Hak Dong Cho

Prof. Hak Dong Cho

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Research Focus & Metrics

Academic Career Length

34Years (1993-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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10 December 2022 in Nanomaterials
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Journal Article
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EEEugenii V. Emelin
Eugenii V. Emelin
HCHak Dong Cho
Hak Dong Cho
VKVitaly Korepanov
Vitaly Korepanov
LVLiubov A. Varlamova
Liubov A. Varlamova
SESergey V. Erohin
Sergey V. Erohin
GPGennady Panin
Gennady Panin
In the presented paper, we studied bilayer CVD graphene transferred to a langasite substrate and irradiated with a focused electron beam through a layer of polymethyl methacrylate (PMMA). Changes in the Raman spectra and an increase in the electrical resistance of bigraphene after irradiation indicate a local phase transition associated with graphene diamondization. The results are explained in the framework of the theory of a chemically induced phase transition of bilayer graphene to diamane, which can be associated with the release of hydrogen and oxygen atoms from PMMA and langasite due to the “knock-on” effect, respectively, upon irradiation of the structure with an electron beam. Theoretical calculations of the modified structure of bigraphene on langasite and the experimental evaluation of sp3-hybridized carbon fraction indicate the formation of diamane nanoclusters in the bigraphene irradiated regions. This result can be considered as the first realization of local tunable bilayer graphene diamondization.

8 February 2024 in Nanomaterials
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CPChang-Soo Park
Chang-Soo Park
YKYounghae Kwon
Younghae Kwon
YKYoujoong Kim
Youjoong Kim
HCHak Dong Cho
Hak Dong Cho
HKHeetae Kim
Heetae Kim
DKDeuk Young Kim
Deuk Young Kim
Ferromagnetic materials have been attracting great interest in the last two decades due to their application in spintronics devices. One of the hot research areas in magnetism is currently the two-dimensional materials, transition metal dichalcogenides (TMDCs), which have unique physical properties. The origins and mechanisms of transition metal dichalcogenides (TMDCs), especially the correlation between magnetism and defects, have been studied recently. We investigate the changes in magnetic properties with a variation in annealing temperature for the nanoscale compound MoS2. The pristine MoS2 exhibits diamagnetic properties from low-to-room temperature. However, MoS2 compounds annealed at different temperatures showed that the controllable magnetism and the strongest ferromagnetic results were obtained for the 700 °C-annealed sample. These magnetizations are attributed to the unpaired electrons of vacancy defects that are induced by annealing, which are confirmed using Raman spectroscopy and electron paramagnetic resonance spectroscopy (EPR).

1 May 2021 in Journal of Materials Research and Technology
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HCHak Dong Cho
Hak Dong Cho
PIP. Ilanchezhiyan
P. Ilanchezhiyan
GKG. Mohan Kumar
G. Mohan Kumar
DKD.Y. Kim
D.Y. Kim

10 February 2021 in Nanomaterials
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HCHak Dong Cho
Hak Dong Cho
DKDeuk Young Kim
Deuk Young Kim
Jong-Kwon LeeJong-Kwon Lee
Jong-Kwon Lee
High crystalline ZnO nanorods (NRs) on Zn pre-deposited graphene/Cu sheet without graphene transfer process have been fabricated by self-catalyzed vapor-phase transport synthesis. Here, the pre-deposited Zn metal on graphene not only serves as a seed to grow the ZnO NRs, but also passivates the graphene underneath. The temperature-dependent photoluminescence spectra of the fabricated ZnO NRs reveal a dominant peak of 3.88 eV at 10 K associated with the neutral-donor bound exciton, while the redshifted peak by bandgap shrinkage with temperature and electron-lattice interactions leads a strong emission at 382 nm at room temperature. The optical absorption of the ZnO NRs/graphene hetero-nanostructure at this ultraviolet (UV) emission is then theoretically analyzed to quantify the absorption amount depending on the ZnO NR distribution. By simply covering the ZnO NR/graphene/Cu structure with the graphene/glass as a top electrode, it is observed that the current-voltage characteristic of the ZnO NR/graphene hetero-nanojunction device exhibits a photocurrent of 1.03 mA at 3 V under a light illumination of 100 μW/cm2. In particular, the suggested graphene/ZnO NRs/graphene hybrid-nanostructure-based devices reveal comparable photocurrents at a bidirectional bias, which can be a promising platform to integrate 1D and 2D nanomaterials without complex patterning process for UV device applications.

20 November 2023 in Nanomaterials
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EEEvgeny V. Emelin
Evgeny V. Emelin
HCHak Dong Cho
Hak Dong Cho
VKVitaly Korepanov
Vitaly Korepanov
LVLiubov A. Varlamova
Liubov A. Varlamova
DKDarya O. Klimchuk
Darya O. Klimchuk
GPGennady Panin
Gennady Panin
Memristors, resistive switching memory devices, play a crucial role in the energy-efficient implementation of artificial intelligence. This study investigates resistive switching behavior in a lateral 2D composite structure composed of bilayer graphene and 2D diamond (diamane) nanostructures formed using electron beam irradiation. The resulting bigraphene/diamane structure exhibits nonlinear charge carrier transport behavior and a significant increase in resistance. It is shown that the resistive switching of the nanostructure is well controlled using bias voltage. The impact of an electrical field on the bonding of diamane-stabilizing functional groups is investigated. By subjecting the lateral bigraphene/diamane/bigraphene nanostructure to a sufficiently strong electric field, the migration of hydrogen ions and/or oxygen-related groups located on one or both sides of the nanostructure can occur. This process leads to the disruption of sp3 carbon bonds, restoring the high conductivity of bigraphene.

15 April 1993 in Journal of Applied Physics
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MKM. D. Kim
M. D. Kim
TKT. W. Kang
T. W. Kang
GKG. H. Kim
G. H. Kim
MHM. S. Han
M. S. Han
HCHak Dong Cho
Hak Dong Cho
TKT. W. Kim
T. W. Kim
Photoluminescence measurements were carried out to investigate the dependence of the optical properties of p‐CdTe and p‐Cd0.96Zn0.04Te on various relative concentrations of bromine in a mixture of methanol and bromine. As the bromine concentration increased, the intensity of the luminescence increased; additionally, an exciton bound to a neutral acceptor (A°X) peak at 1.588 eV in p‐CdTe was resolved into an exciton bound to neutral donor (D°X) peak at 1.592 eV and an A°X peak. The mixed bands of the 1.574 and 1.546 eV peaks were well resolved by using an etching bromine concentration of 2%; in particular, the intensities of the D°X and 1.574 eV peaks increased as much as five and seven times, respectively. The intensity of the peak at 1.48 eV related to defects also increased. The intensity of A°X at 1.609 eV in p‐Cd0.96Zn0.04Te changed slightly with the bromine concentration. The intensities of the luminescence peaks due to the recombination of the electrons in conduction band with acceptors and to the defect relation did not vary. These results indicated that the number of Cd vacancies could be reduced due to the addition of Zn.