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Direct Cd-to-Pb Exchange of CdSe Nanorods into PbSe/CdSe Axial Heterojunction Nanorods
Lee, Dongkyu,Kim, Whi Dong,Lee, Seokwon,Bae, Wan Ki,Lee, Sangheon,Lee, Doh C. American Chemical Society 2015 Chemistry of materials Vol.27 No.15
<P>We report synthesis of PbSe nanorods (NRs) and PbSe/CdSe axial heterojunction NRs via direct Cd-to-Pb cation exchange in CdSe NRs. Use of suited ligand–cation combinations enables the cation exchange while keeping the nanomaterial morphology intact. For example, solvation of Cd<SUP>2+</SUP> using oleylamine (OLA) allows for the cation exchange process, which would not be possible by using oleic acid instead of OLA. A mild cation exchange process, such as mixing Pb-oleate and OLA with CdSe NRs at 130 or 150 °C, results in anisotropic replacement of CdSe into PbSe along the ⟨0001⟩ direction of wurtzite CdSe, and a partial conversion leads to the formation of heterostructure NRs containing axial CdSe/PbSe heterojunctions. While the cation exchange proceeds at both tips of CdSe NRs, exchange appears to be faster on (0001̅) planes. Binding energy calculation based on density functional theory reveals that OLA binds strongly to the (0001̅) facet of CdSe NRs, leading to asymmetric cation exchange. This protocol to convert CdSe nanocrystals directly into PbSe broadens the design range of CdSe/PbSe heterojunction nanomaterials potentially with various morphologies because template CdSe nanocrystals can be prepared in different shapes via colloidal synthesis.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-15/acs.chemmater.5b01548/production/images/medium/cm-2015-01548m_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5b01548'>ACS Electronic Supporting Info</A></P>
임베디드 시스템에서 고해상도 멀티미디어 플레이어 설계 및 구현
이상헌(Sangheon Lee),군순영(Soonyoung Kwon),이동하(Dongha Lee),이상혁(Sanghyuk Lee) 한국멀티미디어학회 2007 한국멀티미디어학회 학술발표논문집 Vol.2007 No.1
디지털 컨버전스 환경에서 모바일 기기를 중심으로 다양한 기능들이 통합되고 있다. 각 기능 들이 통합되면서 예전보다 더 높은 CPU 성능, 배터리 용량, 메모리 등이 필요하게 되었다. 본 논문에서는 현재 사용자들을 널리 확보해 가고 있는 모바일 기기인 PMP(Portable Multimedia Player)에서 성능이 한층 강화된 TI(Texas Instruments)에서 출시한 DM6441 CPU를 기반으로 한 고해상도 멀티미디어 플레이어를 구현하였다. 다양한 MPEG-1/2/4비디오 코텍 뿐만 아니라 최근 DMB에서도 각광받고 있는 고성능 비디오 코텍인 H.264와 최대 XGA급(1024×768)의 동영상을 무리없이 재생활 수 있어 휴대형 멀티미디어 플레이어 시장에서 경쟁력을 확보할 것으로 기대된다.
Oxygen-Controlled Seed Layer in DC Sputter-Deposited ZnO:Al Substrate for Si Thin-Film Solar Cells
Seung-Yoon Lee,Taehyun Hwang,Woojin Lee,Sangheon Lee,Hongsik Choi,Seh-Won Ahn,Heon-Min Lee,Byungwoo Park IEEE 2015 IEEE journal of photovoltaics Vol.5 No.2
<P>Oxygen-controlled seed layer in Al-doped ZnO (ZnO:Al) thin films deposited by the industrially compatible dynamic dc magnetron sputter results in both enhanced electron mobilities and appropriate etched morphologies for the Si thin-film solar cells. At the relatively low deposition temperature of 300 °C, optimized ZnO:Al film grown on the seed layer has the carrier mobility of 45 cm<SUP>2</SUP>/V·s and proper postetching morphology with around 1-2-μm crater size. Reduced angular distribution of the (002) grains analyzed by the diffraction rocking curve is shown as the key structural feature for the improved carrier mobility. Finally, the performance of the microcrystalline Si solar cell on the developed ZnO:Al substrate shows high-efficiency potential of the tandem solar cell adapting this transparent conductive oxide substrate.</P>
Sangheon Oh,Jaesung Jo,Hyunjae Lee,Gyo Sub Lee,Jung-Dong Park,Changhwan Shin 대한전자공학회 2015 Journal of semiconductor technology and science Vol.15 No.3
As semiconductor devices are being scaled down, random variation becomes a critical issue, especially in the case of static random access memory (SRAM). Thus, there is an urgent need for statistical methodologies to analyze the impact of random variations on the SRAM. In this paper, we propose a novel sampling method based on the concept of a confidence ellipse. Results show that the proposed method estimates the SRAM margin metrics in highsigma regimes more efficiently than the standard Monte Carlo (MC) method.
Adam Smith in the Tradition of Natural Law Philosophy
Sangheon Lee 서울대학교 경제연구소 1998 經濟論集 Vol.37 No.3
Smith's notion of an invisible hand comes from the discussion of 17th century natural law philosophers and Scottish moral philosophers. Natural jurists argued that social norms are immanent in human nature, but it should be explicated by reasons and upheld by social enforcement. Scottish moral philosophers argued that self-interested individuals spontaneously adopted social norms, once they are explicated by reasons. Smith rejected the necessity of reasons to identify social norms, and argued that spontaneous activities of self-interested individuals bring forward social norms immanent in human nature. Smith also argued that politics of creating social institutions is beyond moral judgement and would provide solutions to the systematic breakdown of a free commercial society.
Lee, Byungho,Lee, Sangheon,Cho, Duckhyung,Kim, Jinhyun,Hwang, Taehyun,Kim, Kyung Hwan,Hong, Seunghun,Moon, Taeho,Park, Byungwoo American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.45
<P>Organic-inorganic hybrid perovskite solar cells have emerged as promising candidates for next-generation solar cells. To attain high photovoltaic efficiency, reducing the defects in perovskites is crucial along with a uniform coating of the films. Also, evaluating the quality of synthesized perovskites via facile and adequate methods is important as well. Herein, CH3NH3PbI3 perovskites were synthesized by applying second solvent dripping to nonstoichiometric precursors containing excess CH3NH3I. The resulting perovskite films exhibited a larger average grain size with a better crystallinity compared to that from stoichiometric precursors. As a result, the performance of planar perovskite solar cells was significantly improved, achieving an efficiency of 14.3%. Furthermore, perovskite films were effectively analyzed using a conductive AFM and noise spectroscopy, which have been uncommon in the field of perovskite solar cells. Comparing the topography and photocurrent maps, the variation of photocurrents in nanoscale was systematically investigated, and a linear relationship between the grain size and photocurrent was revealed. Also, noise analyses with a conductive probe enabled examination of the defect density of perovskites at specific grain interiors by excluding the grain-boundary effect, and reduced defects were clearly observed for the perovskites using CH3NH3I-rich precursors.</P>
Lee, Daeseok,Woo, Jiyong,Park, Sangsu,Cha, Euijun,Lee, Sangheon,Hwang, Hyunsang Institute of Pure and Applied Physics 2014 Japanese Journal of Applied Physics Vol. No.
<P>As semiconductor devices are being increasingly scaled down, complex and high-aspect-ratio (AR) structures become necessary. The spin-on-glass (SOG) method has been considered to be effective for filling high-AR (>50) structures, because it enables low-cost fabrication and it has greater amenability to such structures. However, this method requires high temperatures (>600 degrees C) that can lead to degradation (i.e., oxidation) of adjoining active regions, and additional processes to restore these regions are necessary. We propose a low process temperature (similar to 400 degrees C) SOG method involving high-pressure annealing, for the filling of high-AR structures without the creation of voids. (C) 2014 The Japan Society of Applied Physics</P>
Dirty-Block Tracking in a Direct-Mapped DRAM Cache with Self-Balancing Dispatch
Lee, Dongwoo,Lee, Sangheon,Ryu, Soojung,Choi, Kiyoung Association for Computing Machinery 2017 ACM transactions on architecture and code optimiza Vol.14 No.2
<P>Recently, processors have begun integrating 3D stacked DRAMs with the cores on the same package, and there have been several approaches to effectively utilizing the on-package DRAMs as caches. This article presents an approach that combines the previous approaches in a synergistic way by devising a module called the dirty-block tracker to maintain the dirtiness of each block in a dirty region. The approach avoids unnecessary tag checking for a write operation if the corresponding block in the cache is not dirty. Our simulation results show that the proposed technique achieves a 10.3% performance improvement on average over the state-of-the-art DRAM cache technique.</P>