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기능화에 의한 단일벽 탄소나노튜브 정제 및 페이퍼 제조와 전계방출 특성 연구
곽정춘,이승환,이한성,이내성,Goak, Jeung-Choon,Lee, Seung-Hwan,Lee, Han-Sung,Lee, Nae-Sung 한국전기전자재료학회 2008 전기전자재료학회논문지 Vol.21 No.5
Single-walled carbon nanotubes (SWCNTs) were currently produced together with some contaminants such as a metallic catalyst, amorphous carbon, and graphitic nanoparticles, which should be sometimes purified for their applications. This study aimed to develop efficient, scalable purification processes but less harmful to SWCNTs. We designed three-step purification processes: acidic treatment, surface functionalization and soxhlet extraction, and heat treatment. During the soxhlet extraction using tetrahydrofuran, specifically, carbon impurities could be easily expelled through a glass thimble filter without any significant loss of CNTs. Finally, SWCNTs were left as a bulky paper on the filter through membrane filtration. Vertically aligned SWCNTs on one side of bulky paper were well developed in a speparation from the filter paper, which were formed by being sucked through the filter pores during the pressurized filtration. The bucky paper showed a very high peak current density of field emission up to $200\;mA/cm^2$ and uniform field emission images on phosphor, which seems very promising to be applied to vacuum microelectronics such as microwave power amplifiers and x-ray sources.
곽정춘,이내성,Goak, Jeung-Choon,Lee, Nae-Sung 한국전기전자재료학회 2008 전기전자재료학회논문지 Vol.21 No.2
Single walled carbon nanotubes (SWCNTs) can be modified to produce a new concept of hybrid materials by introducing atoms or molecules inside their cylindrical empty space. Such an endohedral doping of the SWCNTs is expected to decisively alter their electronic transport and mechanical properties, In this study, we purified SWCNTs by three-step purification processes and formed the peapod structure by introducing $C_{60}$ fullerenes inside the SWCNTs. $C_{60}$ molecules were observed to be regularly arranged by transmission electron microscopy. In Raman spectra, the radial breathing mode (RBM) rather than the other modes was significantly affected by the endohedral injection of $C_{60}$. The RBM intensity was more greatly reduced in the large-diameter SWCNTs than the small-diameter ones, Raman spectroscopy is expected to be a key technique for analyzing $C_{60}$-encapsulated SWCNTs.
곽정춘,Junseop Kim,이한성,김진희,서용호,이내성 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.2
This study investigated an oxidative reaction of carbon nanotubes (CNTs) with other ingredients in a CNT paste, which was developed for field-emission applications, during firing in air at 420℃. In the thermogravimetric analysis of the mixtures of CNTs and other ingredients of the paste, PbO brought the oxidation temperature of CNTs down by as much as ~79℃ from that of pristine CNTs, probably due to catalytic acceleration of their oxidation. Ethyl cellulose (EC), which was used as an organic binder, also lowered the burning temperature of the CNTs by ~62℃. When both PbO and EC were mixed together with CNTs at the same time, they had a synergetic effect on the decomposition of the CNTs. This problem was overcome by replacing the PbO frit with a Pb-free, SnO frit in such a way that most of CNTs could survive during the firing of the paste. Consequently, the field-emission current of the CNT paste prepared from the Pb-free, SnO frit was improved by as much as 250%, compared to that of the PbO-containing paste. This study seems to be of great significance not only for improving the field-emission characteristics but also for eliminating Pb for environmental protection.
곽정춘 ( Jeung Choon Goak ),김태양 ( Tae Yang Kim ),정종완 ( Jong Wan Jung ),서영수 ( Young Soo Seo ),석중현 ( Jung Hyun Sok ),이내성 ( Nae Sung Lee ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.2
This study evaluated the purity of single-walled carbon nanotubes (SWCNTs) in the arc-synthesized SWCNT samples by using thermogravimetric analysis (TGA). The as-produced SWCNT samples were heat-treated in air for 20 h at 275-475℃ and characterized by scanning and transmission electron microscopes and TGA to establish oxidation temperature ranges of SWCNTs and carbonaceous impurities comprising the samples. Based on these oxidation temperature ranges, derivative thermogravimetric curves were deconvoluted, and differentiated peaks were assigned to SWCNTs and carbonaceous impurities. The compositions and the SWCNT purities of the samples were obtained simply by calculating the areal ratios under the deconvoluted curves. TGA studies on purity evaluation and thermal stabilities of SWCNTs and carbonaceous impurities are likely to provide us with a simple route of thermal oxidation purification to acquire high-purity SWCNT samples.
알루미늄 하부층이 탄소나노튜브의 성장 및 전계방출 특성에 미치는 영향
이승환,곽정춘,이한성,이내성,Lee, Seung-Hwan,Goak, Jeung-Choon,Lee, Han-Sung,Lee, Nae-Sung 한국전기전자재료학회 2008 전기전자재료학회논문지 Vol.21 No.2
We studied the effect of an Al underlayer on the growth of carbon nanotubes (CNTs) and their field emission characteristics, First of all, CNTs were grown on the Invar catalyst layers with different thickness of 1 to 10 nm, showing that the CNT length was saturated for the catalyst 5 nm or thicker. The CNTs grown on the 5-nm-thick catalyst were ${\sim}10{\mu}m$ long and ${\sim}30nm$ in diameter. Second, an Al underlayer was applied between the catalyst layer and the Ti diffusion barrier to reduce the diameters of CNTs for better field emission properties by forming spherical Al oxide particles on which smaller catalyst nanoparticles would occur. The optimal thickness of an Al underlayer underneath the 5-nm-thick catalyst was ${\sim}15nm$, producing the CNTs with the length of ${\sim}15{\mu}m$ and the diameter of ${\sim}15nm$. The field emission measurements, following the tape activation, showed that the thinner and longer CNTs gave rise to better field emission performance with the lower turn-on and threshold electric fields.
이한성,전지현,곽정춘,김기범,Young Chul Choi,Hun Soo Kim,Jeonyoung Sun,Youngdon Park,Jaiyoung Park,이내성 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1
Carbon-nanotube (CNT) emitters prepared by screen printing a CNT paste vary widely in height. Upon applying electric fields, field enhancement occurs strongly on long CNTs, enabling them to emit electrons in a vacuum. In this situation, electron-emitting CNTs may be Joule-heated, during which an introduction of a small amount of an O3 gas can cause the long, Joule-heated CNTs to burn out rapidly by oxidation. We observed that such O3 electrical trimming considerably reduced not only the average height but also the height variation of CNTs. O3 trimming greatly increased both the emission uniformity of CNT emitters by several percent and their lifetime by ~4 times because it might increase the number of CNT emitters participating in field emission even though the emission voltage had to be raised to keep the emission current constant.
김영래,전홍준,이한성,곽정춘,황호수,공병윤,이내성,Kim, Young-Rae,Jeon, Hong-Jun,Lee, Han-Sung,Goak, Jeung-Choon,Hwang, Ho-Soo,Kong, Byung-Yun,Lee, Nae-Sung 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.4
This study investigated the growth characteristics of carbon nanotubes (CNTs) by changing a period of annealing time and a $C_{2}H_{2}/H_2$ flow ratio at temperature as low as $450^{\circ}C$ with inductively coupled plasma chemical vapor deposition. The 1-nm-thick Fe-Ni-Co alloy thin film served as a catalyst layer for the growth of CNTs, which was thermally evaporated on the 15-nm-thick Al underlayer deposited on the 50-nm-thick Ti diffusion barrier. The annealing at low temperature of $450^{\circ}C$ brought about almost no granulation of the catalyst layer, and the CNT growth was not affected by a period of annealing time. A study of changing the flow rate of $C_{2}H_{2}$ and $H_2$ showed that as the ratio of the $C_{2}H_{2}$ flow rate to the $H_2$ flow rate was lowered, the CNTs were grown to be longer With further decreasing the flow ratio, the length of CNTs reached the maximum and then became shorter. Under the optimized gas flow rates, we successfully synthesized CNTs with a uniform length over a 4-inch Si wafer at $450^{\circ}C$.