Yonsei University · Materials Science
Professor Kwanpyo Kim's research lab specializes in the synthesis, characterization, and application of two-dimensional nanomaterials, with a strong focus on graphene and its heterostructures. The lab investigates the atomic-scale structure, electronic properties, and mechanical behavior of graphene-based systems, including grain boundaries, twisted bilayer structures, folded graphene (grafold), and graphene nanoribbons. By combining advanced electron microscopy techniques with theoretical modeling, the lab explores how nanostructure engineering can tailor electronic and mechanical properties for next-generation nanoelectronics and 2D heterostructures.
Figures are computed from collected data and may differ slightly.
We report direct mapping of the grains and grain boundaries (GBs) of large-area monolayer polycrystalline graphene sheets, at large (several micrometer) and single-atom length scales. Global grain and GB mapping is performed using electron diffraction in scanning transmission electron microscopy (STEM) or using dark-field imaging in conventional TEM. Additionally, we employ aberration-corrected TEM to extract direct images of the local atomic arrangements of graphene GBs, which reveal the altern
We present a systematic Raman study of unconventionally stacked double-layer graphene, and find that the spectrum strongly depends on the relative rotation angle between layers. Rotation-dependent trends in the position, width and intensity of graphene 2D and G peaks are experimentally established and accounted for theoretically. Our theoretical analysis reveals that changes in electronic band structure due to the interlayer interaction, such as rotational-angle dependent Van Hove singularities,
The folding of paper, hide, and woven fabric has been used for millennia to achieve enhanced articulation, curvature, and visual appeal for intrinsically flat, two-dimensional materials. For graphene, an ideal two-dimensional material, folding may transform it to complex shapes with new and distinct properties. Here, we present experimental results that folded structures in graphene, termed grafold, exist, and their formations can be controlled by introducing anisotropic surface curvature during
The understanding of crack formation due to applied stress is key to predicting the ultimate mechanical behavior of many solids. Here we present experimental and theoretical studies on cracks or tears in suspended monolayer graphene membranes. Using transmission electron microscopy, we investigate the crystallographic orientations of tears. Edges from mechanically induced ripping exhibit straight lines and are predominantly aligned in the armchair or zigzag directions of the graphene lattice. El
Graphene, with its unique electronic and structural qualities, has become an important playground for studying adsorption and assembly of various materials including organic molecules. Moreover, organic/graphene vertical structures assembled by van der Waals interaction have potential for multifunctional device applications. Here, we investigate structural and electrical properties of vertical heterostructures composed of C60 thin film on graphene. The assembled film structure of C60 on graphene
We describe a clean method of graphene nanoribbon (GNR) extraction from multiwall carbon nanotubes (MWNTs), performed in a high vacuum, nonchemical environment. Electrical current and nanomanipulation are used to unwrap a portion of the MWNT and thus produce a GNR of desired width and length. The unwrapping method allows GNRs to be concurrently characterized structurally via high-resolution transmission electron microscopy (TEM) and evaluated for electrical transport, including situations for wh
Abstract We report in situ Joule heating on suspended single‐layer graphene in a transmission electron microscope (TEM). Thermally‐driven degradation of pre‐deposited nanoparticles on the membrane is monitored and used for local temperature estimation. By extrapolating the Joule heating power and temperature relation, we find that the suspended single‐layer graphene has exceptional thermal stability up to at least 2600 K. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The family of group IV-VI monochalcogenides has an atomically puckered layered structure, and their atomic bond configuration suggests the possibility for the realization of various polymorphs. Here, we report the synthesis of the first hexagonal polymorph from the family of group IV-VI monochalcogenides, which is conventionally orthorhombic. Recently predicted four-atomic-thick hexagonal GeSe, so-called γ-GeSe, is synthesized and clearly identified by complementary structural characterizations,
Organic-graphene system has emerged as a new platform for various applications such as flexible organic photovoltaics and organic light emitting diodes. Due to its important implication in charge transport, the study and reliable control of molecular packing structures at the graphene-molecule interface are of great importance for successful incorporation of graphene in related organic devices. Here, an ideal membrane of suspended graphene as a molecular assembly template is utilized to investig
Scanning transmission electron microscopy (STEM) is an indispensable tool for atomic-resolution structural analysis for a wide range of materials. The conventional analysis of STEM images is an extensive hands-on process, which limits efficient handling of high-throughput data. Here, we apply a fully convolutional network (FCN) for identification of important structural features of two-dimensional crystals. ResUNet, a type of FCN, is utilized in identifying sulfur vacancies and polymorph types o
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