• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.399-405
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• 2018

We report the fabrication of organic field-effect transistors (OFETs) via spray coating of electrochemically exfoliated graphene (EEG) and conducting polymer hybrid as electrodes. To reduce the roughness and sheet resistance of the EEG electrodes, subsequent coating of conducting polymer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)) and acid treatment was performed. After that, active channel layer was developed by spin coating of semiconducting poly(3-hexylthiophene) on the hybrid electrodes to define the bottom gate bottom contact configuration. The OFET devices with the EEG/PEDOT:PSS hybrid electrodes showed a reasonable electrical performances (field effect mobility = $0.15cm^2V^{-1}\;s^{-1}$, on/off current ratio = $10^2$, and threshold voltage = -1.57V). Furthermore, the flexible OFET devices based on the Polydimethlsiloxane (PDMS) substrate and ion gel dielectric layer exhibited higher electrical performances (field effect mobility = $6.32cm^2V^{-1}\;s^{-1}$, on/off current ratio = $10^3$, and threshold voltage = -1.06V) and excellent electrical stability until 1000 cycles of bending test, which means that the hybrid electrode is applicable to various organic electronic devices, such as flexible OFETs, supercapacitors, organic sensors, and actuators.

• Composites Research
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• v.29 no.4
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• pp.179-185
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• 2016

A self-charging supercapacitor is constructed through simple integration of the energy storage and photo exited materials at the photo electrode. The large band gap of $NiO/Fe_3O_4$ heterostructure generates photo electron at the photo electrode and store the charges through redox mechanism at the counter electrode. Sulfanilic acid azocromotrop/reduced graphene oxide layer at the photo electrode trapped the photo generated hole and store the charge by forming double layer. The solar supercapacitor device is charged within 400 s up to 0.5 V and exhibited a high specific capacitance of ~908 F/g against 1.5 A/g load. The solar illuminated supercapacitor shows a high energy and power density of 33.4 Wh/kg and 385 W/kg along with a very low relaxation time of ~15 ms ensuring the utility of the self charging device in the various field of energy storage and optoelectronic application.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.79-79
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• 2013

Quantum-structures with nanoparticles have been attractive for various electronic and photonic devices [1,2]. In recent, nonvolatile memories such as nano-floating gate memory (NFGM) and resistance random access memory (ReRAM) have been studied using silicides, metals, and metal oxides nanoparticles [3,4]. In this study, we fabricated nonvolatile memories with silicides (WSi2, Ti2Si, V2Si) and metal-oxide (Cu2O, Fe2O3, ZnO, SnO2, In2O3 and etc.) nanoparticles embedded in polyimide matrix, and photovoltaic device also with SiC nanoparticles. The capacitance-voltageand current-voltage data showed a threshold voltage shift as a function of write/erase voltage, which implies the carrier charging and discharging into the metal-oxide nanoparticles. We have investigated also the electrical properties of ReRAM consisted with the nanoparticles embedded in ZnO, SiO2, polyimide layer on the monolayered graphene. We will discuss what the current bistability of the nanoparticle ReRAM with monolayered graphene, which occurred as a result of fully functional operation of the nonvolatile memory device. A photovoltaic device structure with nanoparticles was fabricated and its optical properties were also studied by photoluminescence and UV-Vis absorption measurements. We will discuss a feasibility of nanoparticles to application of nonvolatile memories and photovoltaic devices.

• Advances in nano research
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• v.16 no.1
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• pp.81-90
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• 2024

In the oil and gas industry, composite materials should exhibit high flexibility and strength for offshore structures. Therefore, weak points in the composites should be improved, such as brittleness, moisture penetration, and diffusion of detrimental ions into nanometric pores. This study aimed to increase the strength, flexibility, and plugging of nanopores using single-layer graphene oxide (SGO) nanosheets. Therefore, SGO is added to unsaturated polyester resin at concentrations of 0.015 and 0.15 % with Normal Methyl Pyrrolidone (NMP) as a solvent for the formation of Nanographene Oxide Reinforced Polymer (NGORP). The mechanical properties of the prepared samples were tested using tensile testing (ASTM-D 638). It has been shown that incorporating SGO, approximately 0.015%, into the base resin resulted in enhanced properties such as rupture resistance forces increased by 745.61 N, applied stress tolerances increased by 4.1 MPa, longitude increased to 1.58 mm, elongation increased by about 2.38%, and rupture energy increased by about 204.51 J. Despite the decrease in tensile force strength properties in the manufactured nanocomposite with 0.15% SGO, it has exclusive flexibility properties such as a high required energy level for rupture of 5,576 times and a formability of 40% more than the base sample. It would be best to use NGORP manufactured from 0.015% nanosheets with exclusive properties rather than base samples for constructing parts and equipment, such as rebars, composite sheets, and transmission pipes, on offshore platforms.

• Applied Chemistry for Engineering
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• v.30 no.3
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• pp.371-378
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• 2019

Graphene nanoplatelet (GnP)/reused phenolic foam (re-PF)/wood composite boards were fabricated with different GnP content as 5, 10 and 20 w/w% to investigate the effect of GnP on thermal- and flame retardant properties of wood-based composite boards. The thermal- and flame retardant properties of fabricated composite boards were investigated by thermogravimetric analysis (TGA) and limiting oxygen index (LOI), respectively. The thermal stability of the composite boards increased proportionally with respect to the amount of GnP, and the char yield of these boards increased up to 22% compared to that of the pure wood board. The LOI values of composite boards were about 4.8~7.8% higher than those of using pure wood boards. It was also confirmed that the flame retardant properties of composite boards were remarkably improved by the addition of re-PF and GnP. These results were because of the fact that the re-PF and GnP with a high thermal stability delayed the initial thermal degradation temperature of composite boards and made their char layers denser and thicker which led the overall combustion delay effect of the composite board. Especially, GnP as a carbon-based material, facilitated the char layer formation and increased remarkedly the char yield, which showed higher effect on flame retardant properties than those of the re-PF.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.473-473
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• 2013

전자종이, 입을 수 있는 디스플레이, 플렉서블 터치 스크린, 투과성 면 등과 같은 차세대 플렉서블 투명 전자소자는 기계적으로 유연하고 광학적으로 투명하며 무게가 가벼운 특성을 지녀야 할 것으로 예상된다. 현재까지는Indium tin oxide (ITO), zinc tin oxide (ZTO), carbon nano tube (CNT)와 polyimide 계열의 물질들이flexible, wearable, and transparent electronics (FWTEs) 소자의 electrode, active channel, dielectric layers로 제안되어 활발히 연구되었다. 최근에는 높은 이동도(~200,000 cm2/Vs) 및 유연성(fracture strain of 30%), 투명도 (97.5% for monolayer)와 같은 특성을 갖는 그래핀에 대한 연구가 활발히 진행되고 있다. 그러나 그래핀을 차세대 플렉서블 투명 전자소자 구현에 적용하기 위해서는 플렉서블하고 투명한 절연체의 확보 및 그래핀의 진성(intrinsic) 특성 유지 등과 같은 문제점들을 해결해야 한다. 따라서, 본 연구팀에서는 그래핀 기반 플렉서블 투명 전자소자의 게이트 절연층으로 적합한 poly-4-vinylphenol/poly (melamineco-formaldehyde) (PVP/PMF) 물질을 제시하고 이에 대한 전기적 재료적 분석을 수행하였다. 특히 다양한 PVP와 PMF의 비율 및 가열(annealing 혹은 curing) 온도에서 형성된 PVP/PMF 층의 화학 및 전기적 특성을 FT-IR, I-V, 그리고 C-V 측정을 통해 확인하였다. PVP/PMF는 유기절연 물질의 하나로서 높은 유연성과 투명도를 갖고 있을 뿐만 아니라 그래핀에 적용 시 그래핀의 진성 특성을 확보할 수 있다. 이는 PVP/PMF에 존재하는 hydroxyl (-OH) 그룹과 그래핀 상에서 정공(hole)을 공급하는 것으로 알려져 있는 -OH 그룹들간의 cross-linking 메커니즘에 의한 것으로 예상된다. 마지막으로 최적화된 PVP/PMF (낮은 hysteresis 전압)를 게이트 절연층에 적용하여 polyethylene terephthalate (PET) 기판 및 연구원의 손가락 위에 95.8%의 투명도 및 0에 가까운 Dirac point를 갖는 그래핀 기반 플렉서블 투명 전자소자를 성공적으로 집적하였다.

• Journal of IKEEE
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• v.22 no.4
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• pp.1226-1229
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• 2018

We investigated the improvement of surface roughness and states after high temperature annealing using reduced-graphene oxide (r-GO) capping layer on ion-implanted 4H-SiC epitaxial layer. The specification of the 4H-SiC wafer grown on n-type $4^{\circ}$ off-axis 4H-SiC was $10{\mu}m$-thick and n-type epitaxial layer with a dose of $1.73{\times}10^{15}cm^{-2}$. The $n^+$ region were formed by multiple nitrogen ion-implantations and r-GO capping layer was produced by spray coating method. AFM measurements revealed that RMS value of the sample capped with r-GO was tenfold decrease compared to the sample without r-GO capping. The improvement of surface states was also verified by the improvement of leakage current level.

• Journal of the Korean Wood Science and Technology
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• v.35 no.3
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• pp.61-69
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• 2007

The building materials used for improving indoor air quality, the wood charcoal mixed with cement mortar or natural water paint were examined for their potential removing ability of formaldehyde. After the reaction of samples with formaldehyde in the glass flasks designed in our lab, the remaining formaldehyde was collected using DNPH (2,4-dinitrophenyl hydrazine) cartridges, and their concentration was determined using HPLC. From the results, it was found that the removing amount of formaldehyde per one gram sample containing 5, 10, or 15% of wood charcoal was more than three times compared to that of control (100% cement mortar or water paint). Their elimination percentages from the initial formaldehyde was about 80~90%. The experimental results for wood charcoal-water paint showed a similar trend with those of wood charcoal-cement mortar samples. Their elimination percentages from the initial formaldehyde was about 90%. It is proposed that formaldehyde is adsorbed on the adsorbed 'O' or 'OH' groups in the graphene layers formed through the re-arrangement of lignocellulose in the wood during the carbonization procedure.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.368-368
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• 2016

그래핀(Graphene)은 탄소 원자가 6각 구조로 이루진 2차원 알려진 물질 중 가장 얇은(0.34 nm) 두께의 물질이며 그 밴드구로조 인해 우수한 전자 이동도($200000cmV^{-1}s^{-1}$)를 가지고 있며, 이외에도 기계적, 화학적으로 뛰어난 특성을 가진다. 대면적화 된 그래핀을 성장시키기 위한 방법으로는 화학적 기상 증착법(Chemical Vapor Deposition)이 있다. 하지만 실제 여러 전이금속에서 합성되는 그래핀은 다결정으로, 서로 다른 면 방향을 가진 계면에서 전자의 산란이 일어나며, 고유의 우수한 특성이 저하되게 된다. 따라서 전자소재로 사용되기 위해서는 단결정의 대면적화 된 그래핀에 대한 연구가 지속적으로 이루어지고 있다. 앞서의 두 문제점 중, 단결정의 그래핀 합성에 크게 영향을 미치는 요인으로는 크게 합성 온도, 촉매 기판의 탄소 용해도, 촉매 표면에서의 탄소 원자의 확산성이 있다. 본 연구에서는 구리, 니켈, 실리콘에 비해 탄소 용해도가 낮으며, 탄소 원자의 높은 확산성으로 인해 단결정의 단층 그래핀을 합성에 적합하다고 보고된 저마늄(Germanium) 기판을 사용하여 그래핀을 합성하였다. 단결정의 그래핀을 성장시키기 위해 메탄(Methane; $CH_4$)가스의 주입량과 수소 가스의 주입량을 제어하여 성장 속도를 조절 하였으며, 성장하는 그래핀의 면방향을 제어하고자 하였다. 표면의 산화층(Oxidized layer)을 제거하기 위하여 불산(Hydrofluoric acid)를 사용하였다. 불산 처리 후 표면의 변화는 원자간력현미경(Atomic force microscopipe)을 통하여 분석하였다. 합성된 그래핀의 특성을 저 에너지 전자현미경(Low energy electron microscopy), 광전자 현미경(Photo emission electron microscopy), 라만 분광법(Raman spectroscopy), 원자간력현미경(Atomic force microscopy)와 투과전자현미경 (transmission electron microscopy)을 이용하여 기판 표면의 구조와 결정성을 분석하였다.

• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.2045-2050
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• 2011

Using first principles density functional theory the formation energies of various binary compounds of lithium graphite and its homologues were calculated. Lithium and graphite react to form $Li_1C_6$ (+141 mV) but not form $LiC_4$ (-143 mV), $LiC_3$ (-247 mV) and $LiC_2$ (-529 mV) because they are less stable than lithium metal itself. Properties of structure and reaction potentials of $C_5B$, $C_5N$ and $B_3N_3$ materials as iso-structural graphite were studied. Boron and nitrogen substituted graphite and boron-nitrogen material as a iso-electronic structured graphitic material have longer graphene layer spacing than that of graphite. The layer spacing of $Li_xC_6$, $Li_xC_5B$, $Li_xC_5N$ materials increased until to x=1, and then decreased until to x=2 and 3. Nevertheless $Li_xB_3N_3$ has opposite tendency of layer spacing variation. Among various lithium compositions of $Li_xC_5B$, $Li_xC_5N$ and $Li_xB_3N_3$, reaction potentials of $Li_xC_5B$ (x=1-3) and $Li_xC_5$ (x=1) from total energy analyses have positive values against lithium deposition.