Ultrafast hot electron relaxation processes in plasmonic titanium nitride films.

Rotta Loria S., Bricchi B.R., Schirato A., Li Bassi A., Della Valle G., Zavelani-Rossi M.
  Lunedì 12/09   14:00 - 19:00   Aula D - Marianna Ciccone   II - Fisica della materia   Presentazione
Titanium nitride (TiN) has raised increasing attention due to its refractory nature, CMOS- and bio-compatibility and chemical stability. Moreover, its optical response presents a permittivity tunable by synthesis and a broadband plasmonic resonance, making it an interesting plasmonic material. However, a clear description of the transient optical response of TiN is still missing, mainly concerning the timescale of electron-phonon interactions following photoexcitation. Here, we present the ultrafast dynamics of TiN films ({\sim 200 ${nm}$ thick), with tailored characteristics, produced by pulsed laser deposition (PLD). We use pump-probe spectroscopy with temporal resolution down to almost $15 {fs}$, tunable pump and broadband probe, extending over the plasmon resonance. The experimental analysis is supported by numerical modelling based on a two-temperature model (TTM), including a dispersed contribution for the modulation of interband transitions. Electron-phonon coupling in TiN is shown to be much stronger than in gold, with relaxation taking place in about $200 {fs}$. Our findings lead to a deeper understanding of the physics of TiN, and provide relevant insights in view of device design.