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Improvement and optimization of the growth quality of upright ZnOrod arrays by the response surface methodology
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0003-3060-9987
2015 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 351, 451-459 p.Article in journal (Refereed) Published
Abstract [en]

Response surface methodology was employed to guide the growth of ZnO rod arrays. With its assistance, the growth quality of the obtained samples was improved dramatically. The morphologies evolved from sparsely, randomly oriented rods to dense and upright rod arrays. Moreover, the significant parameters for ZnO rod arrays growth and their optimal regions were also determined. Furthermore, with the optimized parameters, the obtained aspect ratio of the vertically aligned ZnO rod arrays reached a value of 31. This is relatively a high value of ZnO rod arrays synthesized by wet chemical methods without capping agents in neutral solutions.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2015. Vol. 351, 451-459 p.
Keyword [en]
ZnO rod arrays; Response surface methodology; Design of experiment
National Category
Other Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-172943DOI: 10.1016/j.apsusc.2015.05.144ISI: 000359496600058Scopus ID: 2-s2.0-84964528913OAI: oai:DiVA.org:kth-172943DiVA: diva2:850825
Note

QC 20150903

QC2 0150914

Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Synthesis of well arrayed structures with assistance of statistical experimental design
Open this publication in new window or tab >>Synthesis of well arrayed structures with assistance of statistical experimental design
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During the synthesis of well arrayed nano/micro structures through wet chemical methods, plenty of parameters are usually involved. Consequently, it is extremely time- and cost-consuming to find out the optimized synthesis conditions by using the conventional "changing one separate factor at a time" (COST) strategy. Instead, the "statistical experimental design" method has been proven in a few works to be an efficient method for experiments involving many parameters.  With this method, the responses could be optimized efficiently by using only a few experiments. Besides, several responses can be optimized simultaneously. Also, models could be built up and the changing tendency can be plotted to predict the required experimental settings for specific tasks.

Two types of well arrayed structures including monolayer arrays of silica spheres and vertically aligned ZnO rod arrays were investigated in this work. Monolayer arrays of silica spheres were synthesized by using a dual-speed spin coating method. With assistance of statistical experimental design, the accelerating rate, the second rotation speed and time of the dual-speed spin coating system were found as non-significant parameters to the ordering degree of the obtained monolayer, and thus they can be fixed. This finding could remarkably increase the feasibility of optimizing the practical process. On the other hand, the relative humidity, the first rotation speed and the suspension concentration are identified as the significant parameters to the structures of the monolayer. Moreover, the optimal values for these three parameters were identified: 23% for the relative humidity, 1000 rpm for the first rotation speed and 30 wt.% for the suspension concentration. With these optimized parameters, the area of the obtained silica sphere monolayers reached over 1 cm2 and the defect-free domain size reached over 4000 μm2. These values are considerably higher compared to the previously reported values.

Vertically aligned ZnO rod arrays were fabricated by chemical bath deposition. Parameters including precursor concentration, pH value, reaction temperature, reaction time and addition of capping agent were optimized by using statistical experimental design to improve and optimize the growth quality of ZnO rod arrays. Through several stages of optimization, the growth quality of the obtained structures was remarkably enhanced from sparse or clustered ZnO rods to upright and dense ZnO rods. The boundary conditions to achieve vertically aligned ZnO rods, such as a neutral solution and a precursor concentration over 0.02M, were determined. The changing tendency of the texture coefficient and aspect ratio with the factors was also plotted to predict the required experimental settings for specific requests. The points or regions to achieve the optimal properties were identified as well. For instance, the concentration should be as close as to 0.1 M, while the reaction temperature should be limited to 80-90 ◦C, to achieve the ideal preferential growth. With the optimized parameters, the texture coefficient reached almost the perfect value 1, and the aspect ratio was elevated to 21. Moreover, to obtain a dense ZnO thin film, tri-sodium citrate was added to the reaction system. The diameter was systematically controlled through varying the parameters. When both the diameter and the texture coefficient reached the optimal values, the rods were merged together to form a dense ZnO thin film.

Furthermore, comments on the statistical experimental method are proposed, and both the advantages and disadvantages are presented according to the present thesis work. This might help the researchers to avoid the disadvantages and thus to employ this method more efficiently in the future. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. x, 54 p.
Keyword
optimization, experimental design, statistical analysis, monolayer arrays of silica spheres, vertically aligned ZnO rod arrays
National Category
Other Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-172938 (URN)978-91-7595-676-3 (ISBN)
Public defence
2015-09-25, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150903

Available from: 2015-09-03 Created: 2015-09-02 Last updated: 2016-09-23Bibliographically approved

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