Optical and Electronic Microscopic Characterization of Plasmonic Modes on a Self-assembled Metallic Grating
Efficient coupling of single-photon nanoemitters to photonic or plasmonic structures requires spatial and spectral matching of the emitting dipoles to the nanostructure. It is especially crucial to ensure an orientation matching between the electric field of the photonic or plasmonic mode and the fluorescent dipole. Therefore, it is necessary to determine the distribution of the electric field associated to the excited mode as well as the dipole orientation. My seminar will be divided into two different parts.
First, I will present the polarimetric method I have developed and applied to high-quality CdSe/CdS dot-in-rods and spherical nanocrystals in order to retrieve the 3D-orientation of the associated dipole [1,2]. I could correlate optical dipolar properties to the shape of the emitter. In the main part of my talk, I will focus on the coupling between light and surface plasmons polaritons (SPP) . SPP are known to enhance light matter interaction with applications in fields such as bio-imaging, light-emitting diodes, photovoltaics and single-photon sources. Metallic surface gratings offer the opportunity to absorb light with almost 100 percent of efficiency and to enhance the fluorescence of nanoemitters close to their surface.
In order to take advantage of SPP modes, which are not coupled to far-field radiative modes in the case of a planar metallic surface, a periodically patterned metallic surface can be used. We used self-assembly to produce centimeter-sized plasmonic crystals with 400-nm periodic structure, by evaporating a thick layer of gold on artificial silica opals used as a periodic template. We performed optical specular reflection spectra and evidenced a dip of almost complete absorption. This dip is explained by theoretical calculations and can be attributed to a coupling to SPP.
We demonstrated, at a given incidence angle, a broad continuum of coupled wavelengths over the visible spectrum. Complementary photo-emission electron microscopy (PEEM) measurements give a high-resolution (25 nm) map of the electric field of the photo-excited plasmonic modes. This technique enables us to distinguish between the coupling of incident light modes to SPP and localized plasmons by the observation of interference fringes and hot spots. The arrangement of the hot spots is discussed as a function of the crystallographic quality of the opal. These results stress the important role of disorder at different scales and open new possibilities for the study of optical disordered media.