Plasmonic Antennas for Surface-Enhanced Raman Scattering: From Classical to Quantum

Surface-enhanced Raman scattering (SERS) is an analytical technique that enables molecules to be identified from their vibrational spectra, even at single-molecule level. It employs plasmonic antennas to enhance Raman cross-section of molecules by orders of magnitude. In this seminar, I will begin by introducing two examples in optimizing the plasmonic antenna designs for SERS applications. First, electron-beam lithography incorporated with chromium shadow mask is developed to achieve plasmonic dimers with gap-width well below 10 nm. Second, nanoscale directional antenna designs are exploited to achieve beamed Raman scattering. Furthermore, I will discuss the emergence of electron tunneling at optical frequencies for plasmonic antennas with gap-widths in the single-digit angstrom range, and experimentally demonstrate that it limits the maximum achievable plasmonic enhancement through SERS measurements. This reveals the impacts of electron tunneling on the "near-field" properties of plasmonic antennas and could enable future applications of quantum plasmonics.