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Sintered nanoparticle structures are macroscopically brittle but quite robust if deposited on a flexible substrate. The effects of a polymer substrate on the stretchability of both brittle and ductile coatings and traces are well established. Systematic effects of substrate properties on the fatigue resistance of aerosol printed nano-Ag are slightly more complex. The present work is focused on the early stages of fatigue, where the resistance increases significantly but cracks are not yet visible. Overall, the fatigue behavior is seen to vary with the combination of substrate modulus and viscoelastic deformation properties. Comparing two common polyimides, the rate of damage was seen to increase faster with increasing amplitude on the less compliant one. Consistently with this increasing the minimum strain in the cycle led to a significantly stronger reduction in damage rates. However, the damage rate remained lower on the less compliant substrate at all amplitudes and strain ranges of practical concern.

Polymer metallization is widely used in a variety of micro and nano system technologies, and magnetron sputtering of a metal film is one of the essential processes of polymer metallization. However, some defects are likely generated in sputtered metal films on a polymer substrate. In this work, the defect generation mechanism in the sputtered Au film on a polymethylmethacrylate (PMMA) substrate was investigated for the first time. The characteristics of defects on the PMMA surface and in the Au film were examined by an optical microscope, a scanning electron microscope (SEM) and a confocal microscope. Detailed characterization results indicate that the ejected Au atoms bombard the PMMA substrate and cause snowflake-like defects on the PMMA surface because of the low hardness of PMMA, then Au atoms nucleate and grow at PMMA defect sites and form a partially suspended metal film, subsequently dropping the photoresist makes the suspended metal film conformally adhere to the PMMA defect, and the snowflake-like morphology is replicated to the metal film. The effects of sputtering parameters on the defects were studied, and the amount of defects in the Au film reduced with the decrease of the sputtering power or the sputtering pressure.

When a graphene film is coated onto a flexible polymer substrate, weak adhesion can cause delamination of the film under mechanical bending. Moreover, as each graphene layer restacks, the performance of the film as an electrode for a supercapacitor becomes limited. In this study, facile laser welding and surface modification processes are demonstrated to overcome these limitations. First, a continuous wave laser beam is applied to the interface between the coated graphene and the underlying transparent polycarbonate substrate. This welding process significantly improves their adhesion and enables excellent mechanical bendability. Second, surface modification of graphene is achieved under ambient conditions by irradiating the graphene film surface with a nanosecond pulsed laser. Sandwich-type supercapacitors are fabricated using these surface-modified graphene electrodes with a PVA-H3PO4 electrolyte. The effect of the laser fluence on the performance of the supercapacitor is investigated. At an optimal laser power, an areal capacitance of 4.7 mF/cm2 is achieved.

Low-energy Xenon flash pulses permit sintering of spray-pyrolyzed submicron Ag particles (SMPs) into conductive tracks with acceptable electrical resistivity (16.7 μΩ cm) on polyimide film in several seconds without extra heating. Mixed with Ag nanoparticles (20% in weight ratio), the resistivity of the obtained sintered mixed pastes can be reduced to 12.6 μΩ cm, which is nearly the same as those formed using nanoparticle pastes (11.2 μΩ cm). Using irradiation on the polymer substrate side, more uniform sintered deposits with better electrical conductance (ρ

The effects of surface pretreatment and deposition conditions on the gas permeation properties—including permeability of He, O2, and H2O; the size; and the density of permeation-enhancing defects—and mechanical flexibility of Al2O3 films on polymer substrates by atomic layer deposition (ALD) were investigated to develop flexible gas barrier films for organic and flexible electronics. Pretreating polyimide (PI) and poly(ethylene terephthalate) (PET) substrates with an aqueous KOH solution greatly lowered the gas permeability of the ALD Al2O3 films as a result of improved affinity between the substrate surface and the ALD precursors. Varying the ALD conditions—including lengthening the precursor exposure, elevating the deposition temperature, and changing the precursor sequence—enhanced physisorption of ALD precursors on the polymer substrate, which improved nucleation of the ALD films to reduce defects in the films and lower their gas permeability. Activation energy for permeation determined from the temperature dependence of the permeability of the ALD films indicated that the ALD films deposited under the optimized condition contained smaller and few permeation-enhancing defects. The optimized ALD films possessed a low water vapor transmission rate of ~ 10−6 g/m2 day that met the stringent requirement of organic and flexible electronics, while also exhibiting excellent mechanical flexibility by withstanding repeated bending with small increases in gas permeability. Our results provide valuable insights into the development of flexible barrier thin films for the encapsulation of organic and flexible electronics.

Low-temperature solution processable TiO2 nano-sol for electron transporting layer (ETL) of flexible perovskite solar cells is prepared by synthesizing TiO2 nano-sols by peptization in acidic aqueous solution and re-dispersing the TiO2 nanoparticles in H2O, ethanol (EtOH), dimethylsulfoxied (DMSO), and N,N-dimethylformamide (DMF). By considering dielectric constant, zeta potential, and surface tension of solvent media, we found that the DMF is the best to form uniform TiO2 ETL by spin-coating among them because it has low surface tension and high zeta potential. Accordingly, we could demonstrate 18.2% power conversion efficiency (PCE) for rigid glass substrate based perovskite solar cells and 15.8% PCE for flexible polymer substrate based devices by low-temperature solution process.

Chalcogenide PbS has been extensively studied as a p-type semiconductor material for various optoelectronic devices. Here, an effective two-step chemical bath deposition process is introduced to achieve dense microstructure of PbS thin films specifically for a flexible polyethylene terephthalate (PET) substrate. Three different types of substrates, such as Cu foils, glass substrate and PET, were initially examined to compare different crystal growth behaviors of PbS thin films depending on the choice of substrate. Only the PET substrate demonstrated an unacceptable coverage of films even with the extended deposition due to a retarded growth presumably with more scattered initial distribution of nuclei. Conclusively, two-step deposition processing at a low temperature of 40 °C for the PET substrate was successful in achieving homogeneous microstructures with proper bandgap and film thickness. As a promising result, the 60 min plus 60 min-double depositions at 40 °C produced an ideal bandgap of ~1.58 eV with a proper film thickness of ~200 nm.

Single-asperity scratching is used as a simplified contact problem to investigate the deformation due to two materials touching each other. Coupling the intrinsic polymer characteristics to the scratch response for blends of polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with varying composition is the main challenge of this study. The intrinsic deformation properties of these blends are strongly influenced by their composition. A combination of experiments and simulations is essential to understand the influence of friction on the interplay between intrinsic deformation properties and contact mechanics. Without an adhesive component in the numerical simulations, no influence of scratch velocity on the penetration depth or lateral force is observed. Furthermore, the lateral force is highly underestimated. Inclusion of an adhesive component between the indenter tip and polymer substrate results in a bow-wave in front of the sliding indenter tip. The experimentally measured lateral forces can only be predicted when the velocity-independent constant friction coefficient varies with blend composition. Therefore, knowing the intrinsic material properties, i.e. deformation kinetics and the intrinsic friction parameter, enables a quantitative prediction of the single-asperity scratch response.

The electro-mechanical reliability of the metal layer on flexible substrates under repetitive mechanical deformations should be guaranteed for real commercialization of flexible electronics. The mechanical and electrical properties of metal films are closely related to their microstructure, which can be changed by thermal annealing during the fabrication process. This study investigates the reliability of an annealed Cu film on flexible substrates using tensile and bending fatigue tests, comparing it with a non-annealed sample. For the tensile test, the annealed Cu film exhibits a superior stretchability due to microstructure change including large grains. For the fatigue test, however, the annealed sample reliability decreases due to the acceleration of fatigue damage formation induced by the repetitive bending deformation. This study can provide useful information for designing of highly reliable flexible electronics.

In flexible display technology, the electronic components are constructed on a flexible polymer substrate film and are released from a carrier glass with the detachment of the polymer film. During the debonding process, however, strong polymer-glass bonding often causes the formation of wrinkles and buckles of the polymer film and thereby the damage of electronics. Here, we report on a novel debonding layer (DBL) of graphene/MnO hybrids for scalable and stable detachment of the polymer film. The DBL acted to decrease the polymer-glass bonding strength. The weakly bonded polymer film was safely detached from the glass in ∼170 s by gas-evolution at DBL. The gas-induced debonding (GID) process was functional in H2O2 solution, not in other tested solutions, indicating its good solution selectivity. As proof of concept, flexible thin-film transistors (TFTs) were fabricated using our DBL and exhibited the similar transfer characteristics before and after the GID process. We believe our DBL will also pave the ways for flexible photovoltaic cells, flexible flash memories and flexible sensor arrays as well as flexible displays.

In this work, intense pulsed light (IPL) sintering process was investigated with vacuum stretching and heating of the polymer substrate for warpage free printed electronics circuit. The IPL irradiation energy and substrate heating temperature were optimized to obtain high electrical conductivity, high adhesion strength, and little warpage of printed Cu electrodes pattern on the polyimide (PI) substrate. Scanning electron microscopy and x-ray diffraction were conducted to characterize microstructure and transformation crystal phase of the IPL sintered Cu nanoparticle (NP)/microparticle (MP)-ink film. The resistivity of IPL sintered Cu NP/MP-ink films was measured using the four-point probe method and profilometer. In order to monitor IPL sintering process, in-situ resistance and temperature monitoring of Cu NP/MP-ink were conducted. Also, a transient heat transfer analysis was performed using finite-element analysis software to predict temperature gradients of Cu NP/MP-ink and polymer substrate during IPL light sintering process. As a result, the optimal IPL light sintered Cu NP/MP-ink film (vacuum applied, 150 °C heating, and irradiation energy: 3.5 J/cm2) had a low resistivity 6.94 μΩ·cm and 5 B level of adhesion strength with almost no warpage of PI substrate.

A facile and simple chelation assisted in-situ growth approach for the preparation of thin uniform metal organic framework composite membranes has been developed. Coherent zeolite imidazolate framework ZIF-7 and ZIF-67 layers were successfully grown on porous polypropylene substrate covered with metal-chelating polyaniline interface layer. These membranes exhibited a H2 permeance of 1.6 × 10−7 mol m−2 s−1 Pa−1 and an ideal H2/CO2 separation factor of 7.9. The incorporation of the second organic linker 2-aminobenzimidazole in the ZIF-7 framework afforded ZIF-7-NH2 layer enabling gate-opening and flexibility. This new hybrid ZIF-7-NH2 membrane featured a significantly increased H2 permeance of 4.9 × 10−6 mol m−2 s−1 Pa−1 and an ideal H2/CO2 separation factor of 10.6.

Stretchable electronics are of rapidly increasing interest due to their unique ability to function under complex deformations. Strain isolation of stiff functional components from the substrate represents a key challenge in the development of stretchable electronics since their mechanical mismatch may yield undesirable strains to degrade the device performance. The results presented here report an approach to develop a soft strain-isolating polymer substrate with programmable stiffness by spatioselective ultraviolet exposure for stretchable electronics. The approach being compatible with the well-established lithographic process reduces the fabrication complexity significantly and offers a simple yet robust strain-isolation mechanism to ensure the system stretchability of more than 100%. Combined experimental and numerical studies reveal the fundamental aspects of the design, fabrication, and operation of the strain-isolating substrate. Demonstration of this concept in a stretchable inorganic metal-based resistive temperature sensor and a stretchable organic photodiode array with unusually high performance shows the simplicity of the approach and the robustness in strain isolation in both component and device levels. This type of strain-isolation design not only creates promising routes for potential scalable manufacturing of stretchable electronics but also engineering opportunities for stretchable electronics involving the integration of various functional components, which require the quantitative control of the strain levels to achieve optimal performance.

The hybrid blends consisting of ethylene–propylene–diene monomer (EPDM) and vinyl polyhedral silsesquioxane (vinyl-POSS) nanoparticles were studied. Increasing filler concentrations, namely 2, 4, 6 and 8 phr, were added to the polymer substrate. The thermal stability was tested by chemiluminescence, while infrared spectroscopy describes the degradation development. The accelerated oxidative degradation promoted by thermal γ-irradiation treatments revealed that the low concentrations of vinyl-POSS create favorable conditions for hindering the development of the oxidation aging of host polymer. The most stable hybrid of this series contains 6 phr of vinyl-POSS. The addition of vinyl-POSS in the waste EPDM formulations is a proper solution for its reclaiming. The structural aspects related to the contribution of vinyl-POSS to oxidation prevention are discussed.

We develop a facile route to the scalable fabrication of flexible reattachable ionomer nanopatterns (RAINs) by continuous nanoinscribing and low-temperature roll imprinting, which are repeatedly attachable to and detachable from arbitrarily shaped surfaces. First, by sequentially performing continuous nanoinscribing over a polymer substrate along the multiple directions, we readily create the multidimensional nanopattern, which otherwise demands complex nanofabrication. After its transfer to an elastomer pad for use as a soft nanoimprinting stamp, we then conduct a low-temperature roll imprinting of the ionomer film to fabricate a flexible and highly transparent RAIN. Reversible loosening of ionic units in the ionomer material at the mild temperature as low as ∼60-70 °C enables the faithful nanopatterning over thermosensitive organic compounds and fragile materials under a slight pressure. The excellent adhesion purely emerging from ionic interactions uniquely realizes the conformal attachability and clean detachability of RAINs for universal targets in ambient conditions, particularly beneficial for individual wearable and mobile devices requiring the user-specific "on/off" of the nanopattern-driven functionalities. As one vivid example, we demonstrate that a single light-emitting device can be switched from the focused pointer to the widespread flashlight depending on the RAIN application upon user's purpose.

A novel adhesion process called “plasma press” has been investigated for achieving stronger bonding between two different materials. It was first developed to be applied in multilayer flexible printed circuit boards for next generation flexible mobile electronics. The plasma process is a hot pressing method employing plasma between the two materials in order to activate the material surfaces. Compared to the conventional hot-pressed sample, the plasma-pressed sample exhibited up to 130% higher adhesion strength. The stronger bond strength achieved in the plasma-pressed sample is attributed to the formation of active carboxyl functional groups and dangling bonds on the material surfaces by the presence of the plasma during the hot pressing process for bonding.

In this paper, using one-step method of sub-surface initiated atom transfer radical polymerization (SSI-ATRP), the novel polymer brushes accompanied with structured surface were prepared on the resin base. Compared with the traditional surface initiated atom transfer radical polymerization (SI-ATRP) method, either surface chemical composition or topography was obtained through SSI-ATRP synchronously. Besides, we found that the structured polymers brush interface had better stability and long-term synergistic antifouling effect under seawater medium through soaking experiment and ocean field assay for long time. While, the bio-fouling assay results indicated that their excellent antifouling performances would be hindered by salt responsiveness of 3-sulfopropyl methacrylate potassium salt (SPMA) polymer brushes. Because it could be screened by high salt (e.g. Ca2+ or Mg2+) concentration, which decreased the hydration effect and further weakened the antifouling effect. The zwitterionic polymer (sulfobetaine methacrylate, SBMA), however, still showed excellent antifouling performances under high salt concentration since it produced stabilized ionic bonds with water molecules than those created from other hydrophilic materials. Given this, the structured zwitterionic and anionic copolymer brushes were fabricated as well, which realized the ideal stability and long-term antifouling effect under marine environment, ever high salt concentration medium. This research is of great value to marine antifouling in the long run and some other relevant fields.

Competing interface fracture paths in the transfer of 2D materials from their growth substrate to a flexible polymer substrate are examined by developing finite element and semi-analytical beam theory models. With limited data on interface characterization for 2D materials, a parameter space is chosen based on the polyimide-graphene-copper foil system. Cohesive zone models with two different damage initiation criteria are explored. Algebraic equations to predict load, crack length, damage zone length, rotation and mode-mix are extracted through scaling analysis and correlation of the numerical data. Successful transfer of graphene to a polymer substrate is observed to be dependent on relative interface strengths rather than fracture energies.

Purpose Despite almost limitless possibilities of rapid prototyping, the idea of 3D printed fully functional electronic device still has not been fulfilled – the missing point is a highly conductive material suitable for this technique. The purpose of this paper is to present the usage of the photonic curing process for sintering highly conductive paths printed on the polymer substrate. Design/methodology/approach This paper evaluates two photonic curing processes for the conductive network formulation during the additive manufacturing process. Along with the xenon flash sintering for aerosol jet-printed paths, this paper examines rapid infrared sintering for thick-film and direct write techniques. Findings This paper proves that the combination of fused deposition modeling, aerosol jet printing or paste deposition, along with photonic sintering, is suitable to obtain elements with low resistivity of 3,75·10−8 Ωm. Presented outcomes suggest the solution for fabrication of the structural electronics systems for daily-use applications. Originality/value The combination of fused deposition modelling (FDM) and aerosol jet printing or paste deposition used with photonic sintering process can fill the missing point for highly conductive materials for structural electronics.

This work presents decorative TiO2, TiO2/Al layers deposited on poly(methyl methacrylate) (PMMA) substrates. We chose the Gas Injection Magnetron Sputtering (GIMS) technique for layer deposition. Choosing this technique, we expected a lower thermal load of polymer substrate than in other commonly used magnetron techniques. The pulse plasma, generated in the GIMS method, is controlled by a periodical injection of gas dosages in the region of the magnetron target. The process of deposition operated with a 1 Hz frequency of a plasma generation and the life time of plasma was ∼500 ms. Under these conditions, the energetic impact into the substrate, integrated over the time, is lower than during the continuous process, so it should not cause any damage to the polymer surface. For our experiment we deposited a thick ∼700 nm aluminum layer and thin 17–116 nm TiO2 films, which exhibited the interference effect, on non – heated PMMA substrates. The optical properties of the prepared systems were investigated by spectroscopic ellipsometry and spectrophotometric measurements.

In this paper, we report on the fabrication of light and pressure sensors based on the piezo- and pyro-material polyvinylidene fluoride (PVDF). In addition, to the operation as sensors, the presented devices are characterized as energy harvesters. To form an electrical connection to the $39\:\mu \text{m}$ thick PVDF foil, solution-based and transparent electrode (TE) materials, such as silver nanowires (AgNWs) and poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) are utilized and compared with commercial aluminum electrodes on polymer substrate. We show that the performance with regard to sensitivity and generated output power of the TE-PVDF devices outperforms the one for the aluminum foil devices. For the piezo- and pyroelectric effect, a pressure and light sensitivity of 3.6 mV/Pa and 42 Vcm2/W, respectively, are measured. The maximum RMS power for the piezo- and pyro effect yield to 1 and $0.42~\mu \text{W}$ , respectively, for an active PVDF area of 8 cm2. At the end of this contribution, we show that this power suffices to drive an energy autarkic wireless sensor node that is capable of measuring and transmitting an analog sensor signal using ultra-low power components. This application contributes substantially to the notion of the Internet of Things since paramount aspects, such as wireless technology, embedded electronics, and environmental sensor data together with an ultra-low power management are addressed.

Surface-enhanced Raman spectroscopy (SERS) is a promising technique for future high-sensitivity chemical sensors. The main deficiencies that restrict the large-scale application of SERS lie in its high cost, low reproducibility, and poor signal uniformity. In this letter, we report the primary exploration of a facile dip coating – thermal shrinking method to produce gold (Au) nanoparticle decorated flexible polymer substrate for SERS. Briefly, Au nanoparticles dispersed in DI-water were anchored on to a polystyrene film via controlled dip coating, which was followed by a thermal treatment process to shrink the polymer film. We observe a polymer volume shrinking rate of 20% after heating, which results in a particle density increase of more than 10 times. Significant enhancement of Raman signals was observed for the R6G molecules anchored on the shrunk substrate, demonstrating our methodology is feasible, reliable, and promising for future large-scale application of SERS-based chemical sensors.

Purpose Polymer substrates with micron size roughness features have been found to play an important role in the mechanical performance of thin functional films which are used extensively in stretchable and flexible micro electromechanical systems. The purpose of this study is to report the stretchability and flexibility limits of micro size silver nano platelet films on a soft polymer substrate having two different orientations of micro grating with respect to the applied load. Design/methodology/approach Parallel and perpendicular micro gratings on the surface of a soft polymer substrate polydimethylsiloxane were patterned using a carefully machined master aluminum block and thin aluminum foils. Silver nano platelet-based films were rod coated on the substrate surface containing the micro gratings. These films were dried in ambient air and were tested for their stretchability and flexibility limits using homemade tools. Finite element modeling has also been performed and was found to support the experimental observations. Findings Experiments indicate that stretchability of silver nano platelet-based thin films tends to increase when the grating orientation remains parallel to the axis of the applied load, while its flexibility improves when the orientation becomes perpendicular to the loading axis. Originality/value The effect of grating orientation with respect to the applied load was investigated. The experiments show that micro grating roughness features are capable of enhancing the mechanical performance of nano platelet-based silver films on a soft polymer substrate and can be used in various stretchable and flexible micro electro mechanical device applications.

We herein demonstrate a novel concept for the one-pot synthesis of metal–organic framework (MOF) films on a metal ion-doped polymer substrate based on control of the nucleation and growth processes. This strategy allows the ready fabrication of densely-packed uniform MOF films.

A metal grid (MG) incorporated with a polymer substrate is a promising candidate for replacing indium tin oxide in flexible transparent electrodes (TEs). Here, a simple yet highly efficient method of fabricating a new class of flexible MG TEs based on wet chemical aluminum (Al) deposition on a seamless polymer mesh template is proposed. The polymer mesh template is readily fabricated by a single-step selective photo-curing of an ultraviolet-curable resin followed by conformal coating with solution-processed Al. The Al-coated mesh is then embedded in a polymer substrate, maintaining the smoothness of the device surface. The fabricated flexible MG TE exhibits a low sheet resistance of 10.6 ± 0.6 Ω sq−1, high transmittance of 85.6 ± 1.4% at λ = 550 nm, and low haze of 3.2 ± 0.7% at λ = 550 nm. The electrical and optical properties of the device can be balanced by controlling the mesh geometry, with a high figure of merit of ∼220.4 that is comparable to those of next-generation flexible TEs. Moreover, the device is highly reliable and can maintain its excellent performance even after a cyclic tape peeling test (1000 times) and bending tests (1000 times each under tensile and compressive stresses). Based on the excellent optoelectronic performance in conjunction with the mechanical flexibility and stability, the MG TEs are successfully implemented in various flexible devices including transparent film heaters and touch screen panels.

This work describes the fabrication of temperature responsive light reflectors deposited on flexible single substrates, the photonic cholesteric liquid crystal system encapsulated by a protective polymer layer generated by photo-enforced stratification. A bendable orange reflector was fabricated by this single application step. Furthermore, a blue shift of 400 nm of an infrared reflecting cholesteric was demonstrated upon increasing the temperature from room temperature to 100 °C. Such reflectors on flexible substrates could be used for the retrofitting of existing windows to save energy and visible reflectors in clothing or other aesthetically-pleasing applications

We report a facile approach for producing highly omnidirectional and frequency tunable antennas based on multilayer graphene/multi-walled carbon nanotube (MG/MWNTs) electrodes. The MG sheets are obtained by ball milling graphite, followed by sonication. Monopole patch antennas are prepared by screen printing the MG/MWNTs paste onto a polymer substrate. The resulting antennas show excellent performance due to the bridge effect of the MWNTs between well-dispersed adjacent MG layers, which increases the contact area between MG sheets along the horizontal and vertical axes. The antennas formed from the MG/MWNTs exhibit smaller return losses than the antennas formed from pristine graphite, as well as high radiation efficiency (∼44.9%). Moreover, the MG/MWNTs antennas require a relatively small quantity, which leads to low production costs. In addition, the dimensions of the antennas can be simply adjusted by controlling the screen printing mask or cutting with scissors to achieve frequency tunability. These results demonstrate the potential of these MG/MWNTs antennas for applications in wireless communications for ubiquitous sensor networks.

Advances in solution-phase graphene patterning has provided a facile route for rapid, low-cost and scalable manufacturing of electrochemical devices, even on flexible substrates. While graphene possesses advantageous electrochemical properties of high surface area and fast heterogenous charge transport, these properties are attributed to the edge planes and defect sites, not the basal plane. Herein, we demonstrate enhancement of the electroactive nature of patterned solution-phase graphene by increasing the porosity and edge planes through the construction of a multidimensional architecture via salt impregnated inkjet maskless lithography (SIIML) and CO2 laser annealing. Various sized macroscale pores ( 10 000 to ∼50 Ω sq−1). We demonstrate that this multidimensional porous graphene fabrication method can improve electrochemical device performance through design and manufacture of an electrochemical organophosphate biosensor that uses the enzyme acetylcholinesterase for detection. This pesticide biosensor exhibits enhanced sensitivity to acetylthiocholine compared to graphene without macropores (28.3 μA nM−1 to 13.3 μA nM−1) and when inhibited by organophosphate pesticides (paraoxon) has a wide linear range (10 nM to 500 nM), low limit of detection (0.6 nM), and high sensitivity (12.4 nA nM−1). Moreover, this fabrication method is capable of patterning complex geometries [i.e. interdigitated electrodes (IDEs)] even on flexible surfaces as demonstrated by an IDE supercapacitor made of SIIML graphene on a heat sensitive polymer substrate. The supercapacitor demonstrates a high energy density of 0.25 mW h cm−3 at a power density of 0.3 W cm−3. These electrochemical devices demonstrate the benefit of using SIIML and CO2 laser annealing for patterning graphene electrodes with a multidimensional porous surface even on flexible substrates and is therefore a platform technology which could be applied to a variety of different biosensors and other electrochemical devices.

Soft electronic skins (e-skins) with superior sensing performance have attracted significant attention in numerous applications. However, most of the reported e-skins have been prepared based on an inert polymer substrate without completely considering its self-healing ability; this severely limits the practical application of these e-skins. In addition, the fabrication of most of the e-skins is conducted via photolithography and other tedious processes; therefore, it is difficult to equilibrate high sensing performance and preparation simplification. Herein, a simple and general fabrication strategy of self-healable and highly sensitive electrical sensor, consisting of a sensing component, i.e. Au-deposited toothbrush-hair micro-prick arrays, and a substrate component, i.e. a P-TDI-IP elastomer obtained via the block polymerization of polytetramethylene glycol (P), 2,4′-tolylene diisocyanate (TDI), and isophorone diisocyanate (IP), is reported. The self-healable P-TDI-IP elastomer acting as a substrate endows the reported electrical sensor with an excellent self-healing capability (96% with 6 h) and an outstanding stretchability (1200%). Importantly, due to the presence of unique micro-prick arrays, the electrical sensor could detect multiaxial tactile stimuli including pressing and shearing. Moreover, this device exhibited high sensitivities (3.32 kPa−1 for pressing, GF = 2.82 for shearing), the rapid response time of 25 ms, and the low detection limit of 5 Pa. Owing to these prominent properties, the electrical sensor presented anticipated abilities for distinguishing ultrafine surfaces with different roughnesses and monitoring various human motions.

Terahertz metasurfaces based on 3D quasi Ω-elements were proposed and studied experimentally as well as numerically. An original method was developed for shaping new types of metallic 3D micro- and nanostructures by direct imprinting of lithographically structured 2D elements on a polymer substrate. It is shown that the embedding of microstrips into the polymer changes the magnitude of their embedding depth, making it possible to control the optical activity of the metamaterial. In this case, it is possible to achieve rotation of the plane of polarization of the transmitted linearly polarized THz radiation at an angle of more than 50° due to half-wavelength, guided-mode resonances, and diffraction effects. The results obtained pave the way to the development of large-area chiral structures for high-frequency ranges, including infrared and visible.

Funding Information: This work was supported by Business Finland (FEDOC 211637 and FEPOD 2117731 projects) and Aalto ELEC Doctoral School. Publisher Copyright: © Disposable single-use electrochemical sensor strips were used for quantitative detection of small concentrations of morphine in untreated capillary whole blood. Single-walled carbon nanotube (SWCNT) networks were fabricated on a polymer substrate to produce flexible, reproducible sensor strips with integrated reference and counter electrodes, compatible with industrial-scale processes. A thin Nafion coating was used on top of the sensors to enable direct electrochemical detection in whole blood. These sensors were shown to detect clinically relevant concentrations of morphine both in buffer and in whole blood samples. Small 38 μL finger-prick blood samples were spiked with 2 μL of morphine solution of several concentrations and measured without precipitation of proteins or any other further pretreatment. A linear range of 0.5-10 μM was achieved in both matrices and a detection limit of 0.48 μM in buffer. In addition, to demonstrate the applicability of the sensor in a point-of-care device, single-determination measurements were done with capillary samples from three subjects. An average recovery of 60% was found, suggesting that the sensor only measures the free, unbound fraction of the drug. An interference study with other opioids and possible interferents showed the selectivity of the sensor. This study clearly indicates that these Nafion/SWCNT sensor strips show great promise as a point-of-care rapid test for morphine in blood.

Thin spin-coated polymer films of amphiphilic copolymer obtained by partial acetalization of poly (vinyl alcohol) are used as humidity-sensitive media. They are deposited on polymer substrate (PET) in order to obtain a flexible humidity sensor. Pre-metallization of substrate is implemented for increasing the optical contrast of the sensor, thus improving the sensitivity. The morphology of the sensors is studied by surface profiling, while the transparency of the sensor is controlled by transmittance measurements. The sensing behavior is evaluated through monitoring of transmittance values at different levels of relative humidity gradually changing in the range 5–95% and the influence of up to 1000 bending deformations is estimated by determining the hysteresis and sensitivity of the flexible sensor after each set of deformations. The successful development of a flexible sensor for optical monitoring of humidity in a wide humidity range is demonstrated and discussed.

The fabrication of a transparent and flexible ultraviolet photodetector based on hydrothermally grown ZnO nanorods requires an annealing step to render the sol–gel spin-coated ZnO seed layer crystalline. As high-temperature annealing deforms low-melting-point polymer substrates, we herein devised a thermal dissipation annealing (TDA) method in which heat transfer to ZnO thin films is synchronized with heat release from the polymer substrate to crystallize the ZnO seed layer without polymer substrate deformation and melting. ZnO nanorods (NRs) were hydrothermally grown on non-annealed and annealed ZnO seed layers, and NR density and diameter were shown to be higher in the latter case, as the crystallized ZnO seed layer provided heterogeneous nucleation sites for NR growth. In addition, the larger density and diameter of ZnO NRs grown on the annealed ZnO seed layer were confirmed by analysis of O 1s signal intensities. A transparent and flexible UV photodetector based on ZnO NRs grown on the annealed ZnO seed layer exhibited a higher photocurrent/dark current ratio, photosensitivity, and photoresponsivity than that fabricated using a non-annealed seed layer. Taken together, the above results suggest that the TDA method is an effective way of fabricating transparent and flexible UV photodetectors with high photosensitivity, photoresponsivity, and photocurrent stability and it means that the next generation wearable devices can be easily realized by using the TDA method.

Polymer banknotes are the trend for printed currency and have been adopted by more than fifty countries worldwide. However, over the past years, the quantity of polymer counterfeits has been increasing, so has the quality of counterfeits. This shows that the initial advantage of bringing a new polymer technology to fight against counterfeiting is reducing. To maintain one step ahead of counterfeiters, we propose a novel anti-counterfeiting technique called Polymer Substrate Fingerprinting (PSF). Our technique is built based on the observation that the opacity coating, a critical step during the production of polymer notes, is a stochastic manufacturing process, leaving uneven thickness in the coating layer and the random dispersion of impurities from the ink. The imperfections in the coating layer result in random translucent patterns when a polymer banknote is back-lit by a light source. We show these patterns can be reliably captured by a commodity negative-film scanner and processed into a compact fingerprint to uniquely identify each banknote. Using an extensive dataset of 6,200 sample images collected from 340 UK banknotes, we show that our method can reliably authenticate banknotes, and is robust against rough daily handling of banknotes. Furthermore, we show the extracted fingerprints contain around 900 bits of entropy, which makes it extremely scalable to identify every polymer note circulated globally. As compared with previous or existing anti-counterfeiting mechanisms for banknotes, our method has a distinctive advantage: it ensures that even in the extreme case when counterfeiters have procured the same printing equipment and ink as used by a legitimate government, counterfeiting banknotes remains infeasible because of the difficulty to replicate a stochastic manufacturing process., 13 pages, 11 figures, 6 tables. This manuscript has been accepted for publication in IEEE Transactions on Information Forensics & Security in 2021

An important property of high-precision mechanical sensors such as force transducers or torque sensors is the so-called creep error. It is defined as the signal deviation over time at a constant load. Since this signal deviation results in a reduced accuracy of the sensor, it is beneficial to minimize the creep error. Many of these sensors consist of a metallic spring element and strain gauges. In order to realize a sensor with a creep error of almost zero, it is necessary to compensate for the creep behavior of the metallic spring element. This can be achieved by creep adjustment of the used strain gauges. Unlike standard metal foil strain gauges with a gauge factor of 2, a type of strain gauges based on sputter-deposited NiCr-carbon thin films on polymer substrates offers the advantage of an improved gauge factor of about 10. However, for this type of strain gauge, creep adjustment by customary methods is not possible. In order to remedy this disadvantage, a thorough creep analysis is carried out. Five major influences on the creep error of force transducers equipped with NiCr-carbon thin-film strain gauges are examined, namely, the material creep of the metallic spring element (1), the creep (relaxation) of the polymer substrate (2), the composition of the thin film (3), the strain transfer to the thin film (4), and the kind of strain field on the surface of the transducer (5). Consequently, we present two applicable methods for creep adjustment of NiCr-carbon thin- film strain gauges. The first method addresses the intrinsic creep behavior of the thin film by a modification of the film composition. With increasing Cr content (at the expense of Ni, the intrinsic negative creep error can be shifted towards zero. The second method is not based on the thin film itself but rather on a modification of the strain transfer from the polyimide carrier to the thin film. This is achieved by controlled cutting of well-defined deep trenches into the polymer substrate via a picosecond laser.

Printing nano-ink with platinum nanoparticles to generate conductive microstructures for electronics on different types of substrates has gained increasing interest in recent years. To solve the problem of the low conductivity of platinum (Pt) nano-ink, we synthesized chemically pure Pt nanoparticles with sizes of 18.2 ± 9.0 nm by spark discharge method. A low toxic solvent, ethylene glycol with water, was used to ensure the aggregation stability of Pt nanoparticles. Polyvinylpyrrolidone was used as an adhesive additive and binder in the nano-ink. Narrow and conductive Pt lines were generated by aerosol jet printing technology. The resistivity of the Pt lines sintered at 750 °C on alumina substrate was found to exceed the bulk Pt by about 13%. Moreover, the Pt film fabricated on polymer substrates has demonstrated excellent mechanical flexibility in terms of twisting tests.

The need for effective Electro Magnetic Interference (EMI) Shielding became inevitable due to the rise of terahertz range technologies based electronic devices in civil, military and healthcare domains. In this paper we analyzed shielding performances of multilayered textile sheets with flexible polymeric substrate. The analysis considered factors like sensitivity of shielding effectiveness, conductivity of polymer inter-layers, thickness of textiles and frequency range. Many researchers contributed to the problem of EM shielding. The literature revealed that carbon based shielding is not mechanically flexible. Metal based shielding is heavy weight and not easy for tuning performance. Synthetic material with laminated sheets containing textile fabrics and conductive polymers was found a promising solution. Recently Aloia et al. explored shielding performances of flexible multilayer screens based on chemically doped graphene on polymer substrate. However, their research was not considering textiles. Textiles with polymer substrate will have impact in making EM shielding. Therefore further investigation is required to focus on textiles with conductive polymers in making EM shielding. This is the focus of the paper which analyzes various combinations and permutations of textile sheets and polymer substrate. Our mathematical and analytical results revealed that the proposed methodology can help improve decision making on EM shielding effectiveness significantly.

Graphene holds great potential for fabricating ultrathin selective membranes possessing high permeability without compromising selectivity and has attracted intensive interest in developing high-performance separation membranes for desalination, natural gas purification, hemodialysis, distillation, and other gas-liquid separation. However, the scalable and cost-effective synthesis of nanoporous graphene membranes, especially designing a method to produce an appropriate porous polymer substrate, remains very challenging. Here, we report a facile route to fabricate decimeter-scale (∼15 × 10 cm2) nanoporous atomically thin membranes (NATMs) via the direct casting of the porous polymer substrate onto graphene, which was produced by chemical vapor deposition (CVD). After the vapor-induced phase-inversion process under proper experimental conditions (60 °C and 60% humidity), the flexible nanoporous polymer substrate was formed. The resultant skin-free polymer substrate, which had the proper pore size and a uniform spongelike structure, provided enough mechanical support without reducing the permeance of the NATMs. It was demonstrated that after creating nanopores by the O2 plasma treatment, the NATMs were salt-resistant and simultaneously showed 3-5 times higher gas (CO2) permeance than the state-of-the-art commercial polymeric membranes. Therefore, our work provides guidance for the technological developments of graphene-based membranes and bridges the gap between the laboratory-scale "proof-of-concept" and the practical applications of NATMs in the industry.

In this study, a new cost-effective and high-precision process chain for the fabrication of large-scale diffractive lens arrays on chalcogenide glass is proposed. First, a positive diffractive lens array is fabricated on a PMMA master substrate by employing a step-and-repeat hot imprinting process. The direct hot imprinting can transfer the microstructures from a heated mold to the polymer substrate accurately. Repeating the hot imprinting process according to a predetermined path, the desired diffractive lens array is obtained. Unlike photolithography and electron-beam writing, which are expensive technologies with sophisticated process, the hot imprinting is an easier, cheaper and more eco-friendly method for fabricating diffractive features with continuous profile. Afterwards a casting process is applied to create a PDMS mold with the negative features. The diffractive lens array with continuous profile is successfully transferred from the master substrate to the PDMS elastomer, which is used as a mold for subsequent precision glass molding. Finally, the microstructures of PDMS mold are replicated to the chalcogenide glass by non-isothermal glass molding. In this process, the mold and workpiece are set at different temperatures. The PDMS mold at low temperature maintains enough rigidity, so as to press the features into the softened chalcogenide glass more easily, which is at relatively higher temperature, resulting in a positive high-fidelity diffractive lens array on the chalcogenide glass. Surface profiles and optical performance of the fabricated components are characterized quantitatively. Results showed that large-scale diffractive lens array with continuous profile can be successfully fabricated on Chalcogenide glass by this proposed process chain with high quality and integrity.

Neural regeneration after lesions is still limited by several factors and new technologies are developed to address this issue. Here, we present and test in animal models a new regenerative nerve cuff electrode (RnCE). It is based on a novel low-cost fabrication strategy, called “Print and Shrink”, which combines the inkjet printing of a conducting polymer with a heat-shrinkable polymer substrate for the development of a bioelectronic interface. This method allows to produce miniaturized regenerative cuff electrodes without the use of cleanroom facilities and vacuum based deposition methods, thus highly reducing the production costs. To fully proof the electrodes performance in vivo we assessed functional recovery and adequacy to support axonal regeneration after section of rat sciatic nerves and repair with RnCE. We investigated the possibility to stimulate the nerve to activate different muscles, both in acute and chronic scenarios. Three months after implantation, RnCEs were able to stimulate regenerated motor axons and induce a muscular response. The capability to produce fully-transparent nerve interfaces provided with polymeric microelectrodes through a cost-effective manufacturing process is an unexplored approach in neuroprosthesis field. Our findings pave the way to the development of new and more usable technologies for nerve regeneration and neuromodulation.

Polymer toughness is preserved at chronic timepoints in a new class of modulus-changing bioelectronics, which hold promise for commercial chronic implant components such as spinal cord stimulation leads. The underlying ester-free chemical network of the polymer substrate enables device rigidity during implantation, soft, compliant, conforming structures during acute phases in vivo, and gradual stabilization of materials properties chronically, maintaining materials toughness as device stiffness changes. In the past, bioelectronics device designs generally avoided modulus-changing and materials due to the difficulty in demonstrating consistent, predictable performance over time in the body. Here, the acute, and chronic mechanical and chemical properties of a new class of ester-free bioelectronic substrates are described and characterized via accelerated aging at elevated temperatures, with an assessment of their underlying cytotoxicity. Furthermore, spinal cord stimulation leads consisting of photolithographically-defined gold traces and titanium nitride (TiN) electrodes are fabricated on ester-free polymer substrates. Electrochemical properties of the fabricated devices are determined in vitro before implantation in the cervical spinal cord of rat models and subsequent quantification of device stimulation capabilities. Preliminary in vivo evidence demonstrates that this new generation of ester-free, softening bioelectronics holds promise to realize stable, scalable, chronically viable components for bioelectronic medicines of the future.

This study reports on the fabrication of biocompatible organic devices by means of inkjet printing with a novel combination of materials. The devices were fabricated on Parylene C (PaC), a biocompatible and flexible polymer substrate. The contact tracks were inkjet-printed using a silver nanoparticle ink, while the active sites were inkjet-printed using a poly (3,4ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) solution. To insulate the final device, a polyimide ink was used to print a thick film, leaving small open windows upon the active sites. Electrical characterization of the final device revealed conductivities in the order of 103 and 102 S.cm−1 for Ag and PEDOT based inks, respectively. Cell adhesion assays performed with PC-12 cells after 96 h of culture, and B16F10 cells after 24 h of culture, demonstrated that the cells adhered on top of the inks and cell differentiation occurred, which indicates Polyimide and PEDOT:PSS inks are non-toxic to these cells. The results indicate that PaC, along with its surface-treated variants, is a potentially useful material for fabricating cell-based microdevices.