Bringing nanophotonics to the atomic scale
Surface-enhanced molecular spectroscopy relies on the effect of enhanced electromagnetic fields to boost the signal from electronic and vibrational molecular excitations. Through the years, techniques such as fluorescence, infrared absorption, or Raman scattering have taken advantage of plasmonic nanoantennas to achieve such a signal enhancing effect. As fabrication and chemical synthetic methods are standardly reaching atomic-scale configurations, for instance in plasmonic nanogaps, more sophisticated theoretical methods are needed to address the quantum nature of electronic states, or to account for the quantization of plasmonic fields. The effect of strongly inhomogeneous fields localized at the atomic scale will be reported, as in tunneling gaps or in particle-on-a-mirror configurations, to modify fluorescence in molecules, as well as selection rules in plasmon-enhanced Raman scattering. The presence of “picocavities” in plasmonic gaps redefines the landscape of Raman molecular activity. By adopting ab-initio methods to obtain the electronic structure and vibrational fingerprints of organic molecules, the effect of these field inhomogeneities can be properly considered, providing an understanding of relevant spectral information, including strong coupling of molecular emitters, and molecular optomechanics. On the other hand, the quantization of plasmonic fields, following cavity-Quantum Electrodynamics (QED) methods, can be also considered to reveal the complex dynamics of molecular fluorescence from hybrid molecule-cavity polaritonic branches, or to trace the population of vibrations interacting with a plasmonic cavity, pumped by a detuned external laser field. The quantum regime in surface-enhanced molecular spectroscopy is currently at hand, and accurate quantum theories can reveal a new variety of phenomena with implications in the control of quantum molecular states, as well as in plasmon-induced chemical reactivity.
Sprecher: Prof. Dr. Javier Aizpurua, Center for Materials Physics of the Spanish Council for Scientific Research (CSIC)
Kontakt: Prof. S. Götzinger