• 한국결정학회지
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• 제14권2호
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• pp.51-55
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• 2003

YBa₂CU₃O/sub 7-8/(YBCO) coated conductor의 완충층 구조를 개선하기 위하여 2축배향된 Ni-3 wt%W 합금 기판위에 단일 완충층으로 SrTiO₃(STO) 박막을 증착하였다. YBCO와 STO 박막은 펄스레이저 증착법으로 성장시켰다. STO 박막의 표면은 증착온도에 따라 다른 미세조직을 보여 주었고, XRD 분석에서는 STO와 YBCO 박막이 금속기판의 배향성을 가지면서 성장되었음을 알 수 있었다. 액체질소 온도에서 1.2 MA/㎠의 임계전류밀도와 86 K의 임계온도를 가지는 짧은 길이의 coated conductor를 STO 단일완충층을 이용하여 제조하였다.

• 한국결정성장학회지
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• 제22권1호
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• pp.1-4
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• 2012

O- and Zn-polar ZnO films were grown by DC magnetron sputtering. Growth of high-quality, single-crystal ZnO thin films were confirmed by XRD and pole figure analysis. O-polar ZnO was grown on an $Al_2O_3$ substrate, which was confirmed by a slow growth rate (378 nm/hr), a fast etching rate (59 nm/min), and by the hillocks on the surface after etching. Zn-polar ZnO was grown on a GaN/$Al_2O_3$ substrate, which was confirmed by a fast growth rate (550 nm/hr), a slow etching rate (28 nm/min), and by pits on the surface after etching. Results from the present study show that it is possible to use DC-sputtering to grow ZnO film with the same polarity as other epitaxial growth methods.

• 한국전기전자재료학회논문지
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• 제25권9호
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• pp.692-701
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• 2012

Recently, many lead-free piezoelectric materials have been investigated for the replacement of existing Pb-based piezoelectric ceramics because of globally increasing environmental interest. There has been remarkable improvement in piezoelectric properties of some lead-free ceramics such as $(Bi,Na)TiO_3-(Bi,K)TiO_3-BaTiO_3$, $(Na,K)NbO_3-LiSbO_3$, and so on. However, no one still has comparable piezoelectric properties to lead-based materials. Therefore, new lead-free piezoelectric ceramics are required. $BiFeO_3$ has a rhombohedrally distorted perovskite structure at room temperature and a very high Curie temperature ($T_C$= 1,100 K). And a very large electric polarization of 50 ~ 60 ${\mu}C/cm^2$ has been reported both in epitaxial thin film and single crystal $BiFeO_3$. Therefore, a high piezoelectric effect is expected also in a $BiFeO_3$ ceramics. The recent research activities on $BiFeO_3$ or $BiFeO_3$-based solid solutions are reviewed in this article.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.56-60
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• 2000

Cube texture를 갖는 Ni기판위에 MOCVD(Metal Chemical Vapor Deposition)를 이용하여 NiO, CeO$_2$, YBCO 박막을 제조하였다. NiO(200)와 CeO$_2$(200) buffer layer는 450${\sim}$470$^{\circ}$C에서 10분간 MOCVD방법으로 (100)<001>Ni 기판위에 직접 증착하였다. 제조된 NiO, CeO$_2$ buffer layer는 조직이 치밀하며 표면의 상태가 매우 좋으며 Ni기판 위에 epitaxial하게 성장하였다. NiO는 Ni기판과 NiO<100>//Ni<100>의 방위관계를 가지고 성장하였으며, CeO$_2$는 증착조건에 따라 CeO$_2$ <100>//Ni<100> 및 CeO$_2$ <110>//Ni<100> 의 방위관계를 가지고 성장하였다. 증착된 NiO막과 CeO$_2$막에서 균열은 발생하지 않았다. MOCVD법으로 표면에 biaxial texture를 갖는 ceramic buffer를 증착시킨 NiO/Ni및 CeO$_2$/Ni 기판위에 YBCO박막을 MOCVD법으로 제조하였다. YBCO막은 기판온도 800$^{\circ}$C,증착압력 10torr, 산소분압을 0.7torr로 하여 10분간 행하였다. 공급원료의 조성에 따라 YBCO의 막의 texture와 형성되는 상이 변화되었다. NiO/Ni및 CeO$_2$/Ni 기판 위에 증착된 YBCO막은 c축 배향성을 가지고 성장하였으며, -scan 및 ${\varphi}$ -scan으로 측정한 (500)면의 in-plane과 (110)면의 out-of-plane의 FWHM(Full Width Half Maximum)값은 각각 10$^{\circ}$ 미만으로 우수하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.490-490
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• 2011

Graphene, hexagonal network of carbon atoms forming a one-atom thick planar sheet, has been emerged as a fascinating material for future nanoelectronics. Huge attention has been captured by its extraordinary electronic properties, such as bipolar conductance, half integer quantum Hall effect at room temperature, ballistic transport over ${\sim}0.4{\mu}m$ length and extremely high carrier mobility at room temperature. Several approaches have been developed to produce graphene, such as micromechanical cleavage of highly ordered pyrolytic graphite using adhesive tape, chemical reduction of exfoliated graphite oxide, epitaxial growth of graphene on SiC and single crystalline metal substrate, and chemical vapor deposition (CVD) synthesis. In particular, direct synthesis of graphene using metal catalytic substrate in CVD process provides a new way to large-scale production of graphene film for realization of graphene-based electronics. In this method, metal catalytic substrates including Ni and Cu have been used for CVD synthesis of graphene. There are two proposed mechanism of graphene synthesis: carbon diffusion and precipitation for graphene synthesized on Ni, and surface adsorption for graphene synthesized on Cu, namely, self-limiting growth mechanism, which can be divided by difference of carbon solubility of the metals. Here we present that large area, uniform, and layer controllable graphene synthesized on Cu catalytic substrate is achieved by acetylene-assisted CVD. The number of graphene layer can be simply controlled by adjusting acetylene injection time, verified by Raman spectroscopy. Structural features and full details of mechanism for the growth of layer controllable graphene on Cu were systematically explored by transmission electron microscopy, atomic force microscopy, and secondary ion mass spectroscopy.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.53-53
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• 2011

This paper describes results for surface and bulk characterization of the most promising thin film solar cell material for high performance devices, (Ag,Cu) (In,Ga) Se2 (ACIGS). This material in particular exhibits a range of exotic behaviors. The surface and general materials science of the material also has direct implications for the operation of solar cells based upon it. Some of the techniques and results described will include scanning probe (AFM, STM, KPFM) measurements of epitaxial films of different surface orientations, photoelectron spectroscopy and inverse photoemission, Auger electron spectroscopy, and more. Bulk measurements are included as support for the surface measurements such as cathodoluminescence imaging around grain boundaries and showing surface recombination effects, and transmission electron microscopy to verify the surface growth behaviors to be equilibrium rather than kinetic phenomena. The results show that the polar close packed surface of CIGS is the lowest energy surface by far. This surface is expected to be reconstructed to eliminate the surface charge. However, the AgInSe2 compound has yielded excellent atomic-resolution images of the surface with no evidence of surface reconstruction. Similar imaging of CuInSe2 has proven more difficult and no atomic resolution images have been obtained, although current imaging tunneling spectroscopy images show electronic structure variations on the atomic scale. A discussion of the reasons why this may be the case is given. The surface composition and grain boundary compositions match the bulk chemistry exactly in as-grow films. However, the deposition of the heterojunction forming the device alters this chemistry, leading to a strongly n-type surface. This also directly explains unpinning of the Fermi level and the operation of the resulting devices when heterojunctions are formed with the CIGS. These results are linked to device performance through simulation of the characteristic operating behaviors of the cells using models developed in my laboratory.

• 한국재료학회지
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• 제4권2호
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• pp.136-142
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• 1994

초청장 Si(111)기탄상에 초고진공 챔버에서 Ti을 증착하여 $TiSi_{2}$를 에피층으로 성장시켰다. 재구성된 (reconstructed) Di(111)표면에 상온에서 50$\AA$ 두께의 Ti을 증착한 후 $100^{\circ}C$간격으로 $800^{\circ}C$까지 열처리 하였다. $TiSi_{2}$박막의 구조는 전자회절 패턴 분석을 통하여 준안정상인 C49상임을 확인하였다. SEM 사진은 세가지 형태의 island를 보이고 있다. 각 island 는 단결정이며 그 구조는 서로 다른 결정학적 방향을 갖는 에피구조이다. 이러한 TiSi$_{2}$ island[112]C49 TiSi$_{2}$/[110]Si, (021) C49 $TiSi_{2}$/(111)Si의 방향관계를 가지고 있다.

• 한국자기학회지
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• 제22권5호
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• pp.162-166
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• 2012

Fe(100)/MgO(100)/CuPc/Co 자성터널접합 소자의 온도에 따른 전압-전류 특성 변화를 관찰하였다. 화학적 열적 안정성이 비교적 우수한 Cu-Phthalocyanine(CuPc)의 유기박막을 에피성장된 2 nm MgO(100) 박막 위에 2~10 nm 두께로 적층하여 두 강자성 Fe(100)와 Co 전극 사이의 무기-유기 복합 절연격벽으로 이용하였다. 저온 77 K에서 측정된 거대자기저항현상은 CuPc의 두께가 증가함에 따라 급격히 감소하여 10 nm의 CuPc 두께의 경우 전하축적에 의한 쌍안정 스위칭 거동(bistable switching behavior)이 관찰되었다. 이 스위칭 거동은 약 240 K의 온도에 이르면서 점차 소멸되어 상온에서는 정류기와 유사한 비대칭적 전압-전류 특성을 보였다. 이 연구에서 우리는 MgO/CuPc 층상구조에대해 유기물 스핀소자의 절연격벽뿐만 아니라 Polymer Random Access Memory(PoRAM)를 위한 응용 가능성에 대해 논하였다.

• 마이크로전자및패키징학회지
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• 제26권4호
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• pp.113-118
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• 2019

In this study, we investigated the growth of single-crystallinity α-Ga₂O₃ thin films on c-plane sapphire substrates using halide vapor pressure epitaxy. We also found the optimal growth conditions to suppress the phase transition of α-Ga₂O₃. Our results confirmed that the growth temperature and partial pressure of the reactive gas greatly influenced the crystallinity. The optimal growth temperature range was about 460~510℃, and the α-Ga₂O₃ thin films with the highest crystallinity were obtained at a III/VI ratio of 4. The thickness and surface morphology of the thin films was observed by scanning electron microscopy. The film thickness was 6.938 ㎛, and the full width at half maximum of the ω-2θ scan rocking curve was as small as 178 arcsec. The optical band gap energy obtained was 5.21 eV, and the films were almost completely transparent in the near-ultraviolet and visible regions. The etch pit density was found to be as low as about 6.0 × 10⁴ cm^-2.

• 한국산학기술학회논문지
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• 제7권5호
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• pp.801-804
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• 2006

[ $YBa_2Cu_3O_{7-{\delta}}(YBCO)$ ]계 초전도 선재용 $GdAlO_3(GAO)$ 버퍼층을 졸-겔(sol-gel) 공정에 의해 제조하였다. 전구체 용액은 Gd 질산염과 Al 질산염을 1:1 화학양론비로 하여 메탄올에 용해하여 준비하였다. 전구체 용액을 $SrTiO_3(STO)$ (100) 단결정 기판위에 스핀 코팅하고, 수분이 포함된 $N_2-5%\; H_2$ 분위기에서 $1000^{\circ}C$에서 2시간 열처리 하였다. 열처리 후 GAO 층의 표면에 대한 주사전자현미경 관찰에 의해 GAO 층이 에피택셜의 특징인 각면 형상을 갖는 것을 알 수 있었다. X-선 회절분석에 의하면 GAO 버퍼층은 c-축으로 우선 배향된 에피택셜 박막으로써 반가폭이 각각 (002)면에서 $0.29^{\circ}(out-of-plane)$, {112}지면에서 $1.10^{\circ}(in-plane)$의 우수한 배향성을 나타내었다.