Polyethylene Naphthalate Substrates Research Articles

Mechanical Flexibility and Electrical Reliability of ZnO-Al Thin Films on Polymer Substrates Under Different External Deformation

Abstract Aluminum-doped zinc oxide (AZO) films have emerged as promising transparent electrodes for various optoelectronic applications due to their superior transparency, electrical conductivity, and cost-effectiveness compared to indium tin oxide (ITO). Despite their widespread use, investigations into the electromechanical properties of AZO films, especially under various mechanical deformations, remain limited. This study employs RF magnetron sputtering to deposit AZO films on polyethylene naphthalate (PEN) substrates and explores their mechanical behavior through uniaxial tensile fragmentation and bending tests, coupled with in-situ optical microscopy. Changes in electrical resistance of AZO films were monitored in situ during deformation. Fatigue behavior was examined to further understand mechanical failure, and SEM was used for surface characterization. A critical strain of about 3.1 percent was detected during uniaxial tensile testing, marking the onset of cracks in AZO-coated PEN. In contrast to thicker films, thinner films demonstrated improved stretchability beyond the initiation of crack onset strain. Tension and compression bending tests revealed that the material has excellent bendability, as shown by its critical radii of 5.4 mm and 3.9 mm, respectively. The bending reliability of AZO films under compression was found to be superior than that under tension. Bending fatigue experiments demonstrated that AZO films could withstand cyclic stress without experiencing no ticeable cracks after 100 cycles and with very minor resistance change. This study contributes to the creation of more reliable and optimized flexible optoelectronic devices by giving substantial quantitative data on the performance of AZO films when exposed to mechanical stress.

LIPSS pattern induced by polymer surface instability for myoblast cell guidance

The presented study highlights the efficiency of employing a KrF excimer laser to create diverse types of periodic nanostructures (LIPSS – laser induced periodic surface structures) on polyether ether ketone (PEEK) and polyethylene naphthalate (PEN) substrates. LIPSS structures are very important both in tissue engineering and find also strong application in the field of sensor construction, and SERS analysis. By exposing the polymer films below their ablation threshold to laser fluence ranging from 4 to 16 mJ·cm−2 at 6,000 pulses, we studied both single-phase exposure at beam incidence angles of 0° and 45°, and two-phase exposure. Atomic force microscopy analysis revealed that the laser-treated samples contained distinctive periodic patterns such as waves, globules, and pod-like structures each exhibiting unique surface roughness. Moreover, using analytical methods like EDS and XPS shed light on the changes in the atomic composition, specifically focusing on the C and O elements, as a result of laser exposure. Notably, in almost all cases, we observed an increase in oxygen percentage on the sample surfaces. This increase not only led to a decrease in the contact angle with water but also lowered the zeta potential value, thus showing that the modified samples have enhanced hydrophilicity of the surface and altered electrostatic properties. Last but not least, the samples were assessed for biocompatibility; we studied the interaction of the prepared replicates with mouse myoblasts (C2C12). The impact of globular/dot structures on the cell growth in comparison to pristine or linear LIPSS-patterned surfaces was determined. The linear pattern (LIPSS) induced the myoblast cell alignment along the pattern direction, while dot/globular pattern even enhanced the cytocompatibility compared to LIPSS samples. Through this comprehensive analysis, the research underscores the multifaceted implications of employing KrF excimer laser-induced nanostructures, ranging from surface morphology alterations to biocompatibility enhancements, thus, opening new avenues for advanced material engineering.

Enhanced efficiency in two-terminal all-perovskite tandem solar cells via binary functional high polymer doping strategy

An enhanced power conversion efficiency (PCE) of 26.1 % has been achieved in two-terminal (2T) all-perovskite tandem perovskite solar cells (TPSCs) via a binary functional high polymer doping strategy. By incorporating methylene diphenyl diisocyanate polyurethane (MDI-PU) and PJ71 into the wide bandgap (WBG) and narrow bandgap (NBG) perovskite layers, respectively, the perovskite crystalline quality of them was significantly improved. The optimized PCE of the WBG top cell and the NBG bottom cell achieved 17.6 % and 20.9 %, respectively. After continuous dark storage of 150 days in nitrogen-filled glovebox, the PCE of optimized TPSC remained 94.2 % of initial. TPSCs on flexible substrates of polyethylene naphthalate (PEN) and silk-derived substrate (SDS) were also studied. With the binary polymer doping strategy, the PEN-based TPSC achieved a champion PCE of 22.2 %, and exhibited excellent anti-bending ability compared with control. The champion SDS-based TPSC achieved the PCE of 11.6 %, and showed enhanced anti-stretching ability. We demonstrate that strong coordinate bonding formed between the O atom in the carbonyl group of MDI-PU and the Pb2+ ions at the grain boundaries (GBs) in WBG perovskite. For the NBG layer, the S atoms in the thiophene structure of PJ71 interact with the Pb2+ and Sn2+ ions in the NBG perovskite and effectively passivate the GB defects. The study suggests the potential for developing new generation multi-functional optoelectronic high polymers to further boost the performance of 2T all-perovskite TPSCs.

Properties of surface layers of polyethylene naphthalate substrates modified by ultraviolet light irradiation for their electroless deposition

Properties of surface layers of polyethylene naphthalate substrates modified by ultraviolet light irradiation for their electroless deposition

Silver Printed Electrode on Poly-Imide (Pi) Film And Polyethylene Naphthalate (PEN) Film For ECG Monitoring Device: A Case Study

According to World Health Organization (WHO), cardiovascular disease (CVD) is among the tenth of primary global cause of death in 2017. However, this problem could be alleviated via early detections, especially for patients with a history of heart-related problems. In addition, ECG monitoring could reduce the cause of CVD if diagnose earlier thus reduce the risk of sudden death. The measurement of ECG signals is important to assist physicians about people heart and health conditions. The sophisticated characteristics of ECG signals could be acquired by using the good electrodes. Thus, electrodes play a vital role in ECG recording. The commercially available electrodes are the conventional wet electrode (gel) using silver/silver chloride (Ag/AgCl). The gel usage tends to dry gradually and could cause skin problems like dermal inflammation and skin irritation. Due to the limitations associated with conventional gelled electrode, dry electrode is expected to overcome the main limit of Ag/AgCl electrode. By fabricating the silver ink onto the polyimide (PI) and polyethylene naphthalate (PEN) substrates to produce a dry ECG sensor, which could withstand high temperature, reusable, and has been shown to be biocompatible. This study is a case study to measure the performance of dry electrode based by silver printed electrode on PI and PEN films in ECG application.

Spectral response regulation strategy by downshifting materials to improve efficiency of flexible perovskite solar cells

Polyethylene naphthalate (PEN) has been widely employed in highly desired flexible perovskite solar cells (F-PSCs) because of its better chemical stability and higher temperature tolerance. However, the naphthalene ring in the PEN induces poor transmittance in the ultraviolet (UV) region below 380 nm, which significantly lowers the power conversion efficiency (PCE) of F-PSCs. Here, a novel strategy is adopted by introducing UV–visible downshifting material before the PEN substrate to increase the spectral response under the UV region. The PCE of modified F-PSCs increases from 22.19 % to 22.81 % and retains the same stability as that of the control device. The optimized device shows improved photocurrent due to the enhanced spectral response in the UV region. Interestingly, the humidity resistance characteristic of the target device had also improved because of the hydrophobicity of downshifting materials. This novel strategy is distinguishable where downshifting material has been externally employed without altering the internal device architecture, which is also broadly applicable to other types of flexible solar cells.

Substrate Dependence of CdSe/ZnS Quantum-Dot Light-Emitting Diodes: A Comparative Study between Rigid Glass and Flexible Plastic Substrates.

The purpose of this study was to investigate the effect of substrate characteristics on the performance of quantum-dot light-emitting diodes (QLEDs) with the aim of developing high-performance flexible QLEDs. Specifically, we compared QLEDs made with a flexible polyethylene naphthalate (PEN) substrate to those made with a rigid glass substrate, using the same materials and structure except for the substrates. Our findings indicate that the PEN QLED had a 3.3 nm wider full width at half maximum and a 6 nm redshifted spectrum in comparison to the glass QLED. Additionally, the PEN QLED exhibited a 6% higher current efficiency, a flatter current efficiency curve, and a 2.25-V lower turn-on voltage, indicating superior overall characteristics. We attribute the spectral difference to the optical properties of the PEN substrate, such as light transmittance and refractive index. Our study also revealed that the electro-optical properties of the QLEDs were consistent with the electron-only device and transient electroluminescence results, which suggests that the improved charge injection properties of the PEN QLED were responsible. Overall, our study provides valuable insights into the relationship between substrate characteristics and QLED performance, which can be used to develop high-performance QLEDs.

A Flexible Sensitive Visible‐NIR Organic Photodetector with High Durability

AbstractLow‐cost, deformable visible‐near‐infrared (visible‐NIR) photodetectors can be configured into non‐planar shapes to meet emerging optical needs. However, it remains challenging to develop low‐cost flexible visible‐NIR photosensor with excellent mechanical deformability and high optical detectivity. Herein, we report a flexible visible‐NIR organic photodetector (OPD) based on a blend film of D18:BTP‐4F as the active layer on a polyethylene naphthalate substrate. Owing to the low exciton binding energy of BTP‐4F and the preferred orientation of the D18:BTP‐4F film, the as‐fabricated OPD exhibits excellent self‐powered optoelectronic performances with a high responsivity, high detectivity, and fast response time of 206 mA W−1, 6.45 × 1012 Jones (1 Jones = 1 cm Hz1/2 W−1), and 9 µs at the wavelength of 800 nm and bias voltage of 0 V, respectively. After 1000 bending/releasing cycles with an angle of 150° at a radius of curvature of 3 mm, the current‐voltage curves remain stable both measured under dark and light illumination, indicating obvious device operation robustness. The reliable linear photosensitivity of the as‐obtained OPD is demonstrated by the photoresponse under a range of different incident light intensities and its practical application for wearable health monitoring such as heart rate measurement is well demonstrated. Furthermore, a flexible visible‐NIR image sensor for imaging acquisition is shown by demonstrating 5 × 5 OPD array under 850 nm light irradiation. The collective results on blend film design, flexible device fabrication and characterization, and imager development shed light on sought‐after visible‐NIR photosensing and imaging systems.

Improvement of electrical characteristics of flexible AZO/Ag/Cu/AZO transparent conductive films by Cu deposition

Flexible electrodes are prepared by deposition on polyethylene naphthalate substrates, which melt at elevated temperatures, and are, therefore, generally unsuitable for deposition at high temperatures. However, only limited improvement in the conductivity can be achieved for Al-doped ZnO (AZO) films formed at low temperatures. Multilayer transparent conductive films (AZO/Ag/AZO), in which a conductive metal such as Ag is sandwiched between AZO, exhibit superior resistivity and electrical stability against bending compared to AZO films and have attracted considerable attention. In this study, AZO transparent conducting films were investigated as alternatives to indium tin oxide. The electrical characteristics of AZO/Ag/AZO films are not optimal at low temperatures owing to oxidation of Ag and its diffusion into the AZO layer. We, therefore, developed transparent conductive films with an AZO/Ag/Cu/AZO structure in which an intermediate Cu layer suppresses the oxidation of Ag and inhibits its diffusion into the substrate-side AZO layer, changing the deposition conditions of Cu. The optimal characteristics were obtained at a Cu deposition rate of 0.08 nm/s. A further increase in Cu layer thickness suppresses the oxidation of the Ag layer and its diffusion into the substrate-side AZO layer, thereby improving resistivity. Notably, a 5 nm thick Cu layer exhibited exclusive Cu regions, which further prevented the oxidation of Ag and its diffusion into the substrate side of the AZO layer, with a resistivity of 5.12 × 10−5 Ω cm. This resistivity is comparable to that of existing transparent conducting films used in practical applications; however, the transmittance of the AZO/Ag/Cu/AZO film was reduced owing to the low transparency of Cu.

High-performance carbon nanotube field-effect transistors with electron mobility of 39.4 cm2V−1s−1 using anion–π interaction doping

Single-walled carbon nanotube (SWNT) is desirable next generation semiconductor for flexible, transparent and even stretchable with exceptional electrical characteristics. Here, high-performance n-type semiconducting SWNT field-effect transistors (s-SWNT-FETs) are achieved by chemical doping using anion-π interaction between SWNT and anion of tetrabutylammonium fluoride (TBAF) salt. The Fermi level (EF) of SWNT shifts to the conduction band edge with increasing dopant concentration. The doped s-SWNT-FETs exhibit significant improvement in electron mobility (39.4 cm2V−1s−1) with high current on/off ratio (>104) compared to those of un-doped device. The doping using anion–π interaction leads to populate electron density of channel and reduces both channel and contact resistance by 99.0% and 99.6%. Excess carriers introduced by the doping compensate traps by shifting the EF toward conduction band edge. The doped device showed improved current stability after 10 h of bias stress test, while the current of undoped FET decreased by 40.4%. Finally, flexible FETs with TBAF doped s-SWNT network are demonstrated on polyethylene naphthalate substrate and show stable operation after 2000 times bending test.

Direct measurement of electrocaloric effect in P(VDF-TrFE-CFE) film using infrared imaging

Poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) P(VDF-TrFE-CFE) is a relaxor ferroelectric polymer, which exhibits a temperature-independent electrocaloric effect at room temperature. In this work, the electrocaloric effect in P(VDF-TrFE-CFE) film was directly analysed using infrared imaging. P(VDF-TrFE-CFE) 64.8%/27.4%/7.8% (in mole) film of (15 ± 1) μm thickness was deposited on polyethylene naphthalate substrate. Direct ECE of P(VDF-TrFE-CFE) film was measured from 15 to 35 °C at different electric fields. A maximum adiabatic temperature change (ΔTad) of 3.58 K was measured during the cooling cycle at a field of 100 V/μm at 30 °C. Finite element analysis of temperature dissipation through the sample estimated that the actual temperature change within P(VDF-TrFE-CFE) film was 4.3 K. Despite the thermal mass of the substrate, a substantial ECE was observed in P(VDF-TrFE-CFE) films. This electrocaloric terpolymer composition could be of interest for electrocaloric cooling applications.

Highly transmitted silver nanowires-SWCNTs conductive flexible film by nested density structure and aluminum-doped zinc oxide capping layer for flexible amorphous silicon solar cells

• Ag NWs-SWCNTs (AS) composites with high and sparse density networks were fabricated by ultrasonic. • The AS/AZO (ASA) bilayer showed superior transmittance (92%@550 nm), mechanicity, stability, and adhesion. • The film demonstrates high stability with a ΔR/R 0 = 10% after 10,000 bending times, boiling, taping, and CO 2 plasma. • The power conversion efficiency of photovoltaic devices with flexible ASA TCFs was increased by 26%. • No significant reduction in power conversion efficiency was observed even after bending for 3000 times. Indium tin oxide (ITO) is widely used in transparent conductive films (TCFs); however, several disadvantages, such as high cost and toxicity of indium, limit its applications. Therefore, it is necessary to develop other materials that can replace ITO. Silver nanowires or single walled carbon nanotubes (SWCNTs) have attracted considerable interest owing to their unique electrical, optical, and thermal stabilities, and thus, they are ideal for transparent electrodes for flexible or stretchable devices. In this study, we develop a novel architecture of composite TCFs on a polyethylene naphthalate (PEN) flexible substrate. Herein, the silver nanowires-SWCNTs films with nested density structure were fabricated through ultrasonic spraying technology by varying the spraying width. For achieving enhanced transmittance, we combined the larger irregular grids and holes with fewer nanowires stacked in the longitudinal direction, more optical channels, and good carrier transport. Thereafter, aluminum-doped zinc oxide (AZO) was used as capping to the structure for enhancing the optical properties of the TCFs. The silver nanowires-SWCNTs/AZO (ASA) bilayer was obtained in the optimized architecture, which showed superior optoelectronic performance to that shown by commercial ITO with a high optical transmittance of 92% at the wavelength of 550 nm and low sheet resistance of 17 Ω/sq. In the specially structured conductive film, the significant improvement in the transmittance and uniformity of the sheet resistance was attributed to the effective nanowire junction contact compared to that in ordinary structure of silver nanowires, which reduced the mean density of small clusters of nanowires. Compared with the silver nanowires-SWCNTs films, the ASA bilayer film exhibited excellent resistance to boiling, mechanical bending (10,000 cycles), and CO 2 plasma. Moreover, the sheet resistance of ASA changed slightly after the tape tests, thereby illustrating a strong adhesion to the PEN substrate after the enclosure of AZO. Meanwhile, the AZO capping layer can enhance the optical transmittance between 600 and 1500 nm. In addition, the amorphous silicon photovoltaic devices with flexible ASA TCFs exhibited a power conversion efficiency (PCE) of 8.67%. After bending for 3000 times, the PCE was decreased to 8.20%, thereby demonstrating the potential of developed films to replace traditional ITO.

Impact of dielectric substrates on chipless RFID tag performance

AbstractA five-slot hexagonal shape chipless RFID tag is designed, simulated, and manufactured on FR4 substrate. The designed tag's copper geometry was replicated on a wide range of dielectric substrate to quantify the impact on resonance quality factor (RQF) and resonating frequencies. The tag's performance was assessed in three configurations. First, a hexagonal shape tag's radar cross section (RCS) was studied over different dielectric substrates. The various dielectric substrate effects were investigated over the maximum read range, resonant frequencies and RQF. In the second evaluation, the physical geometry of the tag was adjusted to achieve the spectral signatures in 2–7 GHz frequency band with high RQF. In step three, the optimized tag geometry was manufactured on FR4, Roger Duroid 5880, and polyethylene naphthalate (PEN) substrates. Denford milling machine for PCB engraving and inkjet printing for silver nanoparticles deposition were used for tags manufacturing. During tag manufacturing, copper and silver were used as conducting materials for RCS backscattering. The tag RCS response was measured by vector network analyzer with bi-static antenna setup. The analysis of different dielectric substrate provides a pathway of designing a novel substrate by using various nanomaterials.

Performance improvement of organic solar cells using a hybrid hole transport layer of poly(triarylamine) and molybdenum trioxide

In this study, we improved the performance of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′] dithiophene-co-3-fluorothieno [3,4-b]thiophene-2-carboxylate] (Liu et al., 2020; Liu et al., 2020) [6,6]:-phenyl-C 70 -butyric acid methyl ester (PTB7-Th:PC 71 BM)-based organic solar cells (OSCs) by using molybdenum trioxide (MoO 3 ) covered poly(triarylamine) (PTAA) as a hybrid hole transport layer (HTL). Using this technique, an average power conversion efficiency (PCE) of 9.82% was achieved, which was higher than that (8.95%) of OSCs using conventional HTL of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The best performing OSC using PTAA/MoO 3 showed a highest PCE of 10.16%, with a stable power output and negligible hysteresis. Due to the high hydrophobicity of the PTAA/MoO 3 film, the stability of the OSCs was improved simultaneously. After a measurement of 20 days, the PCE degradation was suppressed to 17.5% upon using PTAA/MoO 3 , which was lower than that (28.2%) of PEDOT:PSS-based devices. Additionally, the flexible devices (on polyethylene-naphthalate substrates) showed a high PCE of 8.51%, indicating the good flexibility of PTAA/MoO 3 . • PTAA was protected by MoO 3 and applicable for OSCs. • PCE and stability of the OSCs were improved simultaneously. • PCE of 10.16% was achieved for PTB7-Th:PC 71 BM-based OSCs. • Flexible devices showed a high PCE of 8.51%.

A novel strategy of fabricated flexible ITO electrode by liquid metal ultra-thin oxide film

Flexible transparent conductive films are gaining attention day by day over the last few years due to it is a key component of next generation flexible electronics and optoelectronic devices. Indium tin oxide (ITO) as one of the most widely used transparent conductive material is limited by the traditional deposition approach cannot be achieve ultra-thin, which results in its brittle nature. Herein, a novel strategy for fabricating highly transparent conductive films by liquid metal interface phase separation technique based on low-melting liquid metal of InxSn100-x alloy is reported, during the solid-to-liquid phase transition of alloy, the monolayer of surface oxide film segregated with the bulk phase and was printed on the flexible polyethylene-naphthalate (PEN) substrate under the van der Waals. This novel strategy can directly print the ultra-thin self-oxide with the structure of ITO on PEN substrate, with the resulting of transparency over 97.5% and resistivity as low as 0.21 kΩ cm, providing a new way of low-cost raw ITO material as well as the personalized preparation strategy. The desirable highly transparent conductive films are comparable to recently reported ITO film, together with advantages of pretty steady, make them attractive as various flexible transparent conductive electrodes, for example, an ultra-thin ITO film is developed for luminescent devices.

Hysteresis Dynamic Modeling and Analysis of Flexible Nano Silver-Polyvinyl Alcohol Humidity Sensor Based on the Microscopic Process and Langmuir-Fick Theory.

In recent years, advances in materials science and manufacturing technologies have facilitated the development of flexible sensors. However, there are still performance gaps between emerging flexible sensors and traditional silicon-based rigid sensors, especially lacking dynamic modeling and optimization analysis for addressing above challenges. This paper describes a hysteresis dynamic modeling method for flexible humidity sensors. Through inkjet printing and coating methods, the polyvinyl alcohol (PVA) sensitive layer and nano silver interdigital electrode are fabricated on flexible polyethylene naphthalate substrates. The performance characterization results show that the sensitivity and maximum hysteresis within the range of 12–98% relative humidity (RH) are −0.02167 MΩ/% RH and 2.7% RH, respectively. The sensor also has outstanding dynamic response ability and stability in a wide range of humidity variation. The hysteresis mechanism of flexible humidity sensors is theoretically analyzed from microscopic hysteresis processes, Langmuir monomolecular adsorption dynamic modeling, and Fick diffusion dynamic modeling. These hysteresis models provide a path for the hysteresis optimization of flexible PVA humidity sensors. Further exploration of the diffusion rate of water molecules and the proportion of PVA in ink represents promising hysteresis optimization directions of flexible humidity sensors based on PVA-sensitive material.

Gate‐Deterministic Remote Doping Enables Highly Retentive Graphene‐MXene Hybrid Memory Devices on Plastic

AbstractIn this work, a highly retentive and synaptic‐functional transistor memory device architecture based on the gate‐deterministic remote doping of graphene via surface‐oxidized Ti3C2TX MXene nano‐floating‐gates (NFG) is presented. By using solution‐phase size‐sorting followed by controlled surface oxidation process, a regulated distribution of MXene nanoflakes comprising metallic Ti3C2TX as the core surrounded by TiO2‐a high dielectric constant insulator‐as the shell is achieved. The size‐sorted core/shell‐like MXene nanoflakes show a self‐sustainable charge trapping/detrapping behavior, which is highly feasible for realizing non‐embed NFGs for transistor memory devices. Interestingly, unlike the conventional NFG‐embedded architecture, the introduction of core/shell‐like MXene under an electrolyte‐gated graphene field‐effect transistor (GFET) architecture induces a cooperative evolution of the hysteresis loop associated with ionic motion in the electrolyte gates and charge trapping/detrapping in the nanoflakes, resulting in a deterministic remote doping of the graphene layer. The resulting device exhibited a highly retentive memory behavior, which can be optimized by the nanoflake size distribution. In addition, synaptic functions having mechanical flexibility can be successfully emulated using MXene‐based GFETs fabricated on a flexible polyethylene naphthalate substrate.

Localized and structured growth of polymer brushes using ink jet printing approach

Inkjet printing (IJP) technique has been used for the deposition of silica nanoparticles with controlled position and shape onto flexible polyethylene naphthalate (PEN) substrate. The printed silica areas have been chemically functionalized with a silane molecule bearing an ATRP initiator group. Surface-initiated atom transfer radical polymerisation (SI-ATRP) methodology has been betrothed to grow polymer brushes onto the silica printed areas. X-ray photoelectron spectroscopy (XPS) has been used after each step of functionalisation in order to determine the elemental surface composition. In addition, IJP has been used to design specific pattern at 250 micrometer scale. By combining maskless IJP technic and XPS line-scan mode, this work clearly demonstrates that the position and the pattern shape of printed areas can be controlled on demand, and that, structurally polymer brushes are only generated onto the functionalised silica printed areas.

Anti-counterfeiting SERS security labels derived from silver nanoparticles and aryl diazonium salts.

The development of anti-counterfeiting inks based on surface-enhanced Raman scattering (SERS) labels have attracted great interest in recent years for their use as security labels in anti-counterfeiting applications. Indeed, they are promising alternatives to luminescent inks, which suffer from several limitations including emission peak overlap, toxicity and photobleaching. Most of the reported SERS security labels developed so far rely on the use of thiolate self-assembled monolayers (SAMs) for the immobilization of Raman reporters on metallic nanoparticle surface. However, SAMs are prone to spontaneous desorption and degradation under laser irradiation, thereby compromising the ink long-term stability. To overcome this issue, we develop herein a new generation of SERS security labels based on silver nanoparticles (Ag NPs) functionalized by aryl diazonium salts, carrying various substituents (-NO2, -CN, -CCH) with distinguishable Raman fingerprints. The resulting SERS tags were fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis absorption and SERS. Then, they were incorporated into ink formulations to be printed on polyethylene naphthalate (PEN) substrates, using handwriting or inkjet printing. Proof-of-concept Raman imaging experiments confirmed the remarkable potential of diazonium salt chemistry to design Ag NPs-based SERS security labels.

Printed dual-gate organic thin film transistors and PMOS inverters on flexible substrates: role of top gate electrode

We report printed single and dual-gate organic thin film transistors (OTFTs) and p-channel metal-oxide-semiconductor (PMOS) inverters fabricated on 125 µm thick flexible polyethylene naphthalate substrate. All the electrodes (gate, source, and drain) are inkjet-printed, while the parylene dielectric is formed by chemical vapor deposition. A dispenser system is used to print the active channel material using a blend of 2,7-dihexyl-dithieno[2,3-d;2′,3′-d′]benzo [1,2-b;4,5-b′]dithiophene and polystyrene in tetralin solvent, which gives highest mobility of 0.43 cm2 V−1s−1. Dual-gate OTFTs are characterized by keeping the other gate electrode either in grounded or floating state. Floating gate electrode devices shows higher apparent mobility and current ratio due to additional capacitance of the parylene dielectric. PMOS inverter circuits are characterized in terms of gain, trip point and noise margin values calculated from the voltage transfer characteristics (VTC). Applied top gate voltage on the load OTFT control the conductivity or threshold voltage (V Th) of the bottom TFT and shift the trip point towards the middle of the VTC curve, and hence increase the noise margin.