Waterproof Electronic-Bandage with Tunable Sensitivity for Wearable Strain Sensors

We demonstrate high-performance wearable electronic-bandage (E-bandage) based on carbon nanotube (CNT)/silver nanoparticle (AgNP) composites covered with flexible media of fluoropolymer-coated polydimethylsiloxane (PDMS) films. The E-bandage can be used for motion-related sensors by directly attaching them to human skin, which achieves a fast and accurate electric response with high sensitivity according to the bending and stretching movements that induce changes in the conductivity. This advance in the E-bandage is realized as a result of the sensitivity that can be achieved by controlling the concentration of AgNPs in CNT pastes and by modifying the device architecture. The fluoropolymer encapsulation with hydrophobic surface characteristics allows for the E-bandage to operate in water and protects it from physical and chemical contact with the daily life conditions of the human skin. The reliability and scalability of the E-bandage as well as the compatibility with conventional microfabrication allow new possibilities to integrate flexible human-interactive nanoelectronics into mobile health-care monitoring systems combined with Internet of things (IoTs)

Improved Performance in Diketopyrrolopyrrole-Based Transistors with Bilayer Gate Dielectrics

There has been significant progress in the past 2 decades in the field of organic and polymer thin-film transistors. In this paper, we report a combination of stable materials, device architecture, and process conditions that resulted in a patterned gate, small channel length (<5 μm) device that possesses a scaled field-induced conductivity in air that is higher than any organic/polymer transistor reported thus far. The operating voltage is below 10 V; the on-off ratio is high; and the active materials are solution-processable. The semiconducting polymer is a new donor–acceptor polymer with furan-substituted diketopyrrolopyrrole and thienyl-vinylene-thienyl building blocks in the conjugated backbone. One of the major striking features of our work is that the patterned-gate device architecture is suitable for practical applications. We also propose a figure of merit to meaningfully compare polymer/organic transistor performance that takes into account mobility and operating voltage. With this figure of merit, we compare leading organic and polymer transistors that have been hitherto reported. The material and device architecture have shown very high mobility and low operating voltage for such short channel length (below 5 μm) organic/polymer transistors

Enhanced Triboelectric Effects of Self-Poled MoS₂‑Embedded PVDF Hybrid Nanocomposite Films for Bar-Printed Wearable Triboelectric Nanogenerators

Self-poled molybdenum disulfide embedded polyvinylidene fluoride (MoS2@PVDF) hybrid nanocomposite films fabricated by a bar-printing process are demonstrated to improve the output performances of triboelectric nanogenerators (TENGs). Comparative analyses of MoS2@PVDF films with different MoS2 concentrations and the synergic effect based on postannealing at different temperatures were examined to increase the triboelectric open-circuit voltage and the short-circuit current (∼200 V and ∼11.8 μA, respectively). A further comprehensive study of the structural and electrical changes that occur on the surfaces of the proposed hybrid nanocomposite films revealed that both MoS2 incorporation into PVDF and postannealing can individually promote the formation of the β-crystal phase and generate polarity in the PVDF. In addition, MoS2, which provides triboelectric trap states, was found to play a significant role in improving the charge capture capacity of the nanocomposite film and increasing the potential difference between two electrodes of TENGs. The produced electrical energy of the developed wearable TENGs with excellent operational stability for a long duration was utilized to power a variety of mobile smart gadgets in addition to low-power electronic devices. We believe that this study can provide a simple and effective approach to improving the energy-harvesting capabilities of wearable TENGs based on hybrid nanocomposite films

Enhanced Triboelectric Effects of Self-Poled MoS₂‑Embedded PVDF Hybrid Nanocomposite Films for Bar-Printed Wearable Triboelectric Nanogenerators

Self-poled molybdenum disulfide embedded polyvinylidene fluoride (MoS2@PVDF) hybrid nanocomposite films fabricated by a bar-printing process are demonstrated to improve the output performances of triboelectric nanogenerators (TENGs). Comparative analyses of MoS2@PVDF films with different MoS2 concentrations and the synergic effect based on postannealing at different temperatures were examined to increase the triboelectric open-circuit voltage and the short-circuit current (∼200 V and ∼11.8 μA, respectively). A further comprehensive study of the structural and electrical changes that occur on the surfaces of the proposed hybrid nanocomposite films revealed that both MoS2 incorporation into PVDF and postannealing can individually promote the formation of the β-crystal phase and generate polarity in the PVDF. In addition, MoS2, which provides triboelectric trap states, was found to play a significant role in improving the charge capture capacity of the nanocomposite film and increasing the potential difference between two electrodes of TENGs. The produced electrical energy of the developed wearable TENGs with excellent operational stability for a long duration was utilized to power a variety of mobile smart gadgets in addition to low-power electronic devices. We believe that this study can provide a simple and effective approach to improving the energy-harvesting capabilities of wearable TENGs based on hybrid nanocomposite films

Enhanced Triboelectric Effects of Self-Poled MoS₂‑Embedded PVDF Hybrid Nanocomposite Films for Bar-Printed Wearable Triboelectric Nanogenerators

Self-poled molybdenum disulfide embedded polyvinylidene fluoride (MoS2@PVDF) hybrid nanocomposite films fabricated by a bar-printing process are demonstrated to improve the output performances of triboelectric nanogenerators (TENGs). Comparative analyses of MoS2@PVDF films with different MoS2 concentrations and the synergic effect based on postannealing at different temperatures were examined to increase the triboelectric open-circuit voltage and the short-circuit current (∼200 V and ∼11.8 μA, respectively). A further comprehensive study of the structural and electrical changes that occur on the surfaces of the proposed hybrid nanocomposite films revealed that both MoS2 incorporation into PVDF and postannealing can individually promote the formation of the β-crystal phase and generate polarity in the PVDF. In addition, MoS2, which provides triboelectric trap states, was found to play a significant role in improving the charge capture capacity of the nanocomposite film and increasing the potential difference between two electrodes of TENGs. The produced electrical energy of the developed wearable TENGs with excellent operational stability for a long duration was utilized to power a variety of mobile smart gadgets in addition to low-power electronic devices. We believe that this study can provide a simple and effective approach to improving the energy-harvesting capabilities of wearable TENGs based on hybrid nanocomposite films

Highly Uniform and Stable n‑Type Carbon Nanotube Transistors by Using Positively Charged Silicon Nitride Thin Films

Air-stable n-doping of carbon nanotubes is presented by utilizing SiN_<i>x</i> thin films deposited by plasma-enhanced chemical vapor deposition. The fixed positive charges in SiN_<i>x</i>, arising from ⁺SiN₃ dangling bonds induce strong field-effect doping of underlying nanotubes. Specifically, an electron doping density of ∼10²⁰ cm^–3 is estimated from capacitance voltage measurements of the fixed charge within the SiN_<i>x</i>. This high doping concentration results in thinning of the Schottky barrier widths at the nanotube/metal contacts, thus allowing for efficient injection of electrons by tunnelling. As a proof-of-concept, n-type thin-film transistors using random networks of semiconductor-enriched nanotubes are presented with an electron mobility of ∼10 cm²/V s, which is comparable to the hole mobility of as-made p-type devices. The devices are highly stable without any noticeable change in the electrical properties upon exposure to ambient air for 30 days. Furthermore, the devices exhibit high uniformity over large areas, which is an important requirement for use in practical applications. The work presents a robust approach for physicochemical doping of carbon nanotubes by relying on field-effect rather than a charge transfer mechanism

Transformation of the Electrical Characteristics of Graphene Field-Effect Transistors with Fluoropolymer

We report on the improvement of the electronic characteristics of monolayer graphene field-effect transistors (FETs) by an interacting capping layer of a suitable fluoropolymer. Capping of monolayer graphene FETs with CYTOP improved the on–off current ratio from 5 to 10 as well as increased the field-effect mobility by as much as a factor of 2 compared to plain graphene FETs. Favorable shifts in the Dirac voltage toward zero with shift magnitudes in excess of 60 V are observed. The residual carrier concentration is reduced to ∼2.8 × 10¹¹ cm^–2. Removal of the fluoropolymer from graphene FETs results in a return to the initial electronic properties before depositing CYTOP. This suggests that weak, reversible electronic perturbation of graphene by the fluoropolymer favorably tune the electrical characteristics of graphene, and we hypothesize that the origin of this improvement is in the strongly polar nature of the C–F chemical bonds that self-organize upon heat treatment. We demonstrate a general method to favorably restore or transform the electrical characteristics of graphene FETs, which will open up new applications

25 GHz Embedded-Gate Graphene Transistors with High‑K Dielectrics on Extremely Flexible Plastic Sheets

Despite the widespread interest in graphene electronics over the past decade, high-performance graphene field-effect transistors (GFETs) on flexible substrates have been rarely achieved, even though this atomic sheet is widely understood to have greater prospects for flexible electronic systems. In this article, we report detailed studies on the electrical and mechanical properties of vapor synthesized high-quality monolayer graphene integrated onto flexible polyimide substrates. Flexible graphene transistors with high-k dielectric afforded intrinsic gain, maximum carrier mobilities of 3900 cm²/V·s, and importantly, 25 GHz cutoff frequency, which is more than a factor of 2.5 times higher than prior results. Mechanical studies reveal robust transistor performance under repeated bending, down to 0.7 mm bending radius, whose tensile strain is a factor of 2–5 times higher than in prior studies. In addition, integration of functional coatings such as highly hydrophobic fluoropolymers combined with the self-passivation properties of the polyimide substrate provides water-resistant protection without compromising flexibility, which is an important advancement for the realization of future robust flexible systems based on graphene

25 GHz Embedded-Gate Graphene Transistors with High‑K Dielectrics on Extremely Flexible Plastic Sheets

Despite the widespread interest in graphene electronics over the past decade, high-performance graphene field-effect transistors (GFETs) on flexible substrates have been rarely achieved, even though this atomic sheet is widely understood to have greater prospects for flexible electronic systems. In this article, we report detailed studies on the electrical and mechanical properties of vapor synthesized high-quality monolayer graphene integrated onto flexible polyimide substrates. Flexible graphene transistors with high-k dielectric afforded intrinsic gain, maximum carrier mobilities of 3900 cm²/V·s, and importantly, 25 GHz cutoff frequency, which is more than a factor of 2.5 times higher than prior results. Mechanical studies reveal robust transistor performance under repeated bending, down to 0.7 mm bending radius, whose tensile strain is a factor of 2–5 times higher than in prior studies. In addition, integration of functional coatings such as highly hydrophobic fluoropolymers combined with the self-passivation properties of the polyimide substrate provides water-resistant protection without compromising flexibility, which is an important advancement for the realization of future robust flexible systems based on graphene

Ultrasensitive Room-Temperature Operable Gas Sensors Using p‑Type Na:ZnO Nanoflowers for Diabetes Detection

Ultrasensitive room-temperature operable gas sensors utilizing the photocatalytic activity of Na-doped p-type ZnO (Na:ZnO) nanoflowers (NFs) are demonstrated as a promising candidate for diabetes detection. The flowerlike Na:ZnO nanoparticles possessing ultrathin hierarchical nanosheets were synthesized by a facile solution route at a low processing temperature of 40 °C. It was found that the Na element acting as a p-type dopant was successfully incorporated in the ZnO lattice. On the basis of the synthesized p-type Na:ZnO NFs, room-temperature operable chemiresistive-type gas sensors were realized, activated by ultraviolet (UV) illumination. The Na:ZnO NF gas sensors exhibited high gas response (<i>S</i> of 3.35) and fast response time (∼18 s) and recovery time (∼63 s) to acetone gas (100 ppm, UV intensity of 5 mW cm^–2), and furthermore, subppm level (0.2 ppm) detection was achieved at room temperature, which enables the diagnosis of various diseases including diabetes from exhaled breath