Vibrational Dynamics of Silver Nanocubes and Nanowires Studied by Single-Particle Transient Absorption Spectroscopy

The vibrational response of single silver nanocubes and nanowires to ultrafast laser-induced heating has been studied through transient absorption measurements. The traces show pronounced modulations due to coherent excitation of the breathing modes of the particles. Analysis of the data yields the period and the homogeneous lifetime of the vibrational motion. Different particles show different values for the period and lifetime. The distribution of the periods is due to the distribution of particle sizes in the sample. For the nanocubes the vibrational lifetimes are only weakly correlated with the periods, whereas, for the nanowires there is a medium correlation between the period and lifetime. The difference between the nanocubes and the nanowires is attributed to differences in how the particles are deposited on the substrate. In both cases the distribution for the lifetimes is significantly broader than that for the periods. This implies that the lifetimes are strongly affected by the particle's local environment, and that there is significant heterogeneity in the environment. Overall, these experiments provide detailed information about how nanoparticles interact mechanically with their surroundings.