Direct laser printing of tunable IR resonant nanoantenna arrays

Abstract

We report on the application of direct femtosecond laser printing for manufacturing periodic nanoantenna structures with various geometry and period, printed on pure or alloyed noble metal films over a silica substrate. By varying applied pulse energy, we have realised a wide range of possible morphologies, from smooth nano-bumps to protruding nanojets with up to 1 μm height, and finally to through microholes. Using several pulse energy levels, we have printed periodic nanojet arrays with periods from 1.75 to 4 μm, and measured their IR reflection spectra. The resonance frequency and magnitude of the resulting absorbance were found to essentially depend on both the periodicity of the arrays and nanojet geometry. We explain these observations by considering nanojet-assisted plasmon excitation running along the nanojets and along the surface, and found a convincing agreement to the experiments. To this end, we have shown that the reported approach is suitable for designing structures with distinct IR resonances, tunable over a range of at least 2–6 μm. Finally, we have also applied direct laser printing to a variety of noble metal alloys, involving gold, silver and palladium in various combinations and compositions, and showed that nanojets can be reliably printed for such alloys, preserving their chemical composition and its homogeneous volumetric distribution.