• 한국재료학회지
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• 제2권6호
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• pp.398-407
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• 1992

Cholesteryl S-alkoxybenzene thiocarbonates를 합성하여 그들의 상전이 온도를 조사하였다. 이 계열 화합물들은 모두 호변성 cholesteric 액정상을 나타낸다. 상전이 온도는 시차주사열분석기 (DSC)로 측정하였으며, 측정된 cholesteric-isotropic 상전이 온도는 alkoxy 사슬 길이 증가에 따라 감소한다.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.453-459
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• 2013

In phtosynthetic light harvesting complexes, the electronic transition energies of chlorophylls are influenced by the Coulombic interaction with nearby molecules. Variation of the interactions caused by structural inhomogeneity in biological environment results in a distribution of disordered electronic transition energies of chlorophylls. In order to provide a practical guide to predict qualitative tendency of such distribution, we model four porphyrin derivatives including chlorophyll a molecule interacting with an external positive charge and calculate their transition energies using the time dependent density functional method. It is found that ${\pi}-{\pi}^*$ transition energies of the molecules are generally blue-shifted by the charge because this stabilizes occupied molecular orbitals to a greater extent than unoccupied ones. Furthermore, new transitions in the visible region emerge as a result of the red-shift in energy of an unoccupied Mg orbital and it is suggested that light-induced electron transfer may occur from the tetrapyrrole ring to the central magnesium when the molecules are interacting with a positive charge.

• 한국진공학회지
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• 제9권2호
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• pp.130-135
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• 2000

Photoluminescence(PL)와 photoreflectance(PR)를 이용하여 $Al_{0.25}/Ga_{0.75}/As/In_{0.15}/Ga_{0.85}$/AS/GaAS 슈우도형 고 전자 이동도 트랜지스터 구조에 대한 특성을 조사하였다. 온도 10K의 PL측정에서 InGaAs 양자우물에 의한 e2-hl 및 e2-hl 전이 피크가 각각 1.322 및 1.397 eV에서 관측되었다. 온도 의존성으로부터 첫번째 가전자 띠와 두번째 가전자 띠의 에너지 차이는 약 23'meV로 나타났다. 또한 300 K에서의 PR 측정으로 e2-h2및 e2-hl 전이에 의한 피크를 관측하였고, 두번째 전도 띠의 에너지 준위에 의한 피크가 띠 채움으로 인해 첫번째 전도 띠의 에너지 준위에 의한 피크보다 상대적으로 우세하였다. 반면에 PL 측정에서는 전자 가리개 효과 때문에 첫번째 전도 띠에 의한 피크가 우세하였다.

• 한국재료학회지
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• 제26권1호
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• pp.35-41
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• 2016

The electrical transport properties of $La_{0.5}Sr_{0.5}CrO_3$ below room temperatures were investigated by dielectric, dc resistivity, magnetic properties and thermoelectric power. Below $T_c$, $La_{0.5}Sr_{0.5}CrO_3$ contains a dielectric relaxation process in the tangent loss and electric modulus. The $La_{0.5}Sr_{0.5}CrO_3$ involves the transition from high temperature thermal activated conduction process to low temperature one. The transition temperature corresponds well to the Curie point. The relaxation mechanism has been discussed in the frame of electric modulus spectra. The scaling behavior of the modulus suggests that the relaxation mechanism describes the same mechanism at various temperatures. The low temperature conduction and relaxation takes place in the ferromagnetic phase. The ferromagnetic state in $La_{0.5}Sr_{0.5}CrO_3$ indicates that the electron - magnon interaction occurs, and drives the carriers towards localization in tandem with the electron - lattice interaction even at temperature above the Curie temperature.

• Bulletin of the Korean Chemical Society
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• 제15권12호
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• pp.1098-1103
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• 1994

Atomic force microscopy (AFM) images of two conducting layered transition-metal ditellurides, $TaTe_2$ and $Ta_{0.5}$$V_{0.5}$$Te_2$, were examined and their surface and bulk structural features were compared. All the measured unit cell parameters from AFM image were consistent and in complete agreement with the results of the X-ray diffraction. The microscopic structures of corrugated surface tellurium sheets were strongly affected by the modification of metal double zig-zag chains underneath Te surface. Large difference in the height amplitudes of AFM images in $TaTe_2$ and $Ta_{0.5}$$V_{0.5}$$Te_2$ phases was observed and this reflects large difference in the surface electron densities of two phases. On surface, the shorter intralayer Te…Te contacts in $TaTe_2$ induce more electron transfer from Te p-block bands to Ta d-block bands, thus electron density on surface observed in $TaTe_2$ is much lower than that of $Ta_{0.5}$$V_{0.5}$$Te_2$. However, in bulk, interlayer Te…Te contacts in V substituted phase are shorter than those in $TaTe_2$ phase, thus tellurium-to-metal electron transfer occurs more easily in $Ta_{0.5}$$V_{0.5}$$Te_2$ phase.

• Journal of Astronomy and Space Sciences
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• 제36권3호
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• pp.121-131
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• 2019

The ionospheric mid-latitude trough (IMT) is the electron density depletion phenomenon in the F region during nighttime. It has been suggested that the IMT is the result of complex plasma processes coupled to the magnetosphere. In order to statistically investigate the characteristics of the IMT, we analyze topside sounding data from Alouette and ISIS satellites in 1960s and 1970s. The IMT position is almost constant for seasons and solar activities whereas the IMT depth ratio and the IMT feature are stronger and clearer in the winter hemisphere under solar minimum condition. We also calculated transition heights at which the densities of oxygen ions and hydrogen/helium ions are equal. Transition heights are generally higher in daytime and lower in nighttime, but the opposite aspects are seen in the IMT region. Utilizing the Incoherent Scatter Radar (ISR) electron temperature measurements, we find that the electron temperature in the IMT region is enhanced at night during winter. The increase of electron temperature may cause fast transport of the ionospheric plasma to the magnetosphere via ambipolar diffusion, resulting in the IMT depletion. This mechanism of the IMT may work in addition to the simply prolonged recombination of ions proposed by the traditional stagnation model.

• Bulletin of the Korean Chemical Society
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• 제7권4호
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• pp.262-266
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• 1986

A multi-reference many-body perturbation theory (MRMBPT) method is critically tested in second order by comparing with the corresponding configuration interaction (CI) calculations. Excitation energies of the four-valence-electron states of transition metal atoms and ions are used for the comparison. The agreement between the second order MRMBPT and CI calculations is very reasonable, confirming the reliability of the second order MRMBPT method. The reliability of calculations with the present second order MRMBPT method was only been inferred empirically in the past since most results have been gauged by the agreement with experiment and/or with other MRMBPT calculations based upon different sets of orbitals and configuration spaces. The present MRMBPT method appears to be an efficient ab initio multi-reference method for the calculation of electron correlation effects in atoms and molecules, and it is shown how MRMBPT can be used to estimate core-core and core-valence correlation effects which are often omitted in CI calculations because too many configurations and correlating electrons are involved.

• Journal of Magnetics
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• 제18권4호
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• pp.405-411
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• 2013

The structural, magnetic and magnetocaloric properties of $CoMn_{1-x}Cr_xGe$ (x=0.05-0.125) have been investigated by using electron microscopy, x-ray diffraction, calorimetric and magnetic measurements. In this study, our aim is to justify the magnetocaloric effect by tuning the structural and magnetic transition temperature with Cr doping on CoMnGe pure system. The substitution of Cr for Mn leads to a decrease of both structural and magnetic transition temperatures. However, structural and magnetic transition temperatures do not close to each other. From magnetization measurement, we calculate that isothermal entropy change associated with magnetic transition can be as high as 3.82 J $kg^{-1}K^{-1}$ at 302 K in a field of 7 T. Meanwhile, structural phase transition contribution to isothermal entropy change is calculated as 5.85 J $kg^{-1}K^{-1}$ at 322 K for 7 T.

• 전기전자학회논문지
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• 제23권2호
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• pp.502-507
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• 2019

우리는 준 2차원 Landau 분할 시스템의 양자 광학 전이 특성을 실리콘(Si)에서 이론적으로 고찰하였다. Squre wall 구속 포텐셜에 의한 전자 구속 시스템에 양자 수송 이론(QTR)을 적용하였습니다. 평형 평균 투영 계획(Equilibrium Average Projection Scheme : EAPS)으로 계획된 Liouville 방정식 방법을 사용하였으며, 양자 전이를 분석하기 위해 포톤 방출 전이과정과 포논 흡수 전이 과정의 두 전이 과정에서 QTLW와 QTLS의 온도와 자기장 의존성을 비교하였습니다. 이 연구를 통해 Si의 QTLW와 QTLS의 온도와 자기장의 증가하는 특성을 발견하였으며, 또한 우세한 산란 과정이 포논 방출 전이 과정이라는 것을 발견했다.

• Applied Microscopy
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• 제45권4호
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• pp.199-202
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• 2015

A simple and novel transmission electron microscopy (TEM) sample preparation method for phase change nanowire is investigated. A $Ge_2Sb_2Te_5$ (GST) nanowire TEM sample was meticulously prepared using nanomanipulator and gas injection system in a field emission scanning electron microscopy for efficient and accurate TEM analysis. The process can minimize the damage during the TEM sample preparation of the nanowires, thus enabling the crystallographic analysis of as-grown GST nanowires without unexpected phase transition caused by e-beam heating.