| Summary: | 博士 === 國立臺灣大學 === 化學研究所 === 97 === 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.
We also examined photoinduced ultrafast structural dynamics such as coherent acoustic waves in many shapes of fcc metallic nanomaterials. Experimental data of nano-sized thin films, prisms, spheres, rods, disks and pyramids from transient optical absorption/reflectance measurements were analyzed based on a combined Fermi-Pasta-Ulam model and two-temperature model. This work elucidates the structural dynamics induced by femtosecond laser heating, its size and shape effects on the period and phase of the excited acoustic phonon modes.
|
|---|
