| 1. |
- Ahmad, Mohammed Metwally Gomaa, et al.
(författare)
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Effect of precursor solutions on the structural and optical properties of sprayed NiO thin films
- 2017
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Ingår i: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 64, s. 32-38
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Tidskriftsartikel (refereegranskat)abstract
- Nickel oxide thin films were deposited by a simple and low-cost spray pyrolysis technique using three different precursors: nickel nitrate, nickel chloride, and nickel acetate on corning glass substrates. X-ray diffraction show that the NiO films are polycrystalline and have a cubic crystal structure, although predominantly with a preferred 111-orientation in the growth direction and a random in-plane orientation. The deconvolution of the Ni 2p and O 1s core level X-ray photoelectron-spectra of nickel oxides produced by using different precursors indicates a shift of the binding energies. The sprayed NiO deposited from nickel nitrate has an optical transmittance in the range of 60-65% in the visible region. The optical band gap energies of the sprayed NiO films deposited from nickel nitrate, nickel chloride and nickel acetate are 3.5, 3.2 and 3.43 eV respectively. Also, the extinction coefficient and refractive index of NiO films have been calculated from transmittance and reflectance measurements. The average value of refractive index for sprayed films by nickel nitrate, nickel chloride and nickel acetate are 2.1, 1.6 and 1.85 respectively. It is revealed that the band gap and refractive index of NiO films by using nickel nitrate corresponds to the commonly reported values. We attribute the observed behavior in the optical band gap and optical constants as due to the change of the Ni/O ratio.
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| 2. |
- Alnoor, Hatim, et al.
(författare)
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Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods
- 2015
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 5:8
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Tidskriftsartikel (refereegranskat)abstract
- Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 degrees C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (mu-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.
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| 3. |
- Alnoor, Hatim, et al.
(författare)
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Influence of ZnO seed layer precursor molar ratio on the density of interface defects in low temperature aqueous chemically synthesized ZnO nanorods/GaN light-emitting diodes
- 2016
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 119:16, s. 165702-
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Tidskriftsartikel (refereegranskat)abstract
- Low temperature aqueous chemical synthesis (LT-ACS) of zinc oxide (ZnO) nanorods (NRs) has been attracting considerable research interest due to its great potential in the development of light-emitting diodes (LEDs). The influence of the molar ratio of the zinc acetate (ZnAc): KOH as a ZnO seed layer precursor on the density of interface defects and hence the presence of non-radiative recombination centers in LT-ACS of ZnO NRs/GaN LEDs has been systematically investigated. The material quality of the as-prepared seed layer as quantitatively deduced by the X-ray photoelectron spectroscopy is found to be influenced by the molar ratio. It is revealed by spatially resolved cathodoluminescence that the seed layer molar ratio plays a significant role in the formation and the density of defects at the n-ZnO NRs/p-GaN heterostructure interface. Consequently, LED devices processed using ZnO NRs synthesized with molar ratio of 1:5M exhibit stronger yellow emission (similar to 575 nm) compared to those based on 1:1 and 1:3M ratios as measured by the electroluminescence. Furthermore, seed layer molar ratio shows a quantitative dependence of the non-radiative defect densities as deduced from light-output current characteristics analysis. These results have implications on the development of high-efficiency ZnO-based LEDs and may also be helpful in understanding the effects of the ZnO seed layer on defect-related non-radiative recombination. Published by AIP Publishing.
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| 4. |
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Book of Abstracts : 1st International Workshop on Functional Oxide (FOX) Materials
- 2015
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Proceedings (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Oxide semiconductors are an important part of the functional materials field. Technological accessibility (physical & chemical synthesis), diversity of geometrical shapes (bulk, films, nanostructures) and environmental stability combined with ambience sensitivity makes them promising materials for plenty of future applications. Among other, ZnO, Al2O3, GaO, NiO, TiOx, Gd2O3, Fe3O4 and graphene oxide are considered as materials for both active and passive components in many applications: transparent conductive coatings, gas sensors, biosensors, tomography markers, light emitters, thermoelectric materials, catalysts and many others. We expect the experts to present their latest results on fabrication, characterization and application of the oxide materials.
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| 5. |
- Echresh, Ahmad, et al.
(författare)
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Effect of NiO intermediate layer on the optical and electrical properties of n-ZnO nanorods/p-GaAs heterojunction
- 2015
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Ingår i: Applied Physics A. - : Springer Verlag (Germany). - 0947-8396 .- 1432-0630. ; 119:3, s. 1013-1018
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Tidskriftsartikel (refereegranskat)abstract
- ZnO nanorods were grown hydrothermally on bare and NiO-coated p-GaAs substrate to fabricate p-n heterojunctions. The NiO intermediate layer was deposited using thermal evaporation technique. The X-ray diffraction patterns revealed that ZnO nanorods grown on the bare p-GaAs do not have any preferential orientation along the c-axis, but those on the NiO-coated p-GaAs have preferential orientation along the c-axis, i.e. along the (002) direction. The scanning electron microscope images show that the NiO intermediate layer improved the uniformity and the alignment of the ZnO nanorods. Photoluminescence spectra demonstrated that increasing the thickness of NiO intermediate layer leads to improve the optical quality of the ZnO nanorods. Current-voltage characteristics showed that the presence of the NiO intermediate layer leads to increase the threshold voltage and decrease the leakage current of the n-ZnO nanorods/p-GaAs heterojunction. The energy band diagram of heterojunctions drown using Anderson model revealed that the NiO intermediate layer acts as an electron-blocking layer in the ZnO side and at the same time increases the hole injection from the GaAs to the ZnO side. Therefore, most of electron-hole pair recombination could occur at the ZnO site.
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| 6. |
- Echresh, Ahmad, et al.
(författare)
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High photocurrent gain in NiO thin film/M-doped ZnO nanorods (M = Ag, Cd and Ni) heterojunction based ultraviolet photodiodes
- 2016
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Ingår i: Journal of Luminescence. - : ELSEVIER SCIENCE BV. - 0022-2313 .- 1872-7883. ; 178, s. 324-330
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Tidskriftsartikel (refereegranskat)abstract
- The thermal evaporation method has been used to deposit p-type NiO thin film, which was combined with hydrothermally grown n-type pure and M-doped ZnO nanorods (M=Ag, Cd and Ni) to fabricate a high performance p-n heterojunction ultraviolet photodiodes. The fabricated photodiodes show high rectification ratio and relatively low leakage current. The p-NiO/n-Zn0.94Ag0.06O heterojunction photo diode displays the highest photocurrent gain (similar to 1.52 x 10(4)), a photoresponsivity of similar to 4.48 x 10(3) AW(-1) and a photosensitivity of similar to 13.56 compared with the other fabricated photodiodes. The predominated transport mechanisms of the p-n heterojunction ultraviolet photodiodes at low and high applied forward bias may be recombination-tunneling and space charge limited current, respectively. (C) 2016 Elsevier B.V. All rights reserved.
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| 7. |
- Echresh, Ahmad, et al.
(författare)
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UV photo-detector based on p-NiO thin film/n-ZnO nanorods heterojunction prepared by a simple process
- 2015
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 632, s. 165-171
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Tidskriftsartikel (refereegranskat)abstract
- A UV photo-detector based on p-NiO thin film/n-ZnO nanorods heterojunction was fabricated using a simple two-step fabrication process. The aqueous chemical hydrothermal and thermal evaporation methods were combined to grow the ZnO nanorods and the NiO thin film, respectively. Structural investigation indicated that well aligned ZnO nanorods with hexagonal face having a preferential orientation along the c-axis (002) have been achieved and that the NiO thin film is covering all the ZnO nanorods. X-ray photoelectron spectroscopy (XPS) was used to investigate the band alignment of the heterojunction and the valence and the conduction band offsets were determined to be 1.50 eV and 1.83 eV, respectively. The current-voltage characteristics of the p-NiO thin film/ZnO nanorods heterojunction showed a clear rectifying behavior under both dark and UV illumination conditions. The response of the heterojunction diode was excellent regarding the photocurrent generation. Although other similar heterojunction diodes demonstrated lower threshold voltage, the rectification ratio and the sensitivity of the fabricated diode were superior in comparison to other similar heterojunctions reported recently, implying the vitality of the presented two-step process. (C) 2015 Elsevier B.V. All rights reserved.
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| 8. |
- Elhag, Sami, et al.
(författare)
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Efficient Donor Impurities in ZnO Nanorods by Polyethylene Glycol for Enhanced Optical and Glutamate Sensing Properties
- 2016
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 16:2
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we show that the possibility of using polyethylene glycol (EG) as a hydrogen source and it is used to assist the hydrothermal synthesis of ZnO nanorods (ZNRs). EG doping in ZNRs has been found to significantly improve their optical and chemical sensing characteristics toward glutamate. The EG was found to have no role on the structural properties of the ZNRs. However, the x-ray photoelectron spectroscopy (XPS) suggests that the EG could induce donor impurities effect in ZnO. Photoluminescence (PL) and UV-Vis. spectra demonstrated this doping effect. Mott-Schottky analysis at the ZNRs/electrolyte interface was used to investigate the charge density for the doped ZNRs and showed comparable dependence on the used amount of EG. Moreover, the doped ZNRs were used in potentiometric measurements for glutamate for a range from 10(-6) M to 10(-3) M and the potential response of the sensor electrode was linear with a slope of 91.15 mV/decade. The wide range and high sensitivity of the modified ZNRs based glutamate biosensor is attributed to the doping effect on the ZNRs that is dictated by the EG along with the high surface area-to-volume ratio. The findings in the present study suggest new avenues to control the growth of n-ZnO nanostructures and enhance the performance of their sensing devices.
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| 9. |
- Elhag, Sami, et al.
(författare)
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Habit-modifying additives and their morphological consequences on photoluminescence and glucose sensing properties of ZnO nanostructures, grown via aqueous chemical synthesis
- 2015
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Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 116, s. 21-26
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Tidskriftsartikel (refereegranskat)abstract
- Generally, the anisotropic shape of inorganic nano-crystal can be influenced by one or more of different parameters i.e. kinetic energy barrier, temperature, time, and the nature of the capping molecules. Here, different surfactants acting as capping molecules were used to assist the aqueous chemical growth of zinc oxide (ZnO) nanostructures on Au coated glass substrates. The morphology, crystal quality and the photoluminescence (PL) properties of the ZnO nanostructures were investigated. The PL properties of the prepared ZnO nanostructures at room temperature showed a dominant UV luminescence peak, while the "green yellow" emissions were essentially suppressed. Moreover, the ZnO nanostructures were investigated for the development of a glucose biosensor. An adsorbed molecule has direct contribution on the glucose oxidase/ZnO/Au sensing properties. We show that the performance of a ZnO-based biosensor can be improved by tailoring the properties of the ZnO biomolecule interface through engineering of the morphology, effective surface area, and adsorption capability.
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| 10. |
- Elhag, Sami, et al.
(författare)
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Low-temperature growth of polyethylene glycol-doped BiZn2VO6 nanocompounds with enhanced photoelectrochemical properties
- 2017
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Ingår i: Journal of Materials Chemistry A. - Cambridge : Royal Society of Chemistry. - 2050-7488. ; 5:3, s. 1112-1119
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate scalable, low-cost and low-temperature (<100 °C) aqueous chemical growth of bismuth–zinc vanadate (BiZn2VO6) nanocompounds by BiVO4 growth on ZnO nanobelts (NBs). The nanocompounds were further doped with polyethylene glycol (PEG) to tune the electronic structure of the materials, as a means to lower the charge carrier recombination rate. The chemical composition, morphology, and detailed nanostructure of the BiZn2VO6 nanocompounds were characterized. They exhibit rice-like morphology, are highly dense on the substrate and possess a good crystalline quality. Photoelectrochemical characterization in 0.1 M lithium perchlorate in carbonate propylene shows that BiZn2VO6 nanocompounds are highly suitable as anodes for solar-driven photoelectrochemical applications, providing significantly better performance than with only ZnO NBs. This performance could be attributed to the heterogeneous catalysis effect at nanocompound and ZnO NB interfaces, which have enhanced the electron transfer process on the electrode surface. Furthermore, the charge collection efficiency could be significantly improved through PEG doping of nanocompounds. The photocurrent density of PEG-doped BiZn2VO6 nanocompounds reached values of 2 mA cm−2 at 1.23 V (vs. Ag/AgCl), over 60% larger than that of undoped BiZn2VO6 nanocompounds. Photoluminescence emission experiments confirmed that PEG plays a crucial role in lowering the charge carrier recombination rate. The presented BiZn2VO6 nanocompounds are shown to provide highly competitive performance compared with other state-of-the art photoelectrodes.
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