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) differs substantially from their response under interband 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.

Unconventional Shrinkage of Hot Electron Distribution in Metal Directly Visualized by Ultrafast Imaging

“…Because the density of states at the top of the d‐band is much higher than that at the s/p band near the Fermi level, the optical response is thus dominated by the interband transitions. [ 41–43 ] In the meantime, the perturbation of free electron density from d‐band is negligible as long as the pump fluence is low enough to ensure initial T e < 2500 K. [ 23,44 ] Therefore, the pump wavelength is set to be 700 nm (1.77 eV), which only excites the s/p electrons and changes the electron distribution near the Fermi level; the probe wavelength is chosen as 520 nm (2.39 eV), which is slightly lower than the ITT (2.47 eV) to monitor the electron behaviors near the Fermi level.…”

Boosted charge transport through Au-modified NiFe layered double hydroxide on silicon for efficient photoelectrochemical water oxidation

“…Au has emerged as the practical element for improving PEC water splitting properties of photoelectrodes for its virtues of facile light absorption, chemical stability, and electronic structure modication. [34][35][36][37] An optimized amount of Au could be effectively incorporated into Ni and Fe vacancy sites through consecutive two-step electrodeposition processes. Only with a minimum Au precursor concentration, compared to the concentration of the NiFe precursor, can synergistic interactions between metallic elements derive efficient electronic and band structure modication in a way much more favorable to PEC water oxidation.…”

Seed-Mediated Growth of Oxidation-Resistant Copper Nanoparticles

“…However, for CuNPs, changes in size often result in minimal observed shifts in peak wavelength due to the strong overlap with the interband transition. In the case of nanorods or shells, the longer wavelength peak of the double peak feature is shifted with changes in length or shell thickness; however, the peak centered near the interband transition remains unchanged. , …”

“…9,14,15 Additionally, changing the shape to rods or shells results in a double peak feature due to the introduction of additional LSPR modes at longer wavelengths. 13,16 Further complicating the extinction spectra of CuNPs is the fact that the LSPR overlaps with the interband transition associated with the bandgap of bulk copper at 2.1 eV (590 nm). This overlap causes dampening of the LSPR and a broad background spectrum that extends into the UV.…”