Large-scale sub-100 nm compound plasmonic grating arrays to control the interaction between localized and propagating plasmons Arash Farhang, a Thomas Siegfried, b Yasin Ekinci, b Hans Sigg, b and Olivier J. F. Martin a a EPFL-STI-IMT-NAM, Station 11, ELG 239, CH-1015 Lausanne, Switzerland olivier.martin@epfl.ch b Paul Scherrer Institute, Laboratory for Micro- and Nanotechnology, ODRA/100, 5232 Villigen-PSI, Switzerland Abstract. Compound plasmonic resonances arise due to the interaction between discrete and continuous metallic nanostructures. Such combined nanostructures provide a versatility and tun- ability beyond that of most other metallic nanostructures. In order to observe such resonances and their tunability, multiple nanostructure arrays composed of periodic metallic gratings of varying width and an underlying metallic film should be studied. Large-area compound plas- monic structures composed of various Au grating arrays with sub-100 nm features spaced nano- meters above an Au film were fabricated using extreme ultraviolet interference lithography. Reflection spectra, via both numerical simulations and experimental measurements over a wide range of incidence angles and excitation wavelengths, show the existence of not only the usual propagating and localized plasmon resonances, but also compound plasmonic reso- nances. These resonances exhibit not only propagative features, but also a spectral evolution with varying grating width. Additionally, a reduction of the width of the grating elements results in coupling with the localized dipolar resonance of the grating elements and thus plasmon hybridi- zation. This newly acquired perspective on the various interactions present in such a plasmonic system will aid in an increased understanding of the mechanisms at play when designing plas- monic structures composed of both discrete and continuous elements. © 2014 Society of Photo- Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.JNP.8.083897] Keywords: compound plasmonics; grating; coupling; hybridization; surface plasmons; thin film. Paper 13068SS received Aug. 8, 2013; revised manuscript received Nov. 27, 2013; accepted for publication Dec. 5, 2013; published online Jan. 9, 2014. 1 Introduction Plasmonic systems composed of metallic nanostructures surrounded by a dielectric environment support surface plasmons, i.e., optical resonances bound to the metal-dielectric interface that are based on the excitation of free electrons in the metal. 1–3 In small discrete systems, such as nano- spheres, dimers, nanoprisms, and subwavelength gratings, these resonances exhibit a localized response and are commonly referred to as localized surface plasmons (LSPs). 3 In extended sys- tems, such as a continuous film, long metallic strips, or gratings that extend over several wave- lengths, they exhibit a delocalized/propagative response and are simply referred to as surface plasmon-polaritons (SPPs). 1,2,4,5 LSPs have shown to be useful in applications such as trapping, 6,7 cancer treatment, 8–11 sur- face-enhanced Raman spectroscopy, 12–15 and light harvesting, 16,17 while SPPs have shown great use in applications such as biosensing 18,19 and as optical interconnects in conventional integrated circuits. 20–23 Systems composed of both continuous and discrete structures are of particular inter- est since they exhibit enhanced optical properties, 24–44 improved light harvesting, 45–50 matching of radiative and nonradiative losses, 51 and additional degrees of freedom for the tuning of their spectral properties. 24–44 0091-3286/2014/$25.00 © 2014 SPIE Journal of Nanophotonics 083897-1 Vol. 8, 2014 Downloaded From: https://www.spiedigitallibrary.org/journals/Journal-of-Nanophotonics on 12/20/2018 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use