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The development of plasmonic and metamaterial devices requires the research of high-performance materials alternative to standard noble metals. Recently refractory Titanium Nitride has been proposed as a valid alternative to gold, [1] even for application in harsh and high-temperature environments. Indeed, being refractory this compound exhibits extraordinary mechanical stability over a large range of temperatures (∼2000 ◦ C) and pressures (∼3.5 Mbar), well above the melting point of standard noble metals (∼800 ◦ C). This material is furthermore resistant to corrosion and compatible with silicon technology. TiN has optical and plasmonic properties (color, electron density, plasmon frequency) very similar to gold and has been exploited for the realization of waveguides, broadband absorbers, local heaters, and hyperbolic metamaterials in connection with selected dielectric media (e.g., MgO, AlN, sapphire, etc.).
Even though the fundamental mechanical and optoelectronic properties of TiN have been largely studied so far from experimental and theoretical points of view, very little is know about its plasmonic behavior. Here, we present a fully-first-principles investigation, based on time-dependent density functional theory (TDDFT), of the plasmon properties of stoichiometric titanium nitride.[2] The microscopic origin of plasmonic excitations are analyzed in terms of the fundamental collective and/or radiative exctations of TiN electronic structure. From the simulation of energy-loss spectra at different momentum transfer, we derive the TiN plasmon dispersion relations that are directly accessible by experimental measurements.
We furthermore analyze different interfaces between TiN and conventional semiconductors in order to describe TiN surface-plasmon polaritons for the realization of hyperbolic metamaterials and waveguides. We also investigated the optoelectronic charcateristics of the compound in relation to the crystal phase transition, experimentally observed at very high pressure. The microscopic origin of the plasmon resonances and their dispersions have been discussed on the basis of the analysis of the electronic structure and of the interplay between collective and single-particle excitations, which determine the screening and dissipation effects of the electronic system.
The similarities and the differences with other noble metals, in particular with gold, are thoroughly discussed all along the paper.
Our ab initio results confirm that at standard conditions TiN exhibits plasmonic properties in the visible and near-IR regime, very close to gold, in agreement with experimental data. In contrast with malleable noble metals, the hardness of refractory ceramics allows for the exploitation of plasmonic properties also at high temperature and under pressure, conditions where standard plasmonic materials cannot be used.
[1] G. V. Naik, V. M. Shalaev, and A. Boltasseva, Science 344, 263 (2014).
[2] A. Catellani and A. Calzolari, Phys. Rev. B 95, 115145 (2017)
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