• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.291.1-291.1
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• 2016

Graphene by one of the two-dimensional (2D) materials has been focused on electronic applications due to its ultrahigh carrier mobility, outstanding thermal conductivity and superior optical properties. Although graphene has many remarkable properties, graphene devices have low on/off current ratio due to its zero bandgap. Despite considerable efforts to open its bandgap, it's hard to obtain appropriate improvements. To solve this problem, heterojunction barristor was proposed based on graphene. Mostly, this heterojunction barristor is made by transition metal dichalcogenides (TMDs), such as molybdenum disulfide ($MoS_2$) and tungsten diselenide ($WSe_2$), which have extremely thickness scalability of TMDs. The heterojunction barristor has the advantage of controlling graphene's Fermi level by applying gate bias, resulting in barrier height modulation between graphene interface and semiconductor. However, charged impurities between graphene and $SiO_2$ cause unexpected p-type doping of graphene. The graphene's Fermi level modulation is expected to be reduced due to this p-doping effect. Charged impurities make carrier mobility in graphene reduced and modulation of graphene's Fermi level limited. In this paper, we investigated theoretically and experimentally a relevance between graphene's Fermi level and p-type doping. Theoretically, when Fermi level is placed at the Dirac point, larger graphene's Fermi level modulation was calculated between -20 V and +20 V of $V_{GS}$. On the contrary, graphene's Fermi level modulation was 0.11 eV when Fermi level is far away from the Dirac point in the same range. Then, we produced two types heterojunction barristors which made by p-type doped graphene and graphene treated 2.4% APTES, respectively. On/off current ratio (32-fold) of graphene treated 2.4% APTES was improved in comparison with p-type doped graphene.

• Transactions on Electrical and Electronic Materials
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• v.15 no.6
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• pp.291-296
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• 2014

In recent years, researchers have extensively investigated polymers filled with inorganic nanoparticles because these materials present improved physical properties relative to those of conventional unfilled polymers. Oxides, silica in particular, are the most commonly used inorganic particles because they possess good properties and can be fabricated at a low cost. However, oxides are hydrophilic in nature, and this leads to the presence of water at the interface between the nanoparticles and the polymer matrix. Due to the predominance of particle-matrix interfaces in nanocomposites, the presence of water at the interlayer region can be problematic. Moreover, the hydrophobic nature of most polymers, particularly for polyolefins such as polyethylene, may make it difficult to remove this interfacial water. In this paper, as-received and moistened samples of agglomerated nanosilica/polyethylene were dried using an isothermal treatment at $60^{\circ}C$, and the efficacy of this treatment was studied using dielectric spectroscopy. The Maxwell-Wagner-Sillars relaxation peaks were observed to shift to lower frequencies by three decades, and this was linked to a modification of the water content, due to drying, at the interfaces between silica and polyethylene and at the interfaces within the nanosilica agglomerates. The evolution of the extracted retardation time is explained by the nanosilica hydrophily and the free volume introduced by the nanoparticles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.11a
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• pp.75-79
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• 1993

The Thermally Stimulated Current(TSC) method has been allied to study the influence of the structural change and interface on the electrical properties of epoxy composites. Three DGBA- MeTHPA matrix model samples mixed different ratios arts silica(SiO$_2$) filled sample and silaln treating-filled sample have been studied. Above room temperature, the relaxation mode ${\alpha}$ peak associated with T$\_$g/ has been located at 110$^{\circ}C$. Below glass transition temperature(T$\_$g/), three relaxation modes are observed in all samples : a ${\beta}$ mode situated at 10$^{\circ}C$, a ${\gamma}$ mode located at -40$^{\circ}C$ and a $\delta$mode appeared in -120$^{\circ}C$, which may be due to segmental motion, side chains, substitution and terminal groups. The analysis of its fine structure indicates that constitution of elementary processes is characterized by the activation energy and relaxation time. Also the change of the molecular structure and their thermal motion are compared with the relaxation mode and conduction mechanism in TSC spectra through the dielectric properties and FTIR measurements.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1162-1164
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• 1993

The Thermally Stimulated Current(TSC) spectroscopy has been applied to study the influence of the structual cahange and interface on the electrical properties of epoxy composites. Three DGEBA-MeTHPA matrix model samples mixed different ratios and silica($SiO_2$) filled sample and silaln treating-filled sample has been studied. Above room temperature, the relaxation mode $\alpha$ peak associated with Tg has been located at $110^{\circ}C$. Below glass transition temperature(Tg), three relaxation modes are observed in all samples: a $\beta$ mode situated at $10^{\circ}C$, a $\gamma$ mode located at $-40^{\circ}C$ and a $\delta$ mode appeared in $-120^{\circ}C$. The analysis of its fine structure indicates that constitution of elementary processes is characterized by the activation energy and relaxation time. Also the dielectric relaxation properties have been investigated to compare the the change of the molecular structure and motion to the relaxation properties and conduction mechanism in TSC spectra.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.5
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• pp.507-511
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• 2024

Various process modifications have been used to minimize SiO₂ gate oxide aging in metal-oxide-semiconductor field-effect transistors (MOSFETs). In particular, post-metallization annealing (PMA) with a deuterium ambient can effectively eliminate both bulk traps and interface traps in the gate oxide. However, even with the use of PMA, it remains difficult to prevent high levels of radiation-induced gate oxide damage such as total ionizing dose (TID) during long-term missions. In this context, additional low-temperature heat treatment (LTHT) is proposed to recover from radiation-induced damage. Positive traps in the damaged gate oxide can be neutralized using LTHT, thereby prolonging device reliability in harsh radioactive environments.

• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.242-255
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• 2008

In lithium-ion batteries(LIB), the development of electrolytes had mainly focused on the characteristics of lithium cobalt oxide($LiCoO_2$) cathode and graphite anode materials since the commercialization in 1991. Various studies on compatibility between electrode and electrolytes had been actively developed on their interface. Since then, as they try to adopt silicon and tin as anode materials and three components(Ni, Mn, Co), spinel, olivine as cathode materials for advanced lithium batteries, conventional electrolyte materials are facing a lot of challenges. In particular, requirements for electrolytes performance become harsh and complicated as safety problems are seriously emphasized. In this report, we summarized the research trend of electrolyte materials for the electrode materials of lithium rechargeable batteries.

• Applied Chemistry for Engineering
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• v.35 no.4
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• pp.303-308
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• 2024

Currently, lithium secondary batteries have been used as medium- or large-sized energy sources such as electric vehicles and energy storage system (ESS) due to their high energy and eco-friendly characteristics. Currently commercialized lithium secondary batteries do not fully meet the demands for high energy density and safety. Many studies on solid electrolytes are being conducted to satisfy these requirements. In order to commercialize a solid electrolyte, it is important to supplement the low ion conductivity and high interface resistance with an electrode compared to the organic liquid electrolyte. Therefore, in this study, oligo(3,4-ethylenedioxythiophene (EDOT)) is added to poly(vinyl alcohol) (PVA), which is a polymer matrix with ion conductivity and sticky characteristics, to decrease the interfacial resistance with the same type of polythiophene (PTh)-based electrode. In addition, the addition of porous silicon dioxide (SiO₂) filler improves lithium salt dissociation ability and increases ionic conductivity. And the electrochemical stability of the solid electrolyte, which has been lowered due to additives, is improved by introducing a cross-linked structure using boric acid (BA).

• Journal of Sensor Science and Technology
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• v.5 no.5
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• pp.79-84
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• 1996

A $1\;{\mu}m$ thick n-type GaAs layer with Si doping density of $1{\times}10^{17}/cm^{3}$ and a $500{\AA}$ thick undoped single crystalline AlAs layer were subsequently grown by molecular beam epitaxy on the $n^{+}$ GaAs substrate. The AlAs/GaAs layer was oxidized in $N_{2}$ bubbled $H_{2}O$ vapor($95^{\circ}C$) ambient at $400^{\circ}C$ for 2 and 3 hours. From the result of XPS analysis, small amounts of $As_{2}O_{3}$, AlAs, and elemental As were found in the samples oxidized up to 2 hours. After 3 hours oxidation, however, various oxides related to As were dissolved and As atoms were diffused out toward the oxide surface. The as-grown AlAs/GaAs layer was selectively converted to $Al_{2}O_{3}/GaAs$ at the oxidation temperature $400^{\circ}C$ for 3 hours. The oxidation temperature and time is very critical to stop the oxidation at the AlAs/GaAs interface and to form a defect-free surface layer.

• Economic and Environmental Geology
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• v.40 no.4
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• pp.361-374
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• 2007

Rare earth elements(REEs) have been used as an useful tool in understanding the various geological processes such as evolution and differentiation in the crust. The REEs also have been used as an analog of actinides for radioactive wastes at the water-rock interactions. Using physicochemical properties of the REEs and actinides, we have shown that Eu is an optimum analogue for understanding the behavior of Am in subsurface environments. Factors affecting sorption behavior of radioactive nuclides in groundwater were investigated by batch experiments. Four nuclides such as $^{241}Am,\;^{152}Eu,\;^{160}Tb\;and\;^{60}Co$ were selected to test our hypothesis, and $^{160}Tb$ and $^{60}Co$ were specifically used to compare to the sorption behavior between $^{241}Am-^{152}Eu$ and other radioactive nuclides. Four different rock samples and one groundwater were used in the batch experiments where solution pH for all experiments was fixed at 5.5. Our results demonstrate that $^{241}Am,\;^{152}Eu,\;and\;^{160}Tb$ show similar sorption behavior whereas $^{60}Co$ is different in sorption behavior at the mineral-water interface, suggesting that the sorption behavior of $^{60}Co$ is affected by different rock types. Our results also show that 1) Eu in REEs is optimum analogue of fate and transport of Am in subsurface environments, and 2) mineral compositions such as $SiO_2,\;TiO_2,\;P_2O_5$ and distribution of REEs such as Eu anomaly play key roles in affecting sorption behavior of radioactive nuclides even though physicochemical properties of geological materials such as specific surface area and cation exchange capacity can not be ruled out.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.461-467
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• 2021

Among the defect factors that can occur when a wafer-level lens is molded using a thermosetting material, the mold sticking problem of a molded lens during the release process can damage the molded substrate and deform the substrate at the wafer level. An experiment was conducted to examine the factors affecting the demolding force in the lens forming process. The demolding force was examined according to the coating material of the molds. The mold was surface-treated with ITO and Ti, followed by plasma treatment in an O2 atmosphere. A DLC coating was then performed, and the curing and releasability were examined. A coating method for the pull-off experiment was selected based on the results. To measure the demolding force according to the curing process conditions, a method of curing at a constant pressure and a method of curing at a constant position were applied. As a result, the TiO2 surface treatment reduced the release force. When cured by controlling the location, curing shrinkage can reduce the adhesion energy of the interface during curing, resulting in better demolding.