The Experts below are selected from a list of 10827 Experts worldwide ranked by ideXlab platform
R P H Chang - One of the best experts on this subject based on the ideXlab platform.
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fabrication of ZnO Nanorods and nanotubes in aqueous solutions
Chemistry of Materials, 2005Co-Authors: Vageesh Kumar, Haitao Zhang, Tobin J Marks, R P H ChangAbstract:A novel aqueous solution method has been developed for growing well-aligned crystalline ZnO Nanorods (NRs) and nanotubes (NTs) on a variety of substrates including Si wafers, poly(ethylene terephth...
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growth mechanism and properties of ZnO Nanorods synthesized by plasma enhanced chemical vapor deposition
Journal of Applied Physics, 2004Co-Authors: X Liu, Hui Cao, R P H ChangAbstract:Uniformly distributed ZnO Nanorods have been grown by plasma-enhanced chemical vapor deposition using a two-step process. By controlling the oxygen content in the gas mixture during the nucleation and growth steps, no catalyst is required for the formation of ZnO Nanorods. High-resolution transmission electron microscopy studies show that ZnO Nanorods are single crystals and that they grow along the c axis of the crystal plane. Alignment of these Nanorods with respect to the substrates depends on the lattice mismatch between ZnO and the substrate, the surface electric field, and the amount of defects in the starting nuclei. Room-temperature photoluminescence measurements of these ZnO Nanorods have shown ultraviolet peaks at 380 nm with a full width at half-maximum of 106 meV, which are comparable to those found in high-quality ZnO films. Photoluminescence measurements of annealed ZnO Nanorods in hydrogen and oxygen atmospheres indicate that the origins of green emission are oxygen vacancies and zinc inter...
Ahmad Umar - One of the best experts on this subject based on the ideXlab platform.
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growth properties and dye sensitized solar cells applications of ZnO Nanorods grown by low temperature solution process
Superlattices and Microstructures, 2009Co-Authors: A Alhajry, Ahmad Umar, Yoonbong Hahn, Donghui KimAbstract:Abstract Hexagonal-shaped small ZnO Nanorods were grown in a large-quantity via simple aqueous solution process by using zinc nitrate as a source of zinc ions at low temperature under stirring. The as-grown hexagonal-shaped ZnO Nanorods were characterized in detail in terms of their structural, optical and photovoltaic properties. The detailed structural investigations by HRTEM, SAED and FFT revealed that the as-synthesized ZnO Nanorods are well-crystalline, possessing a perfect hexagonal ideal growth habits of wurtzite zinc oxide and grown along the [0001] direction in preference. The optical properties, composition and quality of the as-synthesized Nanorods were examined by using UV-visible and FTIR spectroscopy. Moreover, films of as-grown Nanorods were used as photoanode materials to fabricate the dye sensitized solar cells (DSSCs). An overall light to electricity conversion efficiency of 0.70% with a fill factor of 47.2%, short-circuit current of 1.8 mA/cm2 and open-circuit voltage of 0.76 V were achieved for the solar cell based on hexagonal-shaped small ZnO Nanorods.
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ultraviolet emitting javelin like ZnO Nanorods by thermal evaporation growth mechanism structural and optical properties
Chemical Physics Letters, 2007Co-Authors: Ahmad Umar, Y B HahnAbstract:Abstract Ultraviolet-emitting, single-crystalline aligned javelin-like zinc oxide (ZnO) Nanorods were synthesized on copper foil by thermal evaporation at low temperature of 500 °C without catalysts or additives. Detailed structural characterizations confirmed that the formed products are single-crystalline, they possess a wurtzite hexagonal phase and are grown along the c -axis direction. Raman-active optical-phonon E 2 mode at 437 cm −1 with sharp and strong UV emission at 381 nm in room-temperature photoluminescence spectrum showed that the obtained ZnO Nanorods have a good crystal quality with excellent optical properties. Moreover, a detailed growth mechanism was proposed for the formation of the javelin-like ZnO Nanorods.
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structural and optical properties of single crystalline ZnO Nanorods grown on silicon by thermal evaporation
Nanotechnology, 2006Co-Authors: Ahmad Umar, B Karunagaran, Yoonbong HahnAbstract:The growth of perfectly hexagonal-shaped ZnO Nanorods, with Zn-terminated (0001) facets bounded with surfaces, has been performed on nickel-coated Si(100) substrate via thermal evaporation using metallic zinc powder and oxygen. Detailed structural investigations confirmed that the synthesized Nanorods are single crystalline with the wurtzite hexagonal phase and preferentially grow along the c-axis direction. Raman spectra of the as-grown ZnO Nanorods showed an optical-phonon E2 mode at 438?cm?1, indicating that as-grown nanostructures are in good crystallinity with the wurtzite hexagonal phase. The ZnO Nanorods were found to show strong band edge emission with very weak or no deep-level emission, as shown by photoluminescence measurements. The clear observation of free excitons at low temperatures (13?50?K) indicates that the as-grown ZnO Nanorods are of high quality.
Huilian Liu - One of the best experts on this subject based on the ideXlab platform.
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low temperature growth and optical properties of ce doped ZnO Nanorods
Applied Surface Science, 2008Co-Authors: Jinghai Yang, Ming Gao, Lili Yang, Yongjun Zhang, Jihui Lang, Dandan Wang, Yaxin Wang, Huilian LiuAbstract:Abstract Ce-doped ZnO Nanorods were prepared by sol–gel method with low annealing temperature of 500 °C. The effects of Ce doping on the structural and optical properties of ZnO Nanorods were investigated in detail. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman-scattering spectroscopy measurements. The XRD results showed that Ce was doped into ZnO Nanorods because of no diffraction peaks of Ce or cerium oxide in the pattern. The synthesis temperature of Ce-doped ZnO Nanorods decreased from 900 to 500 °C compared to that of pure ZnO Nanorods. Compared with pure ZnO, UV peaks shifted towards the blue color and the intensity of visible peaks decreased after Ce doping. The PL properties of Ce-doped ZnO Nanorods depend on both the synthesis temperatures and the dopant. In Raman spectra of doped samples, some classical modes, such as A 1 and E 1 modes, disappear, and the E 2 modes blue shift.
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low temperature growth and optical properties of ZnO Nanorods
Journal of Alloys and Compounds, 2008Co-Authors: Jinghai Yang, Lili Yang, Yongjun Zhang, Jihui Lang, Dandan Wang, Huilian Liu, Hougang FanAbstract:Abstract Zinc oxide (ZnO) Nanorods were grown on ITO conducting glass by the chemical solution deposition method (CBD) in an aqueous solution that contained zinc nitrate hexahydrate (Zn(NO 3 ) 2 ·6H 2 O) and methenamine (C 6 H 12 N 4 ). The size of ZnO Nanorods increased with molar concentration of zinc nitrate, and the Nanorods with different aspect ratios also formed through tuning the reaction time when the molar concentration was 0.1 M. The length of Nanorods increased significantly with the reaction time, but the thickness of the film deposited on the substrate only slightly increased. From the X-ray measurement results, it can be seen that the growth orientation of the as-prepared ZnO Nanorods was [0 0 2]. Photoluminescence measurements were also carried out, the result showed a blue shift in violet emission with the reduction in crystal size.
Magnus Willander - One of the best experts on this subject based on the ideXlab platform.
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Hydrothermal growth of vertically aligned ZnO Nanorods using a biocomposite seed layer of ZnO nanoparticles
Materials, 2013Co-Authors: Zafar Hussain Ibupoto, Mohammad Alsalhi, Anees Ansari, Martin Eriksson, Muhammad Atif, Kimleang Khun, Magnus WillanderAbstract:Well aligned ZnO Nanorods have been prepared by a low temperature aqueous chemical growth method, using a biocomposite seed layer of ZnO nanoparticles prepared in starch and cellulose bio polymers. The effect of different concentrations of biocomposite seed layer on the alignment of ZnO Nanorods has been investigated. ZnO Nanorods grown on a gold-coated glass substrate have been characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. These techniques have shown that the ZnO Nanorods are well aligned and perpendicular to the substrate, and grown with a high density and uniformity on the substrate. Moreover, ZnO Nanorods can be grown with an orientation along the c-axis of the substrate and exhibit a wurtzite crystal structure with a dominant (002) peak in an XRD spectrum and possessed a high crystal quality. A photoluminescence (PL) spectroscopy study of the ZnO Nanorods has revealed a conventional near band edge ultraviolet emission, along with emission in the visible part of the electromagnetic spectrum due to defect emission. This study provides an alternative method for the fabrication of well aligned ZnO Nanorods. This method can be helpful in improving the performance of devices where alignment plays a significant role.
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Comparative study of ZnO Nanorods and thin films for chemical and biosensing applications and the development of ZnO Nanorods based potentiometric strontium ion sensor
Applied Surface Science, 2013Co-Authors: Kimleang Khun, Zafar Hussain Ibupoto, Chan Oeurn Chey, Omer Nur, Magnus WillanderAbstract:In this study, the comparative study of ZnO Nanorods and ZnO thin films were performed regarding the chemical and biosensing properties and also ZnO Nanorods based strontium ion sensor is proposed. ...
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effect of different seed solutions on the morphology and electrooptical properties of ZnO Nanorods
Journal of Nanomaterials, 2012Co-Authors: Muhammad Kashif, Zafar Hussain Ibupoto, U Hashim, Md Eaqub Ali, Syed Usman M Ali, M Rusop, Magnus WillanderAbstract:The morphology and electrooptical properties of ZnO Nanorods synthesized on monoethanolamine-based seed layer and KOH-based seed layer were compared. The seed solutions were prepared in monoethanolamine in 2-methoxyethanol and potassium hydroxide in methanol, respectively. Zinc acetate dihydrate was as a common precursor in both solutions. The nanorod-ZnOs were synthesized via the spin coating of two different seed solutions on silicon substrates followed by their hydrothermal growth. The scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and Raman studies revealed that the ZnO Nanorods obtained from monoethanolamine-based seed layer had fewer defects, better crystals, and better alignment than those realized via KOH-based seed layer. However, the current-voltage (I-V) characteristics demonstrated better conductivity of the ZnO Nanorods obtained via KOH-based seed layer. The current measured in forward bias was 4mA and 40 µA for ZnO-Nanorods grown on KOH-based seed layer and monoethanolamine-based with the turn on voltage of approximately 1.5 V and 2.5V, respectively, showing the feasibility of using both structures in optoelectric devices.
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Growth and Structure of ZnO Nanorods on a Sub-Micrometer Glass Pipette and Their Application as Intracellular Potentiometric Selective Ion Sensors
MDPI AG, 2010Co-Authors: Lars Hultman, Magnus Willander, Omer Nur, Ulrika H. Englund, Fredrik Elinder, Cecilia Brännmark, Peter Strålfors, Muhammad H. AsifAbstract:This paper presents the growth and structure of ZnO Nanorods on a sub-micrometer glass pipette and their application as an intracellular selective ion sensor. Highly oriented, vertical and aligned ZnO Nanorods were grown on the tip of a borosilicate glass capillary (0.7 µm in diameter) by the low temperature aqueous chemical growth (ACG) technique. The relatively large surface-to-volume ratio of ZnO Nanorods makes them attractive for electrochemical sensing. Transmission electron microscopy studies show that ZnO Nanorods are single crystals and grow along the crystal’s c-axis. The ZnO Nanorods were functionalized with a polymeric membrane for selective intracellular measurements of Na+. The membrane-coated ZnO Nanorods exhibited a Na+-dependent electrochemical potential difference versus an Ag/AgCl reference micro-electrode within a wide concentration range from 0.5 mM to 100 mM. The fabrication of functionalized ZnO Nanorods paves the way to sense a wide range of biochemical species at the intracellular level
Yunfa Che - One of the best experts on this subject based on the ideXlab platform.
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highly formaldehyde sensitive transition metal doped ZnO Nanorods prepared by plasma enhanced chemical vapor deposition
Sensors and Actuators B-chemical, 2012Co-Authors: Dangwe Zhang, Yunfa CheAbstract:One of the challenges in realizing metal oxide semiconductor gas sensors is to enhance the sensitivity of active materials in order to respond to the low concentration of detecting gases effectively and efficiently. In this report, transition metals such as Mn. Ni, Cu, and Co are used as dopants for the synthesis of highly formaldehyde-sensitive ZnO Nanorods prepared by plasma enhanced chemical vapor deposition (PECVD) method. All the doped ZnO Nanorods show improved formaldehyde-sensitivity as compared to undoped ZnO Nanorods, and a gas sensitivity maximum of similar to 25/ppm was obtained by using 10 mol% CdO activated 1.0 mol% Mn doped ZnO Nanorods. Moreover, the ZnO Nanorods have a higher sensitivity as compared to ZnO nanomaterials prepared by other methods such as precipitation and hydrothermal, which can be attributed to the abundant crystal defects induced by the dopants in a short crystallization process in this PECVD method. (C) 2012 Elsevier B.V. All rights reserved.
