Studies on the Growth of Multilayer Graphene on Copper Surface by Chemical Vapor Deposition

DoctorGraphene is a two-dimensional carbon allotrope exhibiting high charge-carrier mobility, thermal conductivity and Young’s modulus with flexibility. When graphene layers are stacked, distinctive electronic structure develops depending on the number of graphene layers and stacking orientation with preserving superior properties of graphene. High sheet resistance of single layer graphene (SLG) due to atomic thickness goes down as increasing the thickness of graphene film which makes it promising material for transparent electrode. The most intriguing property of multilayer graphene (MLG) is that its electronic structure is tunable by generating differences in the on-site energy between graphene layers; In contrast to SLG is zero bandgap semimetal, MLG exhibits bandgap under a vertical electric field. In this motivation, I have studied the synthesis method for the Bernal-stacked multilayer graphene on Cu surface by chemical vapor deposition (CVD). This objective was achieved by introducing heteroatom (Nickel, Sulfur, Phosphorus) in Cu foil. In Chapter 1, I introduce the background of the research field for MLG. First, I review the factors which determine the electronic structure of MLG. Then, various applications based on tunable optoelectronic properties of MLG is introduced. After that, previous CVD methods for the growth of MLG and post-growth processes for applying electric field in MLG are addressed. Finally, research objectives of thesis are introduced by defining research direction based on the limitations of previous approaches. In Chapter 2, the growth of Bernal-stacked graphene on Cu foil which has asymmetric-carbon-solubility is studied. For this, I deposited a thin Ni film on the back of Cu foil. C atoms are absorbed through back side instead of forming graphene and diffuse toward the front side. Gradient Ni profile facilitates the bulk diffusion of C atoms. As a result, Bernal-stacked graphene with low sheet resistance and high uniformity in large-scale is obtained. The number of graphene layers is easily controlled by adjusting the initial thickness of the Ni film. In Chapter 3, the growth of Bernal-like stacked graphene with vertical electric-field is investigated. Sulfur-dissolved Cu foil was used as a catalyst to grow MLG. There exists gradient S atom concentration in c-axis of synthesized graphene. Therefore, electric field inside of thick MLG could be applied. The reduction of S atoms in Cu foil affects the growth of MLG and doping at the same time. Thus, electronic structure of Bernal-stacked graphene can be modified at the synthesis stage. The photovoltaic effect of MLG signify that electric field inside of MLG is strong enough to separate photogenerated carriers. This approach could be expanded to other heteroatom, phosphorus. In Chapter 4, the growth of Bernal-stacked graphene with tunable doping types on eutectic P-Cu binary system by CVD was studied. I used P-dissolved Cu foil as a catalyst. Synthesized MLG is intrinsically n-type due to adsorption of Pcomplexes in MLG, and doping type can be overturned to p-type by adsorption of H2O. I controlled the doping type and doping level of single MLG sample by interface modification. Based on mechanistic studies, simultaneous control of graphene growth and doping were achieved as well as the elaborate patterned growth MLG by 1-step CVD

Role of Extra Cu Vapors in the Growth of Graphene on Cu via Chemical Vapor Deposition

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Role of Cu Vapors in the Growth of Graphene on Cu Surface via Chemical Vapor Deposition

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Joined Wing UAV의 다분야 최적 설계

학위논문(석사) - 한국과학기술원 : 항공우주공학전공, 2014.2, [ 126 p. ]Joined wing configuration has been attained the spotlight for the future aircraft, the high altitude long endur-ance unmanned aerial vehicle (HALE UAV), et cetera. This is because numerous researches have suggested that the joined wing configuration contains positive characteristics on aerodynamics, structures, and stability. Most of these researches have focused on analyzing given joined wing configuration’s performances in each field of study.In this paper, we have focused on designing the optimum joined wing configuration. Since the joined wing configuration is the concept based on the prodigious ability on structure performance, we have focused on the aerodynamics and stability when designing the joined wing configuration. The purpose of this research is to cal-culate and produce the optimum joined wing configuration based on the multi-objective optimization method.Through this research, we have developed, implemented, and validated the ‘aero-stability optimization framework’. This framework includes aerodynamics, stability, and mathematical optimization method. For the aerodynamics, the vortex lattice method, which calculates aerodynamic performances within short time, was used, because the optimization framework requires numerous calculations. For the stability, the flying quality evaluation is applied in order to measure the dynamic stability and express the measurement in numerical value. For the optimization method, multi-objective genetic algorithms are utilized since the purpose of the framework is to find the optimum joined wing configuration in terms of aerodynamics and stability.With the aero-stability optimization framework, the optimum joined wing configuration is produced. To check the increment of the multidisciplinary performances of the optimum joined wing, we set baseline joined wing configuration which was designed by traditional way of constructing aircraft, the trial and error technique. This baseline joined wing configuration was desig...한국과학기술원 : 항공우주공학전공

A STUDY FOR AERODYNAMIC DESIGN OPTIMIZATION OF AIRFOIL USING e-SCIENCE BASED AERODYNAMIC DESIGN OPTIMIZATION FRAMEWORK

In this study, aerodynamic design optimization of airfoil was performed to minimize drag of baseline airfoil at transonic flow by using e-Science based design framework. Prior to the design optimization, parameter sensitivity studies were performed to determine the step-size and the sensitivity of the objective function. In this research, the weight of a Hicks-Henne bump function served as a design variable. Aerodynamic analysis was carried out by EDISON_CFD Solver. An aerodynamic design optimization framework of airfoil selected a drag-minimized optimal configuration by using the gradient-based optimization algorithm. Design results showed that the drag and lift performances of an optimized airfoil have been improved by 95% and 7% respectively. In addition, the performance of an optimized airfoil was validated by performing the off-design study in different design flow conditions. Through this study, A aerodynamic design optimization framework of airfoil can be utilized as an educational & research aerodynamic design optimization resource

Chemical Vapor Deposition of Bernal-stacked Multilayer Graphene on Cu Surface

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Synthesis of Bernal-Stacked Multilayer Graphene on Cu Surface via Chemical Vapor Deposition

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Efficient Photon Harvesting in Planar Heterojunction Solar Cells Using Highly-Oriented Molecular Crystals on Graphene

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Lateral Organic Solar Cells with Self-Assembled

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