열처리를 통한 금 나노입자의 크기 제어와 일벽 탄소나노튜브의 합성 촉매로의 이용

이승환,정구환,Lee, Seung-Hwan,Jeong, Goo-Hwan 한국재료학회 2013 한국재료학회지 Vol.23 No.12

We demonstrated size control of Au nanoparticles by heat treatment and their use as a catalyst for single-walled carbon nanotube (SWNTs) growth with narrow size distribution. We used uniformly sized Au nanoparticles from commercial Au colloid, and intentionally decreased their size through heat treatment at 800 oC under atmospheric Ar ambient. ST-cut quartz wafers were used as growth substrates to achieve parallel alignment of the SWNTs and to investigate the size relationship between Au nanoparticles and SWNTs. After the SWNTs were grown via chemical vapor deposition using methane gas, it was found that a high degree of horizontal alignment can be obtained when the particle density is low enough to produce individual SWNTs. The diameter of the Au nanoparticles gradually decreased from 3.8 to 2.9 nm, and the mean diameter of the SWNTs also changed from 1.6 to 1.2 nm for without and 60 min heat treatment, respectively. Raman results reconfirmed that the prolonged heat treatment of nanoparticles yields thinner tubes with narrower size distribution. This work demonstrated that heat treatment can be a straightforward and reliable method to control the size of catalytic nanoparticles and SWNT diameter.

열화학증기증착법을 이용한 그래핀의 합성 및 투과전자현미경 관찰용 그리드 멤브레인으로의 응용

이병주,정구환,Lee, Byeong-Joo,Jeong, Goo-Hwan 한국재료학회 2012 한국재료학회지 Vol.22 No.3

We present a method of graphene synthesis with high thickness uniformity using the thermal chemical vapor deposition (TCVD) technique; we demonstrate its application to a grid supporting membrane using transmission electron microscope (TEM) observation, particularly for nanomaterials that have smaller dimensions than the pitch of commercial grid mesh. Graphene was synthesized on electron-beam-evaporated Ni catalytic thin films. Methane and hydrogen gases were used as carbon feedstock and dilution gas, respectively. The effects of synthesis temperature and flow rate of feedstock on graphene structures have been investigated. The most effective condition for large area growth synthesis and high thickness uniformity was found to be $1000^{\circ}C$ and 5 sccm of methane. Among the various applications of the synthesized graphenes, their use as a supporting membrane of a TEM grid has been demonstrated; such a grid is useful for high resolution TEM imaging of nanoscale materials because it preserves the same focal plane over the whole grid mesh. After the graphene synthesis, we were able successfully to transfer the graphenes from the Ni substrates to the TEM grid without a polymeric mediator, so that we were able to preserve the clean surface of the as-synthesized graphene. Then, a drop of carbon nanotube (CNT) suspension was deposited onto the graphene-covered TEM grid. Finally, we performed high resolution TEM observation and obtained clear image of the carbon nanotubes, which were deposited on the graphene supporting membrane.

방열소재 응용을 위한 알루미나 분말 표면 위 탄소나노튜브의 직접 성장 거동 고찰

이종환(Jong-Hwan Lee),한현호(Hyun-Ho Han),정구환(Goo-Hwan Jeong) 한국표면공학회 2023 한국표면공학회지 Vol.56 No.1

As a preliminary study to produce functional nanocomposites in a heat dissipation device, we performed the direct synthesis of carbon nanotubes (CNTs) on the surface of alumina (Al₂O₃) powders. A thermal chemical vapor deposition (TCVD) system was used to grow CNTs directly on the Al₂O₃ surface. In order to investigate the growth behavior of CNTs, we varied both furnace temperature of the TCVD ranging from 700 to 850 ℃ and concentration of the ferritin-dissolved DI solution from 0.1 to 2.0 mg/mL. From the previous results, the gas composition and duration time for CNT growth were fixed as C₂H₄ : H₂ = 30 : 500 (vol. %) and 10 min, respectively. Based on the analysis results, the optimized growth temperature and ferritin concentration were found to be 825 ℃ and 0.5 mg/mL, respectively. The obtained results could be adopted to achieve mass production of nanocomposites with heat dissipation functionality.

수평형 유도결합 플라즈마를 이용한 그래핀의 질소 도핑에 대한 연구

조성일(Sung-Il Jo),정구환(Goo-Hwan Jeong) 한국표면공학회 2021 한국표면공학회지 Vol.54 No.6

In this study, optical diagnosis of plasma was performed for nitrogen doping in graphene using a horizontal inductively coupled plasma (ICP) system. Graphene was prepared by mechanical exfoliation and the ICP system using nitrogen gas was ignited for plasma-induced and defect-suppressed nitrogen doping. In order to derive the optimum condition for the doping, plasma power, working pressure, and treatment time were changed. Optical emission spectroscopy (OES) was used as plasma diagnosis method. The Boltzmann plot method was adopted to estimate the electron excitation temperature using obtained OES spectra. Ar ion peaks were interpreted as a reference peak. As a result, the change in the concentration of nitrogen active species and electron excitation temperature depending on process parameters were confirmed. Doping characteristics of graphene were quantitatively evaluated by comparison of intensity ratio of graphite (G)-band to 2-D band, peak position, and shape of G-band in Raman profiles. X-ray photoelectron spectroscopy also revealed the nitrogen doping in graphene.

열화학기상증착법에 의한 백금 기판 위의 그래핀 합성

이병주(Lee, Byeong-Joo ),정구환(Jeong, Goo-Hwan) 강원대학교 산업기술연구소 2015 産業技術硏究 Vol.35 No.1

Graphene is a carbon-based two dimensional honeycomb lattice with monoatomic thickness and has attracted much attention due to its superior mechanical, electronic, and physical properties. Here, we present a synthesis of high quality graphene on Pt substrate using a chemical vapor deposition (CVD). We optimized synthesis condition with various parameters such as synthesis temperature, time, and cooling rate. Based on the results, we concluded that graphene synthesis is driven by mainly carbon adsorption on surface rather than precipitation of carbon which is dominant in other metal substrate. In addition, Pt substrate can be repeatedly used several times with high quality graphene.

대기압 마이크로웨이브 플라즈마를 이용한 다양한 크기의 ZnO tetrapod 합성 및 광촉매 특성 평가

허성규(Sung-Gyu Heo),정구환(Goo-Hwan Jeong) 한국표면공학회 2021 한국표면공학회지 Vol.54 No.6

Among various metal oxide semiconductors, ZnO has an excellent electrical, optical properties with a wide bandgap of 3.3 eV. It can be applied as a photocatalytic material due to its high absorption rate along with physical and chemical stability to UV light. In addition, it is important to control the morphology of ZnO because the size and shape of the ZnO make difference in physical properties. In this paper, we demonstrate synthesis of size-controlled ZnO tetrapods using an atmospheric pressure plasma system. A micro-sized Zn spherical powder was continuously introduced in the plume of the atmospheric plasma jet ignited with mixture of oxygen and nitrogen. The effect of plasma power and collection sites on ZnO nanostructure was investigated. After the plasma discharge for 10 min, the produced materials deposited inside the 60-㎝-long quartz tube were obtained with respect to the distance from the plume. According to the SEM analysis, all the synthesized nanoparticles were found to be ZnO tetrapods ranging from 100 to 600-㎚-diameter depending on both applied power and collection site. The photocatalytic efficiency was evaluated by color change of methylene blue solution using UV-Vis spectroscopy. The photocatalytic activity increased with the increase of (101) and (100) plane in ZnO tetrapods, which is caused by enhanced chemical effects of plasma process.

수평형 CVD 장치에서 기판 위치에 따른 단일벽 탄소나노튜브의 합성 수율 및 직경 분포 고찰

조성일(Sung-Il Jo),정구환(Goo-Hwan Jeong) 한국표면공학회 2019 한국표면공학회지 Vol.52 No.6

We investigated a synthesis yield and diameter distribution of single-walled carbon nanotubes (SWNTs) with respect to the growth position in a horizontal chemical vapor deposition (CVD) chamber. Thin films and line-patterned Fe films (0.1 ㎚ thickness) were prepared onto ST-cut quartz substrates as catalyst to compare the growth behavior. The line-patterned samples showed higher growth density and parallel alignment than those of the thin film catalyst samples. In addition, line density of the aligned SWNTs at central region of the chamber was 7.7 tubes/㎛ and increased to 13.9 tubes/㎛ at rear region of the CVD chamber. We expect that the enhanced amount of thermally decomposed feedstock gas may contribute to the growth yield enhancement at the rear region. In addition, the lamina flow in the chamber also contribute to the perfect alignment of the SWNTs based on the value of gas velocity, Reynold number, and Knudsen coefficient we employed.

암모니아 플라즈마 표면처리를 통한 그래핀의 질소도핑

이병주(Byeong-Joo Lee),정구환(Goo-Hwan Jeong) 한국표면공학회 2015 한국표면공학회지 Vol.48 No.4

Graphene has attracted much attention due to its remarkable physical properties and potential applications in many fields. In special, the electronic properties of graphene are influenced by the number of layer, stacking sequence, edge state, and doping of foreign elements. Recently, many efforts have been dedicated to alter the electronic properties by doping of various species, such as hydrogen, oxygen, nitrogen, ammonia and etc. Here, we report our recent results of plasma doping on graphene. We prepared mechanically exfoliated graphene, and performed the plasma treatment using ammonia gas for nitrogen doping. The direct-current plasma system was used for plasma ignition. The doping level was estimated from the number of peak shift of G-band in Raman spectra. The upshift of G-band was observed after ammonia plasma treatment, which implies electron doping to graphene.

콜타르피치를 이용한 Invar 합금 위 탄소나노튜브의 합성

김준우(Joon-Woo Kim),정구환(Goo-Hwan Jeong) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.6

We report the growth of carbon nanotubes (CNT) on Invar-42 plates using coal tar pitch (CTP) by chemical vapor deposition (CVD) method. The solid phase CTP is used as an inexpensive carbon source since it produces a bunch of hydrocarbon gases such as CH₄ and other CxHv by thermal decomposition over 450℃. The Invar-42 is a representative Ni-based ferrous alloy and can be used repetitively as a substrate for CNT growth because Ni and Fe are used as very active catalytic elements. We changed mixing ratio of carrier gases, argon and hydrogen, and temperature of growth region. It was found that the optimum gas ratio and temperature for high quality CNT growth are Ar:H₂ = 400:400 sccm and 1000℃, respectively. In addition, the carbon nanoball (CNB) was also obtained by just changing the mixing ratio to Ar:H₂ = 100:600 sccm. Finally, CTP can be employed as a versatile carbon source to produce various carbon-based nanomaterials, such as CNT and CNB.

탄소나노튜브의 합성수율 증대와 저온 합성에 미치는 기판 전처리의 영향

신의철(Eui-Chul Shin),조성일(Sung-Il Jo),정구환(Goo-Hwan Jeong) 강원대학교 산업기술연구소 2019 産業技術硏究 Vol.39 No.1

Carbon nanotubes (CNT) on metal substrates are definitely beneficial because they can maintain robust mechanical stability and high conductivity between CNT and metal interfaces. Here, we report direct growth of CNT on Ni-based superalloy, Inconel 600, using thermal chemical vapor deposition (CVD) with acetylene feedstock in the growth temperature range of 400-725°C. Furthermore, we studied the effect of substrate pretreatment on the growth yield enhancement and growth temperature decrease of CNT on Inconel 600. Activation energy (AE) for CNT growth was estimated from the CNT height change with respect to the growth temperature. The AE values significantly decreased from 205.03 to 24.35 kJ/mol by the pretreatment of thermal oxidation of Inconel substrate at 725°C under ambient. Higher oxidation temperature tends to have lower activation energy. The results have shown the importance of pretreatment temperature on CNT growth yield and growth temperature decrease.