Plasmonic Optical Interferences for Phase-Monitored Nanoscale Sensing in Low-Loss Three-Dimensional Metamaterials

We report a powerful and general concept for the design of three-dimensional metamaterials suitable for optically probed nanoscale sensing, combining the environmental sensitivity of localized surface plasmon resonances (LSPRs) and a low absorption of the probe light, even when the LSPRs are supported by lossy plasmonic elements. This concept is based on the tuning of the plasmon-induced Brewster conditions (angle of incidence and photon energy) of the material by suitable tailoring of its structure. This tuning is made possible by the interplay between LSPRs and optical interferences, i.e., the so-called plasmonic optical interferences. The plasmon-induced Brewster photon energy can be set outside the spectral range of the LSPR, thus in a spectral region of low optical absorption. Such off-resonant' plasmon-induced Brewster conditions are examplified in a self-assembled lamellar three-dimensional metamaterial consisting of stacked polymer layers doped with gold nanoparticles alternating with undoped polymer layers. At the off-resonant' plasmon-induced Brewster conditions, an abrupt jump of the ellipsometric phase angle δ occurs in the photon energy space. In the spectral vicinity of this jump, δ shows strong sensitivity to the spectral features of the LSPR, potentially allowing the detection of infinitesimal LSPR energy shifts (