Pushing the Limits of Plasmonic Nanoantenna Design Using New Materials and Nanofabrication Tools

Plasmonic nanoantennas are of interest for their capacity of controlling light on the nanoscale [1]. In particular, precise control of plasmonic near-field interactions on sub-nanometer scales is of interest for achieving strongly enhanced local fields as well as for exploring the fundamental limits of nonlocal and quantum plasmonic effect [2]. Such applications require pushing the limits of nanofabrication to new levels of precision and control.

Helium ion microscopy (HIM) is a surface imaging technique which involves scanning a helium ion beam across a sample surface and forming an image from secondary electron emission which is similar to an SEM. The larger mass and therefore smaller de Broglie wavelength of a helium ion compared to that of an electron enables the HIM to focus the charged beam to a smaller spot on a sample. The latest commercially available version of the HIM are rated at an edge resolution of 0.35nm[3]. The helium ion microscope is also a patterning tool which can be used to pattern resist like electron beam lithography or can be used for direct writing on a substrate like a focused ion beam.

In our recent work, we have demonstrated the ultrafine control of milling partial antenna gaps and narrow conducting bridges with nanometer precision using a helium ion beam microscope (HIM) [4].  A conducting bridge of nanometer height is found sufficient to shift the antenna from the capacitive to conductive coupling regime, in agree with the circuit theory.

In addition to new fabrication tools, we are developing new materials systems to combine plasmonics in electrically and optically controlled environments. I will present recent results showing how we can use new hybrid nonlinearities to achieve tunable and reconfigurable plasmonic devices.

[1] Novotny, L.; van Hulst, N. Nat. Photonics 2011, (5) 83-90

[2] Savage, K. J.; Hawkeye, M. M.; Esteban, R.; Borisov, A. G.; Aizpurua, J.; Baumberg, J. J. Nature 2012, (491) 574-577.

[3] Bell, D. C.; Lemme, M. C.; Stern, L. A.; Williams, J. R. and Marcus, C. M. 2009 Nanotechnology (20) 455301

[4] Wang, Y.; Abb, M.; Boden, S. A.; Aizpurua, J.; de Groot, C. H.; Muskens, O. L. Nano Lett. 2013, 13(11), 5647-5653

Figure 1 (left panel) Illustration showing analogy between radiowave antenna and plasmonic nanoantenna. Bottom: SEM image of antenna fabricated using e-beam lithography. (right panel) SEM image showing nano-gap obtained by helium ion beam milling.