Tuning Plasmonic Coupling from Capacitive to Conductive Regimes via Atomic Control of Dielectric Spacing
Tuning Plasmonic Coupling from Capacitive to Conductive Regimes via Atomic Control of Dielectric Spacing
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DOI：
10.1021/acsphotonics.0c00225
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发表时间：
2020-03-18
期刊：
影响因子：
7
通讯作者：
Habteyes, Terefe G.
中科院分区：
文献类型：
--
作者：
Haq, Sharmin;Tesema, Tefera E.;Habteyes, Terefe G.
等离子体纳米粒子之间的间隙长度决定了光学耦合的强度，从而导致光谱和其他应用中的电磁场增强。尽管带隙等离子激元共振一直是越来越多的研究热点，但实验观察主要局限于球形纳米粒子之间的耦合，这种耦合可能不会提供清晰的光谱对比度，因为随着带隙尺寸减小到亚纳米，相互作用从电容演化到电荷转移。在这里，我们利用胶体金纳米棒与金膜耦合的尖锐的等离子体共振，给出了当颗粒-膜间距从30 nm以上到接触极限变化时，GaP等离子体共振的光谱演化。我们发现，耦合系统的电容带隙等离子体共振不断红移和变窄，直到它在量子隧道极限处消失，而非局域和朗道衰减效应预计会导致相对蓝移和光谱展宽。当隔离层厚度进一步减小时，出现高次腔模，最终出现具有隧穿和直接接触粒子-薄膜相互作用特征的单峰宽谐振。实验观察表明，纳米棒更适合于产生高品质因数的腔等离子体共振，而跃迁处的光谱对比度为发展亚纳米带隙长度的光学耦合提供了改进的理论模型。
The gap length between plasmonic nanoparticles determines the strength of the optical coupling that results in electromagnetic field enhancement for spectroscopic and other applications. Although gap plasmon resonances have been the focus of increasing research interest, experimental observations have primarily been limited to the coupling of spherical nanoparticles that may not provide clear spectral contrast of the optical response as the interaction evolves from capacitive to charge transfer with the gap size decreasing to sub-nanometer. Here, by taking advantage of the sharp plasmon resonances of colloidal gold nanorods coupled to gold film, we present the spectral evolution of gap plasmon resonance as the particle-film spacing varies from over 30 nm to the touching limit. We find that the capacitive gap plasmon resonance of the coupled system red-shifts and narrows continuously until it vanishes at the quantum tunneling limit, in contrast to the nonlocal and Landau damping effects that are expected to result in relative blue-shifting and spectral broadening. When the spacer thickness is further decreased, high order cavity modes appear, and eventually single peak broad resonances that are characteristic of tunneling and direct contact particle-film interaction emerge. The experimental observations show that nanorods are better suited for creating cavity plasmon resonances with high quality factor, and the spectral contrast at the transition provides clarity to develop improved theoretical modeling of optical coupling at sub-nanometer gap lengths.