Plasmonic Structures for Near Infrared Applications
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Plasmonic Structures for Near Infrared Applications Francesco Floris1, Franco Marabelli1, Maddalena Patrini1, Lucia Fornasari1, Francesco Quochi2, Cristiana Figus2, Giovanni Bongiovanni2, Andrea Mura2, Michele Saba2, Paola Pellecani3 and Andrea Valsesia3 1
Department of Physics – University of Pavia, Via Agostino Bassi 6, I-27100 Pavia (PV), Italy. Department of Physics – University of Cagliari, S.P. 8 Km 0.7, I-09042 Monserrato (CA), Italy. 3 Plasmore S.r.l. – Via Grazia Deledda 4, I-21020 Ranco (VA), Italy. 2
ABSTRACT We report on the development of a plasmonic-photonic coupled platform based on a plasmonic periodic nanostructure and a host matrix for active media in the visible-near infrared range, constituted by a thin film of sol-gel glass. Here, we report on preliminary results about two main tasks of the research work. On one side, we have studied and optimized the surface that supports plasmonic resonances with tunable wavelengths. On the other side, we focused on improving the sol-gel techniques to form and deposit thin films appropriate for covering the previous surface as well as to protect it (i.e. for sensing applications), embed suitable fluorophores (for active device applications) while avoiding metal-induced radiative emission quenching. Besides structural and optical characterization of the considered structures and films, finite-difference time-domain numerical simulations have been performed, in order to give a feedback on the structure features and thereby interpret its optical response. INTRODUCTION Plasmonics represents a way to concentrate electromagnetic (e.m.) energy into volumes lower than that corresponding to the diffraction limit, with a consequent significant spatial squeezing and confinement of the e.m. field at a metal-dielectric interface [1-4]. In this case, the large density of states at the metal-dielectric interface makes it possible to enhance light-matter interaction and improve the performance of detection and light emission [5,6]. Nevertheless, to realize a usable device, the external coupled system (an e.m. field perturbation from an external unknown agent to be identified for sensing applications or an emitter for active device applications) must be placed in the near-field surrounding area and within the decay length (a few tens of nanometers) of the plasmonic mode [7]. To this aim, we made use of a plasmonic surface consisting of a gold film embedded in a two-dimensional array of polymeric pillars [8-10]. This device has been shown to work as a surface plasmon resonance (SPR) sensitive surface for biosensing application in medical diagnostics [11]. In this work, we choose the structure with main plasmonic resonance peak at 795 nm because of its spectral affinity with many rare-earth emitters of practical interest. We also optimized the dip-coating process [12] to cover a surface by an ultrathin film of silica matrix with controlled thickness. We adopted atomic force microscopy (AFM), spectroscopic ellipsometry and reflectance Fourier-transform (FT) spectroscopy, as wel
