Statistical and Correlative Characterization of Individual Nanoparticle in Gap Plasmon Resonator Sensors

Abstract

Plasmonic nanocavities are receving increased attention from the nanophotonics, nanoelectronics, and quantum optics community due to their ability to confine light in extremely small volumes. Coupling colloidal plasmonic nanocrystals to metal films is an inexpensive approach to fabricate virtually unlimited individual resonators that can be tuned by adjusting nanoparticle size, gap thickness, and refractive index. The focus is on silver nanocubes separated from a gold mirror by thin amorphous dielectric layers (Al2O3, TiO2). The optical response is measured and correlative electron microscopy is performed on a large number (>800) of individual resonators to unveil the statistical distribution of gap plasmon modes and assess systematically their sensitivity. A sensitivity as large as 8 nm/nm to nanocube size variation, 50 nm/nm to Al2O3 thickness variation, and 130 nm/RIU for index change of the spacer layer is found. With the help of numerical simulations, this approach enables to infer a quantitative statistical distribution of molecular coatings present on the nanocubes surface, such as polyvinylpyrrolidone, which can affect the performance of nanoelectronic devices and assess the strategy to remove it. Finally, polarization‐resolved measurements enable to unveil a birefringent behavior when nanocubes are supported on annealed TiO2 layers (2–4 nm).