Non-catalytic growth of metal oxide nanowires : properties and growth mechanism investigations
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Perustieteiden korkeakoulu |
Doctoral thesis (article-based)
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Date
2011
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Degree programme
Language
en
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Verkkokirja (5644 KB, 39 s.)
Series
Aalto University publication series DOCTORAL DISSERTATIONS ,
132/2011
Abstract
This thesis is devoted to the non-catalytic syntheses of metal oxide nanowires (NWs), and investigations of their properties and growth mechanisms. Two different approaches were applied for the syntheses - metal resistive heating and vapor growth methods. The products were thoroughly characterized by electron microscopy, optical and X-ray characterization techniques. The synthesized NWs were examined for field emission (FE) and ultraviolet (UV) sensing applications. The resistive heating of various metals was demonstrated to be an efficient, simple and rapid method for the synthesis of CuO, Fe2O3, V2O5 and ZnO NWs under ambient air conditions. Fe2O3 NW formation was detected after just 2 s of heating; other metal oxide NWs were grown after 10 s. The NW growth mechanism during metal oxidation was explained based on observations of ZnO and Fe2O3 NW growth. The mechanism is based on the diffusion of metal ions to the surface through grain boundaries and to the tip of the growing NW through defect diffusion and by surface diffusion. FE from NWs grown by the resistive heating method exibited promising results for applications in vacuum electronic devices. Cold electron FE measurements showed that CuO NWs have a very low threshold electric field of 4 V/µm at a current density of 0.01 mA/cm². For the vapor growth of ZnO tetrapods (ZnO-Ts) a vertical flow reactor was designed and constructed. It was shown that the morphology of ZnO-Ts could be adjusted via the Zn vapor pressure in the reactor. The highest aspect ratio of ZnO-T legs was obtained at 700 °C, at a Zn partial pressure of 0.08 atm. ZnO-Ts demonstrated application possibilities for transparent and flexible UV sensors. Sensors based on ZnO-Ts showed a 45-fold current increase under UV irradiation with an intensity of 30 µW/cm² at a wavelength of 365 nm, and a response time of 0.9 s. The high performance of the device was explained by the multiple contact barriers.Description
Supervising professor
Kauppinen, Esko I., Prof.Thesis advisor
Nasibulin, Albert G., Dr.Keywords
metal oxide nanowires, non-catalytic, synthesis, growth mechanism, field emission, UV sensing
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Parts
- [Publication 1]: Albert G. Nasibulin, Simas Rackauskas, Hua Jiang, Ying Tian, Prasantha Reddy Mudimela, Sergey D. Shandakov, Larisa I. Nasibulina, Jani Sainio, and Esko I. Kauppinen. 2009. Simple and rapid synthesis of α-Fe2O3 nanowires under ambient conditions. Nano Research, volume 2, number 5, pages 373-379.
- [Publication 2]: Simas Rackauskas, Albert G. Nasibulin, Hua Jiang, Ying Tian, Gintare Statkute, Sergey D. Shandakov, Harri Lipsanen, and Esko I. Kauppinen. 2009. Mechanistic investigation of ZnO nanowire growth. Applied Physics Letters, volume 95, number 18, 183114, 3 pages. © 2009 American Institute of Physics (AIP). By permission.
- [Publication 3]: Simas Rackauskas, Albert G. Nasibulin, Hua Jiang, Ying Tian, Victor I. Kleshch, Jani Sainio, Elena D. Obraztsova, Sofia N. Bokova, Alexander N. Obraztsov, and Esko I. Kauppinen. 2009. A novel method for metal oxide nanowire synthesis. Nanotechnology, volume 20, number 16, 165603, 8 pages.
- [Publication 4]: Victor I. Kleshch, Simas Rackauskas, Albert G. Nasibulin, Esko I. Kauppinen, Elena D. Obraztsova, and Alexander N. Obraztsov. 2012. Field emission properties of metal oxide nanowires. Journal of Nanoelectronics and Optoelectronics, volume 7, number 1, pages 35-40.
- [Publication 5]: Simas Rackauskas, Kimmo Mustonen, Terhi Järvinen, Marco Mattila, Olga Klimova, Hua Jiang, Oleg Tolochko, Harri Lipsanen, Esko I. Kauppinen, and Albert G. Nasibulin. 2012. Synthesis of ZnO tetrapods for flexible and transparent UV sensors. Nanotechnology, volume 23, number 9, 095502, 7 pages. © 2012 by authors and © 2012 Institute of Physics Publishing (IOPP). By permission.