Graphene-Based Physically Unclonable Functions with Dual Source of Randomness

Nanostructured Surfaces with Plasmonic Activity and Superhydrophobicity: Review of Fabrication Strategies and Applications

Plasmonics and superhydrophobicity have garnered broad interest from academics and industry alike, spanning fundamental scientific inquiry and practical technological applications. Plasmonic activity and superhydrophobicity rely heavily on nanostructured surfaces, providing opportunities for their mutually beneficial integration. Engineering surfaces at microscopic and nanoscopic length scales is necessary to achieve superhydrophobicity and plasmonic activity. However, the dissimilar surface energies of materials commonly used in fabricating plasmonic and superhydrophobic surfaces and different length scales pose various challenges to harnessing their properties in synergy. In this review, an overview of various techniques and materials that researchers have developed over the years to overcome this challenge is provided. The underlying mechanisms of both plasmonics and superhydrophobicity are first overviewed. Next, a general classification scheme is introduced for strategies to achieve plasmonic and superhydrophobic properties. Following that, applications of multifunctional plasmonic and superhydrophobic surfaces are presented. Lastly, a future perspective is presented, highlighting shortcomings, and opportunities for new directions.

Coffee-Ring Mediated Thinning and Thickness-Dependent Dewetting Modes in Printed Polymer Droplets Coupled with Assembly of Quantum Dots for Anti-Counterfeiting

Molecular transport processes in printed polymer droplets hold enormous importance for understanding wetting phenomena and designing systems in applications such as encoding, electronics, photonics, and sensing. This paper studies thickness-dependent dewetting modes that are activated by thermal annealing and driven by interfacial interactions within microscopically confined polymeric features. The printing of poly(2-vinylpyridine) is performed in a regime where coffee-ring effects lead to strong thinning of the central region of the deposit. Thermal annealing leads to two different modes of dewetting that depend on the thickness of the central region. Mode I refers to the formation of randomly positioned small features surrounded by large hemispherical ones located along the periphery of the printed features and occurs when the central regions are thin. Observed at large central thicknesses, Mode II mediates significant molecular transport from edges toward the center of the printed droplet with thermal annealing and forms a hemispherical feature from the initial ring-like deposit. The selective adsorption of red, green, and blue emitting quantum dots over the poly(2-vinylpyridine) results in photoluminescent patterns. The selective assembly of photoluminescent quantum dots over patterned surfaces leads to deterministic and stochastic features beneficial to creating security labels for anti-counterfeiting applications.

Physical Unclonable Functions with Hyperspectral Imaging System for Ultrafast Storage and Authentication Enabled by Random Structural Color Domains

Physical unclonable function (PUF) is attractive in modern encryption technologies. Addressing the disadvantage of slow data storage/authentication in optical PUF is paramount for practical applications but remains an on-going challenge. Here, a highly efficient PUF strategy based on random structural color domains (SCDs) of cellulose nanocrystal (CNC) is proposed for the first time, combing with hyperspectral imaging system (HIS) for ultrafast storage and authentication. By controlling the growth and fusion behavior of the tactoids of CNC, the SCDs display an irregular and random distribution of colors, shapes, sizes, and reflectance spectra, which grant unique and inherent fingerprint-like characteristics that are non-duplicated. Based on images and spectra, these fingerprint features are used to develop two sets of PUF key generation methods, which can be respectively authenticated at the user-end and the manufacturer-front-end that achieving a high coding capacity of at least 22304. Notably, the use of HIS greatly shortens the time of key reading and generation (≈5 s for recording, 0.5-0.7 s for authentication). This new optical PUF labels can not only solve slow data storage and complicated authentication in optical PUF, but also impulse the development of CNC in industrial applications by reducing color uniformity requirement.

Ultradurable Embedded Physically Unclonable Functions

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.

Continuous-Wave Pumped Monolayer WS2 Lasing for Photonic Barcoding

Micro/nano photonic barcoding has emerged as a promising technology for information security and anti-counterfeiting applications owing to its high security and robust tamper resistance. However, the practical application of conventional micro/nano photonic barcodes is constrained by limitations in encoding capacity and identification verification (e.g., broad emission bandwidth and the expense of pulsed lasers). Herein, we propose high-capacity photonic barcode labels by leveraging continuous-wave (CW) pumped monolayer tungsten disulfide (WS2) lasing. Large-area, high-quality monolayer WS2 films were grown via a vapor deposition method and coupled with external cavities to construct optically pumped microlasers, thus achieving an excellent CW-pumped lasing with a narrow linewidth (~0.39 nm) and a low threshold (~400 W cm-2) at room temperature. Each pixel within the photonic barcode labels consists of closely packed WS2 microlasers of varying sizes, demonstrating high-density and nonuniform multiple-mode lasing signals that facilitate barcode encoding. Notably, CW operation and narrow-linewidth lasing emission could significantly simplify detection. As proof of concept, a 20-pixel label exhibits a high encoding capacity (2.35 × 10108). This work may promote the advancement of two-dimensional materials micro/nanolasers and offer a promising platform for information encoding and security applications.

Water-Molecule-Induced Reversible Fluorescence in a One-Dimensional Mn-Based Hybrid Halide for Anticounterfeiting and Digital Encryption-Decryption

Hybrid metal halides with reversible transformation of structure and luminescence properties have attracted significant attention in anticounterfeiting. However, their long transition time and slow response rate may hinder the rapid identification of confidential information. Here, a one-dimensional hybrid manganese-based halide, i.e., (C5H11N3)MnCl2Br2·H2O, is prepared and demonstrates the phenomenon of water-molecule-induced reversible photoluminescence transformation. Heating for <40 s induces a dynamic transfer of red-emissive (C5H11N3)MnCl2Br2·H2O to green-emissive (C5H11N3)MnCl2Br2. In addition, the green emission can gradually revert to red emission during a cooling process in a moist environment, demonstrating excellent reversibility. It is found that the water molecule acts as an external stimulus to realize the reversible transition between red and green emission, which also exhibits remarkable stability during repeated cycles. Furthermore, with the assistance of heating and cooling, a complex digital encryption-decryption and an optical "AND" logical gate are achieved, facilitating the development of anticounterfeiting information security.