Gun-Do Lee

Gun-Do Lee
Seoul National University | SNU · Department of Materials Science and Engineering

Dr.

About

110
Publications
20,054
Reads
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3,043
Citations
Citations since 2017
39 Research Items
1852 Citations
2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300
Additional affiliations
June 2008 - present
Seoul National University
Position
  • Professor
September 1996 - September 1998
Iowa State University
Position
  • Visiting Scientist

Publications

Publications (110)
Article
Defects in crystalline lattices cause modulation of the atomic density, and this leads to variations in the associated electrostatics at the nanoscale. Mapping these spatially varying charge fluctuations using transmission electron microscopy has typically been challenging due to complicated contrast transfer inherent to conventional phase contrast...
Article
Al-Zn-Mg alloys are widely used in the transportation industry owing to their high strength-to-weight ratio. In these alloys, the main strengthening mechanism is precipitation hardening that occurs because of the formation of nano-sized precipitates. Herein, an interfacial structure of η4 precipitates, one of the main precipitates in these alloys,...
Preprint
Full-text available
Although many years have passed since the discovery of high-critical-temperature (high-$T_c$) superconducting materials, the underlying mechanism is still unknown. The B1g phonon anomaly in high-Tc cuprate superconductors has long been studied; however, the correlation between the B1g phonon anomaly and superconductivity has yet to be clarified. In...
Article
Ruddlesden-Popper oxides (A2 BO4 ) have attracted significant attention regarding their potential application in novel electronic and energy devices. However, practical uses of A2 BO4 thin films have been limited by extended defects such as out-of-phase boundaries (OPBs). OPBs disrupt the layered structure of A2 BO4 , which restricts functionality....
Article
The effect of local atomic arrangement of CuZn alloys was demonstrated on enhanced ethanol selectivity from CO 2 RR and supported by density functional theory (DFT) calculations.
Article
Full-text available
Interhalogen compounds (IHCs) are extremely reactive molecules used for halogenation, catalyst, selective etchant, and surface modification. Most of the IHCs are unstable at room temperature especially for the iodine-monofluoride (IF) whose structure is still unknown. Here we demonstrate an unambiguous observation of two-dimensional (2D) IF bilayer...
Article
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For steady electroconversion to value-added chemical products with high efficiency, electrocatalyst reconstruction during electrochemical reactions is a critical issue in catalyst design strategies. Here, we report a reconstruction-immunized catalyst system in which Cu nanoparticles are protected by a quasi-graphitic C shell. This C shell epitaxial...
Article
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For graphene-based 2D materials, charge transfer at the interface between graphene and ferromagnetic metal leads to many intriguing phenomena. However, because of the unidirectional spin orientation in ferromagnetic transition metals, interface interaction plays a detrimental role in diminishing the magnetic parameters on 2D surfaces. To overcome t...
Article
Precise controlled filling of point vacancies in hBN with carbon atoms is demonstrated using a focused electron beam method, which guides mobile C atoms into the desired defect site. Optimization of the technique enables the insertion of a single C atom into a selected monovacancy, and preferential defect filling with sub-2 nm accuracy. Increasing...
Article
The nature of the electronic interaction of precursor molecules with functionalized surfaces are still uncertain. Here, DFT calculations were performed to study the dissociative reactions of TiCl4 on non-hydroxylated and hydroxylated α-Al2O3 (0 0 0 1) surface based on DFT calculation. For non-hydroxylated α-Al2O3 (0 0 0 1) surface, residual Cl atom...
Article
The nature and the mechanism of the film interaction with the substrate at the film/substrate interface are still far from being fully understood. Here, we demonstrate an ab initio investigation of the thermodynamic driving force across the initial phase among amorphous and crystalline structures in the film formation of TiN on an alumina substrate...
Article
Point defects in freestanding graphene monolayers such as monovacancies and divacancies have been investigated at atomic scale with aberration-corrected transmission electron microscopy and theoretical calculations. In general, these defects can be formed simply by the absence of individual carbon atoms and carbon bond reconstructions in the graphe...
Article
Full-text available
The structural transformations of graphene defects have been extensively researched through aberration-corrected transmission electron microscopy (AC-TEM) and theoretical calculations. For a long time, a core concept in understanding the structural evolution of graphene defects has been the Stone-Thrower-Wales (STW)–type bond rotation. In this stud...
Article
Electrocatalysts for CO2 electroreduction require not only high-performance active materials to control the series reaction but also conductive and durable supports to ensure long-term stability under harsh operating conditions. Instead of conventional heterogeneous catalysts made by attaching metal on supports, we manufactured a self-formed tandem...
Article
Electrochemical reduction reaction of CO 2 (CO 2 RR) to valuable products offers potential for storing excessed renewable energy as well as chance to close the carbon loop, displacing the fossil fuel in chemical industries. Major efforts have been made to direct conversion of CO 2 to ethylene which is widely used building blocks for chemical indust...
Article
Scanning moiré fringe (SMF) is a widely utilized technique for the precise measurement of the strain field in semiconductor transistors and hetero-interfaces. With the growing challenges of traditional chip scaling, two-dimensional (2D) materials turn out to be ideal candidates for incorporation into semiconductor devices. Therefore, a method to ef...
Article
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Amorphous carbon (a-C) films have attracted significant attention due to their reliable structures and superior mechanical, chemical and electronic properties, making them a strong candidate as an etch hard mask material for the fabrication of future integrated semiconductor devices. Density functional theory (DFT) calculations and ab initio molecu...
Article
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Amorphous carbon (a-C) films have received significant attention due to their reliable structures and superior mechanical, chemical and electronic properties, making them a strong candidate as a hard mask material. We investigated the energetics, structure, and electronic and mechanical properties of the B, N, and Cl doped a-C films based on densit...
Article
For the future mass production of silicon-based devices, the deposition process of hydrogenated silicon (Si:H) thin films must not only satisfy several important material properties, it must also be highly productive. Therefore, a deep understanding of the reactivities of silicon precursors such as SiH4 and Si2H6 on substrate surfaces is required t...
Article
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We investigated the effects of nitrogen doping in amorphous carbon layers on the diffusion of fluorine atoms based on density functional theory calculations. For N doping at both substitutional and interstitial sites, the F atom binds to the surrounding C atoms rather than the N atom during structural relaxation due to the electrostatic repulsion b...
Article
Full-text available
Though numerous first-principle studies have suggested candidate materials for enhanced electrocatalyst, to synthesize such phase is quite another challenge. Furthermore, it has been still required to combine the active material with supporting matrix in optimized structure for stability and surface accessibility. Herein, we report predictive fabri...
Article
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We present an atomic level study of reversible cyclization processes in suspended nanoconstricted regions of graphene that form linear carbon chains (LCCs). Before the nanoconstricted region reaches a single linear carbon chain (SLCC), we observe that a double linear carbon chain (DLCC) structure often reverts back to a ribbon of sp² hybridized oli...
Article
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We investigated the overall ALD reaction mechanism for W deposition on TiN surfaces based on DFT calculation as well as the detailed dissociative reactions of WF6. Our calculated results suggest that the overall reactions of the WF6 on the B-covered TiN surfaces are energetically much more favorable than the one on the TiN surfaces, which means tha...
Article
Solid-phase epitaxy (SPE), a solid-state phase transition of materials from an amorphous to a crystalline phase, is a convenient crystal growing technique. In particular, SPE can be used to grow α-Al2O3 epitaxially with a novel structure that provides an effective substrate for improved performance of light-emitting diodes (LEDs). However, the inev...
Article
The recent emergence of vertically stacked two-dimensional van der Waals (vdW) heterostructures provides new opportunities for these materials to be employed in a wide range of novel applications. Understanding the interlayer coupling in the stacking geometries of the heterostructures and its effect on the resultant material properties is particula...
Article
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For the development of the future ultrahigh-scale integrated memory devices, a uniform tungsten (W) gate deposition process with good conformal film is essential for improving the conductivity of the W gate, resulting in the enhancement of device performance. As the memory devices are further scaled down, uniform W deposition becomes more difficult...
Article
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Following the celebrated discovery of graphene, considerable attention has been directed toward the rich spectrum of properties offered by van der Waals crystals. However, studies have been largely limited to their 2D properties due to lack of 1D structures. Here, the growth of high‐yield, single‐crystalline 1D nanobelts composed of transition meta...
Article
Changes in lattice constants of epitaxial SiGe layers by boron (B) doping were studied by using high resolution X-ray diffraction (HRXRD) by using SiGe:B with Ge and B concentrations in the range of 11-23% and (1.5-4.2)×10¹⁹cm⁻³, respectively. The lattice contraction coefficient (β) of B in SiGe was measured to be (9.6 ± 0.6) ×10⁻²⁴cm³, which was a...
Article
Full-text available
In the fabrication process of memory devices, a void-free tungsten (W) gate process with good conformability is very important for improving the conductivity of the W gate, leading to enhancement of device performance. As the downscaling continues to progress, void-free W deposition becomes more difficult due to the experimental limitations of conf...
Article
Full-text available
An unconventional phase-change memory (PCM) made of In2Se3, which utilizes reversible phase changes between a low-resistance crystalline β phase and a high-resistance crystalline γ phase is reported for the first time. Using a PCM with a layered crystalline film exfoliated from In2Se3 crystals on a graphene bottom electrode, it is shown that SET/RE...
Article
Full-text available
The special properties of graphene can be largely influenced by point defects in the lattice. However, TEM studies of topological defects in few-layered graphene have rarely been reported. In this work, two simplest forms of point defects, monovacancy and divacancy in twisted bilayer graphene are characterized using aberration-corrected transmissio...
Article
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Vapor phase carbon (C)-reduction-based syntheses of C nanotubes and graphene, which are highly functional solid C nanomaterials, have received extensive attention in the field of materials science. This study suggests a revolutionary method for precisely controlling the C structures by oxidizing solid C nanomaterials into gaseous products in the op...
Article
We demonstrated AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with periodic air-voids-incorporated nanoscale patterns enabled by nanosphere lithography and epitaxial lateral overgrowth (ELO) on a 4-in. sapphire substrate. The nanoscale ELO improved the crystal quality of overgrown epitaxial layers at a relatively low growth temperat...
Article
Metal-doped graphene produces magnetic moments that have potential application in spintronics. Here we use density function theory computational methods to show how the magnetic interaction between metal atoms doped in graphene can be controlled by the degree of flexure in a graphene membrane. Bending graphene by flexing causes the distance between...
Article
Full-text available
1 T phase incorporation into 2H-MoS2 via an optimal electron irradiation leads to induce a weak ferromagnetic state at room temperature, together with the improved transport property. In addition to the 1T-like defects, the electron irradiation on the cleaved MoS2 surface forms the concentric circle-type defects that are caused by the 2 H/1 T phase...
Article
Full-text available
Dopants in two-dimensional dichalcogenides have a significant role in affecting electronic, mechanical, and interfacial properties. Controllable doping is desired for the intentional modification of such properties to enhance performance; however, unwanted defects and impurity dopants also have a detrimental impact, as often found for chemical vapo...
Article
Full-text available
An in situ heating holder inside an aberration-corrected transmission electron microscope (AC-TEM) is used to investigate the real-time atomic level dynamics associated with heterogeneous nucleation and growth of graphene from Au nanoparticle seeds. Heating monolayer graphene to an elevated temperature of 800 °C removes the majority of amorphous ca...
Article
There has been significant research interest in controlling and imaging molecular dynamics, such as translational and rotational motions, especially at a single molecular level. Here we applied aberration-corrected transmission electron microscopy (ACTEM) to actuate and directly image the rotational motions of molecules anchored on a single-layer-g...
Article
Full-text available
We study the detailed bond reconstructions that occur in S vacancies within monolayer MoS2 using a combination of aberration-corrected transmission electron microscopy, density functional theory (DFT), and multislice image simulations. Removal of a single S atom causes little perturbation to the surrounding MoS2 lattice, whereas the loss of two S a...
Article
We study the bond lengths of silicon (Si) atoms attached to both armchair and zigzag edges using aberration corrected transmission electron microscopy with monochromation of the electron beam. An in situ heating holder is used to perform imaging of samples at 800 °C in order to reduce chemical etching effects that cause rapid structure changes of g...
Article
The atomic structure of subnanometer pores in graphene, of interest due to graphene's potential as a desalination and gas filtration membrane, is demonstrated by atomic resolution aberration corrected transmission electron microscopy. High temperatures of 500 °C and over are used to prevent self-healing of the pores, permitting the successful imagi...
Article
Thermally induced dislocation movements are important in understanding the effects of high temperature annealing on modifying the crystal structure. We use an in situ heating holder in an aberration corrected transmission electron microscopy to study the movement of dislocations in suspended monolayer graphene up to 800 °C. Control of temperature e...
Article
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We demonstrate the formation of partial dislocations in graphene at elevated temperatures of ≥500 °C with single atom resolution aberration corrected transmission electron microscopy. The partial dislocations spatially redistribute strain in the lattice, providing an energetically more favorable configuration to the perfect dislocation. Low-energy...
Article
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The atomic structure and dynamics of silicon nanoclusters covalently bonded to graphene are studied using aberration-corrected transmission electron microscopy. We show that as the cluster size increases to 4-10 atoms, ordered crystalline cubic phases start to emerge. Anisotropic crystals are formed due to higher stability of the Si-C bond under el...
Article
Vacancy defects play an important role in influencing the properties of graphene, and understanding their detailed atomic structure is crucial for developing accurate models to predict their impact. Divacancies (DVs) are one of the most common defects in graphene and can take three different structural forms through various sequences of bond rotati...
Article
A tomically thin transition metal di-chalcogenides (TMDs) are 2D materials that consist of two hexagonal planes of chalcogen atoms X (S, Se) bonded to transition metal atoms M (Mo, W) arranged hexagonally. Bulk TMDs play an important role as dry lubricants and have properties different than those of 2D monolayer and few-layer thin films. 1 Two-dime...
Article
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Graphene has three experimentally confirmed periodic edge terminations, zigzag, reconstructed 5-7, and arm-chair. Theory predicts a fourth periodic edge of graphene called the extended Klein (EK) edge, which consists of a series of single C atoms protruding from a zigzag edge. Here, we confirm the existence of EK edges in both graphene nanoribbons...
Article
We show that dislocations located at the edge of graphene cause different lattice deformations to those located in the bulk lattice. When a dislocation is located near an edge, a decrease in the rippling and increase of the in-plane rotation occurs relative to the dislocations in the bulk. The increased in-plane rotation near the edge causes bond r...
Article
We use time-dependent HRTEM to reveal that stable dislocation pairs in graphene are formed from an initial complex multi-vacancy cluster that undergoes multiple bond rotations and adatom incorporation. In the process, it is found that the transformation from the formed complex multi-vacancy cluster can proceed without the increase of vacancy becaus...
Article
Vacancy defects in graphene with an odd number of missing atoms, such as the trivacancy, have been imaged at atomic resolution using aberration corrected transmission electron microscopy. These defects are not just stabilized by simple bond reconstructions between under-coordinated carbon atoms, as exhibited by even vacancies such as the divacancy....
Article
Full-text available
We present an atomic resolution structural study of covalently bonded dopant pairs in the lattice of monolayer graphene. Two iron (Fe) metal atoms that are covalently bonded within the graphene lattice are observed and their interaction with each other is investigated. The two metal atom dopants can form small paired clusters of varied geometry wit...
Article
The relative prevalence of various configurations of the tetravacancy defect in monolayer graphene has been examined using aberration corrected transmission electron microscopy (TEM). It was found that the two most common structures are extended linear defect structures, with the 3-fold symmetric Y-tetravacancy seldom imaged, in spite of this being...
Article
Graphene edges and their functionalization influence the electronic and magnetic properties of graphene nanoribbons. Theoretical calculations predict saturating graphene edges with hydrogen lower its energy and form a more stable structure. Despite the importance, experimental investigations of whether graphene edges are always hydrogen-terminated...
Article
Full-text available
Light-emitting diodes (LEDs) become an attractive alternative to conventional light sources due to high efficiency and long lifetime. However, different material properties between GaN and sapphire cause several problems such as high defect density in GaN, serious wafer bowing, particularly in large-area wafers, and poor light extraction of GaN-bas...
Article
Extended linear arm chair defects are intentionally fabricated in suspended monolayer graphene using controlled focused electron beam irradiation. The atomic structure is accurately determined using aberration-corrected transmission electron microscopy with monochromation of the electron source to achieve ∼80 pm spatial resolution at an acceleratin...
Article
The motion and annihilation of a grain boundary (GB) in graphene are investigated by tight-binding molecular dynamics (TBMD) simulation and ab initio local density approximation total energy calculation. A meandering structure of the GB is found to be energetically more favorable than other structures, in good agreement with experiment. It is obser...
Article
The formation and development processes of dislocation in graphene are investigated by performing tight-binding molecular dynamics (TBMD) simulation and ab initio total energy calculation. It is found that the coalescence of pentagon-heptagon (5-7) pairs with vacancy defects induces the formation of dislocation due to the separation of two 5-7 pair...
Article
Full-text available
Although graphene looks attractive to replace indium tin oxide (ITO) in optoelectronic devices, the luminous efficiency of light emitting diodes (LEDs) with graphene transparent conducting electrodes has been limited by degradation in graphene taking place during device fabrication. In this study, it was found that the quality of graphene after the...
Article
A simple and inexpensive technique to improve the emission efficiency of nonpolar a-plane light emitting diodes (LEDs) is proposed. The 3-dimensional growth nature of a-plane GaN was utilized to form the regrowth template of a-plane GaN. Subsequently, the controlled integration of silica nano-spheres (CIS) into the regrowth template is performed to...
Article
The mechanism for suppressing the formation of abnormally large islands during the conventional quantum dot (QD) growth was investigated. In comparison of the periodic arsine interruption method to the conventional method, InAs QDs grown on GaAs substrate by metal organic chemical vapor deposition has a higher density and aspect ratio without large...
Article
A divacancy (DV) is one of the most abundant and most important defects in irradiated graphene, which modifies electronic and chemical properties of graphene. In this paper, we present ab initio calculations to study the dynamics and stability of DVs in graphene. Divacancies in graphene have various reconstructed structures, such as triple pentagon...