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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>
Adversarial Detection with Gaussian Process Regression-based Detector
( Sangheon Lee ),( Noo-ri Kim ),( Youngwha Cho ),( Jae-young Choi ),( Suntae Kim ),( Jeong-ah Kim ),( Jee-hyong Lee ) 한국인터넷정보학회 2019 KSII Transactions on Internet and Information Syst Vol.13 No.8
Adversarial attack is a technique that causes a malfunction of classification models by adding noise that cannot be distinguished by humans, which poses a threat to a deep learning model. In this paper, we propose an efficient method to detect adversarial images using Gaussian process regression. Existing deep learning-based adversarial detection methods require numerous adversarial images for their training. The proposed method overcomes this problem by performing classification based on the statistical features of adversarial images and clean images that are extracted by Gaussian process regression with a small number of images. This technique can determine whether the input image is an adversarial image by applying Gaussian process regression based on the intermediate output value of the classification model. Experimental results show that the proposed method achieves higher detection performance than the other deep learning-based adversarial detection methods for powerful attacks. In particular, the Gaussian process regression-based detector shows better detection performance than the baseline models for most attacks in the case with fewer adversarial examples.
Lee, Sangheon,Flanagan, Joseph C.,Lee, Byungho,Hwang, Taehyun,Kim, Jaewook,Gil, Bumjin,Shim, Moonsub,Park, Byungwoo American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.37
<P>One-dimensionally elongated nanoparticles with type-II staggered band offset are of potential use as light-harvesting materials for photovoltaics, but only a limited attention has been given to elucidate the factors governing the cell performance obtainable from such materials. Herein, we describe a combined strategy to enhance charge collection from CdSe/CdSexTe1-x type-II heterojunction nanorods (HNRs) utilized as light harvesters for sensitized solar cells. By integrating morphology- and composition-tuned type-II HNRs into solar cells, factors that yield interfaces favorable both for the electron injection into TiO2 and hole transfer to electrolyte are examined. Furthermore, it is shown that a more efficient photovoltaic system results from cosensitization with CdS quantum dots (QDs) predeposited on a TiO2 scaffold, which improves charge collection from HNRs. Electrochemical impedance spectroscopy (EIS) analysis suggests that such a synergistically enhanced system benefits from the decreased recombination within HNRs and facilitated charge transport through the cosensitized TiO2 electrode, even with the activation of a recombination path presumably related to the photogenerated holes in CdS QDs.</P>
Lee, Sangheon,Flanagan, Joseph C.,Kim, Jaewook,Yun, Alan Jiwan,Lee, Byungho,Shim, Moonsub,Park, Byungwoo American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.21
<P>Here, we report the successful application of core/patchy-shell CdSe/CdSe<SUB><I>x</I></SUB>Te<SUB>1-<I>x</I></SUB> type-II heterojunction nanorods (HNRs) to realize efficient sensitized solar cells. The core/patchy-shell structure designed to have a large type-II heterointerface without completely shielding the CdSe core significantly improves photovoltaic performance compared to other HNRs with minimal or full-coverage shells. In addition, cosensitization with CdS grown by successive ionic layer adsorption and reaction further improves the power conversion efficiency. One-diode model analysis reveals that the HNRs having exposed CdSe cores and suitably grown CdS result in significant reduction of series resistance. Investigation of the intercorrelation between diode quality parameters, diode saturation current density (<I>J</I><SUB>0</SUB>) and recombination order (β = (ideality factor)<SUP>−1</SUP>) reveals that HNRs with open CdSe cores exhibit reduced recombination. These results confirm that the superior performance of core/patchy-shell HNRs results from their fine-tuned structure: photocurrent is increased by the large type-II heterointerface and recombination is effectively suppressed due to the open CdSe core enabling facile electron extraction. An optimized power conversion efficiency of 5.47% (5.89% with modified electrode configuration) is reported, which is unmatched among photovoltaics utilizing anisotropic colloidal heterostructures as light-harvesting materials.</P> [FIG OMISSION]</BR>
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.