Design, fabrication and characterization of metamaterial inspired structures for sensing application
In the last few years the interest in nanostructures for sensing application has grown increasingly, leading to the development of new designs based on the surface plasmon resonance of metallic structures. By carefully tuning the geometry of the nanostructures, it is possible to adjust the resonance frequencies, resulting in amplification and confinement of the electromagnetic field around specific areas of the structure. The oscillating plasmonic field obtained may be exploited for bio-chemical detection. In this work we present the design, the fabrication and the characterization of gold nano split ring resonators on transparent substrate, combining finite element simulation, lithographic techniques and transmittance ellipsometry. Bearing in mind the importance of the control of the geometric parameters, we approach the structure fabrication using top-down lithographic techniques. We explore and develop, in particular, an X-ray Lithography based process for producing high volumes of tall, nanometric split ring resonators. The choice of X-ray Lithography as the main technique is justified by the possibility to obtain higher aspect ratio and to achieve large areas array of split ring resonators in a single, fast exposure, compared to other techniques, such as nanoimprinting or Electron Beam Lithography. The structure we focused our research on is the split ring resonator, one of the most popular and studied geometries for metamaterials. As metamaterial building block, the split ring resonator exhibits characteristic plasmonic resonances and a tunable frequency magnetic resonance. Besides, the split ring resonator shows a strong polarization dependance and a strong mechanical stability. In this thesis we will analyze the optical properties of the split ring nanostructure when illuminated in normal incidence. The analysis of the response in transmission at two polarization is presented. The preliminary detection test performed using a monolayer of dodecanthiol evidence the detection potential of this geometry.