Lu Wenzheng, Cui Ximin, Chow Tsz Him, Shao Lei, Wang Hao, Chen Huanjun, Wang Jianfang
Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
Nanoscale. 2019 May 16;11(19):9641-9653. doi: 10.1039/c9nr01653h.
The interference between spectrally overlapping superradiant and subradiant plasmon resonances generates plasmonic Fano resonance, which allows for attractive applications such as electromagnetically induced transparency, light trapping, and refractometric sensing with high figures of merit. The active switching of plasmonic Fano resonance holds great promise in modulating optical signals, dynamically harvesting light energy, and constructing switchable plasmonic sensors. However, structures enabling the active control of plasmonic Fano resonance have rarely been achieved because of the fabrication complexity and cost. Herein we report on the realization of active plasmonic Fano resonance switching on Au nanosphere-nanoplate heterodimers. The active switching is enabled by varying the refractive index of a layer of polyaniline that fills in the gap between the Au nanosphere and the Au nanoplate. A reversible spectral shift of 20 nm is observed on the individual heterodimers during switching. The maximal spectral shift decreases as the interparticle gap distance is enlarged, showing a strong dependence of the spectral shift on the local electric field intensity enhancement in the gap region. This trend agrees with the predicted dependence of the refractive index sensitivity on the local field intensity enhancement. Our results provide insights into the development of plasmonic structures supporting actively switchable Fano resonances, which can lead to new technological applications, such as switchable cloaking and display, dynamic coding of optical signals, color sorting and filtering. The Au heterodimers with polyaniline in the gap can also be applied for the sensing of local environmental parameters such as pH values and heavy metal ions.
光谱重叠的超辐射和亚辐射等离子体共振之间的干涉产生了等离子体法诺共振，这使得诸如电磁诱导透明、光捕获以及具有高优值的折射传感等有吸引力的应用成为可能。等离子体法诺共振的主动切换在调制光信号、动态收集光能以及构建可切换等离子体传感器方面具有巨大潜力。然而，由于制造复杂性和成本，能够主动控制等离子体法诺共振的结构很少被实现。在此，我们报道了在金纳米球 - 纳米板异质二聚体上实现主动等离子体法诺共振切换。通过改变填充在金纳米球和金纳米板之间间隙的一层聚苯胺的折射率来实现主动切换。在切换过程中，在单个异质二聚体上观察到了20纳米的可逆光谱位移。随着粒子间间隙距离增大，最大光谱位移减小，这表明光谱位移强烈依赖于间隙区域的局部电场强度增强。这种趋势与预测的折射率灵敏度对局部场强增强的依赖性一致。我们的结果为支持主动可切换法诺共振的等离子体结构的发展提供了见解，这可能会带来新的技术应用，如可切换隐身和显示、光信号的动态编码、颜色分选和滤波。间隙中含有聚苯胺的金异质二聚体也可用于传感局部环境参数，如pH值和重金属离子。
