Elsevier

Acta Materialia

Volume 55, Issue 15, September 2007, Pages 5039-5044
Acta Materialia

Zinc/ZnO core–shell hexagonal nanodisk dendrites and their photoluminescence

https://doi.org/10.1016/j.actamat.2007.05.025Get rights and content

Abstract

We report the electrodeposition of novel zinc dendrites composed of self-assembled regular hexagonal zinc nanodisks shelled with ZnO layers. The Zn nanodisks range in diameter from about 100 nm to several hundreds of nanometers and are about 20–40 nm thick. The thickness of ZnO layer is about 3–4 nm. In the as-prepared condition, the photoluminescence (PL) spectra of the dendrites are composed of a violet emission band at about 415 nm and a green emission band at about 550 nm at room temperature. The violet and green emissions are attributed to the radiative recombination of a delocalized electron close to the conduction band with a deeply trapped hole in the VZn- and VO+ centers, respectively. The PL of the dendrites can be tuned by heat treatment. With an increase in the heating temperature, the intensity of the green emission increases, while the intensity of the violet emission decreases.

Introduction

Nanocrystals exhibit a wide range of electrical, magnetic and optical properties, and are therefore of both fundamental and technological interest [1], [2], [3], [4]. When developing nanocrystals the most important requirements are shape and size control. Scientific interest is based upon the fact that the shape and size of nanocrystals strongly influence their widely varying properties, and the ability to tune the shape and size of nanocrystals is directly related to the ability to tune their properties [5], [6], [7], [8], [9], [10]. To date, many efforts have been devoted to the synthesis of nanocrystalline materials with various shapes, such as nanotubes [11], [12], [13], nanowires [14], [15], [16], nanorods [17], [18], [19], nanobelts [20], [21], nanocubes [22] and dendrites [23]. As a new nanostructural morphology, nanodisks have attracted much attention for their potential applications in information storage media and as nanosensors [24], [25], [26], [27]. More recently, Zn/ZnO core–shell nanodisks have been prepared by using a solid–vapor synthetic approach at 1100–1150 °C [28]. This gas-phase method requires high temperature and expensive equipment. Here, we report a simple electrochemical approach for the synthesis of Zinc/ZnO core–shell hexagonal nanodisk dendrites. The morphology control and formation mechanism of the dendrites have been discussed. Finally, the influence of heat treatment on the structure and photoluminescence of the dendrites has been investigated.

Section snippets

Experimental section

Electrodeposition of zinc dendrites was performed in a rectangular cell of area 50 mm × 40 mm and height 20 mm. Electrodes were high purity (99.99%) zinc foils covering the centers of the two opposite interior sidewalls separated by 50 mm. The cathode was a rectangular foil 10 mm long and 1.5 mm wide, while the anode was a circular foil of diameter 10 mm. A glass plate was placed horizontally just below the cathode to support the deposit which would otherwise break spontaneously during growth due to

Results and discussion

Fig. 1 shows the SEM images of the zinc deposits. It can be seen that the zinc deposits consist of small dendrites with regular shapes in random directions (Fig. 1a). We believe that these dendrites constitute not only dangling branches but also the conducting backbone of the overall aggregate, since no other structure of substantial size or connectivity had been identified in these regions. Fig. 1b shows a high-magnification SEM image in which the morphology of individual dendrites can be

Conclusions

In conclusion, using a simple electrochemical synthetic approach, we have successfully fabricated Zn/ZnO core–shell hexagonal nanodisks which aligned to constitute quasi-planar dendrites with high regularity. The zinc core and zinc oxide shell have an epitaxial relationship. These zinc nanodisk dendrites exhibit high sensitivity to electron beam irradiation. The structure and photoluminescence of the Zn/ZnO core–shell nanostructure at different heating temperatures have been studied. The PL

Acknowledgments

This work was supported by the Australian Research Council (DP0773160) and Hong Kong Polytechnic University. X. Zhang thanks the Australian Research Council for an Australian Research Fellowship.

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