Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Toward the Optimization of Low-temperature Solution-based Synthesis of ZnO Nanostructures for Device Applications
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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).

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. , p. 67
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1871
National Category
Condensed Matter Physics Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-141753DOI: 10.3384/diss.diva-141753ISBN: 9789176854815 (print)OAI: oai:DiVA.org:liu-141753DiVA, id: diva2:1147511
Public defence
2017-10-27, K3, Kåkenhus, Campus Norrköping, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2017-10-06 Created: 2017-10-06 Last updated: 2017-10-06Bibliographically approved
List of papers
1. Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods
Open this publication in new window or tab >>Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods
Show others...
2015 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 5, no 8, article id 087180Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2015
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-122070 (URN)10.1063/1.4929981 (DOI)000360655900089 ()
Note

Funding Agencies|Avdanced Functional Materials (AFM) SFO project at Linkoping Univeristy, Sweden

Available from: 2015-12-18 Created: 2015-10-19 Last updated: 2017-12-01
2. 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
Open this publication in new window or tab >>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
Show others...
2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 16, p. 165702-Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2016
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-129174 (URN)10.1063/1.4947593 (DOI)000375929900043 ()
Note

Funding Agencies|Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]

Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2017-11-28
3. Seed layer synthesis effect on the concentration of interface defects and emission spectra of ZnO nanorods/p-GaN light-emitting diode
Open this publication in new window or tab >>Seed layer synthesis effect on the concentration of interface defects and emission spectra of ZnO nanorods/p-GaN light-emitting diode
2017 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 214, no 1, article id 1600333Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2017
Keyword
GaN; interface defects; light-emitting diodes; low-temperature aqueous chemical synthesis; seed layers; ZnO
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-136230 (URN)10.1002/pssa.201600333 (DOI)000394423400006 ()
Note

Funding Agencies|Swedish Government Strategic Research Area in Materials Science on Functional Materials (Faculty Grant SFO-Mat-LiU) at Linkoping University [2009-00971]

Available from: 2017-03-31 Created: 2017-03-31 Last updated: 2017-11-29
4. EPR investigation of pure and Co-doped ZnO oriented nanocrystals
Open this publication in new window or tab >>EPR investigation of pure and Co-doped ZnO oriented nanocrystals
Show others...
2017 (English)In: NANOTECHNOLOGY, ISSN 0957-4484, Vol. 28, no 3, article id 035705Article in journal (Refereed) Published
Abstract [en]

Pure and cobalt-doped zinc oxide aligned nanorods have been grown by the low-temperature (90 degrees C) aqueous chemical method on amorphous ZnO seed layer, deposited on a sapphire substrate. High crystallinity of these objects is demonstrated by the electron paramagnetic resonance investigation at liquid helium temperature. The successful incorporation of Co2+ ions in substitution of Zn2+ ones in the ZnO matrix has also been confirmed. A drastic reduction of intrinsic ZnO nanorods core defects is observed in the Co-doped samples, which enhances the structural quality of the NRs. The quantification of substitutional Co2+ ions in the ZnO matrix is achieved by comparison with a reference sample. The findings in this study indicate the potential of using the low-temperature aqueous chemical approach for synthesizing material for spintronics applications.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keyword
nanorods; magnetic properties; electron paramagnetic resonance; diluted magnetic semiconductors
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-134300 (URN)10.1088/1361-6528/28/3/035705 (DOI)000391289300001 ()27966469 (PubMedID)
Note

Funding Agencies|NATO project [SfP 984735]

Available from: 2017-02-06 Created: 2017-02-03 Last updated: 2017-10-06
5. An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods
Open this publication in new window or tab >>An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods
Show others...
2017 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 21, article id 215102Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2017
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-138890 (URN)10.1063/1.4984314 (DOI)000402768900026 ()
Note

Funding Agencies|NATO [984735]

Available from: 2017-06-27 Created: 2017-06-27 Last updated: 2017-10-06
6. Core-defect reduction in ZnO nanorods by cobalt incorporation
Open this publication in new window or tab >>Core-defect reduction in ZnO nanorods by cobalt incorporation
Show others...
2017 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 28, no 28, article id 285705Article in journal (Refereed) Published
Abstract [en]

Zinc oxide (ZnO) nanorods grown by the low-temperature (90 degrees C) aqueous chemical method with different cobalt concentration within the synthesis solution (from 0% to 15%), are studied by electron paramagnetic resonance (EPR), just above the liquid helium temperature. The anisotropic spectra of substitutional Co2+ reveal a high crystalline quality and orientation of the NRs, as well as the probable presence of a secondary disordered phase of ZnO: Co. The analysis of the EPR spectra indicates that the disappearance of the paramagnetic native core-defect (CD) at g similar to 1.96 is correlated with the apparition of the Co2+ ions lines, suggesting a gradual neutralization of the former by the latter. We show that only a little amount of cobalt in the synthesis solution (about 0.2%) is necessary to suppress almost all these paramagnetic CDs. This gives insight in the experimentally observed improvement of the crystal quality of diluted ZnO: Co nanorods, as well as into the control of paramagnetic defects in ZnO nanostructures.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keyword
nanorods; ZnO; physics defects; electron paramagnetic resonance
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-139388 (URN)10.1088/1361-6528/aa716a (DOI)000404344400005 ()28475103 (PubMedID)
Note

Funding Agencies|NATO project Science for Peace (SfP), Novel nanostructures [984735]

Available from: 2017-08-07 Created: 2017-08-07 Last updated: 2017-10-06

Open Access in DiVA

Toward the Optimization of Low-temperature Solution-based Synthesis of ZnO Nanostructures for Device Applications(1697 kB)39 downloads
File information
File name FULLTEXT01.pdfFile size 1697 kBChecksum SHA-512
dd18e2a52cbdccf6275c1971e54f931e965a6c3c24dc61bf9a55b8957c49caff556f36374761201e4ea3f5f1c1c3885896149696f94870d65ce124ddd138dfca
Type fulltextMimetype application/pdf
omslag(51 kB)5 downloads
File information
File name COVER01.pdfFile size 51 kBChecksum SHA-512
c31b6405da286ecdfa02cf7326ca3bc0303fa92c24f9de52446f01a77716b418b1a2c33361297754e51420e0db7f067ce13583d00e96ca359a761eed5a1e34ad
Type coverMimetype application/pdf

Other links

Publisher's full text

Search in DiVA

By author/editor
Alnoor, Hatim
By organisation
Physics and ElectronicsFaculty of Science & Engineering
Condensed Matter PhysicsMaterials Chemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 39 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

doi
isbn
urn-nbn

Altmetric score

doi
isbn
urn-nbn
Total: 376 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf