Vertically Aligned Single Crystalline ZnO Nanorods Grown by Hydrothermal Synthesis and the Theoretical Model for Predict
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Vertically Aligned Single Crystalline ZnO Nanorods Grown by Hydrothermal Synthesis and the Theoretical Model for Predicting the Rod Density Soo Jin Chua1,2, Hong Quang Le1, Chuan Beng Tay3, Kian Ping Loh4, and Eugene Fitzgerald5 1 Singapore-MIT Alliance, E4-04-10, 4 Engineering Drive 3, Singapore, Singapore, 117576, Singapore 2 Institute of Materials Research and Engineering, 3 Research Link, Singapore, Singapore, 117602, Singapore 3 Dept of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore, Singapore, 117576, Singapore 4 Dept of Chemistry, National University of Singapore, 21 Lower Kent Ridge, Singapore, Singapore, 117907, Singapore 5 Dept of Materials Science and Engineering, MIT, Massachusetts Institute of Technology, Cambridge, MA, 02139 Introduction ZnO is a II-VI direct wide bandgap semiconductor (3.37 eV) with a large exciton binding energy (60 meV), a high piezoelectric coefficient, with potential applications for gas sensing, surface acoustic devices, varistors, optoelectronic devices. In the last few decades, one dimensional (1D) semiconductor nanostructures, such as nanorods and nanowires, have become important fundamental building block for nano-photonic devices and offer substantial promise for integrated nanosystems. In nanostructure, the density of states of carrier is concentrated at some specific energy levels, which enable enhancement of exciton oscillator strength and light emitting efficiency. As a result, the performance of nanostructure based optical devices is expected to improve and to be less temperature dependent. Many deposition methods have been used to fabricate the ZnO nanorods such as metal organic chemical vapor deposition (MOCVD), pulse laser deposition, radio frequency magnetron sputtering, and anodized aluminum oxide membrane. In this report, the ZnO nanorods were epitaxially grown by using the aqueous solution. This growth method showed some advantages compared with others, such as use of simple equipment, low temperature deposition (100oC), low cost, less hazardous, and no need for use of metal catalysts. Here, the GaN film was used as a template for the ZnO nanorod growth since these materials have the same wurtzite crystal structure, low lattice constant misfit (1.9%) and similar thermal expansion. Due to similar crystal properties, the ZnO nanorods are expected to epitaxially grow on the GaN template. Experimental details and results In this piece of work, the hydrothermal method is investigated to grow ZnO nanorods. A theoretical model is proposed to predict the areal density and length of rods grown by this method
Uniformly distributed ZnO nanorods with diameter 80-120 nm and 2µm long have been grown at low temperatures on GaN by a catalyst free and inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. The experimental procedure for ZnO nanorod growth consists of dissolving Zn (CH3COO)2 .2H2O in deionize
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