ZnO submicron structures of controlled morphology synthesized in zinc-hexamethylenetetramine-ethylenediamine aqueous sys
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Sam Zhangb) School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798
Wei-Dong Yu and Ji-Jun Qiu State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, People’s Republic of China (Received 31 October 2006; accepted 1 February 2007)
The morphology of ZnO submicron crystals formed in a weak alkaline environment (pH value less than 11.0) was systematically studied for the first time. ZnO submicron particles with different morphologies (flowers, rod, and wire) were synthesized from an aqueous solution by adopting ethylenediamine as the source of hydroxyl group, hexamethylenetetramine (HMT) as the additive, and potassium chloride (KCl) as the background electrolyte. The effects of primary experimental parameters such as HMT and KCl addition, precursor concentration, and reaction temperature on the microstructure, crystallinity of the resultant particles, and their distribution on substrate are discussed in this paper. In the flowerlike structure, the particle size is more controlled by the precursor concentration, and the microstructure is modulated by increasing the concentration of HMT and the reaction temperature. The introduction of ZnO seed layer on substrate promotes even distribution of ZnO flowers. High concentration KCl electrolyte inhibits formation of the flowerlike structure and promotes the growth of submicron ZnO crystals in rod or wire shape. Mechanism studies indicate that the degree of supersaturation of Zn(OH)2 and the adsorption of organic/inorganic species on the surface of ZnO are the prime factors influencing the nucleation, growth rate, and eventual morphology.
I. INTRODUCTION
ZnO has been one of the most intensively investigated functional oxides in recent years due to its versatile properties such as stability at high temperature, good biological compatibility, near-ultraviolet (UV) emission,1 transparent conductivity,2 piezoelectricity,3 and high gas sensitivity.4 Because of the successful demonstration of room-temperature UV lasing by Yang’s group5 and piezoelectric nanogenerators by Wang et al.6
a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr_policy DOI: 10.1557/JMR.2007.0250 J. Mater. Res., Vol. 22, No. 7, Jul 2007
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recently based on ZnO nanorod arrays, morphology control of ZnO nano- and submicron structure has received much attention in the fundamental study of structure– property relations as well as technological potential in catalysts, selective separations, sensor arrays, wave-guides, drug carriers, biomedical implants with macroporosity, and photonic crystals. Up to now, ZnO nanostructures with an abundant variety of shapes have been demonstrated, such as n
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