| 1. |
- Adam, Rania Elhadi, 1978-, et al.
(författare)
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Synthesis of Mg-doped ZnO NPs via a chemical low-temperature method and investigation of the efficient photocatalytic activity for the degradation of dyes under solar light
- 2020
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Ingår i: Solid State Sciences. - : Elsevier. - 1293-2558 .- 1873-3085. ; 99
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Tidskriftsartikel (refereegranskat)abstract
- Doped semiconductors nanostructures (NSs) have shown great interest as a potential for green and efficient photocatalysis activities. Magnesium (Mg)-doped zinc oxide (ZnO) nanoparticles (NPs) has been synthesized by a one-step chemical low temperature (60 °C) co-precipitation method without further calcination and their photocatalytic performance for photodegradation of Methylene blue (MB) dye under the illumination of solar light is investigated. The crystal structure of the synthesized NPs is examined by X-ray diffraction (XRD). XRD data indicates a slight shift towards higher 2θ angle in Mg-doped samples as compared to the pure ZnO NPs which suggest the incorporation of Mg2+ into ZnO crystal lattice. X-ray photoelectron spectroscopy (XPS), UV–Vis spectrophotometer and cathodoluminescence (CL) spectroscopy, were used to study electronics, and optical properties, respectively. The XPS analysis confirms the substitution of the Zn2+ by the Mg2+ into the ZnO crystal lattice in agreement with the XRD data. The photocatalytic activities showed a significant enhancement of the Mg-doped ZnO NPs in comparison with pure ZnO NPs. Hole/radical scavengers were used to reveal the mechanism of the photodegradation. It was found that the addition of the Mg to the ZnO lattices increases the absorption of the hydroxyl ions at the surface of the NPs and hence acts as a trap site leading to decrease the electron-hole pair and consequently enhancing the photodegradation.
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| 2. |
- Alnoor, Hatim, et al.
(författare)
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An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods
- 2017
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:21
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an efficient possibility to synthesize vertically aligned pure zinc oxide (ZnO) and Co-doped ZnO nanorods (NRs) using the low-temperature aqueous chemical synthesis (90 degrees C). Two different mixing methods of the synthesis solutions were investigated for the Co-doped samples. The synthesized samples were compared to pure ZnO NRs regarding the Co incorporation and crystal quality. Electron paramagnetic resonance (EPR) measurements confirmed the substitution of Co2+ inside the ZnO NRs, giving a highly anisotropic magnetic Co2+ signal. The substitution of Zn2+ by Co2+ was observed to be combined with a drastic reduction in the core-defect (CD) signal (g similar to 1.956) which is seen in pure ZnO NRs. As revealed by the cathodoluminescence (CL), the incorporation of Co causes a slight red-shift of the UV peak position combined with an enhancement in the intensity of the defect-related yellow-orange emission compared to pure ZnO NRs. Furthermore, the EPR and the CL measurements allow a possible model of the defect configuration in the samples. It is proposed that the as-synthesized pure ZnO NRs likely contain Zn interstitial (Zn-i(+)) as CDs and oxygen vacancy (V-O) or oxygen interstitial (O-i) as surface defects. As a result, Co was found to likely occupy the Zn-i(+), leading to the observed CDs reduction and hence enhancing the crystal quality. These results open the possibility of synthesis of highly crystalline quality ZnO NRs-based diluted magnetic semiconductors using the low-temperature aqueous chemical method. Published by AIP Publishing.
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| 3. |
- 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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| 4. |
- Alnoor, Hatim, et al.
(författare)
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Exploring MXenes and their MAX phase precursors by electron microscopy
- 2021
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Ingår i: Materials Today Advances. - : Elsevier. - 2590-0498. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- This review celebrates the width and depth of electron microscopy methods and how these have enabled massive research efforts on MXenes. MXenes constitute a powerful recent addition to 2-dimensional materials, derived from their parent family of nanolaminated materials known as MAX phases. Owing to their rich chemistry, MXenes exhibit properties that have revolutionized ranges of applications, including energy storage, electromagnetic interference shielding, water filtering, sensors, and catalysis. Few other methods have been more essential in MXene research and development of corresponding applications, compared with electron microscopy, which enables structural and chemical identification at the atomic scale. In the following, the electron microscopy methods that have been applied to MXene and MAX phase precursor research are presented together with research examples and are discussed with respect to advantages and challenges.
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| 5. |
- 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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| 6. |
- Alnoor, Hatim, et al.
(författare)
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Seed layer synthesis effect on the concentration of interface defects and emission spectra of ZnO nanorods/p-GaN light-emitting diode
- 2017
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Ingår i: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 214:1
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Tidskriftsartikel (refereegranskat)abstract
- As the low-temperature aqueous chemical synthesis (LT-ACS), holds great promises for the synthesis of one-dimensional (1D) ZnO nanostructure-based light-emitting diodes (LEDs) and hence require parameter tuning for optimal performance. N-ZnO nanorods (NRs)/p-GaN heterojunction LEDs have been synthesized by the LT-ACS using ZnO nanoparticle (NPs) seed layers prepared with different precursor solutions. The effect of these seed layers on the interface defect properties and emission intensity of the as-synthesized n-Zn/p-GaN heterojunction LEDs has been demonstrated by spatially resolved cathodoluminescence (CL) and electroluminescence (EL) measurements, respectively. A significant reduction of the interface defects in the n-ZnO NRs/p-GaN heterostructure synthesized from a seed layer prepared from zinc acetate (ZnAc) with a mixture of potassium hydroxide (KOH) and hexamethylenetetramine (HMTA) (donated as ZKH seed) compared with those prepared from ZnAc and KOH (donated as ZK seed) is observed as revealed by spatially resolved CL. Consequently, the LEDs based on n-ZnO NRs/p-GaN prepared from ZKH seed show an improvement in the yellow emission (approximate to 578nm) compared to that based on the ZK seed as deduced from the electroluminescence measurements. The improvement in the yellow EL emission on the ZKH LED probably attributed to the low presence of the non-radiative defect as deduced by light-output current (L-I) characteristics analysis.
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| 7. |
- Alnoor, Hatim, 1979-
(författare)
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Toward the Optimization of Low-temperature Solution-based Synthesis of ZnO Nanostructures for Device Applications
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One-dimensional (1D) nanostructures (NSs) of Zinc Oxide (ZnO) such as nanorods (NRs) have recently attracted considerable research attention due to their potential for the development of optoelectronic devices such as ultraviolet (UV) photodetectors and light-emitting diodes (LEDs). The potential of ZnO NRs in all these applications, however, would require synthesis of high crystal quality ZnO NRs with precise control over the optical and electronic properties. It is known that the optical and electronic properties of ZnO NRs are mostly influenced by the presence of native (intrinsic) and impurities (extrinsic) defects. Therefore, understanding the nature of these intrinsic and extrinsic defects and their spatial distribution is critical for optimizing the optical and electronic properties of ZnO NRs. However, identifying the origin of such defects is a complicated matter, especially for NSs, where the information on anisotropy is usually lost due to the lack of coherent orientation.Thus, the aim of this thesis is towards the optimization of the lowtemperature solution-based synthesis of ZnO NRs for device applications. In this connection, we first started with investigating the effect of the precursor solution stirring durations on the deep level defects concentration and their spatial distribution along the ZnO NRs. Then, by choosing the optimal stirring time, we studied the influence of ZnO seeding layer precursor’s types, and its molar ratios on the density of interface defects. The findings of these investigations were used to demonstrate ZnO NRs-based heterojunction LEDs. The ability to tune the point defects along the NRs enabled us further to incorporate cobalt (Co) ions into the ZnO NRs crystal lattice, where these ions could occupy the vacancies or interstitial defects through substitutional or interstitial doping. Following this, high crystal quality vertically welloriented ZnO NRs have been demonstrated by incorporating a small amount of Co into the ZnO crystal lattice. Finally, the influence of Co ions incorporation on the reduction of core-defects (CDs) in ZnO NRs was systematically examined using electron paramagnetic resonance (EPR).
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| 8. |
- Chey, Chan Oeurn, et al.
(författare)
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Fast piezoresistive sensor and UV photodetector based on Mn-doped ZnO nanorods
- 2015
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Ingår i: Physica Status Solidi. Rapid Research Letters. - : John Wiley & Sons. - 1862-6254 .- 1862-6270. ; 9:1, s. 87-91
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Tidskriftsartikel (refereegranskat)abstract
- A low cost hydrothermal synthesis method to synthesize Mn-doped ZnO nanorods (NRs) with controllable morphology and structure has been developed. Ammonia is used to tailor the ammonium hydroxide concentration, which provides a source of OH– for hydrolysis and precipitation during the growth instead of HMT. The morphological, chemical composition, structural, and electronic structure studies of the Mn-doped ZnO NRs show that the Mn-doped ZnO NRs have a hexagonal wurtzite ZnO structure along the c-axis and the Mn ions replace the Zn sites in the ZnO NRs matrix without any secondary phase of metallic manganese element and manganese oxides observed. The fabricated PEDOT:PSS/Zn0.85Mn0.15O Schottky diode based piezoresistive sensor and UV photodetector shows that the piezoresistive sensor has pressure sensitivity of 0.00617 kPa–1 for the pressure range from 1 kPa to 20 kP and 0.000180 kPa–1for the pressure range from 20 kPa to 320 kPa with relatively fast response time of 0.03 s and the UV photodetector has both relatively high responsivity and fast response time of 0.065 A/W and 2.75 s, respectively. The fabricated Schottky diode can be utilized as a very useful human-friendly interactive electronic device for mass/force sensor or UV photodetector in everyday living life. This developed device is very promising for small-size, low-cost and easy-to-customize application-specific requirements. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)
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| 9. |
- Chey, Chan Oeurn, et al.
(författare)
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Fast synthesis, morphology transformation, structural and optical properties of ZnO nanorods grown by seed-free hydrothermal method
- 2014
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 211:11, s. 2611-2615
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Tidskriftsartikel (refereegranskat)abstract
- A fast and low cost seed-free hydrothermal synthesis method to synthesize zinc oxide (ZnO) nanorods with controllable morphology, size and structure has been developed. Ammonia is used to react with water to tailor the ammonium hydroxide concentration, which provides a continuous source of OH− for hydrolysis and precipitation of the final products. Hence, allowing ZnO nanorods to growth on large areas of metal (Au and Ag coated glass), p-type Si and organic flexible (PEDOT: PSS) substrates. Increasing the growth time, the morphology transforms from pencil-like to hexagonal shape rod-like morphology. Within one hour the length of the ZnO nanorods has reached almost 1 µm. The optical characteristics has shown that the grown ZnO nanorods are dominated by two emission peaks, one is in the UV range centered at 381 nm and other one with relatively high intensity appears in the visible range and centered at 630 nm. While the growth duration was increased from 2 h to 6 h, the optical band gap was observed to increase from 2.8 eV to 3.24 eV, respectively. This fast and low cost method is suitable for LEDs, UV-photodetector, sensing, photocatalytic, multifunctional devices and other optoelectronic devices, which can be fabricated on any substrates, including flexible and foldable substrates.
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| 10. |
- Chey, Chan Oeurn, et al.
(författare)
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ZnO nanorods based piezoresistive sensor synthesized by rapid mixing hydrothermal method
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We have successfully synthesized well-aligned, shape controlled and uniform size distribution of ZnO nanorods by using a rapid mixing hydrothermal method. The scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) characterizations showed that the ZnO nanorods grow along the c-axis with hexagonal wurtzite ZnO structure. The room temperature cathodoluminescence (CL) investigation revealed that the ZnO nanorods have optical emissions in both the UV and visible ranges and the crystal quality of the ZnO nanorods can be improved by increasing the growth duration. The well-aligned and uniform ZnO nanorods were used to fabricate efficient piezoresistive sensor. The piezoresistive sensor has demonstrated a pressure sensitivity of 0.033 KPa-1 with a fast response and recovery times within 0.088 and 0.29 s, respectively. The piezoresistive sensor has potential applications in industrial, civil and transportation fields. Furthermore, the fabricated sensor can be utilized as a very useful human-friendly interactive electronic device for load sensing.
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