산화철 나노입자의 금속-절연체 전이 현상

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 화학생물공학부, 2019. 2. 현택환.나노입자는 적어도 한쪽 방향의 너비가 100 nm, 다시 말해 천만 분의 1미터 이하의 크기를 가진 입자이다. 나노입자는 기존의 벌크 물질과는 달리, 하나의 입자를 구성하는 원자 개수가 매우 적다. 이로 인해서 기존과는 매우 다른 물리적, 화학적 성질을 지닐 수 있다. 지난 수십 년에 걸쳐서 이러한 차이를 확인하는 연구 및 공학적으로 이용하려는 연구가 많이 진행되고 있다. 한편, 원하는 성질의 나노입자를 실질적으로 활용하기 위해서는 나노입자를 균일하면서도 원하는 모양으로 만들 수 있어야 한다. 본 논문의 첫 번째 장에서는 어떻게 나노입자를 합성해야 균일하면서도 원하는 모양으로 만들 수 있는지 알아보았다. 이렇게 합성된 나노입자를 가지고 나노입자만이 가지는 특이한 성질을 연구할 수 있었다. 두 번째 장에서는 다양한 크기로 합성된 산화철 나노입자를 가지고 금속-절연체 전이 현상을 관찰하였다. 나노입자의 크기가 작아질수록 금속-절연체 전이 현상에 큰 변화가 생기는 것을 알 수 있었다. 세 번째 장에서는 산화철 나노입자에 껍질구조를 만들어서 금속-절연체 전이 현상의 변화를 관찰하였다. 껍질 물질의 종류 및 두께가 달라짐에 따라서 금속-절연체 전이 현상에도 변화가 생기는 것을 알 수 있었다.Nanocrystals are particles that are at least 100 nm wide in one direction. Nanocrystals, unlike their bulk counterparts, contain very few atoms that make up a single particle, leading to very different physical and chemical properties. In order to utilize the desired nanocrystals, nanocrystals must be able to be synthesized in a uniform and desired shape. In the first chapter of this thesis, I will discuss how nanocrystals can be synthesized in a uniform and desired shape. These synthesized nanocrystals allow us to study their unusual properties. In the second chapter, I studied size-dependent metal-insulator transition phenomena on uniform-sized iron oxide (magnetite) nanocrystals with various sizes. The smaller the nanocrystals, the greater the change in metal-insulator transition phenomena. In the third chapter, I synthesized core/shell Fe3O4/ferrite nanocrystals and investigated their metal-insulator transition phenomena. As the types and thickness of the shell materials are varied, changes in the metal-insulator transition phenomena were observed.Chapter 1. Introduction: Nucleation and growth of inorganic nanoparticles 1 1.1 Introduction 1 1.2 Molecule-to-solid transition 5 1.2.1 Structure of molecular clusters 5 1.3 Prenucleation and nucleation periods 9 1.3.1 Nucleation models 9 1.3.2 Stepwise phase transitions 12 1.3.3 Aggregation of nuclei 18 1.4 Growth by assembly and merging 21 1.4.1 Oriented attachment 22 1.4.2 Mesocrystals formation 34 1.5 Heterogeneous nucleation 36 1.5.1 Heterogeneous nucleation process 36 1.5.2 Interface energy minimization and property tuning by lattice strain 42 1.6 Conclusions 50 1.7 References 54 Chapter 2. Size Dependence of Metal–Insulator Transition in Stoichiometric Fe3O4 Nanocrystals 71 2.1 Introduction 71 2.2 Experimental section 73 2.3 Synthesis of uniform sized Fe3O4 nanocrystals 81 2.4 Metal-insulator transition of Fe3O4 nanocrystals 98 2.5 Conclusions 108 2.6 References 110   Chapter 3. Metal–Insulator Transition of Fe3O4 Nanocrystals by Shell Formation 117 3.1 Introduction 117 3.2 Experimental section 121 3.3 Fe3O4-Fe3O4 core-shell nanocrystals 128 3.4 Fe3O4-MFe2O4 (M= Mn, Co, Ni, CU, Zn) core-shell nanocrystals 131 3.5 Conclusions 144 3.6 References 145 Bibliography 151 국문 초록 (Abstract in Korean) 154Docto

DC와 RF 마그네트론 스퍼터링 시 하전된 플럭스를 고려한 압력과 기판 바이어스가 박막 증착 거동에 미치는 영향

학위논문(박사) -- 서울대학교대학원 : 공과대학 재료공학부, 2023. 2. 황농문.최근 DC 및 RF 마그네트론 스퍼터링 공정에서 하전된 플럭스의 생성과 필름 증착에 대한 하전된 플럭스의 영향이 연구되었다. 따라서 하전된 플럭스 생성에 영향을 미치는 증착 파라미터를 DC 및 RF 스퍼터링 시스템에서 연구하였다. 특히, 플라즈마를 생성하기 위해 사용되는 아르곤(Ar) 압력과 기판 바이어스 하에서의 하전 거동을 연구하였다. 먼저, DC 마그네트론 스퍼터링에 의해 증착된 은(Ag) 박막의 성장 속도, 결정도 및 비저항에 대한 스퍼터링 파워, 작동 압력 및 바이어스의 영향을 연구하였다. 박막은 20, 50, 100, 200 W의 스퍼터링 파워, 2.5, 5, 10, 20 mTorr의 공정 압력과 -300, 0, +300 V의 기판 바이어스 공정 조건 하에서 30분 동안 증착되었다. 모든 스퍼터링 파워에서 박막의 성장률은 양의 바이어스에 의해 증가한 반면, 음의 바이어스에 의해 감소하였다. 예를 들어, 스퍼터링 파워 100W와 공정 압력 2.5mTorr에서, 박막의 두께는 각각 -300, 0, +300V에서 346, 378, 416nm였다. 기판 바이어스 효과는 공정 압력이 감소함에 따라 두드러졌다. 바이어스에 따른 박막성장속도의 변화를 고려하면 음으로 하전된 플럭스의 양은 대략 10%로 추정된다. 공정 압력이 감소함에 따라 증착된 막의 결정화도는 양의 바이어스에 의해 증가한 반면, 네거티브 바이어스에 의해 감소하였다. 박막의 저항값도 같은 경향을 보였다. 은 필름의 증착 거동의 이러한 변화는 하전된 플럭스의 효과로 이해할 수 있다. 또한, RF 마그네트론 스퍼터링에 의해 증착된 텅스텐(W) 막에 아르곤 가스 압력과 기판 바이어스가 미치는 영향을 조사하였다. 텅스텐은 일반적으로 반도체용 구리 배선을 대체하는 재료로 사용되고 있다. 실온에서 스퍼터링에 의해 증착된 텅스텐 박막은 상대적으로 저항이 높은 준안정 β상을 갖고, 특정 조건 하에서 상대적으로 저항이 낮은 안정한 α상으로 변환되는 것이 일반적으로 관찰되어 왔다. 20 mTorr 및 -100 V의 기판 바이어스 하에서 1초간의 짧은 증착 초기 단계에서, 투과 전자 현미경(TEM)을 사용하여 β상 텅스텐의 나노 크기의 입자를 관찰하였다. 그러나 동일한 압력 및 바이어스 조건에서 증착 시간이 10분으로 증가함에 따라 텅스텐 필름은 α상과 β상이 공존하였다. α상 텅스텐의 비율은 음의 바이어스가 -100에서 -200V로 증가함에 따라 더 증가하였다. 또한 바이어스가 +100에서 -100V로 변경됨에 따라 필름 밀도가 증가하고 표면 거칠기가 감소했다. 이러한 결과는 음의 바이어스가 β상에서 α상으로 텅스텐의 상을 변화시킨 것을 나타낸다. α상 텅스텐의 형성과 필름의 저항값에 대한 바이어스 효과는 압력이 증가함에 따라 더욱 두드러졌다. 또한, DC 스퍼터링 시 이온화율을 높이기 위해서 DC 마그네트론 스퍼터링 시스템에 유도 결합 플라즈마(ICP)를 설치하였다. 텅스텐 박막은 -200, 0, +200V의 기판 바이어스 조건에서 ICP 파워를 0에서 200W로 증가시키면서 증착되었다. ICP 파워가 증가하고 기판에 음의 바이어스가 가해질 때 α상 텅스텐의 성장이 향상되고 텅스텐 막의 저항이 감소하였다. 그러나 XRD(X-ray diffraction) 데이터와 비저항 측정 결과로부터 α상 텅스텐의 성장을 위한 최적화된 공정 조건이 있음을 알 수 있었다. 이 연구에서 가장 낮은 저항을 가지는 텅스텐 박막은 ICP 파워가 100W이고 기판 바이어스가 -200V일 때 얻어졌다.In recent years, the generation of charged flux during direct current (DC) and radio frequency (RF) magnetron sputtering and its effects on film deposition were studied. Thus, the deposition parameter that affects the generation of charged flux was examined in both DC and RF sputtering system. In particular, the charging behavior under the argon (Ar) pressure which is utilizing to generate plasma and the substrate bias were studied. First of all, effects of sputtering power, working pressure, and bias on the growth rate, crystallinity, and resistivity of Ag thin films deposited by DC magnetron sputtering were investigated. Thin films were deposited on the substrate under the electric biases of − 300, 0, and + 300 V for 30 minutes with sputtering powers of 20, 50, 100, and 200 W and working pressures of 2.5, 5, 10, and 20 mTorr. Under all sputtering powers, the growth rate of the thin film was increased by the positive bias, whereas it was decreased by the negative bias. For example, the film thicknesses were 345.7, 377.9, and 416.0 nm at − 300, 0, and + 300 V, respectively, at a sputtering power of 100 W and a working pressure of 2.5 mTorr. The bias effect was enhanced as the working pressure decreased. Considering the change of the film growth rate according to the bias, the amount of negatively charged flux was estimated to be roughly 10 %. As the working pressure decreased, the crystallinity of the deposited films increased by the positive bias whereas it decreased by the negative bias, which is indicated by the full width at half maximum (FWHM) determined by X-ray diffraction of the Ag (111) peak. The film resistivity had the same tendency. This change in the deposition behavior of the Ag film can be understood as the effect of the charged flux. In addition, effects of Ar pressure and substrate bias on tungsten (W) films deposited by RF magnetron sputtering were investigated. W is generally used as a material to replace copper interconnects for semiconductors. It is commonly observed that tungsten thin films deposited by sputtering at room temperature have a metastable β-phase with relatively high resistivity and transform into a stable α-phase with relatively low resistivity under certain conditions. In this study, to obtain W films with low resistivity suitable for interconnect materials for semiconductors, we tried to identify deposition parameters for the formation of α-phase W by varying the substrate bias and argon (Ar) pressure in an RF magnetron sputtering system. In the initial stage for 1 s of deposition under 20 mTorr and a substrate bias of –100 V, β-phase W nanoparticles were observed using transmission electron microscopy (TEM). However, as the deposition time increased to 10 min under the same pressure and bias condition, the W film became a mixture of α- and β-phases. The fraction of α-phase W increased further as the negative bias increased from –100 to –200 V. In addition, the film density increased and the surface roughness decreased as the bias changed from +100 to –100 V. These results indicate that the negative bias triggered the phase transformation of W from β to α. The bias effect on the formation of α-phase W and film resistivity became more pronounced as pressure increased. Furthermore, inductively coupled plasma (ICP) was installed in the DC magnetron sputtering system to increase the ionization rate during DC sputtering. W thin films were deposited at substrate biases of -200, 0, and +200 V with increasing the ICP power from 0 to 200 W. The growth of α-phase W was enhanced and the resistivity of W film decreased when the ICP power was increased and a negative bias was applied to the substrate. However, from the X-ray diffraction (XRD) data and resistivity measurement results, it is shown that there are optimized process conditions for growing α-phase W. The W thin film with the lowest resistivity in this study was obtained when the ICP power was 100 W and the substrate bias was -200 V.Chapter 1. Introduction 1 1.1. Non-classical crystallization 1 1.1.1. Theory of charged nanoparticles 2 1.1.2. Charge enhanced kinetics 3 1.2. Physical vapor deposition (PVD) 11 1.2.1. Sputter deposition 11 1.2.2. Direct current (DC) sputtering 14 1.2.3. Radio frequency (RF) sputtering 15 1.3. Purpose of this study 18 Chapter 2. Effects of Sputtering Power, Working Pressure, and Electric Bias on the Deposition Behavior of Ag Films during DC Magnetron Sputtering Considering the Generation of Charged Flux 19 2.1. Introduction 19 2.2. Experimental 22 2.3. Result and Discussion 25 2.4. Conclusion 33 Chapter 3. Effects of substrate bias and Ar pressure on growth of α-phase in W thin films deposited by RF magnetron sputtering 44 3.1. Introduction 44 3.2. Experimental 46 3.3. Results 48 3.4. Discussion 56 3.5. Conclusion 62 Chapter 4. Effects of ICP power on growth of low-resistivity W thin films deposited by DC magnetron sputtering assisted by ICP 75 4.1. Introduction 75 4.2. Experimental 76 4.3. Result and Discussion 78 4.4. Conclusion 81 Bibliography 88 Abstract in Korean 102박

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Kinetic features of the formation of epoxy nanocomposites with carbon (nanotubes, graphene, and graphite), metal-containing, and aluminosilicate (montmorillonite and halloysite) fillers are considered. In contrast to linear polymers, epoxy nanocomposites are obtained only via the curing of epoxy oligomers in the presence of filler or the corresponding precursor. These additives may affect the kinetics of the process and the properties of the resulting matrix. A high reactivity of epoxy groups and a thermodynamic miscibility of epoxy oligomers with many substances make it possible to use diverse curing agents and to accomplish curing reactions under various technological conditions. The mutual effect of both a matrix and nanoparticles on the kinetics of the composite formation is discussed

In-situ TEM을 이용한 기판의 전도성에 따른 금속 입 거동의 동역학적 분석 : 하전 효과

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2018. 2. 김미영.나노 구조체의 형성은 고전적으로 원자나 이온, 분자에 의한 소립자의 적층으로 성장한다는 것이 일반적인 메커니즘으로 받아들여져 왔다. 다양한 분야의 나노 구조체의 응용이 가능하게 된 오늘날 다양한 연구에서 고전적인 성장 메커니즘으로 설명할 수 없는 기하학적인 구조들이 생성 또는 합성이 되고 있다. 이는 비 고전적 결정 성장 (Non-classical Crystallization)로 명명 되는 새로운 학문 분야로서 나노 구조체의 조합이 나노 입자 단위로 생성된다는 새로운 접근 방법을 제공한다. 이 새로운 학문 분야의 정립은 대부분 액상에서 합성된 물질을 관찰 및 보고를 통하여 되고 있으나, 일찍이 본 실험실에서는 액상 뿐만 아니라 기상에서 또한 이 현상이 일어남을 간접적으로 증명해왔다. 다만, 이를 해석하는데 있어서 독창적으로 적용되는 것이 하전에 대한 효과로, 기상에서 생성되는 나노 입자가 하전을 가질 때 Liquid-like한 성질을 가져 이것이 나노 구조체를 형성하는 기본 단위가 된다는 것이 핵심이고, 이것을 하전된 나노 입자 이론(Theory of Charged Nanoparticle) 로 명명해왔다. 앞선 비 고전적 결정 성장방법에 대한 메커니즘은 아직 명확하게 정립되지 않는 영역으로, 다만, 중간 단계는 Oriented attachment가 일어나는 것은 잘 알려져 있다. 이런 나노입자에 의한 성장의 주도니 원동력은 표면 에너지의 감소를 위한 것으로 이를 예측하기 위한 다양한 모델들이 제시되고 있다. 이에 맞춰 제공되는 핵심 증거는 직접적인 육안 관찰이 가능한 투과전자현미경(TEM)을 이용한 실시간 관찰을 통하여 다양한 주장들이 제기되고 있다. 논의 되고 있는 다양한 메커니즘 속에서 투과전자현미경을 사용했을 때에 높은 에너지를 가지는 가속된 전자에 의한 타켓 물질과의 상호 작용에서 발생할 수 있는 하전의 영향을 간과하고 있는바, 본 학위논문에서는 하전에 초점을 두고 이것이 시스템 내에 존재했을 때 나노 구조체에 어떠한 영향을 미치는지에 대해서 체계적인 실험을 진행하였다. 일차적으로 타켓으로 삼은 금 입자를 기판의 전도성에 따라 입자의 거동 차이를 확인하였다. 인위적으로 하전을 띠고 있는 비 전도성 기판 위에서의 금 입자는 매우 불안정한 거동을 띠고 있음을 확인하였으나 대조군인 전도성 기판에서는 긴 시간동안에도 안정적인 형태를 띰을 확인하였다. 이에 더해, 비 전도성 기판 위의 금 입자가 기판에서 탈락됨을 통하여 척력, 즉 정전기적 반발력이 입자와 기판 사이에 작용하는 것이 관찰됨에 따라 시스템 내 입자에 하전을 인위적으로 구현할 수 있었다. 이에 더 나아가 하전 유무에 따른 나노 입자들간의 상관관계를 2개 이상의 입자가 존재하였을 때 관찰하였다. 나노 입자의 표면 에너지를 줄이기 위한 방법 중 하나인 coalescence가 일어나는 시스템 내에서, 하전이 존재할 때 약 15배 정도의 시간적인 빠르기를 가지고 이 메커니즘이 작용함을 확인함에 따라 나노 구조체를 형성하는데 있어서 하전은 나노 입자의 불안정성을 야기 시킴과 동시에 동역학적인 장벽을 낮추는 효과까지 가짐을 확인하였다. 마지막으로 이러한 관찰을 TEM을 이용하여 진행할 때에 제기될 수 있는 온도 상승, Hydrocarbon 오염, 다양한 기판을 사용함에 따른 타켓 물질이 처한 환경적 차이에 따른 논란을 해결하는데 중점을 두었다. 온도 상승은 관찰하는 환경의 전체적인 온도를 액체 질소 온도 까지 내림으로서 활성 장벽을 높였음에도 불구하고 coalescence가 일어나 이 것에 대한 온도 영향을 배제하려고 하였고, 전도성과 비전도성 물질의 관찰간 발생하는 시간적인 간극에 따른 TEM의 환경과 샘플의 변화를 배제 하기 위하여 이를 하나의 TEM Grid 위에 하전이 존재할 수 있는 환경과 존재할 수 없는 환경을 한 번에 구현함으로서 해결하고자 하였다. 동일한 물질을 사용한 Floating & Ground 시스템은 명확하게 하전만 변수로 삼을 수 있는 환경을 제공하였으며, 관찰 전 후의 명확한 차이를 통하여 나노 구조체를 형성하는 환경 내에서 하전이 중요변수로 작용할 수 있음을 보였다. 또한, 이를 은 입자에 적용함으로서 금 입자로 구성된 앞의 실험을 넘어 하전 효과를 다른 물질로 적용하여 일반화 시킬 수 있는 작은 단서를 같이 제공하였다.Non-classical crystallization is a remarkable phenomenon in the nanostructure fabrication, which suggests that nanoparticle is the smallest unit as building block in crystal growth. In-situ transmission electron microscopy (in-situ TEM) provides crucial clues in understanding its mechanism. However, many mechanisms still remain unclear, especially the lack of understanding the charge effect caused by inelastic collision of the electron beam with sample in TEM. Here, we report that the structural instability and coalescence are promoted by charging through real-time observation of Au particles on substrates with difference conductivity. From a kinetic point view, this difference implies that the charge enhanced diffusion. This investigation broadens current knowledge of non-classical crystallization that grows by nanoparticles, sheds light on a potential factor to control the nanostructure fabrication. In this thesis, I carefully pay attention to the charge effect caused by the interaction between injected electron beam with high energy and sample during real-time TEM observation. In order to clarify the effect of charging in TEM, first, we clearly reproduced the difference in structure stability of a nanoparticle according to the substrate conductivity. Furthermore, the coalescence of multi-particles according to the degree of activation by charge was confirmed from the viewpoint of dynamics. Finally, we attempted to exclude various interpretations occurring within in-situ TEM by constructing a well-established artificial charging systemCh. 1 Introduction 1 1.1 Non-classical Crystallization 2 1.2 In-situ TEM Observation of Non-classical crystallization 9 1.3 Theory of Charged Nanoparticle 12 1.4 Charged Particle in Transmission Electron Microscope (TEM) 19 Ch. 2 An isolated Nanoparticle Observation 25 2.1 Structure instability of Nanoparticle 25 2.2 Experiment 27 2.3 Result & Discussion 31 2.4 Conclusion 41 Ch. 3 Two or more Nanoparticles Observation 43 3.1 Aggregation and Coalescence of Nanoparticles 44 3.2 Experiment 48 3.3 Result & Discussion 52 3.4 Conclusion 60 Ch. 4 Artificial current path systems : Floating & Ground environment formed simultaneously in a TEM grid 61 4.1 Controversy over the observation of charged nanoparticles using in-situ TEM 62 4.2 Experiment 65 4.3 Result & discussion 69 4.4 Behavior of Ag Nanoparticles in Floating & Ground systems 79 4.5 Conclusion 81 Ch.5 Summary 82 Reference 85 국문 초록 91Docto

Proceedings of the Flat-Plate Solar Array Project Research Forum on Photovoltaic Metallization Systems

A photovoltaic Metallization Research forum, under the sponsorship of the Flat-Plate Solar Array Project consisted of five sessions, covering: (1) the current status of metallization systems, (2) system design, (3) thick-film metallization, (4) advanced techniques, and (5) future metallization challenges

Non-classical crystallization of Al2O3 films by positively charged nanoparticles during aerosol deposition

학위논문(박사) -- 서울대학교대학원 : 공과대학 재료공학부(하이브리드 재료), 2022. 8. 황농문.Thin film growth through non-classical crystallization with a building block of charged nanoparticles (CNPs) has been studied in several fields, including chemical vapor deposition (CVD) and physical vapor deposition (PVD). To determine whether the same mechanism can be applied for aerosol deposition (AD) at room temperature, the generation and deposition behavior of CNPs were studied in the AD process for the first time. By measuring the current and examining the bias effect on the deposition behavior, it was confirmed that the fragmentation of Al2O3 particles generated numerous positively charged secondary nanoparticles as well as electrons by fracto-emission. In this work, the secondary particles passing between the two parallel biased and grounded electrodes were captured by the TEM grid membrane on each electrode, and it was revealed that they were mainly positively charged. Neutral secondary nanoparticles, not deflected by the electric field, produced a porous film on the silicon substrate, whereas charged secondary nanoparticles produced a dense film. The excess positive charging effects on the stacking fault energies of main slip systems were examined by density functional theory (DFT) calculations. When the electrons were removed, the activation barriers to create the stacking fault were decreased. The hypothesis that positive charges induce plastic deformation of secondary particles was supported by experiments and ab initio calculations. These results suggest that the positively charged secondary particles may be a major flux for film growth in the AD process. Combining the results, an aerosol deposition mechanism considering the charging effect was proposed.하전 된 나노 입자 (CNPs)를 빌딩 블록으로 박막이 성장한다는 비고전적 결정화 이론은 화학 기상 증착법 (CVD) 와 물리 기상 증착법 (PVD)을 비롯한 다양한 분야에서 연구되고 있다. 상온에서 치밀한 세라믹 박막을 형성하는 에어로졸 증착 (AD) 공정은 아직 그 메커니즘이 명확하게 이해되지 않았으며, 에어로졸 증착 공정을 비고전적 결정화 이론으로 설명하기 위해 하전 된 나노 입자의 생성과 증착 거동에 대한 연구를 하였다. 전류측정과 바이어스에 의한 증착 거동 비교를 통해 에어로졸 증착 공정에서 산화알루미늄 입자의 파단이 많은 양의 전자를 방출하며 양으로 하전 된 이차 나노 입자 들을 생성하는 것을 확인하였다. 본 연구에서는 전기장 영역을 통과하는 이차 나노 입자들을 각 전극에서 전자현미경 (TEM) 그리드의 멤브레인에 포집하여 이차 나노 입자들이 주로 양으로 하전 되어 있음을 확인하였다. 전기장을 이용해 하전 입자의 양을 제어했을 경우, 양으로 하전 된 이차 나노 입자들은 실리콘 기판에 치밀한 막을 형성한 반면 중성 이차 나노 입자들은 다공성 막을 형성하였다. 밀도범함수 이론으로 산화알루미늄의 주요 슬립 시스템에 대한 양전하의 효과를 계산한 결과 양전하 증가에 따라 적층 결함 형성의 에너지 장벽이 감소하는 경향이 있었다. 본 연구에서는 실험과 계산을 통해 에어로졸 증착 공정에서 양전하가 이차입자의 소성변형을 유도한다는 가설을 뒷받침하고 비고전적 결정화 이론을 통해 에어로졸 증착 공정의 메커니즘을 제시하였다.Chapter 1. Introduction 1 1.1 Non-classical crystallization 2 1.2 Aerosol deposition 7 Chapter 2. Generation of electrons and positively charged secondary nanoparticles by fracto-emission 10 2.1 Introduction 11 2.2 Experimental method 13 2.3 Results and discussion 17 2.4 Conclusion 36 Chapter 3. Deposition behavior of secondary nanoparticles with and without positive charge 37 3.1 Introduction 38 3.2 Experimental method 40 3.3 Results and discussion 43 3.4 Conclusion 53 Chapter 4. Positive charge effect on plastic deformation of Al2O3 (ab-initio calculation) 54 4.1 Introduction 55 4.2 Computational method 56 4.3 Results and discussion 59 4.4 Conclusion 66 Chapter 5. Effect of discharge on optical and mechanical properties of Al2O3 films 67 5.1 Introduction 68 5.2 Experimental method 70 5.3 Results and discussion 72 5.4 Conclusion 84 Chapter 6. Aerosol deposition mechanism of Al2O3 films 85 Referernces 92 Abstract in Korean 103박

High humidity fabrication of rGO incorporated perovskite absorber and MoS2 electrode for prospective inverted PSC

Methylammonium lead triiodide (MAPbI3) is a perovskite material that is widely used in perovskite solar cells due to its potential for high power conversion efficiency. However, it is sensitive to humid environments, heat, oxygen and UV radiation, which can cause it to degrade and negatively affect crystal growth and the morphology of the material. This can ultimately affect the efficiency of the solar cell. Therefore, MAPbI3 is typically produced at a low humidity, which requires expensive equipment. The aim of this research study is to propose a facile fabrication process for fully solution-processable inverted perovskite solar cells employing reduced graphene oxide (rGO)-based material under high humidity conditions suitable for the weather in Malaysia. Overall, the research design was divided into three phases. The aim of phase 1 is to study the influence of incorporating sulfonated rGO (srGO) into the MAPbI3 absorber layer for the deposition of a high-quality thin film under open-air conditions with high relative humidity. Three different samples were prepared with different weight percentage (wt%) of srGO: 0% (T), 50% (TS B) and 15% (TS D). The morphology of the srGO-MAPbI3 films was improved by the addition of srGO, resulting in fewer defects and larger perovskite grain sizes approaching micron size. In phase 2, the study aimed to determine the optimal process parameter of molybdenum disulfide (MoS2) composite with rGO as a viable solution-processed top electrode for an effective electron-collecting electrode by taking advantage of Taguchi analysis. The results of the Taguchi analysis showed that a ratio of rGO:MoS2 (1:1), a heating temperature of 75°C, and a heating period of 15 minutes were the optimal parameters for the electrode manufacturing process. The discovered optimal parameters were deployed to fabricate rGO:MoS2 composite electrode that showed a promising electrical conductivity of 9.36 Ω/sq. In phase 3, the device performance of the inverted perovskite solar cells with the designated configuration of ITO/CuSCN/srGO-MAPbI3/PCBM/BCP/rGO-MoS2 was analyzed by numerical simulation with SCAPS-1D. The results proved that the device performance for the samples was affected by the addition of srGO to the absorber layer. The 15% srGO sample exhibited the highest PCE of 10.37% with Ag as the top electrode. However, when the conventional electrode was replaced with a rGO-MoS2 composite electrode, the PCE of the same sample was improved to 13.23%, with a significant increase in FF. In summary, the findings of this research study indicate that incorporation of srGO into the MAPbI3 absorber layer can improve the morphology of the srGO-MAPbI3 films, resulting in fewer defects and larger perovskite grain sizes. The study also provides insight into the use of rGOMoS2 composite material as a workable solution-processed top electrode for an effective electron-collecting electrode, particularly in inverted configuration of perovskite solar cells. The numerical simulation results showed that the device performance of the samples could be improved by replacing Ag with rGO-MoS2. The findings of this study could have significant implications for the growth of cost-effective, solution-processed perovskite solar cells under high relative humidity

Biomolecule Mediating Synthesis Of Inorganic Nanoparticles And Their Applications

Project 1. The conventional phage display technique focuses on screening peptide sequences that can bind on target substrates, however the selected peptides are not necessary to nucleate and mediate the growth of the target inorganic crystals, and in many cases they only show moderate affinity to the targets. Here we report a novel phage display approach that can directly screen peptides catalytically growing inorganic nanoparticles in aqueous solution at room temperature. In this study, the phage library is incubated with zinc precursor at room temperature. Among random peptide sequences displayed on phages, those phages that can grow zinc oxide (ZnO) nanoparticles are selected with centrifugation. After several rounds of selection, the peptide sequences displayed on the phage viruses are analyzed by DNA sequencing. Our screening protocol provide a simple and convenient route for the discovery of catalytic peptides that can grow inorganic nanoparticles at room temperature. This novel screening protocol can extend the method on finding a wide range of new catalysts. Project 2. Genetically engineered collagen peptides are assembled into freestanding films when quantum dots (QDs) are co-assembled as joints between collagen domains. These peptide-based films show excellent mechanical properties with Young\u27s modulus of ~20 GPa, much larger than most of the multi-composite polymer films and previously reported freestanding nanoparticle-assembled sheets, and it is even close to that reported for the bone tissue in nature. These films show little permanent deformation under small indentation while the mechanical hysteresis becomes remarkable when the load approaches near and beyond the rupture point, which is also characteristic of the bone tissue. Project 3. The shape-controlled synthesis of nanoparticles have been established in single-phase solutions by controlling growth directions of crystalline facets on seed nanocrystals kinetically; however, it is difficult to rationally predict and design nanoparticle shapes. Here we introduce a methodology to fabricate nanoparticles in smaller sizes by evolving shapes thermodynamically. This strategy enables a more rational approach to fabricate shaped nanoparticles by etching specific positions of atoms on facets of seed nanocrystals in reverse micelle reactors where the surface energy gradient induces desorption of atoms on specific locations on the seed surfaces. From seeds of 12 nm palladium nanocubes, the shape is evolved to concave nanocubes and finally hollow nanocages in the size ~10 nm by etching the center of {200} facets. The high surface area-to-volume ratio and the exposure of a large number of palladium atoms on ledge and kink sites of hollow nanocages are advantageous to enhance catalytic activity and recyclability

In situ XAFS Study of Palladium Electrodeposition at the Liquid/Liquid Interface

We report the use of XAFS (X-ray absorption fine structure) as an in situ method to follow the electrochemically driven deposition of palladium nanoparticles at a liquid/liquid interface. A novel glass/plastic hybrid electrochemical cell was used to enable control of the potential applied to the liquid/liquid interface. In situ measurements indicate that the nucleation of metallic nanoparticles can be triggered through chronoamperometry or cyclic voltammetry. In contrast to spontaneous nucleation at the liquid/liquid interface, whereby fluctuations in Pd oxidation state and concentration are observed, under a fixed interfacial potential the growth process occurs at a steady rate leading to a build-up of palladium at the interface. Raman spectroscopy of the deposit suggests that the organic electrolyte binds directly to the surface of the deposited nanoparticles. It was found that the introduction of citric acid results in the formation of spherical nanoparticles at the interface