Plasmon coupling and coherent acoustic phonon dynamics of periodic gold pair nanocuboids by near-IR transient absorption spectroscopy

Gold pair nanocuboids (size: 150 nm × 150 nm × 20 nm) with different nanogaps ranging from 0 to 10.6 nm were prepared by the electron-beam lithography. Effect of plasmon coupling on coherent acoustic phonon dynamics of gold pair nanocuboids was examined as a function of nanogaps by near-IR transient absorption spectroscopy at 400-nm excitation. The similar oscillation periods of coherent acoustic phonon vibration (88 ± 1 ps) were observed for all the gold pair nanocubiods irrespective of the nanogaps, which was analyzed by the oscillation of bleaching peaks of SPR bands and the transient absorption dynamics. The coherent acoustic phonon vibration of gold nanocuboids was only influenced by the nanostructure itself, even though SPR band was much influenced due to the dipole coupling between the adjacent Au nanocuboids. In addition, it was revealed that the electron–phonon coupling (∼0.7 ps) was followed by the initial size change of gold nanocuboid with the time scale that was a little slower (∼1.7 ps) than the electron–phonon coupling.