• 대한화학회지
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• 제55권3호
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• pp.502-508
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• 2011

[ $Nd_{2x}Cd_{2-3x}SiO_4$ ]($0.01{\leq}x{\leq}0.21$) [S1-S3: x=0.01, 0.11 and 0.21] 고용체를 졸-겔 방법을 통해 합성하였다. X선 분말회절(XRD) 측정은 $P2_1$/m 공간군의 단사정계를 보여준다. 평균 결정 크기는 20-45 nm이다. 주사전자현미경(SEM)으로 살펴본 모양은 구형의 특성을 보인다. 에너지 분산 X 선 분광기(EDS) 결과로부터 모든 구성 원소의 존재를 확인하였다. ~750 nm에서의 흡수 밴드는 $Nd^{3+}$ 이온의 $^4I_{9/2}{\rightarrow}^4F_{7/2}+^4S_{3/2}$ 전이에 기인한다. 10, 40, 77, 300 K에서 S1-S3의 전자 상자성 공명 (EPR) 선모양은 $Nd^{3+}$ 이온의 빠른 스핀 격자 이완에 기인하는 폭이 넓은 구분되지 않은 등방성의 선모양을 보여준다.

• 한국전기전자재료학회논문지
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• 제15권11호
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• pp.923-932
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• 2002

A stoichiometric mixture of evaporating materials for CdIn$\_$2/S$\_$4/ single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, CdIn$\_$2/S$\_$4/ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by hot wall epitaxy(HWE) system. The source and substrate temperatures were 630 $\^{C}$ and 420 $\^{C}$, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction(DCXD). The carrier density and mobility of CdIn$\_$2/S$\_$4/ single crystal thin films measured from Hall effect by van der Pauw method are 9.01$\times$10$\^$16/ cm$\^$-3/ and 219 ㎠/V$.$s at 293 K, respectively. From the optical absorption measurement, the temperature dependence of energy band gap on CdIn$\_$2/S$\_$4/ single crystal thin films was found to be Eg(T) ＝ 2.7116 eV - (7.74 $\times$ 10$\^$-4/ eV) T$\^$2//(T＋434). After the as-grown CdIn$\_$2/S$\_$4/ single crystal thin films was annealed in Cd-, S-, and In-atmospheres, the origin of point defects of CdIn$\_$2/S$\_$4/ single crystal thin films has been investigated by the photoluminescence(PL) at 10 K. The native defects of V$\_$cd/, V$\_$s/, Cd$\_$int/ and S$\_$int/ obtained by PL measurements were classified as donors or accepters type. And we concluded that the heat-treatment in the S-atmosphere converted CdIn$\_$2/S$\_$4/ single crystal thin films to an optical p-type. Also, we confirmed that In in CdIn$\_$2/S$\_$4/GaAs did not from the native defects because In in CdIn$\_$2/S$\_$4/ single crystal thin films existed in the form of stable bonds.

• 한국전기전자재료학회논문지
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• 제20권10호
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• pp.829-838
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• 2007

The stochiometric mix of evaporating materials for the $CdGa_2Se_4$ single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, $CdGa_2Se_4$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were $630^{\circ}C$ and $420^{\circ}C$, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD).The carrier density and mobility of $CdGa_2Se_4$ single crystal thin films measured from Hall effect by van der Pauw method are $8.27{\times}10^{17}\;cm^{-3},\;345\;cm^2/V{\cdot}s$ at 293 K. respectively. The temperature dependence of the energy band gap of the $CdGa_2Se_4$ obtained from the absorption spectra was well described by the Varshni's relation, $Eg(T)\;=\;2.6400\;eV\;-\;(7.721{\times}10^{-4}\;eV/K)T^2/(T+399\;K)$. After the as-grown single crystal $CdGa_2Se_4$ thin films were annealed in Cd-, Se-, and Ga -atmospheres, the origin of point defects of single crystal $CdGa_2Se_4$ thin films has been investigated by PL at 10 K. The native defects of $V_{Cd}$, $V_{Se}$, $Cd_{int}$, and $Se_{int}$ obtained by PL measurements were classified as donors or accepters. We concluded that the heat-treatment in the Cd-atmosphere converted single crystal $CdGa_2Se_4$ thin films to an optical p-type. Also, we confirmed that Ga in $CdGa_2Se_4/GaAs$ did not form the native defects because Ga in single crystal $CdGa_2Se_4$ thin films existed in the form of stable bonds.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.399-399
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• 2008

Synthesis and characterization of ZnO structure such as nanowires, nanorods, nanotube, nanowall, etc. have been studied to multifunctional application such as optical, nanoscale electronic and chemical devices because it has a room-temperature wide band gap of 3.37eV, large exiton binding energy(60meV) and various properties. Various synthesis methods including chemical vapor deposition (CVD), physical vapor deposition, electrochemical deposition, micro-emulsion, and hydrothermal approach have been reported to fabricate various kinds of ZnO nanostructures. But some of these synthesis methods are expensive and difficult of mass production. Wet chemical method has several advantage such as simple process, mass production, low temperature process, and low cost. In the present work, ZnO nanorods are deposited on ITO/glass substrate by simple wet chemical method. The process is perfomed by two steps. One-step is deposition of ZnO seeds and two-step is growth of ZnO nanorods on substrates. In order to form ZnO seeds on substrates, mixture solution of Zn acetate and Methanol was prepared.(one-step) Seed layers were deposited for control of morpholgy of ZnO seed layers by spin coating process because ZnO seeds is deposited uniformly by centrifugal force of spin coating. The seed-deposited samples were pre-annealed for 30min at $180^{\circ}C$ to enhance adhesion and crystallinnity of ZnO seed layer on substrate. Vertically well-aligned ZnO nanorods were grown by the "dipping-and-holding" process of the substrates into the mixture solution consisting of the mixture solution of DI water, Zinc nitrate and hexamethylenetetramine for 4 hours at $90^{\circ}C$.(two-step) It was found that density and morphology of ZnO nanorods were controlled by manipulation of ZnO seeds through rpm of spin coating. The morphology, crystallinity, optical properties of the grown ZnO nanostructures were carried out by field-emission scanning electron microscopy, high-resolution electron microscopy, photoluminescence, respectively. We are convinced that this method is complementing problems of main techniques of existing reports.

• 한국결정성장학회지
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• 제22권5호
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• pp.233-240
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• 2012

백색 발광다이오드(white light-emitting diodes)를 이용한 광소자는 소비전력이 상대적으로 작고, 안정적이며, 수은과 같은 유해 중금속을 포함하지 않기 때문에, 에너지 절약 및 친환경 산업측면에서 유망한 산업으로 급속히 발전하고 있다. 국내의 경우 LED 조명의 효율, 신뢰성, 연색성을 향상시키는데 필수 소재인 형광체의 기술 확보에 대한 관심이 높아지고 있다. 이러한 관점에서 기존의 YAG, TAG, silicate 계열 산화물 형광체 뿐만 아니라 고온특성이 우수한 산/질화물계 형광체 개발에 대한 관심이 높아지고 있다. 특히 산/질화물계 형광체 조성에서 $M_2Si_5N_8$ : $Eu^{2+}$, $MAlSiN_3$ : $Eu^{2+}$ M-SiON(M = Ca, Sr, Ba), ${\alpha}/{\beta}$-SiAlON : $Eu^{2+}$과 같은 재료는 440~460 nm 영역에서의 넓은 여기파장과 우수한 발광효율로 청색 LED 칩을 이용한 백색 LED에 넓게 사용되고 있다. 이 논문에서는 이러한 산/질화물계 형광체 조성의 결정학적, 광학적 특성 및 응용에 대해서 정리하였다. 또한 최근에 주목받고 있는 양자점(quantum dots) 형광체를 응용한 white LEDs의 개발동향에 대해서도 알아보도록 한다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.111-112
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• 2005

To obtain the single crystal thin films, $CuInSe_2$, mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wail epitaxy (HWE) system. The source and substrate temperatures were 620$^{\circ}C$ and 410$^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobilily of $CuInSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $9.62\times10^{16}$ $cm^{-3}$ and $296cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the CulnSe$_2$ obtained from the absorption spectra was well described by the Varshni's relation E$_g$(T) = 1.1851 eV - ($8.99\times10^{-4}$ ev/K)T$_2$/(T + 153K). After the as-grown $CuInSe_2$ single crystal thin films was annealed in Cu-, Se-, and In-atmospheres the origin of point defects of $CuInSe_2$ single crystal thin films has been investigated by the photoluminescence(PL) at 10 K. The nat ive defects of V$_{Cu}$, $V_{Se}$, Cu$_{int}$, and $Se_{int}$ obtained by PL measurements were classified as a donors or accepters type. And we concluded that the heat-treatment in the Cu-atmosphere converted $CuInSe_2$ single crystal thin films to an optical n-type. Also, we confirmed that In in $CuInSe_2$/GaAs did not form the native defects because In in $CuInSe_2$ single crystal thin films existed in the form of stable bonds.

• 한국자기학회지
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• 제6권6호
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• pp.405-410
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• 1996

방사광 광전자분광법을 이용하여 $Co_{x}Pd_{100-x}$ 합금박막들(x = 0, 25, 40, 65)의 가전자띠 스펙트럼들을 측정하고, Co 3d 전자와 Pd 4d 전자들에 의한 각각의 부분스펙트럼 무게분포(partial spectral weight distribution : PSW)를 결정하였다. Co-Pd 합금박막에서의 Co 3d PSW는 수직자기이방성을 나타내는 영역에 해당하는 Co 함량 25% 이하에서 순수 Co 박막의 스펙트럼과 상당히 다른 구조를 보인 반면, Co 함량이 약 40% 이상이 되면 순수 Co 박막의 PES스펙트럼과 거의 일치하였다. Co 함량이 25% 이하의 Co 3d PSW에서 관찰된 페르미준위 근처의 봉우리 구조와 결합에너지 2 eV 근처의 어깨구조는 혼성에 의한 Co 3d 전자구조의 변화를 반영한다. 따라서 Co 3d 전자와 Pd 4d 전자 간의 혼성상호작용이 수직자기이방성의 결정에 중요한 역할을 하는 것으로 추측되었다. Co-Pd 합금박막에서의 Pd 4d PSW는 순수 Pd 스펙트럼에 비하여 그 폭이 넓고, 주 봉우리의 결합에너지가 크며, 페르미준위에서의 스펙트럼의 세기가 작게 관찰되었다. 그리고 Pd 함량이 감소함에 따라 Pd 4d PSW의 반치폭이 증가하였는데, 이러한 결과는 Co-Pd 합금이 형성될 때의 무질서 효과 또는 Co 3d 전자와 Pd 4d 전자간의 혼성상 호작용으로 인한 Pd 4d 전자구조의 변화를 반영하는 것으로 추측되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.14-15
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• 2010

Recently there has been growing interest in topological insulators or the quantum spin Hall (QSH) phase, which are insulating materials with bulk band gaps but have metallic edge states that are formed topologically and robust against any non-magnetic impurity [1]. In a three-dimensional material, the two-dimensional surface states correspond to the edge states (topological metal) and their intriguing nature in terms of electronic and spin structures have been experimentally observed in bulk Bi1-xSbx single crystals [2,3,4]. However, if we want to know the transport properties of these topological metals, high purity samples as well as very low temperature will be needed because of the contribution from bulk states or impurity effects. In a recent report, it was also shown that an intriguing coupling between the surface and bulk states will occur [5]. A simple solution to this bothersome problem is to prepare a topological metal on an ultrathin film, in which the surface-to-bulk ratio is drastically increased. Therefore in the present study, we have investigated if there is a method to make an ultrathin Bi1-xSbx film on a semiconductor substrate. From reflection high-energy electron diffraction observation, it was found that single crystal Bi1-xSbx films (0${\sim}30\;{\AA}A$ can be prepared on Si(111)-$7{\times}7$. The transport properties of such films were characterized by in situ monolithic micro four-point probes [6]. The temperature dependence of the resistivity for the x=0.1 samples was insulating when the film thickness was $240\;{\AA}A$. However, it became metallic as the thickness was reduced down to $30\;{\AA}A$, indicating surface-state dominant electrical conduction. Figure 1 shows the Fermi surface of $40\;{\AA}A$ thick Bi0.92Sb0.08 (a) and Bi0.84Sb0.16 (b) films mapped by angle-resolved photoemission spectroscopy. The basic features of the electronic structure of these surface states were shown to be the same as those found on bulk surfaces, meaning that topological metals can be prepared at the surface of an ultrathin film. The details will be given in the presentation.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.220-220
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• 2013

Surface-normal transmission electro-absorption modulator (EAM) are attractive for high-definition (HD) three-dimensional (3D) imaging application due to its features such as small system volume and simple epitaxial structure [1,2]. However, EAM in order to be used for HD 3D imaging system requires uniform modulation performance over large area. To achieve highly uniform modulation performance of EAM at the operating wavelength of 850 nm, it is extremely important to remove the GaAs substrate over large area since GaAs material has high absorption coefficient below 870 nm which corresponds to band-edge energy of GaAs (1.424 eV). In this study, we propose and experimentally demonstrate a transmission EAM in which highly selective backside etching methods which include lapping, dry etching and wet etching is carried out to remove the GaAs substrate for achieving highly uniform modulation performance. First, lapping process on GaAs substrate was carried out for different lapping speeds (5 rpm, 7 rpm, 10 rpm) and the thickness was measured over different areas of surface. For a lapping speed of 5 rpm, a highly uniform surface over a large area ($2{\times}1\;mm^2$) was obtained. Second, optimization of inductive coupled plasma-reactive ion etching (ICP-RIE) was carried out to achieve anisotropy and high etch rate. The dry etching carried out using a gas mixture of SiCl4 and Ar, each having a flow rate of 10 sccm and 40 sccm, respectively with an RF power of 50 W, ICP power of 400 W and chamber pressure of 2 mTorr was the optimum etching condition. Last, the rest of GaAs substrate was successfully removed by highly selective backside wet etching with pH adjusted solution of citric acid and hydrogen peroxide. Citric acid/hydrogen peroxide etching solution having a volume ratio of 5:1 was the best etching condition which provides not only high selectivity of 235:1 between GaAs and AlAs but also good etching profile [3]. The fabricated transmission EAM array have an amplitude modulation of more than 50% at the bias voltage of -9 V and maintains high uniformity of >90% over large area ($2{\times}1\;mm^2$). These results show that the fabricated transmission EAM with substrate removed is an excellent candidate to be used as an optical shutter for HD 3D imaging application.

• 청정기술
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• 제27권4호
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• pp.291-296
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• 2021

물에 잔존하는 유기오염물질이 인체 및 환경에 미치는 악영향을 해결하기 위한 방법으로 오염물질을 친환경적으로 분해할 수 있는 광촉매 기술이 대두되고 있다. 대표적인 광촉매 물질로 TiO₂ 입자가 사용되고 있지만 비싼 가격으로 인해 이를 대체하고자 하는 노력이 지속적으로 수행되었다. 본 연구에서는 이러한 노력의 일환으로 미세유체공정을 사용하여 보다 가격경쟁력이 우수한 ZnO입자를 합성하였다. ZnO의 넓은 밴드갭으로 인해 촉매활성이 제한되는 단점을 해결하고자 동일 공정을 사용하여 은(Ag) 나노입자를 ZnO 표면에 증착하여 Ag-ZnO 나노복합체를 생산하였다. 다양한 분석법을 사용하여 나노복합체의 형상, 구조, 및 성분 분석을 진행한 결과 고품질의 Ag-ZnO 나노복합체가 합성됨을 확인했으며, 메틸렌블루 분해 실험을 통해서 광촉매 활성을 측정하였다. Ag-ZnO 나노복합체의 플라스몬 효과와 광반응에 의해 생성된 전자와 정공의 분리 효과에 의해 광촉매 활성 효율이 순수한 ZnO 입자와 비교하여 향상되었음을 확인하였다. Microreactor-assisted nanomaterials (MAN) 공정 기반의 나노복합체는 가격경쟁력이 우수하고 공정이 용이하다는 장점이 있기에 나노복합체 광촉매를 대량 생산하기 위한 잠재력이 우수하다고 사료된다.