The rapid heating induced by ultrafast excitation of metal nanostructures coherently excites the breathing vibrational modes of the structure. Detailed information about these modes can be obtained by studying single nanoparticles with transient absorption microscopy. However, in single particle experiments the breathing modes are usually heavily damped by radiation losses into the substrate. Recently we discovered that using low density substrates drastically reduces radiation losses and creates very high vibrational quality factors for gold nanoplates. This allows several new phenomena to be explored, including strong vibrational coupling between stacked nanoplates, and new vibrational modes that correspond to motion of the nanoplates relative to the substrate and, for the stacked nanoplates, relative to each other. The results from these experiments will be described in this talk, along with studies of mass loading effects for the nanoplates. In the mass loading experiments a localized change in vibrational frequency is observed when a particle is adsorbed onto the surface of a nanoplate. This is an unusual result, as the breathing modes of the nanoplates are normal modes that are spread out over the entire plate. This implies that the adsorbed mass hybridizes the normal modes.

Vibrational coupling in metal nanostructures studied by ultrafast microscopy

ACS Spring Meeting 2021

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