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Toward the Optimization of Low-temperature Solution-based Synthesis of ZnO Nanostructures for Device Applications
Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska fakulteten.
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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).

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2017. , s. 67
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1871
Nationell ämneskategori
Den kondenserade materiens fysik Materialkemi
Identifikatorer
URN: urn:nbn:se:liu:diva-141753DOI: 10.3384/diss.diva-141753ISBN: 9789176854815 (tryckt)OAI: oai:DiVA.org:liu-141753DiVA, id: diva2:1147511
Disputation
2017-10-27, K3, Kåkenhus, Campus Norrköping, Norrköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2017-10-06 Skapad: 2017-10-06 Senast uppdaterad: 2019-10-11Bibliografiskt granskad
Delarbeten
1. Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods
Öppna denna publikation i ny flik eller fönster >>Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods
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2015 (Engelska)Ingår i: AIP Advances, E-ISSN 2158-3226, Vol. 5, nr 8, artikel-id 087180Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
AMER INST PHYSICS, 2015
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-122070 (URN)10.1063/1.4929981 (DOI)000360655900089 ()
Anmärkning

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

Tillgänglig från: 2015-12-18 Skapad: 2015-10-19 Senast uppdaterad: 2024-01-08
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
Öppna denna publikation i ny flik eller fönster >>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
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2016 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, nr 16, s. 165702-Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
AMER INST PHYSICS, 2016
Nationell ämneskategori
Materialkemi
Identifikatorer
urn:nbn:se:liu:diva-129174 (URN)10.1063/1.4947593 (DOI)000375929900043 ()
Anmärkning

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

Tillgänglig från: 2016-06-13 Skapad: 2016-06-13 Senast uppdaterad: 2024-01-08
3. Seed layer synthesis effect on the concentration of interface defects and emission spectra of ZnO nanorods/p-GaN light-emitting diode
Öppna denna publikation i ny flik eller fönster >>Seed layer synthesis effect on the concentration of interface defects and emission spectra of ZnO nanorods/p-GaN light-emitting diode
2017 (Engelska)Ingår i: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 214, nr 1, artikel-id 1600333Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
WILEY-V C H VERLAG GMBH, 2017
Nyckelord
GaN; interface defects; light-emitting diodes; low-temperature aqueous chemical synthesis; seed layers; ZnO
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-136230 (URN)10.1002/pssa.201600333 (DOI)000394423400006 ()
Anmärkning

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

Tillgänglig från: 2017-03-31 Skapad: 2017-03-31 Senast uppdaterad: 2024-01-08
4. EPR investigation of pure and Co-doped ZnO oriented nanocrystals
Öppna denna publikation i ny flik eller fönster >>EPR investigation of pure and Co-doped ZnO oriented nanocrystals
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2017 (Engelska)Ingår i: NANOTECHNOLOGY, ISSN 0957-4484, Vol. 28, nr 3, artikel-id 035705Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
IOP PUBLISHING LTD, 2017
Nyckelord
nanorods; magnetic properties; electron paramagnetic resonance; diluted magnetic semiconductors
Nationell ämneskategori
Materialkemi
Identifikatorer
urn:nbn:se:liu:diva-134300 (URN)10.1088/1361-6528/28/3/035705 (DOI)000391289300001 ()27966469 (PubMedID)
Anmärkning

Funding Agencies|NATO project [SfP 984735]

Tillgänglig från: 2017-02-06 Skapad: 2017-02-03 Senast uppdaterad: 2024-01-08
5. An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods
Öppna denna publikation i ny flik eller fönster >>An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods
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2017 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, nr 21, artikel-id 215102Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
AMER INST PHYSICS, 2017
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-138890 (URN)10.1063/1.4984314 (DOI)000402768900026 ()
Anmärkning

Funding Agencies|NATO [984735]

Tillgänglig från: 2017-06-27 Skapad: 2017-06-27 Senast uppdaterad: 2024-01-08
6. Core-defect reduction in ZnO nanorods by cobalt incorporation
Öppna denna publikation i ny flik eller fönster >>Core-defect reduction in ZnO nanorods by cobalt incorporation
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2017 (Engelska)Ingår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 28, nr 28, artikel-id 285705Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
IOP PUBLISHING LTD, 2017
Nyckelord
nanorods; ZnO; physics defects; electron paramagnetic resonance
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-139388 (URN)10.1088/1361-6528/aa716a (DOI)000404344400005 ()28475103 (PubMedID)
Anmärkning

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

Tillgänglig från: 2017-08-07 Skapad: 2017-08-07 Senast uppdaterad: 2024-01-08

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