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

Fong, James and Young, Robert and Robinson, Benjamin (2022) Novel Physical Security Devices Exploiting the Optical Properties of Low-Dimensional Materials. PhD thesis, Physics.

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Abstract

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.