A Non-Thermal Plasma Route to Plasmonic TiN Nanoparticles

In this contribution, we present a high-throughput method for the synthesis of titanium nitride nanoparticles. The technique, based on a continuous-flow nonthermal plasma process, leads to the formation of free-standing titanium nitride particles with crystalline structures and below 10 nm in size. Extinction measurements of the as-synthesized particles show a clear plasmonic resonance in the near-infrared region, with a peak plasmon position varying between 800 and 1000 rim. We have found that the composition can be controllably tuned by modifying the process parameters and that the particle optical properties are strongly dependent upon composition. XPS and STEM/EDS analyses suggest that nitrogen-poor particles are more susceptible to oxidation, and the extinction spectra show a decrease and a red-shift in plasmon peak position as the degree of oxidation increases. The role of oxidation is confirmed by real-time, time-dependent density functional tight binding (RT-TDDFTB) calculations, which also predict a decrease in the localized surface plasmon resonance energy when a single monolayer of oxygen is added to the surface of a titanium nitride nanocrystal. This study highlights the opportunity and challenges presented by this material system. Understanding the processing-properties relationships for alternative plasmonic materials such as titanium nitride is essential for their successful use in biomedical, photocatalytic, and optoelectronic applications.