Tailoring the plasmonic properties of metals: The case of substoichiometric titanium nitride

The development of nanoplasmonic devices is hampered by the lack of metallic systems that are at the same time chemically stable, mechanically robust, easy to grow, and have tailorable optical properties. Gathering together all these characteristics in a single material is very unusual: in particular the controlled modification of the plasmonic properties of metallic bulk and films still represents an unsolved task. Here, we present a first principles study of the interplay between composition and plasmonic properties in substoichiometric ${\mathrm{TiN}}_{x}$ crystals, which combine superior structural properties and tunable optical response. We investigate the stability of defective ${\mathrm{TiN}}_{x}$ over a large range of vacancy concentrations, and we describe the microscopic character and the plasmonic properties of these systems. Our results indicate a clear trend in the modification of the plasmonic activity of ${\mathrm{TiN}}_{x}$ as a function of nitrogen concentration, and show that for this class of materials the fine manipulation of the internal stoichiometry is a unique tool to tailor the plasmonic properties.