The development of low-dimensional transparent conducting systems is nowadays gaining interest in view of novel optoelectronic applications. In this paper, we investigate the evolution of optical and electronic properties of...

Localised Surface Plasmon Resonances (LSPR) are fascinating optical phenomena occurring in metal nanostructures, like gold nanoparticles (Au NPs). Plasmonic excitation can be tailored efficiently in the visible range by acting on size, shape and NP surrounding, whereas carrier density is fixed, thus restricting the LSPR modulation. Transparent Conductive Oxides (TCOs), on the other hand, are gaining increasing interest for their transparency, charge carrier tunability and plasmonic features in the infrared. The combination of these two materials into a metal-TCO nanocomposite can give access to unique electrical and optical characteristics, to be tailored in view of the desired optoelectronic application. In this study Au NPs and Ta-doped TiO2 TCO films have been merged with the aim to master the Au plasmon resonance by acting on the dielectric properties of the surrounding TCO. Morphology, structure and electrical properties have been investigated as well, in order to understand the optical response of the nano-systems. The role of the embedding geometry has been explored, revealing that the largest LSPR shift (550-760 nm) occurs when the nanoparticles are sandwiched in the middle of the film, and not at the "bottom" of the film (substrate/film interface). Ta doping in the TCO has been varied (5-10% at. and bare TiO2) to induce a permittivity change of the matrix. As a result, Au LSPR is clearly blue-shifted when decreasing the dielectric permittivity at higher Ta content in the sandwich configuration. Despite the non-optimal electrical performance caused by defectivity of the films, Au-Ta:TiO2 multifunctional nanocomposites are promising candidates for their optical behavior as highly tunable plasmonic conductive metamaterials for advanced light management.

Ultrafast plasmonics is driving growing interest for the search of novel plasmonic materials, overcoming the main limitations of noble metals. In this framework, titanium nitride (TiN) is brought in the spotlight for its refractory properties combined with an extremely fast electron‐lattice cooling time (<100 fs) compared to gold (≈ 1 ps). Despite the results reported in literature, a clear‐cut explanation of the origin of the ultrafast and giant optical response of TiN‐based materials upon excitation with femtosecond laser pulses is still missing. To address this issue, an original model is introduced, capable of unfolding the modulation of TiN optical properties on a broad bandwidth, starting from the variations of electronic and lattice temperatures following ultrafast photoexcitation. The numerical analysis is validated on ultrafast pump–probe spectroscopy experiments on a simple structure, a TiN film on glass. This approach enables a complete disentanglement of the interband and intraband contributions to the permittivity modulation. Moreover, it is also shown that, varying the synthesis conditions of the TiN film, not only the static, but also the dynamical optical response can be efficiently tuned. These findings pave the way for a breakthrough in the field: the design of TiN‐based ultrafast nanodevices for all‐optical modulation of light.

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