Department of Physics, Sharif University of Technology, Tehran, Iran.
Department of Laser and Optical Engineering, University of Bonab, Bonab, Iran.
Sci Rep. 2021 Jul 23;11(1):15115. doi: 10.1038/s41598-021-94409-9.
In this work, the optical properties of asymmetric nanoshells with different geometries are comprehensively investigated in the quasi-static regime by applying the dipolar model and effective medium theory. The plasmonic behaviors of these nanostructures are explained by the plasmon hybridization model. Asymmetric hybrid nanoshells, composed of off-center core or nanorod core surrounded by a spherical metallic shell layer possess highly geometrically tunable optical resonances in the near-infrared regime. The plasmon modes of this nanostructures arise from the hybridization of the cavity and solid plasmon modes at the inner and outer surfaces of the shell. The results reveal that the symmetry breaking drastically affects the strength of hybridization between plasmon modes, which ultimately affects the absorption spectrum by altering the number of resonance modes, their wavelengths and absorption efficiencies. Therefore, offsetting the spherical core as well as changing the internal geometry of the nanoparticle to nanorod not only shift the resonance frequencies but can also strongly modify the relative magnitudes of the absorption efficiencies. Furthermore, higher order multipolar plasmon modes can appear in the spectrum of asymmetric nanoshell, especially in nanoegg configuration. The results also indicate that the strength of hybridization strongly depends on the metal of shell, material of core and the filling factor. Using Au-Ag alloy as a material of the shell can provide red-shifted narrow resonance peak in the near-infrared regime by combining the specific features of gold and silver. Moreover, inserting a high permittivity core in a nanoshell corresponds to a red-shift, while a core with small dielectric constant results in a blue-shift of spectrum. We envision that this research offers a novel perspective and provides a practical guideline in the fabrication of efficient tunable absorbers in the nanoscale regime.
在这项工作中，通过应用偶极子模型和有效介质理论，在准静态条件下全面研究了具有不同几何形状的不对称纳米壳的光学性质。这些纳米结构的等离子体行为通过等离子体杂化模型来解释。由偏心核或纳米棒核组成的不对称混合纳米壳，周围环绕着球形金属壳层，在近红外区域具有高度几何可调谐的光学共振。这些纳米结构的等离子体模式源于壳内层和外层的空腔和固体等离子体模式的杂化。结果表明，对称性破缺会极大地影响等离子体模式之间的杂化强度，从而通过改变共振模式的数量、波长和吸收效率来改变吸收光谱。因此，将球形核偏移以及将纳米粒子的内部几何形状改变为纳米棒，不仅会改变共振频率，而且还可以强烈改变吸收效率的相对大小。此外，高阶多极等离子体模式可以出现在不对称纳米壳的光谱中，特别是在纳米蛋结构中。结果还表明，杂化强度强烈依赖于壳的金属、核的材料和填充因子。使用 Au-Ag 合金作为壳的材料可以通过结合金和银的特性，在近红外区域提供红移的窄共振峰。此外，在纳米壳中插入高介电常数的核会导致红移，而介电常数小的核会导致光谱蓝移。我们预计，这项研究提供了一个新的视角，并为在纳米尺度上制造高效可调谐吸收器提供了实用的指导。
