Multiscale Disordered Photonics Metamaterials: Novel Complex Media for Sensing Applications

Abstract

The twentieth century was a golden period for the global scientific advancement: revolutionary ideas and progressive thought were setting the fundamental for our modern world. The drastic advance of mathematics has led physics and chemistry to develop relativistic and quantum theories to understand the unexplored macro- and nano- world, respectively. Biology was doing giant leaps in the comprehension of life with the deduction of the double helical structure of DNA and the discovery of the basic constituent of proteins. Meanwhile, with the help of the extraordinary engineering and technological advancement, medicine was developing an increasing understanding of a wide spectrum of diseases. Those fundamental steps were the outcome of an evolution of the concept of scientific method: the human intellect moved from the standard iterative observation & testing process to a deeper phenomenological understanding of the complicatedness of Nature by falsifiable theories and paradigm shifts. This consequence was dictated by an increased variability of the considered problems which led to the advent of the probabilistic and statistic mathematics theories to deal, predict and understand organized complexity. Indeed, the Natural word is plenty of -at first sight- irregular and disordered structures which follow self-similar patterns, for instance, snowflakes, lightning bolts, heartbeat, and pulmonary vessels. These systems all fall in the category of random fractals: complex objects that show a statistical recursive pattern at different magnifications. Enabled by nanotechnology, the human being is trying to harness the richness of this inherently disordered word by developing new strategies for the understanding, replication and taming of complexity for different applications. Efficient proof of concepts for the use of these disordered structures are always more popular and can be found in different research fields, ranging from energy harvesting, bio-imaging, and advanced opto-electronic materials. On the other side, in this frenetic modern age, the human being is demanding always more measurement to track, monitor and communicating information essential to our daily life. In this big scenario, technological advances demand more and more precise measurement of existence or absence of harmful substances, with low concentrations, in various environments. Sensing technology has already impacted many aspect of our daily lives, through many application, including but not limited to gas alarms, medical diagnostics, healthcare, safety, defense and security, automotive and environmental monitoring. Particularly, gas and biomolecule sensing is becoming considered as the key technology to avoid or reduce growing global challenges including global warming, pollution, safety, non-invasive diagnostic and security. High sensitivity, fast response, and good selectivity are the target requirements for a high throughput sensor in today's technology. Among all the nanotechnology-enabled gas sensors, the optical ones are most promising and attracting options thanks to their high sensitivity, long lifetime, high resistivity to electromagnetic noise and the possibility to work at room temperature. This thesis work aims to study, understand and exploit the properties and advantages of the light-matter interaction in complex systems for sensing applications, with particular focus on the interaction between metallic and dielectric materials. The candidate has hence focused on the optical properties of disordered metallo-dielectric networks, exploiting the localized surface plasmons polaritons and their intrinsic sensitivity to the local environment to develop a scalable and efficient platform for sensing applications. Show more