Fabrication and surface-enhanced Raman scattering properties of gold nanostructures

Gold nanoneedles arrays were fabricated on glass substrates using an ion-beam sputtering technique. Gold nanoneedles with a tunable length and base diameter of 200 nm were formed with a density of 20 ¿m^-2. The sharp tips of the nanoneedles exhibited an apex diameter of 20 nm and an apex angle of 20°. These arrays were evaluated as potential surface-enhanced Raman scattering (SERS) substrates using malachite green molecules and exhibited the maximum SERS enhancement factor of greater than 10⁸. The SERS enhancement is attributed to the localized electron field enhancement around the apex of needle and the surface plasmon coupling originated from the periodic structure. This work demonstrates a new technique for producing controllable and reproducible SERS substrates potentially applicable for chemical and biological assay.