• Composites Research
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• 제29권4호
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• pp.145-150
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• 2016

Polyvinylidene fluoride (PVDF)는 압전성을 나타내는 대표적인 고분자로 1960년대부터 많은 연구가 진행되어 왔다. PVDF는 반결정의 고분자로써 5가지의 결정 구조(${\alpha}$, ${\beta}$, ${\gamma}$, ${\delta}$, 그리고 ${\varepsilon}$형)로 구성되어 있다. ${\alpha}$형과 ${\delta}$형 결정은 전기적으로 반응하지 않는 무극성 결정구조이나 ${\beta}$형, ${\gamma}$형 그리고 ${\varepsilon}$형은 전기적으로 반응하는 극성 결정구조이다. 그 중에서도 ${\beta}$형 결정구조는 트랜스 형 분자 쇄가 평행으로 충진 된 형태로서 PVDF 단위체가 갖는 영구 쌍극자가 모두 한 방향으로 배열되어 있는 구조이기 때문에 자발 분극이 커지게 되고 압전성을 나타내게 된다. 일반적으로 ${\beta}$형 결정구조는 연신을 통한 ${\alpha}$형 결정구조의 변환을 통하여 얻을 수 있고, 연신 후 후처리 공정을 통해 그 양을 증가시킬 수 있다. 습식방사로 제조된 PVDF 섬유는 응고욕에서 극성 용매의 확산 메커니즘에 의해 ${\beta}$형 결정구조가 형성되는 장점을 가지고 있지만 극성 용매가 빠져나감과 동시에 섬유 고화가 진행되기 때문에 용매의 확산 경로가 섬유 내부 기공으로 남게 되는 단점을 가지고 있다. 이 기공은 폴링(Poling) 공정에서 전기장에 의한 분극을 방해하여 그 효과를 감소시키는 역할을 한다. 또한, PVDF 섬유가 압전 특성을 필요로 하는 응용분야에 사용되기 위해서는 섬유 가공 후에 전극이 반드시 부착되어야 하는데 섬유 형태로 제조된 PVDF에 전극을 형성하기는 매우 어렵다. 본 연구에서는 압전성을 갖는 PVDF 섬유를 습식 방사와 건식 방사의 혼합 공정으로 제조하여 기공 문제를 해결하였고, 전극이 섬유 내부에 삽입된 Core/Shell 형태의 PVDF 섬유를 제조하여 까다로운 전극형성 문제를 해결하였다.

• 한국결정성장학회지
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• 제7권2호
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• pp.197-206
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• 1997

6H-SiC 위에 SiC 에피층이 화학 기상 증착(CVD)에 의하여 성장되었다. 성장된 SiC 에피층의 결정구조는 X-선 회절과 Raman 분광을 사용하여 조사되었으며, 이 에피층은 6H-SiC로서 성장되었음을 확인하였다. 수정된 Lely법으로 성장된 한 SiC 결정 분말의 결정구조를 확인하기 위하여 전형적인 SiC polytype들의 X-선 회절상을 계산하였으며, 측정된 X-선 회절상과 비교하여 이 SiC 결정에는 15R-SiC가 약간 혼재되어 있음을 확인하였다.

• Journal of Microbiology and Biotechnology
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• 제33권4호
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• pp.485-492
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• 2023

Methylorubrum extorquens, a facultative methylotroph, assimilates C₁ compounds and accumulates poly-β-hydroxylbutyrate (PHB) as carbon and energy sources. The ethylmalonyl pathway is central to the carbon metabolism of M. extorquens, and is linked with a serine cycle and a PHB biosynthesis pathway. Understanding the ethylmalonyl pathway is vital in utilizing methylotrophs to produce value-added chemicals. In this study, we determined the crystal structure of the mesaconyl-CoA hydratase from M. extorquens (MeMeaC) that catalyzes the reversible conversion of mesaconyl-CoA to β-methylmalyl-CoA. The crystal structure of MeMeaC revealed that the enzyme belongs to the MaoC-like dehydratase domain superfamily and functions as a trimer. In our current MeMeaC structure, malic acid occupied the substrate binding site, which reveals how MeMeaC recognizes the β-methylmalyl-moiety of its substrate. The active site of the enzyme was further speculated by comparing its structure with those of other MaoC-like hydratases.

• Transactions on Electrical and Electronic Materials
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• 제18권6호
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• pp.323-329
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• 2017

This reports the electrical behavior, bonding structure and Schottky contact of gallium-zinc-oxide (GZO) thin film annealed at $100{\sim}400^{\circ}C$. The mobility of GZO with high density of PL spectra and crystal structure was also increased because of the structural matching between GZO and Si substrate of a crystal structure. However, the GZO annealed at $200^{\circ}C$ with an amorphous structure had the highest mobility as a result of a band to band tunneling effect. The mobility of GZO treated at low annealing temperatures under $200^{\circ}C$ increased at the GZO with an amorphous structure, but that at high temperatures over $200^{\circ}C$ also increased when it was the GZO of a crystal structure. The mobility of GZO with a Schottky barrier (SB) was mostly increased because of the effect of surface currents as well as the additional internal potential difference.

• Archives of Pharmacal Research
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• 제2권2호
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• pp.99-110
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• 1979

The crystal structure of sulfapyridine, $C_{11}H_{11}N_{3}O_{2}S$, has been determined by X-ray diffraction method. The compound crystallizees in the monoclinic space group C2/c with a = 12, 80(4), b= 11.72(4), $c= 15.36(5){\AA}, {\beta}= 94(3)^{\circ}$and Z = 8. A total of 1133 observed reflections were collected by the Weissenberg method with CuKaradiation. Structure was solved by the heavy atom method and refined by isostropic block-diagonal least-squares method to the R value of 0.14. The nitrogen in the pyridine ring of sulfapyridine is associated with an extra-annular hydrogen. The C (benzene ring) S-N-C (pyridine ring) group adopts the gauche form with a fonformational angle of $71^{\circ}$. The benzene ring are inclined at angle of $84^{\circ}.to the pyridine ring plane. Sulfapyridine shows three different hydrogen bonding in the crystal. They are two N-H...O hydrogen bonds with the distance of 2.90 and 2.98${\AA}$ respectively, and on N-H...N with the distance of 3.06 ${\AA}$.

• Bulletin of the Korean Chemical Society
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• 제16권3호
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• pp.248-251
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• 1995

The crystal structure of Ba46-X, Ba46Al92Si100O384 [a= 25.297(1) Å], has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd&bar{3}at 21(1) ℃. The crystal was prepared by ion exchange in flowing stream of 0.05 M Ba(OH)2 aqueous solution for 5 days. The crystal was then dehydrated at 380 ℃ and 2 × 10-6 Torr for 2 days. The structure was refined to the final error indices R1= 0.051 and Rw= 0.054 with 369 reflections for which I > 3σ(I). In this structure, all Ba2+ ions are located at the three different crystallographic sites: fourteen Ba2+ ions are located at site Ⅰ, the centers of the double six rings, two Ba2+ ions lie at site Ⅰ', in the sodalite cavity opposite double six rings(D6R's) and another thirty Ba2+ ions are located at site Ⅱ in the supercage. Two Ba2+ ions are recessed ca. 0.27 Å into the sodalite cavity from their three O(3) oxygen plane and thirty Ba2+ ions are recessed ca. 1.11 Å into the supercage from their three O(2) oxygen planes, respectively (Ba(1)-O(3) = 2.76(1) Å, O(3)-Ba(1)-O(3) = 180(0)°, Ba(2)-O(3) = 2.45(1) Å, O(3)-Ba(2)-O(3) = 108(1)°, Ba(3)-O(2)=2.65(1) Å, and O(2)-Ba(3)-O(2)=103.9(4)°).

• 한국결정성장학회지
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• 제30권1호
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• pp.1-6
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• 2020

본 연구에서는 패턴화된 사파이어 기판 위에 HVPE(Hydride Vapor Phase Epitaxy System) 법에 의해 50 nm 두께의 AlN thin film을 증착한 뒤, 에피층 구조가 MO CVD에서 성장되었다. AlN 버퍼층 박막의 표면형상이 SEM, AFM에 의해서, 에피층 구조의 GaN 박막의 결정성은 X-선 rocking curve에 의해 분석되었다. 패턴화된 사파이어 기판 위에 증착된 GaN 박막은, 사파이어 기판 위에 증착된 GaN 박막의 경우보다 XRD 피크 세기가 다소 높은 결과를 나타냈다. AFM 표면 형상에서 사파이어 기판 위에 AlN 박막이 증착된 경우, GaN 에피층 박막의 p-side 쪽의 v-pit 밀도가 상대적으로 낮았으며, 결함밀도가 낮게 관찰되었다. 또한, AlN 버퍼층이 증착된 에피층 구조는 AlN 박막이 없는 에피층의 광출력에 비해 높은 값을 나타냈다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 C
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• pp.1933-1935
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• 2002

In this paper, we present a study of the structure and electro-optic behavior of hybrid liquid-crystal-silica sphere composite photonic crystals, formed by filling the (26% by volume) void space of fee (face centered cubic) silica opals infiltrated with a nematic liquid crystal. Three dimensional photonic crystals of visible range were fabricated via a self assembly method of silica spheres of submicron diameter. The expected fee structure was confirmed by scanning electron microscopy (SEM) of the dehydrated crystal with glass removed. The photonic crystal exhibited significant electric-field-induced shift of the optical Bragg reflection peak when the liquid crystal has the long molecular axis oriented parallel to the sphere surfaces.

• Bulletin of the Korean Chemical Society
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• 제30권11호
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• pp.2608-2612
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• 2009

The unequivocal solid-state structure and stereochemistry of the hetaryl leuco-TAM dye, 2,2’-(2-phenyl propane- 1,3-diylidene) bis(1,3,3- trimethylindoline) derivatives were established using X-ray single crystal analysis. The X-ray crystal analysis showed that the (Z, E)-isomers only formed stereoselectively, with a so-called “threebladed propeller” conformation, from the reaction of a Fischer base and benzaldehyde derivatives. These isomers were stacked in a juxtaposition to form a dimer or a double dimer, adopting either a triclinic, with P-1, or monoclinic crystal system with a space group P21/n in the unit cell of the crystal.

• 한국분말재료학회지
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• 제19권4호
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• pp.285-290
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• 2012

The present study was focused on the analysis of the electric and thermal properties of spark plasma sintered $Bi_{0.5}Sb_{1.5}Te_3$ thermoelectric material. The crystal structure, microstructure, electric and thermal properties of the sintered body were evaluated by measuring XRD, SEM, electric resistivity, Hall effect and thermal conductivity. The $Bi_{0.5}Sb_{1.5}Te_3$ sintered body showed anisotropic crystal structure. The c-axis of the $Bi_{0.5}Sb_{1.5}Te_3$ crystal aligned in a parallel direction with applied pressure during spark plasma sintering. The degree of the crystal alignment increased with increasing sintering temperature and sintering time. The electric resistivity and thermal conductivity of the $Bi_{0.5}Sb_{1.5}Te_3$ sintered body showed anisotropic characteristics result from crystal alignment.