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Highly reflective Al-based alloy ohmic contact to p-type GaN
Sanghan Lee,Jun Ho Son,Gwan Ho Jung,Kisoo Kim,Jong-Lam Lee 대한전자공학회 2008 ICEIC:International Conference on Electronics, Inf Vol.1 No.1
We report a metallization scheme of high-reflectance, low-resistance ohmic contact on p-type GaN. The high reflectance of 84 % at the 460 ㎚ wavelength and the specific contact resistivity as low as 8.59 × 10??㎠ were obtained from MgAl-alloy(50 A )/ Ag(3000 A) / Ru(500 A) after annealing at 450 ℃ in air. The formation of Ag-Ga solid solution due to the outdiffusion of Ga after annealing leads to ohmic behavior of the contact. Employing highly reflective MgAl as an contact layer and Ru as an overlayer that suppress the agglomeration and the oxidation of Ag resulted in the high reflectance of the contact.
Lee, Min-Joon,Lee, Sanghan,Oh, Pilgun,Kim, Youngsik,Cho, Jaephil American Chemical Society 2014 NANO LETTERS Vol.14 No.2
<P>Tremendous research works have been done to develop better cathode materials for a large scale battery to be used for electric vehicles (EVs). Spinel LiMn<SUB>2</SUB>O<SUB>4</SUB> has been considered as the most promising cathode among the many candidates due to its advantages of high thermal stability, low cost, abundance, and environmental affinity. However, it still suffers from the surface dissolution of manganese in the electrolyte at elevated temperature, especially above 60 °C, which leads to a severe capacity fading. To overcome this barrier, we here report an imaginative material design; a novel heterostructure LiMn<SUB>2</SUB>O<SUB>4</SUB> with epitaxially grown layered (<I>R</I>3̅<I>m</I>) surface phase. No defect was observed at the interface between the host spinel and layered surface phase, which provides an efficient path for the ionic and electronic mobility. In addition, the layered surface phase protects the host spinel from being directly exposed to the highly active electrolyte at 60 °C. The unique characteristics of the heterostructure LiMn<SUB>2</SUB>O<SUB>4</SUB> phase exhibited a discharge capacity of 123 mAh g<SUP>–1</SUP> and retained 85% of its initial capacity at the elevated temperature (60 °C) after 100 cycles.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-2/nl404430e/production/images/medium/nl-2013-04430e_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl404430e'>ACS Electronic Supporting Info</A></P>
SangHan Lee,Insung Lee,Yul Roh 한국지질과학협의회 2003 Geosciences Journal Vol.7 No.3
Formation of Fe(II)-containing mineral throughmicrobial processes may play an important role in iron and car-bon geochemistry in subsurface environments. Fe(III)-reducingbacteria form Fe(II)-containing minerals such as siderite, magne-tite, vivianite, and green rust using iron oxides. A psychrotolerantFe(III)-reducing bacterium, Shewanella alga (PV-4), was used toexamine the reduction and biomineralization of a poorly crystal-line iron oxide, akaganeite (b-FeOOH), in the absence of a solubleelectron shuttle, anthraquinone disulphonate (AQDS), under dif-ferent atmospheric compositions as well as in HCO3- bufferedmedium (30 to 210 mM). Iron biomineralization was also exam-ined under different growth conditions such as incubation time,electron donors, and electron acceptors. The Fe(III)-reducing bac-terium, PV-4, reduced akaganeite, Fe(III)-citrate, and Co(III)-EDTA using lactate or H2 as an electron donor. The iron biomin-eralization of Fe(III) oxide, akaganeite-as it undergos reductionby an iron reducing bacterium-is a complex process influenced bybiogeochemical factors including microorganisms, bicarbonatebuffer concentration, atmospheric composition, electron donors/acceptors, incubation time, and Eh/pH. From this research wefound that microorganisms do participate in the formation ofdiverse iron minerals and that microbial iron biomineralizationmay affect Fe and C biogeochemistry in subsurface environments.
Estimating monotone convex functions via sequential shape modification
Lee, Sanghan,Lim, Johan,Kim, Seung-Jean,Joo, Yongsung Taylor Francis 2009 JOURNAL OF STATISTICAL COMPUTATION AND SIMULATION Vol.79 No.8
<P> We propose a sequential method to estimate monotone convex functions that consists of: (i) monotone regression via solving a constrained least square (LS) problem and (ii) convexification of the monotone regression estimate via solving a uniform approximation problem with associated constraints. We show that this method is faster than the constrained LS method. The ratio of computation time increases as data size increases. Moreover, we show that, under an appropriate smoothness condition, the uniform convergence rate achieved by the proposed method is nearly comparable to the best achievable rate for a non-parametric estimate which ignores the shape constraint. Simulation studies show that our method is comparable to the constrained LS method in estimation error. We illustrate our method by analysing ground water level data of wells in Korea.</P>
Lee, Sanghan,Cho, Yonghyun,Song, Hyun‐,Kon,Lee, Kyu Tae,Cho, Jaephil WILEY‐VCH Verlag 2012 Angewandte Chemie Vol.124 No.35
<P><B>Elektrisierende Ergebnisse</B>: Die Entladungsrate von Lithiumionenbatterien (LIBs) lässt sich durch Verkleinern der Abmessungen des aktiven Materials erhöhen, was allerdings zu LIBs mit unzureichenden Elektrodendichten führen würde. Dieses Problem wurde gelöst, indem kohlenstoffbeschichtete einkristalline LiMn<SUB>2</SUB>O<SUB>4</SUB>‐Nanopartikelcluster als LIB‐Kathodenmaterial synthetisiert wurden; dieses Material kann auf dem Stromkollektor dicht gepackt werden.</P>
Stacked porous tin phosphate nanodisk anodes
Lee, Sanghan,Cho, Jaephil Royal Society of Chemistry 2010 Chemical communications Vol.46 No.14
<P>Stacked porous octahedral tin phosphate Sn<SUB>2</SUB>P<SUB>2</SUB>O<SUB>7</SUB> nanodisks, with a thickness and a width of 20 nm and 200 nm, respectively, were prepared from quenching hydrothermally prepared (SnHPO<SUB>4</SUB>)<SUB>2</SUB>·H<SUB>2</SUB>O at 600 °C. The first discharge capacity was 600 mA h g<SUP>−1</SUP> while the capacity retention, even after 220 cycles, was 93%.</P> <P>Graphic Abstract</P><P>Stacked porous octahedral tin phosphate Sn<SUB>2</SUB>P<SUB>2</SUB>O<SUB>7</SUB> nanodisks, with a thickness and a width of 20 nm and 200 nm, respectively, were prepared from quenching hydrothermally prepared (SnHPO<SUB>4</SUB>)<SUB>2</SUB>·H<SUB>2</SUB>O at 600 °C. The first discharge capacity was 600 mA h g<SUP>−1</SUP> while the capacity retention, even after 220 cycles, was 93%. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b924381j'> </P>