Ultrafast Dynamics of Colloidal Copper Nanorods: Intraband versus Interband Excitation

Abstract

Colloidal copper nanorods (NRs) display transverse and longitudinal localized surface plasmon resonances. The longitudinal localized surface plasmon modes are tunable through the near‐infrared electromagnetic radiation energies with NR aspect ratios. Visible and near‐infrared transient optical response of the copper NRs is investigated under excitation conditions spanning intraband and interband excitation (0.79−3.50 eV). In both the visible and near‐infrared regions, the spectral response of the samples under intraband excitation (2 eV). However, the timescale of the electron−phonon coupling estimated from pump fluence‐dependent measurements (τep) is less sensitive to excitation conditions than reports for gold. τep shortens slightly from ≈616 fs with intraband excitation (at visible probe energies) to ≈565 fs with interband excitation. The observed dynamics correspond to an average sample electron−phonon coupling parameter varying across all conditions from 4.4 × 1016 to 6.4 × 1016 J m−3 K−1, which is similar to bulk copper. Furthermore, coherent acoustic phonons are observed for the longitudinal localized surface plasmon resonance with a range of oscillatory periods reflecting sample size dispersion.

Keywords

• coherent acoustic phonons
• copper
• electron−phonons
• nanorods