Stabilizing the Plasmonic Response of Titanium Nitride Nanocrystals with a Silicon Oxynitride Shell: Implications for Refractory Optical Materials

Abstract

We discuss the synthesis and properties of nanoparticles and thin films for refractory plasmonic applications. The approach focuses on titanium nitride (TiN), which overcomes the limitations of more common plasmonic materials like silver and gold with respect to temperature stability. Freestanding TiN-based nanoparticles are produced in two serially connected plasma reactors, where TiN nanocrystals are nucleated in a first plasma stage, then aerodynamically dragged in a second stage, and conformally coated with a silicon nitride layer. An in-depth comparison between bare and coated TiN nanoparticles is presented in terms of the structural, chemical, and optical properties. Coating of the titanium nitride core reduces its oxidation upon exposure to air, drastically improving the plasmonic response. Thin films realized using the core–shell structure show practically no change in reflectivity, even when the thin films are heated to 900 °C in an inert atmosphere. This study introduces a simple surface passivation scheme that enhances the functionality of the material, providing further confirmation of the potential of nitride-based plasmonic materials as high-quality refractory optical compounds for a broad range of applications.

Laser‐induced cavitation in plasmonic nanoparticle solutions: A comparative study between gold and titanium nitride

“…However, after longer times of periodic cavitation exposure (25 to 50 min), oxidation effects become more prominent, which is reflected by a slight red shift in the peak. The correlation between oxidation and the presence of red shift was also previously reported by Berrospe et al 39 …”

“…The synthesized TiN NP's had a stoichiometric single‐crystal with rock‐salt structure and an average size of 10 ± 3 nm (see Figure 2a). The addition of the 1.5 ± 0.4 nm coating layer of silicon nitride does not produce any noticeable change in the structure of the particles (see Figure 1b), as was reported by Berrospe‐Rodriguez et al 39 The lattice fringes in the core and the absence of any ordered structure in the shell, indicates an amorphous but uniform coating. Commercial GNR solutions with the plasmonic peak at 808 and 1,064 nm wavelength were used for a comparative study with our synthesized materials.…”

“…In contrast, as shown in Figure 3(d,e), the initial plasmonic peaks for TiN and TiN‐Si, located at 800 and 840 nm respectively, are significantly broader compared to GNR's. However, TiN‐Si presents a narrower and more pronounced peak, as was discussed by Berrospe‐Rodriguez et al 39 After only 12.5 min of laser exposure, the plasmonic peak for 1,064 nm GNR solution completely vanishes. In contrast, for 808 nm it disappears at a slower rate, after 25 min of irradiation.…”

“…Bare TiN and Silicon coated (TiN‐Si) shell NP's were synthesized using a non‐thermal plasma reactor, following the method developed by Barragan et al 38,39 This novel approach allows the fast conversion of chemical precursors into nanomaterials with relatively narrow size distributions and high structural quality, as was proven before for carbides, 40,41 and other nitride materials 42‐44 . The system consisted of a quartz tube reactor, where TiN NPs were synthesized in a gas mixture of Ar, TiCl 4, and NH 3 .…”

“…Based on previous results from laser‐induced cavitation in plasmonic nanoparticles solutions , 34‐37 and considering the crucial role of thermal stability for high temperature/high power density applications, we decided to perform an experimental comparative study between commercially available GNR and TiN NP's synthesized in house via a non‐thermal plasma reactor 38,39 . Both materials were evaluated in terms of their thermal stability, cavitation dynamics, and nonlinear optical properties.…”