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Synthesis and Optical Properties of ZnO Nanostructures
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
2008 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

One-dimensional ZnO nanostructures have great potential applications in the fields of optoelectronic and sensor devices. Therefore, it is really important to realize the controllable growth of one-dimensional ZnO nanostructures and investigate their properties. The main points for this thesis are not only to successfully realize the controllable growth of ZnO nonawires, nanorods and quantum dots (QDs), and also investigate the structure and optical properties in detail by the methods of scan electron microscope(SEM), transmission electron microscope(TEM), resonant Raman, photoluminescence(PL) and low-temperature time resolved PL spectrum.

to grown ZnO nanorod arrays (ZNAs) on Si substrates. Firstly, the effects of ZnO nanoparticles, pH value of chemical solution, angel θ between substrate and beaker bottom on the structures of the samples were symmetrically investigated and the optimized growth condition to grow ZNAs can be concluded as follows: seed layer of ZnO nanoparticles, pH=6 and θ=70°. On the basis of these, the diameter of ZNAs was well controlled from 150nm~40nm through adjusting the diameter and density of the ZnO nanoparticles pretreated on the Si substrates. The experimental results indicated that both diameter and density of ZnO nanoparticles on the substrates determined the diameter of ZNAs. But when the density is higher than the critical value of 2.3×108cm-2, the density will become the dominant factor to determine the diameter of ZNAs.

One the other hand, the optical properties of ZNAs were investigated in detail. The Raman and photoluminescence (PL) results showed that after an annealing treatment around 500oC in air atmosphere, the crystal structure and optical properties became much better due to the decrease of surface defects. The resonant Raman measurements excited by 351.1nm not only revealed that the surface defects play a significant role in the as-grown sample, but also suggested that the strong intensity increase of some Raman scatterings was due to both outgoing resonant Raman scattering effect and deep level defects scattering contribution for ZnO nanorods annealed from 500°C to 700°C. It is the first time to the best of our knowledge that the Raman measurements can be used to monitor the change of surface defects and deep level defects in the CBD grown ZnO nanorods. We have also presented, for the first time, a time resolved PL study in CBD grown ZnO nanorods with different diameters. The results show that the decay time of the excitons in the nanorods strongly depends on the diameter of the nanorods. The altered decay time is mainly due to the surface recombination process. The effective time constant related to the surface recombination velocity was deduced. A thermal treatment under 500°C will suppress the surface recombination channel, resulting in an improvement of the optical quality for the ZnO nanorods.

This thesis not only provides the effective way to control the size of ZNAs, but also obtains some beneficial results in aspects of their optical properties, which builds theoretical and experimental foundation for much better and broader applications of one-dimensional ZnO nanostructures.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2008. , 32 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1384
Keyword [en]
ZnO nanorods; size-controllable growth; post-annealing; optical properties
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:liu:diva-15535ISBN: 978-91-7393-758-0 (print)OAI: oai:DiVA.org:liu-15535DiVA: diva2:117508
Presentation
(English)
Supervisors
Available from: 2008-11-14 Created: 2008-11-14 Last updated: 2014-01-15Bibliographically approved
List of papers
1. Size-controlled growth of well-aligned ZnO nanorod arrays with two-step chemical bath deposition method
Open this publication in new window or tab >>Size-controlled growth of well-aligned ZnO nanorod arrays with two-step chemical bath deposition method
2009 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, Vol. 469, no 1-2, 623-629 p.Article in journal (Refereed) Published
Abstract [en]

Well-aligned ZnO nanorod arrays (ZNAs) with different sizes in diameter were fabricated on Si substrates by two-step chemical bath deposition method (CBD), i.e. substrate pre-treatment with spin coating to form ZnO nanoparticles layer and CBD growth. The effects of substrate pre-treatments, pH, angel (θ) between substrate and beaker bottom and growth time (t) on the structure of ZNAs were investigated in detail by X-ray diffraction (XRD), field emission scan electronic microscope (SEM) and photoluminescence (PL). The results show that substrate pre-treatment, pH, θ and t indeed have great influence on the growth of ZNAs, and their influence mechanisms have been, respectively, explained in detail. The introduction of a ZnO nanoparticle layer on the substrate not only helps to decrease the diameter but also has a strong impact on the orientation of ZNAs. Under the growth condition of pH 6, θ = 70° and t = 2 h, the well-aligned ZnO nanorod arrays with 50 nm diameter was obtained on the pre-treated Si substrates. And only a strong UV peak at 385 nm appears in room temperature PL spectrum for this sample, which indicates that as-synthesized ZnO nanorods have a perfect crystallization and low density of deep level defects.

Keyword
ZnO nanorods, Chemical bath deposition, Optical properties
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-15532 (URN)10.1016/j.jallcom.2008.08.002 (DOI)
Note
Original Publication:LiLi Yang, Qingxiang Zhao and Magnus Willander, Size-controlled growth of well-aligned ZnO nanorod arrays with two-step chemical bath deposition method, 2009, Journal of Alloys and Compounds, (469), 1-2, 623-629.http://dx.doi.org/10.1016/j.jallcom.2008.08.002Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com/Available from: 2009-03-27 Created: 2008-11-14 Last updated: 2014-01-15Bibliographically approved
2. Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition
Open this publication in new window or tab >>Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition
2009 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, no 4, 1046-1050 p.Article in journal (Refereed) Published
Abstract [en]

The diameter of well-aligned ZnO nanorod arrays (ZNAs) grown on Si substrates has been well controlled from 150nm to 40nm by two-step chemical bath deposition method (CBD), i.e. substrate pretreatment with spin coating to form ZnO nanoparticles seed layer and CBD growth. The effects of ZnO nanoparticles density and diameter on size and alignment of ZNAs were investigated in detail by atomic force microscope (AFM), X-ray diffraction (XRD), scan electronic microscope (SEM), transmission electron microscope (TEM) and photoluminescence (PL). The results indicate that both diameter and density of ZnO nanoparticles which were pre-coated on the substrates will influence the size and alignment of ZNAs, but the density will play a key role to determine the diameter of ZNAs when the density is higher than the value of 2.3×108cm-2. Moreover, only a strong UV peak at 385 nm appears in room temperature PL spectrum for these samples, which indicates that  as-synthesized ZnO nanorods have a perfect crystallization and low density of deep level defects.

Keyword
ZnO nanorods arrays, CBD, Size-controlled growth
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-15533 (URN)10.1016/j.jcrysgro.2008.12.028 (DOI)
Note
Original Publication: Li-Li Yang, Qingxiang Zhao, Magnus Willander and J.H. Yang, Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition, 2009, Journal of Crystal Growth, (311), 4, 1046-1050. http://dx.doi.org/10.1016/j.jcrysgro.2008.12.028 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2008-11-14 Created: 2008-11-14 Last updated: 2014-01-15
3. Annealing effects on optical properties of low temperature grown ZnO nanorod arrays
Open this publication in new window or tab >>Annealing effects on optical properties of low temperature grown ZnO nanorod arrays
Show others...
2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, Vol. 105, no 5, 053503- p.Article in journal (Refereed) Published
Abstract [en]

Vertically well-aligned ZnO nanorods on Si substrates were prepared by a two-step chemical bath deposition method. The structure and optical properties of the grown ZnO nanorods were investigated by Raman and photoluminescence spectroscopy. The results showed that after an annealing treatment at around 500 degrees C in air atmosphere, the crystal structure and optical properties became much better due to the decrease in surface defects. The resonant Raman measurements excited by 351.1 nm not only revealed that the surface defects play a significant role in the as-grown sample, which was supported by low temperature time-resolved photoluminescence measurements, but also suggested that the strong intensity increase in some Raman scatterings was due to both outgoing resonant Raman scattering effect and deep level defect scattering contribution for ZnO nanorods annealed from 500 to 700 degrees C.

Keyword
annealing, crystal structure, deep levels, II-VI semiconductors, liquid phase deposition, nanostructured materials, nanotechnology, photoluminescence, Raman spectra, time resolved spectra, wide band gap semiconductors, zinc compounds
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17508 (URN)10.1063/1.3073993 (DOI)
Note
Original Publication:Lili Yang, Qingxiang Zhao, Magnus Willander and Ivan Gueorguiev Ivanov , Annealing effects on optical properties of low temperature grown ZnO nanorod arrays, 2009, JOURNAL OF APPLIED PHYSICS, (105), 5, 053503.http://dx.doi.org/10.1063/1.3073993Copyright: American Institute of Physicshttp://www.aip.org/Available from: 2009-04-07 Created: 2009-03-27 Last updated: 2014-01-15Bibliographically approved
4. Surface recombination in ZnO nanorods grown by chemical bath deposition
Open this publication in new window or tab >>Surface recombination in ZnO nanorods grown by chemical bath deposition
Show others...
2008 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 104, no 7, 073526- p.Article in journal (Refereed) Published
Abstract [en]

Verticallywell-aligned ZnO nanorods on Si substrates were prepared by atwo-step chemical bath deposition (CBD) method. The optical properties ofthe grown ZnO nanorods were investigated by time resolved photoluminescencespectroscopy. It was found that the effective decay time ofthe near bandgap recombination in the CBD grown ZnO nanorodsstrongly depends on the diameter of the ZnO nanorods. Typically,the decay curves obtained from these ZnO nanorods show acombination of two exponential decays. The experimental results show thatthe fast exponential decay is related to the surface recombinationand the slow decay is related to the “bulk” decay.The measured decay time of the effective surface recombination decreaseswith decreasing diameter, while the bulk decay time remains unchanged.The results also show that an annealing treatment around 500 °Csignificantly reduces the surface recombination rate. A simple carrier andexciton diffusion equation is also used to determine the surfacerecombination velocity, which results in a value between 1.5 and4.5 nm/ps.

Keyword
Annealing, excitons, II-VI semiconductors, nanostructured materials, nanotechnology, photoluminescence, semiconductor growth, surface recombination, time resolved spectra, wide band gap semiconductors, zinc compounds
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-15425 (URN)10.1063/1.2991151 (DOI)
Note

Original publication: Q. X. Zhao, L. L. Yang, M. Willander, B. E. Sernelius and P. O. Holtz, Surface recombination in ZnO nanorods grown by chemical bath deposition, 2008, Journal of Applied Physics, (104), 073526.http://dx.doi.org/10.1063/1.2991151. Copyright: Institute of Physics and IOP Publishing Limited, http://www.iop.org/EJ/journal/PM

Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2014-06-24Bibliographically approved

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