Huang Wenyu, Qian Wei, El-Sayed Mostafa A
Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA.
J Phys Chem B. 2005 Oct 13;109(40):18881-8. doi: 10.1021/jp0526647.
Using femtosecond transient spectroscopy, we studied the optically detected laser-induced coherent phonon oscillation of monolayers of periodic arrays of prismatic-shaped silver and gold nanoparticles, assembled by using the technique of nanosphere lithography. In this method, the same size of polystyrene sphere and the same vacuum conditions are used. Under these circumstances, the gold nanoprisms formed are found to have sharper tips than the corresponding silver nanoprisms. For both gold and silver nanoparticles, the surface plasmon absorption maximum is found to depend linearly on size. The coherent lattice oscillation periods are also found to depend linearly on size. However, although the observed dependence for the silver nanoparticle is found to follow the calculated dependence of a single particle on size (based on a one-dimensional standing wave model), the gold nanoparticle deviates from this model, and the deviation is found to increase with the size of the nanoparticles. This deviation can be explained by considering interparticle coupling. A simple interparticle lattice oscillating dipolar coupling model of the dimer is found to qualitatively account for both the sign and the size dependence of the deviation. The absence of this deviation in the silver nanoparticle arrays is blamed on the weak interparticle coupling due to their rounded tips and the possibility of oxidation of their surfaces.
我们使用飞秒瞬态光谱技术，研究了通过纳米球光刻技术组装的棱柱形银和金纳米粒子周期性阵列单层的光探测激光诱导相干声子振荡。在这种方法中，使用相同尺寸的聚苯乙烯球和相同的真空条件。在这些情况下，发现形成的金纳米棱柱比相应的银纳米棱柱具有更尖锐的尖端。对于金和银纳米粒子，表面等离子体吸收最大值都线性依赖于尺寸。相干晶格振荡周期也线性依赖于尺寸。然而，虽然发现银纳米粒子的观察到的依赖性遵循单个粒子对尺寸的计算依赖性（基于一维驻波模型），但金纳米粒子偏离了该模型，并且发现这种偏差随着纳米粒子尺寸的增加而增大。这种偏差可以通过考虑粒子间耦合来解释。发现二聚体的简单粒子间晶格振荡偶极耦合模型定性地解释了偏差的符号和尺寸依赖性。银纳米粒子阵列中不存在这种偏差归因于其圆形尖端导致的粒子间耦合较弱以及其表面氧化的可能性。
