Journal of Alloys and Compounds 504S (2010) S368–S371 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Epitaxial growth of self-arranged periodic ZnO nanostructures on sapphire substrates grown by MOCVD Hou-Guang Chen a,∗ , Sheng-Rui Jian a , Zheng-Wei Li a , Kuan-Wei Chen b , Jhih-Cheng Li a a Department of Materials Science and Engineering, I-Shou University, Kaohsiung 840, Taiwan b Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan article info Article history: Received 2 July 2009 Received in revised form 28 January 2010 Accepted 27 February 2010 Available online 7 March 2010 Keywords: ZnO Nanostructure XRD TEM Epitaxial growth abstract This article reports an investigation on the growth behaviour of ZnO epitaxial nanostructures and thin films grown by metalorganic chemical vapour deposition (MOCVD). Self-arranged periodic ZnO nanos- tructures consisting of a large number of ZnO nano-columns can be directly grown on bare sapphire surface without any lithography or other pre-patterning processes. The spacing of periodic nanos- tructures was ∼117 nm. The measurements of XRD 2/ω and ϕ scans indicated that epitaxial and non-epitaxial ZnO grains coexisted on the same substrate. According to cross-sectional transmission electron microscopy observation, these periodic ZnO nanostructures were epitaxially grown on sapphire substrates and separated by non-epitaxial ZnO grains. However, the in-plane periodic arrangement of ZnO nanostructures disappeared while increasing the growth temperature. Initial sapphire surface struc- ture and CVD growth kinetics closely relate to the growth of self-arranged periodic ZnO nanostructures. © 2010 Elsevier B.V. All rights reserved. 1. Introduction One-dimensional ZnO nanostructures have been received extensively interest due to their fascinating physical proper- ties, including wide band gap (3.36 eV), high exciton binding energy at room temperature (60 meV), piezoelectrisity, extraor- dinary structural diversity, and chemical-sensing effect [1–4]. Therefore, various novel applications in electronics, optoelectron- ics and electromechanical nanodevices have demonstrated, such as nanolasers [1,5], nanowire-field transistors [6], solar cells [7], and piezo-nanogenerators [2]. A regular spatial organization of ZnO nanostructures is necessary for the realization of above-mentioned nanodevices. Thus, many attempts to make significant advance in the control of spatial position, density, and morphology of ZnO nanostructures have been devoted by numerous groups, and var- ious methods have been proposed to achieve spatial organization of ZnO nanostructures, including electron-beam lithography [8], self-assembled nanosphere array templates [9], and nano-imprint technologies [10]. Epitaxial growth has been regarded as a key technology for advanced optoelectronic device applications. Recently, various self- organized III-V semiconductor nanostructures can be successfully ∗ Corresponding author at: Department of Materials Science and Engineering, I-Shou University, No. 1, Sec. 1, Syuecheng Rd., Dashu Township, Kaohsiung 840, Taiwan. Tel.: +886 7 6577711x3113; fax: +886 7 6578444. E-mail address: houguang@isu.edu.tw (H.-G. Chen). obtained through heteroepitaxial growth processes [11]. While a wide range of substrates have been used for growing high qual- ity ZnO epitaxial thin film and nanostructures [12–15], sapphire is more favored substrate for the epitaxial growth of ZnO thin films or nanostructures, owing to low cost and large size single- crystal being commercially available. In this article, we show that self-arranged periodic striped ZnO nanostructures can be directly grown on the (0 0 0 1) plane sapphire surface by controlling CVD growth kinetic and substrate surface structure without any com- plicated lithographies or sophisticated processes. The mechanism of the growth of self-arranged periodic ZnO nanostructures on sap- phire is proposed and discussed. 2. Experimental procedure A reduced pressure hot-wall type MOCVD apparatus was employed to imple- ment the epitaxial growth of ZnO nanostructures on c-plane sapphire substrates. Zinc acetylacetonate (Zn(acac)2, 99.995 purity) and O2 (99.999 purity) were used as the zinc and oxygen source, respectively. The precursor of Zn(acac)2 was heated at 90 ◦ C before introduction into the chamber by carrier gas of nitrogen (99.99%), which was separated from oxygen flow before reaching the substrate surface to avoid to direct reaction of oxygen with zinc source. Prior to ZnO growth, as-received c-plane sapphire substrates in 1 cm × 1 cm size was annealed at 1200 ◦ C in air for 4h and then were ultrasonically cleaned by acetone. The ZnO nanostructures were grown at temperatures of 450 and 500 ◦ C, respectively, for 120 min. X-ray diffraction characterization of ZnO nanostructures was carried out by a Philips X’Pert diffractometer with a Cu K radiation source. The field emission scan- ning electron microscopy (FESEM, Hitachi S-4700) and atomic force microscopy (AFM, Digital Instrument: NanoMan NS4+D3100) were used to examine the topog- raphy of ZnO nanostructures and sapphire surface, respectively. Cross-sectional transmission electron microscopy (XTEM) observation was performed on a Philips 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.02.195