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Mechanical Characterization and Electrochemical Sensor Applications of Zinc Oxide Nanostructures
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanotechnology is emerging to be one of the most important scientific disciplines that physics, chemistry and biology truly overlap with each other. Over the last two decades science and technology have witnessed tremendous improvement in the hope of unveiling the true secrets of the nature in molecular or atomic level. Today, the regime of nanometer is truly reached.

ZnO is a promising material due to the wide direct band gap (3.37 eV) and the room temperature large exciton binding energy (60 meV). Recent studies have shown considerable attraction towards ZnO nanostructures, particularly on one-dimensional ZnO nanorods, nanowires, and nanotubes due to the fact that, for a large number of applications, shape and size of the ZnO nanostructures play a vital role for the performance of the devices. The noncentrosymmetric property of ZnO makes it an ideal piezoelectric material for nanomechanical devices. Thus, mechanical characterization of one dimensional ZnO nanostructures including strength, toughness, stiffness, hardness, and adhesion to the substrate is very important for the reliability and efficient operation of piezoelectric ZnO nanodevices. Moreover, owing to the large effective surface area with high surface-to-volume ratio, the surface of one dimensional ZnO nanowires, nanorods, and nanotubes is very sensitive to the changes in surface chemistry and hence can be utilized to fabricate highly sensitive ZnO electrochemical sensors.

This thesis studies mechanical properties and electrochemical sensor applications of ZnO nanostructures.

The first part of the thesis deals with mechanical characterization of vertically grown ZnO nanorods and nanotubes including buckling, mechanical instability, and bending flexibility. In paper I, we have investigated mechanical instability and buckling characterization of vertically aligned single-crystal ZnO nanorods grown on Si, SiC, and sapphire substrates by vapor-liquid-solid (VLS) method. The critical loads for the ZnO nanorods grown on Si, SiC, and sapphire were measured and the corresponding buckling and adhesion energies were calculated. It was found that the nanorods grown on SiC substrate have less residual stresses and are more stable than the nanorods grown on Si and sapphire substrates.

Paper II investigates nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of vertically aligned single crystal ZnO nanorods/nanowires grown by VLS and aqueous chemical growth (ACG) methods. We observed that the loading and unloading behaviors during the bending test of the as-grown samples were highly symmetrical and the highest point on the bending curves and the first inflection and critical point were very close. The results also show that the elasticity of the ZnO single crystal is approximately linear up to the first inflection point and is independent of the growth method.

In Paper III, we quantitatively investigated the buckling and the elastic stability of vertically well aligned ZnO nanorods and ZnO nanotubes grown on Si substrate by nanoindentation technique. We found that the critical load for the nanorods was five times larger than the critical load for nanotubes. On the contrary, the flexibility for nanotubes was five times larger than nanorods. The discovery of high flexibility for nanotubes and high elasticity for nanorods can be utilized for designing efficient piezoelectric nanodevices.

The second part of this thesis investigates electrochemical sensor applications of ZnO nanorods, nanotubes , and nanoporous material.

In paper IV, we utilized functionalized ZnO nanorods on the tip of a borosilicate glass capillary coated with ionophore-membrane to construct intracellular Ca2+ selective sensor. The sensor exhibited a Ca2+-dependent electrochemical potential difference and the response was linear over a large dynamic concentration range, which enabled this sensor to measure Ca2+ concentrations in human adipocytes or in frog oocytes. The results were consistent with the values of Ca2+ concentrations reported in the literature.

In paper V, ZnO nanotubes and nanorods were used to create pH sensor devices. The developed ZnO pH sensors display good reproducibility, repeatability, and long-term stability. The ZnO pH sensors exhibited a pH-dependent electrochemical potential difference over a large dynamic pH range. We found that the ZnO nanotubes provide sensitivity as high as twice that of the ZnO nanorods. The possible reasons of enhanced sensitivity were explained.

Paper VI investigates an improved potentiometric intracellular glucose biosensor based on the immobilization of glucose oxidase on the ZnO nanoporous material. We demonstrated that using ZnO nanoporous material as a matrix material for enzyme immobilization improves the sensitivity of the biosensor as compared to using ZnO nanorods. In addition, the fabrication method of the intracellular biosensor was simple and excellent performance in sensitivity, stability, selectivity, reproducibility, and anti-interference was achieved.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2010. , 61 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1323
Keyword [en]
Nanotechnology, Zinc Oxide, nanorods, nanotubes, nanoporous, buckling, electrochemical sensor
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-57297ISBN: 978-91-7393-369-8 (print)OAI: oai:DiVA.org:liu-57297DiVA: diva2:324728
Public defence
2010-06-04, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15
Opponent
Supervisors
Available from: 2010-06-16 Created: 2010-06-16 Last updated: 2014-01-15Bibliographically approved
List of papers
1. Buckling and mechanical instability of ZnO nanorods grown on different substrates under uniaxial compression
Open this publication in new window or tab >>Buckling and mechanical instability of ZnO nanorods grown on different substrates under uniaxial compression
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2008 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Nanotechnology, Vol. 19, no 41Article in journal (Refereed) Published
Abstract [en]

Mechanical instability and buckling characterization of vertically aligned single-crystal ZnO nanorods grown on different substrates including Si, SiC and sapphire (a-Al2O3) was done quantitatively by the nanoindentation technique. The nanorods were grown on these substrates by the vapor-liquid-solid (VLS) method. The critical load for the ZnO nanorods grown on the Si, SiC and Al2O3 substrates was found to be 188, 205 and 130 µN, respectively. These observed critical loads were for nanorods with 280 nm diameters and 900 nm length using Si as a substrate, while the corresponding values were 330 nm, 3300 nm, and 780 nm, 3000 nm in the case of SiC and Al2O3 substrates, respectively. The corresponding buckling energies calculated from the force displacement curves were 8.46 × 10-12, 1.158 × 10-11 and 1.092 × 10-11 J, respectively. Based on the Euler model for long nanorods and the J B Johnson model (which is an extension of the Euler model) for intermediate nanorods, the modulus of elasticity of a single rod was calculated for each sample. Finally, the critical buckling stress and strain were also calculated for all samples. We found that the buckling characteristic is strongly dependent on the quality, lattice mismatch and adhesion of the nanorods with the substrate. © IOP Publishing Ltd.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49654 (URN)10.1088/0957-4484/19/41/415708 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
2. Bending flexibility, kinking, and buckling characterization of ZnO nanorods/nanowires grown on different substrates by high and low temperature methods
Open this publication in new window or tab >>Bending flexibility, kinking, and buckling characterization of ZnO nanorods/nanowires grown on different substrates by high and low temperature methods
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2008 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 104, no 10, 104306- p.Article in journal (Refereed) Published
Abstract [en]

Nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of vertically aligned single crystal ZnO nanorods/nanowires were performed quantitatively by nanoindentation technique. These nanostructures were grown by the vapor liquid solid (VLS) method, a relatively high temperature approach, and the aqueous chemical growth (ACG) method, a relatively low temperature approach on different substrates, including SiC and Si. The first critical load at the inflection point found for the ZnO nanorods/nanowires grown by ACG method was 105 mu N on the SiC substrates and 114 mu N on the Si substrates. The corresponding buckling energies calculated from the force-displacement curves were 3.15x10(-12) and 2.337x10(-12) J, respectively. Similarly, for the samples grown by the VLS method, the first critical load at the inflection point and the corresponding buckling energies were calculated from the force-displacement curves as 198 mu N and 7.03x10(-12) J on the SiC substrates, and 19 mu N and 1.805x10(-13) J on the Si substrates. Moreover, the critical buckling stress, strain, and strain energy were also calculated for all samples. The strain energy for all samples was much less than the corresponding buckling energy. This shows that our as-grown samples are elastic and flexible. The elasticity measurement was performed for all the samples before reaching the first critical and kinking inflection point, and we subsequently observed the bending flexibility, kinking, and buckling phenomena on the same nanorods/nanowires. We observed that the loading and unloading behaviors during the bending test of the as-grown samples were highly symmetrical, and also that the highest point on the bending curves and the first inflection and critical point were very close. ZnO nanorods/nanowires grown on SiC by the ACG method, and those grown by the VLS method on Si substrates, show a linear relation and high modulus of elasticity for the force and displacement up to the first inflection and critical point. The results also show that the elasticity of the ZnO single crystal is approximately linear up to the first inflection point, is independent of the growth method and is strongly dependent on the verticality on the surface of the substrates. In addition, the results show that after the first buckling point, the nanorods/nanowires have plasticity, and become more flexible to produce multiple kinks.

Keyword
bending, buckling, crystal growth from solution, elastic moduli, II-VI semiconductors, indentation, plasticity, semiconductor quantum wires, zinc compounds
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16618 (URN)10.1063/1.3018090 (DOI)
Note
Original Publication: Riaz Muhammad, Alimujiang Fulati, Lili Yang, O Nour, Magnus Willander and P Klason , Bending flexibility, kinking, and buckling characterization of ZnO nanorods/nanowires grown on different substrates by high and low temperature methods, 2008, JOURNAL OF APPLIED PHYSICS, (104), 10, 104306-. http://dx.doi.org/10.1063/1.3018090 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2009-02-18 Created: 2009-02-06 Last updated: 2017-12-14Bibliographically approved
3. Buckling and elastic stability of vertical ZnO nanotubes and nanorods
Open this publication in new window or tab >>Buckling and elastic stability of vertical ZnO nanotubes and nanorods
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2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 3, 034309- p.Article in journal (Refereed) Published
Abstract [en]

Buckling and elastic stability study of vertical well aligned ZnO nanorods grown on Si substrate and ZnO nanotubes etched from the same nanorods was done quantitatively by nanoindentation technique. The critical load, modulus of elasticity, and flexibility of the ZnO nanorods and nanotubes were observed and we compared these properties for the two nanostructures. It was observed that critical load of nanorods (2890 mu N) was approximately five times larger than the critical load of the nanotubes (687 mu N). It was also observed that ZnO nanotubes were approximately five times more flexible (0.32 nm/mu N) than the nanorods (0.064 nm/mu N). We also calculated the buckling energies of the ZnO nanotubes and nanorods from the force displacement curves. The ratio of the buckling energies was also close to unity due to the increase/decrease of five times for one parameter (critical load) and increase/decrease of five times for the other parameter (displacement) of the two samples. We calculated critical load, critical stress, strain, and Young modulus of elasticity of single ZnO nanorod and nanotube. The high flexibility of the nanotubes and high elasticity of the ZnO nanorods can be used to enhance the efficiency of piezoelectric nanodevices. We used the Euler buckling model and shell cylindrical model for the analysis of the mechanical properties of ZnO nanotubes and nanorods.

Keyword
buckling, crystal growth, II-VI semiconductors, semiconductor growth, semiconductor nanotubes, Youngs modulus, zinc compounds
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-20404 (URN)10.1063/1.3190481 (DOI)
Available from: 2009-09-08 Created: 2009-09-07 Last updated: 2017-12-13
4. Functionalized zinc oxide nanorod with ionophore-membrane coatingas an intracellular Ca2+ selective sensor
Open this publication in new window or tab >>Functionalized zinc oxide nanorod with ionophore-membrane coatingas an intracellular Ca2+ selective sensor
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2009 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, no 2, 23703- p.Article in journal (Refereed) Published
Abstract [en]

The tip of a borosilicate glass capillary with functionalized hexagonal ZnO nanorods was used to make a sensitive electrochemical intracellular Ca2+ sensor. To adjust the sensor for Ca2+ measurements with sufficient selectivity and stability, polyvinyl chloride (PVC) membrane containing Ca2+ ionophores were coated on the surface. The membrane covered ZnO nanorods exhibited a Ca2+-dependent electrochemical potential difference versus an Ag/AgCl reference electrode. The potential difference was linear over a large concentration range (100 nM to 10 mM). The measurements of Ca2+ concentrations using our ZnO nanorods sensor in human fat cells or in frog egg cells were consistent with values of Ca2+ concentrations reported in the literature. This nanoelectrode device paves the way to measurements of intracellular biochemical species in specific locations within single living cells.

Place, publisher, year, edition, pages
EBSCO/American Institute of Physics, 2009
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-19516 (URN)10.1063/1.3176441 (DOI)
Note
On the day of the defence date the status of this article was Submitted.Available from: 2009-06-25 Created: 2009-06-25 Last updated: 2017-12-13Bibliographically approved
5. Miniaturized pH Sensors Based on Zinc Oxide Nanotubes/Nanorods
Open this publication in new window or tab >>Miniaturized pH Sensors Based on Zinc Oxide Nanotubes/Nanorods
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2009 (English)In: SENSORS, ISSN 1424-8220, Vol. 9, no 11, 8911-8923 p.Article in journal (Refereed) Published
Abstract [en]

ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The developed ZnO nanotube and nanorod pH sensors display good reproducibility, repeatability and long-term stability and exhibit a pH-dependent electrochemical potential difference versus an Ag/AgCl reference electrode over a large dynamic pH range. We found the ZnO nanotubes provide sensitivity as high as twice that of the ZnO nanorods, which can be ascribed to the fact that small dimensional ZnO nanotubes have a higher level of surface and subsurface oxygen vacancies and provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods, thus affording the ZnO nanotube pH sensor a higher sensitivity. Experimental results indicate ZnO nanotubes can be used in pH sensor applications with improved performance. Moreover, the ZnO nanotube arrays may find potential application as a novel material for measurements of intracellular biochemical species within single living cells.

Keyword
ZnO nanotubes, ZnO nanorods, pH sensors, potentiometric measurements
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-52415 (URN)10.3390/s91108911 (DOI)
Available from: 2010-01-11 Created: 2009-12-18 Last updated: 2014-10-01
6. An intracellular glucose biosensor based on nanoflake ZnO
Open this publication in new window or tab >>An intracellular glucose biosensor based on nanoflake ZnO
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2010 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 150, no 2, 673-680 p.Article in journal (Other academic) Published
Abstract [en]

In this study, an improved potentiometric intracellular glucose biosensor was fabricated with immobilization of glucose oxidase on a ZnO nanoporous material. The ZnO nanoporous material with a wall thickness around 200 nm was grown on the tip of a borosilicate glass capillary and used as a selective intracellular glucose sensor for the measurement of glucose concentrations in human adipocytes and frog oocytes. The results showed a fast response within 4 s and a linear glucosedependent electrochemical response over a wide range of glucose concentration (500 nM-10 mM). The measurements of intracellular glucose concentrations with our biosensor were consistent with the values of intracellular glucose concentrations reported in the literature. The sensor also demonstrated its capability by detecting an increase in the intracellular glucose concentration induced by insulin. We found that the ZnO nanoporous material provides sensitivity as high as 1.8 times higher than that obtained using ZnO nanorods under the same conditions. Moreover, the fabrication method in our experiment is simple and the excellent performance of the developed nanosensor in sensitivity, stability, selectivity, reproducibility and anti-interference was achieved. All these advantageous features of this intracellular glucose biosensor based on functionalised ZnO nanoporous material compared to ZnO nanorods demonstrate a promising way of enhancing glucose biosensor performance to measure reliable intracellular glucose concentrations within single living cells.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
Glucose oxidase (GOD), Intracellular, Potentiometric biosensor, Nanoflake ZnO, Nafion membrane
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-57294 (URN)10.1016/j.snb.2010.08.021 (DOI)000284339800026 ()
Note

Original Publication:Alimujiang Fulati, Syed M. Usman Ali, Muhammad H. Asif, Naveed Ul Hassan Alvi, Magnus Willander, Cecilia Brännmark, Peter Strålfors, Sara I. Börjesson and Fredrik Elinder, An intracellular glucose biosensor based on nanoflake ZnO, 2010, Sensors and actuators. B, Chemical, (150), 2, 673-680.http://dx.doi.org/10.1016/j.snb.2010.08.021Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com/

Available from: 2010-06-16 Created: 2010-06-16 Last updated: 2017-12-12Bibliographically approved

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