Fabrication of Wearable Transistor with All-Graphene Electrodes via Hot Pressing.

Textile electronics are ideal for novel electronic devices owing to their flexibility, light weight, and wearability. In this work, wearable organic field-effect transistors (OFETs) with all-graphene electrodes, fabricated using hot pressing, are described. First, highly conductive and flexible electrodes consisting of a cotton textile substrate and electrochemically exfoliated graphene (EEG) were prepared via hot pressing. The EEG/textile electrodes exhibited a low sheet resistance of 1.3 Ω sq-1 and high flexibility; these were used as gate electrodes in the wearable OFETs. In addition, spray-coated EEG was also used as the source/drain (S/D) electrodes of the wearable OFETs, which recorded a sheet resistance of 14.8 Ω sq-1 after hot pressing. The wearable OFETs exhibited stable electrical performance, a field-effect mobility of 13.8 cm2 V-1 s-1, and an on-off current ratio of ~103 during 1000 cycles of bending. Consequently, the fabrication method for wearable transistors developed using textiles and hot-pressed graphene electrodes has potential applications in next-generation wearable devices.

Functionalization of Tailored Porous Carbon Monolith for Decontamination of Radioactive Substances.

As the control over radioactive species becomes critical for the contemporary human life, the development of functional materials for decontamination of radioactive substances has also become important. In this work, a three-dimensional (3D) porous carbon monolith functionalized with Prussian blue particles was prepared through removal of colloidal silica particles from exfoliated graphene/silica composite precursors. The colloidal silica particles with a narrow size distribution were used to act a role of hard template and provide a sufficient surface area that could accommodate potentially hazardous radioactive substances by adsorption. The unique surface and pore structure of the functionalized porous carbon monolith was examined using electron microscopy and energy-dispersive X-ray analysis (EDS). The effective incorporation of PB nanoparticles was confirmed using diverse instrumentations such as X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). A nitrogen adsorption/desorption study showed that surface area and pore volume increased significantly compared with the starting precursor. Adsorption tests were performed with 133Cs ions to examine adsorption isotherms using both Langmuir and Freundlich isotherms. In addition, adsorption kinetics were also investigated and parameters were calculated. The functionalized porous carbon monolith showed a relatively higher adsorption capacity than that of pristine porous carbon monolith and the bulk PB to most radioactive ions such as 133Cs, 85Rb, 138Ba, 88Sr, 140Ce, and 205Tl. This material can be used for decontamination in expanded application fields.

Comparison of Surface Modification Methods for Improving the Compatibility of Recycled Plastic Film-Based Aggregates.

The surface modification of recycled plastic film-based aggregates was investigated to improve the compatibility between the aggregates and a cement paste. Surface modification was performed using ultraviolet-ozone treatment (UV-O3), a silane coupling agent, O2 atmospheric pressure plasma, and acrylic binder coating methods. The surface properties of the modified aggregates were analyzed using a contact angle measuring instrument. The results revealed that for all surface modification methods, the contact angle decreased with an increase in the treatment time. According to the comparative evaluation results of the changes in the surface characteristics of the aggregates through various surface modification methods, the contact angle reduction rates were 58.9%, 51.4%, 25.5%, and 24.5% for the O2 atmospheric pressure plasma, the acrylic binder coating, the silane coupling agent, and the UV-O3 method, respectively. After 48 h, the contact angle had increased by 110.9%, 29.9%, 16.4%, and 5.9% for the O2 atmospheric pressure plasma, UV-O3, the silane coupling agent, and the acrylic binder coating, respectively. Namely, the surface modification using the acrylic binder coating method was found to be the most effective method in terms of the wettability increase effect and the long-term storage stability.

Development of the Functionalized Nanocomposite Materials for Adsorption/Decontamination of Radioactive Pollutants.

A polymer-based nanofiber membrane with a high specific surface area, high porosity and abundant adsorption sites is demonstrated for selective trapping of radionuclides. The Prussian blue (PB)/poly(methyl methacrylate) (PMMA) nanofiber composites were successfully prepared through a one-step, single-nozzle electrospinning method. Various analytical techniques were used to examine the physical and chemical properties of PB nanoparticles and electrospun nanofibers. It is possible to enhance binding affinity and selectivity to radionuclide targets by incorporation of the PB nanoparticles into the polymer matrix. It is noteworthy that the maximum 133Cs adsorption capacity of hte PB/PMMA nanofiber filter is approximately 28 times higher than that of bulk PB, and the removal efficiency is measured to be 95% at 1 ppm of 133Cs. In addition, adsorption kinetics shows that the PB/PMMA nanofiber has a homogenous surface for adsorption, and all sites on the surface have equal adsorption energies in terms of ion-exchange between cyano groups of the introduced PB nanoparticles and radionuclides.

A Review of Polymer Composites Based on Carbon Fillers for Thermal Management Applications: Design, Preparation, and Properties.

With the development of microelectronic devices having miniaturized and integrated electronic components, an efficient thermal management system with lightweight materials, which have outstanding thermal conductivity and processability, is becoming increasingly important. Recently, the use of polymer-based thermal management systems has attracted much interest due to the intrinsic excellent properties of the polymer, such as the high flexibility, low cost, electrical insulation, and excellent processability. However, most polymers possess low thermal conductivity, which limits the thermal management applications of them. To address the low thermal conduction of the polymer materials, many kinds of thermally conductive fillers have been studied, and the carbon-based polymer composite is regarded as one of the most promising materials for the thermal management of the electric and electronic devices. In addition, the next generation electronic devices require composite materials with various additional functions such as flexibility, low density, electrical insulation, and oriented heat conduction, as well as ultrahigh thermal conductivity. In this review, we introduce the latest papers on thermally conductive polymer composites based on carbon fillers with sophisticated structures to meet the above requirements. The topic of this review paper consists of the following four contents. First, we introduce the design of a continuous three-dimensional network structure of carbon fillers to reduce the thermal resistance between the filler-matrix interface and individual filler particles. Second, we discuss various methods of suppressing the electrical conductivity of carbon fillers in order to manufacture the polymer composites that meet both the electrical insulation and thermal conductivity. Third, we describe a strategy for the vertical alignment of carbon fillers to improve the through-plane thermal conductivity of the polymer composite. Finally, we briefly mention the durability of the thermal conductivity performance of the carbon-based composites. This review presents key technologies for a thermal management system of next-generation electronic devices.

Giant enhancement of third-harmonic generation in graphene-metal heterostructures.

Nonlinear nanophotonics leverages engineered nanostructures to funnel light into small volumes and intensify nonlinear optical processes with spectral and spatial control. Owing to its intrinsically large and electrically tunable nonlinear optical response, graphene is an especially promising nanomaterial for nonlinear optoelectronic applications. Here we report on exceptionally strong optical nonlinearities in graphene-insulator-metal heterostructures, which demonstrate an enhancement by three orders of magnitude in the third-harmonic signal compared with that of bare graphene. Furthermore, by increasing the graphene Fermi energy through an external gate voltage, we find that graphene plasmons mediate the optical nonlinearity and modify the third-harmonic signal. Our findings show that graphene-insulator-metal is a promising heterostructure for optically controlled and electrically tunable nano-optoelectronic components.

Far-field excitation of single graphene plasmon cavities with ultracompressed mode volumes.

Acoustic graphene plasmons are highly confined electromagnetic modes carrying large momentum and low loss in the mid-infrared and terahertz spectra. However, until now they have been restricted to micrometer-scale areas, reducing their confinement potential by several orders of magnitude. Using a graphene-based magnetic resonator, we realized single, nanometer-scale acoustic graphene plasmon cavities, reaching mode volume confinement factors of ~5 × 1010 Such a cavity acts as a mid-infrared nanoantenna, which is efficiently excited from the far field and is electrically tunable over an extremely large broadband spectrum. Our approach provides a platform for studying ultrastrong-coupling phenomena, such as chemical manipulation via vibrational strong coupling, as well as a path to efficient detectors and sensors operating in this long-wavelength spectral range.

Preparation of Porous Carbon Nanofibers with Tailored Porosity for Electrochemical Capacitor Electrodes.

Porous carbon electrodes that accumulate charges at the electrode/electrolyte interface have been extensively investigated for use as electrochemical capacitor (EC) electrodes because of their great attributes for driving high-performance energy storage. Here, we report porous carbon nanofibers (p-CNFs) for EC electrodes made by the formation of a composite of monodisperse silica nanoparticles and polyacrylonitrile (PAN), oxidation/carbonization of the composite, and then silica etching. The pore features are controlled by changing the weight ratio of PAN to silica nanoparticles. The electrochemical performances of p-CNF as an electrode are estimated by measuring cyclic voltammetry and galvanostatic charge/discharge. Particularly, the p-CNF electrode shows exceptional areal capacitance (13 mF cm-2 at a current of 0.5 mA cm-2), good rate-retention capability (~98% retention of low-current capacitance), and long-term cycle stability for at least 5000 charge/discharge cycles. Based on the results, we believe that this electrode has potential for use as high-performance EC electrodes.

Paraffin-enabled graphene transfer.

The performance and reliability of large-area graphene grown by chemical vapor deposition are often limited by the presence of wrinkles and the transfer-process-induced polymer residue. Here, we report a transfer approach using paraffin as a support layer, whose thermal properties, low chemical reactivity and non-covalent affinity to graphene enable transfer of wrinkle-reduced and clean large-area graphene. The paraffin-transferred graphene has smooth morphology and high electrical reliability with uniform sheet resistance with ~1% deviation over a centimeter-scale area. Electronic devices fabricated on such smooth graphene exhibit electrical performance approaching that of intrinsic graphene with small Dirac points and high carrier mobility (hole mobility = 14,215 cm2 V-1 s-1; electron mobility = 7438 cm2 V-1 s-1), without the need of further annealing treatment. The paraffin-enabled transfer process could open realms for the development of high-performance ubiquitous electronics based on large-area two-dimensional materials.

Correction: All-solution-processed, flexible thin-film transistor based on PANI/PETA as gate/gate insulator.

[This corrects the article DOI: 10.1039/C5RA23848J.].

Integrin-Induced Signal Event Contributes to Self-Assembled Monolayers on Au-Nanoparticle-Regulated Cancer Cell Migration and Invasion.

Gold nanoparticles (Au NPs) have received much attention because of their distinct physicochemical properties. The surface terminal functional groups of Au NPs can facilitate easy conjugation with biological molecules for targeting cancer cells and controlling drugs/genes release. However, little is known regarding molecular mechanisms involved in their regulation of cancer cell migration and invasion. In the present study, Au NPs were successfully conjugated with functional groups (CH3, NH2, OH and COOH) by self-assembled monolayer (SAM) technique. The endocytosis of SAM-Au NPs mediating HepG2 cell migration and invasion in integrin-induced cascaded events were examined. Our results showed that the combination of integrins-Caveolin-1 together contributed to the internalization of SAM-Au NPs. The CH3-Au NPs showed fast cell motility than COOH- and OH- groups by upregulating PI3K expression, but reducing FAK phosphorylation level. Additionally, CH3-Au NPs showed the strongest activated GTP-bound Rac1 and RhoA. Taken together, these results concluded that internalization of SAM-Au NPs inhibited cancer cell migration via FAK/PI3K and downstream Rho-GTPase signaling pathway in a time-dependent manner. This work provides a further understanding of SAM-Au NPs regulating cancer cell migration, which might be helpful to functionalize the Au NP surface in drug delivery system.

Revealing molecular-level surface redox sites of controllably oxidized black phosphorus nanosheets.

Bulk and two-dimensional black phosphorus are considered to be promising battery materials due to their high theoretical capacities of 2,600 mAh g-1. However, their rate and cycling capabilities are limited by the intrinsic (de-)alloying mechanism. Here, we demonstrate a unique surface redox molecular-level mechanism of P sites on oxidized black phosphorus nanosheets that are strongly coupled with graphene via strong interlayer bonding. These redox-active sites of the oxidized black phosphorus are confined at the amorphorized heterointerface, revealing truly reversible pseudocapacitance (99% of total stored charge at 2,000 mV s-1). Moreover, oxidized black-phosphorus-based electrodes exhibit a capacitance of 478 F g-1 (four times greater than black phosphorus) with a rate capability of ~72% (compared to 21.2% for black phosphorus) and retention of ~91% over 50,000 cycles. In situ spectroelectrochemical and theoretical analyses reveal a reversible change in the surface electronic structure and chemical environment of the surface-exposed P redox sites.

Probing the ultimate plasmon confinement limits with a van der Waals heterostructure.

The ability to confine light into tiny spatial dimensions is important for applications such as microscopy, sensing, and nanoscale lasers. Although plasmons offer an appealing avenue to confine light, Landau damping in metals imposes a trade-off between optical field confinement and losses. We show that a graphene-insulator-metal heterostructure can overcome that trade-off, and demonstrate plasmon confinement down to the ultimate limit of the length scale of one atom. This is achieved through far-field excitation of plasmon modes squeezed into an atomically thin hexagonal boron nitride dielectric spacer between graphene and metal rods. A theoretical model that takes into account the nonlocal optical response of both graphene and metal is used to describe the results. These ultraconfined plasmonic modes, addressed with far-field light excitation, enable a route to new regimes of ultrastrong light-matter interactions.

Distortion of DNA Origami on Graphene Imaged with Advanced TEM Techniques.

While graphene may appear to be the ultimate support membrane for transmission electron microscopy (TEM) imaging of DNA nanostructures, very little is known if it poses an advantage over conventional carbon supports in terms of resolution and contrast. Microscopic investigations are carried out on DNA origami nanoplates that are supported onto freestanding graphene, using advanced TEM techniques, including a new dark-field technique that is recently developed in our lab. TEM images of stained and unstained DNA origami are presented with high contrast on both graphene and amorphous carbon membranes. On graphene, the images of the origami plates show severe unwanted distortions, where the rectangular shape of the nanoplates is significantly distorted. From a number of comparative control experiments, it is demonstrated that neither staining agents, nor screening ions, nor the level of electron-beam irradiation cause this distortion. Instead, it is suggested that origami nanoplates are distorted due to hydrophobic interaction of the DNA bases with graphene upon adsorption of the DNA origami nanoplates.

Hot Electron Transistor with van der Waals Base-Collector Heterojunction and High-Performance GaN Emitter.

Single layer graphene is an ideal material for the base layer of hot electron transistors (HETs) for potential terahertz (THz) applications. The ultrathin body and exceptionally long mean free path maximizes the probability for ballistic transport across the base of the HET. We demonstrate for the first time the operation of a high-performance HET using a graphene/WSe2 van der Waals (vdW) heterostructure as a base-collector barrier. The resulting device with a GaN/AlN heterojunction as emitter, exhibits a current density of 50 A/cm2, direct current gain above 3 and 75% injection efficiency, which are record values among graphene-base HETs. These results not only provide a scheme to overcome the limitations of graphene-base HETs toward THz operation but are also the first demonstration of a GaN/vdW heterostructure in HETs, revealing the potential for novel electronic and optoelectronic applications.

Omnidirectionally Stretchable and Transparent Graphene Electrodes.

Stretchable and transparent electrodes have been developed for applications in flexible and wearable electronics. For customer-oriented practical applications, the electrical and optical properties of stretchable electrodes should be independent of the directions of the applied stress, and such electrodes are called omnidirectionally stretchable electrodes. Herein, we report a simple and cost-effective approach for the fabrication of omnidirectionally stretchable and transparent graphene electrodes with mechanical durability and performance reliability. The use of a Fresnel lens-patterned electrode allows multilayered graphene sheets to achieve a concentric circular wavy structure, which is capable of sustaining tensile strains in all directions. The as-prepared electrodes exhibit high optical transparency, low sheet resistance, and reliable electrical performances under various deformation (e.g., bending, stretching, folding, and buckling) conditions. Furthermore, computer simulations have also been carried out to investigate the response of a Fresnel lens-patterned structure on the application of mechanical stresses. This study can be significant in a large variety of potential applications, ranging from stretchable devices to electronic components in various wearable integrated systems.

Electro-response of MoS2 Nanosheets-Based Smart Fluid with Tailorable Electrical Conductivity.

The correlation between electrical conductivity and electro-responsive behavior is identified by introducing few-layer molybdenum disulfide (MoS2) nanosheets to electrorheological (ER) fluid. Few-layer MoS2 nanosheets are successfully fabricated, with a high yield of above 60%, using a straightforward method, and applied to an electro-responsive smart fluid. The electrical conductivity of MoS2 is easily tunable by adjusting the annealing temperature because of its semiconducting behavior. From an in-depth study on the conductivity-dependent ER behavior of few-layer MoS2 nanosheets, it can be verified that an optimum value of the electrical conductivity exists for the electro-responsive material, corresponding to the Wagner model. To the best of our knowledge, this is the first report on the potential of a transition-metal dichalcogenide as a candidate material for an ER fluid. This study may provide promising approaches for the performance improvement of electro-responsive smart fluids.

Cartilage-inspired superelastic ultradurable graphene aerogels prepared by the selective gluing of intersheet joints.

In this study, we demonstrate a cartilage-inspired superelastic and ultradurable nanocomposite strategy for the selective inclusion of viscoelastic poly(dimethylsiloxane) (PDMS) into graphene sheet junctions to create effective stress-transfer pathways within three-dimensional (3D) graphene aerogels (GAs). Inspired by the joint architectures in the human body, where small amounts of soft cartilage connect stiff (or hard) but hollow (and thus lightweight) bones, the 3D internetworked GA@PDMS achieves synergistic toughening. The resulting GA@PDMS nanocomposites exhibit fully reversible structural deformations (99.8% recovery even at a 90% compressive strain) and high compressive mechanical strength (448.2 kPa at a compressive strain of 90%) at repeated compression cycles. Owing to the combination of excellent mechanical and electrical properties, the GA@PDMS nanocomposites are used as signal transducers for strain sensors, showing very short response and recovery times (in the millisecond range) with reliable sensitivity and extreme durability. Furthermore, the proposed system is applied to electronic scales with a large detectable weight of about 4600 times greater than its own weight. Such bio-inspired cartilage architecture opens the door to fabricate new 3D multifunctional and mechanically durable nanocomposites for emerging applications, which include sensors, actuators, and flexible devices.

Correction: Cartilage-inspired superelastic ultradurable graphene aerogels prepared by the selective gluing of intersheet joints.

Correction for 'Cartilage-inspired superelastic ultradurable graphene aerogels prepared by the selective gluing of intersheet joints' by Jin-Yong Hong, et al., Nanoscale, 2016, DOI: 10.1039/c6nr01986b.

A Rational Strategy for Graphene Transfer on Substrates with Rough Features.

Graphene grown by chemical vapor deposition is transferred by a very simple, yet effective approach from the growth substrate onto substrates with rough features. This novel and facile method not only results in satisfactory transfer on substrates with terraces or grooves, but also gives rise to a successful result for uneven growth substrates.