Polyethylene Terephthalate Substrate Research Articles

MXene/Bacterial Cellulose Hybrid Materials for Sustainable Soft Electronics

This work evaluated bacterial cellulose (BC) as a possible biodegradable soft electronics substrate in comparison to polyethylene terephthalate (PET), while also focusing on evaluating hybrid MXene/BC material as potential flexible electronic sensor. Material characterization studies revealed that the BC material structure consists of nanofibers with diameters ranging from 70 to 140 nm, stacked layer-by-layer. BC samples produced are sensitive to post-treatment with isopropanol resulting in a change of structural and mechanical properties. The viscoelastic properties of the BC substrates have been studied experimentally in comparison with the PET film. Aged BC substrate showcased similar viscoelastic properties stability, while exhibiting better properties above 70 °C, with total storage modulus change of −15% and loss modulus change of 21%. MXenes prepared using the Minimally Intensive Layer Delamination (MILD) method were screen-printed onto BC substrates and PET films to form MXene/BC (MX/BC) and MXene/PET (MX/PET) devices. The electrical properties results showcased different resistive behavior on both BC and PET substrate samples with different impedance moduli. MX/PET presented lower sheet resistance of around 156 Ω·sq−1, while MX/BC was 2733 Ω·sq−1. Finally, the MX/BC and MX/PET devices were subjected to repeatable quasi-static load tests and the piezoresistive sensing behavior of the devices has been reported.

Stress-induced artificial neuron spiking in diffusive memristors

Diffusive memristors owing to their ability to produce current spiking when a constant or slowly changing voltage is applied are competitive candidates for development of artificial electronic neurons. These artificial neurons can be integrated into various prospective autonomous and robotic systems as sensors, e.g. ones implementing object grasping and classification. We report here Ag nanoparticle-based diffusive memristor prepared on a flexible polyethylene terephthalate substrate in which the electric spiking behaviour was induced by the electric voltage under an additional stimulus of external mechanical impact. By changing the magnitude and frequency of the mechanical impact, we are able to manipulate the spiking response of our artificial neuron. This functionality to control the spiking characteristics paves a pathway for the development of touch-perception sensors that can convert local pressure into electrical spikes for further processing in neural networks. We have proposed a mathematical model which captures the operation principle of the fabricated memristive sensors and qualitatively describes the measured spiking behaviour. Employing such flexible diffusive memristors that can directly translate tactile information into spikes, similar to force and pressure sensors, could offer substantial benefits for various applications in robotics.

Crack Development and Electrical Degradation in Chromium Thin Films Under Tensile Stress on PET Substrates

The mechanical and electrical deterioration of chromium (Cr) thin films sputtered onto polyethylene terephthalate (PET) substrates under tensile strain was studied. Understanding mechanical and electrical stability due to imposed strain is particularly important for device reliability, as the demand for flexible electronic devices increases. Cr thin films, widely spread across the field of electronic and sensor applications, face crack propagation with electrical degradation with tensile stress that can seriously compromise the performance. Accordingly, this study offers new findings on how Cr film thickness might influence crack formation and electrical resistance differently and also the general guidelines for flexible electronic component design with respect to long-term durability. Electrical resistances were measured while mechanically stretching 100- and 200 nm thin sheets. The study focused on crack development and propagation mechanisms in both film thicknesses and their effects on percentage change in electrical resistance (PCER). Scanning electronic microscopy (SEM) was used to characterize surface morphology and observe cracks as the strain rose. Early crack formation in 100 nm Cr films led to rapid PCER increases due to quick crack propagation and fast electrical degradation. Thicker 200 nm films, however, showed a more gradual PCER rise with fewer but deeper cracks, indicating a regulated strain response. Unlike the sharp PCER spike in 100 nm films, 200 nm samples were more variable, with three out of four showing a slight PCER decrease at the end, hinting at partial crack repair or conductive realignment before full failure. These results underscore the role of layer thickness in managing crack propagation and electrical stability, relevant for flexible electronics and strain sensors. This paper is aligned with the ninth goal of the United Nations Sustainable Development Goals, specifically Target 9.5: Enhance Research and Upgrade Industrial Technologies.

Optical and stress properties of ZrO2/SiO2 and TiO2/SiO2 anti-reflective coatings deposited by ion-beam-assisted deposition on a flexible substrate

Dielectric films of ZrO2,TiO2, and SiO2 were deposited on flexible polycarbonate (PC) and polyethylene terephthalate (PET) substrates by using ion-beam-assisted deposition (IBAD). Each layer had a thickness ranging from 30 to 210 nm. The optical and anisotropic stress properties were investigated. Two anti-reflective coatings (ARCs), ZrO2/SiO2 and TiO2/SiO2, were selected and deposited on the PET flexible substrate. The anisotropic stresses of the single layer and ARCs were measured using a phase-shifting moiré interferometer. Experimental results showed that the optimal oxygen flow rates for the ZrO2,TiO2, and SiO2 films deposited with IBAD were 10, 10, and 15 sccm, respectively. The refractive index (n) was TiO2(2.37)>ZrO2(2.05)>SiO2(1.46), and the extinction coefficient (k) for all samples was below 10−3. The thermal expansion coefficient of the PC substrate was three times that of the PET substrate, and the high-refraction ZrO2 and TiO2 single-layer films presented cracks and distortions on the PC substrate. Only the low-refractive-index SiO2 sample did not present cracks. The three dielectric films did not crack or distort when deposited on the PET substrate. The anisotropic stress analysis provided the maximum principal and shear stresses for the three dielectric films on the PET substrate. Therefore, the maximum principal stress of the 210 nm single-layer film on a PET substrate is TiO2>ZrO2>SiO2. It was also discovered that the principal stress of the AR multilayer film is significantly decreased due to the damping stacking effect (DSE) of the high- and low-refractive-index materials, ZrO2/SiO2 ARC (−297.3MPa)>TiO2/SiO2ARC(−132.6MPa). Thus, the high packing density of TiO2 gives a better DSE than ZrO2.

Structure and Properties of Thin Films Prepared on Flexible Substrates from SnCl4-Derived Solutions

Thin transparent films of SnO2 were obtained from aqueous–alcohol solutions of SnCl4 on a flexible polyethylene terephthalate (PET) substrate by spray pyrolysis at 100 °C. The influence of the addition of aqueous ammonia to the film-forming solution on the different properties has been studied. Properties studied include surface morphology, phase composition and transparency of the formed films and the crystallization processes and band gap of the film material. It was found that the addition of aqueous ammonia causes the formation of skeletal crystals (NH4)2[SnCl6] with a perovskite structure in the film structure. The resulting films are promising for use in the technology of manufacturing flexible solar cells.

Fabrication and electrical properties of flexible polymer-based MIM capacitors of high-k nanolaminate dielectrics of HfO2–SnO2–TiO2 with ultrathin Al2O3 insertion layer by plasma-enhanced atomic layer deposition

Abstract Flexible metal–insulator–metal (MIM) capacitors of high-k nanolaminate HfO2–SnO2–TiO2 thin films were fabricated on several polymer substrates of polyethylene terephthalate, polyimide and epoxy resin at 80 °C by plasma-enhanced atomic layer deposition. The electrical properties were optimized by adjusting the sub-cycle ratio of Hf: Sn: Ti to 6: 5: 4. In order to reduce the leakage current density of flexible capacitors, the ultrathin Al2O3 layer varying from 0.5 to 1.5 nm was inserted to form Al2O3/HfO2–SnO2–TiO2/Al2O3 stacking capacitors. The effect of the Al2O3 insertion layer thickness and the super-cycle number of HfO2–SnO2–TiO2 on the capacitance density, leakage, and quadratic voltage linearity was investigated. Under optimal processing, flexible MIM capacitors could stand 40 000 bending cycles at curvature radius of 8.2 mm, indicative of better electrical stability. Moreover, compared with the polymer-based HfO2–SnO2–TiO2 capacitors, the introduction of 1 nm Al2O3 ultrathin layer greatly decreases the leakage current density by 4 orders of magnitude (10−8 A cm−2) with relative lower voltage linearity (350–540 ppm V−2), but the capacitance density also declines (∼3 fF μm−2) simultaneously. Despite this, the method of inserting Al2O3 ultra-thin layer is still an effective method to improve the electrical performances of polymer-based HfO2–SnO2–TiO2 nanolaminate capacitors for flexible electronics.

Low-temperature growth of CuS thin film on flexible substrates for photodetection

Abstract The covellite phase of copper sulfide thin film (CuS), owing to its excellent electronic, optical, and chemical properties, has attracted enormous attention in cutting-edge research. This research work emphasizes a comprehensive study of structural, optical, morphological, and electrical properties of CuS thin film deposited by chemical bath deposition (CBD) technique on flexible polyethylene terephthalate (PET) substrate at different deposition temperatures, i. e. 25 °C, 40 °C, 55 °C, and 70 °C for fabrication of flexible photodetector. XRD and Raman studies depict presence of hexagonal covellite phase (CuS), where as the RMS roughness of CuS thin film increases with a rise in deposition temperature. The optical bandgap of CuS thin film gets reduced with a rise in deposition temperature. The optimized CuS thin film, deposited at 70 °C, has exhibited a homogeneous surface with RMS roughness of 13.72 nm, mobility of 25.09 cm2/Vs, and bandgap of 1.86 eV. The mobility of CuS thin film is found to be increased with the rise in deposition temperature. The flexible CuS photodetector, deposited at 70 °C, has shown better photoresponse characteristics, exhibiting the highest responsivity of 0.18 mA/W, detectivity of 1.39×108 Jones, and sensitivity of 173.25 % upon light illumination. The photocurrent established possesses an outstanding dependence on various intensities of illuminated light. Furthermore, the bending test of flexible CuS photodetectors reveals the absence of any sign of deterioration up to a bending angle of 30°. The CuS thin film-based photodetector device exhibits the optimized photodetector device with reproducibility and steady photoresponse after bending. This suggests that the Al/CuS-PET/Al photodetector device could be used in various wearable optoelectronic device applications.

Flexible PET/Carbon/NiFe‐LDH Electrode for Oxygen Evolution Reaction in Water‐Splitting

AbstractThe development of low‐cost, readily scalable catalytic systems for green hydrogen production is crucial for diverse research and industrial applications. This work demonstrates the facile coupling of carbon/NiFe‐layered double hydroxide (LDH) onto flexible polyethylene terephthalate (PET) substrates deposited by blade coating and spray coating techniques. These low‐temperature solution processes enable high‐throughput electrode fabrication. The resulting carbon electrode exhibits sheet resistance of 25 Ω sq−1, comparable to other state‐of‐the‐art works, and displays excellent adhesion to the substrate and catalyst layer, thereby ensuring system stability. Remarkably, the developed electrode exhibits high catalytic activity for the oxygen evolution reaction (OER), achieving an overpotential of 215.9 and 267.4 mV at 10 mA cm−2 in rigid and flexible substrates respectively, and maintaining its performance even at 10 mA cm−2 for 24 h. This work highlights the potential of this methodology for producing readily transportable, flexible electrocatalytic systems with exceptional performance and minimal surface treatment of the substrate. Additionally, the use of low‐cost, readily recyclable PET plastic aligns with the principles of circular economy, promoting the integration of this platform into both research and industrial environments.

Structural, Morphological, and Optoelectronic Properties of RF Sputtered AZO Thin Films on Glass and Polymer Substrates: A Comparative Study

This paper investigates the thickness-dependent structural, morphological, and optoelectronic properties of Al-doped ZnO (AZO) thin films deposited on glass and flexible polyethylene terephthalate (PET) substrates via confocal magnetron sputtering. The film’s thickness ranged from 50 to 130 nm. X-ray diffraction results show that all AZO films on glass have better structural properties than those on PET. Furthermore, the (002) peak intensity and crystallite size on both substrates improved progressively with thickness. Field emission scanning electron microscopy and atomic force microscopy images revealed that the film morphology and surface roughness are dependent on substrate and thickness. According to the UV–vis-NIR measurement results, the air-referenced transmittance spectra of films on PET were slightly lower than those on glass; however, compared to films on glass, the substrate-referenced transmittance of PET films was higher. Moreover, for both substrates, it is found that the bandgap of fabricated thin films decreases with thickness. Photoluminescence spectra show that for glass and PET substrates, the total luminescence of AZO decreases with increasing film thickness and that green and red emissions are absent from AZO films deposited on PET substrates. AZO films deposited on glass substrates exhibit superior electrical and optoelectronic characteristics.

Enhancing the Efficiency of Flexible, Large-Area, ITO-Free Organic Photovoltaic Devices.

The development of flexible ITO-free devices is crucial for the industrial advancement of organic photovoltaic (OPV) technology. Here, a novel ITO-free device architecture is proposed, and ITO-free OPV devices are realized on glass substrates with performance comparable to that of ITO-based devices. It is also demonstrated that the performance of ITO-free devices on polyethylene terephthalate (PET) substrates is limited due to the higher surface roughness of PET, leading to high voltage losses, low device quantum efficiency, and high device leakage current. To address the issue of high roughness on the PET surface, a polyimide (PI) modification strategy is developed and the PI-modified PET is employed as the substrate to construct flexible ITO-free OPV devices and large-area modules with an active area of up to 16.5cm2. This approach leads to decreased trap-assisted recombination losses, enhanced exciton dissociation efficiency, and a reduced density of pinholes in flexible OPV devices, resulting in improved photovoltaic performance under both strong and weak illumination conditions. The outcomes of this work are expected to advance the industrial development of flexible organic photovoltaic technology.

Substrate functionalization by cold plasma treatments as an alternative process to the cultivation of microalgae in biofilm: Application to Botryococcus

Microalgae are renowned for their diverse production of molecules, including biofuels. However, biotechnological processes aiming at producing these biomolecules have yet to achieve economic sustainability due to the high costs associated with downstream processing, which can make up to 80 % of the total production costs. Since microalgae immobilized on a flat surface are characterized by a higher productivity and an easier harvesting than bulk culture systems, flat cultures may present better economic viability. Nevertheless, immobilizing filamentous or colonial microalgae on a flat surface is challenging due to their inherent 3D development. In this study, we explored the effectiveness of a plasma-modified polyethylene terephthalate flat surface for improving the immobilization of the green freshwater colonial microalga Botryococcus protuberans, a promising taxon for biofuel production. Plasma treatments were found to alter the wettability and surface energy of polyethylene terephthalate substrates. Botryococcus adhesion was enhanced significantly on O2 plasma-modified substrates compared to untreated substrates. The adhesion was strong enough to prevent colony development in the water column while allowing the development of a biofilm over one month, with minimal impact on their physiology.

Active and passive infrared emittance tuning using optically transparent unpatterned ITO thin films

Tailoring of thermal emittance has applications in smart radiators, camouflage, infrared (IR) scene generation, stealth, and thermal management. Various studies have explored avenues to achieve both passive and active emittance tuning using methods such as meta-surfaces, phase change materials, composites, nanostructure arrays and multi-layer stacks. Most of these methods often involve complex fabrication processes like multilayer depositions and micro/nano patterning, limiting their scalability for large-scale applications. This study presents a straightforward and scalable approach for passive and active emittance tuning using Indium Tin Oxide (ITO) films deposited on a high emissivity flexible polyethylene terephthalate (PET) substrate. By changing the deposition time, the thickness of the ITO film is controlled which changes the observed emissivity of the ITO/PET composite structure over a wide range (0.2–0.94) while maintaining optical transparency. Using this approach for passive emittance tuning, we demonstrate an IR scene generation application. As the ITO film is conducting, by applying voltage to the ITO/PET sheet, its temperature is changed using which active emittance tuning is also achieved. Compared to existing methods of emittance tuning, the presented approach is simpler, gives flexible films with optical transparency, and has the potential for large-scale integration, enabling cost-effective and scalable manufacturing of emittance-tuned surfaces.

Flexible screen-printed supercapacitors with asymmetric PANI/CDC–AC electrodes and aqueous electrolyte

Abstract We report the fabrication and electrical performance of screen-printed flexible supercapacitors based on activated carbon (AC) and polyaniline (PANI)/carbide-derived carbon (CDC) composite electrodes, and neutral aqueous electrolytes. The devices are entirely constructed from safe, low-cost, and non-toxic materials, fabricated through a mass production capable screen printing process, and fully disposable with normal household waste. Symmetric and asymmetric cells with a thin planar face-to-face structure were fabricated on polyethylene terephthalate (PET) substrate, using eco-friendly chitosan binder based electrode inks, and printed graphite current collectors. The asymmetric cell configuration, with a PANI/CDC positive electrode and an AC negative electrode, demonstrated significantly improved electrochemical performance, through increased operating voltage, energy density and power density, improved cyclic stability and rate capability, and decreased equivalent series resistance (ESR) and leakage current, compared to previously reported symmetric PANI/CDC supercapacitors. The fabricated asymmetric devices had an average capacitance of 250–270 mF, ESR of 20–23 Ω, and leakage current of 140–150 µA, depending on the PANI/CDC variant used. Energy densities of 4.8 Wh kg-1 and 4.9 Wh kg-1, power densities of 1.6 kW kg-1 and 1.5 kW kg-1, and capacitance retention rates of 93 % and 97 % after 2,000 charge-discharge cycles, were achieved with PANI/CDC (10:1) and (30:1) variants, respectively.

Unraveling the Interplay between Stability and Flexibility in the Design of Polyethylene Terephthalate (PET) Hydrolases.

The accumulation of polyethylene terephthalate (PET), a widely used polyester plastic in packaging and textiles, has led to a global environmental crisis. Biodegradation presents a promising strategy for PET recycling, with PET hydrolases (PETase) undertaking the task at the molecular level. Unfortunately, PETase operates only at ambient temperatures with low efficiency, limiting its industrial application. Current engineering efforts focus on enhancing the thermostability of PETase, but increased stability can reduce the structural dynamics needed for substrate binding, potentially slowing enzymatic activity. To elucidate the balance between stability and flexibility in optimizing PETase catalytic activity, we performed theoretical investigations on both wild-type PETase (WT-PETase) and a thermophilic variant (Thermo-PETase) using molecular dynamics simulations and frustration analysis. Despite being initially designed to stabilize the native structure of the enzyme, our findings reveal that Thermo-PETase exhibits an unprecedented increase in structural flexibility at the PET-binding and catalytic sites, beneficial for substrate recruitment and product release, compared to WT-PETase. Upon PET binding, we observed that the structural dynamics of Thermo-PETase is largely quenched, favoring the proximity between the catalytic residues and the carbonyl of the PET substrate. This may potentially contribute to a higher probability of a catalytic reaction occurring in Thermo-PETase compared to WT-PETase. We suggest that Thermo-PETase can exhibit higher PET-degradation performance than WT-PETase across a broad temperature range by leveraging stability and flexibility at high and low temperatures, respectively. Our findings provide valuable insights into how PETase optimizes its enzymatic performance by balancing stability and flexibility, which may contribute to future PETase design strategies.

Research on FBG curvature sensor based on PET substrate and silicone package

To address the low repeatability and accuracy in single package form and lack of strain transfer theory analysis in composite material form of fiber Bragg grating (FBG) curvature sensors, a flexible curvature sensing test scheme for FBG based on polyethylene terephthalate (PET) substrate and silicone package is proposed. Firstly, the factors affecting the strain response of the FBG are obtained through the analysis of the multilayer strain transfer theory, and the relationship between different material encapsulation forms and the strain response of the FBG is explored through finite element simulation. Secondly, the FBG curvature sensor with optimized simulation parameters is fabricated in package, and the curvature calibration verification experiments are performed on the sensor. Finally, the experimental results show that the deviation index of the FBG curvature sensor is between −1.89 % and 1.62 %, which indicates a better repeatability consistency. Based on the computation, the maximum sensitivity of the FBG curvature sensor is 13.32 µε/m−1 when the spacing between the fiber and the substrate layer is 2.50 mm, and its error is 0.30 % comparing with the simulation of the same condition, which supports the accuracy of the theoretical analysis and simulation of the multilayer strain transfer of the encapsulated FBG sensor conducted in this paper, meanwhile, the optimal encapsulation process of the FBG curvature sensor is obtained.

Flexible Single-Crystal Perovskite Photodetectors via Polymer-Controlled Transfer.

The large-sized perovskite single-crystal sheet (SCS) serves as the ideal research platform for perovskite photodetectors due to its outstanding carrier photophysics, pronounced geometric aspect ratio, and ultrahigh material utilization rate. However, its performance in flexible device applications is relatively lackluster due to the rigid and brittle nature of the three-dimensional cubic lattices. In this work, the indium tin oxide (ITO)-based multimillimeter-sized MAPbBr3 SCS is transformed into MAPbI3 SCS via ion exchange strategy. Significantly, we proposed and implemented a polymer-controlled transfer strategy─utilizing the dichloromethane (DCM) solution of poly(methyl methacrylate) (PMMA)─to nondestructively transfer the whole perovskite SCS off the ITO substrates and subsequently adhere it onto a flexible polyethylene terephthalate (PET) substrate of interdigital electrode, thereby fabricating a lateral-structured photodetector with a PMMA-SCS-Au-PET multilayer configuration. The tight self-encapsulation between the top PMMA membrane and the bottom PET substrate imparts excellent waterproof stability and concurrently excellent mechanical flexibility to these devices; additionally, the MAPbI3 device exhibits comprehensively superior performance to the MAPbBr3 one. This work represents a proactive attempt and exploration of the high-performance advancement of large-sized SCS photodetectors, undoubtedly introducing novel momentum and solutions to this domain.

Flexible hybrid nanostructured chemiresistive sensing platform for low-temperature trace hydrogen detection

The prevalence of hydrogen (H2) utilization across commercial and industrial sectors has spurred the innovation of various H2 gas sensors. However, their practical implementation has been hindered by issues such as cost inefficiency, low sensitivity, inadequate selectivity, and limitations in low-temperature sensing capabilities. Consequently, the development of a sensor capable of surmounting these challenges is paramount for widespread adoption. In this study, a cost-effective approach has been used to fabricate a flexible hybrid nanostructured platform on polyethylene terephthalate (PET) substrate incorporating a combination of zinc oxide (ZnO), titanium oxide (TiO2), and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). This platform has undergone meticulous morphological characterization and comprehensive evaluation for H2 gas sensing applications at both room temperature and 50˚C. The results reveal that the developed PEDOT:PSS/TiO2/ZnO NWs sensor exhibits superior H2 gas sensing characteristics with 141 % and 163 % higher response by proportions at 100 ppb and 100 ppm, respectively outperforming other prepared devices in the same environment. Thus demonstrating exceptional sensitivity of 0.448 %/ppm with three cycle repeatability, H2 selectivity and nine months of stability at low temperatures. Moreover, the sensor has an ultralow limit of detection (LOD) of ∼9 ppt, along with a rapid response time of 65 s and a recovery time of 42 s at an H2 concentration of 100 ppb. This research drives the advancement of efficient, rapid-responsive, and discerning trace detection of H2 gas at low temperatures.

Fast Responsive and Highly Sensitive Ethanol Gas Sensors Designed by Agar‐Laponite Hybrid Hydrogels

AbstractLaponite, a synthetic nanosilicate clay and agar, a natural polysaccharide, both imbibe large amount of water and form into hydrogels. Various physical and chemical stimuli elicit the hydrogel response, which has been applied in designing diverse sensors and biomedical systems. In this work, we exploit the change in hydrogel's ionic conductivity due to volatile organic compounds (VOCs) (e. g. ethanol) interaction with the surfaces of Laponite‐Agar hybrid hydrogel films. Gas sensing studies are carried out on silicon (Si) and flexible polyethylene terephthalate (PET) substrates by monitoring the resistance changes. Pristine Laponite hydrogel has shown increase in resistance as it interacted with the ethanol, whereas pure agar and Laponite‐Agar have shown decrease in resistance. Moreover, Laponite‐Agar gel films have exhibited high sensitivity, fast response (4 s) and recovery time (15 s) with lowest detection limit of 6 ppm. Selectivity test carried shows high ethanol sensing response and exhibited very good reproducibility. Observed responses and sensing mechanism are discussed based on changes in ionic conduction resulted due to interacting ethanol with the gel surface network structure. Present study paves the way for understanding and designing low cost, soft and flexible hydrogel gas sensors.

Niobium Oxide Thin Films Grown on Flexible ITO-Coated PET Substrates

Niobium oxide thin films were grown on both rigid and flexible substrates using DC magnetron sputtering for electrochromic applications. Three experimental series were conducted, varying the oxygen to argon flow rate ratio and deposition time. In the first series, the oxygen to argon ratio was adjusted from 0 to 0.32 while maintaining a constant growth time of 30 min. For the second and third series, the oxygen to argon ratios were fixed at 0.40 and 0.56, respectively, with deposition times ranging from 15 to 60 min. A structural transition from crystalline to amorphous was observed at an oxygen to argon flow rate ratio of 0.32. This transition coincided with a change in appearance, from non-transparent with metallic-like electrical conductivity to transparent with dielectric behavior. The transparent niobium oxide films exhibited thicknesses between 51 nm and 198 nm, with a compact, dense, and featureless morphology, as evidenced by both top-view and cross-sectional images. Films deposited on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates displayed a maximum surface roughness (Sq) of 9 nm and a maximum optical transmission of 83% in the visible range. The electrochromic response of niobium oxide thin films on ITO-coated PET substrates demonstrated a maximum coloration efficiency of 30 cm2 C−1 and a reversibility of 96%. Mechanical performance was assessed through bending tests. The ITO-coated PET substrate exhibited a critical bending radius of 6.5 mm. Upon the addition of the niobium oxide layer, this decreased to 5 mm. Electrical resistance measurements indicated that the niobium oxide film mitigated rapid mechanical degradation of the underlying ITO electrode beyond the critical bending radius.

Measuring PETase enzyme kinetics by single-molecule microscopy

Polyethylene terephthalate (PET) is one of the most widely produced man-made polymers and is a significant contributor to microplastics pollution. The environmental and human health impacts of microplastics pollution have motivated a concerted effort to develop microbe- and enzyme-based strategies to degrade PET and similar plastics. A PETase derived from the bacteria Ideonella sakaiensis was previously shown to enzymatically degrade PET, triggering multidisciplinary efforts to improve the robustness and activity of this and other PETases. However, because these enzymes only erode the surface of the insoluble PET substrate, it is difficult to measure standard kinetic parameters, such as kon, koff, and kcat, complicating interpretation of the activity of mutants using traditional enzyme kinetics frameworks. To address this challenge, we developed a single-molecule microscopy assay that quantifies the landing rate and binding duration of quantum dot-labeled PETase enzymes interacting with a surface-immobilized PET film. Wild-type PETase binding durations were well fit by a biexponential with a fast population having a 2.7 s time constant, interpreted as active binding events, and a slow population interpreted as nonspecific binding interactions that last tens of seconds. A previously described hyperactive mutant, S238F/W159H had both a faster apparent on-rate and a slower off-rate than wild-type PETase, potentially explaining its enhanced activity. Because this single-molecule approach provides a more detailed mechanistic picture of PETase enzymatic activity than standard bulk assays, it should aid future efforts to engineer more robust and active PETases to combat global microplastics pollution.