning electron microscopy (FESEM), glass, high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), vapor-liquid-solid (VLS) process, X-ray diffraction (XRD), ZnO nanowires.