Investigation of the Grain Boundary Effect on the Electrical Property of Graphene

김기주 서울대학교 대학원 2021 국내박사

그래핀은 뛰어난 전기적, 기계적 광학적 특성을 보여주는 2차원 재료로, 2D 재료 연구 분야를 여는데 있어 크게 이바지한 물질이다. 그러나, 대부분의 유망한 특성은 단결정 그래핀으로부터 나오는데, 이때 단결정 그래핀은 수십 마이크로 미터 단위밖 에 제작이 불가능하다. 웨이퍼 스케일로 그래핀을 합성하기 위하여, 화학적 방법으로 합성하는 방법 (chemical exfoliation), SiC 기판에서 Si을 선택적으로 승화하는 방법 및 CVD (Chemical vapor deposition) 방법이 있는데, CVD는 거의 무한한 크기로의 합성이 가능하며 품질이 좋아 가장 각광받는 방법 중 하나이다. 하지만 CVD로 합성 한 그래핀은 몇 가지의 이유로 단결정 그래핀의 좋은 특성을 보여주지 않기 때문에 CVD 그래핀의 전기적 특성을 높이기 위한 대규모 노력과 연구가 수행되었다. 1장과 2장은 서론으로, 1 장에서는 그래핀의 기본 물성과 합성하는 방법에 대하여 소개하였다. 2 장에서는 그래핀의 전기적 특성을 제한하는, 기판 산란, 결정립 산란 및 기타 산란 인자의 대하여 고찰해 보았으며, 이러한 한계를 극복하고 그래핀의 전 기적 특성을 향상시키기 위하여 현재 어떠한 연구가 이루어지고 있는지에 대하여 요 약하였다. 그 중에서도 도핑하는 방법과 그래핀의 도메인 크기를 키우는 방법이 현재 주된 연구의 흐름이다. 3장은 4장의 준비 부분으로, 그래핀의 결정립이 미치는 영향을 살펴보기 위하여 다양한 크기의 그래핀을 합성하였다. 그래핀의 CVD 성장에 대한 기본 이론을 통하 여, 메탄가스의 양을 감소시킴으로써 도메인 크기 성장을 꾀할 수 있었으며 실험 상 태의 최적화를 위하여 heterogeneous 핵생성을 막기 위한 전기연마 공정과, 낮은 메 탄가스 공급에 의하여 그래핀의 성장이 저해되는 현상을 막기 위하여 2 단계 성장 과정이 제안되었다. 4장은 이 연구의 두 본문 중 하나로, 그래핀의 결정립이 전기적 특성에 미치는 영 향에 대하여 고찰하였다. 그 결과 도핑 유무에 관계없이 도메인 크기가 증가함에 따 라 면저항의 감소를 관찰할 수 있었으며, 이는 캐리어 이동도의 증가에 기인한다는 현상을 발견하였다. Ohmic scaling 모델을 통하여 추가로 분석한 결과 17 um의 도메 인을 가지는 그래핀의 경우 20% 만큼의 면저항의 비중을 결정립이 차지하고 있다는 것을 알 수 있었다. 또한 Mayadas-Shatzkes 모델에 적용한 결과 R 값이 0.97로 굉 장히 높은 값을 띄고 있다는 것을 확인할 수 있었으며, 결국 두 모델을 이용한 연구 를 통하여 그래핀의 결정립이 강산 캐리어 산란 효과를 가지고 있음을 밝힐 수 있었 다. 도핑 공정은 또한 다양한 크기의 그래핀에 적용을 하여, 그래핀의 결정립이 도핑 하지 않았을 때와 유사하게 강한 산란효과를 가짐을 확인할 수 있었고, 추가적으로 관찰된 사실 중 하나는 그래핀의 도핑 효율이 결정립에서 더 높다는 것이었다. 도핑 방법과 그래핀의 도메인 크기를 키우는 두 가지 방법을 종합한 결과, 10 um 이상의 그래핀을 증착한 후 도핑을 수행하는 것이 가장 효과적으로 그래핀의 전기적 특성을 향상시킬 수 있다는 사실을 발견하였다. 5장에서는 Ru을 단원자증착법을 (ALD) 통하여 결정립에만 선택적으로 도펀트를 증착하였으며, 그래핀의 결정립이 도핑에 미치는 영향에 대하여 고찰하였다. 그 결과 ALD 20 사이클에서 180 ohm/sq, 50 사이클에서 125 ohm/sq 로 전기적 특성이 뛰어 난 그래핀을 증착할 수 있었다. 또한 Ru evaporation을 그래핀에 수행하여 그래핀 표 면에 homogeneous하게 Ru을 증착함으로써, ALD 를 통하여 도핑하였을 때와 비교하 였으며, 그 결과 그래핀의 결정립에서 도핑의 효율이 더 높다는 것을 밝혀내게 되었 다. 위 연구를 통하여 그래핀의 결정립이 전기적 특성에 미치는 영향에 대하여 잘 파 악할 수 있었으며, 추후 그래핀의 결정립을 포함하는 전기적 특성, 도핑 효과에 대한 연구에 기초로 활용할 수 있을 것으로 기대한다 Graphene is two-dimensional (2D) material showing outstanding electrical, mechanical, optical property, which opens the 2D material research field. However, most promising properties is from the single crystal graphene which only can collect dozens of um size. To synthesize wafer scale graphene chemical exfoliation, selective sublimation of Si from SiC, and CVD process were proposed, CVD is the one of the most promising method because of its unlimited scalability and high quality. The CVD grown graphene, however, does not showing remarkable property as single crystal graphene for several reason. Therefore, massive efforts and studies were conducted to increase electrical property of graphene. Chapters 1 and 2 are the introductory sections. In Chapter 1, basic property and synthesis method for graphene is placed. In chapter 2, the electrical limiting factors will be described, the bulk resistivity of graphene, substrate scattering, grain boundary scattering and other scattering factors. Then, the current approaches to overcome the limits and to enhancing electrical property of graphene will be summarized. Among them, doping and enlarging grain size emphasized as a major electrical property enhancing methods. Chapter 3 is the preparation part of chapter 4, synthesizing various size of graphene to study grain boundary effect. The basis theory for CVD growth is studied and reducing carbon source supply enlarging grain size of graphene was achieved. During optimizing experimental condition, the electropolishing process and two-step growth process were proposed, to prevent heterogeneous nucleation and unfilled gap problem because of low carbon source supply. In chapter 4, one of the two main part on this study, grain size dependence on electrical property of undoped/doped graphene is evaluated. The sheet resistance is reduced as the grain size increased since the carrier mobility enhanced, regardless of undoping/doping. Further analysis conducted by ohmic scaling model, it shows that 17 um size of graphene has 20 % of grain boundary sheet resistance. Another model, Mayadas-Shatzkes model, also applied on graphene, the resultant shows 0.97 of reflection coefficient, much large than other metals. In both model studies, grain boundary is considerably act as strong scattering center and controlling grain size turned out to be very important. The doping process also applied on various size of graphene and the similar result was observed form both models, considering grain boundary, the noticeable presumptive fact revealed that the doping efficiency is higher on the grain boundary of graphene. The conjugated experiment of doping and enlarging grain size shows that at small grain size i.g., 1 um, grain size effect is too strong, even doping process applied about 1000 ohm/sq can be achieved, however, more than 10 um of grain size, doping process becomes more effect than enlarging grain size. Therefore, it was confirmed that the most efficient way for enhancing electrical property of graphene is growing over 10 um size of graphene and conducting doping process. In Chapter 5 grain boundary effect on doping is further studied by employing Ru ALD on graphene. By the selective Ru deposition on grain boundary of graphene 180 ohm/sq at 20 cycle, 125 ohm/sq at 50 cycle is achieved. The control experiment, Ru evaporation is conducted to compare the doping effect with Ru ALD. The result shows that doping is occurred more efficiently on grain boundary of graphene. To conclude, the characteristic of graphene grain boundary on electrical property massively performed in this study. The grain boundary is revealed to the high impact on electrical property of graphene. Interestingly, the grain boundary acts as scattering center for carrier transport, however, it also acts as aa efficient doping site for doping process. In this study, the basics of the grain boundary property on undoped/doped graphene is established and expected to the fundamentals for the grain boundary involving electrical property researches.

Soft Nanoelectronic Devices Based on Novel 2D Nanomaterials and Self-assembled Organic Semiconductors

Eun Kwang Lee Graduate School of UNIST 2017 국내박사

Recent advances in electronic device are focused on a fabrication of flexible and stretchable electronic gadgets in a low-cost and sustainable ways. The fabrication of flexible and stretchable electronic devices is highly challenging using inorganic or Si-based electronic materials due to its fragile nature upon a strain. Utilization of solution-processable organic materials including small molecules and polymer in organic field effect transistors (OFETs), light emitting diodes, and solar cells, facilitates a low-cost, large-area, cheap, and environment-friendly mass production for the fabrication of flexible and stretchable electronic devices. Conjugated small molecules and polymers continue to be studied intensively as semiconducting and conducting materials due to its tunability of their electronic and optoelectronic properties. Graphene, a single layer of two-dimensional (2D) carbon atoms in a honeycomb lattice, has attracted enormous attention due to its unique electronic, optical, thermal, and mechanical properties. It has an extremely high charge carrier mobility (~ 200,000 cm2V–1s–1), an optical transmittance of 97.7%, a theoretical sheet resistance of 30 Ω/sq, a high fracture strain resistance greater than 20%, and chemical stability. These features make it highly promising for applications in flexible electronics and energy conversion devices, including touch screens, field-effect transistors (FETs), capacitors, batteries, solar cells, and light-emitting diodes (LEDs). However, the zero-band gap, small optical absorption, and chemical inertness have limited its practical application in switching and optoelectronic devices. Similar to graphene, transition metal dichalcogenides (TMDCs) are 2D materials stacked by van der Waals forces. Contrary to graphene, which does not have a bandgap energy, TMDCs have tunable bandgaps unlike to graphene. Typically, bulk TMDCs show indirect bandgap. On the other hand, the bandgap of TMDCs gradually decrease to one monolayer. Herein, I present a forward-looking my research results which are mainly focused on the interface studies between organic electronic materials and 2D nanomaterials including graphene and MoSe2, because of the importance of the mechanism and the behavior of electrical property change when organic electronic materials and 2D nanomaterials comes together in the electronic device system. When it comes to the interface study between heterogeneous electronic materials, doping of organic semiconductor and 2D nanomaterials is one of the important steps to enhance the electrical performance. Especially, n-doping of organic semiconductor is more challenging than p-doping because the n-dopants have to show a very low ionization potential to enable electrons to be transferred effectively, which renders most possible candidates unstable in air. Among the various doping strategies, surface transfer doping technique has been investigated for graphene and MoSe2 to modify or enhance their electrical or optoelectrical properties without severe damage on the surface of matrix. In addition, new carbon-based materials with honey comb structure or graphitic structure applying heterogenous atoms such as nitrogen (nitrogen doped reduced graphene oxide and 2D polyaniline) are explored to figure out their unique electrical properties and potential of electronic application. The experimental results and discussion in this thesis represent a forward-looking insight in charge transport behavior when organic electronic materials and 2D nanomaterials make junction together and pave the way of the applicability of organic semiconductors in conventional microelectronic infrastructures, which will lead to progress in the realization of soft nanoelectronic devices.

원자 분해능 TEM에 의한 그래핀-관련 2차원 물질의 물성 및 구조 분석

이원기 전북대학교 일반대학원 2023 국내박사

Although graphene and graphene-related materials have various industrial applications, their theoretical properties have not been fully realized. In general, the properties of a material are determined by its elements and its structural make-up. Thus, the goal of this study is to identify and determine the properties of graphene and graphene-related materials to advance the characterizations of carbon materials. First, the correlation between the thickness and oxidation degree of graphene Oxide (GO) samples fabricated by various oxidation processes was revealed using a combination of macroscopic and microscopic analyses. The degree of oxidation of GO varies depending on the manufacturing process, which is crucial to determine the characteristics of graphene after reduction. Four GO specimens were prepared with different manufacturing processes; subsequently, their degree of oxidation was evaluated by X-ray photoelectron spectroscopy (XPS). The d-spacing of each specimens classified by the degree of oxidation was measured via X-ray diffraction (XRD) and transmission electron microscopy (TEM). Additionally, through comparative analysis between layers with atomic force microscopu (AFM) and Raman spectroscopy, it was confirmed that the degree of oxidation was directly proportional to the thickness as well as the d-spacing of GO. Secondly, in this thesis presents and analyzes the efficient reduction and defect healing mechanisms through pulsed wire discharge (PWD) process in a GO dispersed in an organic solvent. The energy generated during the electric explosion allows the organic solvent to serve as a carbon precursor for simultaneous reduction and defect healing within one process. To investigate the reduction efficiency of solution-based PWD method and property changes due to structural recovery, two different conductive media such as copper wire and carbon fiber were used for explosion control. The copper wire acted as a very efficient conducting medium for the reduction of GO result in very low oxygen content of less than 1 % in the GO after reduction, while the carbon fiber produced non-metal contaminated reduced graphene oxide (rGO), exhibiting excellent electrical conductivity. Electrical conductivity results of the prepared rGO powder revealed that, under the same density conditions of 0.5 g/cc, carbon fiber exhibited higher conductivity (2057.6 S/m). Third, we present a method for measuring defect density using scanning transmission electron microscopy (STEM)-based electron energy loss spectroscopy (EELS) for graphene and graphene-related two-dimensional materials. The electron energy structure of carbon atoms varies according to the irradiation direction of the electron beam or the direction of the sample facing electron beam. It can be detected mainly through the change of π* and σ* peaks at the carbon K-edge. This tendency is apparent in the π* peak, which also has information about the sp2 bonding direction. Since graphene is a single-layer sp2 hybrid structure with a clear electron energy structure, the intensity ratio between π* and σ* peaks for an ideal graphene would be 1:3, which is the same for the π/σ bond ratio. Since graphene and its generated defects are considered different materials, changes occur in the electronic energy structure. These results enable numerical analysis, interpretation, and imaging of defects in 2D carbon materials to provide a deeper meaning behind the spectroscopic results obtained from the specimens. In summary, this thesis suggests the methods for process, measurement, and analysis of graphene-related materials, which will provide additional insight to the field of materials science.

Graphene-based Mask, Origami, and Growth Template for Advanced Fabrication of 3D Structures

김지우 서울대학교 대학원 2025 국내박사

Graphene is renowned for its atomic thickness and exceptional electrical and thermal conductivity. This has spurred extensive research into its use as a material for electronic devices. However, the robust mechanical and chemical properties of graphene, coupled with its atomic thinness and flexibility, have expanded its applications beyond electronics. This dissertation explores the potential of graphene as a sacrificial and auxiliary material, leveraging its unique properties to develop advanced fabrication technologies. First, a novel approach utilizing graphene as an etch mask was developed to fabricate three-dimensional (3D) microstructures. By utilizing XeF2 gas for isotropic dry etching of silicon, graphene's perfect etch resistance against XeF2 enabled the easy creation of graphene-based suspended structures. The extreme thinness and flexibility of graphene facilitated the wrapping of etch mask, enabling the fabrication of complicated 3D structures, such as mushroom- and step-like structures. As a practical demonstration, this technique was applied to fabricate omniphobic surfaces and gas sensors. Second, graphene was utilized in origami-inspired microfabrication using an electron beam (e-beam). E-beam induced the strain in poly(methyl methacrylate) (PMMA) with graphene layer, leading to precise bending and folding of PMMA/graphene composite. Graphene's exceptional mechanical properties were integrated with PMMA (polymethyl methacrylate) to control the bending direction. This approach facilitated the fabrication of intricate origami structures, including chair-like and box shapes. Lastly, graphene was used as a growth template to control the morphology of molybdenum disulfide (MoS2). Using plasma-enhanced chemical vapor deposition(PECVD)-grown graphene directly on molybdenum film, the study demonstrated how graphene’s structural and chemical properties influence MoS2 growth. Variations in graphene's crystallinity and functionalization were found to modulate the lateral and vertical growth characteristics of MoS2. These studies collectively highlight graphene's versatility as a sacrificial and structural material for the advanced fabrication of 3D structures, offering new opportunities in various research fields requiring complex 3D microstructures. 그래핀은 원자 수준의 두께와 우수한 전기적, 열적 전도성으로 잘 알려져 있으며, 이를 기반으로 그래핀을 전자소자 재료로 활용하고자 하는 연구가 활발히 진행되어 왔다. 그래핀은 뛰어난 기계적 및 화학적 안정성을 가지면서도 쉽게 구부러질 수 있고 낮은 기체 투과율을 가지는데, 이러한 그래핀의 특성을 이용하면 그래핀의 응용 범위를 전자소자를 넘어 확장시킬 수 있다. 본 논문에서는 그래핀을 식각 마스크, 오리가미, 성장 템플릿과 같은 보조적 재료로 사용한 3차원 구조 제조 기술에 대해 소개한다. 우선, 그래핀을 식각 마스크로 활용하여 3차원 미세구조체를 제작하는 새로운 방법을 개발하였다. XeF2 가스를 사용한 실리콘의 등방성 건식 식각 공정을 통해, 그래핀이 XeF2에 대해 완벽한 식각 저항성을 가지는 점을 활용하여, 그래핀 기반의 suspended 구조체를 쉽게 제작할 수 있었다. 또한, 그래핀의 극도로 얇고 유연한 특성을 활용하여 공정 중 식각 마스크의 변형을 활용해 버섯 모양이나 계단 모양과 같은 복잡한 3차원 구조체를 제작하였다. 그래핀 식각 마스크 기반의 공정 기술로 제작한 3차원 구조체를 이용하여 초소수성 표면과 높은 효율의 NO2 가스 센서를 구현하였으며, 다양한 분야에 그래핀 식각 마스크가 응용될 수 있음을 확인하였다. 다음으로, 전자빔을 활용한 오리가미 구조체 제작에 그래핀을 활용하였다. 전자빔을 통해 그래핀 층이 포함된 폴리메틸메타크릴레이트(PMMA)에 응력을 유도하여, PMMA/그래핀 복합체를 정밀하게 굽히고 접을 수 있다. 특히, 그래핀의 우수한 기계적 특성으로 인해 굽힘 방향을 제어할 수 있었으며, 이를 활용하여 의자나 상자 같이 포함한 복잡한 오리가미 구조를 구현하였다. 마지막으로, 그래핀을 성장 템플릿으로 사용하여 성장된 MoS2의 형상을 제어하였다. 플라즈마 강화 화학 기상 증착(PECVD) 방식을 통해 Mo 박막에 직접 성장시킨 그래핀을 활용하여 그래핀의 구조적 및 화학적 특성이 MoS2의 성장에 미치는 영향을 확인하였다. 그래핀의 결정성과 기능화에 따른 변화를 통해 MoS2의 수평 및 수직 성장 특성을 조절할 수 있음을 확인하였다. 본 연구는 3차원 미세구조체의 제조를 위한 재료로서의 그래핀의 다용성을 강조하며, 복잡한 3차원 미세구조가 요구되는 다양한 연구 분야에서의 응용가능성을 제시한다.

Study on graphene composite anode materials prepared by spray pyrolysis for lithium ion battery : 분무열분해 공정에 의해 합성된 리튬이차전지용 그래핀 복합체 음극 소재 연구

이수민 건국대학교 대학원 2015 국내석사

Graphene-MnO composite and hollow-structured MnO powders are prepared by a simple one-pot spray pyrolysis process. Based on the results of thermogravimetric analysis, the graphene content in the graphene-MnO composite powder is estimated to be 10 wt.%. Furthermore, morphological analysis of the graphene-MnO composite powder indicate that the fine MnO crystals of size several tens of nanometers are uniformly distributed all over the graphene. The BET specific surface areas of the graphene-MnO composite and hollow-structured MnO powders are found to be 20 and 5 m2 g-1, respectively. The graphene-MnO composite powders have high initial discharge and charge capacities of 1207 and 849 mA h g-1, respectively, at a current density of 500 mA g-1. The initial discharge and charge capacities of the hollow-structured MnO powders are 1004 and 673 mA h g-1, respectively. The discharge capacities of the graphene-MnO composite and hollow-structured MnO powders for the 130th cycle at a current density of 500 mA g-1 are 1313 and 701 mA h g-1, respectively. In the measurement of the rate performances, the gap between the discharge capacities of both the graphene-MnO composite and hollow-structured MnO powders increases with increase in the current densities. Hierarchically structured tin oxide-reduced graphene oxide (RGO)-carbon composite powders are prepared using a one-pot spray pyrolysis process. SnO nanoflakes several hundred nanometers in diameter and a few nanometers thick are uniformly distributed over the micron-sized spherical powder particles, as are ultrafine nanometer-scale SnO2 particles. The initial discharge and charge capacities of the tin oxide-RGO-carbon composite powders at a current density of 1000 mA g-1 are 1543 and 1060 mA h g-1, respectively. The discharge capacity of the tin oxide-RGO-carbon composite powders after 175 cycles is 844 mA h g-1 and the capacity retention measured from the second cycle is 80%. The transformation during cycling of SnO nanoflakes, uniformly dispersed in the tin oxide-RGO-carbon composite powder, into ultrafine nanocrystals, results in hollow nanovoids that act as buffers for the large volume changes that occur during cycling, and thereby improve the cycling and rate performance of the tin oxide-RGO-carbon composite powders. Nickel sulfide-reduced graphene oxide (RGO) composite powders with spherical shapes were prepared by a one-pot spray pyrolysis process. The optimum mole ratio of nickel nitrate and thiourea to obtain nickel sulfide–RGO composite powders with high initial capacities and good cycling performance is 1:8. The bare nickel sulfide and nickel sulfide–RGO composite powders prepared directly by spray pyrolysis from spray solutions with Ni nitrate and thiourea in a mole ratio of 1:8 had mixed crystal structures of hexagonal -NiS and cubic Ni3S4 phases. The bare nickel sulfide powders were prepared from the spray solution without graphene oxide sheets. The nickel sulfide–RGO composite powders had sharp mesopores approximately 3.5 nm in size. The discharge capacities of the nickel sulfide–RGO composite powders for the 1st and 200th cycles at a current density of 1000 mA g-1 were 1046 and 614 mA h g-1, respectively, and the corresponding capacity retention measured from the second cycle was 89%. However, the discharge capacities of the bare nickel sulfide powders for the 1st and 200th cycles at a current density of 1000 mA g-1 were 832 and 16 mA h g-1, respectively, and the corresponding capacity retention measured from the second cycle was 2%. The electrochemical impedance spectroscopy (EIS) measurements revealed the high structural stability of the nickel sulfide–RGO composite powders during cycling. 이차전지는 현재까지 상용화되어 산업 분야 및 일상생활 등의 여러 분야에 사용되고 있으나 새로운 기술 기반의 충족하는 고안정성, 장수명 이차전지의 필요성이 대두되고 있다. 최근에 이차전지의 고안정성 및 장수명 전지개발을 위하여 금속 산화물계 및 금속 황화물계 전극 소재에 대한 전기화학적 반응 기구에 대한 연구가 가장 큰 핵심 이슈가 되고 있다. 현재까지 이차전지 전극재료로 기존에 사용하고 있는 흑연은 낮은 용량의 한계를 가지고 있어서 흑연을 대체할 많은 연구들이 되고 있으며 고용량의 주석(Sn), 실리콘(Si) 계열의 물질들이 많은 관심을 가지고 연구가 되었다. 그러나 이러한 전극재료들은 부피팽창 및 분쇄로 인한 전지의 성능감소를 가져오는 등의 여러 가지 개선해야 할 문제점을 가지고 있다. 이런 문제점을 극복하고 고안정성, 장수명의 이차전지 개발을 위한 여러 가지 방법들이 모색되고 있으나 아직까지 극복해야 할 많은 문제점을 가지고 있다. 본 연구는 이러한 문제점을 극복하기 위하여 이차전지 음극 재료로 사용되는 금속 산화물과 금속황화물을 분무열분해 공정으로 합성하고 그래핀 첨가로 인한 전기화학적 특성을 증가시키고자 한다. 그래핀은 음극활물질의 전기화학적 특성을 향상시키는데 중요한 역할을 한다. 충방전 동안의 음극활물질의 뭉침 현상을 방지해주어 그 구조를 안정하게 해준다. 또한 리튬의 삽입과 탈리 과정 중에 일어나는 부피팽차을 보호해주는 역할을 한다. 분무열분해 공정에 의해 MnO-graphene 복합체 분말을 합성하였고 비교를 위해 순수한 MnO 분말을 같은 공정을 이용하여 제조하였다. 그래핀 시트에 수십 나노의 MnO 입자들이 고루 퍼져 있는 형태를 갖는 MnO-graphene 분말은 Graphene 함량은 10%이고, BET 표면적은 20 m2 g 1로, 순수한 MnO 분말에 4배정도이다. 전류밀도가 500mA g-1일 때, 방전용량은 130 cycle에서 1313mA h g-1으로 우수한 특성을 나타내었다. Tin oxide-graphene-carbon 복합체는 nanoflake 형태의 SnO와 nanoparticle인 SnO2의 혼합된 상으로 존재한다. 충전, 방전을 진행 시 SnO nanoflake가 산화되어 SnO2로 변형되며 그 빈 공간이 완충역할을 수행함으로써 리튬이온의 삽입과 탈리로 발생하는 부피팽창으로 인한 내부 스트레스를 줄여준다. 175번의 충방전 후 방전용량은 844 mA h g-1로 80%의 보존율을 기록했다. Nickel sulfide-graphene 복합체는 분무열분해 공정에 의해 니켈과 황의 여러 비율의 복합체 분말을 합성하였다. 최적의 조건인 니켈과 황의 몰비는 1:8로 높은 용량과 고안정성을 나타내었다. 200번의 충방전 후 방전용량은 614 mA h g-1로 89%의 보존율을 기록했다.

Modifications of Electronic and Structural Properties of Graphene by Using Alkali Metal Ions

류민태 포항공과대학교 일반대학원 2017 국내박사

Graphene has been widely studied in recent years due to its superior electronic properties as well as potential applications for graphene-based next-generation devices. As an effort to utilize its unique structural and electronic properties of graphene, we have investigated the modifications of its properties by doping low-energy alkali metal ions (Li + and Na+ ) on single layer graphene (SLG) and also on bilayer graphene (BLG) grown on SiC(0001) substrate. We have utilized the synchrotron-based angle-resolved photoemission spectroscopy (ARPES) and high-resolution core-level spectroscopy (HRCLS) as main experimental tools to understand any changes in electronic properties of the alkali iondoped graphene system. As a first system, we have studied the band gap engineering of SLG formed on SiC(0001) by using slow Li+ ions of energy 5 eV. In order to utilize the superb electronic properties of graphene in future electronic nano-devices, a dependable means of controlling the transport properties of its Dirac electrons has to be devised by forming a tunable band gap. We find the opening of a sizable and tunable band gap up to 0.85 eV, which depends on the Li+ ion dose () together with thermal treatment. This band gap of 0.85 eV turns out to be the largest band gap in the π-band of SLG by any means reported so far. Our Li 1s core-level data together with the valence band data suggest that Li+ ions do not intercalated below the topmost graphene layer, but cause a significant charge asymmetry between the carbon AB-sublattices of SLG to drive the opening of the band gap. We thus provide a route to producing a tunable graphene band gap by doping Li+ ions, which may play a pivotal role in utilizing graphene in future graphene-based electronic nano-devices. We have investigated modification of thermal and electronic properties of BLG by using Na+ ions as our second system in this thesis. BLG has an extensive list of industrial applications in graphene-based nano-devices such as energy storage devices, flexible displays, and thermoelectric devices. By doping slow Na+ ions on Li-intercalated BLG, which is formed by intercalation of neutral Li atoms below SLG on SiC(0001) substrate, we find significantly improved thermal and electronic properties of BLG by using ARPES and HRCLS with synchrotron photons. Our HRCLS data reveal that the adsorbed Na+ ions on a BLG produced by Li-intercalation through SLG spontaneously intercalate below the BLG and substitute Li atoms bound to silicon atoms in the Si-C bilayer of 6H-SiC(0001) to form Na-Si bonds at the SiC interface while preserving the same phase of BLG. This is in sharp contrast with no intercalation of Na+ ions on SLG though neutral Na atoms intercalate. The Na+ -induced BLG is found to be stable upon heating up to T=400 °C, but returns to SLG when heated at T d =500 °C. The evolution of the πbands upon doping the Na+ ions followed by thermal annealing show that the carrier concentration of the π-band may be artificially controlled within an order of magnitude without damaging the Dirac nature of the π-electrons. The doubled desorption temperature from that (T d =250 °C) of the Na-intercalated SLG together with the electronic stability of the Na+ -intercalated BLG may find more practical and effective applications in advancing graphene-based thermoelectric devices and anode materials for rechargeable batteries.

Potential of Graphene as a Mask and Controllability for Hole Density

안수영 경희대학교 대학원 2025 국내석사

This thesis introduce Graphene as novel mask material that can ultimately help growing high quality GaN inspect of decreasing threading dislocation (TD) than using other mask material. In prior studies, it is clearly confirmed that mask material can decrease specific defect called threading dislocation (TD) by the Epitaxial Lateral Overgrowth (ELO) method. This ELO method demand mask material with hole that GaN growing through. As above statement, hole can help decreasing TD density of GaN. In ELO method, the size of hole is important factor that can determine TD density. Generally, smaller size hole can help more decreasing TD density of GaN. Patterning method use mask material that underwent lithography for hole. Lithography method has difficulty in control the size of hole under specific size and the cost for lithography is set in high level. So, recent studies introduce thru-hole method that using 2d materials as mask material with smaller hole than lithography method. However, it is difficult to control thru-hole of 2d mask material. Because when using chemical vapor deposition (CVD), 2d material deposition process is very sensitive with deposition condition such as pressure, temperature, gas flow. To overcome those difficulty, we used Graphene as 2d mask material with oxygen plasma etching process. Surface of Graphene can be easily etched by oxygen plasma process. By changing etching condition, Graphene can be etched in various form in deliberate way. So the size of the thru-hole can be much smaller than hole generated from lithography method and thru-hole density can be more easily controlled than manipulating it by depositing 2d materials by changing the generation time of oxygen plasma on Graphene mask. There are few conditions are needed for Graphene to work as controllable mask material: The coverage and uniformity of Graphene, proper etching condition for make a thru-hole on Graphene. In this thesis, We demonstrated conditions for the graphene work as mask material and also analyze the evidence that show the controllability of thru-hole on Graphene.

Synthesis and Biomedical Applications of Isotope-Labeled Graphene Quantum Dots

정영진 서울대학교 대학원 2025 국내박사

2. 1. Abstract Increased calcium influx is associated with mitochondrial dysfunction, leading to podocyte injury and proteinuria. However, the mechanisms underlying transient receptor potential channel 5 (TRPC5)-induced calcium signaling in renal mitochondrial dysfunction remain largely unknown. Therefore, we investigated whether graphene quantum dots (GQDs) can downregulate TRPC5-controlled calcium influx signaling pathways and reverse mitochondrial dysfunction or impaired kidney function. The anti-inflammatory, anti-fibrotic, and anti-apoptotic effects of GQDs were evaluated in vitro using mRNA sequencing, qRT-polymerase chain reaction (PCR), western blotting, immunostaining analysis, Annexin-propidium iodide (PI), senescence, and a wound healing assay. Intracellular calcium signals, mitochondrial function, and morphological changes were also assessed. In vitro validation indicated that GQDs reduced renal fibrosis in human podocytes under oxidative stress and rotational force-driven pressure by preserving the scaffold architecture of renal cells. GQDs also regulated intracellular calcium signaling and TRPC5 expression and restored mitochondrial function, morphology, energy metabolism, and mitochondrial membrane potential. Moreover, GQDs attenuated fibrosis and apoptosis in fibroblasts and tubular epithelial cells, demonstrating their effectiveness on various renal cells. These results suggest that GQDs are a crucial therapeutic nanomaterial for renal cell injury and modulate calcium-dependent apoptosis associated with mitochondrial injury in the pathophysiology of renal diseases. Thus, GQDs have potential as therapeutic agents for various kidney diseases by slowing the onset and progression of fibrosis. 3. 1. Abstract Previous In modern medical imaging, the integration of multiple imaging modalities has become increasingly crucial for comprehensive disease assessment and treatment monitoring. Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) provide complementary information about physiological and pathological processes. However, both techniques have limitations that can impede their efficacy in certain clinical scenarios. To address these limitations and capitalize on their strengths, the development of dual modal imaging techniques has emerged as a promising approach. Carbon-13 Graphene Quantum Dots (13C-GQDs) and Copper-64 (64Cu) have gained attention as versatile imaging agents for MRI and PET, respectively. 13C-GQD exhibits favorable biocompatibility and imaging properties suitable for MRI applications, while 64Cu offers excellent PET imaging capabilities due to its favorable decay characteristics. In this study, we propose integrating 13C-GQDs and 64Cu for dual-modal imaging to enhance their respective strengths in MRI and PET. By combining these agents, our goal is to achieve simultaneous anatomical and functional imaging with improved sensitivity and spatial resolution. We introduce a stable dual-modal imaging agent by conjugating 64Cu to 13C-GQD using a chelator-free approach. 4. 1. Abstract This study investigated whether hydroxyapatite (HAp)-mineralized graphene film could support osteogenic differentiation of human adipose-derived, stromal cell (hASCs) in vitro. Graphene was produced by a chemical vapor deposition (CVD) method and the physical and chemical characteristics of the graphene film, which was functionalized with hydroxyapatite mineralization following ultraviolet-ozone (GR_UVO) treatment, were subsequently validated. Results of scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy showed GR_UVO for 5 min yielded applicable graphene coverage (97.98 ± 0.85%), conversion of chemical composition ratio (29.78% C-O, 18.34% C=O and 8.49% O-C=O) and degree of oxidation, (I2D /IG ratios 2.22) with maximal density of HAp-graphene layer. In vitro-cell proliferation, viability and adhesion of hASCs after being cultured on HAp-mineralized, graphene-coated glass (HAp/GR) with the optimized GR_UVO treatment (5 min) demonstrated a significant increment of proliferation (1.560.1 vs. 1 to 1.130.1, p<0.05) without changing in viability (94.831% to 95.31.6%, p=0.9651) compared with the control (intact glass). There were no differences in F-actin and Vinculin on day 1 (p=0.1422 and 0.5025, respectively) and on day 4 (p=0.3787 and 0.9208) of culture. Osteogenic differentiation of hASCs was significantly improved on the HAp/GR with increasing of osteogenesis-related genes (Runx2 and Osteocalcin). The hASCs culture with the HAp/GR glass promoted phospho-SMAD1/5/9 and SMAD4 expression with increased patterns of BMP/Smad signal-related genes, regardless of differentiation induction or not. These results demonstrated that hydroxyapatite-mineralized graphene film prepared by CVD method and optimal ultraviolet treatment promoted osteogenic differentiation of hASCs, which BMP/Smad signaling was involved. Since the successful exfoliation of graphene in 2004, it has garnered global attention for its exceptional physical, electrical, and chemical properties. In addition, graphene-based materials with controlled sizes and functionalities exhibit unique biological characteristics useful for bioimaging and therapeutic applications. Particularly, graphene quantum dots (GQDs) have been intensively studied for their excellent biocompatibility, capability of reversing the amyloid fibrillation and removing reactive oxygen to suppress inflammation, tunability with various chemical functional groups for targeting or imaging, etc., which are expected to provide further opportunities in the field of nanomedicine for combating incurable diseases. This thesis delves into the extensive applications of graphene-based nanomaterials, particularly focusing on graphene quantum dots (GQDs). It begins with an overview of graphene and its derivatives, exploring synthesis methods such as Chemical Vapor Deposition (CVD) for graphene and specific techniques for GQD synthesis. The therapeutic potential of GQDs in mitigating renal fibrosis by alleviating oxidative stress and restoring mitochondrial membrane potential is highlighted. Additionally, the development of dual isotope-labelled GQDs for enhanced MRI and PET imaging capabilities, emphasizing their synthesis, characterization, and imaging efficacy, is investigated. Chapter 1 provides an overview of graphene and its derivatives, detailing various synthesis methods, including Chemical Vapor Deposition (CVD) for graphene and specific methods for graphene quantum dots (GQDs). It explores practical applications of graphene-based nanomaterials, particularly in fibrosis treatment, MRI contrast agents, and tissue engineering. Additionally, it discusses the paramagnetic properties of GQDs as analyzed through Electron Paramagnetic Resonance (EPR). Chapter 2 presents a study demonstrating the therapeutic potential of GQDs in reducing renal fibrosis. The research highlights how GQDs alleviate oxidative stress and restore mitochondrial membrane potential, leading to significant improvements in kidney function and structure. Chapter 3 discusses the development and application of dual isotope-labelled GQDs for both MRI and PET imaging. The study showcases the synthesis process, characterization, and dual-modality imaging capabilities, emphasizing the potential of these GQDs in enhancing diagnostic accuracy and imaging efficiency. Chapter 4 investigates the enhanced osteogenesis of human adipose-derived stromal cells cultured on hydroxyapatite-mineralized graphene films. The findings indicate that this composite material significantly improves cell proliferation and differentiation, making it a promising candidate for bone tissue engineering applications. 2004년 그래핀의 성공적인 박리 이후, 그래핀은 뛰어난 물리적, 전기적, 화학적 특성으로 전 세계적인 주목을 받았다. 추가로, 크기와 기능이 제어된 그래핀 기반 재료들은 생체 이미징 및 치료 응용에 유용한 독특한 생물학적 특성을 나타낸다. 특히, 그래핀 양자점(GQDs)은 우수한 생체 적합성, 아밀로이드 섬유화 역전 및 반응성 산소 제거를 통해 염증을 억제하는 능력, 타겟팅 또는 이미징을 위한 다양한 화학적 기능 그룹과의 조정 가능성 등으로 집중적으로 연구되었다. 이러한 특성들은 난치병과 싸우기 위한 나노의학 분야에서 더 많은 기회를 제공할 것으로 기대된다. 이 논문은 그래핀 기반 나노재료, 특히 그래핀 퀀텀 닷(GQDs)의 광범위한 응용을 탐구한다. 먼저 그래핀과 그 유도체의 개요를 시작으로, 화학 기상 증착(CVD) 및 GQD 합성 방법을 설명한다. GQD의 신장 섬유증 완화에 대한 치료 잠재력과 산화 스트레스 완화 및 미토콘드리아 막 전위 회복에 대해 강조한다. 또한, MRI 및 PET 이미징을 향상시키기 위한 이중 동위원소 라벨링된 GQD의 개발, 합성, 특성화 및 이미징 효능을 조사한다. 1장에서는 그래핀과 그 유도체의 개요를 제공하며, 화학 기상 증착(CVD) 및 그래핀 퀀텀 닷(GQDs)의 다양한 합성 방법을 상세히 설명한다. 그래핀 기반 나노재료의 실용적인 응용, 특히 섬유증 치료, MRI 조영제, 조직 공학에서의 응용을 탐구한다. 또한, 전자 스핀 공명(EPR) 분석을 통해 GQD의 상자성 특성을 논의한다. 2장에서는 GQD가 신장 섬유증을 줄이는 데 있어 치료 잠재력을 입증하는 연구를 소개한다. 연구는 GQD가 산화 스트레스를 완화하고 미토콘드리아 막 전위를 회복시켜 신장 기능과 구조를 크게 개선하는 방법을 강조한다. 3장은 MRI와 PET 이미징 모두를 위해 이중 동위원소로 라벨링된 GQD의 개발과 응용을 다룬다. 연구는 합성 과정, 특성화, 이중 모드 이미징 능력을 보여주며, 이러한 GQD가 진단 정확도와 이미징 효율성을 향상시킬 수 있는 잠재력을 강조한다. 4장은 하이드록시아파타이트로 미네랄화된 그래핀 필름에서 배양된 인간 지방 유래 간질 세포의 향상된 골 형성을 조사한다. 연구 결과는 이 복합 재료가 세포 증식과 분화를 크게 개선하여 뼈 조직 공학 응용에 유망한 후보가 됨을 나타낸다.

그래핀 기반 코어쉘 구조의 재료 및 투명전극의 제조에 관한 연구

김희진 인하대학교 대학원 2016 국내박사

This study has two main objectives: preparation of a new anode material by hybridizing graphene with silicon, improving the charge capacity of a secondary battery, and application of the graphene in a transparent electrode and a display industry. There are 5 chapters. Chapter 1 describes physical properties, a manufacturing method and applications of graphene. Also it introduces the current technological trend of anode materials for a secondary battery and deals with the materials and the manufacturing method of transparent electrode for ITO replacement. Chapter 2 describes the study on the manufacture of silicon encapsulated with graphene (Si-GB) using polystyrene. Concerning application of graphene, a lot of efforts have been made to improve performance of nanomaterials in many fields, such as electric and electronic devices. Some examples are preparation of 3-dimension structured nanomaterials like nanoballs by CVD process and hybridizing with silicon. These graphene-based materials are proven to be available for secondary battery, EMI and ACF in electronics. Especially, some research has shown that they were very effective to enhance safety and volumetric capacity when they were used as anode materials of secondary battery. Although graphite and its compound with metal have been used as an anode material due to their high stability and reversibility, it still has lower charge capacity. On the contrary, silicon is known as a material which increases the charge capacity up to four times, compared with carbon-based materials, but it has lower stability and reversibility. For that reason, a few researchers just started to improve the charge capacity by hybridization of carbon-based material with silicon. In this paper, we prepared nanocarbon based material which has a new structure of graphene encapsulated silicon nanoball as an anode material which is applicable to high-capacity secondary battery. In order to form a graphene encapsulated silicon nanoballs, the polystyrene encapsulated silicon nanoballs were prepared by emulsion polymerization of styrene monomer with silicon nanoparticles. The resulting nanoballs were immersed in iron chloride solution and then dried. Finally they were treated in high temperature through CVD and etched by hydrogen chloride. Morphology of the graphene encapsulated silicon nanoballs was observed by the field emission scanning electron microscope (FESEM) and the field emission transmission electron microscope (FETEM) to search for core-shell structured nanoball. Spherical structure of graphene encapsulated silicon nanoball was investigated by the Raman, the X-ray Photoelectron Spectroscopy to identify graphene layers on the surface of the inner silicon core. Chapter 3 details preparation of silicon nanoball encapsulated with a graphene shell. We carried out preparing silicon-graphene hybrid material. As the silicon tends to expand in volume, we intended to put some empty space between a grephene shell and a silicon ball, so that grephene shell can be protected. We intended to make the graphene vertically grow from inner silicon core. In order to form a core/shell structured graphene encapsulated silicon nanoball, nickel was coated on the surface of a silicon nanoball by an electroless plating method. Then, a graphene layer was synthesized on the surface of the nickel shell by a CVD process. We were able to make Si-GBs and Si-GFs by etching the nickel layer. The Si-GF was a particle including a vertically grown graphene from inner silicon core. The Si-GBs and Si-GFs were formed with a spherical void between the silicon particle and the graphene layer, which increases the safety against to volumetric change of anode during lithiation/delitiation of repeated charging-discharging in secondary battery cycles. Morphology of the graphene encapsulated silicon nanoball was observed by the field emission transmission electron microscope (FETEM) to find core-shell structured nanoball. Spherical structure of graphene encapsulated silicon nanoball was investigated by the Raman, the X-ray Photoelectron Spectroscopy to identify graphene layer on the surface of the inner silicon core. Chapter 4 describes applications of grephene in the transparent electrode and flexible transparent electrode for display. Large-scale transparent conducting electrodes were fabricated using the electrospray method on a glass wafer and polyethylene terephthalate film using chemically reduced graphene oxide and poly (3,4-ethylene dioxy thiophene) (PEDOT). Graphene oxide (GO) is prepared by the modified Hummers method, and reduced GO (RG) is prepared at low temperature. By varying the concentration of RG and PEDOT of the composite material on the substrate, the electrical conductivity and transmittance of the electrode was controlled. The optical transmittance values of the graphene-based electrode at a wavelength of 550 nm were between 81 and 95 % and had sheet resistances from 370 to 5400 Ωsq-1. After 1000 cycles of a bending test, the sheet resistances of the graphene-based composite films were unchanged. Different types of graphene and graphene-based electrodes were characterized by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, high resolution Raman spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, transmittance, and electrical conductivity measurements. Chapter 5 summarizes the conclusions that each chapter investigated were investigated in each chapter.

Graphene-Polyimide 복합 Film 기판을 적용한 Flexible OLED 제작 및 특성에 관한 연구

임현빈 경북대학교 대학원 2012 국내석사

The graphene-polyimide composite films were fabricated for application to the flexible substrates of flexible organic light emitting diodes(OLEDs). We first synthesised poly(amic acid)s which could be converted to lear polyimide film with high transmittance to visible light and high thermal stability. In order to increased the mechanical property of the polyimide film we tried to make graphene-polyimide composite films and then used them as flexible substrates to make flexible OLEDs. Some important results are as following. 1. The poly(amic acid)s exhibited high clarity and transmittance to visible light when bulky –CF3 group containing aromatic dianhydride and aromatic diamine monomers were used. 2. The imidization of poly(amic acid)s to polyimide film was close to 100% after heat treatment at 250℃ for 120 min. as checked by FT-IR spectrometer. The Tg of the polyimide films could be optimized by the control of the aromatic diamine monomers with the requirement of optical property of the polyimide films. 3. The addition of very small amount of partially reduced graphene oxide(rGO) resulted in significant increase of mechanical property in the graphene-polyimide composite film. Up to 0.3 wt% of rGO the graphene-polyimide composite film exhibited high transmittance and low b* values in the haze meter measurement. The thermal degradation temperature was also increased with the rGO filler and weight loss was 10% at 500℃. The coefficient of thermal expansion(CTE) was also decreased with the rGO filler. 4. The mechanical strength of the graphene-polyimide composite film was increased up to 0.7 wt% of rGO and then decreased when rGO content was 1.0 wt%. 5. The flexible OLED devices made with graphene-polyimide composite films as substrate showed both higher luminescence (8,788 cd/m2) and current efficiency (2.37 cd/A) compare to the commercial polyimide film. 본 연구에서는 기계적 물성 및 열적 특성이 향상된 플렉시블 디스플레이 기판 소재용 Graphene-Polyimide 복합 필름의 제작과 특성에 관한 연구를 진행하였다. PI 필름은 디스플레이 고온 공정에 비교적 적합한 열안정성을 보유하고 있으나 광투과성의 향상이 요구된다. 하지만 광투과성을 확보하기 위해 –CF3기와 같은 작용기가 적용이 되면서 일반적인 갈색 PI 필름에 비하여 기계적 물성 및 열적 안정성이 떨어지게 된다. 따라서 이를 보완하기 위하여 그래핀을 적용하여 높은 투과율이 유지되면서 기계적 물성 및 열적 안정성이 보완된 Graphene-Polyimide 복합 필름을 제작하였다. 그리고 flexible OLED의 기판으로서 적용을 하여 소자를 제작하고 휘도 및 전류효율 특성을 측정하였다. 본 연구의 중요한 결과를 정리하면 다음과 같다. 1. 투명한 PI 필름을 만들기 위해 전기음성도가 크고 부피가 큰 –CF3기 포함하는 방향족 디아민과 방향족 무수물 단량체를 사용하여 PAA를 합성하였다. 이렇게 만들어진 PI 필름은 가시광선 영역에서 높은 선명도와 투과율을 나타내는 것을 확인 할 수 있었다. 2. PAA의 열처리 온도와 시간이 증가함에 따라 이미드화율이 증가됨을 확인할 수 있었고, 250℃에서 120분 일 때 이미드화율이 거의 100%에 가깝게 나타난다는 것을 확인 할 수 있었다. 그리고 PI 필름의 Tg는 광학적 특성과 함께 방향족 디아민 단량체의 제어에 의해 최적화 할 수 있다는 것을 확인 할 수 있었다. 3. Graphene-Polyimide 복합 필름에 사용된 rGO는 극소량의 첨가만으로도 기계적 물성이 상당히 증가한다는 결과를 확인할 수 있었다. 그리고 UV-Vis spectrometer로 측정한 결과 rGO 함량이 최대 0.3wt%로 합성되었을 때 높은 투과율과 낮은 b*값을 나타냄을 확인하였다. 열분해 온도의 경우 rGO의 함량이 증가함에 따라 10%의 무게손실이 발생하는 온도가 500℃ 이상에서 점차 증가하는 측정결과를 확인 할 수 있었다. 또한, 열팽창 계수도 마찬가지로 rGO의 함량이 증가함에 따라 감소하는 경향을 보임을 확인 할 수 있었다. 4. Graphene-Polyimide 복합 필름의 기계적 강도는 rGO 함량이 0.7wt%로 증가할 때 까지는 그 특성이 증가함을 확인하였고 rGO 함량 1.0wt%에서는 감소하는 결과를 확인 할 수 있었다. 5. Graphene-Polyimide 복합 필름 기판으로 Flexible OLED 소자를 제작한 결과 최대 휘도는 rGO(0.1wt%~0.3wt%)/PIF가 7909~8788 cd/m2, 상용 PI가 3405 cd/m2 로 나타났음을 확인하였다. 또한, rGO(0.1wt%~0.3 wt%)/PIF가 2.28~2.37 cd/A, 상용 PI가 2.1 cd/m2 최대 전류 효율이 나타났음을 확인하였다. 결과적으로 합성한 필름 기판이 상용 PI 필름 기판에 비해 flexible OLED 소자 특성이 우수함을 확인할 수 있었다.