편광 EXAFS를 이용한 CoO 박막의 성장 메카니즘 연구

강준호 전북대학교 교육대학원 2025 국내석사

CoO thin films have garnered attention as promising candidates for advanced energy storage systems and electronic applications due to their unique magnetic and electrochemical properties. Achieving high performance in advanced electronic devices requires the use of high-quality metal oxide films, especially in ultrathin layers on the nanometer scale. Understanding the growth mechanisms and controlling growth parameters are crucial for obtaining high-quality films on heterogeneous substrates. In this study, we investigated the growth mechanisms and orientation-dependent structural characteristics of CoO(100) thin films grown on α-() substrates using linearly polarized X-ray absorption fine structure (XAFS). The CoO thin films were epitaxially deposited using an RF sputtering system, and structural characteristics in the in-plane and out-of-plane directions were analyzed through XAFS measurements at the Co K-edge. In the early growth stages, the Co–O and Co–Co bond distances were approximately 0.25 Å shorter than those of bulk CoO, with significant structural disorder observed in the out-of-plane direction. However, after a deposition time of over 10 minutes (with a thickness of approximately 165–183 Å), most structural strain and disorder diminished, and a stable rock salt structure (Fm3m) was formed. These results suggest that the CoO thin films grow in a layer-by-layer fashion, providing important insights into their growth behavior and structural evolution. This study highlights the potential of CoO thin films for practical applications in advanced devices, including lithium cobalt rechargeable batteries.

(A) novel Ni2P catalyst on deep Hydrodesulfurization

조계성 단국대학교 대학원 2011 국내석사

This study includes the structural properties and catalytic activities of the novel hydrotreating Ni2P catalysts. In order to increase the catalytic activity three approaches have been made by increasing dispersion on high surface area supports, adopting less oxidic phosphorous precursor to lower reduction temperature, and using liquid phase phosphidation technique. Characterizations were made by BET, CO uptake, TPR, 27Al-NMR, XRD, HR-TEM, ICP-AES and EXAFS spectroscopy. The catalytic activity for hydrodesulfurization (HDS) was measured at 613 K and 3.1 MPa in a three-phase fixed bed reactor using a model liquid feed containing 500 ppm S as 4,6-DMDBT, 1000 ppm S as DBT, 200 ppm N as quinoline, and 1% aromatics as tetralin in tridecane solvent. First, a study has been made to improve the dispersion of the Ni2P phase by using the high surface area SBA-15 support and examine the effect of dispersion on the catalytic activity. The Ni2P/SBA-15 catalyst gave a steady-state 4,6-DMDBT conversion of 99%, which was much higher than that of conventional Ni2P/SiO2 catalyst (54%). This is due to the better dispersion of Ni2P on the higher surface area SBA-15 support as confirmed by CO chemisorptions, TEM and EXAFS analysis. Second, the Ni2P catalysts were prepared by a new synthetic method with use of less oxidic phosphorus precursor in order to achieve high dispersion on silica support, and their structural properties and catalytic activity in HDS of 4,6-DMDBT were studied. Low temperature reduction technique led to better dispersion of Ni2P particles on SiO2 support. The catalytic activity in the HDS of 4,6-DMDBT followed the order, Ni2P/SiO2 -HT(54%) < Ni2P/SiO2-LT(67%). These results thus suggest that the HDS activity of the Ni2P catalysts highly depend on the dispersion of the Ni2P phase. Third, Ni2P catalyst supported on r-Al2O3 was successfully synthesized by a liquid phase phosphidation. Ni2P phase remained stable during reaction without the formation of AlPO4 phase which led to even better activity in the HDS of 4,6-DMDBT than the Ni2P catalysts obtained by the conventional TPR methods. The liquid phase phosphidation method is found to be effective to prepare the active Ni2P catalysts supported on r-Al2O3 without the formation of AlPO4. 본 연구는 수첨탈황반응에 적용되는 Ni2P촉매의 구조적 특성과 촉매 반응성을 주 대상으로 하며, 촉매활성을 증가시키기 위하여 표면적이 높은 담체, 낮은 산화가를 가지는 인 전구체, 그리고 액상에서의 인화 합성방법을 적용하였다. 다양한 조건에서 제조한 촉매는 BET, CO uptake, TPR, 27Al-NMR, XRD, HR-TEM, ICP-AES, 그리고 EXAFS 등의 분석기법을 이용하여 특성을 조사하였다. 촉매의 탈황에 대한 반응평가는 Tridecane용매상에 4,6-DMDBT의 황 500ppm, DBT의 황1000ppm, Quinoline 의 질소200ppm, tetralin의1% 방향족을 포함하는 모델반응물을 적용하여 613K, 3.1MPa 조건에서 삼상 고정층 반응기에서 실시하였다. 연구를 통하여 얻은 결과를 종합하면 다음과 같다. 첫째, 표면적이 높은 다공성 SBA-15 담체를 사용하여 Ni2P 의 분산도 변화에 따른 촉매활성에 미치는 효과에 대하여 연구하였다. Ni2P/SBA-15 촉매는 4,6-DMDBT 전환율이 99%로 기존 Ni2P/SiO2 촉매의 전환율(54%)에 비해 훨씬 높았다. 이는 CO화학흡착, TEM, EXAFS분석을 통해서도 확인되었듯이, 표면적과 기공크기가 상대적으로 큰 SBA-15 담체를 적용하여 Ni2P의 분산도 및 반응물의 접근성이 향상 되었기 때문으로 판단된다. 둘째, 종래의 고온 환원법(600oC 조건)을 개선하여 활성상인 Ni2P의 분산성을 향상시키기 위하여 낮은 산화가를 갖는 인 전구체를 사용하였다. 400oC 이하의 낮은 온도에서 환원되는 이 방법을 통하여 실리카 담체상에 Ni2P 입자들의 분산도가 향상됨을 확인 하였으며, 4,6-DMDBT 전환율이 다음과 같이 향상되었다. Ni2P/SiO2 -HT(54%) < Ni2P/SiO2-LT(67%). 이 결과는 Ni2P 촉매의 활성은 횔성상인 Ni2P의 분산도에 크게 의존한다는 것을 보여준다. 셋째, 종래의 기상 환원법의 문제점을 개선하기 위하여 액상에서 직접 인화처리가 가능한 리간드 안정화법을 적용하여 알루미나 담체상에 Ni2P촉매를 합성하였다. 알루미나(Al2O3) 담체 상에서 기존 기상 환원법에서 발생하던 AlPO4상의 형성과 관련하여, 액상 환원법을 적용한 결과 합성 단계 및 반응 중에도 AlPO4의 생성 없이 안정하게Ni2P 상이 존재함을 확인 하였다. 4,6-DMDBT에 대한 탈황반응성 평가 결과 99%의 전환율을 나타내어 기존의 기상 환원법으로 제조한 Ni2P/Al2O3촉매(54%)에 비하여 탁월한 활성을 보이는 것으로 나타나, 액상에서의 직접 인화처리 방법은 Ni2P 담지촉매 제조에 효과적임을 입증하였다.

Effect of Co/Ni ratio and Ce amount in cobalt nickel mixed oxide catalyst for methane combustion

임태환 서울대학교 대학원 2015 국내석사

In view of the low emissions of nitrogen oxides, carbon monoxide and toxic hydrocarbons, natural gas vehicles (NGVs) have been attracted considerable attention as one of the substitutes for gasoline and diesel vehicles. However, the emission of unburned methane from NGVs heavily contributes to greenhouse effect since the global warming potential of methane is 21 times higher than that of carbon dioxide. This study aimed at investigating the effect of Co/Ni ratio of cobalt nickel mixed oxides and cerium doping on CoNi (50:50) catalyst for methane combustion to effectively reduce unburned methane. A series of cobalt nickel mixed oxide catalysts were prepared by co-precipitation method with the Cobalt oxide, Nickel oxide, CoNi (75:25), CoNi (67:33), CoNi (50:50) and CoNi (33:67). The notation of CoNi (X:Y) was used to designate the catalyst with the ratio of Co:Ni = X:Y. In addition, a series of cerium doped CoNi (50:50) catalysts were prepared by wet impregnation method with the cerium loading of 5 wt%, 10 wt% and 20 wt%. The catalytic combustion of methane was performed among all prepared catalysts. Various characterizations were performed such as N2 adsorption-desorption with BET method, ICP-AES, XRD, EXAFS, XPS and H2 TPR. It was found that CoNi (50:50) and CoNi (67:33) catalyst exhibit the superior activity for methane combustion. Both catalysts contain NiCo2O4 spinel structure in largely distorted form. Such structure disorder contributes to improvement for the adsorption of surface oxygen species and reducibility of NiCo2O4. In addition, cerium doped catalyst demonstrates the enhancement of the activity. Especially, 10 wt% cerium doped catalyst indicates the highest activity among the catalysts. It implies that cerium doping as well as structure disorder plays an important role for the methane combustion. Both characterization and reaction results lead us to the conclusion that not only optimized cobalt nickel mixed oxide but also proper amount of cerium doping on CoNi (50:50) can improve the activity of methane combustion.

입자/완충층 형태로 증착한 La0.7Sr0.3MnO3 가 GdBa2Cu3O7-δ 박막의 초전도 특성에 미치는 영향

송창윤 충북대학교 2020 국내석사

초전도 박막의 임계전류밀도를 높이기 위해 자속(magnetic flux)의 제어는 필수적인 요소이다. 이에 기존 연구에서는 인위적인 첨가물을 이용한 자속고정(flux pinning)을 사용하였으나 임계온도에 가까운 고온에서는 효과적으로 사용할 수 없다는 단점이 존재하였다. 따라서 본 논문에서는 온도에 대한 의존성이 없는 것으로 알려진 자성 자속고정을 사용하여 임계온도에 가까운 온도까지 임계전류밀도가 향상된 초전도박막 제작 가능성에 대해 연구하였다. 초전도 물질로는 GdBa2Cu3O7-δ (GdBCO)를 사용하였고 자성 자속고정 구현을 위한 강자성 물질로는 La0.7Sr0.3MnO3(LSMO)를 선택하여 두 세트의 시료를 제작하였다. 하나의 세트는 기판장식(surface decoration) 효과가 나타날 것이라고 예상되는 입자 형태의 LSMO를 레이저 펄스 수를 80, 160, 320 으로 각각 증가시킴으로써 밀도를 높여 제작하였고, 다른 세트는 완충층 형태의 LSMO를 두께를 25 nm, 50 nm, 100 nm 로 변화시켜 제작하였다. LSMO 층위에 GdBCO는 모두 동일한 조건으로 약 400 nm 두께로 증착하였다. LSMO를 포함한 모든 시료의 임계온도는 pure GdBCO와 비교하여 큰 차이를 보이지 않았다. LSMO 완충층 시료에서는 오히려 더 높은 임계온도가 나타났는데 Extended Xray Absorption Fine Structure (EXAFS)를 이용한 국소 구조 분석을 통해 확인해 본 결과, 이는 LSMO 완충층 시료가 높은 임계온도를 갖는 최적의 Cu-O bond 길이를 유도하였기 때문이다. LSMO를 증착한 시료의 임계전류밀도는 pure GdBCO와 비교하여 모든 자기장 영역에서 향상된 것을 볼 수 있었다. LSMO 입자 세트에서는 LSMO 입자의 밀도가 낮은 경우 기판 장식의 역할을 하여 효과적으로 자속고정이 작용하였지만 밀도가 증가할수록 입자로서 작용하는 것이 아니라 거친 표면을 갖는 완충층으로 작용함을 확인하였다. 완충층 시료에서는 임계전류밀도의 향상이 자성 자속고정에 의해서 일어난 것이었음을 확인하였고 이때 증가한 임계전류밀도는 LSMO의 도메인 그리고 자화와 밀접한 관계가 있음을 보았다. 또한 50 K 과 77 K 에서의 임계전류밀도의 비교를 통해 pure GdBCO에 비해 GdBCO/LSMO 이중 구조의 온도 의존성이 크게 감소함을 알 수 있었다. 본 실험 결과는 LSMO 완충층을 활용한 고온에서 보다 효율적인 자속고정 가능성을 제시하였다. In order to increase the critical current density of superconducting thin films, controlling of the magnetic flux is essential. Previous studies have reported flux pinning by using artificial additives, but the disadvantage is that artificial additives cannot serve as pinning centers effectively at high temperatures near critical temperatures. Therefore, in this paper, we investigated the possibility of fabricating superconducting thin films with enhanced critical current density at close to critical temperature by using magnetic pinning, which is known to be temperature-independent. La0.7Sr0.3MnO3 (LSMO) was chosen as a ferromagnetic material for making magnetic pinning on GdBa2Cu3O7-δ (GdBCO) superconductor. Two sets of samples were prepared: in one set, LSMO particles were deposited by increasing laser pulse from 80, 160, and 320 by expecting the effect of surface decoration, and in the other set, 25 nm, 50 nm, and 100 nm-thick LSMO layers were prepared as buffer layers. The thicknesses of GdBCO films deposited on the top of LSMO particle/layer on SrTiO3 were kept to be 400 nm under the same deposition conditions. The critical temperatures of all the samples were remained to be close to that of pure GdBCO. The LSMO layer samples showed even higher values of the critical temperatures which is attributed to the optimum Cu-O bond length induced by LSMO buffer layers according to the local structure analysis using EXAFS. All the LSMO deposited samples showed improved critical current densities in all magnetic field region compared to that of pure GdBCO. In the particle set, LSMO particles with low density act as surface decoration and resulted in an effective pinning, but as the density increased, LSMO particles acted as a layer with rough surface rather than as a particle. In the LSMO layer set, it was confirmed that the improvement of the critical current density was induced by the magnetic pinning, and the increased critical current density was closely related to the domain and magnetization of LSMO. In addition, the comparison of the critical current densities at 50 K and 77 K showed that the temperature dependence of the critical current density of GdBCO/LSMO bilayers was significantly reduced. This experimental result suggest the possibility of more efficient flux pinning at high temperature by using LSMO buffer layer.

EXAFS에 관한 硏究

나관주 成均館大學校 1987 국내석사

EXAFS에 依한 銅化合物에 있어서의 原子構造에 관한 硏究

김남수 成均館大學校 1988 국내석사

EXAFS에 依한 β-Cu₂S의 原子 構造에 關한 硏究

남궁청남 成均館大學校 1989 국내석사

EXAFS에 依한 銅化合物의 構造硏究

고영봉 成均館大學校 1986 국내석사

EXAFS법에 의한 Cu₂S의 原子構造에 關한 硏究

박준서 成均館大學校 1989 국내석사

EXAFS에 依한 Cu₂S의 原子 構造에 관한 硏究

조기형 成均館大學校 1990 국내석사