Characteristic features of magnetoplasmonic responses in higher-order multipolar (quadrupolar and octupolar) modes of Ag nanoparticles (from 90 to 200 nm in diameter) are demonstrated for the first time using magnetic circular dichroism (MCD) spectroscopy. In optical extinction spectra, with an increase in the size of the nanoparticles, the red shift of dipolar plasmon peaks and the appearance of higher-order multipolar resonances can reasonably be observed. Aside from the dipolar and quadrupolar modes, the octupolar plasmonic extinction is very weak and almost unresolved. In contrast, strikingly, MCD shows a very sharp and intense peak (or valley) for the octupolar resonance, meaning its unique properties with high sensitivity and enhanced spectral resolution. MCD responses assignable to the quadrupolar mode have a distinct derivative-like shape, which is different from those observed for Ag nanocubes and nanodecahedra in our previous studies. We then discuss this behavior from the viewpoint of size and/or polyhedral shape inhomogeneity.

中文翻译：

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在尺寸在 90 到 200 nm 之间的银纳米粒子的多极等离子体模式中具有高灵敏度和增强的光谱分辨率的磁性圆二色性响应

首次使用磁圆二色性 (MCD) 光谱证明了 Ag 纳米粒子（直径从 90 到 200 nm）的高阶多极（四极和八极）模式中磁等离子体响应的特征。在消光光谱中，随着纳米颗粒尺寸的增加，可以合理地观察到偶极等离子体峰的红移和高阶多极共振的出现。除了偶极和四极模式，八极等离子体消光非常微弱，几乎没有解决。相比之下，令人惊讶的是，MCD 显示出非常尖锐和强烈的八极共振峰（或谷），这意味着其具有高灵敏度和增强的光谱分辨率的独特特性。可分配给四极模式的 MCD 响应具有明显的类似导数的形状，这与我们之前研究中观察到的银纳米立方体和纳米十面体不同。然后我们从大小和/或多面体形状不均匀性的角度讨论这种行为。