Fabrication of ordered Ta 2 O 5 nanodots using an anodic aluminum oxide template on Si substrate
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Jia-Min Shieh National Nano Device Laboratories, Hsinchu 30078, Taiwan, Republic of China
Shun-Min Wang and Shih-Wei Liang Department of Material Science and Engineering, National Chiao Tung University, Hsinchu 30050, Taiwan, Republic of China (Received 11 August 2006; accepted 2 January 2007)
Ordered arrays of Ta2O5 nanodots were prepared using anodic aluminum oxide (AAO) as a template to support localized oxidation of TaN. Films of TaN (50 nm) and Al (1.5 m) were deposited successively on p-type Si wafers and followed by a two-step anodization process at 40 V using oxalic acid as the electrolyte. The first anodization promoted growth of irregular AAO from overlying Al film. After chemical etching, the second anodization was performed to develop well-organized AAO channels and initiate oxidation of underlying TaN film to form tantalum oxide nanodots at the AAO pore bottoms. X-ray photoelectron spectroscopy results confirmed the chemical nature of nanodots as stoichmetric Ta2O5. X-ray diffraction demonstrated the amorphous characteristic of Ta2O5. As shown in field-emission scanning electron microscopy and transmission electron results, the Ta2O5 nanodots exhibited a hillock structure 80 nm in diameter at the bottom and 50 nm in height. We also synthesized 30-nm nanodots by adjusting AAO formation electrochemistry. This demonstrates the general applicability of the AAO template method for nanodot synthesis from nitride to oxide at a desirable size.
I. INTRODUCTION
Semiconductor nanodots possess unique physical properties that might bring significant performance improvement in many optoelectronic and microelectronic devices. In particular, studies of nano-sized tip arrays for autoelectron emitters,1 field emission displays,2,3 and gas sensors4 are pursued aggressively. For example, Chen et al.2 have reported that oxide nanodots with high geometrical enhancement exhibit exceptional field-emission efficiency. To integrate fabrication of nanodots into commercial applications, it is essential to manipulate them into desirable shapes and locations on substrate of interest. The requirements of mass production demand development of low-cost techniques for pattern formation in submicron and nanometer resolution. Many methods have been documented in controlling the spatial arrangement and size distribution of the nanodots.5–8 Of these
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0143 1064 J. Mater. Res., Vol. 22, No. 4, Apr 2007 http://journals.cambridge.org Downloaded: 16 Mar 2015
methods, the electrochemical approach is the most promising because it entails relatively simple setup and operation. Anodic aluminum oxide (AAO) is obtained by anodic oxidation of aluminum in electrolytes such as oxalic and sulfuric acids. It consists of vertical open channels of amorphous Al2O3 arranged in a hexagonal pattern protruding from the underlying aluminum substrate. The pore diameter is tunable from ten to several hundred nanometers, contingent on the type of electrolyte as wel
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