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Fabrication and Characterization of Zinc Oxide Nanostructures for Piezoelectric, Mechanical and Electrical Applications
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
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 [en]
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: urn:nbn:se:liu:diva-106207ISBN: 978-91-7519-316-8 (print)OAI: oai:DiVA.org:liu-106207DiVA: diva2:714612
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
List of papers
1. Piezoelectric power generation from zinc oxide nanowires grown on paper substrate
Open this publication in new window or tab >>Piezoelectric power generation from zinc oxide nanowires grown on paper substrate
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2012 (English)In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 6, no 2, 80-82 p.Article in journal (Refereed) Published
Abstract [en]

In this study, we demonstrate piezoelectric power generation from zinc oxide (ZnO) nanowires grown on paper substrate. Vertically aligned ZnO nanowires are deflected by an atomic force microscopy (AFM) tip in contact mode which generates an output voltage of up to 7 mV. Furthermore, the effects of different parameters mainly influencing the magnitude of the output voltage are discussed. We expect that due to its simplicity, this approach represents an important step within the development of nanoscale power generators. It offers a promising alternative powering source for the next generation of nanodevices on disposable paper.

Place, publisher, year, edition, pages
Wiley-VCH Verlag Berlin, 2012
Keyword
ZnO, nanowires, piezoelectric effects, power generation, paper substrates
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-76026 (URN)10.1002/pssr.201105519 (DOI)000300768400011 ()
Available from: 2012-03-29 Created: 2012-03-23 Last updated: 2017-08-30
2. Nanoscale piezoelectric response of ZnO nanowires measured using a nanoindentation technique
Open this publication in new window or tab >>Nanoscale piezoelectric response of ZnO nanowires measured using a nanoindentation technique
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2013 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 26, 11113-11118 p.Article in journal (Refereed) Published
Abstract [en]

We report the piezoelectric properties of ZnO nanowires (NWs) obtained by using a nanoindenter with a conductive boron-doped diamond tip. The direct piezoelectric effect was measured by performing nanoindentations under load control, and the generated piezoelectric voltage was characterized as a function of the applied loads in the range 0.2-6 mN. The converse piezoelectric effect was measured by applying a DC voltage to the sample while there was a low applied force to allow the tip being always in physical contact with the NWs. Vertically aligned ZnO NWs were grown on inexpensive, flexible, and disposable paper substrates using a template-free low temperature aqueous chemical growth method. When using the nanoindenter to measure the direct piezoelectric effect, piezopotential values of up to 26 mV were generated. Corresponding measurement of the converse piezoelectric effect gave an effective piezoelectric coefficient d(33)(eff) of similar to 9.2 pm V-1. The ZnO NWs were also characterized using scanning electron microscopy, X-ray diffraction, and high-resolution transmission electron microscopy. The new nanoindentation approach provides a straightforward method to characterize piezoelectric material deposited on flexible and disposable substrates for the next generation of nanodevices.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-96500 (URN)10.1039/c3cp50915j (DOI)000320321600061 ()
Available from: 2013-08-23 Created: 2013-08-20 Last updated: 2017-12-06
3. Zinc Oxide Nanowire Based Piezoelectric Nano Generators Grown on Flexible Substrates
Open this publication in new window or tab >>Zinc Oxide Nanowire Based Piezoelectric Nano Generators Grown on Flexible Substrates
2013 (English)In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 1556Article in journal (Refereed) Published
Abstract [en]

Flexible substrates, like plastic, paper and cotton fabrics can be of interest for several reasons in connection to the appealing issue of generating voltage-current from piezoelectric ZnO nanowires (NWs). Zinc oxide NWs have shown very high voltage generation and they are possible to grown on plastic, paper and cotton. Since we with these substrates can get a new freedom to bend and also stretch the NWs and to incorporate them into new applications they are of great potential. Here we will describe the mechanical and piezoelectric properties of ZnO NWs grown on ordinary clean room paper and on cotton fabrics substrates as well as possibility of coating the ZnO NWs to maximize the output generated power. An enhancement of 160 times in the piezo-potential was observed from ZnO NWs coated with P3HT p-type polymer compared to non-coated NWs.

Place, publisher, year, edition, pages
Cambridge Journals Online, 2013
Keyword
energy generation, nano-indentation, solution deposition
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106203 (URN)10.1557/opl.2013.868 (DOI)
Available from: 2014-04-28 Created: 2014-04-28 Last updated: 2017-08-30Bibliographically approved
4. Enhancing the piezopotential from Zinc oxide (ZnO) nanowire usingp-type polymers
Open this publication in new window or tab >>Enhancing the piezopotential from Zinc oxide (ZnO) nanowire usingp-type polymers
2014 (English)In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 124, 123-125 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated the effects of different p-type polymer layers on the piezoelectric potential from ZnO nanowire (NWs) grown on silver (Ag) coated silicon (Si) substrate by the low temperature chemical synthesis method. Piezoelectric measurement was performed by a conductive atomic force microscope (AFM). In the case of the poly(3,4-ethylenedioxythiophene-Tosylate (PEDOT-Tos), the output voltage is enhanced by about 95 mV, compared to 18 mV with the poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (PEDOT-PSS) layer. The enhancement in the output piezopotential was attributed to the reduction of the screening effect due to free charge carriers. It is suggested that the present method may be one of the best possible alternative ways to improve the piezo-potential output from ZnO NWs nanogenerators.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
ZnO, Nanowires, Nanogenerator
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-106204 (URN)10.1016/j.matlet.2014.03.047 (DOI)000336464400034 ()
Available from: 2014-04-28 Created: 2014-04-28 Last updated: 2017-08-30
5. Nanoscale elastic modulus of single horizontal ZnO nanorod using nanoindentation experiment
Open this publication in new window or tab >>Nanoscale elastic modulus of single horizontal ZnO nanorod using nanoindentation experiment
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2012 (English)In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 7, 146-148 p.Article in journal (Refereed) Published
Abstract [en]

We measure the elastic modulus of a single horizontal ZnO nanorod [NR] grown by a low-temperature hydrothermal chemical process on silicon substrates by performing room-temperature, direct load-controlled nanoindentation measurements. The configuration of the experiment for the single ZnO NR was achieved using a focused ion beam/scanning electron microscope dual-beam instrument. The single ZnO NR was positioned horizontally over a hole on a silicon wafer using a nanomanipulator, and both ends were bonded with platinum, defining a three-point bending configuration. The elastic modulus of the ZnO NR, extracted from the unloading curve using the well-known Oliver-Pharr method, resulted in a value of approximately 800 GPa. Also, we discuss the NR creep mechanism observed under indentation. The mechanical behavior reported in this paper will be a useful reference for the design and applications of future nanodevices.

Place, publisher, year, edition, pages
Springer, 2012
National Category
Ceramics Physical Sciences
Identifiers
urn:nbn:se:liu:diva-88523 (URN)10.1186/1556-276X-7-146 (DOI)22353250 (PubMedID)
Available from: 2013-02-11 Created: 2013-02-11 Last updated: 2017-12-06
6. 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
7. Interface trap characterization and electrical properties of Au-ZnO nanorod Schottky diodes by conductance and capacitance methods
Open this publication in new window or tab >>Interface trap characterization and electrical properties of Au-ZnO nanorod Schottky diodes by conductance and capacitance methods
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2012 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 6, 064506- p.Article in journal (Refereed) Published
Abstract [en]

Schottky diodes with Au/ZnO nanorod (NR)/n-SiC configurations have been fabricated and their interface traps and electrical properties have been investigated by current-voltage (I-V), capacitance-voltage (C-V), capacitance-frequency (C-f), and conductance-frequency (G(p)/omega-omega) measurements. Detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements was performed to extract the information about the interface trap states. The discrepancy between the high barrier height values obtained from the I-V and the C-V measurements was also analyzed. The higher capacitance at low frequencies was attributed to excess capacitance as a result of interface states in equilibrium in the ZnO that can follow the alternating current signal. The energy of the interface states (E-ss) with respect to the valence band at the ZnO NR surface was also calculated. The densities of interface states obtained from the conductance and capacitance methods agreed well with each other and this confirm that the observed capacitance and conductance are caused by the same physical processes, i.e., recombination-generation in the interface states. (C) 2012 American Institute of Physics.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85203 (URN)10.1063/1.4752402 (DOI)000309423200151 ()
Available from: 2012-11-09 Created: 2012-11-09 Last updated: 2017-12-07
8. Systematic study of interface trap and barrier inhomogeneities using I-V-T characteristics of Au/ZnO nanorods Schottky diode
Open this publication in new window or tab >>Systematic study of interface trap and barrier inhomogeneities using I-V-T characteristics of Au/ZnO nanorods Schottky diode
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2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 23Article in journal (Refereed) Published
Abstract [en]

This paper presents in-depth analysis of I-V-T characteristics of Au/ZnO nanorods Schottky diodes. The temperature dependence I-V parameters such as the ideality factor and the barrier heights have been explained on the basis of inhomogeneity. Detailed and systematic analysis was performed to extract information about the interface trap states. The ideality factor decreases, while the barrier height increases with increase of temperature. These observations have been ascribed to barrier inhomogeneities at the Au/ZnO nanorods interface. The inhomogeneities can be described by the Gaussian distribution of barrier heights. The effect of tunneling, Fermi level pinning, and image force lowering has contribution in the barrier height lowering. The recombination-tunneling mechanism is used to explain the conduction process in Au/ZnO nanorods Schottky diodes. The ionization of interface states has been considered for explaining the inhomogeneities.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-95963 (URN)10.1063/1.4810924 (DOI)000321011700072 ()
Available from: 2013-08-19 Created: 2013-08-12 Last updated: 2017-12-06
9. Annealing effect on the electrical and optical properties of Au/n-ZnO NWs Schottky diodes white LEDs
Open this publication in new window or tab >>Annealing effect on the electrical and optical properties of Au/n-ZnO NWs Schottky diodes white LEDs
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2013 (English)In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 62, 200-206 p.Article in journal (Refereed) Published
Abstract [en]

We report the post-growth heat treatment effect on the electrical and the optical properties of hydrothermally grown zinc oxide (ZnO) nanowires (NWs) Schottky white light emitting diodes (LEDs). It was found that there is a changed in the electroluminescence (EL) spectrum when post growth annealing process was performed at 600 degrees C under nitrogen, oxygen and argon ambients. The EL spectrum for LEDs based on the as grown NWs show three bands red, green and blue centered at 724, 518 and 450 nm respectively. All devices based on ZnO NWs annealed in oxygen (O-2), nitrogen (N-2) and argon (Ar) ambient show blue shift in the violet and the red emissions whereas a red shift is observed in the green emission compared to the as grown NWs based device. The color rendering index (CRI) and the correlated color temperature (CCT) of all LEDs were calculated to be in the range 78-91 and 2753-5122 K, respectively. These results indicate that light from the LEDs can be tuned from cold white light to warm white light by post growth annealing.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
ZnO nanowires, Schottky diodes, Post growth annealing, Electroluminescence
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-100481 (URN)10.1016/j.spmi.2013.07.014 (DOI)000325588700022 ()
Available from: 2013-11-08 Created: 2013-11-08 Last updated: 2017-12-06

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