Lucia Fornasari
University of Pavia, Plasmore S.r.l.
Lucia Fornasari received the Ph.D in physics from the University of Milan (Italy) in2010. From 2011, she was Post-Doctoral Fellow at the Department of Physics of the University of Pavia (Italy) working on nanostructured plasmonic structures for biosensing application. In the same period she started a collaboration with Plasmore s.r.l., a joint spin-off of the University of Pavia and of the JRC of Ispra. Her research interest regards the study of photonic, plasmonic and meta-structures through optical spectroscopy techniques. She is currently employed in Plasmore and she is responsible of the optical modeling and characterization of the plasmonic surfaces.
Introduction. Hybrid plasmonic-photonic systems attract the attention of the scientific community due to their ability in modifying the light behaviour and the electric field distribution. The study of this type of system could have significant fall-out in fields such as biosensing and optoelectronics. In this work, multilayer porous silicon (PSi) interference structures have been used as a support for arrays of Au nanocavities to combine the photonic properties of the former with the plasmonic properties of the latter and to develop an hybrid photonic-plasmonic device. Finite Difference Time Domain (FDTD) simulation have been implemented in order to interpret the experimental results.
Methods. PSi multilayer stacks were produced by electrochemical etching of p-type monocrystalline silicon wafers to produce contrasting porosity strata and thus achieve a predetermined interference response [1]. On top of this structure, a large area nanostructured plasmonic structure was created by colloidal lithography [2]. These hybrid structures have been characterized by scanning electron microscopy, which has allowed to infer the main characteristics of the system, and by variable-angle spectral-resolved reflectance measurements at each fabrication step that allowed evaluating the individualized optical contribution of each structure and their coupling (Figure 1). FDTD simulations of the plasmonic, photonic and hybrid structures have been performed in order to interpret the results. The sensitivity of the hybrid structure to refractive index changes has been evaluated through the deposition of nanometric polyelectrolyte layers.
Results and Discussion. Results suggest that the optical response of these type of hybrid structures is dominated by the plasmonic features, modulated by the interference fringes of the photonic structure (Figure 2). The analysis of the dispersion mode highlights the presence of the Tamm mode and of a complex interplay between the plasmonic and photonic components (see Figure 3). The estimate of the sensitivity shows that the hybrid structure is most sensitive to refractive index changes in the visible region around 650 nm.
[1] C. Pacholski. Photonic Crystal Sensors Based on Porous Silicon. Sensors 2013, 13, 4694-4713.
[2] B. Bottazzi, et al. Multiplexed label-free optical biosensor for medical diagnostics. Journal of Biomedical Optics 2014, 19 (1), 017006.
