Department of Physics, National University of Singapore, Singapore 117542, Singapore.
ACS Nano. 2010 Dec 28;4(12):7692-8. doi: 10.1021/nn102581g. Epub 2010 Nov 18.
The intriguing optical and catalytic properties of metal-silica core-shell nanoparticles, inherited from their plasmonic metallic cores together with the rich surface chemistry and increased stability offered by their silica shells, have enabled a wide variety of applications. In this work, we investigate the confined vibrational modes of a series of monodisperse Ag@SiO(2) (cubic core)-shell nanospheres synthesized using a modified Stöber sol-gel method. The particle-size dependence of their mode frequencies has been mapped by Brillouin light scattering, a powerful tool for probing hypersonic vibrations. Unlike the larger particles, the observed spheroidal-like mode frequencies of the smaller ones do not scale with inverse diameter. Interestingly, the onset of the deviation from this linearity occurs at a smaller particle size for higher-energy modes than for lower-energy ones. Finite element simulations show that the mode displacement profiles of the Ag@SiO(2) core-shells closely resemble those of a homogeneous SiO(2) sphere. Simulations have also been performed to ascertain the effects that the core shape and the relative hardness of the core and shell materials have on the vibrations of the core-shell as a whole. As the vibrational modes of a particle have a bearing on its thermal and mechanical properties, the findings would be of value in designing core-shell nanostructures with customized thermal and mechanical characteristics.
金属-二氧化硅核壳纳米粒子具有引人注目的光学和催化性质，这源于其等离子体金属核与丰富的表面化学和增加的稳定性，使其能够应用于各种领域。在这项工作中，我们研究了一系列使用改进的 Stöber 溶胶-凝胶法合成的单分散 Ag@SiO2（立方核）-壳纳米球的受限振动模式。通过布里渊光散射（一种探测高超音速振动的强大工具）绘制了它们的模式频率随粒径的变化关系。与较大的颗粒不同，较小颗粒的观察到的类球形模式频率并不与直径的倒数成比例。有趣的是，对于高能模式，偏离这种线性关系的起始点出现在比低能模式更小的颗粒尺寸处。有限元模拟表明，Ag@SiO2 核壳的模式位移分布与均匀 SiO2 球体非常相似。还进行了模拟以确定核形状和核与壳材料的相对硬度对核壳整体振动的影响。由于颗粒的振动模式对其热和机械性能有影响，因此这些发现对于设计具有定制热和机械特性的核壳纳米结构具有重要价值。
