Novel Physical Security Devices Exploiting the Optical Properties of Low-Dimensional Materials

The works in this thesis discuss mechanisms to improve the intrinsic security of nanomaterial-based optical physical unclonable functions (O-PUFs). A PUF is an object which is very difficult or physically impossible to replicate or predict, the security of which originates from random properties which arise during device fabrication, either naturally (implicit), or induced (explicit). Many different PUFs have been discussed and developed for several applications, where each implementation requires the satisfaction of several key figures of merit to be both secure and practical. PUFs are attractive as unique objects in the field of anti-counterfeiting, as secure alternatives to other optical means, including holograms and watermarks. This thesis aims to demonstrate and validate modifications in measurement and construction to quantum-confined optical semiconductors as the basis of an effective O-PUF. The optical properties of quantum dots and 2D materials are exploited, utilising their nonlinear optical response and sensitivity to local defects to improve the PUF’s evaluability and entropy density. The works presented here propose three modifications to an existing category of O-PUF to improve their robustness against replay and simulation attacks and increase their overall entropy density. Firstly, the measurement technique of QD-based O-PUFs is modified: several O-PUFs are based on the position of, or scattering from, optical nanoparticles, so a verification technique of a quantum dot-based O-PUF utilising the fundamental optical properties of the quantum dots used in the tag is developed, ensuring simulation attacks are more difficult. Secondly, the optical emission from the QDs in an O-PUF are modified with the addition of plasmonic nanoparticles, locally enhancing the electromagnetic field to create photoluminescence emission ‘hotspots’ to image the dynamic range of emission peak intensity. Finally, the fabrication of O-PUFs using optically emitting 2D materials is explored, instead of quantum dots (QDs), which potentially paves the way for cheaper, easier to fabricate quantum O-PUFs

De Sistemas quirales 2D a 3D fabricados a partir de bloques plasmónicos y magnetoplasmónicos: fabricación, caracterización y análisis

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 22/01/2021A comprehensive work in plasmonic chiral and achiral nanostructures is presented. The bottom-up fabricated structures range from simple building blocks such as metallic and dielectric disk dimers or rods, to more complex nanostructures built from these individual blocks, arranged in the plane (two dimensional structures) or out of plane (three dimensional structures). The fabrication process uses hole-mask colloidal lithography and multiaxial evaporation, a powerful and cost-effective fabrication technique able to obtain a variety of structures in large areas. Besides morphology changes, parameters such as the composition and the spatial arrangement of the building blocks which compose them have been varied to comprehend their role in the optical response of the structures. These parameters are tailored to obtain active chiral meta-structures with optimum properties. The fabricated structures are morphologically, optically and magneto-optically characterized in depth. A thorough and step-by-step experimental study to explain the chiro-optical response of complex chiral plasmonic nanostructures from the achiral responses of its constituents is shown. To fully characterize the physical properties hidden in the measurements of these structures, an alternative analysis of the Mueller matrix elements is developed. Using this method, the optical, chiro-optical and magnetooptical properties of these complex nano-systems are validated...Se presenta un estudio experimental exhaustivo y detallado para entender la respuesta quiral de nanoestructuras plasmónicas quirales complejas a partir de las respuestas aquirales de sus bloques constituyentes. Esto conlleva diferentes estructuras fabricadas, desde simples nano-objetos como barras o dímeros de discos compuestos por metal o dieléctrico, hasta nanoestructuras más complejas ensambladas en el plano (estructuras bidimensionales) o apiladas perpendicularmente al plano (estructuras tridimensionales). En el proceso de fabricación se utiliza la litografía coloidal de máscara de agujeros y la evaporación multieje, una técnica de fabricación potente y económicamente asequible, capaz de obtener una gran variedad de estructuras en grandes áreas. Además de los cambios morfológicos, se han variado parámetros tales como la composición y la disposición espacial de las piezas constituyentes, a fin de estudiar su influencia en la respuesta óptica. Estos parámetros se optimizan para obtener metaestructuras quirales activas con las mejores propiedades. Posteriormente, las estructuras fabricadas se caracterizan morfológica, óptica y magneto ópticamente. Para identificar plenamente las propiedades físicas ocultas en las medidas de estas estructuras, se desarrolla un análisis alternativo de los elementos de la matriz de Mueller. Con este método, se validan las propiedades ópticas, quiroópticas y magnetoópticas de estos complejos nanosistemas...Fac. de Ciencias FísicasTRUEunpu