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Controlling the near-field oscillations of loaded plasmonic nanoantennas


Optical and infrared antennas1,2,3,4,5,6 enable a variety of cutting-edge applications ranging from nanoscale photodetectors7 to highly sensitive biosensors8. All these applications critically rely on the optical near-field interaction between the antenna and its ‘load’ (biomolecules or semiconductors). However, it is largely unexplored how antenna loading affects the near-field response. Here, we use scattering-type near-field microscopy to monitor the evolution of the near-field oscillations of infrared gap antennas progressively loaded with metallic bridges of varying size. Our results provide direct experimental evidence that the local near-field amplitude and phase can be controlled by antenna loading, in excellent agreement with numerical calculations. By modelling the antenna loads as nanocapacitors and nanoinductors9,10,11, we show that the change of near-field patterns induced by the load can be understood within the framework of circuit theory. Targeted antenna loading provides an excellent means of engineering complex antenna configurations in coherent control applications12, adaptive nano-optics13 and metamaterials14.

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Figure 1: Mapping the near-field distribution of optical antennas with a transmission-mode s-SNOM.
Figure 2: Near-field images of progressively loaded nanoantennas at a wavelength of λ = 9.6 µm.
Figure 3: Time evolution of the antenna's near-field distribution f obtained from the experimental data of Fig. 2.
Figure 4: Comparison of numerical calculations and antenna theory.


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The authors would like to thank A. Ziegler and A. Rigort (both Abteilung Molekulare Strukturbiologie, Max-Planck-Institut für Biochemie) for help with FIB milling and M. Raschke (Seattle) and N. Engheta (University of Pennsylvania) for stimulating discussions. We thank Nanosensors (Erlangen) for providing HF-etched silicon tips, F.J. García de Abajo for BEM tools and C.F. Quate and G.S. Kino (both Stanford University) for previous insights on the optical antennas studied in this Letter. This research was supported by the Etortek program of the Department of Industry of the Basque Government and the Basque Foundation for Science (Ikerbasque). J.A. acknowledges CSIC special intramural project PIE 2008601039.

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Correspondence to R. Hillenbrand.

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Schnell, M., García-Etxarri, A., Huber, A. et al. Controlling the near-field oscillations of loaded plasmonic nanoantennas. Nature Photon 3, 287–291 (2009).

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