Synthesis of segmented silver-gold nanostructures and nanogaps

By interaction of metallic nanowires (NWs) with electromagnetic radiation of appropriate wavelength, resonant surface charge density oscillations, called surface plasmons, can be excited. These oscillations are responsible for a large electromagnetic field enhancement in the NW near-field, turning the wires into promising devices for highly sensitive detection of molecules using surface enhanced infrared spectroscopy and surface enhanced Raman spectroscopy. Recently, much work has been devoted to plasmon coupling at nm-size gaps between two metal nanostructures. The resulting high field enhancement in the vicinity of these gaps depends strongly on the gap size. A current experimental challenge is to develop techniques that enable the reproducible fabrication of large amount of nanogaps with controlled dimensions. 7 Here we report the synthesis of nanogaps by electrochemical deposition of segmented Au/Ag/Au NWs. A nanogap is realized between two gold segments by etching the silver segment which has the width of the intended gap. The NWs were prepared from a single electrolyte containing both silver and gold ions instead of exchanging the electrolyte for each segment. Using this approach, very narrow gaps down to 8 nm were created in a costeffective and well controllable manner. Polycarbonate membranes with randomly distributed cylindrical pores were fabricated by heavy-ion irradiation at the UNILAC (ion energy E =11.1 MeV/u) and subsequent etching of the ion tracks in 6M sodium hydroxide solution at 50°C. Au/Ag/Au wires were electrodeposited in the pores at 60°C, with an electrolyte consisting of KAu(CN)2 and KAg(CN)2, employing a suitable sequence of pulses. We have studied the influence of electrolyte concentration and applied voltage characteristics on composition and