금속 (Pt)과 4H-SiC의 계면상태에 따른 실리콘 카바이드 기반 고온 가스센서 특성 분석

정지철,구상모,Jung, Ji-Chul,Koo, Sang-Mo 한국전기전자재료학회 2011 전기전자재료학회논문지 Vol.24 No.4

Silicon carbide (SiC)-based gas sensors can be operated at very high temperatures. So far, catalytic metal-schottky diodes respond fast to a change between a reducing and an oxidizing atmosphere. Therefore SiC diodes have been suggested for high temperature gas sensor applications. In this work, the effect of reactivity of the catalytic surface on the 4H-SiC sensor-structures in 375 K~775 K have been studied and some fundamental simulations have also been performed.

표면 Texturization을 가진 Photovoltaic Device 내부의 열 분포 특성에 관한 연구

정지철,문경숙,구상모,Jung, Ji-Chul,Moon, Kyoung-Sook,Koo, Sang-Mo 한국전기전자재료학회 2010 전기전자재료학회논문지 Vol.23 No.7

The thermal distribution of 2D and 3D p-n photovoltaic diode structures with and without surface texturing has been studied. By analysis of the numerical simulation results of the I-V characteristics and lattice temperature distributions the effect of different texturing structures on the characteristics of silicon p-n photovoltaic devices has been studied systematically. The efficiency of the device having surface texturing shows more than ~2% enhancement compared to the reference devices which did not have texturing. In addition, the effect of the density of the texturing groove has been studied and it has been confirmed that the texturing structure not only improves the light trapping but also plays an important role in the heat radiation.

Cr- 및 Ni- 소스/드레인 쇼트키 박막 트랜지스터의 장벽 특성에 대한 실험 및 모델링 연구

정지철,문경숙,구상모,Jung, Ji-Chul,Moon, Kyoung-Sook,Koo, Sang-Mo 한국전기전자재료학회 2010 전기전자재료학회논문지 Vol.23 No.10

By improving the conducting process of metal source/drain (S/D) in direct contact with the channel, schottky barrier metal-oxide-semiconductor field effect transistors (SB MOSFETs) reveal low extrinsic parasitic resistances, offer easy processing and allow for well-defined device geometries down to the smallest dimensions. In this work, we investigated the arrhenius plots of the SB MOSFETs with different S/D schottky barrier (SB) heights between simulated and experimental current-voltage characteristics. We fabricated SB MOSFETs using difference S/D metals such as Cr (${\Phi}_{Cr}$ ~4.5 eV) and Ni (${\Phi}_{Ni}$~5.2 eV), respectively. Schottky barrier height (${\Phi}_B$) of the fabricated devices were measured to be 0.25~0.31 eV (Cr-S/D device) and 0.16~0.18 eV (Ni-S/D device), respectively in the temperature range of 300 K and 475 K. The experimental results have been compared with 2-dimensional simulations, which allowed bandgap diagram analysis.

K₂CO₃ 처리된 Coal Tar Pitch 활성탄 전극의 결정성 및 EDLC 성능

최푸름,정지철,임연수,김명수,Choi, Poo Reum,Jung, Ji Chul,Lim, Yun-Soo,Kim, Myung-Soo 한국재료학회 2016 한국재료학회지 Vol.26 No.9

Activated carbons (ACs) have been used as EDLC (electric double-layer capacitor) electrode materials due to their high specific area, stability, and ecological advantages. In order to prepare ACs with high density and crystallinity, coal tar pitch (CTP) was activated by $K_2CO_3$ and the textural and electrochemical properties of the obtained ACs were investigated. Although the CTP ACs formed by $K_2CO_3$ activation had much smaller specific surface area and pore volume than did the CTP ACs formed by KOH activation, their volumetric specific capacitance (F/cc) levels as electrode materials for EDLC were comparable due to their higher density and micro-crystallinity. Structural characterization and EDLC-electrode performance were studied with different activation conditions of $CTP/K_2CO_3$ ratio, activation temperature, and activation period.

EDLC 전극용 카본에어로젤의 합성조건에 따른 기공구조 및 전기화학적 특성

서혜인,정지철,김명수,Seo, Hye Inn,Jung, Ji Chul,Kim, Myung-Soo 한국재료학회 2018 한국재료학회지 Vol.28 No.1

Various carbon aerogels (CAs) were prepared from polymerization of resorcinol and formaldehyde and applied as the electrode materials of an electric double layer capacitor (EDLC) with the aim of controlling the textural and electrochemical properties of CAs by the type of base catalyst and the ratio of resorcinol to catalyst (R/C). The CAs from $NaHCO_3$ and $KHCO_3$ with $H^+$ ions had higher specific surface areas but exhibited lower electrochemical properties than those from $K_2CO_3$ and $Na_2CO_3$, which had more uniform pore size distributions. The electrochemical properties of $Na_2CO_3$ were superior to those of $K_2CO_3$ probably because the polarizing power of $Na^+$ ions was higher than $K^+$ ions. With an increasing R/C ratio, the pore sizes of CA showed a tendency to increase but the uniformity of the pore size distribution got worse. For the four base catalysts, the highest electrochemical property was obtained at the R/C ratio of 500.

유기계 슈퍼커패시터에서 도전재의 양이 전기화학적 특성에 미치는 영향

양인찬,이기훈,정지철,Yang, Inchan,Lee, Gihoon,Jung, Ji Chul 한국재료학회 2016 한국재료학회지 Vol.26 No.12

In this study, we intensively investigated the effect of conductive additive amount on electrochemical performance of organic supercapacitors. For this purpose, we assembled coin-type organic supercapacitor cells with a variation of conductive additive(carbon black) amount; carbon aerogel and polyvinylidene fluoride were employed as active material and binder, respectively. Carbon aerogel, which is a highly mesoporous and ultralight material, was prepared via pyrolysis of resorcinol-formaldehyde gels synthesized from polycondensation of two starting materials using sodium carbonate as the base catalyst. Successful formation of carbon aerogel was well confirmed by Fourier-transform infrared spectroscopy and $N_2$ adsorption-desorption analysis. Electrochemical performances of the assembled organic supercapacitor cells were evaluated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements. Amount of conductive additive was found to strongly affect the charge transfer resistance of the supercapacitor electrodes, leading to a different optimal amount of conductive additive in organic supercapacitor electrodes depending on the applied charge-discharge rate. A high-rate charge-discharge process required a relatively high amount of conductive additive. Through this work, we came to conclude that determining the optimal amount of conductive additive in developing an efficient organic supercapacitor should include a significant consideration of supercapacitor end use, especially the rate employed for the charge-discharge process.

마그네슘열환원법을 이용한 실리콘-탄소 복합재 제조 및 리튬이차전지 음극재로의 이용

김으뜸,권순형,김명수,정지철,Kim, Eudem,Kwon, Soon Hyung,Kim, Myung-Soo,Jung, Ji Chul 한국재료학회 2014 한국재료학회지 Vol.24 No.5

Silicon-carbon composite was prepared by the magnesiothermic reduction of mesoporous silica and subsequent impregnation with a carbon precursor. This was applied for use as an anode material for high-performance lithium-ion batteries. Well-ordered mesoporous silica(SBA-15) was employed as a starting material for the mesoporous silicon, and sucrose was used as a carbon source. It was found that complete removal of by-products ($Mg_2Si$ and $Mg_2SiO_4$) formed by side reactions of silica and magnesium during the magnesiothermic reduction, was a crucial factor for successful formation of mesoporous silicon. Successful formation of the silicon-carbon composite was well confirmed by appropriate characterization tools (e.g., $N_2$ adsorption-desorption, small-angle X-ray scattering, X-ray diffraction, and thermogravimetric analyses). A lithium-ion battery was fabricated using the prepared silicon-carbon composite as the anode, and lithium foil as the counter-electrode. Electrochemical analysis revealed that the silicon-carbon composite showed better cycling stability than graphite, when used as the anode in the lithium-ion battery. This improvement could be due to the fact that carbon efficiently suppressed the change in volume of the silicon material caused by the charge-discharge cycle. This indicates that silicon-carbon composite, prepared via the magnesiothermic reduction and impregnation methods, could be an efficient anode material for lithium ion batteries.

KOH 활성화에 의한 피치계 고품질 활성탄의 제조 및 특성

이은지,권순형,최푸름,우종표,정지철,김명수,Lee, Eun-Ji,Kwon, Soon-Hyung,Choi, Poo-Reum,U, Jong-Pyo,Jung, Ji-Chul,Kim, Myung-Soo 한국응용과학기술학회 2014 한국응용과학기술학회지 Vol.31 No.3

In order to prepare high-quality activated carbons (ACs), coal tar pitch (CTP), and mixtures of CTP and petroleum pitch (PP) were activated with KOH. The ACs prepared by activation of CTP in the range of $700{\sim}1000^{\circ}C$ for 1~5 h had very porous textures with large specific surface areas of $2470{\sim}3081m^2/g$. The optimal activation conditions of CTP were determined as CTP/KOH ratio of 1:4, activation temperature of $900^{\circ}C$, and activation time of 3 h. The obtained AC showed the highest micro-pore volume, and pretty high specific surface area and meso-pore volume. The micro-pore volumes and specific areas of activated mixtures of CTP and PP were similar to each other but the meso-pore volume could be increased. In order to change the degree of crystallinity of precursors before KOH activation process, the CTPs were carbonized in the range of $500{\sim}900^{\circ}C$. As the carbonization temperature increased, the specific surface area and pore volume of the activated ACs with the same activation conditions for CTP decreased dramatically. It was demonstrated that the increased pore size distribution of AC electrodes in the range of 1 to 2 nm plays an important role in the performance of electric double-layer capacitor.

온침의 열전달 특성에 대한 실험적 해석

양승범,박순재,이재건,정지철,김재효,Yang, Seung-Bum,Park, Soon-Jae,Lee, Jae-Gun,Jung, Ji-Chul,Kim, Jae-Hyo 경락경혈학회 2017 Korean Journal of Acupuncture Vol.34 No.3

Objectives : Many researches have studied warm needling technique to standardize its treatment by temperature measurement and material differences in the effectiveness. The purpose of this study is to compare the temperature changes of the acupuncture needle shaft during the combustion process of the moxa stick to determine the heat transfer pattern of the warn needling. Methods : A moxa stick($7{\times}8mm$) was connected to one side of the needle shaft using a stainless steel needle(ø 0.3 mm, ø 0.5 mm, ø 0.8 mm, shaft length 40 mm) with the needle handle removed. During the warm needling, temperature changes of the needle shaft were observed with an infrared camera(Flir E30) and an infrared thermometer(TESTO 845). Results : In the normal condition, heat transmit of needle shaft increased at spots 10 mm and 25 mm below the moxa stick. The amount of heat transmit increased with the diameter of needle shaft. However, when the heat shield was installed to exclude radiant heat from the moxa stick, heat transfer was less at 10 mm below the moxa stick and no temperature change was observed at 25 mm below the moxa stick. Heat transfer by warm needling does not reach the end of needle shaft even in ø 0.8 mm needle. Conclusions : It is suggested that the radiant heat of moxa stick results in the heat transmit of acupuncture needle shaft. Thus, radiant heat transmit must be considered as one of the heat transfer characteristics of the warm needling.

활성탄의 후 처리에 의한 EDLC 전극재의 전기화학 성능 개선

이은지,권순형,최푸름,정지철,김명수,Lee, Eunji,Kwon, Soon Hyung,Choi, Pooreum,Jung, Ji Chul,Kim, Myung-Soo 한국재료학회 2014 한국재료학회지 Vol.24 No.6

Commercial activated-carbon used as the electrode material of an electric double-layer capacitor (EDLC) was posttreated with various acids and alkalis to increase its capacitance. The carbon samples prepared were then heat-treated in order to control the amount of acidic functional groups formed by the acid treatments. Coin-type EDLC cells with two symmetric carbon electrodes were assembled using the prepared carbon materials and an organic electrolyte. The electrochemical performance of the EDLC was measured by galvanostatic charge-discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Among the various activated carbons, the carbon electrodes (CSsb800) prepared by the treatments of coconutshell-based carbon activated with NaOH and $H_3BO_5$, and then heat treated at $800^{\circ}C$ under a flow of nitrogen gas, showed relatively good electrochemical performance. Although the specific-surface-area of the carbon-electrode material ($1,096m^2/g$) was less than that of pristine activated-carbon ($1,122m^2/g$), the meso-pore volume increased after the combined chemical and heat treatments. The specific capacitance of the EDLC increased from 59.6 to 74.8 F/g (26%) after those post treatments. The equivalent series resistance of EDLC using CSsb800 as electrode was much lower than that of EDLC using pristine activated carbon. Therefore, CSsb800 exhibited superior electrochemical performance at high scan rates due to its low internal resistance.