Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed Crystallites
In this study, the ambient condition for the as-coated seed layer (SL) annealing at 350 °C is varied from air or nitrogen to vacuum to examine the evolution of structural and optical properties of ZnO nanorods (NRs). The NR crystals of high surface density (~240 rods/μm2) and aspect ratio (~20.3) sh...
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doaj-71bddd87ae914929bb16e0e99aa0586f2020-11-24T22:47:30ZengMDPI AGNanomaterials2079-49912018-01-01826810.3390/nano8020068nano8020068Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed CrystallitesWaqar Khan0Fasihullah Khan1Hafiz Muhammad Salman Ajmal2Noor Ul Huda3Ji Hyun Kim4Sam-Dong Kim5Division of Electronics and Electrical Engineering, Dongguk University, Seoul 100-715, KoreaDivision of Electronics and Electrical Engineering, Dongguk University, Seoul 100-715, KoreaDivision of Electronics and Electrical Engineering, Dongguk University, Seoul 100-715, KoreaDivision of Electronics and Electrical Engineering, Dongguk University, Seoul 100-715, KoreaSchool of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon-Si, Gyeonggi-Do 16419, KoreaDivision of Electronics and Electrical Engineering, Dongguk University, Seoul 100-715, KoreaIn this study, the ambient condition for the as-coated seed layer (SL) annealing at 350 °C is varied from air or nitrogen to vacuum to examine the evolution of structural and optical properties of ZnO nanorods (NRs). The NR crystals of high surface density (~240 rods/μm2) and aspect ratio (~20.3) show greatly enhanced (002) degree of orientation and crystalline quality, when grown on the SLs annealed in vacuum, compared to those annealed in air or nitrogen ambient. This is due to the vacuum-annealed SL crystals of a highly preferred orientation toward (002) and large grain sizes. X-ray photoelectron spectroscopy also reveals that the highest O/Zn atomic ratio of 0.89 is obtained in the case of vacuum-annealed SL crystals, which is due to the effective desorption of hydroxyl groups and other contaminants adsorbed on the surface formed during aqueous solution-based growth process. Near band edge emission (ultra violet range of 360–400 nm) of the vacuum-annealed SLs is also enhanced by 44% and 33% as compared to those annealed in air and nitrogen ambient, respectively, in photoluminescence with significant suppression of visible light emission associated with deep level transition. Due to this improvement of SL optical crystalline quality, the NR crystals grown on the vacuum-annealed SLs produce ~3 times higher ultra violet emission intensity than the other samples. In summary, it is shown that the ZnO NRs preferentially grow along the wurtzite c-axis direction, thereby producing the high crystalline quality of nanostructures when they grow on the vacuum-annealed SLs of high crystalline quality with minimized impurities and excellent preferred orientation. The ZnO nanostructures of high crystalline quality achieved in this study can be utilized for a wide range of potential device applications such as laser diodes, light-emitting diodes, piezoelectric transducers and generators, gas sensors, and ultraviolet detectors.http://www.mdpi.com/2079-4991/8/2/68ZnO nanorodsvacuum annealingphotoluminescencehydrothermal processsurface defects |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Waqar Khan Fasihullah Khan Hafiz Muhammad Salman Ajmal Noor Ul Huda Ji Hyun Kim Sam-Dong Kim |
spellingShingle |
Waqar Khan Fasihullah Khan Hafiz Muhammad Salman Ajmal Noor Ul Huda Ji Hyun Kim Sam-Dong Kim Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed Crystallites Nanomaterials ZnO nanorods vacuum annealing photoluminescence hydrothermal process surface defects |
author_facet |
Waqar Khan Fasihullah Khan Hafiz Muhammad Salman Ajmal Noor Ul Huda Ji Hyun Kim Sam-Dong Kim |
author_sort |
Waqar Khan |
title |
Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed Crystallites |
title_short |
Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed Crystallites |
title_full |
Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed Crystallites |
title_fullStr |
Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed Crystallites |
title_full_unstemmed |
Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed Crystallites |
title_sort |
evolution of structural and optical properties of zno nanorods grown on vacuum annealed seed crystallites |
publisher |
MDPI AG |
series |
Nanomaterials |
issn |
2079-4991 |
publishDate |
2018-01-01 |
description |
In this study, the ambient condition for the as-coated seed layer (SL) annealing at 350 °C is varied from air or nitrogen to vacuum to examine the evolution of structural and optical properties of ZnO nanorods (NRs). The NR crystals of high surface density (~240 rods/μm2) and aspect ratio (~20.3) show greatly enhanced (002) degree of orientation and crystalline quality, when grown on the SLs annealed in vacuum, compared to those annealed in air or nitrogen ambient. This is due to the vacuum-annealed SL crystals of a highly preferred orientation toward (002) and large grain sizes. X-ray photoelectron spectroscopy also reveals that the highest O/Zn atomic ratio of 0.89 is obtained in the case of vacuum-annealed SL crystals, which is due to the effective desorption of hydroxyl groups and other contaminants adsorbed on the surface formed during aqueous solution-based growth process. Near band edge emission (ultra violet range of 360–400 nm) of the vacuum-annealed SLs is also enhanced by 44% and 33% as compared to those annealed in air and nitrogen ambient, respectively, in photoluminescence with significant suppression of visible light emission associated with deep level transition. Due to this improvement of SL optical crystalline quality, the NR crystals grown on the vacuum-annealed SLs produce ~3 times higher ultra violet emission intensity than the other samples. In summary, it is shown that the ZnO NRs preferentially grow along the wurtzite c-axis direction, thereby producing the high crystalline quality of nanostructures when they grow on the vacuum-annealed SLs of high crystalline quality with minimized impurities and excellent preferred orientation. The ZnO nanostructures of high crystalline quality achieved in this study can be utilized for a wide range of potential device applications such as laser diodes, light-emitting diodes, piezoelectric transducers and generators, gas sensors, and ultraviolet detectors. |
topic |
ZnO nanorods vacuum annealing photoluminescence hydrothermal process surface defects |
url |
http://www.mdpi.com/2079-4991/8/2/68 |
work_keys_str_mv |
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1725681635399041024 |