• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.212-212
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• 2011

In addition to the catalysts' activity and selectivity, the deactivation of catalysts during use is of practical importance. It is crucial to understand the phenomena of the deactivation to predict the loss of activity during catalyst usage so that the high operational costs associated with catalyst replacement can be reduced. In this study, the activity of Ru catalysts, such as nanoparticles (3~6 nm) and polycrystalline thin film (50 nm), have been investigated under CO oxidation and oxidative/reductive reaction conditions at various temperatures with the ambient pressure X-Ray photoelectron spectroscopy (APXPS). With APXPS, the surface oxides on the catalyst are measured and monitored in-situ. It was found that the Ru film exhibited faster oxidation-and-reduction compared to that of nanoparticles showing mild oxidative-and-reductive characteristics. Additionally, the larger Ru nanoparticles showed a higher degree of oxide formation at all temperatures, suggesting a higher stability of the oxide. These observations are in agreement with the catalytic activity of Ru catalysts. The loss of activity of Ru films is correlated with bulk oxide formation, which is inactive in CO oxidation. The Ru nanoparticle, however, does not exhibit deactivation under similar conditions, suggesting that its surface is covered with a highly active ultrathin surface oxide. Since the active oxide is more stable as nanoparticles than as a film, the nanoparticles showed mild oxidative/reductive behavior, as confirmed by APXPS results. We believe these simultaneous observations of both the surface oxide of Ru catalysts and the reactivity in real time enable us to pinpoint the deactivation phenomena more precisely and help in designing more efficient and stable catalytic systems.

• 분석과학
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• 제6권2호
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• pp.239-246
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• 1993

ITO coated glass, bare glass, 그리고 (100)Si 기판 위에 증착된 $(BaSr)TiO_3$ 박막의 구조는 기판의 종류에 관계없이 변하지 않았으나 결정성은 다결정 ITO층과 (100)Si 기판에 있어서 증대되었다. ITO coated glass 기판 위에 증착된 $(BaSr)TiO_3$ 박막의 조성은 거의 화학양론적으로 일치하였으며 ((Ba+Sr)/Ti=1.08~1.09) 증착 중 상당히 치밀하고 균질하였다. 그러나 증착온도가 증가함에 따라 성장한 박막과 ITO층 사이에, 그리고 ITO층과 base glass 사이에 확산이 보다 심화되었다. ITO coated glass 기판 위에 증착된 $(BaSr)TiO_3$ 박막은 상당히 투명하였으며(투과율 약 80%) 굴절률($n_f$)은 기판온도의 증가에 따라 2.138~2.286이었다.

• 분석과학
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• 제6권2호
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• pp.149-156
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• 1993

고온고압하(高溫高壓下)에서의 Ni-C 액상(液相) 중에서 구상흑연입자(球狀黑鉛粒子)의 형성과정을 밝히기 위한 실험적인 관찰을 행하였다. 구상 흑연입자는 다이아몬드 안정역에서 유지하는 동안 안정한 형태로 생성되어 성장하였다. 이 때의 구상 흑연입자는 다결정형태(多結晶形態)가 아닌 연속적으로 성장한 많은 결함을 포함하는 단결정형태(單結晶形態)(fullerene형(型))를 하고 있었다. 표면분석기(表面分析機)(Auger electron spectroscope) 및 고분해능(高分解能) 투과전자현미경(透過電子顯微鏡)을 이용한 분석결과 구상 흑연 입자는 $sp^2$ 및 $sp^3$ 결합을 갖는 탄소원자가 혼재(混在)되어 있는 결정상태임이 밝혀졌다. 다이아몬드 안정역으로부터 흑연 안정역으로 압력이 감소함에 따라 흑연입자의 모양이 구형(球形)에서 평판형(平板形)으로 연속적으로 변해가는 것이 관찰되었다. 다이아몬드 안정역에서 형성되는 구상 흑연입자는 $sp^3$ 결합을 가지는 탄소 원자의 안정적인 존재 때문인 것으로 해석되었다. 많은 결함을 포함하는 큰 크기의 fullerene형(型) 구상 흑연입자가 연속적으로 성장하는 사실은 Kroto가 예측한 대형 fullerene의 성장과정을 실험적으로 뒷받침해 주는 결과라 생각한다.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.219-223
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• 2000

The ferroelectric SBT films were deposited on Pt/Ti/SiO$_2$/Si substrates by liquid injection metalorganic chemical vapor deposition (MOCVD) with single-mixture solution of Sr[Ta(OEt)$_5$(dmae)]$_2$and Bi(C$_6$ 6/H$_5$)$_3$. The Sr/Ta and Bi/Ta ratio in SBT films depended on deposition temperature and mol ratio of precursor in the single-mixture solution. At the substrate temperature of 40$0^{\circ}C$, Sr/Ta and Bi/Ta ratio were close to 0.4 and 1 at precursor mol ratio of 0.5~1.0, respectively. As-deposited film was amorphous. However, after annealing at 75$0^{\circ}C$ for 30 min in oxygen atmosphere, the diffraction patterns indicated polycrystalline SBT phase. The remanent polarization (Pr) and coercive field (Ec) of SBT film annealed at 75$0^{\circ}C$ were 4.7$\mu$C/$\textrm{cm}^2$ and 115.7kV/cm at an applied voltage of 5V, respectively. The SBT films annealed at 75$0^{\circ}C$ showed practically no polarization fatigue up to 10$^10$ switching cycles.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권9호
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• pp.623-627
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• 1999

We report a new in-situ fluorine passivation method without in implantation by employing excimer laser annealing of $SiO_{x}F_{y}$/a-Si structure and its effects on p-channel poly-Si TFTs. The proposed method doesn't require any additional annealing step and is a low temperature process because fluorine passivation is simultaneous with excimer-laser-induced crystallization. A in-situ fluorine passivation by the proposed method was verified form XPS analysis and conductivity measurement. From experimental results, it has been shown that the proposed method is effective to improve the electrical characteristics, specially field-effect mobility, and the electrical stability of p-channel poly-Si TFTs. The improvement id due to fluorine passivation, which reduces the trap state density and forms the strong Si-F bonds in poly-Si channel and $SiO_2/poly-Si$ interface. From these results, the high performance poly-Si TFTs canbe obtained by employing the excimer-laser-induced fluorine passivation method.

• Transactions on Electrical and Electronic Materials
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• 제8권6호
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• pp.241-245
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• 2007

[ $(Ba_{0.9-x}Sr_xCa_{0.10})TiO_3$ ] (x=0.33, 0.36) powders were prepared by sol-gel method. $(Ba,Sr,Ca)TiO_3$(BSCT) thick films, undoped and doped with $MnCO_3$ and $Yb_2O_3(0.1{\sim}0.7mol%)$, were fabricated by the screen printing method on the alumina substrate. The coating and drying procedure was repeated 6-times. The Pt bottom electrode was screen printing method on the alumina substrate. These BSCT thick films were annealed at $1420^{\circ}C$ for 2 hr in atmosphere. The upper electrodes were fabricated by screen printing the Ag paste and then firing at $590^{\circ}C$ for 10 min. And then the structured and dielectric properties as a function of the doping amount of $Yb_2O_3$ were studied. As a result of the TG-DTA, exothermic peak was observed at around $670^{\circ}C$ due to the formation of the polycrystalline perovskite phase. All BSCT thick films showed XRD patterns of typical cubic peroveskite structure. The average thickness of BSCT thick films was about $70^{\mu}m$. The curie temperature and the dielectric constant decreased with increasing $Yb_2O_3$ doped content and the relative dielectric constant of the specimen, doped with 0.5 mol% $Yb_2O_3$ at BSCT(54/36/10), showed a best value of 5018 at curie temperature.

• 한국전기전자재료학회논문지
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• 제20권8호
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• pp.680-684
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• 2007

In this study, we investigated the effects of structural and electrical properties of $(Ba_{0.6},\;Sr_{0.3},\;Ca_{0.1})TiO_3$ thick films with variation $Dy_2O_3$ contents. $(Ba_{0.6},\;Sr_{0.3},\;Ca_{0.1})TiO_3$ powders, prepared by the sol-gel method, were mixed organic vehicle. The BSCT thick films doped with 0.1, 0.3, 0.5, 0.7 mol% $Dy_2O_3$ were fabricated by the screen-printing techniques on the alumina substrates and the structural and dielectric properties were investigated with variation of $Dy_2O_3$ doping contents. All BSCT thick films were sintered at $1420^{\circ}C$, for 2hr. In the TG-DTA analysis, the formation of the polycrystalline perovskite phase was observed at around $670 ^{\circ}C$. In the XRD analysis, all BSCT thick films showed the cubic perovskite structure. The average thickness of BSCT thick films was approximately $65{\mu}m$. The Curie temperature decreased with increasing $Dy_2O_3$ amount. The relative dielectric constant and dielectric loss of BSCT thick films doped with $Dy_2O_3$ 0.1 mol% were 6267 and 2.6 %, respectively.

• 한국자기학회지
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• 제15권2호
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• pp.113-117
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• 2005

4-point focused floating Bone furnace를 이용하여 multiferroic $HoMnO_3$ 단결정을 제조하였으며, 직접합성법으로 $HoMn_{1-x}\;^57Fe_xO_3$ (x=0, 0.01, 0.02, 0.05) 분말 시료를 제조하여 그 결정학적 및 자기적 성질을 연구하였다. 결정구조는 hexagonal 구조로, (110) 방향이 자화용이축 임을 알 수 있었고, 온도 변화에 따른 강유전 상수(dielectric constant $\epsilon$)는 c축과 평행한 방향에서 특이성(anomaly)을 갖는 것으로 나타났다. 이 때 특이성이 나타나는 온도 구간은, c축 방향으로 인가된 자기장 세기에 따라 민감하게 변화함이 관측되고 있어, multiferroic 소자로의 응용 가능성을 제시하고 있다. 한편 Mn 자리에 $^{57}Fe$를 미량 치환한 분말 시료에 대하여 $M\ddot{o}ssbauer$ 분광학적 연구를 수행하였다.

• 한국자기학회지
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• 제6권5호
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• pp.317-322
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• 1996

RF magnetron reactive sputtering 법으로 Fe-Zr-N 박막을 제작하여 열처리 온도와 질소 분압의 변화에 따른 포화자화, 보자력, 고주파에서의 투자율 그리고 열적 안정성을 조사하였다. Fe-Zr-N 박막은 비정질과 결정질의 경계 조성인 $Fe_{72-78}Zr_{7-10}N_{15-18}$의 조성범위에서 연자성을 나타내었다. 이러한 박막은 포화자속밀도 1.55 T, 1 MHz에서의 실효 투자율은 3000 이상의 연자성을 나타내고 열처리 온도 $550^{\circ}C$ 까지도 실효투자율 2500 정도의 열적 안정성을 나타내었다. X-선 회절 분석 결과 열처리에 의해서 ZrN 미결정이 석출하여 $\alpha-Fe$ 결정 성장이 억제되어 우수한 연자기적 성질이 나타난다고 판단된다. 이때 $\alpha-Fe$ 입자 크기는 $40~50\AA$, ZrN의 입자 크기는 $10~15\AA$이었다.

• Journal of Magnetics
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• 제19권2호
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• pp.111-115
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• 2014

X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM) were used to investigate the influence of Ni ions on the structural, electronic, and magnetic properties of nickel-ferrites ($Ni_xFe_{3-x}O_4$). Spinel $Ni_xFe_{3-x}O_4$ ($x{\leq}0.96$) samples were prepared as polycrystalline thin films on $Al_2O_3$ (0001) substrates, using a sol-gel method. XRD patterns of the nickel-ferrites indicate that as the Ni composition increases (x > 0.3), a structural phase transition takes place from cubic to tetragonal lattice. The XPS results imply that the Ni ions in $Ni_xFe_{3-x}O_4$ substitute for the octahedral sites of the spinel lattice, mostly with the ionic valence of +2. The minority-spin d-electrons of the $Ni^{2+}$ ions are mainly distributed below the Fermi level ($E_F$), at around 3 eV; while those of the $Fe^{2+}$ ions are distributed closer to $E_F$ (~1 eV below $E_F$). The magnetic hysteresis curves of the $Ni_xFe_{3-x}O_4$ films measured by VSM show that as x increases, the saturation magnetization ($M_s$) linearly decreases. The decreasing trend is primarily attributable to the decrease in net spin magnetic moment, by the $Ni^{2+}$ ($2{\mu}_B$) substitution for octahedral $Fe^{2+}$ ($4{\mu}_B$) site.