Jeongyong Kim

We performed a nanoscale confocal absorption spectral imaging to obtain the full absorption spectra (over the range 1.5-3.2 eV) within regions having different numbers of layers and studied the variation of optical transition depending on the atomic thickness of the MoS2 film. Three distinct absorption bands corresponding to A and B excitons and a high-energy background (BG) peak at 2.84 eV displayed a gradual redshift as the MoS2 film thickness increased from the monolayer, to the bilayer, to t

Structural defects can critically influence the electrical and optical properties of monolayered molybdenum disulfide (MoS2) grown by chemical vapor deposition (CVD); thus, convenient optical methods that can visualize grain boundaries (GBs) and other structural defects are in great demand. Although photoluminescence (PL) imaging can identify the presence of relatively large defects, the limited spatial resolution of PL imaging prevents the identification of nanosized structural defects in the m

Monolayer (1L) transition metal dichalcogenides (TMDs) are two-dimensional direct-bandgap semiconductors with promising applications of quantum light emitters. Recent studies have shown that intrinsically low quantum yields (QYs) of 1L-TMDs can be greatly improved by chemical treatments. However, nonradiative exciton–exciton annihilation (EEA) appears to significantly limit light emission of 1L-TMDs at a nominal density of photoexcited excitons due to strong Coulomb interaction. Here we show tha

The extreme elastic strain of monolayer transition metal dichalcogenides provides an ideal platform to achieve efficient exciton funneling via local strain modulation; however, studies conducted thus far have focused on the use of substrates with fixed strain profiles. We prepared 1L-WS₂ on a flexible substrate such that the formation of topographic wrinkles could be switched on or off, and the depth or the direction of the wrinkle could be modified by external strain, thereby providi

Alloying two-dimensional transition metal dichalcogenides (2D TMDs) is a promising avenue for band gap engineering. In addition, developing a scalable synthesis process is essential for the practical application of these alloys with tunable band gaps in optoelectronic devices. Here, we report the synthesis of optically uniform and scalable single-layer Mo_{1- x}W _xS₂ alloys by a two-step chemical vapor deposition (CVD) method followed by a laser thinning process. Th

MXene (M_{<italic>n</italic>+1}X_{<italic>n</italic>}) is an emerging class of layered two-dimensional (2D) materials, which are derived from their bulk-state MAX phase (M_{<italic>n</italic>+1}AX_{<italic>n</italic>}, where M: early transition metal, A: group element 13 and 14, and X: carbon and/or nitrogen). MXenes have found wide-ranging applications in energy storage devices, sensors, catalysis, etc. owing to their high electronic conductivity and wide range o

Plasmon coupling and propagation between metallic nanowires (NWs) and atomically thin transition-metal dichalcogenide semiconductors are demonstrated using Ag NW/MoS2 hybrids. The high exciton–plasmon coupling efficiency with large throughput of MoS2 excitons allows quantitative assessment of plasmon waveguide performance. Monolayer MoS2 allows real-space visualization of the propagating plasmons along the NW via direct plasmon–exciton coupling. As a service to our authors and readers, this jour

Exciton transitions are mostly responsible for the optical properties of transition metal dichalcogenide monolayers (1L-TMDs). Extensive studies of optical and structural characterization indicated that the presence of local structural defects and charge population critically influence the exciton emissions of 1L-TMDs. However, due to large variations of sample and experimental conditions, the exact mechanism of the exciton emission influenced by local structural defects and charge population is

In general, the quantum yields (QYs) of monolayer transition metal dichalcogenides (1L-TMDs) are low, typically less than 1% in their pristine state, significantly limiting their photonic applications. Many methods have been reported to increase the QYs of 1L-TMDs; however, the technical difficulties involved in the reliable estimation of these QYs have prevented the general assessment of these methods. Herein, we demonstrate the estimation of the QYs of 1L-TMDs using a poly methyl methacrylate

Abstract Topological defects have received much attention due to their stability against perturbations and potential applications in nonvolatile high-density memory. Topologically non-trivial textures can be compelled by constraints on boundary condition, geometrical structure, and curved space. Ferroelectric vortices have been realized in various finite-sized nanostructures that allow such constraints to be produced. However, manipulation of topological excitations in otherwise topologically tr

As part of the ongoing effort to be independent of petroleum resources and to be free from pollutant emission issues, various electric vehicles have been developed and tested through their integration with real world systems. In the current paper, yet another application specific EV for public transportation, an electric bus, is introduced and explained with results from the pilot test program which was carried out under real traffic conditions. The main feature of the current system is a batter

The electrical and optical characteristics of two-dimensional (2D) transition-metal dichalcogenides (TMDCs) can be improved by surface modification. In this study, distinctive field-effect transistors (FETs) were realized by forming cross-type 2D WSe₂/MoS₂ p-n heterojunctions through surface treatment using poly(methyl methacrylate-<i>co</i>-methacrylic acid) (PMMA-<i>co</i>-PMAA). The FETs were applied to new ternary inverters as multivalued logic circuits (MVLCs). Laser c

Abstract Two‐dimensional transition metal dichalcogenides (2D‐TMDs) are atomically thin semiconductors with a direct bandgap in monolayer thickness, providing ideal platforms for the development of exciton‐based optoelectronic devices. Extensive studies on the spectral characteristics of exciton emission have been performed, but spatially resolved optical studies of 2D‐TMDs are also critically important because of large variations in the spatial profiles of exciton emissions due to local defects

Spatially heterogeneous effects of bis(trifluoromethane)sulfonimide (TFSI) and benzyl viologen (BV) treatment on the optical properties of triangular monolayer tungsten disulfides are investigated by nanoscale spectral imaging.