Tip-enhanced spectroscopy from ordered silver nanoparticle arrays

I will report on recent efforts from our group to develop new methods for enhanced spectroscopy from metal nanoparticle arrays. Triangular-shaped silver nanoparticles (20 -- 200 nm) fabricated via nanosphere lithography have shown dramatic enhancement (10$^{6}$ -- 10$^{10})$ of the resonance Raman spectrum of R6G, which was attributed to the shape of the Ag triangle.\footnote{ J. Schmidt, S. Cross, S. Buratto J. Chem. Phys., \textbf{121}, 10657 (2004).} In addition to the large surface-enhanced resonance Raman spectroscopy (SERRS) enhancement we have also observed enhanced luminescence from the Ag nanoparticle films. In order to further understand the shape dependence of the electric-field enhancement we have used near-field scanning optical microscopy (NSOM) to map both the SERRS and luminescence for a single 200nm Ag nanotriangle. The enahancement is largest for the apex of the triangle or near sharp points. In addition, I will discuss the progress in tip-enhanced SERS (TE-SERS) from these same nanoparticle arrays. In TE-SERS the electric field enhancement is due to the large coupling between the metal tip and the Ag nanoparticle and can be mapped and quantified.