Tunable optical materials for multi-resonant plasmonics: from TiN to TiON [Invited]

Abstract

Alternative plasmonic materials are gaining more and more interest since they deliver a plethora of advantages in designing of optical metadevices. Among other alternatives, titanium nitride (TiN) has shown an exceptional combination of encouraging properties, such as CMOS- and bio-compatibility, high carrier concentration, tunability and outstanding robustness (high mechanical, chemical and temperature durability). Optical constants of TiN can be tuned at the synthesis stage. This allows for the adjustment of the spectral position of a plasmon resonance within the visible and near-infrared (NIR) range in order to match the desired working wavelength of a particular device. Together, these factors made TiN a popular material of choice in a diversity of recent plasmonic applications. Titanium oxynitride (TiON), which can be produced through the oxidation of TiN, have a great potential to build upon the success of TiN. Recently, it has been demonstrated that TiON thin films can exhibit a negative double-epsilon-near-zero (2ENZ) dielectric function. This unusual behavior of the permittivity opens up novel opportunities for the excitation of the plasmon resonance at several distinct frequencies within the visible and NIR region. Multi-resonant plasmonic components are beneficial for applications, where the enhanced light-matter interaction at multiple frequencies is demanded, such as nonlinear optics, up- and down-conversion, wavelength multiplexing and broadband absorption. This work begins with a brief survey of the recent progress in plasmonics made with TiN-based structures. Then we focus on TiON thin films with the 2ENZ behavior by discussing their potential in plasmonics. The experimental approaches useful for characterization of TiON thin films and the corresponding results are analyzed. These results are valuable for the development of 2ENZ plasmonic materials with large figure-of-merits in a diversity of applications. We believe that 2ENZ media is a powerful concept for multi-resonant plasmonics that will augment the functionalities and extend the operation bandwidth of plasmonic devices.

Crystal Orientation-Dependent Oxidation of Epitaxial TiN Films with Tunable Plasmonics

“…44 Such optical behavior is similar to the dielectric properties of titanium oxynitride reported previously. 24,45 The optical properties of thin films are closely connected with their electrical parameters.…”

“…44 Such optical behavior is similar to the dielectric properties of titanium oxynitride reported previously. 24,45 The optical properties of thin films are closely connected with their electrical parameters. Therefore, we also measured their electrical parameters using the standard Van der Pauw fourprobe method through a Hall effect measurement system.…”

“…Since the (001)oriented TiN is more susceptible to oxidation, thus it is most suitable as tunable optical materials for nonlinear optics and multiresonant plasmonic applications. 45 To further explore the orientation-dependent oxidation behaviors, oxidation levels and electronic structures of all titanium (oxy)nitride thin films are investigated via the element-specific X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS). XAS with surfacesensitive total-electron-yield (TEY) mode is a very powerful technique to probe the TiN surface, which quickly forms a few nanometers-thick native oxidation layer after exposure to the atmosphere.…”

Characterisation of oxygen defects and nitrogen impurities in TiO2 photocatalysts using variable-temperature X-ray powder diffraction

“…Thin films can be synthesised using solid-liquid solvothermal conditions 27 , IVD (ion vapour deposition) or CVD (chemical vapour deposition) 28 . Instead of total nitridation of TiO 2 , there are several reports of the formation of titanium oxynitride for application in photocatalytic and photonic materials 29 . However, though phase identification for complex poly-phasic TiO 2 powders yielded by ammonia/argon treatment have been reported 30 , 31 , the structures of titanium oxynitride remain largely inferred and uncharacterised.…”

Unprecedented Thermal Stability of Plasmonic Titanium Nitride Films up to 1400 °C

“…TiN, however, also possesses unique optical properties, similar to those of Au in the visible-near infrared regions. [33,34] In fact, TiN is the only material that can provide structural stability and Au-like optical response at high temperatures.…”