Near-field probing of dielectric screening by hexagonal boron nitride in graphene integrated on silicon photonics.

Hexagonal boron nitride (hBN) is one of the most suitable 2D materials for supporting graphene in electronic devices, and it plays a fundamental role in screening out the effect of charge impurities in graphene in contrast to inhomogeneous supports such as silicon dioxide (SiO). Although many interesting surface science techniques such as scanning tunneling microscopy (STM) revealed dielectric screening by hBN and emergent physical phenomena were observed, STM is only appropriate for graphene electronics. In this paper, we demonstrate the dielectric screening by hBN in graphene integrated on a silicon photonic waveguide from the perspective of a near-field scanning optical microscopy (NSOM) and Raman spectroscopy.

Anomalous K-Point Phonons in Noble Metal/Graphene Heterostructure Activated by Localized Surface Plasmon Resonance.

The metal/graphene interface has been one of the most important research topics with regard to charge screening, charge transfer, contact resistance, and solar cells. Chemical bond formation of metal and graphene can be deduced from the defect induced D-band and its second-order mode, 2D band, measured by Raman spectroscopy, as a simple and nondestructive method. However, a phonon mode located at ∼1350 cm, which is normally known as the defect-induced D-band, is intriguing for graphene deposited with noble metals (Ag, Au, and Cu).

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor.

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using in situ activated MnO and VO electrodes.

Gas adsorbates are Coulomb scatterers, rather than neutral ones, in a monolayer MoS field effect transistor.

Direct current (DC) and low-frequency (LF) noise analyses of a chemical vapor deposition (CVD)-grown monolayer MoS2 field effect transistor (FET) indicate that time-varying carrier perturbations originate from gas adsorbates. The LF noise analysis supports that the natural desorption of physisorbed gas molecules, water and oxygen, largely reduces the interface trap density (NST) under vacuum conditions (∼10-8 Torr) for 2 weeks. After a longer period of 8 months under vacuum, the carrier scattering mechanism alters, in particular for the low carrier density (Nacc) region.

DEVICE TECHNOLOGY. Phase patterning for ohmic homojunction contact in MoTe₂.

Artificial van der Waals heterostructures with two-dimensional (2D) atomic crystals are promising as an active channel or as a buffer contact layer for next-generation devices. However, genuine 2D heterostructure devices remain limited because of impurity-involved transfer process and metastable and inhomogeneous heterostructure formation. We used laser-induced phase patterning, a polymorph engineering, to fabricate an ohmic heterophase homojunction between semiconducting hexagonal (2H) and metallic monoclinic (1T') molybdenum ditelluride (MoTe2) that is stable up to 300°C and increases the carrier mobility of the MoTe2 transistor by a factor of about 50, while retaining a high on/off current ratio of 10(6).

Synthesis of centimeter-scale monolayer tungsten disulfide film on gold foils.

We report the synthesis of centimeter-scale monolayer WS2 on gold foil by chemical vapor deposition. The limited tungsten and sulfur solubility in gold foil allows monolayer WS2 film growth on gold surface. To ensure the coverage uniformity of monolayer WS2 film, the tungsten source-coated substrate was placed in parallel with Au foil under hydrogen sulfide atmosphere.