Controlling spontaneous emission with plasmonic optical patch antennas.

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Nano Letters

Controlling Spontaneous Emission with Plasmonic Optical Patch Antennas

C. Belacel, B. Habert, F. Bigourdan, F. Marquier, J.-P. Hugonin, S. Michaelis de Vasconcellos, X. Lafosse, L. Coolen, C. Schwob, C. Javaux, B. Dubertret, J.-J. Greffet, P. Senellart, and A. Maitre.

We experimentally demonstrate the control of the spontaneous emission rate and the radiation pattern of colloidal quantum dots deterministically positioned in a plasmonic patch antenna. The antenna consists of a thin gold microdisk separated from a planar gold layer by a few tens of nanometers thick dielectric layer.

In collaboration with the groups of Jean Jacques Greffet (LCFIO Palaiseau), Agnès Maitre (INSP Paris) and Benoit Dubertret (LPEM, Paris), we study the emission of colloidal quantum dots inserted in plasmonic optical patch antennas. The plasmonic patch antenna proposed in Phys. Rev. Lett. 104, 026802 (2010), consists in a thin gold microdisk 30 nm above a thick gold layer (fig. 1a), with the emitter positioned in the dielectric spacer (figure a). The small 30 nm separation between the disk and the gold film provide a large confinement of the electromagnetic field in the vertical direction. The finite size of the disk leads to confinement in the plane. Broadband large Purcell factor is theoretically predicted (figure b).

Antenna_post
In the present work, we have inserted small clusters of around 50 CdSe/CdS colloidal nanocrystals in the antenna. The cluster presents a cylinder shape with typical lateral radius of 5 nm and height of 13 nm. A deterministic positioning of clusters inside each antenna with a precision of 25nm is obtained using the in-situ lithography technique. As shown in figures c-d, the emitters below the antenna radiate through the entire patch antenna.

The average cluster show an acceleration of spontaneous emission of 80 for vertical dipoles (figure e). The radiation pattern of the antenna is highly directionnal, as measured in figure 1f.