Evolution of structural and optical properties of ZnO nanorods grown on vacuum annealed seed crystallites

Waqar Khan; Fasihullah Khan; Hafiz Muhammad Salman Ajmal; Noor Ul Huda; Ji Hyun Kim; Sam Dong Kim

doi:10.3390/nano8020068

Evolution of structural and optical properties of ZnO nanorods grown on vacuum annealed seed crystallites

Waqar Khan, Fasihullah Khan, Hafiz Muhammad Salman Ajmal, Noor Ul Huda, Ji Hyun Kim, Sam Dong Kim

Not published at VTT

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30 Citations (Scopus)

Abstract

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.

Original language	English
Article number	68
Journal	Nanomaterials
Volume	8
Issue number	2
DOIs	https://doi.org/10.3390/nano8020068
Publication status	Published - 26 Jan 2018
MoE publication type	A1 Journal article-refereed

Keywords

Hydrothermal process
Photoluminescence
Surface defects
Vacuum annealing
ZnO nanorods

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10.3390/nano8020068

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title = "Evolution of structural and optical properties of ZnO nanorods grown on vacuum annealed seed crystallites",

abstract = "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.",

keywords = "Hydrothermal process, Photoluminescence, Surface defects, Vacuum annealing, ZnO nanorods",

author = "Waqar Khan and Fasihullah Khan and Ajmal, {Hafiz Muhammad Salman} and Huda, {Noor Ul} and Kim, {Ji Hyun} and Kim, {Sam Dong}",

note = "Funding Information: Acknowledgments: This work (project no. 2016006533) was supported by Mid-career Researcher Program Acknowledgments: This work (project no. 2016006533) was supported by Mid-career Researcher Program through National Research Foundation grant funded by the Ministry of Education, Science and Technology, through National Research Foundation grant funded by the Ministry of Education, Science and Technology, Korea. Korea. Author Contributions: The presented work was carried out in the collaboration of all authors which was AsuutpheorrviCseodntbryibSuatmio-nDso: nTghKe ipmr.eWseanqteadr Kwhoarnkpwlaansn ecadrtrhieedexopuet riimn etnhtewcohlillaebFoarsaithiounll aohfKahlla nau, Hthaofrisz Mwhuihcahm wmaasd supervised by Sam-Dong Kim. Waqar Khan planned the experiment while Fasihullah Khan, Hafiz Muhammad Salman Ajmal, Noor Ul Huda, and Ji Hyun Kim helped in performing the experiment, data analysis, and inCteornpfrliecttastioofnI. nWtearqeastr: KThhaena uwtrhootres tdheec mlaarenunsoccriopntf lwichtiocfhiwntaesr eesdt.ited by Sam-Dong Kim. Funding Information: This work (project no. 2016006533) was supported by Mid-career Researcher Program through National Research Foundation grant funded by the Ministry of Education, Science and Technology, Korea. Publisher Copyright: {\textcopyright} 2018 by the authors. Licensee MDPI, Basel, Switzerland.",

year = "2018",

month = jan,

day = "26",

doi = "10.3390/nano8020068",

language = "English",

volume = "8",

journal = "Nanomaterials",

issn = "2079-4991",

publisher = "MDPI",

number = "2",

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TY - JOUR

T1 - Evolution of structural and optical properties of ZnO nanorods grown on vacuum annealed seed crystallites

AU - Khan, Waqar

AU - Khan, Fasihullah

AU - Ajmal, Hafiz Muhammad Salman

AU - Huda, Noor Ul

AU - Kim, Ji Hyun

AU - Kim, Sam Dong

N1 - Funding Information: Acknowledgments: This work (project no. 2016006533) was supported by Mid-career Researcher Program Acknowledgments: This work (project no. 2016006533) was supported by Mid-career Researcher Program through National Research Foundation grant funded by the Ministry of Education, Science and Technology, through National Research Foundation grant funded by the Ministry of Education, Science and Technology, Korea. Korea. Author Contributions: The presented work was carried out in the collaboration of all authors which was AsuutpheorrviCseodntbryibSuatmio-nDso: nTghKe ipmr.eWseanqteadr Kwhoarnkpwlaansn ecadrtrhieedexopuet riimn etnhtewcohlillaebFoarsaithiounll aohfKahlla nau, Hthaofrisz Mwhuihcahm wmaasd supervised by Sam-Dong Kim. Waqar Khan planned the experiment while Fasihullah Khan, Hafiz Muhammad Salman Ajmal, Noor Ul Huda, and Ji Hyun Kim helped in performing the experiment, data analysis, and inCteornpfrliecttastioofnI. nWtearqeastr: KThhaena uwtrhootres tdheec mlaarenunsoccriopntf lwichtiocfhiwntaesr eesdt.ited by Sam-Dong Kim. Funding Information: This work (project no. 2016006533) was supported by Mid-career Researcher Program through National Research Foundation grant funded by the Ministry of Education, Science and Technology, Korea. Publisher Copyright: © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

PY - 2018/1/26

Y1 - 2018/1/26

N2 - 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.

AB - 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.

KW - Hydrothermal process

KW - Photoluminescence

KW - Surface defects

KW - Vacuum annealing

KW - ZnO nanorods

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U2 - 10.3390/nano8020068

DO - 10.3390/nano8020068

M3 - Article

C2 - 29373523

AN - SCOPUS:85041128626

SN - 2079-4991

VL - 8

JO - Nanomaterials

JF - Nanomaterials

IS - 2

M1 - 68

ER -

Evolution of structural and optical properties of ZnO nanorods grown on vacuum annealed seed crystallites

Abstract

Keywords

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