Pulsed laser deposition of indium tin oxide nanowires in argon and helium
Highlights
► Indium tin oxide (ITO) nanowires were formed using pulsed laser deposition. ► These nanowires were 20–30 nm in diameter and 70–80 nm in length. ► Highly crystalline, their lattice plane (400) was aligned to the longitudinal axis. ► These nanowires were possibly formed via the vapor–liquid–solid mechanism.
Introduction
Indium tin oxide (ITO) has been used as the transparent conducting electrode and hole injection anode [1]. ITO nanostructures, which include nanowires, nanorods, nanowhiskers and nanocrystal, were prepared by co-evaporating method [2], sol electrophoresis with a template [3], gold catalyst-assisted vapor–liquid–solid growth process [4], and electron beam evaporation [5]. Raluca Save et al. [6] reported on the ITO nanowires obtained by pulsed laser deposition on a catalyst-free silica substrate at 500 °C with nitrogen as the background gas. It was observed that the nitrogen pressure influenced the orientation of nanowire as well as transformation, at 2 mbar, of ITO from nanowires to nano-pyramids. The effects of different background gases on electrical and optical properties of ITO by pulsed laser deposition were previously reported by Thestrup et al. [7] and our group [8], but ITO nanostructures were not observed. In this paper, we report that ITO nanostructures, in particular, nanowires can be prepared by the Nd:YAG pulsed laser deposition in argon at relatively low temperature of 250 °C, and on the catalyst-free glass substrate.
Section snippets
Experimental
The deposition was performed with a Q-switched Nd:YAG pulsed laser (EKSPLA, NL301) at 355 nm [8]. The ablation target was a sintered, 2-inch diameter disk of ITO target with a composition of 90 wt.% In2O3 and 10 wt.% SnO2 (Target Materials, Inc., USA). The ITO target surface was first cleaned by ablation for 5 min by unfocused laser beam and the glass substrates were placed at 8 cm away. The deposition rate was estimated to be about 0.5 nm/s and the ITO film thickness was always maintained at 200 nm.
Results and discussions
The FESEM and XRD patterns of ITO samples grown in Ar and He ambient are shown in Fig. 1, Fig. 2, respectively. All the ITO nanowires have crystalline structure, which exhibit diffraction peaks only from the cubic bixbyite structure of In2O3[9]. There are four major diffraction peaks corresponding to (222), (400), (440) and (622) orientations. An obvious trend shown by the XRD diffraction pattern was that the (400) diffraction peak became relatively strong. For He, the nanowires could be
Conclusions
In summary, ITO nanowires have been deposited by the Nd:YAG pulsed laser ablation on glass substrates at a relatively low temperature of 250 °C in Ar and He at appropriate pressures. The growth process as a function of the ambient pressure allowed the fabrication of nanowire ITO with the (400) lattice plane being aligned to the longitudinal axis.
Acknowledgments
This project is supported by the research grants from Malaysia Ministry of Science, Technology and Innovation (MOSTI) (Project no: 03-02-01-SF0082) and Academic of Sciences Malaysia under Brain Gain Program.
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