The applications of solution-exfoliated graphene oxide (GO) as an electrical/electrochemical conductor require rational design–based approaches. Herein, we show that reduced GO nanosheets with highly ...ordered or nanoporous structures can be fabricated by treatment of graphite oxide (GrO) having variable-oxidation-degree with hot KOH solution. As model systems, GrO powders fabricated by modified Brodie and Hummers methods (B-GrO and H-GrO, respectively) were exfoliated into GO in alkaline solutions (to afford B-KGO and H-KGO, respectively), followed by 2.5-h refluxing at 100 °C. Notably, B-KGO was exceptionally resistant to hot KOH solution, whereas H-KGO was partially reduced under these conditions, as confirmed by 13C solid-state NMR, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy analyses. Moreover, reduced B-KGO featured highly ordered structures, whereas reduced H-KGO contained nanopores resulting from low-temperature activation in KOH solution. These extraordinary reactions of KGO nanosheets were translated into different electrical properties of reduced KGO nanosheets and different rheological properties of the corresponding pastes.
High-quality or highly porous graphene nanosheets were rationally fabricated by oxidation degree–dependent transformations of graphene oxide in hot alkaline solution. These reactions were translated into exceptionally different electrical properties of reduced graphene oxide nanosheets and the different rheological properties of the corresponding pastes. Display omitted
Soft electronic devices that are bendable and stretchable require stretchable electric or electronic components. Nanostructured conducting materials or soft conducting polymers are one of the most ...promising fillers to achieve high performance and durability. Here, we report silver nanoparticles (AgNPs) embedded with single-walled carbon nanotubes (SWCNTs) synthesized in aqueous solutions at room temperature, using NaBH
as a reducing agent in the presence of highly oxidized SWCNTs as efficient nucleation agents. Elastic composite films composed of the AgNPs-embedded SWCNTs, Ag flake, and polydimethylsiloxane are irradiated with radiation from a Xenon flash lamp within a time interval of one second for efficient sintering of conductive fillers. Under high irradiation energy, the stretchable electrodes are created with a maximum conductivity of 4,907 S cm
and a highly stretchable stability of over 10,000 cycles under a 20% strain. Moreover, under a low irradiation energy, strain sensors with a gauge factor of 76 under a 20% strain and 5.4 under a 5% strain are fabricated. For practical demonstration, the fabricated stretchable electrode and strain sensor are attached to a human finger for detecting the motions of the finger.
Modulation of the carrier concentration and electronic type of monolayer (1L) MoS2 is highly important for applications in logic circuits, solar cells, and light-emitting diodes. Here, we demonstrate ...the tuning of the electronic properties of large-area 1L-MoS2 using graphene oxide (GO). GO sheets are well-known as hole injection layers since they contain electron-withdrawing groups such as carboxyl, hydroxyl, and epoxy. The optical and electronic properties of GO-treated 1L-MoS2 are dramatically changed. The photoluminescence intensity of GO-treated 1L-MoS2 is increases by more than 470% compared to the pristine sample because of the increase in neutral exciton contribution. In addition, the A1g peak in Raman spectra shifts considerably, revealing that GO treatment led to the formation of p-type doped 1L-MoS2. Moreover, the current vs voltage (I–V) curves of GO-coated 1L-MoS2 field effect transistors show that the electron concentration of 1L-MoS2 is significantly lower in comparison with pristine 1L-MoS2. Current rectification is also observed from the I–V curve of the lateral diode structure with 1L-MoS2 and 1L-MoS2/GO, indicating that the electronic structure of MoS2 is significantly modulated by the electron-withdrawing functional group of GO.
In this work, we produced large-area graphene oxide (GO) sheets with fewer defects on the basal plane by application of shear stress in solution to obtain high-quality reduced graphene oxide (RGO) ...sheets without the need for post-annealing processes. This is described as rheologically derived RGO. The large-area GO sheets were generated using a homogenizer in aqueous solution, which induced slippage of the GO in the in-plane direction during the exfoliation process, in contrast with the conventional sonication method. The effects of chemical reduction under mild conditions demonstrated that the formation of structural defects during the exfoliation process affected the RGO properties. In the Raman spectra, the I D/I G ratio of the homogenized RGO (HRGO) increased more than that of the sonicated RGO (SRGO) due to the large number of ordered six-fold rings on the basal plane. The enhanced sheet resistance of the HRGO thin film was found to be 2.2 kΩ/sq at 80% transmittance. The effective exfoliation method has great potential for application to high-performance RGO-transparent conducting films.
Graphene oxide (GO) exfoliated from graphite oxide is a precursor of graphene, which is a highly promising two-dimensional material for energy storage, printing electronics, composites, conducting ...fibers, etc. However, during the fabrication of GO by chemical oxidation, large amounts of oxidants and acid are used, which lead to many concerns, such as severe environmental pollution and high processing cost. In this study, we propose a highly efficient and rational oxidation of various-sized graphite powder by minimizing the amount of acid used (reducing 1/10 times) through kneading, inspired by the concept of kneading dough. First, NaClO3 and graphite were mixed together. Then, a small amount of fuming nitric acid was added, and the mixture was kneaded for several minutes. The ratio of oxidant to graphite and the reaction time, with and without kneading, were investigated based on the lateral size of graphite, because large-sized graphite requires more diffusion time for oxidizing the species through the graphitic layers. The chemically-reduced GO nanosheets exhibit highly crystalline structures based on the Raman spectroscopy and transmission electron microscopy studies, and their films exhibit a high electrical conductivity of over 45,000 S/m from large graphite, which is promising for electrical and electrochemical applications.
To fabricate high quality graphene nanosheets, various sized graphite powders were rationally oxidized by minimizing the amount of acid used (reducing 1/10 times) through kneading. Graphene films bar-coated with reduced graphene oxide pastes exhibit a high electrical conductivity of over 45,000 S/m from large graphite, which is promising for electrical and electrochemical applications. Display omitted
A nanocomposite of polypyrrole/carbon nanotubes prepared by in situ chemical polymerization shows improved conductivity of the polypyrrole as compared with its pure form. Its application as a ...chemical sensor, made using a simple spin‐casting technique, shows a drastically increased sensitivity. The Figure shows a field‐emission scanning electron microscopy (FE‐SEM) image of the SWNT/Ppy nanocomposite.
Clean chemical vapor deposition (CVD)-grown graphene surfaces with intrinsic electrical properties were obtained by a modified poly(methylmethacrylate) (PMMA) transfer method. The modified method ...entails UV irradiation, followed by wet cleaning of the UV-irradiated PMMA layer using a mixture of isopropyl alcohol (IPA), acetone, and methyl isobutyl ketone (MIBK). The chemical structure of the PMMA layer degrades following UV irradiation under atmospheric conditions, via side-chain cleavage of the ester groups, resulting in reduced intermolecular interactions between the PMMA layer and the underlying graphene film. Furthermore, the IPA/MIBK/acetone mixture is shown to be a powerful solvent that can effectively remove the PMMA layer without leaving any PMMA residue, which could act as a source of cracks and scattering centers for charge carrier transport, on the graphene surface. Graphene transistors fabricated by this modified transfer method show high electron and hole mobilities with ideal threshold voltages of near 0V.
The fabrication of a flexible field‐emission device (FED) using single‐walled carbon nanotube (SWNT) network films as the conducting electrodes (anode and cathode) and thin multi‐walled CNT/TEOS ...hybrid films as the emitters is reported. P‐type doping with gold ions and passivation with tetraethylorthosilicate (TEOS) made the SWNT network film highly conductive and environmentally stable, and hence a good alternative to conventional indium tin oxide electrodes. CNT/TEOS hybrid emitters showed high current density, low turn‐on field, and long‐term emission stability, compared with CNT emitters; these characteristics can be attributed to the TEOS sol, acting both as a protective layer surrounding the nanotube tip, and as an adhesive layer enhancing the nanotube adhesion to the substrate. All‐CNT‐based flexible FEDs fabricated by this approach showed high flexibility in field emission characteristics and extremely bright electron emission patterns.
All‐carbon nanotube‐based flexible field‐emission devices were fabricated by the combination of a highly transparent conducting single‐walled carbon nanotube thin film as an anode and a highly efficient carbon nanotube/tetraethylorthosilicate hybrid thin film as a cathode. The devices showed stable emission properties with extremely bright electron emission patterns upon bending.
Wrinkle-free reduced graphene oxide (rGO)/TiO2 hybrid multilayer films were directly fabricated using an rGO solution stabilized by a TiO2 precursor sol applied over a large area by an air spraying ...method without the use of additional reduction processes. In-situ insertion of the TiO2 layer between rGO sheets dramatically increased the conductivity and carrier mobility despite the insulating properties of amorphous TiO2. The TiO2 situated between rGO sheets also induced significant hole doping. Electrical hysteresis caused by adsorbed water molecules and residual oxidative moieties in the rGO nanosheets vanished due to TiO2-assisted screening of charged impurities. These effects decreased the thermal carrier activation energy and increased the density of states at the Fermi level. Ambipolar transport properties were converted into unipolar-like hole transport characteristics by extensive hole doping in the TiO2 layer.
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