Quasi-total omnidirectional light absorption in nanostructured gold films Hanbin Zheng • Renaud Valle ´e • Rui M. Almeida • Thomas Rivera • Serge Ravaine Received: 28 February 2014 / Accepted: 11 August 2014 / Published online: 20 September 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract A series of experiments and simulations have been performed to evidence the omnidirectional light absorption of planar gold structures containing a two- dimensional lattice of spherical beads or pores. We show that more than 90 % of incident light is absorbed at angles of incidence up to 65° for optimum values of the gold film thickness. We also report the tunability of the absorption wavelength by varying the size of the beads/pores. 1 Introduction Few years ago, Teperik et al. [1] theoretically demonstrated that nearly total absorption of light can be achieved in a nanoporous metal surface that sustains localized optical excitations. This occurs when a lattice of spherical voids is buried in the metal substrate at a specific distance from the surface, which ensures optimal coupling of plasmons in the voids to the external light. Furthermore, by varying the diameters of the voids or filling them with dielectric materials, the frequencies of plasma resonances can be easily tuned. In porous metals, the lattice of voids beneath the metal surface has two roles [2]. First, it forms a coupling element which diffracts incident light into surface plasmon polari- tons (SPPs). Secondly, localized Mie plasmons are excited in spherical voids. Since void plasmons are radiative excitations, they can couple to light directly without any special coupling device. These localized void plasmons can also be brought into resonant interaction with the propa- gating SPPs by tuning the structural parameters. It was suggested that total omnidirectional absorp- tion of light can be achieved in nanostructured metal surfaces that sustain localized optical excitations [3]. These nanoporous metal surfaces can simultaneously support delocalized SPPs and localized void plasmons, where the localized void plasmons are responsible for the omnidirectional absorption of light. It was demon- strated that almost total absorption of light can indeed be achieved with a lattice of voids just beneath the surface, and theoretically predicted that omnidirectional absorption is possible for a wide angle range (up to 40°) [3]. It was theoretically demonstrated that this range of angles can be further increased if the voids were filled with a dielectric medium because a dielectric medium can bring down the plasmon void energy to a region that it does not interact with the delocalized SPPs [3]. In this work, we have fabricated gold films with a well- controlled thickness containing a monolayer of spherical polystyrene beads or voids of two different diameters. We have numerically and experimentally demonstrated that these films exhibit a quasi-total absorption of incident light for an optimum value of their thickness. The strongly enhanced absorption is observed for angles of incidence up to 65°, which makes our systems good candidates for high- efficiency absorber materials. H. Zheng Á R. Valle ´e Á S. Ravaine (&) CNRS, CRPP, UPR 8641, Univ. Bordeaux, 33600 Pessac, France e-mail: ravaine@crpp-bordeaux.cnrs-fr H. Zheng Á R. M. Almeida Depart. Eng. Quı ´mica/ICEMS, Instituto Superior Te ´cnico/UL, Av. Rovisco Pais, 1049-001 Lisbon, Portugal T. Rivera Orange Labs Network, rue du Ge ´ne ´ral Leclerc, 92794 Issy Moulineaux, France 123 Appl. Phys. A (2014) 117:471–475 DOI 10.1007/s00339-014-8684-9