Vibrational spectroscopy and energy relaxation of nanocubes, nanoboxes, and nanocages

Irradiating metal particles by an ultrafast laser pulse produces rapid heating of the lattice. This can lead to coherent excitation of the vibrational modes of the particle that correlate with the expansion co-ordinates. By comparing the measured periods to continuum mechanics calculations, these experiments can provide information about the elastic constants of the particle if the size and shape are known. In this paper recent results are presented for particles with cubic symmetry, specifically, nanocubes, nanoboxes (hollow cubes) and nanocages (nanoboxes with holes on the corners and/or facets of the box). The way the vibrational modes are assigned, and the information content of the experiments will be discussed, as well as the energy relaxation dynamics of the particles. Energy relaxation is important for the proposed use of the nanocages in phothermal therapy, where heat dissipation following laser excitation is used to selectively kill cells.