Journal of Alloys and Compounds 509 (2011) 5137–5141 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Growth and optical properties of ZnO nanorods prepared through hydrothermal growth followed by chemical vapor deposition Dong-Suk Kang a , Hyo Sung Lee a , Seok Kyu Han a , Vibha Srivastava a , Eadi Sunil Babu a , Soon-Ku Hong a,b,∗ , Min-Jung Kim c , Jae-Ho Song c , Jung-Hoon Song c , Hyojin Kim a , Dojin Kim a a Department of Advanced Materials Engineering, Chungnam National University, Daejeon 305-764, Republic of Korea b Graduate School of Green Energy Technology, Chungnam National University, Daejeon 305-764, Republic of Korea c Department of Physics, Kongju National University, Gongju 314-701, Republic of Korea article info Article history: Received 30 August 2010 Received in revised form 29 January 2011 Accepted 2 February 2011 Available online 18 February 2011 PACS: 81.10.Dn 81.15.Gh 78.66.Hf Keywords: Zinc oxide Nanorod Optical property Seed layer abstract We report on the synthesis of high-quality ZnO nanorods by combining hydrothermal growth (HG) and chemical vapor deposition (CVD) processes. Vertically aligned and closely packed ZnO nanorods were grown by HG on a sputtered ZnO seed layer on a SiO 2 /Si (0 0 1) substrate. The top surface of the HG- prepared ZnO nanorods showed very flat surfaces compared with that of the sputtered ZnO seed layer. Therefore, the HG-prepared ZnO nanorods were used as a new alternative seed material for the CVD growth of the ZnO nanorods. Vertical ZnO nanorods were grown by CVD on both the new HG-prepared nanorod seed material and the sputtered ZnO seed layer. The CVD-prepared ZnO nanorods on new HG- prepared nanorod seed material showed better crystalline quality and superior optical properties than the CVD-prepared ZnO nanorods on sputtered seed layer. The former showed negligible deep-level emis- sions at room temperature photoluminescence measurements. The intensity ratio of near-band-edge emissions to deep-level emissions from the former was about 910, but that from the latter was about 151. This implies that the HG-prepared ZnO nanorods can be used as a promising new seed material for nanostructure synthesis. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Zinc oxide-based nanostructures have received increasing attention because of their potential applicability as emitters and sensors [1,2]. Catalyst-assisted and catalyst-free syntheses of ZnO nanowires or nanorods, using several methods, such as thermal chemical vapor deposition (CVD) [3], metal organic chemical vapor deposition [4], molecular beam epitaxy [5], and hydrothermal growth (HG) [6] have been reported. Among these methods, HG and CVD are mostly used for synthesizing ZnO-based nanostructures. The synthesized ZnO nanowires or nanorods are grown verti- cally or randomly inclined to the substrate surfaces. In general, vertical ZnO nanorods are usually grown by employing a catalyst, such as Au [7]. However, a catalyst-free process is preferred because of its simplicity and convenience in future device applications. As an alternative, instead of a metal catalyst, ZnO seed layers are fre- quently used to produce vertically grown ZnO on Si substrates, on ∗ Corresponding author at: Chungnam National University, Department of Mate- rials Science and Engineering, 220 Gung-dong, Youseong-gu, Daejeon, Republic of Korea. Tel.: +82 42 821 6640; fax: +82 42 822 3206. E-mail address: soonku@cnu.ac.kr (S.-K. Hong). which the ZnO seed layers are grown by sputtering or general thin film deposition techniques [8,9], although there are a few reports on the vertical growth of ZnO nanorods on Si substrates without using any seed layer [10]. Here, thin film-based ZnO layers are mostly used as seed layers for ZnO nanowires or nanorod synthesis, but the intentional application of ZnO nanorods as an alternative seed or template for re-growth of ZnO nanorods has not been tried. The aqueous solution-based HG, in which zincnitratehex- ahydrate [Zn(NO 3 ) 2 6H 2 O] solution mixed with hexamethylente- tramine [(CH 2 ) 6 N 4 ] solution is generally used as the precursor material to synthesize ZnO nanowires or nanorods [11], is the simplest process compared with other methods. The CVD is an alternative technique in preparing ZnO nanowires, in which ZnO powders mixed with carbon powders are normally used as source materials to grow ZnO nanowires or nanorods [12]. In this study, we tried a combination of HG and CVD processes to grow high-quality ZnO nanorods, in which ZnO nanorods with a diameter of hundreds of nanometers and grown by HG were used successfully as templates for the regrowth of ZnO nanorods by CVD. Vertical ZnO nanorods with high optical properties were synthe- sized by CVD on ZnO nanorod grown by HG. CVD-re-grown ZnO nanorods showed superior optical quality without deep-level emis- sions compared with vertical ZnO nanorods grown solely by HG or 0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2011.02.010