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Pervez, Syed Atif,Kim, Doohun,Doh, Chil-Hoon,Farooq, Umer,Choi, Hae-Young,Choi, Jung-Hee American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.14
<P>A novel design for an anodic WO<SUB>3</SUB> mesosponge @ carbon has been introduced as a highly stable and long cyclic life Li-ion battery electrode. The nanocomposite was successfully synthesized via single-step electrochemical anodization and subsequent heat treatment in an acetylene and argon gas environment. Morphological and compositional characterization of the resultant materials revealed that the composite consisted of a three-dimensional interconnected network of WO<SUB>3</SUB> mesosponge layers conformally coated with a 5 nm thick carbon layer and grown directly on top of tungsten metal. The results demonstrated that the carbon-coated mesosponge WO<SUB>3</SUB> layers exhibit a capacity retention of 87% after completion of 100 charge/discharge cycles, which is significantly higher than the values of 25% for the crystalline (without carbon coating) or 40% for the as-prepared mesosponge WO<SUB>3</SUB> layers. The improved electrochemical response was attributed to the higher stability and enhanced electrical conductivity offered by the carbon coating layer.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-14/acsami.5b00341/production/images/medium/am-2015-00341b_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b00341'>ACS Electronic Supporting Info</A></P>
Pervez, Syed Atif,Kim, Doohun,Farooq, Umer,Yaqub, Adnan,Choi, Jung-Hee,Lee, You-Jin,Doh, Chil-Hoon American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.14
<P>This work is a comparative study of the electrochemical performance of crystalline and amorphous anodic iron oxide nanotube layers. These nanotube layers were grown directly on top of an iron current collector with a vertical orientation via a simple one-step synthesis. The crystalline structures were obtained by heat treating the as-prepared (amorphous) iron oxide nanotube layers in ambient air environment. A detailed morphological and compositional characterization of the resultant materials was performed via transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectroscopy. The XRD patterns were further analyzed using Rietveld refinements to gain in-depth information on their quantitative phase and crystal structures after heat treatment. The results demonstrated that the crystalline iron oxide nanotube layers exhibit better electrochemical properties than the amorphous iron oxide nanotube layers when evaluated in terms of the areal capacity, rate capability, and cycling performance. Such an improved electrochemical response was attributed to the morphology and three-dimensional framework of the crystalline nanotube layers offering short, multidirectional transport lengths, which favor rapid Li<SUP>+</SUP> ions diffusivity and electron transport.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-14/am501370f/production/images/medium/am-2014-01370f_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am501370f'>ACS Electronic Supporting Info</A></P>
Improved Performance of Ag-nanoparticle-decorated TiO2 Nanotube Arrays in Li-ion Batteries
Syed Atif Pervez,Umer Farooq,Adnan Yaqub,Chil-Hoon Doh,김두헌,심성주,황민지,최정희,이유진 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.9
The present work investigates the electrochemical response of silver nanoparticle (Ag-NP)-decorated TiO2 nanotube (NT) layers as an anode material for a lithium-ion battery. Self-organizednanotube layers with a thickness of approximately 1 µm and a diameter of approximately 100nm were grown by anodization of Ti in a fluoride-containing aqueous electrolyte. Ag NPs (averageparticle size of ~ 10 nm) were deposited both inside and outside the nanotube geometry ina well-distributed manner through a simple and efficient photocatalytic reduction process. Themorphology and the chemical composition of the resulting materials were characterized by usingfield-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and energy dispersiveX-ray spectroscopy (EDX). Our results show that the TiO2 NT layers decorated with Ag NPshad a superior electrochemical response in terms of charge/discharge capacity, rate capability, cyclicperformance and columbic efficiency. The enhanced performance is attributed to the improved electronicand ionic conductivity, obtained by providing highly conductive paths to electrons flowingthrough a well-distributed Ag NPs deposition on the walls of the highly-oriented NTs.
셰드(Syed Atif Pervez),김희상(Heesang Kim),라흐만(Atteq-Ur-Rehman),이종호(Jong-Ho Lee),박병국(Byung-Gook Park),신형철(Hyungcheol Shin) 大韓電子工學會 2010 電子工學會論文誌-SD (Semiconductor and devices) Vol.47 No.3
Saddle MOSFET의 모서리의 효과에 대한 고전역학과 양자역학적 시뮬레이션의 비교분석을 3차원 수치 시뮬레이터를 사용하여 수행하였다. 비교분석 결과 양자역학적 시뮬레이션에서는 실리콘 핀의 단면에서의 정확한 최대 전자 밀도의 위치와 크기를 제공함으로써 소자의 정확한 설명을 제공하는 것을 보여 주었고, 이를 이용하여 모서리 효과 및 그것이 소자의 문턱전압의 특성을 미치는 영향의 정확한 분석이 실행되었다. 또한, 모서리 효과를 억제하기 위해서 실리콘 핀의 모서리를 둥글게 하거나 구석의 바디도핑을 낮추는 두 가지 가능한 기법을 제시했다. A comparative analysis of quantum-mechanical and classical simulation regarding corner effect in a Saddle MOSFET has been carried out using a 3-D numerical simulator. The comparison has shown that quantum simulation gives correct description of device by providing accurate peak E-density position and magnitude at the Si-fin cross-section, hence accurate analysis of corner effect and its impact on device threshold voltage (Vth) characteristics is carried out. Moreover, rounding the Si-fin corners or lowering the body doping have been shown as two possible techniques to suppress the undesirable corner effect.
Adnan Yaqub,Syed Atif Pervez,Umer Farooq,Mohsin Saleem,도칠훈,You-Jin Lee,Minji Hwang,Jeong-Hee Choi,Doohun Kim 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.3
A new conductive material, copper/Super-P carbon black composite (Cu-SPB), is prepared viaan efficient ion reducing method for use in low-temperature lithium-ion batteries (LIBs). Thepresent study investigated the effects of copper content on the low-temperature performance ofLIBs. Electrodes prepared with a high-copper-content conductive material (Cu = 18.54%) showedremarkably improved performance in terms of capacity retention (around 40%), cycling stability, andcolumbic efficiency. The electrochemical impedance spectroscopy (EIS) analysis revealed that thepresence of higher Cu contents could reduce the cell’s impedance. The results were also confirmedby using a coin-type full cell’s improved capacity retention, which indicated the significance of Cuparticles in enhancing the low-temperature performance of LIBs.
셰드,김희상,라흐만,이종호,박병국,신형철,Pervez, Syed Atif,Kim, Hee-Sang,Rehman, Atteq-Ur,Lee, Jong-Ho,Park, Byung-Gook,Shin, Hyung-Cheol The Institute of Electronics and Information Engin 2010 電子工學會論文誌-CI (Computer and Information) Vol.47 No.3
Saddle MOSFET의 모서리의 효과에 대한 고전역학과 양자역학적 시뮬레이션의 비교분석을 3차원 수치 시뮬레이터를 사용하여 수행하였다. 비교분석 결과 양자역학적 시뮬레이션에서는 실리콘 핀의 단면에서의 정확한 최대 전자 밀도의 위치와 크기를 제공함으로써 소자의 정확한 설명을 제공하는 것을 보여 주었고, 이를 이용하여 모서리 효과 및 그것이 소자의 문턱전압의 특성을 미치는 영향의 정확한 분석이 실행되었다. 또한, 모서리 효과를 억제하기 위해서 실리콘 핀의 모서리를 둥글게 하거나 구석의 바디도핑을 낮추는 두 가지 가능한 기법을 제시했다. A comparative analysis of quantum-mechanical and classical simulation regarding corner effect in a Saddle MOSFET has been carried out using a 3-D numerical simulator. The comparison has shown that quantum simulation gives correct description of device by providing accurate peak E-density position and magnitude at the Si-fin cross-section, hence accurate analysis of corner effect and its impact on device threshold voltage (Vth) characteristics is carried out. Moreover, rounding the Si-fin comers or lowering the body doping have been shown as two possible techniques to suppress the undesirable corner effect.
Farooq, Umer,Doh, Chil-Hoon,Pervez, Syed Atif,Kim, Doo-Hun,Lee, Sang-Hoon,Saleem, Mohsin,Sim, Seong-Ju,Choi, Jeong-Hee Korean Carbon Society 2016 Carbon Letters Vol.17 No.-
The work presented in this report was a detailed comparative study of the electrochemical response exhibited by graphite anodes in Li-ion batteries having different physical features. A comprehensive morphological and physical characterization was carried out for these graphite samples via X-ray diffraction and scanning electron microscopy. Later, the electrochemical performance was analyzed using galvanostatic charge/discharge testing and the galvanostatic intermittent titration technique for these graphite samples as negative electrode materials in battery operation. The results demonstrated that a material having a higher crystalline order exhibits enhanced electrochemical properties when evaluated in terms of rate-capability performance. All these materials were investigated at high C-rates ranging from 0.1C up to 10C. Such improved response was attributed to the crystalline morphology providing short layers, which facilitate rapid Li<sup>+</sup> ions diffusivity and electron transport during the course of battery operation. The values obtained for the electrical conductivity of these graphite anodes support this possible explanation.
Electrically exploded silicon/carbon nanocomposite as anode material for lithium-ion batteries.
Farooq, Umer,Choi, Jeong-Hee,Kim, Doohun,Pervez, Syed Atif,Yaqub, Adnan,Hwang, Min-Ji,Lee, You-Jin,Lee, Won-Jae,Choi, Hae-Young,Lee, Sang-Hoon,You, Ji-Hyun,Ha, Chung-Wan,Doh, Chil-Hoon American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.12
<P>In this work, silicon (Si) containing carbon coated core-shell nanostructures were synthesized by electrical explosion of Si wires in ethanol solution followed by high energy mechanical milling (HEMM) process. Material characterization was carried-out using transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analysis. HEMM led to very fine and amorphous Si particles in the presence of carbon and inactive Silicon-Carbide (SiC) matrix. These Si based nanocomposites, obtained through electrical explosion followed by HEMM (milled sample), exhibited enhanced electrochemical performance than unmilled nanocomposites, when evaluated as anode material for lithium-ion batteries (LIBs). On completion of (the) 1st cycle, milled and unmilled sample(s) showed specific discharge capacities around 825 mAh/g and 717 mAh/g, respectively. Interestingly, the coulombic efficiencies of milled and unmilled samples were 98.5% and 97% after 60th cycle respectively. The enhanced electrochemical performance is attributed to fine and amorphous Si based nanocomposite obtained through HEMM process.</P>