Research
Selected work
Research from the SKKU-STEM Lab — methods at the intersection of scanning transmission electron microscopy, electron spectroscopy, and machine learning, applied to energy materials.
“A shuttle guiding us to atomic world.”
2026
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A growth mechanism for grain-boundary-free ultraflat silver thin films
STEM revealed a feasible mechanism for a breakthrough in metal thin-film epitaxy, enabling wafer-scale growth of atomically flat, grain-boundary-free Ag films on Cu buffers with a 13% lattice mismatch.
Reports on Progress in Physics · 89(2), 028002
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A machine learning solution for electrode characterization
Machine learning-driven electron spectroscopic imaging (ESI) approach enables nanoscale visualization and statistical analysis of structural degradation in PEMFC electrodes.
Applied Catalysis B: Environment and Energy · 382, 125911
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2025
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Sparse section imaging-based deep learning electron tomography
Deep learning-empowered electron tomography visualizes the 3D structure of porous carbon supports in PEMFC with only a few image frames, reducing data requirements by more than 95%.
Journal of Energy Chemistry · 104, 795-806
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2024
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Revealing the role of oxygen vacancy in an oxide solid electrolyte
The hidden role of the oxygen vacancy (VO) in facilitating Li-ion transport in lithium lanthanum titanate solid electrolytes was unveiled. The VO is directionally interconnected to form a 2D network parallel to the c-plane.
ACS Energy Letters · 9(11), 5606-5615
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4D STEM-based domain mapping for perovskite solar cells
4D STEM-based crystallographic domain mapping unfolded the mystery of aging-induced efficiency improvement of perovskite solar cells, revealing that aging can induce partial lattice strain relaxation.
ACS Energy Letters · 9(7), 3618-3627
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2023
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The interplay of structure-cation defect-oxygen vacancy in doped HfO2 film
Multimodal 4D-STEM (PA)CBED/EDX/EELS at multiple length scales revealed the complicated interplay of structure, cation defects, and oxygen vacancies in La-doped HfO2 films.
ACS Nano · 17(19), 19076-19086
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Unveiling self-oxidation resistance mechanism of a curved Cu surface
Pico-scale precision electron microscopy revealed that porous copper nanostructures self-regulate giant oxidation resistance by constructing a curved surface that generates a series of monoatomic steps.
Advanced Materials · 35(42), 2210564
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Deep learning catalyst particle analysis with Attention U-Net
Proposes a rapid, automated, and reliable analytical method for the morphological distribution of Pt-based electrocatalyst nanoparticles using deep learning processing.
Materials Today Energy · 36, 101348
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Elucidating the growth mechanism of a single crystal Cu thin film
Electron microscopy describes in detail the initial growth of copper thin films required for mono-atom step-level flat surfaces (MSFSs). Deposition by atomic sputtering epitaxy leads to the coherent merging of trillions of islands.
Nature Communications · 14, 685
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Single particle-level spectroscopic mapping for defect distributions
Computation-aided STEM-EELS showed that the distributions of surface oxygen vacancies and reduced Ti valencies enclosing a stoichiometric core were responsible for enhanced photocatalytic activity.
Applied Catalysis B-Environmental · 322, 122140
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2022
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Segmented electron tomography for PEM-fuel cell analysis
Advanced segmented electron tomography visualizes the 3D structure of carbon supports in proton exchange membrane fuel cells (PEM-FCs) and explains structural degradation phenomena.
Journal of Energy Chemistry · 74, 359-367
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Mechanism for ion enhanced polarization in doped HfO2
A multimodal investigation based on microscopy and spectroscopy showed that ferroelectric properties improve when films of hafnium oxide are bombarded with a beam of helium ions.
Science · 376(6594), 731-738
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Hybrid deep learning crystallography with 4D-STEM
Deep learning crystallographic analysis unequivocally addresses structure problems for sub-10 nm polycrystalline hafnium zirconium oxide thin films.
Small · 18(18), 2107620
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Superb oxidation resistance of Cu uncovered by electron microscopy
Comprehensive atomic-resolution microscopy revealed that wafer-scale Cu(111) single-crystal thin films free of multilayer step edges show a semi-permanent oxidation resistance.
Nature · 603(7901), 434-438
2022 Top 10 Nanotechnology Research Excellence (Nanotechnology Research Council)Figure -
Unveiled doping mechanisms in oxide catalysts
Electron microscopy and spectroscopy combined with theoretical modeling can directly resolve the site-specific doping phenomena of transition metals in SnO2 nanoparticles.
Applied Catalysis B-Environmental · 305, 121083
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2021
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Deep learning algorithm for automated defect quantification in 2D TMDs
A deep learning-assisted quantification algorithm reduces the heavy load of data processing for researchers, which has hindered the pace of design and development of two-dimensional transition metal dichalcogenides.
Advanced Science · 8, 2101099
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Picoscale precision lattice strain analysis for multidomain 2D TMDs
STEM-based statistical lattice strain analysis provided the first demonstration of successful control of the lattice structure of anisotropic ReS2, resulting in isotropic responses.
ACS Nano · 15, 13770-13780
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Atomic-scale chemical mapping of Cu dopants (0.2 at.%) in a thermoelectric alloy by STEM-EDX
Successfully mapped copper dopants added at 0.2 at.% into a multi-component thermoelectric alloy (Bi2Te2.7Se0.3) system using advanced energy dispersive X-ray spectroscopy (EDX) spectrum imaging.
Materials Today Physics · 17, 100347
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Cation vacancy mapping by STEM-EDX
STEM-EDX chemical mapping provides an atomic-level picture of what truly occurs with cation vacancies at an oxide interface — Sr and Ti vacancies in SrTiO3 film and Nb ions diffused from a Nb:SrTiO3 substrate.
Materials Today Physics · 16, 100302
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2020
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High-resolution STEM-EELS analysis of doped ZnO nanoparticles
Atomic-scale STEM observations combined with site-specific electron energy loss spectroscopy revealed that two transition metal ions substitute for Zn, in different valence states (Cr3+ and Co2+).
Journal of Materials Chemistry A · 8, 25345-25354
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Atomic resolution analysis of nanoparticles by STEM-EELS/EDX
STEM-EELS/EDX-based work revealed that surface oxygen vacancies in anatase-type Fe@TiO2 nanoparticles for superior photocatalytic activities can be readily controlled by simple pH treatment.
Applied Surface Science · 507, 144916
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2019
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3D electron tomography for Li ion batteries
Demonstrates how the geometrical parameters of active cathode materials are inextricably linked to their battery performance, based on multimodal/multiscale characterizations.
ACS Applied Materials & Interfaces · 11, 4017
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2018
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Atom counting analysis for 2D materials
Investigates the hitherto unsolved conundrum of how organic chemicals can heal chalcogen vacancies in MoS2 monolayer at the atomic scale, observing chalcogen vacancy healing by an organic molecule.
Nano Letters · 18(7), 4523
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Oxygen octahedral tilt mapping for complex oxide thin films
Provides the first demonstration of octahedra-derived multiferroic properties that can be stabilized in a thin film form without the help of complex chemical modifications.
Advanced Functional Materials · 19, 1800839
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Valence state mapping for Li ion batteries
Using atom-resolved STEM-EDX/EELS, this study reveals that the electrochemical properties of Li(NixCoyMnz)O2 (NCM) materials are decisively determined by the interplay of combined cation disordering.
Journal of Materials Chemistry A · 6, 16111
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2017
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Atomic-resolution chemical mapping for energy materials
Atomic-resolution STEM-EDX chemical mapping was conducted for the direct visualization of atomic-scale interstitial and antisite defects in complete single-phase Ti1-xHfxNiSn1-ySby half-Heusler (HH) thermoelectric alloys.
Advanced Materials · 29, 1702091
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2014
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Polarization mapping for ferroelectric materials
By a combination of microscopy and spectroscopy techniques, we directly observed for the first time the field effect in a ferroelectric material that exhibits switchable electrical polarization at the ferroelectric–electrode interface.
Nature Materials · 13, 1019
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2012
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Oxygen vacancy mapping for solid oxide fuel cell cathode materials
Local oxygen stoichiometry in functional oxides has been a long-standing challenge. The method developed in this work quantifies oxygen vacancy distribution and homogeneity, which directly control the operation of solid-oxide fuel cells.
Nature Materials · 11, 888
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