Synthesis of ZnS nanorod arrays by an aqua-solution hydrothermal process on pulse-plating Zn nanocrystallines

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Large-scale, well-aligned, and oriented ZnS nanorod arrays were fabricated by a novel and original template-free hydrothermal method. The ZnS nanorods were grown on the pulse-plating Zn nanocrystallines along a certain Zn crystalline direction. It was found that reaction factors such as hydrothermal reaction time, zinc source, and sulfide source concentration in the precursor solution, the acid–base property of the precursor solution, and the substrate where ZnS nanorod arrays were grown greatly influence the morphology of the final products. The growth mechanism of ZnS nanorod arrays was also studied. Pulse-plating Zn nanocrystallines were found to be essential for the growth of ZnS nanorod arrays. These ZnS nanorod arrays could be theoretically fabricated on almost any raw base plate as long as Zn nanocrystallines could be pulse-plated on it. Therefore, the as-synthesized ZnS nanorod array might be one of the promising candidates for field-emission or sensitive nanomaterials in the future. I. INTRODUCTION

With a direct wide band gap (3.6 eV) and a strong excitonic binding energy (40 meV), zinc sulfide (ZnS) has attracted much attention recently. Meanwhile, ZnS nanostructures have also been used to fabricate multifunctional nanodevices, such as displays, electroluminescence devices, infrared windows, ultraviolet lasers, and sensors.1–3 Because of their high surface-to-volume ratio and special geometry, many possible applications of onedimensional nanomaterials require the formation of well-aligned arrays to accentuate the anisotropy and satisfy the criteria of device design. During the past few years, many efforts have been made to prepare one-dimensional nanomaterial array of the II–VI group compound, among which the hydrothermal method is much more promising in terms of cost and potential for high yield and tight dimension control.4–6 Tang et al.7 synthesized the CdS nanowire array on a cadmium foil at 180  C for 12 h, and ethylenediamine was used as the surfactant. Urchin-like ZnO nanorod arrays were fabricated on the Cu strip by Xu et al.,8 although the morphologies of products in different areas were not uniform. Lu et al.9 reported the ZnS nanobelt obtained at 160  C for 10 h on zinc foil, and ethylenediamine was also used to improve nanostructure growth. These methods usually require relatively high hydrothermal reaction temperatures and a)

Address all correspondence to this author. e-mail: [email protected] Present address: Department of Physics, Wuhan University, Wuhan, 430072, China. DOI: 10.1557/JMR.2009.0353 J. Mater. Res., Vol. 24, No. 9, Sep 2009

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long reaction times. In order to improve the morphology of the products, organic solvents or additives are widely used and largely consumed in the present hydrothermal synthesis processes.10 However, these solvents or additives are usually toxic and will bring on serious environmental problems. To the best of our knowledge, there has been no report of template-free ZnS nanorod arrays synthesized by

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