Physically Unclonable Surfaces via Dewetting of Polymer Thin Films

Abstract

From anti-counterfeiting to biotechnology applications, there is a strong demand for encoded surfaces with multiple security layers that are prepared by stochastic processes and are adaptable to deterministic fabrication approaches. Here, we present dewetting instabilities in nanoscopic (thickness <100 nm) polymer films as a form of physically unclonable function (PUF). The inherent randomness involved in the dewetting process presents a highly suitable platform for fabricating unclonable surfaces. The thermal annealinginduced dewetting of poly(2-vinyl pyridine) (P2VP) on polystyrenegrafted substrates enables fabrication of randomly positioned functional features that are separated at a microscopic length scale, a requirement set by optical authentication systems. At a first level, PUFs can be simply and readily verified via reflection of visible light. Area-specific electrostatic interactions between P2VP and citrate-stabilized gold nanoparticles allow for fabrication of plasmonic PUFs. The strong surface-enhanced Raman scattering by plasmonic nanoparticles together with incorporation of taggants facilitates a molecular vibration-based security layer. The patterning of P2VP films presents opportunities for fabricating hybrid security labels, which can be resolved through both stochastic and deterministic pathways. The adaptability to a broad range of nanoscale materials, simplicity, versatility, compatibility with conventional fabrication approaches, and high levels of stability offer key opportunities in encoding applications.

Organic Light‐Emitting Physically Unclonable Functions

“…Although we have initially performed this annealing in an inert atmosphere, our later experiments (vide infra) have demonstrated that the ambient atmosphere annealing is also possible, thanks to the good thermal stability and the robust chemical structure of 2EHO-TPA-CNPE. While heating above glass transition at relatively high temperatures (>200-250 °C) was typically required for the formation of dewetted structures in polymer thin films, [53,55,56] the dewetting dynamics are quite different in the case of nanoscopic molecular thin-films. The solid-state of molecular semiconductor thin-films, from the cumulative cohesive energetics perspective, are bound by relatively weak π-interactions and van der Waals forces, especially when compared with polymeric materials.…”

“…On the other hand, one would think that the relatively high surface energy (contact angle ≈ 95° and γ ≈ 41.1 mJ m −2 ) of the end‐grafted PS layer is the main thermodynamic driving force for the observed dewetting process, as we have recently seen in polymer films. [ 53 ] Thanks to the great structural mobility, flexible alkyl chains, and amorphous microstructure of the current small molecule, perfect dewetting with randomly positioned features was formed also on a freshly cleaned silicon substrate (contact angle ≈ 0° showing a high surface energy) (Figure 5b). In this case, the thermal annealing was performed in the ambient atmosphere at the same temperature (170 °C).…”

“…We have recently demonstrated that the dewetting of poly(2‐vinyl pyridine) in thin films provides a robust platform to generate PUF‐based security layers. [ 53 ] To this end, oligo( p ‐phenyleneethynylene) π‐frameworks stand out as an ideal f ‐OSC family for PUF applications with their favorable structural (i.e., flexible swallow‐tailed alkyl chains), physicochemical (good solution‐processability, low‐temperature thermal transitions, and amorphous solid‐state) and photophysical (efficient and unique fluorescence) properties.…”

Laser fabrication and evaluation of holographic intrinsic physical unclonable functions

“…Any random physical process is a potential candidate for the realization of PUFs. Indeed, there is already a plethora of research accounts 12 – 19 that include exotic solutions like aerogels 20 , Raman tags 21 , plasmonic nanopapers 22 wrinkles on glasses 23 , perovskite fluorescent dots 24 or even edible unclonable functions 25 to name a few. The PUF scenery in the literature is evolving fast necessitating taxonomy activities like the one presented by McGrath and co authors 12 .…”

Patterning of a Drying Emulsion Film

“…The evaporation, most of the time of part of the external phase, may provoke instabilities 7 . For example, dewetting may appear due to differential evaporation of the solvents [8][9][10][11] . Other capillary phenomena may cause convection that structures the film [12][13][14] .…”