Low-temperature growth of ZnO nanowires
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I-Nan Lin Materials Science Center, National Tsing-Hua University, 101 Section 2 Kuang Fu Road, Hsinchu 300, Taiwan, Republic of China
Kuo-Shung Liu Department of Material Science and Engineering, National Tsing-Hua University, 101 Section 2 Kuang Fu Road, Hsinchu 300, Taiwan, Republic of China
Tzer-Shen Lin and I-Cherng Chena) Materials Research Laboratories, Industrial Technology Research Institute, Bldg. 77, 195 Section 4 Chung Hsing Road, Chutung, Hsinchu 310, Taiwan, Republic of China (Received 1 July 2002; accepted 30 December 2002)
ZnO nanowires with diameters of 40–200 nm were grown with a gold catalyst in bulk quantities on alumina substrates and sapphire substrates. This synthesis procedure was achieved by heating a 1:1 mixture of ZnO and Zn powder to 500 °C with trace water vapor as an oxidizer. X-ray diffraction and transmission electron microscopy revealed that the nanowires were in the pure wurtzite phase. Photoluminescence spectroscopy showed two peaks: one was a strong ultraviolet emission at around 380 nm, which corresponds to the near-band-edge emission; the other was a weak near-infrared emission around 750 nm, which indicates a low concentration of oxygen vacancy. Moreover, we observed that the Zn/Au alloy droplets appeared on the tips of ZnO nanowires. As a consequence, we can select areas to grow ZnO nanowires by patterning the thin metal film on the substrates. These findings prove that the low-temperature growth mechanism is via vapor–liquid–solid rather than vapor transport deposition or vapor supersaturation (vapor–solid) mechanism. On the basis of the site-specific growth and the low-temperature requirement developed from this work, the synthesis of ZnO is compatible to microelectric machining system processing.
I. INTRODUCTION
Semiconductor nanoparticles and nanowires have attracted much attention in recent years, especially in mesoscopic research and for potential applications in nanodevices. The main reasons are their interesting photonic and electronic properties. A crystalline wirelike structure was first formed by the vapor–liquid–solid (VLS) reaction in the 1960s.1–4 In that reaction, a liquid metal cluster or catalyst acts as an energetically favored site for absorption of gas-phase reactants. Then the cluster supersaturates and grows the material in a 1D structure. Most of the studies are focused on Si and III–V systems.5–9 Only a few studies of oxide systems have recently been conducted, including SiO2,10 GeO2,11
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J. Mater. Res., Vol. 18, No. 3, Mar 2003 Downloaded: 11 Mar 2015
ZnO,12–18 indium tin oxide,19 and Al2O3.20 Among them, ZnO is an n-type semiconductor with a wide band gap (3.30 eV). It emits short-wavelength light, conducts transparently, and is piezoelectric. Huang et al.12 reported the successful gas-phase synthesis of nanowires on a patterned Au catalyst by the VLS reaction. They used carbothermal or hydrogen reduction of ZnO as a zinc vapor sour
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