摘要
我們利用飛秒解析瞬態吸收的技術成功的觀測到銀奈米稜鏡中與稜鏡厚度有關的聲支頻-聲子模式，其中這兩種樣品具有差不多的大小31.4~31.6 nm，但是厚度分別是7.8 1.2和8.5 0.69 nm。利用這個技術我們發現奈米稜鏡中有兩種聲子模式。一種是跟稜鏡厚度有關的聲子，頻率介於7.81 cm-1 ~11.7 cm-1之間；另一種與稜鏡的高有關，頻率是介於1.95 cm-1和1.71 cm-1。另外，我們也探討了各種不同形狀的fcc金屬奈米粒子在飛秒雷射脈衝加熱後，結構的動態變化。我們利用Fermi-Pasta-Ulam和two-temperature模型分析包括：奈米尺度的薄膜、稜鏡、球、棒子、圓平面和金字塔等形狀。從這些結果我們可以解釋金屬奈米材料在雷射加熱後的結構動態變化、大小和形狀對振動周期和相位的影響。
並列摘要
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.
參考文獻
延伸閱讀
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