No abstract

Plasmonic nanoconstructs are widely exploited to confine light for applications ranging from quantum emitters to medical imaging and biosensing. However, accessing extreme near-field confinement using the surfaces of metallic nanoparticles often induces permanent structural changes from light, even at low intensities. Here, we report a robust and simple technique to exploit crystal facets and their atomic boundaries to prevent the hopping of atoms along and between facet planes. Avoiding X-ray or electron microscopy techniques that perturb these atomic restructurings, we use elastic and inelastic light scattering to resolve the influence of crystal habit. A clear increase in stability is found for {100} facets with steep inter-facet angles, compared to multiple atomic steps and shallow facet curvature on spherical nanoparticles. Avoiding atomic hopping allows Raman scattering on molecules with low Raman cross-section while circumventing effects of charging and adatom binding, even over long measurement times. These nanoconstructs allow the optical probing of dynamic reconstruction in nanoscale surface science, photocatalysis, and molecular electronics.

Nanoplatelets are strongly anisotropic colloidal nanocrystals confined in only one direction. Perfect thickness control and large lateral dimensions enable a large exciton coherence area that exhibits a high oscillator strength. Here we investigate experimentally the existence of a strong plasmon−exciton coupling regime in a system consisting of a layer of nanoplatelets on top of a gold planar surface. We performed reflectivity measurements to extract geometrical and optical parameters of the system, and we used them to calculate numerically the modes and obtain the dispersion relation of the structure. Our results show a clear Rabi splitting between an upper and a lower polariton branch, thus demonstrating unambiguously that the system is in the strong coupling regime.