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Abstract Desired electrode patterning on two-dimensional (2D) materials is a foremost step for realizing the full potentials of 2D materials in electronic devices. Here, we introduce an approach for damage-free, on-demand manufacturing of 2D material devices using light-emitting diode (LED) lithography. The advantage of this method lies in mild photolithography by simply combining an ordinary optical microscope with a commercially available LED projector; the low-energy red component is utilized for optical characterization and alignment of devices, whereas the high-energy blue component is utilized for photoresist exposure and development of personal computer designed electrode patterns. This method offers maskless, damage-free photolithography, which is particularly suitable for 2D materials that are sensitive to conventional lithography. We applied this LED lithography to device fabrication of selected nanosheets (MoS2, graphene oxides and RuO2), and achieved damage-free lithography of various patterned electrodes with feature sizes as small as 1–2 μm. The LED lithography offers a useful approach for cost-effective mild lithography without any costly instruments, high vacuum, or complex operation.

Abstract Exciton–polariton coupling between transition metal dichalcogenide (TMD) monolayer and plasmonic nanostructures generates additional states that are rich in physics, gaining significant attention in recent years. In exciton–polariton coupling, the understanding of electronic-energy exchange in Rabi splitting is critical. The typical structures that have been adopted to study the coupling are “TMD monolayers embedded in a metallic-nanoparticle-on-mirror (NPoM) system.” However, the exciton orientations are not parallel to the induced dipole direction of the NPoM system, which leads to inefficient coupling. Our proposed one-dimensional plasmonic nanogrooves (NGs) can align the MoS2 monolayers’ exciton orientation and plasmon polaritons in parallel, which addresses the aforementioned issue. In addition, we clearly reveal the maximum surface potential (SP) change on intermediate coupled sample by the photo-excitation caused by the carrier rearrangement. As a result, a significant Rabi splitting (65 meV) at room temperature is demonstrated. Furthermore, we attribute the photoluminescence enhancement to the parallel exciton–polariton interactions.

The presentation of virtual object shapes using a finger-mounted pin-array haptic display is one of the major topics of research in haptics. If this can be realized, the operability of objects and immersive feeling in the virtual space will be improved. For now, previous studies showed that shape recognition performance using such a pin-array display was far inferior from the performance in the real world using a real object. We considered that both the density of contact points and coverage areas are essential to improve the recognition performance. However, the size of the actuator that pushes each pin was a constraint, and the previously developed display could not have a large contact density and coverage area. This study proposes a novel design of a finger-mounted pin-array display that works around the constraint. We adopted a pneumatic drive because the pneumatic actuator, or air cylinder, can be a simple structure and can be arranged in a dense array. Our developed finger-mounted display has a higher contact point density and a larger coverage area than any other previously developed devices. It covered more than 4 times larger area on fingerpad with denser pin arrangements. An experiment to evaluate the recognition performance with the device was conducted. Participants discriminated 10 kinds of 2D patterned alphabet shapes with only haptic information. The result showed participants could recognize the ten kinds of 2D patterned shape with 93.8% accuracy. Though our participants' task in the experiment was more difficult, the accuracy was better than previous studies. It suggests the effect of the higher density and the larger size of the coverage.

Abstract Two‐dimensional (2D) transition metal dichalcogenides (TMDCs) with unique electrical properties are fascinating materials used for future electronics. However, the strong Fermi level pinning effect at the interface of TMDCs and metal electrodes always leads to high contact resistance, which seriously hinders their application in 2D electronics. One effective way to overcome this is to use metallic TMDCs or transferred metal electrodes as van der Waals (vdW) contacts. Alternatively, using highly conductive doped TMDCs will have a profound impact on the contact engineering of 2D electronics. Here, a novel chemical vapor deposition (CVD) using mixed molten salts is established for vapor–liquid–solid growth of high‐quality rhenium (Re) and vanadium (V) doped TMDC monolayers with high controllability and reproducibility. A tunable semiconductor to metal transition is observed in the Re‐ and V‐doped TMDCs. Electrical conductivity increases up to a factor of 108 in the degenerate V‐doped WS2 and WSe2. Using V‐doped WSe2 as vdW contact, the on‐state current and on/off ratio of WSe2‐based field‐effect transistors have been substantially improved (from ≈10–8 to 10–5 A; ≈104 to 108), compared to metal contacts. Future studies on lateral contacts and interconnects using doped TMDCs will pave the way for 2D integrated circuits and flexible electronics.

Graphene oxide (GO) is chemically exfoliated graphene with various oxygen functional groups bound to its sp² basal plane. GO is not only a precursor for graphene in large-scale production but provides a fertile platform for applications from electronics to biology owing to its outstanding characteristics. In this review, we introduce the preparation and reduction methods and discuss recent application examples on electrochemistry and biological sensors. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) walled channels filled by sulfate ions exhibit an optimized proton conductivity, which is higher than the proton conductivity of all other forms of GO. The sulphate ion increases the water absorbing capacity and hydrogen bond reformation process in GO. [ABSTRACT FROM AUTHOR]

Tuning upconversion (UPC) luminescence using external stimuli and fields, as well as chemical reactions, is expected to lead to novel and efficient optical sensors. Herein, highly tunable UPC luminescence was achieved through a host--guest chemistry approach. Specifically, interlayerion exchange reactions reversibly tuned the emission intensity and green-red color of Er/Yb-codoped A2La2Ti3O10 layered perovsldte, where A corresponds to proton and alkali metal ions, enabling the visualization of host--guest interactions and reactions. [ABSTRACT FROM AUTHOR]

Understanding the chemical and physical properties of metal/graphene oxide (M/GO) interfaces is important when GOis used in electronic and electrochemical devices because the metal layer must be firmly attached to GO. Here, permeation of metal from the surface into GO paper bulk at the M/GO interface was observed at room temperature for metals such as Cu, Ag, Ni, Au, and Pt. Cu, Ag, and Ni quickly permeated GO as ions into the bulk under humid conditions. At first, these metals changed to hydrated ions as a result of redox reactions (with reduction of GO) at the surface, and then permeated the interlayers. Au and Pt were observed to permeate GO as atoms into the GO bulk at room temperature, although the permeation rates were low. These surprising results are considered to be due to the presence of many defects and/or edges with oxygenated groups in the GO paper. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) exhibits relatively high proton conduction even at low relative humidity (RH) and temperatures. Thus, multi-layered GO film (GO paper) is a promising electrolyte in various cells and batteries. We report the in-plane and through-plane proton conductivities of GO paper at low RH and room temperature. The conductivities were 10−5-10−4 S/cm at RH of 10–20%. We examined the performance of a graphene oxide fuel cell (GOFC) with GO paper as the electrolyte at low RH (<20%) and room temperature. We demonstrated that a simple membrane electrode assembly (MEA) based on Pt/GO/Pt system functioned as a H2/O2 fuel cell. The GOFC with Pt/C electrodes afforded better fuel cell performance than a MEA composed of Pt/C electrodes and Nafion electrolyte. GO paper composed of nano-sized GO (nanoGO) flakes enhanced the performance of the GOFC, particularly the current density. Furthermore, a composite of Fe phthalocyanine (PcFe) /reduced GO (rGO)/TiO2 could act as the Pt-free oxygen electrode in GOFC, although the fuel cell performance should be improved for practical applications. Our study suggests that a low cost GOFC without a Nafion electrolyte and noble metal electrodes could be fabricated in the near future. [ABSTRACT FROM AUTHOR]

A novel approach for the preparation of “coupling-type noise suppressors” in which ferrite films are directly deposited onto the components of the printed circuit board is reported. Crystalline MnxZnyFe3−x−yO4films were fabricated on IC chips and polyimide substrates by a soft-chemistry route at temperatures below 100 °C. A “reaction-solution” comprising MCl2(M = Mn, Zn, Fe) and an “oxidizing-solution” (pH buffer + oxidizing agent) were sprayed simultaneously onto a substrate maintained at 90 °C on a rotating disk. The as-prepared films were highly crystalline and hence do not require any post annealing. The magnetic and electrical properties of the films were studied. The films exhibited a large magnetic loss (imaginary permeability µ″) in GHz range and also exhibited high resistivity in accordance to overcome the heat treatment during the reflow soldering process. Resistivity of 2 × 105Ω sq−1was found to be the lower limit for the coupling-type noise suppressors. Noise suppression of above 50% at 10 GHz was obtained for a 6.7 µm thick MnZn-ferrite film and was equivalent to that of commercialized composite sheet noise suppressors of 50 µm thickness. [ABSTRACT FROM AUTHOR]

This paper presents an aqueous route to size-controlled and doped CeO 2nanoparticles using the Ce-oleate complex as a chemically modified precursor. In this synthesis, a hydrolytic condensation of Ce-oleate complex by aqueous ammonia solution at room temperature leads to 2.2 nm sized CeO 2nanocrystals. These products are dispersible in nonpolar solvents owing to the hydrophobic nature of the surface oleate ligand. Moreover, the size of the nanocrystals is controllable up to 5.2 nm by subsequent hydrothermal treatment at 200 °C. The proposed method can be extended for the synthesis of rare earth-doped CeO 2nanocrystals as well. The Gd 3+doped CeO 2nanocrystals synthesized by the proposed method exhibit a spherical shape (size ∼ 3.2 nm) and have a designed chemical composition by energy dispersive X-ray analysis, X-ray diffraction, Raman scattering, and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

The fluorescence signal of a DNA sensor based on strand exchange on graphene oxide was amplified using a DNA circuit that consisted of autonomous cyclic reactions catalyzed by the target. Selectivity for the target was retained after signal amplification. The fluorescence signal was enhanced ca. 50-100-fold at sub-nanomolar target concentrations under isothermal conditions at 35 °C. [ABSTRACT FROM AUTHOR]

We have investigated an in-plane electrical transport in an individual titania nanosheet, which forms a lepidocrocite structure with a few atomic layer thickness. The conductivity in the titania nanosheet varied five orders for the change of the relative humidity from 45% to 95%. The drastic change in the conductivity is due to a sensitive response with respect to water molecules adsorbed on the surface of the two-dimensional nanosheet. The results may open an avenue for nanodevices built from various oxide nanosheets. [ABSTRACT FROM AUTHOR]

We report the photocatalytic activities of graphene oxide-alkylated amines (GO-An; GO: graphene oxide and An: alkylamine with n carbons in the alkyl group; n = 0, 1, 4, and 8). The hybrids were synthesized through facile, quick, and reproducible methods and were characterized by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and powder X-ray diffraction (PXRD) analysis. The hybrids exhibited efficient photocataytic activity to generate hydrogen gas by water splitting under UV light irradiation at room temperature. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) and reduced graphite oxide (rGtO) were analyzed by X-ray photoelectron spectroscopy. rGO and rGtO were prepared by photochemical, electrochemical, hydrazine-assisted, and thermal reduction of graphene oxide (GO) and graphite oxide (GtO). The number of CH defects increased for the photochemical and electrochemical reduction, whereas a direct increase in the number of C=C bonds was observed for thermal and hydrazine-assisted reduction. Cyclic voltammograms showed that the electrochemical capacitance of rGtO increased with the number of CH defects. [ABSTRACT FROM AUTHOR]

To increase the thermal and chemical stabilities of trypsin-proteolysis activity, trypsin was immobilized on graphene oxide nanosheets (GONSs) by a one-step diimide-activated amidation. The trypsin-immobilized GONS (1.9mg per mg-GONS) showed significantly higher thermal and chemical stabilities than the free form. After heat treatment at 50 °C for 6h, the trypsin-GONS retained 80% of its initial activity, but free trypsin retained only 4% of its initial activity. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic behaviors of molecularly thin Mndoped titanium oxide nanosheets by X-ray magnetic circular dichroism. Mn atoms in single-layer nanosheets showed a weak ferromagnetic order at room temperature. Fe overlayers deposited on the nanosheets induced a magnetic proximity effect on Mn magnetization. We clearly observed an antiferromagnetic coupling between the Fe overlayers and the Mn-doped nanosheets. [ABSTRACT FROM AUTHOR]

We report an approach for constructing ultrathin microwave dielectrics using two-dimensional (2D) perovskite nanosheets (Ca2Nb3O10). The solution-based layer-by-layer assembly of Ca2Nb3O10 nanosheets enables the tailoring of dielectric responses and breakdown voltage in order to realize miniaturized capacitors with improved performances. Multilayer stacked nanosheet films showed a stable dielectric response of up to 10 GHz; the dielectric constant of ∼200 is the highest among high-κ perovskites in the ultrathin region (<30 nm). Moreover, the nanosheet films realized a high capacitance density (∼20 µF/cm2) with a robust thermal stability up to 250 °C. These superior dielectric properties of perovskite nanosheets offer a new solution for high-performance microwave devices. [ABSTRACT FROM AUTHOR]