Surface plasmon resonances of Cu nanowire arrays

In the recent past, considerable attention has been devoted to the optical signature of noble metal (Au, Ag, and Cu) nanostructures in the ultraviolet, visible, and nearinfrared spectral ranges, because of their promising applications in optical nanodevices. The optical response of metal nanostructures can be ascribed to surface plasmon resonances (SPR) [1]. In this report, we present our results on SPR of Cu nanowire arrays. The arrays were produced by filling the nanopores of ion track-etched polycarbonate (PC) templates with Cu. For this purpose, PC foils (Makrofol N, Bayer Leverkusen) of thickness 30 μm were irradiated at the UNILAC linear accelerator with fluences of 10 8 and 5×10 8 ions/cm 2 . Prior to chemical etching in 5M NaOH at 50 °C, the foils were illuminated by UV light for 2 hours from each side. Subsequently, Cu nanowires were electrochemically deposited at 50 °C by applying a constant voltage of -200 mV. The electrolyte consisted of 75 g/l CuSO4•5H2O and 30 g/l H2SO4. A thin sputtered Au layer reinforced by an electroplated Cu layer was used as cathode for wire deposition. After removing the cathode, extinction spectra of nanowire arrays embedded in the templates were recorded employing an ultraviolet-visible spectrometer (UV4, UNICAM) under ambient conditions. The direction of light propagation was chosen parallel to the wire axis (i.e. the electric field vector was normal to the wire axis). A track-etched template without wires was used as reference sample.