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질화탄소 표면층 및 열처리가 탄소 나노튜브 미세팁의 전계방출 및 장시간 안정성에 미치는 영향
노영록,김종필,박진석,Noh, Young-Rok,Kim, Jong-Pil,Park, Jin-Seok 한국반도체디스플레이기술학회 2010 반도체디스플레이기술학회지 Vol.9 No.1
The effects of thermal treatment on CNTs, which were coated with a-$CN_x$ thin film, were investigated and related to variations of chemical bonding and morphologies of CNTs and also properties of field emission induced by thermal treatment. CNTs were directly grown on nano-sized conical-type tungsten tips via the inductively coupled plasma-chemical vapor deposition (ICP-CVD) system, and a-$CN_x$ films were coated on the CNTs using an RF magnetron sputtering system. Thermal treatment on a-$CN_x$ coated CNT-emitters was performed using a rapid thermal annealing (RTA) system by varying temperature ($300-700^{\circ}C$). Morphologies and microstructures of a-$CN_x$/CNTs hetero-structured emitters were analyzed by FESEM and HRTEM. Chemical composition and atomic bonding structures were analyzed by EDX, Raman spectroscopy, and XPS. The field emission properties of the a-$CN_x$/CNTs hetero-structured emitters were measured using a high vacuum (below $10^{-7}$ Torr) field-emission measurement system. For characterization of emission stability, the fluctuation and degradation of the emission current were monitored in terms of operation time. The results were compared with a-$CN_x$ coated CNT-emitters that were not thermally heated as well as with the conventional non-coated CNT-emitters.
탄소 나노튜브 위에 붕소 및 탄소 질화 박막이 코팅된 이종접합 구조 미세팁의 전자방출 특성
노영록(Young-Rok Noh),김종필(Jong-Pil Kim),박진석(Jin-Seok Park) 대한전기학회 2010 전기학회논문지 Vol.59 No.4
Boron nitride (BN) and carbon nitride (CN) films, which have relatively low work functions and commonly exhibit negative electron affinity behaviors, were coated on carbon nanotubes (CNTs) by magnetron sputtering. The CNTs were directly grown on metal-tip (tungsten, approximately 500nm in diameter at the summit part) substrates by inductively coupled plasma-chemical vapor deposition (ICP-CVD). The variations in the morphology and microstructure of CNTs due to coating of the BN and CN films were analyzed by field-emission scanning electron microscopy (FE-SEM). The energy dispersive x-ray (EDX) spectroscopy and Raman spectroscopy were used to identify the existence of the coated layers (CN and BN) on CNTs. The electron-emission properties of the BN-coated and CN-coated CNT-emitters were characterized using a high-vacuum field emission measurement system, in terms of their maximum emission currents (Imax) at 1kV and turn-on voltage (Von) for approaching 1μA. The results showed that the Imax current was significantly increased and the Von voltage were remarkably reduced by the coating of CN or BN films. The measured values of Imax-Von were as follows; 176μA-500V for the 5nm CN-coated emitter and 289μA-540V for the 2nm BN-coated emitter, respectively, while the Imax-Von of the as-grown (i.e., uncoated) emitter was 134μA-620V. In addition, the CNT emitters coated with thin CN or BN films also showed much better long-term (up to 25h) stability behaviors in electron emission, as compared with the conventional CNT emitter.
탄소 나노튜브에 대한 비정질 질화막의 코팅 및 전계방출 특성
노영록(Young-Rok Noh),김종필(Jong-Pil Kim),박진석(Jin-Seok Park) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
Coating of amorphous nitride thin layers, such as boron nitride (BN) and carbon nitride (CN), has been performed on carbon nanotubes (CNTs) for the purpose of enhancing their electron-emission performances because those nitride films have relatively low work functions and commonly exhibit negative electron affinity behavior. The CNTs were directly grown on metal-tip (tungsten, approximately 500 ㎚ in diameter at the summit part) substrates by inductively coupled plasma-chemical vapor deposition (ICP-CVD). Sharpening of the tungsten tips were carried out by electrochemical etching. Morphologies and microstructures of BN and CN films were analyzed by field-emission scanning electron microscopy (FE-SEM), energy dispersive x-ray (EDX) spectroscopy, and Raman spectroscopy. The electron-emission properties (such as maximum emission currents and turn-on fields) of the BN-coated and CN-coated CNT-emitters were characterized in terms of the thickness of BN and CN layers.
원추형 금속 기판의 팁 각도에 따른 탄소 나노튜브 이미터의 전계방출 특성
김종필,노영록,장한빛,박진석 한국반도체디스플레이기술학회 2011 반도체디스플레이기술학회지 Vol.10 No.2
A tip-type carbon nanotube(CNT)-based field emitter was studied to consider it as electron source for micro-focused x-ray tube. The CNT was grown directly on a metal (tungsten) substrate by using an inductively coupled plasma-chemical vapor deposition (ICP-CVD) method. Prior to CNT growth, the metal substrate was etched to have various tip angles from 10o to 180° (flat-type). The morphologies and microstructures of all the grown CNTs were analyzed via field-emission SEM. Furthermore, the effects of substrate tip-angles on the emission properties of CNT-based field emitters were characterized to estimate the maximum current density, the turn-on voltage, and the spatial distribution of electron beams. Prolonged long-term stability testing of the CNT emitters was also performed. All the experiment results obtained from this study indicated why a tip-type CNT emitter, compared with a flat-type CNT emitter, would be more desirable for a micro-focused x-ray system, in terms of the emission current level, the focused beam area, and the emission stability.
미세 팁 기판 위에 전기영동법으로 성장시킨 탄소 나노튜브의 전계방출 특성
장한빛,노영록,김종필,박진석,Chang, Han-Beet,Noh, Young-Rok,Kim, Jong-Pil,Park, Jin-Seok 한국반도체디스플레이기술학회 2010 반도체디스플레이기술학회지 Vol.9 No.4
Field-emission characteristics of carbon nanotubes(CNTs), which were grown on conical-type tungsten micro-tips by using an electrophoretic deposition(EPD) method, were examined. The EPD method proved to be convenient to manipulate and arrange CNTs from well dispersed suspensions onto such tip-type substrates. The growth rate of CNTs was proportional to the applied d.c. bias voltage and the process time. It was observed from the Raman study that the EPDproduced CNTs showed better crystal qualities with the Raman intensity ratio( $I_D$/$I_G$) of 0.41-0.42 than the CVD-produced CNTs and their crystal qualities could be further improved by thermal annealing. The electron emitters based on the EPDCNTs showed excellent field emission properties, such as the threshold voltage for electron emission of about 620 V and the maximum emission current of about 345 ${\mu}A$. In addition, the EPD-CNTs exhibited the stable long-term(up to 40 h) emission capability and the emission stability was enhanced by thermal annealing.
갈륨이 첨가된 산화아연막의 코팅에 따른 미세팁 구조 탄소나노튜브의 전계방출 특성 및 장시간 안정성
김종필,노영록,조경철,이상렬,박진석,Kim, Jong-Pil,Noh, Young-Rok,Jo, Kyoung-Chul,Lee, Sang-Yeol,Park, Jin-Seok 한국반도체디스플레이기술학회 2009 반도체디스플레이기술학회지 Vol.8 No.4
Carbon nanotubes (CNTs) were coated with undoped zinc oxide (ZnO) or 5 wt% gallium-incorporated ZnO (GZO) using various deposition conditions. The CNTs were directly grown on conical-type tungsten substrates at $700^{\circ}C$ using inductively coupled plasma-chemical vapor deposition. The pulsed laser deposition technique was used to deposit the ZnO and GZO thin films with very low stress. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy were used to monitor the variations in the morphology and microstructure of CNTs prior to and after ZnO or GZO coating. The formation of ZnO and GZO films on CNTs was confirmed using energy-dispersive x-ray spectroscopy. In comparison to the as-grown (uncoated) CNT emitter, the CNT emitter that was coated with a thin (10 nm) GZO film showed remarkably improved field emission characteristics, such as the emission current of $325\;{\mu}A$ at 1 kV and the threshold field of $1.96\;V/{\mu}m$ at $0.1\;{\mu}A$, and it also exhibited the highly stable operation of emission current up to 40 h.
원추형 기판 위에 탄소 나노튜브의 선택적 성장이 전계방출 특성에 미치는 영향
김부종,박진석,노영록 한국반도체디스플레이기술학회 2012 반도체디스플레이기술학회지 Vol.11 No.1
In this study, for use of carbon nanotubes (CNTs) as a cold cathode of x-ray tubes, we examine the effects of selective growth of CNTs on their field emission properties and long-term stability. The selective growth of CNTs was performed by selectively etching the catalyst layer which was used for CNTs’ nucleation. CNTs were grown on conical-type tungsten substrates using an inductively-coupled plasma chemical vapor deposition system. For all the grown CNTs, their morphologies and microstructures were analyzed by field-emission scanning electron microscope and Raman spectroscopy. The electron-emission properties of CNTs and the long-term stability of emission currents were measured and characterized according to the CNTs’ growth position on the substrate.
김종필(Jong-Pil Kim),노영록(Young-Rok Noh),이상렬(Sang-Yeol Lee),박진석(Jin-Seok Park) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
In this research, gallium-incorporated zinc oxide (ZnO:Ga) thin films have been used as a coating material for enhancing the field-emission property of CNT-emitters. Multi-walled CNTs were directly grown on conical-type (250 ㎛ in diameter) metal-tip substrates at 700 °C by inductively coupled plasma-chemical vapor deposition (ICP-CVD). The pulsed laser deposition (PLD) technique was used to produce 5wt% gallium-doped ZnO (5GZO) films with very low stress. The structural properties of ZnO and 5GZO coated CNTs were characterized by Raman spectroscopy. Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) were also used to monitor the variation in the morphology and microstructure of CNTs before and after 5GZO-coating. The measurement of the field emission characteristics showed that the emitter that coated the 5GZO (10㎚) on CNTs exhibited the best performance: a maximum emission current of 325 μA, a threshold field of 2.2 V/㎛.
미세 팁 기판 위에 전기영동법에 의해 성장된 탄소 나노튜브의 전계방출 특성
장한빛(Han-Beet Chang),노영록(Young-Rok Noh),김종필(Jong-Pil Kim),박진석(Jin-Seok Park) 대한전기학회 2010 대한전기학회 학술대회 논문집 Vol.2010 No.7
We present experimental results regarding to the structural properties and field-emission characteristics of carbon nanotubes(CNTs) which have been grown on conical-type tungsten (W) tips by using an electrophoretic deposition(EPD) method. The EPD method has been shown to be a very convenient methode to manipulate and arrange CNTs from well dispersed suspensions onto conductive substrates. When CNTs is grown by EPD, the thickness of CNTs film was increased by increasing the applied voltage and the process time. The crystalline structure of CNTs is also characterized by Raman spectroscopy. The results obtained in this study indicate that the emission current level of the CNT-emitter grown by EPD is better than growing by ICP-CVD for the application of micro-focused x-ray systems.