Effects of the microstructure of ZnO seed layer on the ZnO nanowire density
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Mi Ran Moon and Donggeun Jung Department of Physics, Brain Korea 21 Physics Research Division, Institute of Basic Science, Sungkyunkwan University, Suwon 440-746, Korea
Hyoungsub Kima) and Hoo-Jeong Leeb) School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746, Korea (Received 15 December 2010; accepted 7 March 2011)
In this study, we synthesized ZnO nanowires using Au catalytic particles formed on a ZnO seed layer. We modulated the microstructure of the ZnO seed layer by changing the sputtering power to investigate how the underlying ZnO film microstructure affects the distribution of ZnO nanowires. Examining the samples after each of the three key steps of the growth process (ZnO seed layer deposition, Au catalytic particle formation, and nanowire growth) using various characterization methods such as scanning electron microscopy, transmission electron microscopy, and x-ray diffraction helped us illuminate the profound impacts of the grain size of the seed layer on the nanowire density.
I. INTRODUCTION
With a unique combination of physical properties such as high electron mobility (.2 cm2/Vs), high transparency, high crystallinity, large exciton-binding energy (60 meV), wide direct energy band gap (3.37 eV), etc., ZnO has become the subject of many research studies.1 In particular, recent successes in synthesizing ZnO nanowires have opened a new avenue for the research of this field by realizing nanowire-based optical devices, ZnO nanowirebased transistors, etc.2–4 However, further developments of this material for mass production require full control of the synthesis process and nanowire morphology. In the widely used vapor–liquid–solid5,6 synthesis method, ZnO nanowires are grown from Au particles (serving as a catalyst for the nanowire growth) dispersed either directly on a substrate or on various seeding layers, such as c-plane sapphire, ZnO, etc. Several recent studies have investigated how various parameters associated with nanowires growth processing influence the density and growth direction of nanowires.7,8 For studies using Au particles directly dispersed on a substrate as a catalyst, the control of Au particles is the key to control the density and size of the nanowires. In a study done by Wang et al.,9 e.g., the thickness of a thermally grown Au film was changed from 1 to 8 nm for the control of the nanowire density.
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2011.81 1292
J. Mater. Res., Vol. 26, No. 10, May 28, 2011
http://journals.cambridge.org
Downloaded: 15 Mar 2015
Shin et al.10 confirmed that the density of synthesized nanowires was directly proportional to the concentration of Au-PMMA [poly(methyl methacrylate)] nanoparticles. In a study comparing Si and a sapphire as the substrate, additionally, Yang et al.3 demonstrated that selection of a proper substrate could be an important parameter for the vertical growth of nanowires. Petersen et al.11 delved into how the size of agglomerate
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