Physically Unclonable Surfaces via Dewetting of Polymer Thin Films.

We study the dewetting behaviors of poly(methyl methacrylate) (PMMA) thin films coated in the cylindrical nanopores of anodic aluminum oxide (AAO) templates by thermal annealing. Self-assembled monolayers (SAMs) of n-octadecyltrichlorosilane (ODTS) are introduced to modify the pore surfaces of the AAO templates to induce the dewetting process. By using scanning electron microscopy (SEM), the dewetting-induced morphology transformation from the PMMA thin films to PMMA nanoparticles with asymmetric shapes can be observed. The sizes of the PMMA nanoparticles can be controlled by the original PMMA solution concentrations. The dewetting phenomena on the modified nanopores are explained by taking into account the excess intermolecular interaction free energy (ΔG). This work opens a new possibility for creating polymer nanoparticles with asymmetric shapes in confined geometries.

Physical unclonable functions (PUFs), relying extensively on the random spatial distribution of block elements, are promising technology for generating unclonable cryptograph. Herein, we demonstrate time-dependent PUFs (TD-PUFs) by introducing carbon dots (CDs) with bright and long-lived triplet excitons as block elements. The constructed TD-PUFs evolve into multiple unclonable PUFs over time, effectively breaking the spatial limitation of transitional PUFs and increasing the complexity, making them much more difficult to be attacked. This temporal evolution introduces an additional layer of security, as the dynamic nature of TD-PUFs makes it increasingly challenging for adversaries to predict or replicate their states. We have developed pixel matrix function (PMF) to describe the evolution process of the TD-PUFs, enabling a detailed analysis of the dynamic behavior and unique security features. In addition, we exhibit a TD-PUFs painting (30 × 40 cm2) by an etching technology where the primary structures of the panting undergo a transformation over time, driven by the varying triplet exciton lifetimes of the CDs. The proposed concept of TD-PUFs overcome their spatial limitations and increase the complexity, making the PUF labels more difficulty to be cracked.

Using Physical Unclonable Functions (PUFs) within the server-side has been recently proposed to address security vulnerabilities of the password (PW) authentication mechanism, including attacks on the database (DB) of user credentials. Practicing this idea using available memory technologies and constrained hardware modules may offer an additional hardware security layer. Thus, finding the PWs would require the attacker to access both the hardware containing the PUF and the information stored in the DB. PUFs have been used with other cryptographic algorithms in previous studies to improve the system’s security further. However, these studies have overlooked the challenges of implementing these algorithms with constrained hardware devices. Therefore, the trade-off between the achieved security and desired efficiency is still a challenge. The presented hardware-software PUF-based solutions lead to faster computation in the server-side hardware. Also, the client-side protocol can cope with the resource limitations existing in essential applications, including constrained IoTs. Moreover, the scheme handles the instability and bit alias of the Static Random-Access Memory (SRAM) PUF. This paper’s reliable, low-cost, and efficient prototype shows the functionality of a hardware-dependent protocol that is resistant to insider, PW guessing, and man-in-the-middle attacks. The presented hardware-software can be easily integrated with the server-side. Statistical tests on the embedded SRAM show that this paper protocol improves PUF entropy responses stored in the DB. Besides, the experimental results of this work show the possibility of obtaining an SRAM with very low intra-PUF variation without using any extra hardware overhead.

Aggregation induced luminescence chromism molecule for preparation of physically unclonable function labels

Physical Unclonable Function (PUF) is a function that cannot be modeled as it utilizes the random process variations on a silicon chip to generate a unique bit stream of `1's and `0's (response bits) which can be used for authentication and cryptography applications. As PUF is highly rely upon process variations, the response bits generated are governed by the systematic process variation instead of the stochastic process variation, which will reduce the randomness in the response bits. In this paper we propose the novel Random Patch Mixer (RPM) technique to dismiss the systematic variation effect on the response bits generated. We applied the RPM technique on data obtained from 29 Spartan 3E FPGA chips. We showed that our RPM technique has successfully dismissed the systematic variation effect on the response bits generated from the ROPUF on FPGA. We also proved that the responses generated by applying the RPM Technique passed the National Institute of Standards and Technology NIST statistical test for randomness.

We study the dewetting of thin polymer films deposited on slippery substrate. Recent experiments on these systems have revealed many unexpected features. We develop here a model that takes into account the rheological properties of polymer melts, focussing on two dewetting geometries (the receding of a straight edge, and the opening of a hole). We show that the friction law associated with the slippage between the film and the substrate has a direct influence on the dewetting dynamic. In addition, we demonstrate that residual stresses, which can be stored in the films due to their viscoelasticity, are a source of destabilization for polymer films, and accelerate the dewetting process.

Real-time Traffic monitoring systems need to monitor the vehicles as well as it requires to communicate with the vehicle to provide the real time information about traffic density, road construction, etc. However, insecure communication between these entities can lead to life-threatening scenarios. Therefore, there is a dire need to develop appropriate protocols facilitating communication between vehicles to vehicles and vehicles to the traffic monitoring systems. In this paper, we propose a new AEAD-based protocol embedded with physically Unclonable Function (PUF) based key generation for secure and authenticated transmission of videos for real-time monitoring systems. The proposed protocol consists of a lightweight AEAD primitive - ACORN; and a hardware-efficient LFSR-based Ring Oscillator PUF (RO-PUF). The proposed PUF based key generation adds another layer of security to our protocol. Our protocol is implemented in FPGA using a 640 × 480 resolution camera with 30 frames per second. Detailed implementation study of the entire protocol shows its feasibility for real-world usage.

The surface morphology of thin polymer films (polystyrene) on top of silicon substrates as prepared by spin-coating and after the dewetting of an initially homogeneous polymer film was examined. We investigated the influence of film thickness, molecular weight, annealing temperature, and used solvent. With diffuse X-ray scattering in the region of total external reflection a depth sensitivity was achieved. The in-plane structure of the untreated samples shows significant differences: Starting from a molecular weight of 28k the samples show conformal roughness over a range of film thickness between 50 and 1160 Å, whereas in an equivalent film thickness range for a low molecular weight sample no correlation between the substrate and the polymer surface was detected. Above the glass transition temperature the roughness correlation was lost and therefore has no influence on the dewetting behavior of the polymer films. A variation of the solvent used for the spin-coating gives rise to different dewetting structures that originate from different in-plane film structures right after the preparation. Thus, diffuse scattering is well suited for probing long-range correlations and mobility.

Solid-state dewetting is the process by which thin solid films break up and retract on a substrate, forming nanostructures. While dewetting of single-crystalline films is understood as a surface-energy-driven process mediated by surface diffusion, polycrystalline films exhibit additional complexity due to the presence of grain boundaries. Most theoretical and computational studies have focused on single-crystalline dewetting. Here, we present the application of the grand-potential multi-phase-field model to the dewetting of thin polycrystalline films in three dimensions, reproducing the key phenomenology of this process. By considering isotropic interface/surface energy, we illustrate its consistency with predictions based on energetic arguments and the morphological evolution towards equilibrium. We also provide novel analytical criteria for the onset of three-dimensional dewetting, serving as fundamental theoretical benchmarks, and highlight the critical role of triple junctions. Moreover, we unveil the dewetting behavior of polycrystalline patches, extending the scenarios of their single-crystalline counterparts.

Dewetting of thin polystyrene films deposited onto silicon wafers exhibits unusual dynamics and rim morphologies. Here, we present a new theoretical approach of these phenomena taking into account both the viscoelastic properties of the film and the non-zero velocity of the film at the interface with the substrate (i.e. slippage). We show how these two ingredients lead to: a) a very asymmetric shape of the rim as the film dewets; b) a decrease of the dewetting velocity with time like t−1/2 for times shorter than the reptation time (for larger times, the dewetting velocity reaches a constant value). Recent experiments by Damman, Baudelet and Reiter (Phys. Rev. Lett., 91 (2003) 216101) present, however, a much faster decrease of the dewetting velocity. We then show how this striking result may be explained by the presence of residual stresses in the film.

We explore laser-induced dewetting of thin gold films deposited on different underlayers consisting of optical cavities of gold and silica. Our observations indicate that the morphology and optical response of laser-exposed regions are sensitive to the optical environment in vicinity of the dewetting layer.

We present a study of the impeding influence of a capping, native oxide layer on the solid state dewetting of thin bismuth films on silicon(111) in vacuum. We study the temperature dependence of the film thickness and strain of the thin films through the analysis of crystal truncation rods of clean and capped bismuth films. This analysis reveals a dewetting temperature difference of 40°C between capped and uncapped films. The results are supported by scanning electron microscopy and x-ray photoelectron spectroscopy experiments. Furthermore, a model for the retarding effect of the oxide layer and the final shape of the thin film is presented.

As the use of photonics circuits expands, the optical quality and performance of integrated components in the microscale become a major concern. Aiming to improve the performance while reducing the time processing, new microfabrication approaches are being investigated. The dewetting of glassy thin films have been recently proposed as an alternative for nano and microfabrication of chalcogenide optical components. Besides being the best materials for light transmission in the infrared region, chalcogenide glasses possess a flexible molecular structure that allows using a cheap and simple molding process. Here we investigate the thermal-induced dewetting of chalcogenide As20Se80 thin films, by studying the influence of temperature, atmosphere, and heating rate on the formation of self-assembled microstructures. We found that thin films between 150 and 700 nm dewet via structural relaxation, similarly to liquid agglomeration, and produce solid microstructures with the same composition and molecular structure as the initial film. By controlling the glass viscosity and the kinetics of the nucleation process it was possible to adjust the distribution and size of glassy microstructures. Additionally, we combine the dewetting process with standard photolithography and by avoiding the capillary instabilities, we are capable to obtain waveguides with the smooth and symmetric surfaces required for optical applications in the microscale size.

We study the plane wave scattering on a planar periodic array of silver dimers. It is found that an appropriately designed array provides the sharp turn of TE-polarized incident beam in orthogonal (opposite) directions through the effects of negative-angle refraction (reflection).

An apparatus is described for the measurement of transmission and reflection of visible light through biological materials. The accuracy of the apparatus is independent of any fluctuations of intensity in the light source.