Emerging Technology and Materials group, School of Engineering, Newcastle University, Merz Court, Newcastle Upon Tyne NE1 7RU, UK.
Nanoscale. 2018 Jul 19;10(28):13607-13616. doi: 10.1039/c8nr01527a.
Nanogaps supporting cavity plasmonic modes with unprecedented small mode volume are attractive platforms for tailoring the properties of light-matter interactions at the nanoscale and revealing new physics. Hitherto, there is a concerning lack of analytical solutions to divide the complex interactions into their different underlying mechanisms to gain a better understanding that can foster enhanced designs. Bowtie apertures are viewed as an effective and appealing nanocavity and are studied here within the analytical frame of conformal transformation. We show how the non-radiative Purcell enhancement of a quantum emitter within the bowtie nanocavity depends strongly not only on the geometry of the nanocavity, but also on the position and orientation of the emitter. For a 20 nm diameter (∅ 20 nm) bowtie nanocavity, we report a change of up to two orders of magnitude in the maximum non-radiative Purcell enhancement and a shift in its peak wavelength from green to infra-red. The changes are tracked down to the overlap between the emitter field and the gap plasmon mode field distribution. This analysis also enables us to understand the self-induced trapping potential of a colloidal quantum dot inside the nanocavity. Since transformations can be cascaded, the technique introduced in this work can also be applied to a wide range of nanocavities found in the literature.
支持具有前所未有的小模式体积的纳米间隙的腔等离子体模式是在纳米尺度上调整光物质相互作用的特性并揭示新物理的有吸引力的平台。迄今为止，将复杂的相互作用分解为其不同的基础机制以获得更好的理解，从而促进增强设计，缺乏解析解。蝴蝶结孔被视为一种有效且有吸引力的纳米腔，并且在保角变换的分析框架内进行了研究。我们展示了量子发射器在蝴蝶结纳米腔中的非辐射普塞尔增强如何不仅强烈依赖于纳米腔的几何形状，而且还依赖于发射器的位置和方向。对于直径为 20nm（∅20nm）的蝴蝶结纳米腔，我们报告了最大非辐射普塞尔增强高达两个数量级的变化，并且其峰值波长从绿光转移到近红外。变化可以追溯到发射器场和间隙等离子体模场分布之间的重叠。这种分析还使我们能够了解胶体量子点在纳米腔内的自诱导陷阱势。由于变换可以级联，因此本工作中引入的技术也可以应用于文献中发现的各种纳米腔。
