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Synthesis and Characterization of ZnO Nanostructures
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology. (Physical electronics and nanotechnology)
2010 (English)Doctoral 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 very 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 nanorods (ZNRs), ZnO nanotubes (ZNTs) and ZnMgO/ZnO heterostructures, but also investigate the structure and optical properties in detail by means of scanning electron microscope (SEM), transmission electron microscope (TEM), resonant Raman spectroscopy (RRS), photoluminescence (PL), time resolved PL (TRPL), X-ray photoelectron spectroscopy (XPS) and Secondary ion mass spectrometry (SIMS).

For ZNRs, on one hand, ZNRs have been successfully synthesized by a two-step chemical bath deposition method on Si substrates. The diameter of ZNRs can be well controlled from 150 nm to 40 nm 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 ZNRs. 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 ZNRs.

One the other hand, the surface recombination of ZNRs has been investigated in detail. Raman, RRS and PL results help us reveal that the surface defects play a significant role in the as-grown sample. 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 ZNRs. Then we utilized TRPL technique, for the first time, to investigate the CBD grown ZNRs with different diameters. The results show that the decay time of the excitons in ZNRs strongly depends on the diameter. The altered decay time is mainly due to the surface recombination process. A thermal treatment under 500°C can strongly suppress the surface recombination channel. A simple carrier and exciton diffusion equation is also used to determine the surface recombination velocity, which results in a value between 1.5 and 4.5 nm/ps. Subsequently, we utilized XPS technique to investigate the surface composition of as-grown and annealed ZNRs so that we can identify the surface recombination centers. The experimental results indicated that the OH and H bonds play the dominant role in facilitating surface recombination but specific chemisorbed oxygen also likely affect the surface recombination. Finally, on the basis of results above, we explored an effective way, i.e. sealing the beaker during the growth process, to effectively suppress the surface recombination of ZNRs and the suppression effect is even better than a 500oC post-thermal treatment.

For ZNTs, the structural and optical properties have been studied in detail. ZNTs have been successfully evolved from ZNRs by a simple chemical etching process. Both temperature-dependent PL and TRPL results not only further testify the coexistence of spatially indirect and direct transitions due to the surface band bending, but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their strong enhancement of luminescence intensity.

For ZnMgO/ZnO heterostructures, the Zn0.94Mg0.06O/ZnO heterostructures have been deposited on 2 inch sapphire wafer by metal organic chemical vapor deposition (MOCVD) equipment. PL mapping demonstrates that Mg distribution in the entire wafer is quite uniform with average concentration of ~6%. The annealing effects on the Mg diffusion behaviors in Zn0.94Mg0.06O/ZnO heterostructures have been investigated by SIMS in detail. All the SIMS depth profiles of Mg element have been fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn0.94Mg0.06O layer deposited at 700 oC is two orders of magnitude lower than that of annealing samples, which clearly testifies that the deposited temperature of 700 oC is much more beneficial to grow ZnMgO/ZnO heterostructures or quantum wells.

This thesis not only provides the effective way to fabricate ZNRs, ZNTs and ZnMgO/ZnO heterostructures, but also obtains some beneficial results in aspects of their optical properties, which builds theoretical and experimental foundation for much better understanding fundamental physics and broader applications of low-dimensional ZnO and related structures.

Abstract [sv]

Endimensionella nanostrukturer av ZnO har stora potentiella tillämpningar för optoelektroniska komponenter och sensorer. Huvudresultaten för denna avhandling är inte bara att vi framgångsrikt har realiserat med en kontrollerbar metod ZnO nanotrådar (ZNRs), ZnO nanotuber (ZNTs) och ZnMgO/ZnO heterostrukturer, utan vi har också undersökt deras struktur och optiska egenskaper i detalj.

För ZNRs har diametern blivit välkontrollerad från 150 nm  ner till 40 nm. Den storlekskontrollerande mekanismen är i huvudsak relaterad till tätheten av ZnO partiklarna som är fördeponerade på substratet. De optiska mätningarna ger upplysning om att ytrekombinationsprocessen spelar en betydande roll för tillväxten av ZNR. En värmebehandling i efterhand  vid 500 grader Celsius eller användande av en förseglad glasbägare under tillväxtprocessen kan starkt hålla nere kanalerna för ytrekombinationen.För ZNT, dokumenterar vi inte bara samexistensen av rumsliga indirekta och direkta  övergångar på grund av bandböjning, men vi konstaterar också att vi har mindre icke-strålande bidrag till den optiska emissionsprocessen i ZNT.

För ZnMgO/ZnO heterostrukturer konstaterar vi med hjälp av analys av Mg diffusionen i den växta och den i efterhand uppvärmda Zn(0.94)Mg(0.06)O filmen, att en tillväxt vid 700 grader Celsius är den mest lämpliga för att växa ZnMgO/ZnO heterostrukturer eller kvantbrunnar.

 

Denna avhandling ger en teoretisk och experimentell grund för bättre förståelse av grundläggande fysik och för tillämpningar av lågdimensionella strukturer.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2010. , 107 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1327
Keyword [en]
Zinc oxide; nanostructures; heterostructures; controllable growth; optical properties; postannealing; diffusion coefficient
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-60815ISBN: 978-91-7393-357-5 (print)OAI: oai:DiVA.org:liu-60815DiVA: diva2:359293
Public defence
2010-09-30, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Projects
SSF, VR
Available from: 2010-10-28 Created: 2010-10-27 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, E-ISSN 1089-7550, 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: 2017-12-13Bibliographically 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
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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
5. Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy
Open this publication in new window or tab >>Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy
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2010 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, no 11, 3592-3597 p.Article in journal (Refereed) Published
Abstract [en]

The surface composition of as-grown and annealed ZnO nanorods arrays (ZNAs) grown by a two-step chemical bath deposition method has been investigated by X-ray photoelectron spectroscopy (XPS). XPS confirms the presence of OH bonds and specific chemisorbed oxygen on the surface of ZNAs, as well as H bonds on (1 0 (1) over bar 0) surfaces which has been first time observed in the XPS spectra. The experimental results indicated that the OH and H bonds play the dominant role in facilitating surface recombination but specific chemisorbed oxygen also likely affect the surface recombination. Annealing can largely remove the OH and H bonds and transform the composition of the other chemisorbed oxygen at the surface to more closely resemble that of high temperature grown ZNAs, all of which suppresses surface recombination according to time-resolved photoluminescence measurements.

Place, publisher, year, edition, pages
Amsterdam, Netherlands: Elsevier, 2010
Keyword
ZnO nanorods, Optical properties, Surface recombination, X-ray photoelectron spectroscopy
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54620 (URN)10.1016/j.apsusc.2009.12.160 (DOI)000275515100042 ()
Note

Original Publication: Li-Li Yang, Qingxiang Zhao, Magnus Willander, Xianjie Liu, Mats Fahlman and J H Yang, Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy, 2010, APPLIED SURFACE SCIENCE, (256), 11, 3592-3597. http://dx.doi.org/10.1016/j.apsusc.2009.12.160 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/

Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2017-12-12
6. Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process
Open this publication in new window or tab >>Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process
Show others...
2010 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 10, no 4, 1904-1910 p.Article in journal (Refereed) Published
Abstract [en]

ZnO nanorods arrays are respectively prepared under different vapor pressures with opening (OZN) or sealing (SZN) of the beaker. The results from time-resolved photoluminescence measurements indicate that sealing the beaker during the growth process can effectively suppress the surface recombination of ZnO nanorods, and the suppression effect is even better than a 500 degrees C post-thermal treatment or OZN samples. The results from X-ray photoelectron spectroscopy measurements reveal that the main reason for this phenomenon is that the surfaces of the SZN samples are attached by groups related to NH3 instead of the main surface recombination centers such as OH and groups in the OZN samples. The ammonia surface treatment on both OZN and SZN samples further testifies that the absorption of the groups related to NH3 does not contribute to the surface recombination on the ZnO nanorods.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54866 (URN)10.1021/cg100017b (DOI)000276234500068 ()
Note

This document is the Accepted Manuscript version of a Published Work that appeared in final form in CRYSTAL GROWTH and DESIGN, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see: Li-Li Yang, Qingxiang Zhao, Magnus Willander, Xianjie Liu, Mats Fahlman and J H Yang, Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process, 2010, CRYSTAL GROWTH and DESIGN, (10), 4, 1904-1910. http://dx.doi.org/10.1021/cg100017b Copyright: The American Chemical Society http://pubs.acs.org/

Available from: 2010-04-16 Created: 2010-04-16 Last updated: 2017-12-12Bibliographically approved
7. Indirect optical transition due to surface band bending in ZnO nanotubes
Open this publication in new window or tab >>Indirect optical transition due to surface band bending in ZnO nanotubes
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2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 10Article in journal (Refereed) Published
Abstract [en]

ZnO nanotubes (ZNTs) have been successfully evolved from ZnO nanorods (ZNRs) by a simple chemical etching process. Two peaks located at 382 nm and 384 nm in the UV emission region has been observed in the room temperature photoluminescence (PL) spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending, but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity.

Place, publisher, year, edition, pages
American Institute, 2010
Keyword
Zinc Oxide, Nanotube, Surface band bending, Indirect transition, Temperature-dependent photoluminescence
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-60853 (URN)10.1063/1.3511345 (DOI)000285005000053 ()
Note
Original Publication: Li Li Yang, Qingxiang Zhao, Muhammad Qadir Israr, Jamil Rana Sadaf, Magnus Willander, Galia Pozina and J. H. Yang, Indirect optical transition due to surface band bending in ZnO nanotubes, 2010, Journal of Applied Physics, (108), 10, 103513. http://dx.doi.org/10.1063/1.3511345 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12
8. Mg diffusion in Zn0.94Mg0.06O/ZnO heterostructures grown by MOCVD
Open this publication in new window or tab >>Mg diffusion in Zn0.94Mg0.06O/ZnO heterostructures grown by MOCVD
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Zn0.94Mg0.06O/ZnO heterostructures were grown on 2 inch sapphire wafer by MOCVD equipment. Photoluminescence mapping demonstrated that Mg uniformly distributed on the entire wafer with average concentration of ~6%. The annealing effects on the Mg diffusion behaviors were investigated by secondary ion mass spectrometry (SIMS). All Mg SIMS depth profiles were fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn0.94Mg0.06O layer deposited at 700 oC was two order of magnitude lower than that of annealed samples, which indicated that the deposition temperature of 700 oC is much more beneficial to grow ZnMgO/ZnO heterostructures or quantum wells.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-60854 (URN)
Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2014-01-15

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