EXPERIMENTAL RESULTS AND DICUSSIONS (CONT’D) Cu NANOWIRE ARRAYS PREPARED BY A SIMPLE REDOX DEPOSITION METHOD Leong Feng Ping Angela INTRODUCTION Metallic nanowires possess high functionality due to their multiple attractive properties and characteristics, with potential applications in various fields like nanoscale electronics and magnetic devices. Cu is particularly desirable due to its electrical properties and low cost. Yet the fabrication of Cu nanowires remains largely limited; popular template-based methods of electrodeposition and electroless deposition are energy-consuming, environmentally unfriendly, non-facile and difficult to control. PURPOSE To report the synthesis of Cu nanowires in anodic aluminum oxide (AAO) templates using a simple metal displacement deposition method, which combines the template deposition and metal displacement reaction. This method is based on galvanic contact between the sputtered noble metal film, covering the bottom of the template, and a less noble metal, partially exposed to the solution. REFERENCES 1. A. Huczko, App. Phy. A 70 (2000) 365-376. 2. R. Inguanta, S. Piazza, C. Sunseri, Electrochem. Commun. 11 (2009) 1385-1388. 3. S. L. Xu, X. Sun, H. Ye, T. You, X. Y. Song, S. X. Sun. Mater. Chem. and Phy. 120 (2010) 1-5. 4. G. Kartopu, O. Yalcin, Electrodeposited Nanowires and Their Applications, ISBN 978-953- 7619-88-6, pp.228, 2000. 5. Z.H. Yang, Z.W. Li, L. Liu, L.B. Kong, J. Magn. Magn. Mater. 323 (2011) 2674-2677. 6. Q. L. Xu, G. W. Meng, X. B. Wu, Q. Wei, M. G. Kong, X. G. Zhu, Z. Q. Chu, Chem. Mater. 21 (2009) 2397-2402. 7. Chowdhury, D. P. Casey, J. F. Rohan, Electrochem. Commun. 11 (2009) 1203-1206. 8. W. Lee, R. Ji, U. Gosele and K. Nielsch, Nat. Mater. 5 (2006) 741-747. 9. A. Santos, L. Vojkuvka, J. Pallares, J. Ferre-Borrull, L. F. Marsal, J. Electroanal. Chem. 632 (2009) 139-142. 10. S. S. Djokic, J. Electrochem. Soc. 143 (1996) 1300. 11. A.J. Bard, R. Parsons, J. Jordan, J. Standard Potentials in Aqueous Solution, Marcel Dekker, New York, 1985. CONCLUSION • Regular and uniform arrays of Cu nanowires were successfully synthesized by a simple metal displacement deposition method. • This fabrication technique is easy to control and low-cost, as the deposition can be carried out at room temperature without requiring energy, organic surfactants, specific equipment, or modification on the pore walls. • Considering copper is one of the most important metals in modern electronic technology, this process can be useful for industrial manufacture of copper nanowires. RESULTS AND DISCUSSIONS AAO Template Characterisation FUTURE WORK • Extension of method to fabrication of nanowires of other metals and heterogeneous alloys, since the Al 3+ /Al redox pair has a lower standard reduction potential than many metallic ions • Study potential factors affecting the redox deposition to investigate optimal conditions for this fabrication method XRD Results Properties of Cu nanowires: • Face-centered cubic crystal structures • Strong texturing • Preferred growth direction in the (200) crystal plane (200) peak was larger than expected for a random polycrystalline sample SEM images of Cu nanowire arrays after template removal Redox Deposition Scheme 3 intense peaks Stage 1: Foil DC anodized in 0.5M H 2 C 2 O 4(aq) at 40V for 10-15min 99.99% pure Al foil Annealed at 500°C in air for 5h and cleaned with acetone Immersed in 6 wt% H 3 PO 4(aq) for ~40min to widen pores Al-surrounded AAO floated on 6 wt% H 3 PO 4(aq) to dissolve barrier layer 100nm Pt layer sputtered on one side of template to form conductive layer Sample sputtered with Pt thin layer in vacuum Alumina film on surface partially dissolved by 0.5ml of 1M NaOH (aq) • Morphology of AAO template and Cu nanowire arrays examined by Field Emission SEM • Crystalline structures of nanowires identified by XRD Preparation of AAO Templates Deposition of Cu Nanowire Arrays Characterisation Orderly upstanding Cu nanowires with bases inside AAO templates 0.141 μm 0.136 μm 0.136 μm 0.151 μm (2a) Top-view (2b) Side-view Islands consisting of bundles of Cu nanowires (2d) Low magnification 135.9 nm 107.0 nm 116.3 nm (2e) High magnification Alumina matrix of AAO template has almost been dissolved away Cu Nanowires Characterisation (1a) Top-view (1b) Cross-sectional view 69.88 μm 71.83 μm SEM images of blank AAO templates after pore widening SEM image of cross-section of AAO template after infiltration, with Cu nanowires embedded in pores • Pore center distance: ̴160 nm • Pore diameter: ̴120 nm • Thickness of AAO template: ̴70 μm • Pores are distributed in perfect hexagonal order in defect-free area. ACKNOWLEDGEMENTS This work was supported by the Young Defence Scientists Programme (YDSP), Ministry of Defence, Singapore. I would like to thank Mr. Yang Zhihong from Temasek Laboratories, NUS, for guiding me through the experiments, instructing me in the background knowledge, and clarifying my doubts, as well as Mr. Murali Krishnaswamy for his guidance during the editing of the report, and aiding with administrative details. At cathode: Cu 2+ + 2e - Cu At anode: Al Al 3+ + 3e - Cl - ions in solution etch away the alumina layer on Al foil, exposing pure Al Cu 2+ Cu 2+ (1c) Average diameter of nanowires is ̴120 nm (2c) Remaining Al on back of template etched with 1M CuCl 2(aq) 100nm Pt layer sputtered on one side of template to form conductive layer Template infiltrated by 0.1M CuCl 2(aq) for 4h Cut into Stage 2: Voltage increased to 60V at ̴0.6Vs -1 and maintained for ̴2h Image taken from: http://media.digikey.com/photos/3M% 20Photos/1170-7.7%5EX10%5E.jpg *All images and graphs are self-taken and self-drawn unless otherwise stated. Image taken from: Microstructure and magnetic properties of Co-Cu nanowire arrays fabricated by galvanic displacement deposition. Z.H. Yang, Z.W. Li, L. Liu, L.B. Kong, J. Magn. Magn. Mater. 323 (2011) 2674-2677.