Xinli Zhu, Jiasen Zhang, Jun Xu, and Dapeng Yu demonstrated plasmonic modes in a vertical nanocavity with an air output window at the top surface and Ag reflectors. The resonances of surface plasmon polaritons are investigated using cathodoluminescence spectroscopy. The resonant modes are determined by comparing experimental and theoretical simulations. The plasmon dispersion relation in the vertical nanocavities shows a strong confinement to the electromagnetic field, and the smallest modal volume is only 0.0014μm3. Their work provides insights into the development of nanoscale plasmonic vertical cavity surface-emitting lasers and was recently published on Nano Letters.

Figure 1. Plasmonic vertical nanocavity. (a) Schematic of a single nanocavity. (b) 30°-tilted SEM image of a representative cavity with length, width, and height of 360, 120, and 500 nm, respectively.

Figure 2. Resonances and mode patterns of plasmonic nanocavities with 70 nm widths, 500 nm heights, and increasing lengths. (a) CL spectra of 16 nanocavities with cavity lengths increasing from 120 (bottom) to 770 nm (top). (b) Calculated spectra using the FDTD method. Spectra are offset vertically for clarity. The black arrow at 655 nm indicates that the spectra were collected twice at the same position due to the limited measuring range of the spectrophotometer. (c), (d) Calculated mode field intensity patterns and electric field amplitude of a 260 nm-long cavity at 635 nm in the y = -35 nm and x = 0 planes, respectively. (e), (f) Calculated mode patterns in the y = -35 nm plane of 420 and 610 nm-long cavities at 539 and 523 nm, respectively.

Figure 3. Experimental and calculated dispersions of plasmonic modes (1, 1), (1, 2), and (1, 3) in vertical nanocavities. The grey and black lines respectively represent the dispersions of light in a vacuum and SPPs on an infinite Ag film.

Plasmonic Vertical Resonant Nanocavities, Xinli Zhu, Jiasen Zhang,* Jun Xu, and Dapeng Yu,* Nano Letters, in press (2011).