• Journal of the Korean Chemical Society
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• v.59 no.1
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• pp.9-17
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• 2015

The density functional theory (DFT) calculations on $(H_2O)_n@C_{60}$, (n=1-10) complexes have been performed to elucidate hydrogen interaction between fullerene and water clusters. The optimized geometries, harmonic vibrational frequencies, and binding energies are predicted at various levels of theory. The harmonic vibrational frequencies for the molecules considered in this study show all real numbers implying true minima. We also compare the H-bond interaction between $(H_2O)_n$ and $(H_2O)_n@C_{60}$, (n=1-10) clusters.

• Journal of the Korean Vacuum Society
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• v.19 no.5
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• pp.365-370
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• 2010

The growth interruption effects on growth mode of the GaAs and AlGaAs epitaxial layers grown on GaAs substrate by molecular beam epitaxy were investigated. Growth process of the epitaxial layers as a function of the growth interruption time was observed by reflection high energy electron diffraction (RHEED). The growth interruption time was 0, 15, 30, 60 s. The GaAs/$Al_{0.3}Ga_{0.7}As$ multi quantum wells (MQWs) with different growth interruption time were grown and its properties were investigated. RHEED intensity oscillation and optical property of the MQWs were dependent on the growth interruption time. When the growth interruption time was 30 s, interface between the well and barrier layers became sharper.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.120-120
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• 2018

반도체 소자나 디스플레이 패널 제조 공정에 가장 많이 사용되는 진공 펌프인 터보 분자 펌프는 오일을 사용하지 않고, 설치 방향이 자유로우며 넓은 작동 압력 영역을 가지고 있어서 고가임에도 불구하고 점점 더 사용 영역을 넓혀 가고 있다. 상하의 두 곳에 회전축을 지지하는 베어링이 필요한데, 기계식 금속 베어링을 채용하는 경우에는 반드시 윤활유를 공급해 주어야 하고, 고온, 부식성 또는 산화성 가스의 배기 시에는 퍼지 가스로 비활성인 질소나 알곤등을 이용하여 보호를 해주어야 한다. 반면, 자기 베어링을 채택한 모델은 윤활의 걱정에서 자유로울 수 있기 때문에 채용이 늘어나고 있다. 동일극의 반발력이나 반대극의 인상력을 이용한 구조를 갖게 되는데 갑작스러운 입구 쪽 압력의 증가 시에는 자석 끼리 부딪치는 일이 발생하고 이로 인해서 로터 모듈 전체에 큰 손상을 갖게 되므로 한 곳 정도에 비상용 터치 다운 베어링을 기계식으로 윤활제 없이 설치하기도 한다. 기본적으로 자기 베어링 방식은 로터 모듈의 부상과 제어를 위해서 3축 또는 5축 제어를 하게 되는데 여기에는 전자석의 전류를 미세하게 조정하여 피드백 하는 시스템을 활용하기 때문에 외부에서의 자기장이 일정값 이상 침투하게 되면 제어 회로의 기능에 문제를 일으키게 된다. 또한 축 방향에 수직인 자기장의 강도가 높아지면 고속으로 회전하는 금속 블레이드가 자속을 자르게 되므로 표면에 와전류가 발생하여 문제가 된다. 터보 분자 펌프는 회전자와 고정자 간격이 1 mm 이내로 작아서 약간의 진동이라도 발생하면 회전자와 고정자 간에 충돌이 일어나고 이는 곧 파손으로 이어진다. 그림 1에는 파손 원인 분석을 위한 회전자 모듈의 수치 해석용 모델의 일부를 나타내었고, 그림 2에는 실제로 외부 자기장에 의한 파손이 발생한 사례의 자기 베어링 모듈의 사진을 나타내었다. 본 발표에서는 외부 자기장의 형태에 따라 제어 자기장에 미치는 영향을 CFD-ACE+(ESI corp)를 활용하여 해석하였다.

• Journal of the Korean Chemical Society
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• v.17 no.2
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• pp.115-121
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• 1973

Crystalline products were obtained when$TiCl_4$ was reacted in dichloromethane with acetic, propionic, crotonic, benzoic, furoic and salicylic acids. Chemical analysis has shown that these were all dichlorodicarboxylatotitanium (IV). Cryoscopy of dichlorodipropionatotitanium (IV) indicated the carboxylato-complexes are dimeric. In the IR spectra of these complexes two strong bands both assigned to asymmetric carbonyl stretching vibration have been observed in the region$1500 - 1700cm^{-1}$ and the NMR spectrum of dichlorodipropionatotitanium (IV) has also shown two triplets and two quartets, which indicate that there are two chemically unequivalent carboxylato-ligands in the dimer $[TiCl_2(OOCR)_2]_2$. Their molecular structure was proposed to be bis-carboxo-bridged dimer.

• Journal of the Korean Chemical Society
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• v.34 no.1
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• pp.29-36
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• 1990

Cholesteryl pentyl carbonate $(C_{33}H_{56}O_3)$ is monoclinic, space group P21, with a = 12.484(3), b = 9.043(3), c = 14.053(3)$\AA$, ${\beta} = 94.12(2)^{\circ}$ and z = 2. The intensity data were measured for the 2969 reflections within sin $\theta/\lambda = 0.52 {\AA}^{-1}$, using an automatic four--circle diffractometer and graphite monochromated Mo-K$\alpha$ radiation. The atomic coordinates from cholesteryl octanoate were used in an initial trial structure and the structure was refined by full-matrix least squares methods. The final R-factor was 0.12 for 1164 observed reflections. The pentyl group has shortened bond lengths due to the high thermal vibrations in this region. Adjacent molecules are related by $2_1$ screw axis so that they are arranged in an antiparallel array, corresponding to the Monolayer Type II packing mode. There are close packings of cholesteryl groups within the monolayers. This packing type is similar to those of cholesteryl hexanoate, octanoate, hexyl carbonate and oleate.

• Journal of the Mineralogical Society of Korea
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• v.29 no.4
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• pp.209-220
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• 2016

Clay minerals are a major player to determine geochemical cycles of trace metals and carbon in the critical zone which covers the atmosphere down to groundwater aquifers. Molecular dynamics (MD) simulations can examine the Earth materials at an atomic level and, therefore, provide detailed fundamental-level insights related to physicochemical properties of clay minerals. In the current study, we have applied classical MD simulations with clayFF force field to dioctahedral clay minerals (i.e., gibbsite, kaolinite, and pyrophyllite) to analyze and compare structural parameters (lattice parameter, atomic pair distance) with experiments. We further calculated vibrational power spectra for the hydroxyls of the minerals by using the MD simulations results. The MD simulations predicted lattice parameters and interatomic distances respectively deviated less than 0.1~3.7% and 5% from the experimental results. The stretching vibrational wavenumber of the hydroxyl groups were calculated $200-300cm^{-1}$ higher than experiment. However, the trends in the frequencies among different surface hydroxyl groups of each mineral was consistent with experimental results. The angle formed by the surface hydroxyl group with the (001) plane and hydrogen bond distances of the surface hydroxyls were consistent with experimental result trends. The inner hydroxyls, however, showed results somewhat deviated from reported data in the literature. These results indicate that molecular dynamics simulations with clayFF can be a useful method in elucidating the roles of surface hydroxyl groups in the adsorption of metal ions to clay minerals.

• Journal of the Korean Chemical Society
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• v.19 no.2
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• pp.92-97
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• 1975

The molecular and electronic structures of $TiCl(OC_6H_5)_3{\cdot}C_6H_5OH\;and\;Ti(OC_6H_5)_4{\cdot}C_6H_5OH$ have been studied by employing cryoscopic and electronic spectroscopic methods. The cryoscopic data have shown that the dimeric tetraphenoxytitanium(Ⅳ) phenolate in solid undergoes complete dissociation into monomer in solution and also the chlorocomplex starts dissociation around the concentration of 8 m mole/l. Therefore, these two Ti-complexes are pentacoordinated in dilute solution and the local symmetry of the titanium ion in these complexes seems to be trigonalbipyramid. The electronic spectra of $TiCl(OC_6H_5)_3{\cdot}C_6H_5OH$ and $Ti(OC_6H_5)_4{\cdot}C_6H_5OH$ each show two band, systems, one vibration-structural band characteristic of the aromatic ring in the near UV and another visible band at 26.8 kK, 29.6 kK, respectively, which are assigned as a ligand to metal charge transfer band corresponding to $^1A_1''{\to}^1E'\;or\;^1E''$ transition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.849-855
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• 2012

The effect of electric fields on the response of diffusion flames in a counterflow has been investigated experimentally by varying the AC voltage and frequency. The result showed that the flame was stationary with high AC frequency above the threshold frequency, and it increased with the applied voltage and then leveled off at 35 Hz. Below the threshold frequency, however, the flame oscillated with a frequency that was synchronized with the applied AC frequency. This oscillation can be attributed to the ionic wind effect due to the generation of bulk flow, which arises from the momentum transfer by molecular collisions between neutral molecules and ions, where the ions in the reaction zone were accelerated by the Lorentz force.

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.76-83
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• 1986

Four oxovandium(IV) complexes with carboxylate ligands, $VO(picn)_2$, $VO(htmq)_2$, $VO(quin)_2$ and $VO(pyra)_2{\cdot}2H_2O)$ have been prepared and studied. Infrared spectral data coupled with the results of magnetic susceptibility study strongly suggest that there are relatively strong intermolecular interactions in $VO(picn)_2$ and $VO(htmq)_2$. In all oxovanadium(IV) complexes studied in this work, the carboxylate ligand coordinates to the metal ion in the unidentated fashion. Some fundamental vibration modes of oxovanadium(IV) complexes were empirically assigned from the difference in the spectrum of metal complex with free ligand.

• Korean Journal of Optics and Photonics
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• v.25 no.4
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• pp.193-199
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• 2014

The net effect of the emitter orientation, Mie scatters, and pillow lenses on the outcoupling efficiency (OCE) of a bottom-emitting OLED having an internal photonic crystal layer was investigated by a combined optical simulation based on the finite-difference time-domain method (FDTD) and the ray-tracing technique. The simulation showed that when the emitter orientation was horizontal with respect to the OLED surface, the OCE could be increased by 54% when a photonic crystal layer was employed, while it could be improved by 86% under optimized conditions of Mie scatters and pillow lenses applied to the glass substrate. The peculiar intensity distribution of the OLED, caused by the periodic lattice structure of the photonic crystal layer, could be ameliorated by inserting Mie scatters into the glass substrate. This study suggests that conventional outcoupling structures combined with control of the emitter orientation could improve the OCE substantially.