• Applied Microscopy
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• v.36 no.spc1
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• pp.35-40
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• 2006

Self-assembled InAs/GaAs quantum dots (QDs) were grown by the atomic layer epitaxy (ALE) and molecular beam epitaxy (MBE) techniques, The structure and the thermal stability of QDs have been studied by high resolution electron microscopy with in-situ heating experiment capability, The ALE and MBE QDs were found to form a hemispherical structure with side facets in the early stage of growth, Upon capping by GaAs layer, however, the apex of QDs changed to a flat one. The ALE QDs have larger size and more regular shape than those of MBE QDs. The QDs collapse due to elevated temperature was observed directly in atomic scale, In situ heating experiment within TEM revealed that the uncapped QDs remained stable up to $580^{\circ}C$, However, at temperature above $600^{\circ}C$, the QDs collapsed due to the diffusion and evaporation of In and As from the QDs, The density of the QDs decreased abruptly by this collapse and most of them disappeared at above $600^{\circ}C$.

• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.159-165
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• 2016

The hydrogen has been recognized as a clean, nonpolluting and unlimited energy source that can solve fossil fuel depletion and environmental pollution problems at the same time. Water electrolysis has been the most attractive technology in a way to produce hydrogen because it does not emit any pollutants compared to other method such as natural gas steam reforming and coal gasification etc. In order to improve efficiency and durability of the water electrolysis, comprehensive studies for highly active and stable electrocatalysts have been performed. The platinum group metal (PGM; Pt, Ru, Pd, Rh, etc.) electrocatalysts indicated a higher activity and stability compared with other transition metals in harsh condition such as acid solution. It is necessary to develop inexpensive non-noble metal catalysts such as transition metal oxides because the PGM catalysts is expensive materials with insufficient it's reserves. The optimization of operating parameter and the components is also important factor to develop an efficient water electrolysis cell. In this study, we optimized the operating parameter and components such as the type of AEM and density of gas diffusion layer (GDL) and the temperature/concentration of the electrolyte solution for the anion exchange membrane water electrolysis cell (AEMWEC) with the transition metal oxide alloy anode and cathode electrocatalysts. The maximum current density was $345.8mA/cm^2$ with parameter and component optimization.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.6
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• pp.454-459
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• 2020

In this study, a TiO₂/TiO_2-x-based resistance variable memory was fabricated using a DC/RF magnetron sputtering system and ALD. In order to analyze the effect of oxygen plasma treatment on the performance of resistance random access memory (ReRAM), the TiO₂/TiO_2-x-based ReRAM was evaluated by applying RF power to the TiO_2-x oxygen-holding layer at 30, 60, 90, 120, and 150 W, respectively. The ReRAM was fabricated, and the electrical and surface area performances were compared and analyzed. In the case of ReRAM without oxygen plasma treatment, the I-V curve had a hysteresis curve shape, but the width was very small, with a relatively high surface roughness of the oxygen-retaining layer. However, in the case of oxygen plasma treatment, the HRS/LRS ratio for the I-V curve improved as the applied RF power increased; stable improvement was also noted in the surface roughness of the oxygen-retaining layer. It was confirmed that the low voltage drive was not smooth due to charge trapping in the oxygen diffusion barrier layer owing to the high intensity ReRAM applied with an RF power of approximately 150 W.

• Journal of the Korean Vacuum Society
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• v.9 no.3
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• pp.263-266
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• 2000

This paper is focused on the fabrication of reliable Al/$TiO_2-SiO_2$/Mo antifuse, which could operate at low voltage along with the improvement in on/off state properties. Mo metal as the bottom electrode had smooth surface and high melting point, and was being kept as-deposited $SiO_2$film stable. The breakdown voltage of TiO_2-SiO_2$ stacked antifuse was better than that of same-thickness (100 $\AA$) $SiO_2$antifuse because of Ti diffusion in $SiO_2$. The improving breakdown-voltage and on-resistance can be obtained as well as the influence of hillock in the bottom metal is reduced by using double insulator. Low on-resistance (65 $\Omega$) and low programming voltage (9.0 V) can be obtained in these antifuses with 250 $\AA$ double insulator.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.237.2-237.2
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• 2013

ReRAM cell, also known as conductive bridging RAM (CBRAM), is a resistive switching memory based on non-volatile formation and dissolution of conductive filament in a solid electrolyte [1,2]. Especially, Chalcogenide-based ReRAM have become a promising candidate due to the simple structure, high density and low power operation than other types of ReRAM but the uniformity of switching parameter is undesirable. It is because diffusion of ions from anode to cathode in solid electrolyte layer is random [3]. That is to say, the formation of conductive filament is not go through the same paths in each switching cycle which is one of the major obstacles for performance improvement of ReRAM devices. Therefore, to control of nonuniform conductive filament formation is a key point to achieve a high performance ReRAM. In this paper, we demonstrated the enhanced repeatable bipolar resistive switching memory characteristics by spreading the Ag nanocrystals (Ag NCs) on amorphous GeSe layer compared to the conventional Ag/GeSe/Pt structure without Ag NCs. The Ag NCs and Ag top electrode act as a metal supply source of our devices. Excellent resistive switching memory characteristics were obtained and improvement of voltage distribution was achieved from the Al/Ag NCs/GeSe/Pt structure. At the same time, a stable DC endurance (>100 cycles) and an excellent data retention (>104 sec) properties was found from the Al/Ag NCs/GeSe/ Pt structured ReRAMs.

• Advances in nano research
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• v.5 no.2
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• pp.127-140
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• 2017

Metal nanoparticles have been intensively studied within the past decade. Nano-sized materials have been an important subject in basic and applied sciences. Zinc oxide nanoparticles have received considerable attention due to their unique antibacterial, antifungal, and UV filtering properties, high catalytic and photochemical activity. In this study, microbiological aspects of scale formation in PVC pipelines bacteria and fungi were isolated. In the emerging issue of increased multi-resistant properties in water borne pathogens, zinc oxide (ZnO) nanoparticle are being used increasingly as antimicrobial agents. Thus, the minimum bactericidal concentration (MBC) and minimum fungal concentration of ZnO nanoparticles towards pathogens microbe were examined in this study. The results obtained suggested that ZnO nanoparticles exhibit a good anti fungal activity than bactericidal effect towards all pathogens tested in in-vitro disc diffusion method (170 ppm, 100 ppm and 30 ppm). ZnO nanoparticles can be a potential antimicrobial agent due to its low cost of production and high effectiveness in antimicrobial properties, which may find wide applications in various industries to address safety issues. Stable ZnO nanoparticles were prepared and their shape and size distribution characterized by Dynamic light scattering (35.7 nm) and transmission electron microscopic TEM study for morphology identification (20 nm), UV-visible spectroscopy (230 nm), X-ray diffraction (FWHM of more intense peak corresponding to 101 planes located at $36.33^{\circ}$ using Scherrer's formula), FT-IR (Amines, Alcohols, Carbonyl and Nitrate ions), Zeta potential (-28.8). The antimicrobial activity of ZnO nanoparticles was investigated against Bacteria and Fungi present in drinking water PVC pipelines biofilm. In these tests, Muller Hinton agar plates were used and ZnO nanoparticles of various concentrations were supplemented in solid medium.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.78-86
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• 2000

The objective of this research is to understand the characteristics of a nonpremixed, turbulent, hydrogen jet flame which is stabilized in Mach 1.8 coflowing air flows. In order to investigate the flame structure, flame lengths and fuel trajectories were measured by using direct photography, acetone PLIF, Mie scattering techniques, and numerical simulation. Effect of increasing air velocity was investigated when fuel velocity is fixed. The subsonic flame length was decreased drastically, however the supersonic flame length was increased slowly Then the change of flame blow out characteristics was observed as varying fuel nozzle lip thickness. The flame stability can be increased when fuel nozzle lip thickness was increased, which indicates that the minimum fuel lip thickness ratio is required for the stable supersonic flames. Also, it is found that fuel jet is blocked by high pressure zone and low scattering zone is made. Then the fuel that was moving along the recirculation zone had longer residence time within the supersonic flames, which made partially premixed zone.

• Korean Journal of Metals and Materials
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• v.47 no.9
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• pp.573-579
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• 2009

Titanium/aluminum/stainless steel(Ti/Al/STS) clad materials have received much attention due to their high specific strength and corrosion-resisting properties. However, it is difficult to fabricate these materials, because titanium oxide is easily formed on the titanium surface during heat treatment. The aim of the present study is to derive optimized cladding conditions and thereupon obtain the stable quality of Ti/Al/STS clad materials. Ti sheets were prepared with and without pre-heat treatment and Ti/Al/STS clad materials were then fabricated by cold rolling and a post-heat treatment process. Microstructure of the Ti/Al and STS/Al interfaces was observed using a Scanning Electron Microscope(SEM) and an Energy Dispersed X-ray Analyser(EDX) in order to investigate the effects of Ti pre-heat treatment on the bond properties of Ti/Al/STS clad materials. Diffusion bonding was observed at both the Ti/Al and STS/Al interfaces. The bonding force of the clad material with non-heat treated Ti was higher than that with pre-heat treated Ti before the cladding process. The bonding force decreased rapidly beyond $400^{\circ}C$, because the formed Ti oxide inhibited the joining process between Ti and Al. Bonding forces of STS/Al were lower than those of Ti/Al, because brittle $Fe_3Al$, $Al_3Fe$ intermetallic compounds were formed at the interface of STS/Al during the cladding process. In addition, delamination of the clad material with pre-heat treated Ti was observed at the Ti/Al interface after a cupping test.

• Korean Journal of Metals and Materials
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• v.49 no.4
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• pp.281-290
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• 2011

In order to gain better understanding of the selective surface oxidation and its influence on the galvanizability of a transformation-induced plasticity (TRIP) assisted steel containing 1.5 wt.% Si and 1.6 wt.% Mn, a model experiment has been carried out by depositing Si and Mn (each with a nominal thickness of 10 nm) in either monolayers or bilayers on a low-alloy interstitial-free (IF) steel sheet. After intercritical annealing at $800^{\circ}C$ in a $N_2$ ambient with a dew point of $-40^{\circ}C$, the surface scale formed on 590 MPa TRIP steel exhibited a microstructure similar to that of the scale formed on the Mn/Si bilayer-coated IF steel, consisting of $Mn_{2}SiO_{4}$ particles embedded in an amorphous $SiO_{2}$ film. The present study results indicated that, during the intercritical annealing process of 590 MPa TRIP steel, surface segregation of Si occurs first to form an amorphous $SiO_{2}$ film, which in turn accelerates the out-diffusion of Mn to form more stable Mn-Si oxide particles on the steel surface. During hot-dip galvanizing, particulate $Fe_{3}O_{4}$, MnO, and Si-Mn oxides were reduced more readily by Al in a Zn bath than the amorphous $SiO_{2}$ film. Therefore, in order to improve the galvanizability of 590 TRIP steel, it is most desirable to minimize the surface segregation of Si during the intercritical annealing process.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.1
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• pp.161-165
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• 2021

In general, SOFCs mainly use Ni-YSZ cermet, a mixture of Ni and YSZ, as an anode material, which is stable in a high-temperature reducing atmosphere. However, when SOFCs have operated at a high temperature for a long time, the structural change of Ni occurs and it results in the problem of reducing durability and efficiency. Accordingly, a development of a new anode material that can replace existing nickel and exhibits similar performance is in progress. In this study, SrTiO₃, which is a perovskite-based mixed conductor and one of the candidate materials, was used. In order to increase the electrical conduction properties, Y_0.08Sr_0.92Fe_0.3Ti_0.7O₃, doped with 0.08 mol of Y³⁺ in Sr-site and 0.03 mol of transition metal Fe³⁺ in Ti-site, was synthesized and its chemical diffusion coefficient and reaction constant were measured. Its electrical conductivity changes were also observed while changing the oxygen partial pressure at a constant temperature. The performance as a candidate electrode material was verified by predicting the defect area through the electrical conductivity pattern according to the oxygen partial pressure.