Gold Nanorod Arrays: Excitation of Transverse Plasmon Modes and Surface-Enhanced Raman Applications

We describe a method for the fabrication of gold nanorod arrays and their characterization. The initial requirements were for a robust substrate with strong surface enhancement of Raman scattering with minimal surface contamination. The rods with length up to 20 μm were electrochemically deposited in alumina templates bonded to gold-coated silicon wafers. After the removal of the template, surface-bound cyanide from the deposition process was removed by mild electropolishing. Reflectance and cathodoluminescence measurements revealed transverse dipole and quadrupole plasmon modes. Surface enhancement of 106 was determined by taking Raman spectra of self-assembled monolayers of 4-aminothiophenol. The enhancement factor (EF) was found to be independent of nanorod aspect ratio because only the length of the nanorods was varied while their diameter was kept constant, and because of the large length of nanorods only the transverse plasmons were excited.