Junghyun Sok
Seoul National University
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Publication
Featured researches published by Junghyun Sok.
Korean Journal of Metals and Materials | 2011
KiTae Ahn; HyunChul Jang; SeungChul Lyu; Hansung Lee; Naesung Lee; Moonsup Han; Yunsun Park; Wan-Shick Hong; Kyoungwan Park; Junghyun Sok
Double-walled carbon nanotubes (DWCNTs) with high purity were produced by the catalytic decomposition of tetrahydrofuran (THF) using a Fe-Mo/MgO catalyst at 800°C. The as-synthesized DWCNTs typically have catalytic impurities and amorphous carbon, which were removed by a two-step purification process consisting of acid treatment and oxidation. In the acid treatment, metallic catalysts were removed in HCl at room temperature for 5 hr with magnetic stirring. Subsequently, the oxidation, using air at 380°C for 5 hr in the a vertical-type furnace, was used to remove the amorphous carbon particles. The DWCNT suspension was prepared by dispersing the purified DWCNTs in the aqueous sodium dodecyl sulfate solution with horn-type sonication. This was then air-sprayed on ITO glass to fabricate DWCNT field emitters. The field emission properties of DWCNT films related to transmittance were studied. This study provides the possibility of the application of large-area transparent CNT field emission cathodes. (Received October 8, 2010)
Journal of Semiconductor Technology and Science | 2008
Eunkyeom Kim; Kyongmin Kim; Daeho Son; Jeongho Kim; Kyungsu Lee; Sunghwan Won; Junghyun Sok; Wan-Shick Hong; Kyoungwan Park
We have studied nonvolatile memory properties of MOSFETs with double-stacked Si nanoclusters in the oxide-gate stacks. We formed Si nanoclusters of a uniform size distribution on a 5 nm-thick tunneling oxide layer, followed by a 10 nm-thick intermediate oxide and a second layer of Si nanoclusters by using LPCVD system. We then investigated the memory characteristics of the MOSFET and observed that the charge retention time of a double-stacked Si nanocluster MOSFET was longer than that of a single-layer device. We also found that the double-stacked Si nanocluster MOSFET is suitable for use as a dual-bit memory.
AIP Advances | 2017
Kyoung-Min Lee; Jun Woo Choi; Junghyun Sok; Byoung-Chul Min
The interfacial perpendicular magnetic anisotropy in W/CoFeB (1.2 ∼ 3 nm)/MgO thin film structures is strongly dependent on temperature, and is significantly reduced at high temperature. The interfacial magnetic anisotropy is generally proportional to the third power of magnetization, but an additional factor due to thermal expansion is required to explain the temperature dependence of the magnetic anisotropy of ultrathin CoFeB films. The reduction of the magnetic anisotropy is more prominent for the thinner films; as the temperature increases from 300 K to 400 K, the anisotropy is reduced ∼50% for the 1.2-nm-thick CoFeB, whereas the anisotropy is reduced ∼30% for the 1.7-nm-thick CoFeB. Such a substantial reduction of magnetic anisotropy at high temperature is problematic for data retention when incorporating W/CoFeB/MgO thin film structures into magneto-resistive random access memory devices. Alternative magnetic materials and structures are required to maintain large magnetic anisotropy at elevated tem...
Korean Journal of Metals and Materials | 2012
HyunChul Jang; JungMi Choi; KiTae An; Naesung Lee; Yunsun Park; Junghyun Sok
Studying the long-range ordering of nanopores on the anodic aluminum oxide (AAO) membranes under a hard anodization (HA) approach is crucial in producing well-aligned nanopores on the AAO membranes. Electro-polishing in a mixture of ethanol and perchloric acid for 5 min removed marks formed by rolling and produced flat surfaces on aluminum substrates. The AAO was formed by the first HA process, providing seeds for the subsequent production of uniform AAO nanopores. The second HA process carried out on the seeds produced well-aligned, uniform AAO nanopores. The AAO nanopores, varying in size and shape, were observed with voltages applied for HA. This study provides a route for controlling the size and shape of AAO nanopores by changing the applied voltages. (Received August 22, 2011)
international conference on nanotechnology | 2010
SeungChul Lyu; KiTae Ahn; Jonghun Han; Kwonwoo Shin; Junghyun Sok
The doping of CNTs with boron appears promising in view of the changes brought about in the electronic structures by these dopants. The substitution of boron atom in carbon network gives rise to p-type doping. In this communication, we demonstrate the synthesis of high-quality boron doped DWCNTs by catalytic decomposition of tetra hydro furan (THF) and triisopropyl borate over Fe-Mo/MgO catalyst at 900 °C. In order to achieve in-situ boron doping and growth for DWCNTs, we controlled concentration of boron precursors by passing the Ar gas through the bubbler, which contained liquid triisopropyl borate/methanol. We also evaluate structural properties and doping effect of DWCNTs from the TEM and Raman results.
Journal of the Korean Vacuum Society | 2009
Daeho Son; Eunkyeom Kim; Jeong-Ho Kim; Kyungsu Lee; Taekyung Yim; Seungman An; Sunghwan Won; Junghyun Sok; Wan-Shick Hong; Tae-You Kim; Moongyu Jang; Kyoungwan Park
We fabricated a Si nano floating gate memory with Schottky barrier tunneling transistor structure. The device was consisted of Schottky barriers of Er-silicide at source/drain and Si nanoclusters in the gate stack formed by LPCVD-digital gas feeding method. Transistor operations due to the Schottky barrier tunneling were observed under small gate bias under write/erase voltages. However, the memory window decreased to 0.4V after 104seconds, which was attributed to the Er-related defects in the tunneling oxide layer. Good write/erase endurance was maintained until write/erase times. However, the threshold voltages moved upward, and the memory window became small after more write/erase operations. Defects in the LPCVD control oxide were discussed for the endurance results. The experimental results point to the possibility of a Si nano floating gate memory with Schottky barrier tunneling transistor structure for Si nanoscale nonvolatile memory device.
Carbon | 2011
SeungChul Lyu; J.H. Han; K.W. Shin; Junghyun Sok
Scripta Materialia | 2005
Y.B. An; N.H. Oh; Y.W. Chun; Yongbeom Kim; J. Park; K.O. Choi; T.G. Eom; T.H. Byun; J.Y. Kim; Chang-Young Hyun; Do Kyung Kim; C.S. Byun; Junghyun Sok; J.J. Kwon; Wonmok Lee
Scripta Materialia | 2009
Kyoung-Min Lee; Tae-Hwan Kim; Jae-Dam Hwang; Seunghun Jang; Kiyoung Jeong; Moonsup Han; Sunghwan Won; Junghyun Sok; Kyoungwan Park; Wan-Shick Hong
Applied Surface Science | 2005
Wonmok Lee; J. Park; Junghyun Sok; P.J. Reucroft