Counterfeiting poses a significant threat to global trade and public health. Effectively combating counterfeiting involves benefiting from stochastic physical processes to build physically unclonable functions (PUFs). Polymers, as low-cost materials with a wide range of functionalities, hold huge potential for PUF applications. In this context, while there are ongoing applications and studies related to PUF systems today, the development of PUF systems that provide high stochastic characteristics and robustness through simple and low-cost production methods remains critically important. In this regard, we propose stable and addressable polymer PUFs, utilizing a cross-linkable poly(2-vinylpyridine) (P2VP). The Rayleigh instability phenomenon occurring in electrohydrodynamic processes is used to fabricate randomized polymeric features. A brief thermal annealing process enhances adhesion with the substrate, while UV-ozone treatment cross-links P2VP. When applied through stencil masks, UV-ozone treatment results in localized cross-linking, yielding addressable randomized features. Structural and chemical analysis is employed to examine the cross-linked polymer features. Adjusting the conditions of electrospraying and cross-linking leads to PUFs with outstanding stability against solvents, oxygen plasma, and thermal heating. The randomized response of polymer features is evaluated through various statistical criteria. Feature matching algorithms enable direct authentication of images captured under different rotations and lighting conditions. This study demonstrates a versatile strategy for creating polymer-based PUFs with remarkable stability and addressability, enabled by a cross-linkable polymer system.

Identity security and counterfeiting assume a critical importance in the digitized world. An effective approach to addressing these issues is the use of physically unclonable functions (PUFs). The overarching challenge is a simultaneous combination of extremely high encoding capacity, stable operation, practical fabrication, and a widely available readout mechanism. Herein this challenge is addressed by designing an optical PUF via exploiting the thickness-dependent structural color formation in nanoscopic films of ZnO. The structural coloration ensures authentication using widely available bright-field-based optical readout, whereas the metal oxide provides a high degree of structural stability. True physical randomness in spatial position is achieved by physical vapor deposition of ZnO through stencil masks that are fabricated by pore formation in polycarbonate membranes via photothermal processing of stochastically positioned plasmonic nanoparticles. Structural coloration emerges from thin film interference as confirmed via simulation studies. The rich color variation and stochastic definition of domain size and geometry result in chaotic features with an encoding capacity that approaches (6.4 x 105)(2752x2208). Deep learning-based authentication is further demonstrated by transforming these chaotic features into unbreakable codes without field limitations. This ultra-rich encoding capacity, coupled with outstanding thermal and chemical stability, forms a new cutting edge for state-of-the-art PUF-based encoding systems.

Physically unclonable functions (PUFs) have attracted growing interest for anticounterfeiting and authentication applications. The practical applications require durable PUFs made of robust materials. This study reports a practical strategy to generate extremely robust PUFs by embedding random features onto a substrate. The chaotic and low-cost electrohydrodynamic deposition process generates random polymeric features over a negative-tone photoresist film. These polymer features function as a conformal photomask, which protects the underlying photoresist from UV light, thereby enabling the generation of randomly positioned holes. Dry plasma etching of the substrate and removal of the photoresist result in the transfer of random features to the underlying silicon substrate. The matching of binary keys and features via different algorithms facilitates authentication of features. The embedded PUFs exhibit extreme levels of thermal (∼1000 °C) and mechanical stability that exceed the state of the art. The strength of this strategy emerges from the PUF generation directly on the substrate of interest, with stability that approaches the intrinsic properties of the underlying material. Benefiting from the materials and processes widely used in the semiconductor industry, this strategy shows strong promise for anticounterfeiting and device security applications.

Advanced anti-counterfeiting and authentication approaches are in urgent need of the rapidly digitizing society. Physically unclonable functions (PUFs) attract significant attention as a new-generation security primitive. The challenge is design and generation of multi-color PUFs that can be universally applicable to objects of varied composition, geometry, and rigidity. Herein, tattoo-like multi-color fluorescent PUFs are proposed and demonstrated. Multi-channel optical responses are created by electrospraying of polymers that contain semiconductor nanocrystals with precisely defined photoluminescence. The universality of this approach enables the use of dot and dot-in-rod geometries with unique optical characteristics. The fabricated multi-color PUFs are then transferred to a target object by using a temporary tattoo approach. Digitized keys generated from the red, green and blue fluorescence channels facilitate large encoding capacity and rapid authentication. Feature matching algorithms complement the authentication by direct image comparison, effectively alleviating constraints associated with imaging conditions. The strategy that paves the way for the development of practical, cost-effective, and secure anticounterfeiting systems is presented. Tattoo-like multi-color encoding layers based on random processing of semiconductor nanocrystals of varied composition and geometry are reported. Additive deposition via chaotic electrospraying enables randomness and multiplexing, whereas the tattoo approach provides substrate independence.image

Understanding the wetting behavior of thin films is essential for advanced coatings applications. This paper studies the roughness dependent hydrophobicity of titanium thin films deposited by radio frequency magnetron sputtering. The grafting of mechanochemically activated polydimethylsiloxane (PDMS) onto a titanium thin film is achieved by benefiting from the self-formation of an oxide layer during the sputter-coating process. PDMS grafting results in a liquid-like hydrophobic layer with a nanoscopic (<3 nm) thickness, which makes it possible to investigate the roughness dependent wetting behavior of titanium films. In addition to the structural characterization, atomic force microscopy imaging was used to derive different morphological parameters. Correlating static and dynamic water contact angle measurements with these morphological parameters enabled identification of different wetting states. The findings of this study contribute to the design and fabrication of stochastically structured hydrophobic surfaces with a stable wetting state that is needed in practical applications.

The growing interest in sensing systems based on surface-enhanced Raman scattering (SERS) motivates the development of versatile and eco-friendly methods for the fabrication of nanostructured metallic surfaces. In this study, we report photo-assisted growth of Au nanostructures (NSs) on a similar to 7 nm thick film that consists of endgrafted poly(2-vinyl pyridine). The nanofilm plays a key role in the photo-assisted growth of Au NSs with high SERS activity. The structure, crystallinity, and morphology of Au NSs were probed by different analytical techniques. The limit of detection under laser excitation of 532 nm for rhodamine 6 G was 10 nM with an enhancement factor of 6.4 x 10(5). The sensing of tamoxifen and sulfamethazine drugs was further performed on the Au NSs, showing the application potential of the presented SERS platform.

Counterfeit products in the pharmaceutical and food industries have posed an overwhelmingly increasing threat to the health of individuals and societies. An effective approach to prevent counterfeiting is the attachment of security labels directly on drugs and food products. This approach requires the development of security labels composed of safely digestible materials. In this study, we present the fabrication of security labels entirely based on the use of food-grade materials. The key idea proposed in this study is the exploitation of food-grade corn starch (CS) as an encoding material based on the microscopic dimensions, particulate structure, and adsorbent characteristics. The strong adsorption of a food colorant, erythrosine B (ErB), onto CS results in fluorescent CS@ErB microparticles. Randomly positioned CS@ErB particles can be obtained simply by spin-coating from aqueous solutions of tuned concentrations followed by transfer to an edible gelatin film. The optical and fluorescence microscopy images of randomly positioned particles are then used to construct keys for a physically unclonable function (PUF)-based security label. The performance of PUFs evaluated by uniformity, uniqueness, and randomness analysis demonstrates the strong promise of this platform. The biocompatibility of the fabricated PUFs is confirmed with assays using murine fibroblast cells. The extremely low-cost and sustainable security primitives fabricated from off-the-shelf food materials offer new routes in the fight against counterfeiting.

ABSTRACT: The ability to encode unclonable information using low-cost materials and processes is of significant interest for anticounterfeiting and information security applications. In this study, we present a versatile approach based on electrospraying of polymer solutions to generate randomly positioned complex features as a form of physically unclonable function (PUF). The key advantage of this approach is that readily available low-cost bulk polymeric materials can form small and complex features using a simple process. Polymers of varying composition and molecular weight, together with different solvents and electrospraying conditions, are systematically explored to construct the parameter space for PUFs of varying characteristics. Besides the randomness in the spatial positions and sizes of features, the key advantage of the presented approach is the ability to generate complex 3D shapes, which are very difficult, if not impossible to fabricate with the most advanced fabrication techniques. The inclusion of photoluminescent molecules establishes an additional security layer. The additive nature of operation enables multiplexing, i.e., deposition of multiple materials on the same substrate. The fabricated PUFs have an average uniformity of 0.533 and uniqueness of 0.495, which are highly close to an ideal value of 0.5. The authentication is effectively performed using a feature detection algorithm without the need for markers and precisely defined rotation angles, greatly relaxing constraints associated with the imaging. Direct application of PUFs on the label of goods and authentication via a handheld microscope demonstrate the practical utility of the presented approach.

All-solution processable fabrication of high performance transparent conductive electrodes is vital for next-generation optoelectronics applications. In this study, rapid and versatile fabrication of highperformance transparent electrodes by synergetic integration of electrospun nanofibers and particle-free reactive silver inks is reported. Direct electrospinning of reactive silver ink containing polymer blend solution followed by a swift thermal annealing enables fabrication of transparent conductive electrodes (TCEs) with a sheet resistance of similar to 1.9 Omega/sq with 90% transmission. The high-performance TCEs were fabricated within couple of minutes including the electrospinning and thermal annealing duration. The key aspects of our strategy are the use of a polymer blend consisting of poly(ethylene oxide) (PEO) and polyvinylpyrrolidone (PVP) and particle-free nature of reactive silver inks. Practical utility of the fabricated transparent electrodes in Joule heaters that work at temperatures as high as 300 degrees C is presented. The simple, versatile, inexpensive, and rapid fabrication of transparent conductive electrodes can enable broad range of applications. (c) 2020 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Mechanically durable superhydrophobic coatings have enormous application potential in almost all aspects of our daily lives. In this study, we present a practical strategy for one-step fabrication of robust superhydrophobic coatings based on evaporation driven self-assembly of hydrophobic nanoparticles and wax into hierarchical structures. Depending on the solvent and coating distance, spray-coating a dispersion composed of alkyl-silane functionalized nanoparticles and wax results in extremely water repellent surfaces with a water contact angle of 175 degrees and a sliding angle of 3 degrees. The formation of hierarchically structured surfaces upon evaporation of the solvent enables fabrication of fluorine-free, highly water repellent surfaces and provides high level of structural protection against mechanical abrasion. The coating retains its superhydrophobicity even after 1000 cycles of water spray impact, 45 min of water jet impact, and 180 cm of linear abrasion. The low-cost, scalable, one-step, and fluorine-free fabrication of superhydrophobic coatings that can be applied onto virtually any type of material surface with a satisfactory mechanical robustness based on eco-friendly and industrially available materials presents promising avenues for practical applications.