Giovannini Tommaso, Nicoli Luca, Corni Stefano, Cappelli Chiara
Department of Physics and INFN, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy.
Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy.
Nano Lett. 2025 Jul 9;25(27):10802-10808. doi: 10.1021/acs.nanolett.5c01999. Epub 2025 Jun 25.
Picocavities are plasmonic nanostructures featuring atomistic defects within subnanometer gaps. Such a unique morphology enables extreme light confinement at subnanometer scales and drives substantial field enhancements with applications from molecular sensing to plasmon-driven catalysis. However, the impact of atomistic defects on the plasmonic field morphology, which ultimately determines light-matter interactions at the nanoscale, remains largely unexplored due to the limitations of traditional theoretical models. Here, we employ the frequency-dependent fluctuating charges and dipoles (ωFQFμ) approach, an atomistic yet computationally efficient method previously validated against time-dependent density functional theory calculations, to reveal the plasmonic field morphology in gold picocavities composed of thousands of atoms. Our results uncover pronounced field inhomogeneities induced by the atomic-scale defects, which may trigger novel effects where electric field gradients are pivotal. Our findings establish the physical foundations for rationalizing experimental observations and guiding the design of next-generation nanophotonic devices with unprecedented control over atomic-scale field confinement.
微腔是一种等离子体纳米结构，在亚纳米间隙中存在原子尺度的缺陷。这种独特的形态能够在亚纳米尺度上实现极强的光限制，并通过从分子传感到等离子体驱动催化等应用实现显著的场增强。然而，由于传统理论模型的局限性，原子尺度缺陷对等离子体场形态的影响在很大程度上仍未得到探索，而等离子体场形态最终决定了纳米尺度上的光与物质相互作用。在这里，我们采用频率相关的波动电荷和偶极子（ωFQFμ）方法，这是一种原子尺度但计算效率高的方法，之前已通过与含时密度泛函理论计算对比得到验证，以揭示由数千个原子组成的金微腔中的等离子体场形态。我们的结果揭示了由原子尺度缺陷引起的明显场不均匀性，这可能引发电场梯度起关键作用的新效应。我们的发现为合理解释实验观察结果和指导下一代纳米光子器件的设计奠定了物理基础，从而以前所未有的方式控制原子尺度的场限制。
