Coherent Acoustic Phonon Dynamics of Gold Nanorods and Nanospheres in a Poly(vinyl alcohol) Matrix and Their Temperature Dependence by Transient Absorption Spectroscopy

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• 作者：Li Wang ; Shohei Takeda ; Changchun Liu ; Naoto Tamai
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：January 23, 2014
• 年：2014
• 卷：118
• 期：3
• 页码：1674-1681
• 全文大小：419K
• ISSN：1932-7455

文摘

The ultrafast dynamics of photoexcited gold nanorods (Au NRs) and gold nanospheres (Au NSs) dispersed in poly(vinyl alcohol) (PVA) films were investigated at various temperatures. The extensional mode of the coherent acoustic phonon vibration for Au NRs and breathing mode for Au NSs were both observed. For Au NRs, the vibrational periods in PVA decreased, and those in aqueous solution increased compared to the estimated periods in vacuum. These phenomena were not observed for Au NSs. When the temperature decreased from 296 to 10 K, the vibrational period of Au NRs (9 nm diameter, 46 nm length) decreased by 15%, but the decrease was only 3% for that of Au NSs (108 nm diameter). The environmental effects on coherent acoustic phonon vibrations for Au NRs were discussed in terms of mechanical interaction with the polymer matrix and liquid鈥搒olid coupling with the solution. A simplified model for the coupling of a vibrating rod to a viscoelastic environment, called a pile鈥搒oil interaction, was introduced for Au NRs in a PVA matrix, and the calculated periods were in good agreement with the experimental data. Our results indicate that viscous effects dominate for nanorods in water, whereas elastic effects dominate in PVA, resulting in frequency shifts with opposite signs. Moreover, because of the different interaction for extensional and breathing modes, the environmental sensitivity of Au NRs is obviously higher than that of Au NSs, and this difference can provide guidelines for mechanical applications of metal鈥損olymer nanocomposites.