A Modified Wet Transfer Method for Eliminating Interfacial Impurities in Graphene.

Graphene has immense potential as a material for electronic devices owing to its unique electrical properties. However, large-area graphene produced by chemical vapor deposition (CVD) must be transferred from the as-grown copper substrate to an arbitrary substrate for device fabrication. The conventional wet transfer technique, which uses FeCl3 as a Cu etchant, leaves microscale impurities from the substrate, and the etchant adheres to graphene, thereby degrading its electrical performance. To address this limitation, this study introduces a modified transfer process that utilizes a temporary UV-treated SiO2 substrate to adsorb impurities from graphene before transferring it onto the final substrate. Optical microscopy and Raman mapping confirmed the adhesion of impurities to the temporary substrate, leading to a clean graphene/substrate interface. The retransferred graphene shows a reduction in electron-hole asymmetry and sheet resistance compared to conventionally transferred graphene, as confirmed by the transmission line model (TLM) and Hall effect measurements (HEMs). These results indicate that only the substrate effects remain in action in the retransferred graphene, and most of the effects of the impurities are eliminated. Overall, the modified transfer process is a promising method for obtaining high-quality graphene suitable for industrial-scale utilization in electronic devices.

Surface Plasmon Resonance-Enhanced Near-Infrared Absorption in Single-Layer MoS2 with Vertically Aligned Nanoflakes.

The development of MoS2 with two- or three-dimensional heterostructures can provide a significant breakthrough for the enhancement of photodetection abilities such as increase in light absorption and expanding the detection ranges. Till date, although the synthesis of a MoS2 layer with three-dimensional nanostructures using a chemical vapor deposition (CVD) process has been successfully demonstrated, most studies have concentrated on electrochemical applications that utilize structural strengths, for example, a large specific surface area and electrochemically active sites. Here, for the first time, we report spectral light absorption induced by plasmon resonances in single-layer MoS2 (SL-MoS2) with vertically aligned nanoflakes grown by a CVD process. Treatment with oxygen plasma results in the formation of a substoichiometric phase of MoOx in the vertical nanoflakes, which exhibit a high electron density of 4.5 × 1013 cm-2. The substoichiometric MoOx with a high electron-doping level that is locally present on the SL-MoS2 surface induces an absorption band in the near-infrared (NIR) wavelength range of 1000-1750 nm because of the plasmon resonances. Finally, we demonstrate the enhancement of photodetection ability by broadening the detection range from the visible region to the NIR region in oxygen-treated SL-MoS2 with vertically aligned nanoflakes.

High Durability and Waterproofing rGO/SWCNT-Fabric-Based Multifunctional Sensors for Human-Motion Detection.

Wearable strain-pressure sensors for detecting electrical signals generated by human activities are being widely investigated because of their diverse potential applications, from observing human motion to health monitoring. In this study, we fabricated reduced graphene oxide (rGO)/single-wall carbon nanotube (SWCNT) hybrid fabric-based strain-pressure sensors using a simple solution process. The structural and chemical properties of the rGO/SWCNT fabrics were characterized using scanning electron microscopy (SEM), Raman, and X-ray photoelectron spectroscopy (XPS). Complex networks containing rGO and SWCNTs were homogeneously formed on the cotton fabric. The sensing performance of the devices was evaluated by measuring the effects of bending strain and pressure. When the CNT content was increased, the change in relative resistance decreased, while durability was significantly improved. The rGO/SWCNT (0.04 wt %) fabric sensor showed particularly high mechanical stability and flexibility during 100 000 bending tests at the extremely small bending radius of 3.5 mm (11.6% bending strain). Moreover, the rGO/SWCNT fabric device exhibited excellent water resistant properties after 10 washing tests due to its hydrophobic nature. Finally, we demonstrated a fabric-sensor-based motion glove and confirmed its practical applicability.

Gas molecule sensing of van der Waals tunnel field effect transistors.

van der Waals (vdW) heterostructures with two-dimensional (2D) crystals such as graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDCs) allow us to demonstrate atomically thin field-effect transistors (FETs), photodetectors (PDs) and photovoltaic devices capable of higher performance and greater stability levels than conventional devices. Although there have been studies of gas molecule sensing with 2D crystal channels, vdW heterostructures based on 2D crystals have not been employed thus far. Here, utilizing graphene/WS2/graphene (G/WS2/G) vdW heterostructure tunnel FETs, we demonstrate the rectification behavior of the sensitivity signal by tuning the WS2 potential barriers as a function of the gas molecule concentration and devise a fingerprint map of the sensitivity variation corresponding to an individual ratio of two different molecules in a gas mixture. Because the separation of different gas molecule concentrations from gas mixtures is in high demand in the gas-sensing research field, this result will greatly assist in the progress on selective gas sensing.

Reflection-type spatial amplitude modulation of visible light based on a sub-wavelength plasmonic absorber.

We present a method for reflection-type spatial amplitude modulation using a sub-wavelength plasmonic absorber structure that can operate in the visible region. We utilize a pixelated array of absorbing elements based on a two-dimensional sub-wavelength metal grating, and the reflectance of each pixel is controlled by simple structural modification. For the purpose of validation, numerical simulations were performed on an amplitude modulation hologram fabricated using our method.

Investigation of electric/magnetic local interaction between Si photonic-crystal nanocavities and Au meta-atoms.

We experimentally investigate nanoscale local interaction in a composite system consisting of dielectric photonic-crystal nanocavity and metallic meta-atoms. The Q factor of the composite system changes by a maximum of about 10 dB based on the relative position and the type of meta-atoms. The emission by meta-atoms dominates the nanocavity emission when they are in the electric or magnetic antinodes of the cavity field. Circularly polarized emission is achieved by tuning the polarization, the position, and the coupling phase of each meta-atom with respect to the nanocavity. Utilization of the local interaction with meta-atoms is shown to be useful as a new degree of freedom in tailoring the characteristics of nanocavities.