• 한국진공학회:학술대회논문집
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• 한국진공학회 1995년도 제8회 학술발표회 논문개요집
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• pp.102-102
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• 1995

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2427-2434
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• 2022

Series of unequal quantity Nd/Ce co-doped ceramic nuclear waste forms, (Gd, Nd)₂(Zr, Ce)₂O₇, were prepared to tailor its ordered pyrochlore or disordered fluorite structure. The phase transition, microtopography, and elemental composition of the ceramic samples were systematically investigated, especially the effect of order-disorder structure on the chemical stability. It was confirmed that unequal quantity of Nd/Ce could synchronously replace the Gd/Zr-sites of Gd₂Zr₂O₇. And the phase transition of order-disorder structure could be successfully tailored by regulating the average cationic radius ratio of (Gd, Nd)₂(Zr, Ce)₂O₇ series. The elements of Gd, Nd, Zr, and Ce are uniformly distributed in the ordered or disordered structures. The MCC-1 leaching results showed that (Gd, Nd)₂(Zr, Ce)₂O₇ pyrochlore ceramic nuclear waste forms had excellent chemical stability, whose elements' normalized leaching rates were as low as 10^-4-10^-7 g·m^-2·d^-1 after 7 days. In particular, the chemical stability of disordered structure was superior to that of ordered structure. It was proposed that the force constant and the closest packing were changed with the structure transformation resulting the chemical stability difference.

• 한국재료학회지
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• 제20권9호
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• pp.457-462
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• 2010

Adsorption of a water molecule on a Si (001) surface and its dissociation were studied using density functional theory to study the distribution of -OH fragments on the Si surface. The Si (001) surface was composed of Si dimers, which buckle in a zigzag pattern below the order-disorder transition temperature to reduce the surface energy. When a water molecule approached the Si surface, the O atom of the water molecule favored the down-buckled Si atom, and the H atom of the water molecule favored the up-buckled Si atom. This is explained by the attractions between the negatively charged O of the water and the positively charged down-buckled Si atom and between the positively charged H of the water and the negatively charged up-buckled Si atom. Following the adsorption of the first water molecule on the surface, a second water molecule adsorbed on either the inter-dimer or intra-dimer site of the Si dimer. The dipole-dipole interaction of the two adsorbed water molecules led to the formation of the water dimer, and the dissociation of the water molecules occurred easily below the order-disorder transition temperature. Therefore, the 1/2 monolayer of -OH on the water-terminated Si (001) surface shows a regular distribution. The results shed light on the atomic layer deposition process of alternate gate dielectric materials, such as $HfO_2$.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.6.2-6.2
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• 2011

Block copolymer (BCP) self-assembly in a film geometry has recently been the focus of increased research interest due to their potential use as templates and scaffolds for the fabrication of nanostructured materials. The phase behavior in a thin film geometry that confines polymer chains to the interfaces will be influenced by the interfacial interactions at substrate/polymer and polymer/air and the commensurability between the equilibrium period (L0) of the BCP and the total film thickness. We investigated the phase transitions for the films of block copolymers (BCPs) on the modified surface, like the order-to-disorder transition (ODT) by in-situ grazing incidence small angle x-ray scattering (GISAXS) and transmission electron microscopy (TEM). The selective interactions on the surface by a PS-grafted substrate provide the preferential interactions with the PS component of the block, while a random copolymer (PS-r-PMMA) grafted substrate do the balanced interfacial interactions on the surface. The thickness dependence of order-to-disorder behavior for BCP films will be discussed in terms of the surface interactions.

• 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.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2006년도 동계학술연구발표회 및 자성 스핀트로닉스 국제학술대회
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• pp.138-139
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• 2006

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2007년도 The 1st International Symposium on Advanced Magnetic Materials
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• pp.149.2-149.2
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• 2007

• 한국진공학회:학술대회논문집
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• 한국진공학회 1998년도 제16회 학술발표회 논문개요집
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• pp.123-123
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• 1998

• 한국진공학회:학술대회논문집
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• 한국진공학회 1997년도 제12회 학술발표회 논문개요집
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• pp.142-143
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• 1997

• 한국진공학회:학술대회논문집
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• 한국진공학회 1998년도 제14회 학술발표회 논문개요집
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• pp.149-149
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• 1998