1. Understanding Large Enhancements in Surface-Enhanced Raman Scattering Using Lithographically Fabricated Gold Bowtie Nanoantennas
W. E. Moerner, Department of Chemistry, Stanford University, Stanford, CA 94305
Surface-Enhanced Raman Scattering (SERS)with Nanoscale Metallic Objects: We seek to understand the huge enhancements in Raman scattering that occur when molecules are in close proximity to small metal objects with strong plasmon resonances. Enhancements of up to 1014 have been suggested, enabling detection of signals from individual molecules close to pairs of colloidal gold particles. Understanding this effect is of critical importance, as Raman scattering provides useful information about the structure and local environment of molecules. To go beyond random colloids, we fabricate metallic bowties with two gold triangles tip to tip on a transparent substrate, shown on the left below (bar 100 nm).
Generality: We have extended our earlier SERS enhancement studies to new molecules, such as benzenethiol (figure at right, key modes at red lines).
SERS on Bowtie Antennas with Electrochemical Control: For p-mercaptoaniline on pristine bowties (figure at right), the b2-symmetric modes are not observed, showing that the molecules are laying flat on the surface. Electrochemical cycling over a very small potential range surprisingly roughens the bowties (SEMs at right), enabling the appearance of modes of all symmetry in the Raman spectrum. This highlights the importance of having a well-defined metallic nanoparticle structure for reproducible SERS.