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Synthesis of well arrayed structures with assistance of statistical experimental design
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
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 [en]
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: urn:nbn:se:kth:diva-172938ISBN: 978-91-7595-676-3 (print)OAI: oai:DiVA.org:kth-172938DiVA: diva2:850817
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
List of papers
1. Controllable fabrication of large-area 2D colloidal crystal masks with large size defect-free domains based on statistical experimental design
Open this publication in new window or tab >>Controllable fabrication of large-area 2D colloidal crystal masks with large size defect-free domains based on statistical experimental design
2014 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 313, 144-151 p.Article in journal (Refereed) Published
Abstract [en]

A large-area hexagonal packed monolayer of silica spheres with consistent defect-free domains of a size larger than 3000 mu m(2) was prepared by spin coating on glass substrates with the assistance of experimental design and statistical analysis. The ratio of the defect-free monolayer area to the square of sphere diameter is nearly two times of the previously reported maximum values. Several parameters involved in the spin coating systems were investigated. The results indicated that the relative humidity and the rotational speed of the first step of the spin coating had the most important impact on the ordering degree of the prepared monolayer. Furthermore, the ordering degree of the obtained monolayer increased with a decreased relative humidity. In addition, it reached an optimal value when the first rotational speed during spin coating reached a value of 1000 rpm. From this study, it can be concluded that statistical experimental design is an efficient strategy, especially for multi-factor phenomenon studies.

Keyword
Monolayer colloidal crystals, Statistical experimental design, Defect-free domain size, Quality-control parameters
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-151325 (URN)10.1016/j.apsusc.2014.05.167 (DOI)000340689000020 ()2-s2.0-84904789242 (Scopus ID)
Note

QC 20140918

Available from: 2014-09-18 Created: 2014-09-18 Last updated: 2017-12-05Bibliographically approved
2. Fabrication of large size defect-free domains of 2D colloidal crystal monolayer withassistance of statistical experimental design
Open this publication in new window or tab >>Fabrication of large size defect-free domains of 2D colloidal crystal monolayer withassistance of statistical experimental design
(English)Manuscript (preprint) (Other academic)
National Category
Other Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-172944 (URN)
Note

QS 2015

Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2015-09-03Bibliographically approved
3. Improvement and optimization of the growth quality of upright ZnOrod arrays by the response surface methodology
Open this publication in new window or tab >>Improvement and optimization of the growth quality of upright ZnOrod arrays by the response surface methodology
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
Keyword
ZnO rod arrays; Response surface methodology; Design of experiment
National Category
Other Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-172943 (URN)10.1016/j.apsusc.2015.05.144 (DOI)000359496600058 ()2-s2.0-84964528913 (Scopus ID)
Note

QC 20150903

QC2 0150914

Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2017-12-04Bibliographically approved
4. Optimization of high-quality vertically aligned ZnO rod arrays by the response surface methodology
Open this publication in new window or tab >>Optimization of high-quality vertically aligned ZnO rod arrays by the response surface methodology
2015 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 626, 180-188 p.Article in journal (Refereed) Published
Abstract [en]

Optimization of the deposition parameters was conducted by the response surface methodology to synthesize high-quality ZnO rod arrays with a high texture coefficient, a large aspect ratio and a narrow bandgap. In addition, mathematical models based on statistical analysis were also developed to predict the texture coefficient, aspect ratio and bandgap of the ZnO rod arrays. With the optimized parameters, all of the three involved responses obtained the desired optimum values. The results show that the texture coefficient can be elevated up to a value of 0.998, which represents an almost perfect value. Moreover, wide range of aspect ratios was obtained for various applications and the obtained maximum value of 21.3 is relatively high value by wet chemical method, especially when no capping agent and no refreshing growth solution in a nearly neutral solution is used.

Keyword
ZnO rod arrays, Optimization, Response surface methodology
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-159606 (URN)10.1016/j.jallcom.2014.11.166 (DOI)000348025400028 ()2-s2.0-84919675078 (Scopus ID)
Note

QC 20150210

Available from: 2015-02-10 Created: 2015-02-05 Last updated: 2017-12-04Bibliographically approved
5. Optimization of synthesizing upright ZnO rod arrays with large diameters through response surface methodology
Open this publication in new window or tab >>Optimization of synthesizing upright ZnO rod arrays with large diameters through response surface methodology
(English)Manuscript (preprint) (Other academic)
National Category
Other Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-172945 (URN)
Note

QS 2015

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

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