Department of Bioengineering, Rice University, Houston, Texas 77005, USA.
ACS Nano. 2010 Mar 23;4(3):1521-8. doi: 10.1021/nn901743m.
We present a computational study of the plasmonic properties of gold-silica-gold multilayer nanoshells with the core offset from the center. Symmetry breaking, due to the core offset, makes plasmon resonances that are dark in concentric geometries visible. Applying plasmon hybridization theory, we explain the origin of these resonances from the interactions of an admixture of both primitive and multipolar modes between the core and the shell. The interactions introduce a dipole moment into the higher order modes and significantly enhance their coupling efficiency to light. To elucidate the symmetry breaking effect, we link the geometrical asymmetry to the asymmetrical distribution of surface charges and demonstrate illustratively the diminishing multipolar characteristic and increasing dipolar characteristic of the higher order modes. The relative amplitudes of the modes are qualitatively related by visual examination of the dipolar component in the surface charge distributions. Using polarization-dependent surface charge plots, we illustrate two distinct mode configurations despite their spectral similarities. We further demonstrate a trend of increasing absorption relative to scattering as the resonant wavelength red shifts in response to a larger core offset.
我们提出了一个关于金-硅-金多层纳米壳的等离子体特性的计算研究，其中核心从中心偏移。由于核心的偏移，打破了对称性，使得在同心结构中暗的等离子体共振变得可见。通过应用等离子体杂化理论，我们从核心和壳之间的原始模式和多极模式的混合物的相互作用解释了这些共振的起源。这些相互作用将偶极矩引入到更高阶模式中，并显著提高了它们与光的耦合效率。为了阐明对称性破坏的效果，我们将几何不对称性与表面电荷的不对称分布联系起来，并举例说明了高阶模式的多极特征的减小和偶极特征的增加。通过观察表面电荷分布中的偶极分量，可以定性地将模式的相对幅度联系起来。使用偏振相关的表面电荷图，我们说明了尽管它们的光谱相似，但存在两种不同的模式配置。我们进一步证明了，随着共振波长由于更大的核心偏移而红移，吸收相对于散射的增加趋势。
