Search Results (39)

Deployable thin-film antennas deliver large aperture gains and high stowage efficiency for spaceborne phased arrays but suffer wrinkling-induced planarity loss and radiation distortion. To bridge the lack of electromechanical coupling models for tensioned thin-film patch antennas, we present a unified framework combining structural deformation and electromagnetic simulation. We derive a coupling model capturing the increased bending stiffness of stepped-thickness membranes, formulate a wrinkling analysis algorithm to compute tension-induced displacements, and fit representative unit-cell deformations to a dual-domain displacement model. Parametric studies across stiffness ratios confirm the framework’s ability to predict shifts in pattern, gain, and impedance due to wrinkling. This tool supports the optimized design of wrinkle-resistant thin-film phased arrays for reliable, high-performance space communications. Full article

Palladium phthalocyanine (PdPc) and palladium phthalocyanine integrated with tin–zinc oxide (PdPc:SnZnO) were prepared using a simple chemical approach, and their structural and morphological properties were identified using X-ray diffraction, energy dispersive X-ray analysis, scanning electron microscopy, and transmission electron microscopy techniques. The PdPc:SnZnO nanohybrid revealed a polycrystalline structure combining n-type metal oxide SnZnO nanoparticles with p-type organic PdPc molecules. The surface morphology exhibited wrinkled nanofibers decorated with tiny spheres and had a large aspect ratio. The thin film revealed significant optical absorption within the ultraviolet and visible spectra, with narrow band gaps measured at 1.52 eV and 2.60 eV. The electronic characteristics of Al/n-Si/PdPc/Ag and Al/n-Si/PdPc:SnZnO/Ag Schottky diodes were investigated using the current–voltage dependence in both the dark conditions and under illumination. The photodiodes displayed non-ideal behavior with an ideality factor greater than unity. The hybrid diode showed considerably high rectification ratio of 899, quite a low potential barrier, substantial specific photodetectivity, and high enough quantum efficiency, found to be influenced by dopant atoms and the unique topological architecture of the nanohybrid. The capacitance/conductance–voltage dependence measurements revealed the influence of alternative current signals on trapped centers at the interface state, leading to an increase in charge carrier density. Full article

We demonstrated a versatile and robust strategy to create spatially defined periodic wrinkles in gradient striped polymer films through the coupled process of controlled evaporative self-assembly (CESA) and mechanically driven surface wrinkling. The mechanical properties of patterned-gradient polymer thin films were investigated by wrinkling methodology in a fast and simple manner. Understanding of the complex wrinkles can provide insights into the growth mechanism of most biological species that can be explained by competition between bending and stretching energies, e.g., leaves with gradient thickness range from the central area to edges. Furthermore, it also benefits a wide range of micro-to-nanotechnologies that strongly depend on the mechanical stability and performance of thin polymer membranes for semiconductor applications. Full article

Due to their lightweight characteristics, spatial thin-film structures can generate vibrations far exceeding their film thickness when subjected to external loads, which has become a key factor limiting their performance. This study examines the vibration characteristics of tensioned membrane structures with non-uniform elements subjected to impacts in air, leveraging the Absolute Nodal Coordinate Formulation (ANCF). This model takes into account the wrinkling deformation of thin films under pre-tension and incorporates it into the dynamic equation derived using the absolute node coordinate method. A detailed discussion was conducted on the influence of non-uniform elements, situated at different locations and side lengths, on the vibration characteristics of the thin film. The analytical results obtained from the vibration model were compared with the experimental results, validating the effectiveness of the vibration model. This provides a theoretical foundation for the subsequent vibration control of thin films. Full article

Considering the increasing need for sustainable and economical energy storage solutions, the integration of layered materials such as MoS₂ into these systems represents an important step toward enhancing energy sustainability and efficiency. Exploring environmentally responsible fabrication techniques, this study assesses wrinkled MoS₂ thin films synthesized from distinct Mo and MoS₂ targets, followed by sulfurization conducted in a graphite box. We utilized magnetron sputtering to deposit precursor Mo and MoS₂ films on Si substrates, achieving thicknesses below 20 nm. This novel approach decreases sulfur by up to tenfold during sulfurization due to the confined space technique, contributing also to avoiding the formation of toxic gases such as SO₂ or the necessity of using H₂S, aligning with sustainable materials development. Thinner MoS₂ layers were obtained post-sulfurization from the MoS₂ precursors, as shown by X-ray reflectometry. Raman spectroscopy and grazing X-ray diffraction analyses confirmed the amorphous nature of the as-deposited films. Post-sulfurization, both types of films exhibited crystalline hexagonal MoS₂ phases, with the sulfurized Mo showing a polycrystalline nature with a (100) orientation and sulfurized MoS₂ displaying a (00L) preferred orientation. The X-ray photoelectron spectroscopy results supported a Mo:S ratio of 1:2 on the surface of the films obtained using the MoS₂ precursor films, confirming the stoichiometry obtained by means of energy dispersive X-ray spectroscopy. Scanning electron microscopy and atomic force microscopy images revealed micrometer-sized clusters potentially formed during rapid cooling post-sulfurization, with an increased average roughness. These results open the way for the further exploration of wrinkled MoS₂ thin films in advanced energy storage technologies. Full article

This paper presents a direct 3D numerical simulation of biaxial surface wrinkling of thin metal film on a compliant substrate. The selected compliant substrate is a commercial Scotch tape on which a gold metal thin film has been transferred by using low adhesion between the thin metal film and polyimide substrate. Compared with the previous fabrication of a cylindrical thin-film wrinkling pattern, an undulated wrinkling pattern has been implemented by increasing the width of the thin metal film in order to create biaxial straining in the thin film. To understand the wrinkling behavior due to biaxial loading, a simple direct numerical simulation based on material imperfections defined in the compliant substrate has been conducted. Through modeling and simulation, it was found that the wrinkling mode is determined by the biaxiality ratio (BR), the ratio between transversal strain and longitudinal strain. Depending on the BR, the wrinkling mode belongs to one of the cylindrical, undulated (or herringbone), checkerboard, or labyrinth modes as a function of applied strain. The cylindrical wrinkling is dominant at the input of BR less than 0.5, while the undulated (or herringbone) ones become dominant just after the onset of the wrinkling pattern at BR greater than 0.9. Through the comparison of the wrinkling patterns between simulation and experiment, the applied BR of the fabricated thin film has been successfully estimated. Full article

Surface wrinkling provides an approach to fabricate micron and sub-micron-level biomaterial topographies that can mimic features of the dynamic, in vivo cell environment and guide cell adhesion, alignment, and differentiation. Most wrinkling research to date has used planar, two-dimensional (2D) substrates, and wrinkling work on three-dimensional (3D) structures has been limited. To enable wrinkle formation on architecturally complex, biomimetic 3D structures, here, we report a simple, low-cost experimental wrinkling approach that combines natural silk fibroin films with a recently developed advanced manufacturing technique for programming strain in complex 3D shape–memory polymer (SMP) scaffolds. By systematically investigating the influence of SMP programmed strain magnitude, silk film thickness, and aqueous media on wrinkle morphology and stability, we reveal how to generate and tune silk wrinkles on the micron and sub-micron scale. We find that increasing SMP programmed strain magnitude increases wavelength and decreases amplitudes of silk wrinkled topographies, while increasing silk film thickness increases wavelength and amplitude. Silk wrinkles persist after 24 h in cell culture medium. Wrinkled topographies demonstrate high cell viability and attachment. These findings suggest the potential for fabricating biomimetic cellular microenvironments that can advance understanding and control of cell–material interactions in engineering tissue constructs. Full article

Three distinct homogeneous multilayer self-standing thin films, composed of stacked reduced graphene oxide (rGO) planes, were produced by the improved Hummer’s method. In order to investigate their structural, electrical, and optical properties, the samples were characterized by Raman spectroscopy, field emission scanning electron microscopy (FESEM), four-point probe measurements, and Fourier-transform infrared spectroscopy (FTIR). The Raman spectra of the samples indicate the presence of minor surface defects and a relatively low oxygen content of rGOs. The FESEM images obtained from the samples reveal a smooth sheet-like surface with few wrinkles. Additionally, the cross-sectional images provide confirmation of the presence of multi-stacked layer structures. Based on the resistance decreasing by about 0.35 to 0.65 percent per kelvin within the region of ambient temperature, the electrical resistance vs. temperature curves imply semiconducting behavior in the rGOs. The FTIR analysis of the samples conducted within the wavelength range of 2.5 to 25 µm demonstrates a significant absorption value exceeding 90%. This observation shows that the developed materials possess favorable characteristics, making them an excellent absorber candidate for sensing detectors in the infrared range. We systematically analyzed and confirmed that the structural as well as optical and electrical properties of our obtained rGOs may be fine-tuned by adjusting the initial reactants concentration and annealing temperature. Full article

Copper-coated films are a solution for flexible electronic devices. One of the applications is a flexible-tension film-deployable antenna, which is a large deployable space antenna with broad application prospects. To analyze the possibility of applying coated films to the antenna, surface accuracy evaluation is required. The finite element method (FEM) was used to analyze the surface accuracy of the copper-coated thin-film structures. Both wrinkling and stretching–bending coupling deformation were considered. Simplified models were applied to study factors influencing the surface accuracy under boundary effects. Different sizes of coated area and different boundary conditions were simulated. The results showed the characteristic boundary effects of copper-coated thin-film structures and the influence curve of film thickness and patch size on boundary effects. These findings will inform the design and analysis of variable-stiffness thin-film antennas. On this basis, the application of a flexible-tension film-deployable antenna is discussed, along with a measure to improve the surface accuracy. Full article

This paper presents a 3D direct numerical simulation of buckled thin-film packaging based on transferred elastic thin-film wrinkling bonded on a compliant polymer ring. The mode change of the fabricated thin-film cap is found by measuring the thin-film cap shape at different times after Si substrate debonding. The conventional linear and nonlinear buckling simulations are not adequate to understand the behavior of the thin-film buckling mechanism creating such packaging cap mode change. Direct buckling simulation is recently reported as an easy and useful numerical wrinkling simulation method. A novel 3D FEM model of a thin-film package suitable for direct 3D buckling simulation is built to reduce the mode mixture between different buckling modes. Buckling modes of the packaging cap are investigated in terms of elastic moduli of package materials and applied strain due to thermal expansion coefficient difference. Based on the simulation results, it is found that there are two main modes in the fabricated thin-film buckling package determining the shape of the transferred thin-film packaging cover depending on the elasticity ratio between the cap and sealing ring materials. The mode shift from wrinkling cap mode to out-of-plane cap mode due to applied strain along a polymeric sealing ring is found. Full article

Natural wrinkling of metal films on silicone substrates can appear by means of the metal sputtering process and can be described by the continuous elastic theory and non-linear wrinkling model. Here, we report the fabrication technology and behavior of thin freestanding Polydimethylsiloxane (PDMS) membranes equipped with thermo-electric meander-shaped elements. The Cr/Au wires were obtained on the silicone substrate by magnetron sputtering. We observe wrinkle formation and suppose furrows appear once PDMS returns to its initial state after the thermo-mechanical expansion during sputtering. Although the substrate thickness is usually a negligible parameter in the theory of wrinkle formation, we found that the self-assembled wrinkling architecture of the PDMS/Cr/Au varies due to the membrane thickness of 20 µm and 40 µm PDMS. We also demonstrate that the wrinkling of the meander wire affects its length, and it causes a 2.7 times higher resistance compared to a calculated value. Therefore, we investigate the influence of the PDMS mixing ratio on the thermo-electric meander-shaped elements. For the stiffer PDMS with a mixing ratio of 10:4, the resistance due to wrinkle amplitude alterations is 25% higher compared to the PDMS of ratio 10:1. Additionally, we observe and describe a thermo-mechanically induced motion behavior of the meander wires on completely freestanding PDMS membrane under applied current. These results can improve the understanding of wrinkle formation, which influences thermo-electric characteristics and may promote the integration of this technology in applications. Full article

Wrinkle topographies have been studied as simple, versatile, and in some cases biomimetic surface functionalization strategies. To fabricate surface wrinkles, one material phenomenon employed is the mechanical-instability-driven wrinkling of thin films, which occurs when a deforming substrate produces sufficient compressive strain to buckle a surface thin film. Although thin-film wrinkling has been studied on shape-changing functional materials, including shape-memory polymers (SMPs), work to date has been primarily limited to simple geometries, such as flat, uniaxially-contracting substrates. Thus, there is a need for a strategy that would allow deformation of complex substrates or 3D parts to generate wrinkles on surfaces throughout that complex substrate or part. Here, 4D printing of SMPs is combined with polymeric and metallic thin films to develop and study an approach for fiber-level topographic functionalization suitable for use in printing of arbitrarily complex shape-changing substrates or parts. The effect of nozzle temperature, substrate architecture, and film thickness on wrinkles has been characterized, as well as wrinkle topography on nuclear alignment using scanning electron microscopy, atomic force microscopy, and fluorescent imaging. As nozzle temperature increased, wrinkle wavelength increased while strain trapping and nuclear alignment decreased. Moreover, with increasing film thickness, the wavelength increased as well. Full article

This paper presents a direct numerical simulation for the extraction of material properties based on thin-film wrinkling on scotch tape. Conventional FEM-based buckling simulation sometimes requires complex modeling techniques concerning mesh element manipulation or boundary conditions. The direct numerical simulation differs from FEM (finite element method)-based conventional two-step linear–nonlinear buckling simulation in that mechanical imperfections are directly applied into the elements of the simulation model. Hence, it can be performed in one step to find the wrinkling wavelength and amplitude, which are key parameters to extract the material mechanical properties. Moreover, the direct simulation can reduce simulation time and modeling complexity. Using the direct model, the effect of the number of imperfections on wrinkling characteristics was first studied, and then wrinkling wavelengths depending on the elastic moduli of the associated materials were prepared for the extraction of material properties. Thin-film wrinkling test patterns on scotch tape were fabricated using the transfer technique with low adhesion between metal films and the polyimide substrate. The material properties of the thin metal films were determined by comparing the measured wrinkling wavelengths and the proposed direct simulation results. By consequence, the elastic moduli of 300 nm thick gold film and 300 nm thick aluminum were determined as 250 GPa and 300 GPa, respectively. Full article

Conformable, sensitive, long-lasting, external power supplies-free multifunctional electronics are highly desired for personal healthcare monitoring and artificial intelligence. Herein, we report a series of stretchable, skin-like, self-powered tactile and motion sensors based on single-electrode mode triboelectric nanogenerators. The triboelectric sensors were composed of ultraelastic polyacrylamide (PAAm)/(polyvinyl pyrrolidone) PVP/(calcium chloride) CaCl₂ conductive hydrogels and surface-modified silicon rubber thin films. The significant enhancement of electrospun polyvinylidene fluoride (PVDF) nanofiber-modified hierarchically wrinkled micropyramidal architectures for the friction layer was studied. The mechanism of the enhanced output performance of the electrospun PVDF nanofibers and the single-side/double-side wrinkled micropyramidal architectures-based sensors has been discussed in detail. The as-prepared devices exhibited excellent sensitivity of a maximum of 20.1 V/N (or 8.03 V/kPa) as tactile sensors to recognize a wide range of forces from 0.1 N to 30 N at low frequencies. In addition, multiple human motion monitoring was demonstrated, such as knee, finger, wrist, and neck movement and voice recognition. This work shows great potential for skin-like epidermal electronics in long-term medical monitoring and intelligent robot applications. Full article

Synthesis of a smooth conductive film over an elastomer is vital to the development of flexible optics and wearable electronics, but applications are hindered by wrinkles and cracks in the film. To date, a large-scale wrinkle-free film in an elastomer has yet to be achieved. We present a robust method to fabricate wrinkle-free, stress-free, and optically smooth thin film in elastomer. Targeting underlying mechanisms, we applied nanoparticles between the film and elastomer to jam the interface and subsequently suppress interfacial instabilities to prevent the formation of wrinkles. Using polydimethylsiloxane (PDMS) and parylene-C as a model system, we have synthesized large-scale (>10 cm) wrinkle-free Al film over/in PDMS and demonstrated the principle of interface jamming by nanoparticles. We varied the jammer layer thickness to show that, as the layer exceeds a critical thickness (e.g., 150 nm), wrinkles are successfully suppressed. Nano-indentation experiments revealed that the interface becomes more elastic and less viscoelastic with respect to the jammer thickness, which further supports our assertion of the wrinkle suppression mechanism. Since the film was embedded in a polymer matrix, the resultant film was highly deformable, elastic, and optically smooth with applications for deformable optical sensors and actuators. Full article