J. Phys. Chem. C 2008, 112, 4129-4133
4129
Periodic Growth of ZnO Nanorod Arrays on Two-Dimensional SiNx Nanohole Templates by Electrochemical Deposition Seong Kyong Park,† Young Kwang Lee,† Hyon Tae Kwak,† Chan Ryang Park,† Jeunghee Park,‡ and Young Rag Do*,† Department of Chemistry, Kookmin UniVersity, Seoul 136-702, Korea, and Department of AdVanced Material Chemistry, Korea UniVersity, Jochiwon 339-700, Korea ReceiVed: October 24, 2007; In Final Form: January 4, 2008
Precisely positioned and spatially separated ZnO nanorod arrays were fabricated on holographically predefined two-dimensional (2D) SiNx nanohole-array-coated Pt/Si substrates using a simple electrochemical deposition process. The stems of the 2D nanohole-assisted ZnO nanorods had a single-crystal nature and a preferred (002) growth direction but polycrystalline contact with the Pt surface. This approach provides a facile largescale method for fabricating periodic nanohole-supported ZnO nanorods at low growth temperatures (90 °C). The enhanced UV emission from these nanorods was associated with a lower defect density in the nanoholetemplated ZnO nanorods, which was achieved by electrochemical deposition on a 2D nanohole array at a potential of -1.0 V for 30 min.
1. Introduction The fabrication of one-dimensional (1D) ZnO nanorods has attracted considerable attention in the synthesis of nanostructures and their applications on account of their wide band gap, excellent chemical and thermal stability, and specific electrical and optoelectrical properties. ZnO is a II-VI semiconductor with a large exciton binding energy.1-3 The current trend in 1D ZnO nanorods research is the development of device concepts based on unique nanostructures, such as templatemediated nanostructures consisting of ZnO semiconductors.4,5 Such template integration requires an ability to assemble individual ZnO nanorods into a desired template with control over their diameter and orientation. With the many methods used to fabricate template-mediated ZnO nanorods, control over the alignment of the nanorods has been achieved using the following techniques: anodic aluminum oxide (AAO) templates4-7 or photolithographic template-assisted assembly8 with various types of growth achieved inside the ordered nanohole arrays of the template; and AAO patterned catalyst9 or nanolithographically patterned catalyst-assisted assembly10-12 through vapor-liquid-solid growth. Although nanohole-assisted assembly techniques using AAO or photolithographically patterned templates have been developed in an attempt to limit the effects of interference arising in 1D nanostructures, there are some problems with these methods. For example, AAO nanohole templates4-7 provide a less flexible approach and a photolithographic nanohole templates8 require a photomask with high accuracy. This study examined a simple structural concept for producing precisely positioned and spatially separated nanorods by combining electrochemical growth of ZnO nanorods with holographically predefined two-dimensional (2D) insulator nanohole arrays. Highly stable, patterned 2D SiNx nanohole arrays with * To whom correspondence should be addressed. Tel: +82-2-910-4893. Fax: +82-2-910-4415. E-mail:
[email protected]. † Kookmin University. ‡ Korea University.
uniform and adjustable nanohole diameters ranging from 100 to 500 nm and pitches in the range 300-800 nm were used as insulating templates. The templates were produced by laser hologram lithography without a photomask.13 Another key issue for ZnO nanowires fabricated inside the nanopores of an AAO membrane by electrochemical deposition is their crystalline quality.4,5 In most cases, ZnO nanowires do not grow epitaxially inside the nanopores of AAO membranes and are either amorphous or polycrystalline. The most interesting novelty presented in this study is the possibility of fabricating single crystalline ZnO nanorods on highly periodic insulator nanoholes, with less interference on their physical properties. 2. Experimental Section Si substrates coated with a Pt thin-film by dc-sputtering were used as the working cathode. A ∼80 nm thick platinum layer was deposited on a single-crystal silicon (100) wafer with a resistivity
