Field emission and photoluminescence characteristics of ZnS nanowires via vapor phase growth

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Abstract

Large-area ZnS nanowires were synthesized through a vapor phase deposition method. X-ray diffraction and electron microscopy results show that the products are composed of single crystalline ZnS nanowires with a cubic structure. The nanowires have sharp tips and are distributed uniformly on silicon substrates. The diameter of the bases is in the range of 320–530 nm and that of the tips is around 20–30 nm. The strong ultraviolet emission in the photoluminescence spectra also demonstrates that the ZnS nanowires are of high crystalline perfection. Field emission measurements reveal that the ZnS nanowires have a fairly low threshold field, which may be ascribed to their very sharp tips, rough surfaces and high crystal quality. The perfect field emission ability of the ZnS nanowires makes them a promising candidate for the fabrication of flexible cold cathodes.

Introduction

One-dimensional (1D) nanostructures are potentially ideal functional components for nanoscale electronics and optoelectronics. One-dimensional nanostructural materials have generated great interest as potential cold-cathode field emitters because of their ideal geometry with high aspect ratio [1]. The field emission properties of carbon nanotubes (CNTs) have been widely studied for this reason, and it has been founded that CNT emitters have the advantages of low operating voltage and high current density [2], [3]. Recently, 1D wide band-gap semiconductors such as ZnO, GaN, AlN etc. have also been widely investigated as promising cold-cathode materials [4], [5], [6]. In the present study we attempt to look for another alternative material to serve as a field emission emitter. Semiconductor ZnS has promise as a versatile material for applications such as electroluminescent devices, infrared widows and lasers due to its wide band-gap energy (3.6 eV at 300 K) [7], [8], [9]. However, to the best of our knowledge, few studies have been focused on the field emission from ZnS nanowires. In this paper, high purity ZnS nanowires were synthesized in high yield using a chemical vapor deposition method, and the unique photoluminescence and field emission characteristics of the ZnS nanowires are also presented.

Section snippets

Experiments

ZnS nanowires were synthesized on silicon substrates via a chemical vapor deposition method. A blank silicon substrate was cleaned for 10 min in an ultrasonic bath of absolute acetone before use. ZnS powders were put into a quartz boat, while the cleaned silicon substrate was put aside 30 mm away from the ZnS source. The boat was then loaded into the furnace and heated up to 900 C for 100 min. The carrier gas, argon with 10% (volume ratio) hydrogen, was introduced into the chamber at the flow

Results and discussions

Fig. 1 displays the XRD pattern of the deposition products, where four diffraction peaks at 28.52, 33.02, 47.50 and 56.34 are found to match well to the (111), (200), (220) and (311) diffraction peaks of sphaleritic ZnS (PDF no. 80-0020), which suggests that the products are of pure face-center cubic (FCC) ZnS. The lattice constant derived from XRD for the ZnS nanowires is a=0.538nm.

The representative SEM images shown in Fig. 2(a) exhibit the overall features of the products. The ZnS

Conclusions

In summary, single-crystalline ZnS nanowires with a cubic structure were prepared on silicon wafers via a chemical vapor deposition method. The narrow ends of the nanowires are just 20–30 nm, whereas the thick ends are 320–530 nm in diameter. The strong UV emission in the PL spectra of the ZnS nanowires indicates their highly crystalline nature. Field emission results reveal that the low threshold field is indicative of perfect field emission and is closely related to the emitter radius, rough

Acknowledgements

This project is financially supported by the National Natural Science Foundation of China (no. 50502005) and Beijing Natural Science Foundation (no. 1062008). Chang YQ is supported by the Beijing Novel Program.

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