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 similar to 10 nm diameter nanoparticles. Oxidation limits the resonant plasmon energy from similar to 2.6 eV for ideal unoxidized particles to similar 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 degrees 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.