Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States.
Nano Lett. 2014 Feb 12;14(2):743-8. doi: 10.1021/nl4040362. Epub 2014 Jan 22.
The mechanical properties of anisotropic nanoparticles like gold nanorods (AuNRs) and silver nanorods (AgNRs) are different from those of isotropic shapes such as nanospheres. We probed the coherent lattice oscillations of nanoparticles by following the modulation of the plasmonic band frequency using ultrafast laser spectroscopy. We found that while the frequency of the longitudinal vibration mode of AgNRs is higher than that of AuNRs of similar dimensions, similarly sized gold and silver nanospheres have similar lattice vibration frequencies. Lattice vibrations calculated by finite element modeling showed good agreement with the experimental results for both AgNRs and AuNRs. The accuracy of the calculations was improved by using actual pentagonal shapes rather than cylinders that did not agree well with the experimental results. As the plasmon energy is transferred into lattice vibrations, the temperature of the nanoparticle necessarily increases as a result of this electron-phonon relaxation process. This results in a decrease in the Young's modulus that was accounted for in the calculations. Calculations showed that the tips of the nanorods are "softer" than the rest of the nanorod. Because the tips comprise a larger portion of the overall rod in the smaller rods, the smaller rods were more affected by the tip effects.
各向异性纳米粒子（如金纳米棒（AuNRs）和银纳米棒（AgNRs））的力学性能与各向同性形状（如纳米球）不同。我们通过超快激光光谱学跟踪等离子体带频率的调制来探测纳米粒子的相干晶格振动。我们发现，虽然 AgNRs 的纵向振动模式的频率高于类似尺寸的 AuNRs，但同样大小的金和银纳米球具有相似的晶格振动频率。有限元建模计算的晶格振动与 AgNRs 和 AuNRs 的实验结果吻合良好。通过使用与实验结果不太吻合的实际五边形而不是圆柱体来改进计算的准确性。随着等离子体能量转移到晶格振动中，由于这种电子-声子弛豫过程，纳米粒子的温度必然会升高。这导致杨氏模量的降低，在计算中进行了考虑。计算表明，纳米棒的尖端比纳米棒的其余部分更“柔软”。由于在较小的棒中，尖端占整个棒的比例更大，因此较小的棒受尖端效应的影响更大。
