Plasmonic Core–Shell Zirconium Nitride–Silicon Oxynitride Nanoparticles

We discuss the synthesis and properties of plasmonic zirconium nitride nanocrystals produced using a nonthermal plasma reactor. The process enables the continuous conversion of chemical precursors into free-standing ∼10 nm diameter nanoparticles. Oxidation limits the resonant plasmon energy from ∼2.6 eV for ideal unoxidized particles to ∼2.1 eV for particles exposed to air at room temperature. A simple modification to the plasma process allows the in-flight growth of a conformal silicon oxynitride shell onto the zirconium nitride core. The shell inhibits the oxidation of the core, resulting in particles with a plasmon energy of 2.35 eV. These particles show good plasmonic behavior even after annealing in air at 300 °C, largely improved when compared to unprotected particles that oxidize and lose plasmonic activity at the same temperature. This work represents a step toward the development of earth-abundant, thermally and chemically resistant nanoparticles that can offer an inexpensive alternative to gold and silver and extended applicability in harsh environments.