Jae‐Hyun Lee

The uniform growth of single-crystal graphene over wafer-scale areas remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based on graphene. Here, we describe wafer-scale growth of wrinkle-free single-crystal monolayer graphene on silicon wafer using a hydrogen-terminated germanium buffer layer. The anisotropic twofold symmetry of the germanium (110) surface allowed unidirectional alignment of multiple seeds, which were merg

The competition between quality and productivity has been a major issue for large-scale applications of two-dimensional materials (2DMs). Until now, the top-down mechanical cleavage method has guaranteed pure perfect 2DMs, but it has been considered a poor option in terms of manufacturing. Here, we present a layer-engineered exfoliation technique for graphene that not only allows us to obtain large-size graphene, up to a millimeter size, but also allows selective thickness control. A thin metal

Abstract The metallic 1T phase of WS 2 (1T‐WS 2 ), which boosts the charge transfer between the electron source and active edge sites, can be used as an efficient electrocatalyst for the hydrogen evolution reaction (HER). As the semiconductor 2H phase of WS 2 (2H‐WS 2 ) is inherently stable, methods for synthesizing 1T‐WS 2 are limited and complicated. Herein, a uniform wafer‐scale 1T‐WS 2 film is prepared using a plasma‐enhanced chemical vapor deposition (PE‐CVD) system. The growth temperature

-hybridized, was achieved at high temperatures (>900°C) and a controlled growth rate. We verified that the charge carriers within the Zachariasen carbon monolayer are strongly localized to display Anderson insulating behavior and a large negative magnetoresistance. This new 2D glass also exhibited a unique ability as an atom-thick interface layer, allowing the deposition of an atomically flat dielectric film. It can be adopted in conventional semiconductor and display processing or used in the f

Electrochemical CH4 oxidation is attractive as a strategy capable of conversion with high selectivity, but improving productivity remains a challenge. We demonstrate that CuO/CeO2 can serve as a catalyst for the room-temperature conversion of CH4 to CH3OH in the presence of CO32–. At an optimized ratio of CuO/CeO2 (Cu:Ce = 6:4), we achieve the highest production rate of 752.9 μmol/gcat/h (6 h reaction) at ambient pressure; among the oxygenates, a CH3OH selectivity of 79% is obtained. In an exper

The conventional pH sensor based on the graphene ion-sensitive field-effect transistor (Gr-ISFET), which operates with an electrostatic gating at the solution-graphene interface, cannot have a pH sensitivity above the Nernst limit (∼59 mV/pH). However, for accurate detection of the pH levels of an aqueous solution, an ultrasensitive pH sensor that can exceed the theoretical limit is required. In this study, a novel Gr-ISFET-based pH sensor is fabricated using proton-permeable defect-engineered g

A transparent and flexible film capable of shielding electromagnetic waves over a wide range of frequencies (X and K_u bands, 8-18 GHz) is prepared. The electromagnetic wave shielding film is fabricated using the excellent transmittance, electrical conductivity, and thermal stability of indium tin oxide (ITO), a representative transparent conductive oxide. The inherent mechanical brittleness of oxide ceramics is overcome by adopting a nanobranched structure. In addition, mechanical sta

High Resolution Image Download MS PowerPoint Slide We successfully demonstrated the improvement and stabilization of the electrical properties of a graphene field effect transistor by fabricating a sandwiched amorphous boron nitride (a-BN)/graphene (Gr)/a-BN using a directly grown a-BN film. The a-BN film was grown via low-pressure chemical vapor deposition (LPCVD) at a low growth temperature of 250 °C and applied as a protection layer in the sandwiched structure. Both structural and chemical st

Abstract The octahedral structure of 2D molybdenum disulfide (1T‐MoS 2 ) has attracted attention as a high‐efficiency and low‐cost electrocatalyst for hydrogen production. However, the large‐scale synthesis of 1T‐MoS 2 films has not been realized because of higher formation energy compared to that of the trigonal prismatic phase (2H)‐MoS 2 . In this study, a uniform wafer‐scale synthesis of the metastable 1T‐MoS 2 film is performed by sulfidation of the Mo metal layer using a plasma‐enhanced che

Despite the enormous potential of the single-crystalline two-dimensional (2D) materials for a wide range of future innovations and applications, 2D single-crystals are still suffering in industrialization due to the lack of efficient large-area production methods. In this work, we introduce a general approach for the scalable growth of single-crystalline graphene, which is a representative 2D material, through "transplanting" uniaxially aligned graphene "seedlings" onto a larger-area catalytic g

Abstract The dynamic tuning of ion concentrations has attracted significant attention for creating versatile functionalities of materials, which are impossible to reach using classical control knobs. Despite these merits, the following fundamental questions remain: how do ions affect the electronic bandstructure, and how do ions simultaneously change the electrical and magnetic properties? Here, by annealing platinum‐dotted La 0.67 Sr 0.33 MnO 3 films in hydrogen and argon at a lower temperature

Mass production of one-dimensional, V₂Se₉ crystals, was successfully synthesized using the solid-state reaction of vanadium and selenium. Through the mechanical exfoliation method, the bulk V₂Se₉ crystal was easily separated to nanoribbon structure and we have confirmed that as-grown V₂Se₉ crystals consist of innumerable single V₂Se₉ chains linked by van der Waals interaction. The exfoliated V₂Se₉ flakes can be controlled thickness by the repeated-peeling method. In addition, atomic thick nanori

Since the first development of large-area graphene synthesis by the chemical vapor deposition (CVD) method in 2009, CVD-graphene has been considered to be a key material in the future electronics, energy, and display industries, which require transparent, flexible, and stretchable characteristics. Although many graphene-based prototype applications have been demonstrated, several important issues must be addressed in order for them to be compatible with current complementary metal-oxide-semicond

Centimeter‐size single‐crystalline Nb 3 I 8 , a new family of two‐dimensional materials, is first synthesized by a vapor transport reaction of niobium and iodine. Through the mechanical exfoliation method, the bulk Nb 3 I 8 crystal is cleaved to monolayer and multi‐layered flakes. It is confirmed to consist of numerous monolayers of Nb 3 I 8 bonded by weak van der Waals interaction. By utilizing atomic force microscopy (AFM) and scanning Kelvin probe microscopy (SKPM), the information on structu

Abstract Since the first realization of graphene synthesis through the chemical vapor deposition (CVD) method in 2009, CVD‐graphene is regarded as a key material in the future electronics industry, and one that requires high standard characteristics. However, because graphene itself is not a semiconductor, therefore it does not have a bandgap, a promising application is considered to integrate its use with semiconductors, rather than completely replace Si or Ge. Although numerous methods for a c