This talk will highlight underrated phenomena broadcasted through ultrasensitive surface-enhanced Raman scattering (SERS) and high resolution tip-enhanced Raman scattering (TERS). The ultimate goal of this presentation is to establish that these powerful techniques may be used for much more than mere ultrasensitive chemical detection and nanoscale chemical imaging. Achieving this goal nonetheless necessitates tackling fundamental challenges associated with SERS and TERS, particularly in scenarios where ensemble averaging is no longer appropriate. We identify some of these challenges and describe on-going works aimed at exploring and exploiting the full information content in SERS and TERS.
Tip-enhanced Raman Scattering (TERS) can be used to image plasmon-enhanced local optical fields on the nanoscale. In the few molecule regime where the tensorial nature of Raman scattering is operative, this results in TERS images that directly reflect the local field characteristics. For a well-defined substrate, we can numerically simulate TERS spectral images to identify the effective molecular orientation on the tip that maps any experimentally encountered combination of local electric field components. For a corrugated surface where both the vector components of the local electric fields and the molecular orientation are unknown, we can simulate many spectral features.
We study plasmonic nanostructures in single-crystal gold with scanning electron and femtosecond photoemission electron microscopies. We design an integrated laser coupling and nanowire waveguide structure by focused ion beam lithography in single-crystal gold flakes. The photoemission results show that the laser field is efficiently coupled into a propagating surface plasmon by a simple hole structure and propagates efficiently in an adjacent nano-bar waveguide. A strong local field is created by the propagating surface plasmon at the nano-bar tip. A similar structure, with a decreased waveguide width and thickness, displayed significantly more intense photoemission indicating enhanced local electric field at the sharper tip.