• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.3021-3024
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• 2014

The potential energy surface (PES) for the dissociation of the 2-hydroxypyridine (2-HP) radical cation was determined from G3//B3LYP calculations, including the loss of CO, HCN, and HNC. The formation of the 1H-pyrrole radical cation by decarbonylation through a more stable tautomer, the 2-pyridone (2-PY) radical cation, was the most favorable dissociation pathway. Kinetic analysis by the Rice-Ramsperger-Kassel-Marcus model calculations was carried out based on the obtained PES. It is proposed that the dissociation occurs after a rapid tautomerization to 2-$PY^{{\cdot}+}$, and that most of the ions generated by ionization of 2-HP have the structure of 2-$PY^{{\cdot}+}$ at equilibrium above the tautomerization barrier.

• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.2911-2916
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• 2014

The gas phase structures, energetics, and interconversion pathways of five lowest energy conformers of acetylcholine were examined employing the B3LYP, MP2, and CCSD(T) methods in conjunction with diverse basis sets including the correlation consistent aug-cc-pVDZ and aug-cc-pVTZ basis sets. It is found that use of adequate basis set containing proper polarization and diffuse functions capable of describing the floppy potential energy surface of acetylcholine is important in correctly predicting the relative stability of these conformers. The interconversion pathways and barrier heights between these conformers were elucidated by examining the potential energy surface for torsional motion, which also manifested the presence of chiral conformations of acetylcholine corresponding to the original conformations. On the basis of high level electronic energy calculations and thermal contribution analysis, four lowest energy conformers appear to be populated in the energy range of less than 1 kcal/mol at room temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.1
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• pp.23-29
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• 2000

The agglomeration of titania particles with 30 nm in radii was simulated based on the colloidal stability. For surface potential increase from 4.5 to 16.8 mV the height of energy barrier increased. This tendency may explain the experimentally observed aggregation behavior where particles with smaller size and higher potential exhibited higher stability but form bigger and harder agglomerates with irregular shapes after drying.

• Bulletin of the Korean Chemical Society
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• v.17 no.5
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• pp.461-463
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• 1996

The laser-induced fluorescence excitation spectrum of 7-amino-4-(trifluoromethyl)coumarin in a supersonic jet has been recorded in the 340-352 nm region. The electronic band origin was observed at 28622.8 cm-1. Vibrational assignments for the three fundamental low-frequency modes and eight combination bands have been made for the S1 electronic excited state. The out-of-plane vibrations of this molecule have been characterized from the low-frequency assignments of the spectrum. The periodic potential energy function for the CF3 torsion, which satisfactorily fits the observed data, were also determined to be V(Φ)=95X(1-cos3Φ)-32X(1-cos6Φ) where Φ is the torsional angle. The relatively low torsional barrier of 99 cm-1 in S1 state could be explained by the small steric interactions between the functional groups attached to a bicyclic ring.

• Bulletin of the Korean Chemical Society
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• v.18 no.6
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• pp.567-573
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• 1997

Photoinduced electron transfer from the charge-transfer excited states of Ru(tpy)(bpy(COOH)₂)$CN^+$, Ru(tpy)(bpy(COOH)₂)$Cl^+$, Ru(tpy)(bpy(COOH)₂)H₂+O², and Ru(tpy)(bqu(COOH)₂)$Cl^+$ to the conduction band of TiO₂ has been studied through photoelectrochemical methods. Ru(tpy)(bpy(COOH)₂)$CN^+$ produced the highest current density and open-circuit photovoltage, whereas Ru(tpy)(bqy(COOH)₂)$Cl^+$ produced the lowest values. A potential barrier was employed to explain the experimental result that the rate of the electron transfer increases with increasing the energy difference between the donor and acceptor. A sensitizer with a high current density yielded a high photovoltage and a high conversion efficiency. The reduction rate of the oxidized sensitizer decreased with the increases in the reduction potential of the sensitizer, resulting in a poor stability of a photoelectrochemical cell.

• Corrosion Science and Technology
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• v.17 no.2
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• pp.45-53
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• 2018

A new 80Ti-15Ta-5Zr wt% alloy surface was protected by anodic oxidation in phosphoric acid solution. The protective oxide layer (TiO2, ZrO2 and Ta suboxides and thickness of 15.5 nm) incorporated $PO{_4}^{3-}$ ions from the solution, according to high resolution XPS spectra. The AFM analysis determined a high roughness with SEM detected pores (20 - 50 nm). The electrochemical studies of bare and anodically oxidized Ti-15Ta-5Zr alloy in Carter-Brugirard saliva of different pH values and saliva with 0.05M NaF, pointed to a nobler surface for the protected alloy, with a thicker electrodeposited oxide layer acting as a barrier against aggressive ions. The oxidized alloy significantly decreased corrosion current densities and total quantity of ions released into the oral environment in comparison with the bare one, at higher polarisation resistance and protective capacity of the electrodeposited layer. The impedance data revealed a bi-layered oxidation film formed by: a dense, compact, barrier layer in contact with the metallic substrate, decreasing the potential gradient across the metal/oxide layer/solution interface, reducing the anodic dissolution and a more permissive, porous layer in contact with the electrolyte. The open circuit potential for protected alloy shifted to nobler values, with thickening of the oxidation film signifying long-term protection.

• The Korean Journal of Ceramics
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• v.3 no.4
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• pp.274-278
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• 1997

(Ba, Sr) TiO$_3$(BST) thin films were prepared on RuO$_2$/Si substrates by rf magnetron sputtering and annealing was followed at temperatures ranging from 550 to 80$0^{\circ}C$ in $N_2$or $O_2$atmosphere. The effects of annealing conditions on the properties of BST film deposited on RuO$_2$bottom electrodes were investigated. It was found that the crystallinity. surface roughness, and grain size of BST films vary with the annealing temperature but they are not dependent upon the annealing atmosphere. The flat region in the current-voltage (I-V) curves of BST capacitors shortened with increasing annealing temperature under both atmospheres. This is believed to be due to the lowering of potential barrier caused by unstable interface and the increase of charge The shortening of the flat region by $O_2$annealing was more severe than that by $N_2$-annealing. As a result, there was no flat region when the films were annealed at 700 and 80$0^{\circ}C$ in $O_2$atmosphere. The dielectric properties of BST films were improved by annealing in either atmosphere. however, a degradation with frequency was observed when the films were annealed at relatively high temperature under $O_2$atmosphere.

• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.186-193
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• 2000

Effects of 1.0 mol% CoO addition on sintering and the electrical properties of ZnO-Bi2O3-Sb2O3(ZBS) varistor system with 3.0 mol% co-addition of Sb2O3 and Bi2O3 at various Sb/Bi ratio (0.5, 1.0, and 2.0) were investigated. Cobalt had little influence on the liquid-phase formation and the pyrochlore decomposition temepratures of ZBS, while densification was mainly dependent on Sb/Bi ratio: when Sb/Bi=0.5, excess Bi2O3 irrelevant to the formation of pyrochore(Zn2Sb3Bi3O14) forms eutectic liquid at ~75$0^{\circ}C$ which promotes densification and grain growth; with Sb/Bi=2.0, the second phase Zn7Sb2O12 formed by excess Sb2O3 irrelevant to the formation of the pyrochlore retards densification up to ~100$0^{\circ}C$. These phases caused the coarsening and uneven distribution of the second phase particles on the grain boundaries of ZnO above the pyrochlore decomposition temperature(~105$0^{\circ}C$), which led to broad size dist-ribution of ZnO; the specimen with Sb/Bi=1.0 showed homogeneous microstructure compared with the others, which enabled improved varistor characteristics. Doping of Co increased the nonlinearity and the potential barrier height of ZBS, which is thought to stem from improved sintering behavior such as homogenized microstructure due to size reduction and even distribution of the second phase and suppressed volatility of Bi2O3, as well as the improvement in the potential barrier structure via increased donor and interface electron trap densities.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.9
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• pp.2015-2020
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• 2012

The subthreshold characteristics has been analyzed to investigate the effect of two gate in Double Gate MOSFET using impact factor based on scaling theory. The charge distribution of Gaussian function validated in previous researches has been used to obtain potential distribution in Poisson equation. The potential distribution was used to investigate the short channel effects such as threshold voltage roll-off, subthreshold swings and drain induced barrier lowering by varying impact factor for scaling factor. The impact factor of 0.1~1.0 for channel length and 1.0~2.0 for channel thickness are used to fit structural feature of DGMOSFET. The simulation result showed that the subthreshold swings are mostly effected by impact factor but are nearly constant for scaling factors. And threshold voltage roll-off and drain induced barrier lowering are also effected by both impact factor and scaling factor.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.105-105
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• 2016

Recently, high power impulse magnetron sputtering (HIPIMS) has attracted considerable attentions due to its high potential for industrial applications. By pulsing the sputtering target with high power density and short duration pulses, a high plasma density and high ionization of the sputtered species can be obtained. HIPIMS has exhibited several merits such as increased coating density, good adhesion, microparticle-free and smooth surface, which make the HIPIMS technique desirable for synthesizing hard coatings. However, hard coatings present intrinsic defects (columnar structures, pinholes, pores, discontinuities) which can affect the corrosion behavior, especially when substrates are active alloys like steel or in a wear-corrosion process. Atomic layer deposition (ALD), a CVD derived method with a broad spectrum of applications, has shown great potential for corrosion protection of high-precision metallic parts or systems. In ALD deposition, the growth proceeds through cyclic repetition of self-limiting surface reactions, which leads to the thin films possess high quality, low defect density, uniformity, low-temperature processing and exquisite thickness control. These merits make ALD an ideal candidate for the fabrication of excellent oxide barrier layer which can block the pinhole and other defects left in the coating structure to improve the corrosion protection of hard coatings. In this work, CrN/Al2O3/CrN multilayered coatings were synthesized by a hybrid process of HIPIMS and ALD techniques, aiming to improve the CrN hard coating properties. The influence of the Al2O3 interlayer addition, the thickness and intercalation position of the Al2O3 layer in the coatings on the microstructure, surface roughness, mechanical properties and corrosion behaviors were investigated. The results indicated that the dense Al2O3 interlayer addition by ALD lead to a significant decrease of the average grain size and surface roughness and greatly improved the mechanical properties and corrosion resistance of the CrN coatings. The thickness increase of the Al2O3 layer and intercalation position change to near the coating surface resulted in improved mechanical properties and corrosion resistance. The mechanism can be explained by that the dense Al2O3 interlayer acted as an excellent barrier for dislocation motion and diffusion of the corrosive substance.