Effect of relative humidity on the peeling behavior of a thin film on a rigid substrate

Precision-induced localized molten liquid metal stamps for damage-free transfer printing of ultrathin membranes and 3D objects

Transfer printing, a crucial technique for heterogeneous integration, has gained attention for enabling unconventional layouts and high-performance electronic systems. Elastomer stamps are typically used for transfer printing, where localized heating for elastomer stamp can effectively control the transfer process. A key challenge is the potential damage to ultrathin membranes from the contact force of elastic stamps, especially with fragile inorganic nanomembranes. Herein, we present a precision-induced localized molten technique that employs either laser-induced transient heating or hotplate-induced directional heating to precisely melt solid gallium (Ga). By leveraging the fluidity of localized molten Ga, which provides gentle contact force and exceptional conformal adaptability, this technique avoids damage to fragile thin films and improves operational reliability compared to fully liquefied Ga stamps. Furthermore, the phase transition of Ga provides a reversible adhesion with high adhesion switchability. Once solidified, the Ga stamp hardens and securely adheres to the micro/nano-membrane during the pick-up process. The solidified stamp also exhibits the capability to maneuver arbitrarily shaped objects by generating a substantial grip force through the interlocking effects. Such a robust, damage-free, simply operable protocol illustrates its promising capabilities in transfer printing diverse ultrathin membranes and objects on complex surfaces for developing high-performance unconventional electronics.

Electrochemical corrosion protection of neat and zinc phosphate modified epoxy coating: A comparative physical aging study on Al alloy 6101

Optimizing the pigment volume concentration of zinc phosphate pigments can protect Al alloy 6101 from alkaline media. Additionally, zinc phosphate pigments form a shielding film on the substrate and facilitate stopping the penetration of aggressive corrosion ions. The efficiency of eco-friendly zinc phosphate pigments is almost 98% during the corrosion analysis. A comparative study of physical aging of neat epoxy and Zinc Phosphate (ZP) pigment-modified epoxy coatings on Al alloy 6101 was conducted in Xi'an, China, for one year in all four seasons, where in summer for 3 months, results degraded more due to high UV radiation and humidity; it is found that peeling force of ZP pigments modified epoxy coatings is 50% higher of than that of the neat epoxy coatings though both peel-off adhesion strength and scratch test visibility decreased in both coatings; The electrochemical resistance of ZP pigments modified epoxy coatings is about 30% higher of than that of neat epoxy coatings, the corrosion rate of ZP pigments modified epoxy coatings is about 70% lower of than that of neat epoxy coatings, moreover the gloss retention is 20% higher in the modified epoxy; Optical surface observation of the coatings showed that the ZP modified epoxy coating could effectively restrict the crack and shrinkage in coatings after aging experimentation in the natural environment.

Simulation of the peel of hydrogels with stiff backing

In this work, the peel of hydrogels under a stiff backing constraint was studied using a finite element method. The finite element method was first validated by comparing the simulation results to theoretical predictions and experimental measurements. Then, the method was used to investigate the effects of adhesion thickness, adhesion length and backing thickness on the peel behaviors, as well as the stress distribution within the adhesion layer. The results indicated that the peel force-displacement curve has a constant profile when the adhesion thickness and backing thickness are prescribed so long as the adhesion length is sufficiently long. The peak peel force increases with the adhesion length and then plateaus. The larger the intrinsic peak stress or the thicker the backing, the higher the plateau. The steady-state peel force is independent of the backing thickness, while positively correlated with the strain energy storage of the hydrogel adhesion layer. The critical vertical displacement corresponding to the peak peel force increases with the hydrogel thickness and decreases with the backing thickness. However, the critical vertical displacement corresponding to the steady-state peel force increases with the backing thickness. The present work puts forward an effective numerical approach to probe the peel of hydrogels, which is beneficial for the design of relevant structures.

Recyclable free-polymer transfer of nano-grain MoS2 film onto arbitrary substrates

Clean transfer of transition metal dichalcogenides (TMDs) film is highly desirable, as intrinsic properties of TMDs may be degraded in a conventional wet transfer process using a polymer-based resist and toxic chemical solvent. Residues from the resists often remain on the transferred TMDs, thereby causing a significant variation in their electrical and optical characteristics. Therefore, an alternative to the conventional wet transfer method is needed-one in which no residue is left behind. Herein, we report that our molybdenum disulfide (MoS₂) films synthesized by plasma-enhanced chemical vapor deposition can be easily transferred onto arbitrary substrates (such as SiO₂/Si, polyimide, fluorine-doped tin oxide, and polyethersulfone) by using water alone, i.e. without residues or chemical solvents. The transferred MoS₂ film retains its original morphology and physical properties, which are investigated by optical microscopy, atomic force microscopy, Raman, x-ray photoelectron spectroscopy, and surface tension analysis. Furthermore, we demonstrate multiple recycling of the resist-free transfer for the nano-grain MoS₂ film. Using the proposed water-assisted and recyclable transfer, MoS₂/p-doped Si wafer photodiode was fabricated, and the opto-electric properties of the photodiode were characterized to demonstrate the feasibility of the proposed method.

Solution-Processed Submicron Free-Standing, Conformal, Transparent, Breathable Epidermal Electrodes

Long-term, real-time, and comfortable epidermal electronics are of great practical importance for healthcare monitoring and human-machine interaction. However, traditional physiological signal monitoring confined by the specific clinical sites and unreliability of the epidermal electrodes leads to great restrictions on its application. Herein, we constructed a solution-processed submicron (down to 230 nm), free-standing, breathable sandwich-structured hybrid electrode composed of a silver nanowire network with a conductive polymer film, which is conformal, water-permeable, and noninvasive to the skin while achieving good signal acquisition ability. The free-standing hybrid electrode is prepared via an in situ capillary force lift-off process and can be transferred onto complex surfaces. The whole process is a complete solution process that facilitates large-area preparation and application. The light-weight hybrid electrodes exhibit high optical transmittance, high electrical conductivity, and high gas/ion permeability. When the hybrid electrodes are attached onto the skin, the imperceptible films show high conformality with low electrical impedance, thus exhibiting significantly improved electrocardiology and electromyogram signal monitoring performance compared to that of the commercial gel electrodes.

Effect of thin-film length on the peeling behavior of film-substrate interfaces

Compared with the classical Kendall's model to analyze the steady-state peeling behavior of an infinite length film attaching to a rigid substrate, this paper establishes a model of a finite length thin film adhering on a rigid substrate and analyzes the influence of film's initial adhesion length, film stiffness, and initial cantilever length of films on the whole interface peeling behavior. Both theoretical prediction and finite element calculation are carried out. The typical relationship between the peeling force and the separation distance at the loading point is obtained as well as the morphology of deformed films. It is found that the initial adhesion length has a significant effect on the peeling behavior. Differently from the case of infinite thin films, whether the steady-state peeling process can be achieved or not depends on the film's adhesion length. If the film is long enough, the whole peeling process can be divided into an initial peeling stage, a transition stage, a steady-state stage, and an unstable peeling stage. The maximum peeling force of the interface does not necessarily occur in the steady-state stage, which is influenced by the film's initial adhesion length, film stiffness, and initial cantilever length. The results achieved in this paper can not only provide a systematic understanding of peeling behavior of a thin film on a rigid substrate, but also be helpful for the design of high-quality interface and peeling tests in practical applications.