• Bulletin of the Korean Chemical Society
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• 제30권1호
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• pp.219-223
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• 2009

$TiO_2$ doped with $Er^{3+\;and\;Yb^{3+}$ was used for fabricating a scattering layer and a nano-crystalline $TiO_2$ electrode layer to be used in dye-sensitized solar cells. The material was prepared using a new sol-gel combustion hybrid method with acetylene black as fuel. The $Er^{3+}$-$Yb^{3+}$ co-doped titanium oxide powder synthesized at 700oC had embossed structure morphology with a size between 27 to 54 nm that agglomerated to produce micron size particles, as observed by the scanning electron micrographs. The XRD patterns showed that the $Er^{3+}$-$Yb^{3+}$ co-doped titanium oxide had an amorphous structure, while using the same method without doping $Er^{3+}\;or\;Yb^{3+},\;TiO_2$ was obtained in the crystallite form with thea dominance of rutile phase. Fabricating a bilayer structure consisting of nano-crystalline $TiO_2$ and the synthesized $Er^{3+}$-$Yb^{3+}$ co-doped titanium oxide showed better scattering property, with an overall increase of 15.6% in efficiency of the solar cell with respect to a single nano-crystalline $TiO_2$ layer.

• 한국산학기술학회논문지
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• 제10권7호
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• pp.1489-1496
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• 2009

비정질 인듐-갈륨-아연 산화물 박막트랜지스터를 모델링 하여서, 능동층의 구조, 두께, 평형상태의 전자밀도에 대응하는 박막트랜지스터의 특성을 연구하였다. 단일 능동층 박막트랜지스터의 경우, 능동층이 얇을 때 높은 전계효과이동도를 보였다. 문턱전압의 절대값은 능동층의 두께가 20 nm일 때 최저치를 보였으며, 문턱전압이하 기울기는 두께에 대한 의존성을 보이지 않았다. 복층구조 능동층의 경우, 하부의 능동층이 높은 평형상태 전자밀도를 가질 때보다 우수한 스위칭 특성을 보였다. 이 경우에도 능동층의 두께가 얇을 때에 높은 전계효과 이동도를 보였다. 높은 평형상태 전자밀도의 능동층의 두께를 증가시키면 문턱전압은 음의 방향으로 이동하였다. 문턱전압이하 기울기는 능동층의 구조에 대하여 특별한 의존성을 보이지 않았다. 이상과 같은 데이터는 산화물반도체 박막트랜지스터 능동층의 구조, 두께, 도핑비율을 최적화함에 효과적으로 사용될 것으로 기대된다.

• 한국광물학회지
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• 제26권1호
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• pp.27-34
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• 2013

X-선회절 분석은 결정질 물질의 정량과 정성분석을 위한 가장 효과적인 분석기술이며, 따라서 회절자료를 이용한 매우 다양한 광물조성 정량분석법이 존재한다. 본 연구에서는 비정질 실리카, 석영, 뮬라이트, 강옥으로 제조한 인공광물혼합시료를 대상으로 리트벨트법과 PONKCS (partial or no known crystal structure) 방법을 적용하여 정량 X-선회절 분석을 수행하였다. 100% 비정질 실리카와 내부표준시료 첨가 시료의 회절자료를 이용하여 PONKCS 방법으로 비정질 실리카의 결정 모형을 성공적으로 구축하였다. 비정질 실리카의 경우, 원 중량 대비 치우침의 절대값 평균은 1.85 wt%였다. 비정질 실리카의 함량이 작은 경우 상대적으로 높은 치우침을 보이는데, 이는 배경 회절패턴의 강도가 낮음에 기인하는 것으로 판단된다. 그밖에 석영, 뮬라이트, 강옥의 경우, 치우침의 절대값 평균은 각각 0.53 wt%, 0.87 wt%, 0.57 wt%였다. 내부표준물질 혼합법을 적용한 전통적인 리트벨트 정량분석 결과와 비교할 때 PONKCS 방법이 비정질 실리카를 포함한 인공광물혼합시료에 대하여 신뢰도 높고 성공적인 정량 분석법임을 확인해 주었다.

• 공학논문집
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• 제6권1호
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• pp.97-109
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• 2004

CaO의 첨가량에 따라 $CO_2$가스를 불어넣고 반응시간 변화에 따라 용매로 $C_2 H_5 OH$을 사용하여 에틸렌글리콜을 첨가한 CaO-$C_2 H_5 OH$-$CO_2$계의 기.액반응으로부터 비정질 $CaCO_3$의 합성과 결정구조를 전기전도도, X-선회절 및 주사전자현미경으로 조사하였다. 이 반응에서 900ml의 $C_2 H_5 OH$에 에틸렌글리콜 100ml를 첨가하고 CaO의 양을 10~40g으로 하여 $CO_2$가스를 1$\ell$/min의 유속으로 흡입시켜 얻은 합성분말의 겔형 물질을 신속히 여과, 감압하의 $60^{\circ}C$에서 건조하여 1${\mu}m$이하의 구형 vaterite상과 무정형인 비정질 $CaCO_3$을 얻었다. 그리고 비정질 $CaCO_3$의 일부는 중간생성물로서 연쇄형 calcite로 변화하는 것을 알 수 있었고 침강성 $CaCO_3$의 생성보다 먼저 초기 반응생성물은 비정질 $CaCO_3$이었고 이 경우 생성역역은 pH 7-9의 범위로 상당한 영향을 준다. 또한 비정질 $CaCO_3$은 용액 속에서 불안정하여 용해반응으로 인해서 결국 calcite로 결정화한다. 특히 비정질 $CaCO_3$은 CaO-$C_2 H_5 OH$-$CO_2$계의 반응에 의해서 침강되어 생성되거나 또는 gel상으로 된다.

• 한국표면공학회지
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• 제50권3호
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• pp.177-182
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• 2017

The properties of electroless Ni-B thin film on diamond powder with different parameters (temperature, pH, surfactant etc.) were studied. The surface morphology, structure and composition distribution of the Ni-B film were observed by field effect scanning electron microscope (FE-SEM), energy-dispersive spectrometer (EDS), X-ray diffraction (XRD) and Auger electron spectroscopy (AES). The growth rate of Ni-B film was increased with increase of bath temperature. The B content in Ni-B film was reduced with increase of bath pH. As a result the structure of Ni-B film was changed from amorphous to crystalline structure. The PVP in solution plays multi-functional roles as a dispersant and a stabilizer. The Ni-B film deposited with adding 0.1 mM-PVP was strongly introduced an amorphous structure with higher B content (25 at.%). Also the crystallite size of Ni-B film was reduced from 12.7 nm to 5.4 nm.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.222.2-222.2
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• 2015

A $Ge_2Sb_2Te_5$ nanowire (GST NW) phase change memory device is investigated with Joule heating electrodes. GST is the most promising phase change materials, thus has been studied for decades but atomic structure transition in the phase-change area of single crystalline phase-change material has not been clearly investigated. We fabricated a phase change memory (PCM) device consisting of GST NWs connected with WN electrodes. The GST NW has switching performance with the reset/set resistance ratio above $10^3$. We directly observed the changes in atomic structure between the ordered hexagonal close packed (HCP) structure and disordered amorphous phase of a reset-stop GST NW with cross-sectional STEM analysis. Amorphous areas are detected at the center of NW and side areas adjacent to heating electrodes. Direct imaging of phase change area verified the atomic structure transition from the migration and disordering of Ge and Sb atoms. Even with the repeated phase transitions, periodic arrangement of Te atoms is not significantly changed, thus acting as a template for recrystallization. This result provides a novel understanding on the phase-change mechanism in single crystalline phase-change materials.

• Fibers and Polymers
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• 제3권1호
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• pp.18-23
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• 2002

The structure development and dynamic properties of fibers produced by high-speed spinning of P(EN-ET) random copolymers were investigated. The as-spun fibers were found to remain amorphous up to the spinning speed of 1500 m/min, and subsequent increases in speed resulted in the crystalline domains containing primarily $\alpha$ crystalline modification of PEN. The f modification was not found up to spinning speeds of 4500 m/min. On the other hand, annealing of constrained fibers spun at the 2100 m/min at 180,200, and 240^{\circ}C$ exhibited $\beta$-form crystalline structure, while the annealed fibers spun in 600-1500 m/min range exhibited dominantly $\alpha$-form. However $\beta$-form crystals disappeared above the spinning speed of 3000 m/min. With increasing spinning speeds from 600 to 4500 m/min, the storage modulus of as-spun fibers increased continuously and reached a value of about 10.4 spa at room temperature. The tan $\delta$curves showed the $\alpha$-relaxation peak at about 155-165^{\circ}C$, which is considered to correspond to the glass transition. The $\alpha$-relaxation peaks became smaller and broader, and shift to higher temperatures as the spinning speed increases, meaning that molecular mobility in the amorphous region is restricted by increased crystalline domain.

• Journal of Magnetics
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• 제2권4호
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• pp.147-156
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• 1997

An artificially modulated magnetic Co/Pd multilayer is one of the promising candidates for high density magneto-optic (MO) recording media, due to a large Kerr rotation angle in the wavelength of a blue laser beam. However, since multilayer structure, as well as amorphous structure, is a non-equilibrium state in terms of free energy and a MO recording technology is a kind of thermal recording which is conducted around Curie temperature (Tc) of the recording media, when the Co/Pd mulilayer is used for the MO recording media, changes in the magnetic properties are occurred as the amorphous structure do. Therefore, the assessment of the magnetic properties in the Co/Pd multilayer during interdiffusion is crucially important both for basic research and applications. As the parameter of the magnetic properties in this research, saturation magnetization and perpendicular magnetic anisotropy energy of the Co/Pd multilayer are measured in terms of Ar sputtering pressure and heat treatment temperature. Form the results of the research, we find out that the magnetic exchange energy between Co and Pd sublayers strongly affects the changes in the magnetic properties of the Co/Pd multilayers during the interdiffusion in ferromagnetic state. This discovery will provide the understanding of the magnetic exchange energy in the Co/Pd multilayer structure and suggest the operating temperature range for MO recording in the Co/Pd multilayer for the basic research and applications, respectively.

• 대한금속재료학회지
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• 제49권12호
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• pp.930-936
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• 2011

In the present study, we show that the addition of Ag, an element having a positive enthalpy of mixing with Cu in the liquid state, enables the simultaneous enhancement of the glass forming ability and the plasticity in Cu-Zr-Ag bulk metallic glasses (BMGs). Rods of 4 mm diameter could be prepared with a fully amorphous structure and values of plastic strain up to 18% were measured under a compression mode for compositions around $Cu_{42.5}Zr_{47.5}Ag_{10}$. The possible role of Ag in the change of the atomic structure and the enhancement of the plastic strain in the ternary Cu-Zr-Ag BMGs is discussed based on analyses from transmission electron microscopy and EXAFS (extended X-ray absorption fine structure).

• 정보저장시스템학회논문집
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• 제3권3호
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• pp.118-122
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• 2007

Phase-change wet-etching technology using GeSbTe phase-change films is developed. Selective etching between an amorphous and a crystalline phase can be carried out with an alkaline etchant of NaOH. Etching selectivity is dependent not only on the concentration of the alkaline etchant but also on the film structure. Specifically, metal films for heat control cause marked effects on the etching properties of GeSbTe film. Surviving amorphous pits can be obtained with Al metal layer, however etched amorphous pits are seen with Ag metal layer. An opposite selective etching behavior can be observed between samples with two different metal layers.