Plasmonic nanostructures have the ability to confine optical field at extremely small volume much below diffraction limit (as small as 40nm<sup>3</sup>) producing large vacuum electric field. Interest in infrared plasmonic cavities is growing as molecular vibrational modes can interact strongly with such fields leading to the possibility to control energy and charge transfer and affect the molecular potential landscape, thereby modifying chemical reactivity. Achieving strong coupling conditions requires a large amplitude of electromagnetic field generated by plasmonic structures, which necessitates proper choice of cavity geometry and material. Owing to the latest advances in nanofabrication such structures are becoming available. Realizing strong coupling involves balancing the plasmonic electromagnetic field enhancement with the dissipation induced by the metallic boundaries. To investigate this balance we have studied the dependence of the dipolar response of a molecular emitter on the geometry and shape of a metallic boundaries as well as the relative orientation and position of the emitter and material dielectric function(s). We use the semiclassical theory of Gersten and Nitzan, to compute the coupling of a molecular dipole with a metal nanoparticle and have extended this theory to evaluate the magnitude of the vacuum (quantum) electromagnetic field for infrared plasmonic cavities formed in a nanoparticle on Mirror (NPoM) geometry. Calculations are obtained for few carefully selected materials including n-doped semiconductors, silver and gold. In addition to field calculation, we find the effective mode volume, damping rate and quality factor.  We find that these observables are strongly sensitive to nanoparticle-molecule distance, the dipole orientation and the curvature of the nanoparticle surface. In particular, mode volumes and vacuum field change drastically as a function of the gap in NPoM cavity, and these quantities are sensitive to choice of materials, all in accordance to experimental findings.

Electromagnetic field and strong coupling in infrared cavities

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.