Surface-enhanced infrared spectroscopy using nanometer-sized gaps.

We report on the near-field coupling of individual gold nanoantennas arranged in tip-to-tip dimer configuration, leading to strong electromagnetic field enhancements in the infrared, which is of great interest for sensing applications such as surface-enhanced infrared spectroscopy. We quantitatively evaluated the enhancement of vibrational excitations of a 5 nm thick test layer of 4,4'-bis(N-carbazolyl)-1,1'-biphenyl as a function of different gap sizes. The dimers with the smallest gaps under investigation (∼3 nm) lead to more than 1 order of magnitude higher signal enhancement with respect to gaps of 50 nm width.

120 nm resolution and 55 nm structure size in STED-lithography.

Two-photon direct laser writing (DLW) lithography is limited in the achievable structure size as well as in structure resolution. Adding stimulated emission depletion (STED) to DLW allowed overcoming both restrictions. We now push both to new limits.

Infrared optical properties of nanoantenna dimers with photochemically narrowed gaps in the 5 nm regime.

In this paper, we report on the manipulation of the near-field coupling in individual gold nanoantenna dimers resonant in the infrared (IR) spectral range. Photochemical metal deposition onto lithographically fabricated nanoantennas is used to decrease the gap between the antenna arms down to below 4 nm, as confirmed by finite-difference time-domain simulations. The increased plasmonic coupling in the gap region leads to a shift of the surface plasmon resonances to lower energies as well as to the appearance of hybridized plasmonic modes.