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InAs 양자점의 광학적 성질에 미치는 초격자층의 영향
정연길,최현광,박유미,황숙현,윤진주,이제원,임재영,전민현,Jeong Yonkil,Choi Hyonkwang,Park Yumi,Hwang Sukhyon,Yoon Jin-Joo,Lee Jewon,Leem Jae-Young,Jeon Minhyon 한국재료학회 2004 한국재료학회지 Vol.14 No.2
We investigated the effects of high potential barriers on the optical characteristics of InAs quantum dots (QDs) by using photoluminescence (PL) and photoreflectance (PR) spectroscopy. A sample with regular InAs quantum dots on GaAs was grown by molecular beam epitaxy (MBE) as a reference. Another InAs QDs sample was embedded in single AlGaAs barriers. On the other hand, a sample with GaAs/AlGaAs superlattice barriers was adopted for comparison with a sample with a single AlGaAs layer. In results, we found that the emission wavelength of QDs was effectively tailored by using high potential barriers. Also, it was found that the optical properties of a sample with QDs embedded in GaAs/AlGaAs superlattices were better than those of a sample with QDs embedded in a single layer of AlGaAs barriers. We believe that GaAs/AlGaAs superlattice could effectively prevent the generation of defects.
3-5족 적층형과 CuInGa(S,Se)2 및 Cu2ZnSn(S,Se)4 화합물반도체 박막태양전지
정연길 ( Yonkil Jeong ),박동원 ( Dong Won Park ),이재광 ( Jae Kwang Lee ),이재영 ( Jaeyoung Lee ) 한국공업화학회 2015 공업화학 Vol.26 No.5
신 기후변화대응(Post 2020)을 위한 대체에너지의 역할과 더불어 태양전지의 중요성이 높아져 가고 있다. 태양전지의 종류는 크게 재료관점에서 보면 유기물과 무기물 계열로 구분할 수 있지만 대규모 발전역할에서는 현재까지 실리콘과 같이 양산성과 안정성 기반의 무기물 태양전지가 주된 역할을 하고 있다. 특히 최근 몇 년간 화합물반도체 태양전지에 대한 연구는 급속도로 가속화되면서 3-5족 적층형 태양전지, chalcopyrite 계열 CuInGa(S,Se)2 (CIGSSe) 태양전지와 kesterite 계열 Cu2ZnSn(S,Se)4 (CZTSSe) 태양전지 연구가 대표적으로 주류를 이루어 왔다. 따라서 화합물반도체 태양전지에서 주류를 이루고 있는 3-5족 적층형, CIGSSe 및 CZTSSe 태양전지들의 연구개발동향 및 기술적인 주요내용들에 대해 소개하고자 한다. Solar cells with other alternative energies are being importantly recognized related with post-2020 climate change regime formation. In a point of view of materials, solar cells are classified to organic and inorganic solar cells which can provide a plant-scale electricity. In particular, recent studies about compound semiconductor solar cells, such as III-V tandem solar cells, chalcopyrite-series CIGSSe solar cells, and kesterite-series CZTSSe solar cells were rapidly accelerated. In this report, we introduce a research trend and technical issues for the compound semiconductor solar cells.
Jeong-Pyo Kim,Sung-Il Jung,Young-Suk Sim,백운규,Vijay K. Srivastava,Shraddha Singh,Akash Mohanty,정연길 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.3
The oxidation behavior of graphite substrates with silicon carbide (SiC) and silicon nitride (Si3N4) coatings, prepared by using a solid-vapor reaction process, was investigated in cyclic oxidation tests. The effect of the porosity of the substrate on the oxidation behavior was also investigated. Substrates with the SiC coating showed higher weight loss than those with the Si3N4 coating. Oxidation of the substrates with 10 and 13 % porosities with the Si3N4 coating took place at 900℃ and at 1000℃, respectively. However, after long term cyclic oxidation tests, the substrate with 13 % porosity with the Si3N4 coating was oxidized at a relatively low temperature of 800℃, even though the weight loss was below 10 %. In the case of the SiC coatings, detachment of the coating region or full oxidation of the substrates took place whereas in the case of the Si3N4 coatings, no evidence of delamination or detachment of the coating region was observed after oxidation. The oxidation was affected by the coating thickness and by the type of materials coated on the substrate, not by the porosity of the substrate itself, although the coating thickness did depend on the porosity of the substrate.
Jeong-Pyo Kim,Hyun-Min Cha,명상원,Pyung-Ho Lee,Jae-Hyun Lee,정연길 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.3
Silicon carbide (SiC) nanofibers have been synthesized by a solid-vapor reaction (SVR) between carbon nanofibers (CNFs) and SiO vapor, the CNFs being grown using alloys of Ni-Fe, Fe-Al, and Ni-Fe-Al as catalysts by thermal decomposition of C2H4 in the temperature range of 550-650℃. After removal of the catalysts in the as-synthesized CNFs with 2 mol/l HNO3, the SVR process occurred between the CNFs and the SiO vapor in the temperature range of 1200-1450 ℃ for a fixed dwell time of 5 h, with a heating rate of 5℃·minute−1 under an Ar/H2 (160 : 40) flow of 200 ㎠ (ml/minute). The SiC nanofibers consisted of β-SiC and α-SiC and have a thicker diameter than that of the mother CNFs. The effects of catalyst composition and synthesis temperature on the microstructural evolution of the SiC nanofibers are discussed based on the quantitative and qualitative results obtained.
겔-케스팅한 알루미나 성형체에서 출발입도가 공정변수 및 성형 미세구조에 미치는 영향
하창기,김재원,조창용,백운규,정연길,Ha, Chang-Gi,Kim, Jae-Won,Jo, Chang-Yong,Baek, Un-Gyu,Jeong, Yeon-Gil 한국재료학회 2001 한국재료학회지 Vol.11 No.10
Alumina $(Al_2O_3)$ green bodies were fabricated by gel-casting using three kinds of alumina with different particle size (mean particle size: 4.6 $\mu\textrm{m}$, 0.32 $\mu\textrm{m}$, 10nm). The effects of particle size on gel-casting process and green microstructure were investigated. The optimum dispersion conditions using ammonium salt (D-3019) as dispersant were 0.2 wt% (4.63 $\mu\textrm{m}$), 0.5 wt% (0.32 $\mu\textrm{m}$), and 5.0 wt% (10 nm), in high solid loading. The optimum solid loading of each starting material for gel-casting was obtained as 59 vol% (4.63 $\mu\textrm{m}$), 57 vol% (0.32 $\mu\textrm{m}$), 15 vol% (10 nm), depending on particle size, indicating that nano-size particle (10 nm) represent lower solid loading as high specific surface area than those of other two starting materials. The drying at ambient conditions (humidity; $\thickapprox$90%) was performed more than 48hrs to enable ejection of the part from the mold and then at $120^{\circ}C$ for 2hrs in an air oven, showing no crack and flaw in the dried green bodies. The pore size and distribution of the gelcast green bodies showed the significant decrease with decreasing particle size. Green microstructure was dependent on the pore size and distribution due to the particle size, and on the deairing step. The green density maximum obtained was 58.9% (4.63 $\mu\textrm{m}$), 60% (0.32 $\mu\textrm{m}$), 47% (10 nm) theoretical density (TD), and the deairing step applied before gel-casting did not affect green density.
규소/질화규소 비가 자전연소합성공정을 이용한 다공질 질화규소 세라믹스의 미세구조와 특성에 미치는 영향
김동백,박동수,한병동,정연길,Kim, Dong-Baek,Park, Dong-Su,Han, Byeong-Dong,Jeong, Yeon-Gil 한국기계연구원 2004 硏究論文集 Vol.34 No.-
Porous silicon nitride ceramics were prepared by Self-propagating High Temperature Synthesis from silicon powder, silicon nitride powder and the pore-forming precursor. The microstructure, porosity and the flexural strength of the porous silicon nitride ceramics were varied according to the Si/$Si_3N_4$ ratio, size and amount of the pore-forming precursors. Some samples exhibited as high flexural strength as $162\pm24$ MPa. The high strength is considered to result from the fine pore size and the strong bonding among the silicon nitrid particles.
Formation pattern 연구를 통한 AGM 연축전지의 충전 효율 향상
김성준,손정훈,김봉구,정연길,Kim, Sung Joon,Son, Jeong Hun,Kim, Bong-Gu,Jung, Yeon Gil 한국결정성장학회 2021 韓國結晶成長學會誌 Vol.31 No.1
CO2 가스 발생 감소와 연비향상을 위해서 HEV 차량은 ISG 시스템을 채용하고 있다. 이 ISG 시스템은 배터리가 감당해야 하는 전기 부하를 증대시켰고, 시동 횟수도 급격히 늘어나게 하였다. 이를 위해 AGM 연축전지가 개발되어 사용되고 있으나, 종래의 연축전지에 비해서 formation 중 전해액량 조절이 더 높은 수준으로 유지해야 됨에 따라 충전시간이 약 3배 가량 길어지게 되었다. 본 연구에서는 formation pattern의 최적화를 통해서 충전효율을 증대시켜 충전시간을 단축하고자 하였다. formation pattern의 최적화를 위해서, 16개 multi step에 10개 충전 step과 6개의 방전 step을 적용하고, step별 충전 전류를 조절한 4가지 조건(21 hr, 24hr, 27 hr, 30 hr)으로 시험을 진행하였다. 그 결과 24 hr 시험 조건이 PbO2 변환율이 가장 높게 분석되었고, 용량 103.3 %, 저온시동성능 38 sec, 충전수입성 37.36 A로 나타났다. Multi-step과 방전 step을 적용한 충전 프로그램의 결과, 충전 중에 국부적으로 급격히 발생된 분극화를 제거하고 전류의 손실을 최소함으로써 충전효율을 증가시킬 수 있음을 검증하였다. 이렇게 충전효율을 증가시킴으로써 본 연구에서는 충전시간을 기존에 비해서 약 30 % 감소시키는 탁월한 결과를 얻을 수 있었다. In order to improve fuel economy and reduce CO2, HEV adopts ISG system as a standard. This ISG system increased the electric load that the battery had to bear, and the number of starting increased rapidly. AGM Lead Acid batteries have been developed and used, but the charging time is about three times longer as the electrolyte amount control during formation must be maintained at a higher level compared to conventional lead-acid batteries. In this study, we tried to shorten the charging time by increasing the charging efficiency through the optimization of the formation pattern. In order to optimize the Formation Pattern, 10 charging steps and 6 discharging steps were applied to 16 multi steps, and the charging current for each step was controlled, and the test was conducted under 4 conditions (21 hr, 24 hr, 27 hr, 30 hr). As a result of simultaneous application of multi-step and discharge step, it was verified that minimizing the current loss and eliminating the sudden polarization during charging contributes to the improvement of charging efficiency. As a result, it showed excellent results in reducing the charging time by about 30 % with improved charging efficiency compared to the previous one.
용매열 공정을 이용한 세리아(CeO<sub>2</sub>) 나노분말의 합성 및 분산거동
임태섭,옥지영,최연빈,김봉구,손정훈,정연길,Lim, Tae Seop,Ock, Ji Young,Choi, Yeon Bin,Kim, Bong Gu,Son, Jeong Hun,Jung, Yeon Gil 한국재료학회 2020 한국재료학회지 Vol.30 No.7
CeO<sub>2</sub> nanoparticles, employed in a lot of fields due to their excellent oxidation and reduction properties, are synthesized through a solvothermal process, and a high specific surface area is shown by controlling, among various process parameters in the solvothermal process, the type of solvent. The synthesized CeO<sub>2</sub> nanoparticles are about 11~13 nm in the crystallite size and their specific surface area is about 65.38~84.65 ㎡/g, depending on the amount of ethanol contained in the solvent for the solvothermal process; all synthesized CeO<sub>2</sub> nanoparticles shows a fluorite structure. The dispersibility and microstructure of the synthesized CeO<sub>2</sub> nanoparticles are investigated according to the species of dispersant and the pH value of the solution; an improvement in dispersibility is shown with the addition of dispersants and control of the pH. Various dispersing properties appear according to the dispersant species and pH in the solution with the synthesized CeO<sub>2</sub> nanoparticles, indicating that improved dispersing properties in the synthesized CeO<sub>2</sub> nanoparticles can be secured by applying dispersant and pH control simultaneously.