Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, Illinois 60208, USA.
Nat Nanotechnol. 2011 May 15;6(7):423-7. doi: 10.1038/nnano.2011.72.
Plasmonic nanostructures concentrate optical fields into nanoscale volumes, which is useful for plasmonic nanolasers, surface enhanced Raman spectroscopy and white-light generation. However, the short lifetimes of the emissive plasmons correspond to a rapid depletion of the plasmon energy, preventing further enhancement of local optical fields. Dark (subradiant) plasmons have longer lifetimes, but their resonant wavelengths cannot be tuned over a broad wavelength range without changing the overall geometry of the nanostructures. Also, fabrication of the nanostructures cannot be readily scaled because their complex shapes have subwavelength dimensions. Here, we report a new type of subradiant plasmon with a narrow (∼5 nm) resonant linewidth that can be easily tuned by changing the height of large (>100 nm) gold nanoparticles arranged in a two-dimensional array. At resonance, strong coupling between out-of-plane nanoparticle dipolar moments suppresses radiative decay, trapping light in the plane of the array and strongly localizing optical fields on each nanoparticle. This new mechanism can open up applications for subradiant plasmons because height-controlled nanoparticle arrays can be manufactured over wafer-scale areas on a variety of substrates.
等离子体纳米结构将光场集中到纳米级体积中，这对于等离子体纳米激光器、表面增强拉曼光谱和白光产生非常有用。然而，发射等离子体的短寿命对应于等离子体能量的快速耗尽，从而阻止了局部光场的进一步增强。暗（亚辐射）等离子体的寿命更长，但如果不改变纳米结构的整体几何形状，它们的共振波长就无法在宽波长范围内进行调谐。此外，由于其复杂的形状具有亚波长尺寸，因此难以大规模制造纳米结构。在这里，我们报告了一种新型的亚辐射等离子体，其共振线宽很窄（约 5nm），通过改变二维排列的大（>100nm）金纳米粒子的高度可以很容易地进行调谐。在共振时，平面外纳米颗粒偶极子之间的强耦合抑制了辐射衰变，将光困在阵列平面内，并使光学场在每个纳米颗粒上强烈局域化。这种新机制可以为亚辐射等离子体开辟应用，因为可以在各种衬底上的晶圆级面积上制造高度可控的纳米粒子阵列。
