Double template electrosynthesis of ZnO nanodot array

Abstract

This communication describes the preparation of highly-ordered nanodot arrays of ZnO, a technologically important material, by the double template approach developed by Bartlett and co-workers. Colloidal polystyrene spheres were used as the primary template, and electrodeposited polypyrrole was used as the secondary template in this study. The ZnO nanodot arrays were prepared on a polycrystalline Au substrate by electrodeposition using the pyrrole secondary template after making it insulating by potentiodynamically deactivating it. The ZnO nanodot array was characterized by scanning electron microscopy, energy-dispersive X-ray analyses, and laser Raman spectroscopy.

Introduction

The notion of spatially directing the deposition of nanosized semiconductor particles on targeted areas of a substrate [1], [2], [3] is rapidly gaining currency because of the potential applicability of the resultant architectures in a variety of technologies ranging from sensors to solar cells. Template-based methods have the twin advantages, relative to their lithography counterparts, of simplicity and low cost for producing such patterned arrays of semiconductor nanodots. Two types of templates, based respectively on the use of colloidal polystyrene spheres or anodic alumina pores, have thus received considerable attention in recent years [1], [2], [3], [4], [5], [6], [7]. Templating with polystyrene spheres can be taken one step further by using the initial polystyrene sphere template for the electrodeposition of a second, conducting polymer, template. After removal of the polystyrene and deactivation of the conducting polymer, the second template can be used to deposit an array of metal or semiconductor nanodots [3], [8]. In this communication, we describe the preparation of a patterned array of ZnO nanodots using this “double template” approach.

Zinc oxide (ZnO) is an important material for many applications including varistors, transistors, piezoelectric devices, solar cell windows, UV and blue light emitting diodes and the like. Nanostructures of ZnO have been the subject of considerable recent attention [9], [10], [11], [12], [13], [14]; indeed, even an entire magazine has been devoted to this topic [15]. However, in all these studies, ZnO was grown in nanorod or nanowire form using techniques such as molecular beam epitaxy, metalorganic chemical vapor deposition, vapor–liquid–solid growth etc. Electrodeposition of ZnO [16], [17] offers the advantage of simplicity and low cost, and in this regard, it is eminently compatible with the template based approach as already demonstrated by previous authors for wide bandgap oxide semiconductors such as TiO₂ [18], [19], [20] or SnO₂ [21] and other compound semiconductors such as CuSCN, CdS, and CdSe [2], [22], [23], [24], [25]. In what follows, we describe the combined use of double template synthesis and electrodeposition for the preparation of a highly ordered nanodot array of ZnO on polycrystalline gold substrate.