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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.
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.
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.
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 $450^{\circ}C$.
양극산화 인가전압에 따른 장범위 규칙 다공성 알루미나 멤브레인의 제조
장현철 ( Hyun Chul Jang ),최정미 ( Jung Mi Choi ),안기태 ( Ki Tae An ),이내성 ( Nae Sung Lee ),박윤선 ( Yun Sun Park ),석중현 ( Jung Hyun Sok ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.1
Studying the long-range ordering of nanopores on the anodic aluminum oxide (AAO) membranes under a hard anodization (HA) approach is crucial in producing well-aligned nanopores on the AAO membranes. Electro-polishing in a mixture of ethanol and perchloric acid for 5 min removed marks formed by rolling and produced flat surfaces on aluminum substrates. The AAO was formed by the first HA process, providing seeds for the subsequent production of uniform AAO nanopores. The second HA process carried out on the seeds produced well-aligned, uniform AAO nanopores. The AAO nanopores, varying in size and shape, were observed with voltages applied for HA. This study provides a route for controlling the size and shape of AAO nanopores by changing the applied voltages.
추천 시스템에서의 효율적인 행렬 분해 모델을 위한 정밀도 변환 기법
유재서 ( Jae-seo Yu ),고윤용 ( Yun-yong Ko ),배홍균 ( Hong-kyun Bae ),강석원 ( Seokwon Kang ),유용승 ( Yongseung Yu ),박영준 ( Yongjun Park ),김상욱 ( Sang-wook Kim ) 한국정보처리학회 2021 한국정보처리학회 학술대회논문집 Vol.28 No.1
최근 딥러닝 분야에서 모델 학습을 가속화하기 위해, 실수 표현 시 사용하는 비트 수를 줄이는 양자화 연구가 활발히 진행되고 있다. 본 논문은 추천 시스템 모델 중 하나인 행렬 분해 모델(Matrix Factorization, MF)에 대한 양자화 수행 시, 발생할 수 있는 학습 정확도 손실을 방지하기 위한 정밀도 변환 방안을 제시한다. 우리는 실세계 데이터셋을 이용한 실험을 통해, 제안 방안이 적용된 MF 모델은 양자화 기법이 적용되지 않은 모델과 비슷한 추천 정확도를 보이며, 약 30% 개선된 속도로 학습됨을 확인할 수 있었다.
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.
Growth of carbon nanotubes by microwave plasma-enhanced chemical vapor deposition at low temperature
Lee,Young Hee,Bae,Dong Jae,Choi,Young Chul,Lee,Byung Soo,Park,Gyeong-Su,Choi,Won Bong,Lee,Nae Sung,Kim,Jong Min 국립경상대학교 공과대학 부설 첨단소재연구소 1999 尖端素材 Vol.9 No.-
Carbon nanotubes have been grown on Ni-coated Si substrates by microwave plasma-enhanced chemical vapor deposition with a mixture of methane and hydrogen gases at temperatures ranging from 520 to 700℃. The density and the length of carbon nanotubes increased with increasing growth temperature. At growth temperature of 520℃, carbon nanotubes were curly, whereas the nanotubes were straight and self-aligned upward at temperatures above 600℃. Images of high-resolution transmission electron microscope showed that nanotubes were multiwalled with a few wall-structures. The graphitized structures were also confirmed by Raman spectra. We show that the size of Ni domains on Si substrates is correlated to the diameters of the grown carbon nanotubes.