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

Rapid progress in two-dimensional (2D) crystalline materials has recently enabled a range of device possibilities. These possibilities may be further expanded through the development of advanced 2D glass materials. Zachariasen carbon monolayer, a novel amorphous 2D carbon allotrope, was successfully synthesized on germanium surface. The one-atom-thick continuous amorphous layer, in which the in-plane carbon network was fully <i>sp</i>²-hybridized, was achieved at high temperatures (>9

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

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

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 MnO₃ films in hydrogen and argon a

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

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

A novel semiconductor 1D nanomaterial, Nb₂Se₉, was synthesized on a bulk scale <i>via</i> simple vapor transport reaction between niobium and selenium. Needle-like single crystal Nb₂Se₉ contains numerous single Nb₂Se₉ chains linked by van der Waals interactions, and we confirmed that a bundle of chains can be easily separated by mechanical cleavage. The exfoliated Nb₂Se₉ flakes exhibit a quasi-two-dimensional

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

We report the direct growth of graphene on a dielectric SiO2 surface by utilizing complementary metal oxide semiconductor compatible germane as a gas-phase catalyst. Results of Raman spectroscopy and XPS confirmed that the synthesized graphene consist of a sp2 hybridized carbon network. We were able to fabricate graphene field effect transistors without the wet etching process, and the calculated mobility was ∼160 cm2/V·s at high carrier concentration (n = 3 × 1012 cm−2). Furthermore, the crysta