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Buckling and elastic stability of vertical ZnO nanotubes and nanorods
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
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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.

Place, publisher, year, edition, pages
2009. Vol. 106, no 3, 034309- p.
Keyword [en]
buckling, crystal growth, II-VI semiconductors, semiconductor growth, semiconductor nanotubes, Youngs modulus, zinc compounds
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-20404DOI: 10.1063/1.3190481OAI: oai:DiVA.org:liu-20404DiVA: diva2:234515
Available from: 2009-09-08 Created: 2009-09-07 Last updated: 2017-12-13
In thesis
1. Mechanical Characterization and Electrochemical Sensor Applications of Zinc Oxide Nanostructures
Open this publication in new window or tab >>Mechanical Characterization and Electrochemical Sensor Applications of Zinc Oxide Nanostructures
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
Nanotechnology, Zinc Oxide, nanorods, nanotubes, nanoporous, buckling, electrochemical sensor
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-57297 (URN)978-91-7393-369-8 (ISBN)
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
2. Elastic Stability and Piezoelectric Power Generation Using ZnO Nanostructures
Open this publication in new window or tab >>Elastic Stability and Piezoelectric Power Generation Using ZnO Nanostructures
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanotechnology combines the effort between science and engineering using the approaches of either top-to-bottom or bottom-to-top techniques. A hybrid approach of the above techniques is also used for the fabrication of nanodevices. In nanotechnology one and zero dimensional structures are considered as the basic building blocks for multidimensional systems. One dimensional nanostructure such as nanorods, nanowires and nanotubes has become the research core of science and engineering, because of their unique and interesting properties for device applications.

In this thesis a mechanical property i.e. elastic stability, the behavior of piezoelectric power nanogenerator and the effects of ions irradiations were investigated for ZnO nanostructures.

Buckling phenomena was employed for the elastic stability investigation using Hysitron nanoindentor. ZnO nanostructures were loaded axially to a prescribed controlled load and then unloaded in the same fashion by the tip of a nanoindentor to investigate the first critical load and other unstable configurations. The present buckling study concluded that the elastic stability of ZnO nanostructures were mainly dependent on the slenderness ratio and the verticality of the structures to the substrates.

Piezoelectric power nanogenerators were investigated using ZnO nanowires. The performance of different piezoelectric power nanogenerators were observed on the bases of the aspect ratio, density of state, spatial density and the growth methods. A higher and stable voltage signal was generated by the vapor-liquid-solid (VLS) grown samples compared to the aqueous chemical growth (ACG) grown samples. The finite element (FE) method was also used to calculate the expected output voltage signal from ZnO nanogenerator with different aspect ratio. From the FE results we found that the output voltage of the nanogenerator was decreased above an aspect ratio of 80 for ZnO nanowires.

Ions irradiation effects were investigated using ZnO nanowires grown by the ACG method on Si substrate. Iodine and argon ions of energy 40 MeV and 30 keV were used using fluencies of 3 ×1016 ions/cm2, and 1.3 ×1013 ions/cm2, respectively. The results show that heavy and high energy irradiation modifies the morphology, crystalline structure and optical properties of ZnO nanowires.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 104 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1326
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-65405 (URN)978-91-7393-361-2 (ISBN)
Public defence
2010-08-27, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2011-02-07 Created: 2011-02-07 Last updated: 2014-01-15Bibliographically approved
3. Fabrication and Characterization of Zinc Oxide Nanostructures for Piezoelectric, Mechanical and Electrical Applications
Open this publication in new window or tab >>Fabrication and Characterization of Zinc Oxide Nanostructures for Piezoelectric, Mechanical and Electrical Applications
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanotechnology, the science of manipulating materials on an atomic or molecular scale is one of the fastest growing areas of research and technology. Nanotechnology has a vast range of applications in medicine, electronics, biomaterials and energy production. New developments in nanotechnology are growing all the time. In the near future, nanotechnology is expected to be a mature industry, with countless mainstream products.

Zinc Oxide (ZnO) is an important and optimal material in electronic and photonic applications due to its important properties like direct band gap (3.3 eV) semiconductor with large exciton binding energy (60 meV) which can provide more efficient excitonic emission even at room temperature. Beside that noncentrosymmetric property of ZnO makes it an ideal piezoelectric material. Various onedimensional ZnO nanostructures appear as an interesting material for a variety of mechanical, piezoelectric, optical, and electrical applications. ZnO nanostructures used in study were grown by the lower temperature aqueous chemical growth (ACG) on a variety of substrates.

The main objective of this research studies is to investigate the piezoelectric, mechanical and electrical phenomenon of ZnO nanostructured based nanodevices on cheap, disposable and flexible substrate like paper, plastic. As low cost fabrication of nanodevices is very crucial and best choice for the upcoming years. We have successfully demonstrated that paper substrates can be used for the growth of ZnO nanostructures.

In the first part, piezoelectric power nanogenerators based on ZnO NRs / NWs on flexible paper substrates were demonstrated and output piezopotential was investigated using atomic force microscopy (AFM). Different p-type polymers like poly (3-hexylthiophene) P3HT, poly(3,4-ethylenedioxythiophene-Tosylate (PEDOT-Tos) were coated around the ZnO NRs / NWs in order to minimize the screening effect and increase the output piezopotential and it was found that by introducing a layer of p-type polymer we get more piezopotential compared to non-coated ZnO NRs / NWs. We also demonstrated the direct and converse piezoelectric response from ZnO NWs grown on lighter, flexible paper substrate for the first time by using nanoindentation technique.

In the second part, the mechanical properties like elastic modulus and hardness of ZnO NRs / NWs and NTs were investigated by using nanoindenter. Elastic modulus of a single ZnO horizontal NR was demonstrated by nanoindentation technique based on three point bending configuration.  Buckling phenomena of ZnO NRs and NTs was investigated by nanoindenter and various parameters like buckling energy, elastic modulus, critical stress, and critical strain calculated under different end conditions.

In the third part of thesis fabrication of Au/n-ZnO Schottky devices were fabricated and their electrical and optical properties were investigated by current voltage (I-V), electroluminescence (EL) and impedance spectroscopy. We investigated interface trap states of Au/n-ZnO nanorods interface by temperature dependence I-V parameters. That study reveals that the ideality factor decreases, while the barrier height increases with increase of temperature. Detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements were performed to extract the information about the interface trap states. The energy of the interface states with respect to the valence band at the ZnO NR surface was also calculated. It was found that recombination-generation in the interface states are responsible for capacitance and conductance.

The effect of the post-growth annealing of Au/n-ZnO NWs Schottky diodes were examined and it was shown that light from the LEDs can be tuned from cold white light to warm white light by post growth annealing in different ambient.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 138 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1599
Keyword
Nanotechnology, Zinc oxide, nanowires/ nanorods / nanotubes, piezoelectric effect, nanogenerator, flexible substrate, p-type polymers, elastic modulus, LEDs, electrical characteristics
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-106207 (URN)978-91-7519-316-8 (ISBN)
Public defence
2014-05-27, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-04-28 Created: 2014-04-28 Last updated: 2014-04-28Bibliographically approved

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Riaz, MFulati, AlimujiangAmin, GulAlvi, N HNour, OmerWillander, Magnus

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