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146 results on '"Bae, Changdeuck"'

12. Effect of Hydrogen on Hafnium Zirconium Oxide Fabricated by Atomic Layer Deposition Using H2O2 Oxidant.

Author

Kim, Hyoungkyu, Yun, Seokjung, Kim, Tae Ho, Kim, Hoon, Bae, Changdeuck, Jeon, Sanghun, and Hong, Seungbum

Subjects
ATOMIC layer deposition, ZIRCONIUM oxide, HAFNIUM oxide, STRAY currents, THIN films
Abstract

Hafnium zirconium oxide (HZO) has been studied intensively due to its potential application to memory and logic devices based on its outstanding dielectric and ferroelectric properties. Because many process factors can significantly impact the properties of HZO thin film, an optimized process or post‐treatment is necessary to ensure its performance. Herein, the effect of hydrogen on HZO thin film can make the film degraded. Analysis of the polarization–voltage hysteresis loops and I–V measurements indicate a leaky behavior in the film. To address this issue, post‐oxygen‐plasma treatment is performed on the film, which results in the decrease in hydrogen ions inside the film and consequently reduces the leakage current density. This finding can provide new insight into the effect of hydrogen incorporation for HZO thin films and methodology to remove leaky components inside ferroelectric films using O2 plasma treatment. [ABSTRACT FROM AUTHOR]

Published
2021
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18. Edge-On MoS2Thin Films by Atomic Layer Deposition for Understanding the Interplay between the Active Area and Hydrogen Evolution Reaction

Author

Ho, Thi Anh, Bae, Changdeuck, Lee, Seonhee, Kim, Myungjun, Montero-Moreno, Josep M., Park, Jong Hyeok, and Shin, Hyunjung

Abstract

The edge sites of molybdenum disulfide (MoS2) have been shown to be efficient electrocatalysts for the hydrogen evolution reaction (HER). To utilize these structures, two main strategies have been proposed. The first strategy is to use amorphous structures, which should be beneficial in maximizing the area of the edge-site moieties of MoS2. However, these structures experience structural instability during HER. The other strategy is nanostructuring, in which, to enhance the resulting HER performance, the exposed surfaces of MoS2cannot be inert basal planes. Therefore, MoS2may need critical nanocrystallinity to produce the desired facets. Here, we first describe that when atomic layer deposition (ALD) is applied to layered materials such as MoS2, MoS2exhibits the nonideal mode of ALD growth on planar surfaces. As a model system, the ALD of MoCl5and H2S was studied. This nonideality does not allow for the conventional linear relationship between the growth thickness and the number of cycles. Instead, it provides the ability to control the relative ratios of the edge sites and basal planes of MoS2to the exposed surfaces. The number of edge sites produced was carefully characterized in terms of the geometric surface area and effective work function and was correlated to the HER performance, including Tafel slopes and exchange current densities. We also discussed how, as a result of the low growth temperature, the incorporation of chlorine impurities affected the electron doping and formation of mixed 2H and 1T phases. Remarkably, the resulting 1T phase was stable even upon thermal annealing at 400 °C. With the simple, planar MoS2films, we monitored the resulting catalytic performance, finding current densities of up to 20 mA cm–2at −0.3 V versus the reversible hydrogen electrode (RHE), a Tafel slope of 50–60 mV/decade, and an onset potential of 143 mV versus RHE.

Published
2024
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20. Enhanced stability of guanidinium-based organic-inorganic hybrid lead triiodides in resistance switching.

Author

Kim, Younghoon, Bae, Changdeuck, Jung, Hyun Suk, and Shin, Hyunjung

Subjects
COMPUTER storage devices, DATA warehousing, METHYLAMMONIUM, BISTABLE devices, HYDROGEN bonding, LOW voltage systems, LEAD
Abstract

We describe guanidinium-based organic-inorganic hybrid lead triiodides (GAPbI3) as an active layer in resistive switching structures and compare the switching results to those of the conventional compound, MAPbI3. Both the GAPbI3- and MAPbI3-based ReRAM devices showed bistable switching characteristics with a low operating voltage (<0.25 V) and high on/off ratio (∼106). Remarkably, we found that the GAPbI3-based devices exhibited prolonged switching behaviors for over 40 days under ambient conditions (MAPbI3, only 4 days). The GAPbI3 devices lasted for a larger number of cycles (>1900) in an endurance test and exhibited a longer data storage time (>3 × 104 s) in a retention test. Our results suggest that GAPbI3 has stronger hydrogen bonding in the lattice and thus the potential for application in memory devices. [ABSTRACT FROM AUTHOR]

Published
2019
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30. Fabrication of monodisperse asymmetric colloidal clusters by using contact area lithography (CAL)

Author

Bae, Changdeuck, Jooho Moon, Hyunjung Shin, Jiyoung Kim, and Myung M. Sung

Subjects
Colloids -- Research, Nanotechnology -- Research, Silica -- Atomic properties, Silica -- Optical properties, Chemistry
Abstract

A new technique for the fabrication of monodisperse asymmetric colloidal clusters by contact area lithography (CAL) is discussed. The approach is found to be highly site-specific, leading to the formation of several nanoscale arrays.

Published
2007

33. Heterojunction Photoanode of Atomic-Layer-Deposited MoS2on Single-Crystalline CdS Nanorod Arrays

Author

Ho, Thi Anh, Bae, Changdeuck, Joe, Jemee, Yang, Hyunwoo, Kim, Sungsoon, Park, Jong Hyeok, and Shin, Hyunjung

Abstract

Cadmium sulfide (CdS) is a semiconducting absorber for photoelectrochemical (PEC) hydrogen production with suitable electronic band structures. However, it suffers from severe photocorrosion and rapid charge recombination during the desired PEC reactions. Herein, we describe the identification of the optimal junction thickness of CdS/MoS2core/sheath heterojunction nanostructures by employing atomic layer deposition (ALD) techniques. ALD-grown MoS2sheath layers with different thicknesses were realized on single-crystalline CdS nanorod (NR) arrays on transparent conducting oxide substrates. We further monitored the resulting solar H2evolution performance with our heterojunction photoanodes. The results showed that the junction thickness of MoS2plays a key role in the reduction of photocorrosion and the enhanced photocurrent density by optimizing the charge separation. A better saturation photocurrent (∼46%) was obtained with the 7 nm-thick MoS2@CdS NRs than that with the bare CdS NRs. Moreover, the external quantum efficiency was increased twofold over that of the pristine CdS NRs. The ALD-grown MoS2@CdS heterojunction structures provides an efficient and versatile platform for hydrogen production when combining ALD-grown MoS2with ideal semiconducting absorbers.

Published
2019
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34. Semiconducting TiO2−xSx thin films by atomic layer deposition of TiS2 and its oxidation in ambient.

Author

Nam, Hochul, Yang, Hyunwoo, Kim, Eunsoo, Bae, Changdeuck, and Shin, Hyunjung

Subjects
TITANIUM dioxide films, TITANIUM silicides, ATOMIC layer deposition, OXIDATION, HYDROGEN sulfide
Abstract

The authors describe the atomic layer deposition (ALD) of titanium oxysulfide films (TiO2−xSx). A new ALD chemistry of tetrakis(dimethylamido)titanium and hydrogen sulfide is proposed for fabricating amorphous titanium sulfide layers. They found that the resulting films subsequently underwent oxidation upon reactions under the ambient condition, resulting in TiO2−xSx. The resultant structures were analyzed by using x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy, indicative of the formation of TiO2−xSx. A combined study of Hall effect measurements and Mott–Schottky analysis showed n-type semiconductor behaviors possessing a good conductivity. Optical properties testify that the present system has a moderate bandgap in between the related binary end compounds such as TiS2 and TiO2. [ABSTRACT FROM AUTHOR]

Published
2019
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35. Non-equilibrium fractal growth of MoS2 for electrocatalytic hydrogen evolution.

Author

Park, Taejin, Bae, Changdeuck, Lee, Hyangsook, Leem, Mirine, Kim, Hoijoon, Ahn, Wonsik, Kim, Jinbum, Lee, Eunha, Shin, Hyunjung, and Kim, Hyoungsub

Subjects
*HYDROGEN evolution reactions, *MOLYBDENUM disulfide, *FRACTAL analysis
Abstract

Non-equilibrium fractal growth of MoS2 was induced by establishing an extremely Mo rich chemical vapor deposition (CVD) environment using a rapid heating rate in a confined reaction space. In addition, a detailed shape evolution mechanism was suggested based on the results of thermodynamics and kinetics studies. The extremely Mo rich CVD condition allowed various MoS2 flakes to be synthesized with triangular, star-like, and dendrite-like shapes in series, owing to the thermodynamic preference to increase the number of growth directions. Moreover, numerous small triangular crystals led to the formation of MoS2 flakes with jagged edges, probably as a result of the aggressive nucleation triggered by a fast and abundant supply of MoO3−x vapors. Lastly, using the MoS2 flakes with various fractal shapes, a systematic improvement of the hydrogen evolution reaction performance was demonstrated in accordance with the increase in the surrounding edge length. [ABSTRACT FROM AUTHOR]

Published
2019
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45. Metallic Ni3S2Films Grown by Atomic Layer Deposition as an Efficient and Stable Electrocatalyst for Overall Water Splitting

Author

Ho, Thi Anh, Bae, Changdeuck, Nam, Hochul, Kim, Eunsoo, Lee, Seung Yong, Park, Jong Hyeok, and Shin, Hyunjung

Abstract

We describe the direct preparation of crystalline Ni3S2thin films via atomic layer deposition (ALD) techniques at temperatures as low as 250 °C without postthermal treatments. A new ALD chemistry is proposed using bis(1-dimethylamino-2-methyl-2-butoxy) nickel(II) [Ni(dmamb)2] and H2S as precursors. Homogeneous and conformal depositions of Ni3S2films were achieved on 4 in. wafers (both metal and oxide substrates, including Au and SiO2). The resulting crystalline Ni3S2layers exhibited highly efficient and stable performance as electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline solutions, with a low overpotential of 300 mV and a high turnover frequency for HER and an overpotential of 400 mV for OER (at a current density of 10 mA/cm2). Using our Ni3S2films as both the cathode and the anode, two-electrode full-cell electrolyzers were constructed, which showed stable operation for 100 h at a current density of 10 mA/cm2. The proposed ALD electrocatalysts on planar surfaces exhibited the best performance among Ni3S2materials for overall water splitting recorded to date.

Published
2018
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