Ultrafast Spectroscopy Studies on Thickness Dependence of Acoustic Phonon Modes in Silver Nanoprisms

Time-resolved transient absorption technique is used to investigate the thickness dependence of acoustic phonon modes of silver nanoprisms with two thicknesses, 7.8 +-1.2 and 8.5+-0.69 nm, and a similar bisector length of 31.4 ~ 31.6 nm. Coherent acoustic phonon signals are observed. A new acoustic phonon frequency within 7.81 cm-1 ~ 11.7 cm-1 is found and this phonon mode is associated with the thickness of the nanoprism. Another phonon frequency between 1.95 cm-1 and 1.71 cm-1 is also observed, and its origin can be associated with the bisector length of the nanoprism.