Solid-State Synthesis of UV-Plasmonic Cr2N Nanoparticles

Materials that exhibit plasmonic response in the UV region can be advantageous for many applications such as biological photodegradation, photocatalysis, disinfection, and bioimaging. Transition metal nitrides have recently emerged as chemically and thermally stable alternatives to metal-based plasmonics materials. However, most free-standing nitride nanostructures explored so far have plasmonic response in the visible and near-IR region. Herein, we report the synthesis of UV-plasmonic Cr2N nanoparticles using a solid-state nitridation reaction. The nanoparticles had an average diameter of 9 ± 5 nm and a positively charged surface that yields stable colloidal suspension. The particles were composed of a crystalline nitride core and an amorphous oxide/oxynitride shell whose thickness varied between 1 - 7 nm. Calculations performed using finite element method predicted the localized surface plasmon resonance (LSPR) for these nanoparticles to be in the UV-C region (100 - 280 nm). While a distinctive LSPR peak could not be observed using absorbance measurements, low-loss electron energy loss spectroscopy showed the presence of surface plasmons between 80 - 250 nm and bulk plasmons centered around 50 - 60 nm. Plasmonic coupling was also observed between the nanoparticles resulting in resonances between 250 - 400 nm.