Engineering the shape of Zinc Oxide crystals via sonochemical or hydrothermal solution-based methods
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1087-V06-04
Engineering the shape of Zinc Oxide crystals via sonochemical or hydrothermal solutionbased methods Marco Palumbo1,2, Simon J. Henley1, Thierry Lutz1, Vlad Stolojan1, David Cox1, and S. Ravi P. Silva1 1 Advanced Technology Institute, University of Surrey, Guildford, GU2 7XH, United Kingdom 2 Microelectronics and Nanostructures Group, School of Electrical and Electronic Engineering, University of Manchester, Manchester, M60 1QD, United Kingdom ABSTRACT Recent results in the use of Zinc Oxide (ZnO) nano/submicron crystals in fields as diverse as sensors, UV lasers, solar cells, piezoelectric nanogenerators and light emitting devices have reinvigorated the interest of the scientific community in this material. To fully exploit the wide range of properties offered by ZnO, a good understanding of the crystal growth mechanism and related defects chemistry is necessary. However, a full picture of the interrelation between defects, processing and properties has not yet been completed, especially for the ZnO nanostructures that are now being synthesized. Furthermore, achieving good control in the shape of the crystal is also a very desirable feature based on the strong correlation there is between shape and properties in nanoscale materials. In this paper, the synthesis of ZnO nanostructures via two alternative aqueous solution methods - sonochemical and hydrothermal - will be presented, together with the influence that the addition of citric anions or variations in the concentration of the initial reactants have on the ZnO crystals shape. Foreseen applications might be in the field of sensors, transparent conductors and large area electronics possibly via ink-jet printing techniques or self-assembly methods.
INTRODUCTION In contrast with alternative synthesis methodologies such as electrodeposition, chemical vapour deposition (CVD), metal-organic CVD, or metal-organic CVD, aqueous solution growth offers a range of advantages that make it worthy of investigation. Most importantly, we will concentrate here on the aspect of large scale synthesis at moderate temperature and on the controlled crystal structure complexity of the synthesized ZnO crystals. The Hydrothermal method investigated is based on the thermal decomposition of Zinc Nitrate and Hexamethylenetetramine (HMTA) at 90 °C for several hours (typically six or more) [1]. While this approach suits the necessity of working with very large volumes it is encumbered by the long timelines necessary to complete the crystal growth. Sonochemistry [2] could help reduce the time necessary for the crystal growth, although it is perhaps not immediately suitable for large volumes. In our approach we hybridize the two techniques by sonication of a pre-heated reacting solution. Pre-heating the solution does start the decomposition of HMTA into formaldehyde and ammonia (necessary for the production of hydroxide ions that will react with Zinc to give ZnO crystals) and possibly provides the nucleation sites of our sonochemical ZnO structures [3]. Sonochemical synthesis is
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