Area-Selective Electroless Deposition of Gold Nanostructures on SiC Using Focused-Ion-Beam Preprocessing
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Area-Selective Electroless Deposition of Gold Nanostructures on SiC Using Focused-IonBeam Preprocessing Hiroki Itasaka1, Masayuki Nishi*1, Masahiro Shimizu1, and Kazuyuki Hirao1 1 Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan. ABSTRACT Area-selective electroless deposition of gold nanostructures on a 6H-SiC substrate is demonstrated. Gold nanostructures selectively grow on a focused ion beam (FIB)-irradiated area on the 6H-SiC substrate when the substrate is exposed to a pure HAuCl4 aqueous solution. The nucleation of gold was more favorable on the Si face than on the C face. Quantitative evaluation of the amount of gold grown both on SiC and silicon is conducted to discuss the growth of gold, where silicon is a substrate we used in our previous study on this method. We reveal the mechanism of the growth of gold nanostructures as follows: Dangling bond defects formed in the FIB-irradiated area initiate the nucleation of gold by reducing Au ions in the solution at the surface. Once the SiC-gold or the silicon-gold boundary, which meets the Schottky contact condition, has formed, electrons in the non-FIB-irradiated region under/around the FIB-irradiated one also reduce Au ions on the gold surface through the boundary. INTRODUCTION Nano-sized gold is a promising material for electronic, photonic, and plasmonic applications due to its unique properties, for example localized surface plasmon resonance (LSPR). For these applications, area-selective fabrication of gold with a desired size on a substrate is a key technology. We recently reported a new option to area-selectively fabricate gold nanostructures on crystalline silicon [1,2]: A pure HAuCl4 aqueous solution with no additives is dropped onto a silicon substrate preprocessed with, for instance, a focused ion beam (FIB). Gold nanostructures selectively grow on the preprocessed area. All procedures are performed at room temperature. This maskless and electroless direct method does not use any silane-coupling agents or hydrofluoric acid that commonly used for the electroless deposition of metal onto silicon [3]. Our previous work revealed that silicon-dangling bonds, which are induced by the preprocessing and energetically located at around the Fermi level of silicon, reduce Au ions with the formation of silanol groups, initiating the nucleation of gold. In this study, we apply the above-mentioned method to 6H-SiC, a compound semiconductor, to further understand the mechanism of the selective growth of gold nanostructures and to explore the potential of the method. 6H-SiC has Si-rich (0001) face (Si face) and C-rich (000¯1 ) face (C face). The growth behavior of gold on each crystalline face is investigated. We also quantitatively evaluate the amount of gold that grew on 6H-SiC, comparing the result with that on silicon. This allows us to discuss the growth stage of gold as well as its nucleation.
EXPERIMENT A 6H-SiC substrate (Shinko MechatroTech Co., Ltd., Japan) was cut into 5 mm squares and precleaned by
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