Synthesis and optical properties of aluminum nitride nanowires prepared by arc discharge method

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Abstract

AlN nanowires with hexagonal structure were successfully synthesized by direct reaction of aluminum with nitrogen gas using arc discharge method. The wurtzite AlN nanowires have an average diameter of 40 nm and a length of several tens micrometer. The growth direction of most single-crystalline AlN nanowires is perpendicular to the [0 0 1] direction, while it is also found that the AlN nanowires grow along [0 0 1] direction. The vapor–solid growth mechanism can explain the formation of the AlN nanowires. Raman spectroscopy studies of the AlN nanowires reveal that the stress is rather low and the crystallinity is close to bulk AlN. The UV spectrum of the AlN nanowires shows that the absorption edge at 6.23 eV is comparable with that of the bulk AlN. The photoluminescence of the AlN nanowires suggests that the emission band at 506 nm may be ascribed to the deep level defect due to nitrogen vacancy.

Introduction

One-dimensional (1D) nanostructured materials have attracted much attention because of their unique properties derived their high surface area and low dimensionality [1], [2], which are particularly important not only for understanding fundamental concepts underlying the observed optical, electronic, and mechanical properties of materials, but also for being potentially applicable to nanoscale devices [3], [4], [5], [6]. Therefore, the synthesis and properties of various 1D nanostructured materials are enthusiastically stimulated since the discovery of carbon nanotubes [7].

As an important III–V semiconductor, aluminum nitride (AlN) has a wide band gap (6.2 eV), a large exciton binding energy, and a very small electron affinity. These attractive physical properties make it potential application in surface acoustic wave, ultraviolet sensor, and field-emission devices [8], [9], [10]. Consequently, 1D AlN nanostructures are of fresh interest at present due to its promising application in optoelectronic and field-emission nanodevice [11], [12]. Very recently, several routes have been developed to prepare 1D AlN nanowires, such as carbon nanotubes confined reaction [13], confined method of anodic porous aluminum template [14], extended vapor–liquid–solid growth technique [15] and direct reaction of Al or Al alloy in a mixture of nitrogen and ammonia gas (N2 + NH3) [16], [17]. All these method, the flowing NH3 was employed as necessary nitrogen source and a crucial condition for synthesis of AlN nanowires. Additionally, the NH3 flux and ratio of NH3 to N2 also was accurately controlled and the reaction time is usually not less than two hours. In this paper, we successfully synthesized abundant AlN nanowires in five minutes by direct reaction of Al with N2 using direct current arc discharge method without catalyst and template. The optical properties of the as-synthesized AlN nanowires are also investigated.

Section snippets

Experimental

The direct current arc discharge apparatus used in this experiment has been described elsewhere [18]. In brief, the pure metal Mo (purity 99.99%) rod (10 mm in diameter and 160 mm in length) was used as the cathode. The Al (purity 99.99%) column (30 mm in diameter, 30 mm in height) as raw material was tightly inserted into a water-cooled anode copper crucible. The distance is about 20 mm between the tip of the Mo cathode and the Al column. Before arc discharging, the reaction chamber was evacuated

Results and discussion

Fig. 1(a)–(d) shows the SEM images of the as-synthesized product without affecting their original nature. Fig. 1(a) shows clearly a high density of AlN nanowires, which reveals that the nanowires have the length about tens of micrometers. The high-magnification SEM image of these nanowires is shown in Fig. 1(b), which shows the nanowires have a uniform diameter about 40 nm. Additionally, the quasi-aligned AlN nanowires are also observed, as shown in Fig. 1(c) and (d). These nanowires grow across

Conclusions

High density of wurtzite AlN nanowires with length about several tens micrometer and average diameter 40 nm were successfully synthesized through the direct reaction of Al and N2 without catalyst and template. The arc discharge system provides automatically a chemical-vapor transport and condensation process. The formation of AlN nanowires can be understanded by vapor–solid growth mechanism. The characterization of Raman spectrum results indicates that the crystallization of AlN nanowires is

Acknowledgments

This work was financially supported by the Natural Science Foundation of China (No. 10647138), Scientific Research Foundation of the Educational Bureau of Liaoning Province (No. 20060667), and National Basic Research Program of China (No. 2005CB724400). We thank Dongshan Zhao at center of electron Microscopy in Wuhan University for his technical support.

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