Structure versus Composition: A Single-Particle Investigation of Plasmonic Bimetallic Nanocrystals

Stellated bimetallic nanostructures are a new class of plasmonic colloids in which the interplay between composition and overall architecture can provide tunable optical properties and new functionality. However, decoupling the complex compositional and structural contributions to the localized surface plasmon resonance (LSPR) remains a challenge, especially when the monometallic counterparts are not synthetically accessible for comparison. Here, stellated Au-Pd nanocrystals (NCs) with O-h symmetry are used as a model system to decouple structural and complex compositional effects on LSPR. Single-particle correlation of the LSPR with the structure of octopodal Au-Pd NCs was achieved using optical dark-field spectroscopy with scanning electron microscopy. These measurements were compared to calculations of the optical properties of structurally similar Au-only octopods by the finite difference time domain method. This comparison enabled the role of complex composition, which was determined by scanning transmission electron microscopy energy-dispersive spectrometry measurements, on the LSPR to be elucidated from the structural contributions. This methodology provides a powerful framework to guide the design of new plasmonic colloids through both structure and composition.