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Electronic and optical properties of CdS/CdZnS nanocrystals

Chinese Physics B 2012年第8期21卷 441-448页

作者： A.John Peter chang woo lee epartment of Chemical Engineering and Green Energy Center College of EngineeringKyung Hee University1 SeochunGihungYonginGyeonggi 446-701S.Korea Department of Physics Govt.Arts CollegeMelurMadurai-62510India Department of Chemical Engineering and Green Energy Center College of EngineeringKyung Hee University1 SeochunGihungYonginGyeonggi 446-701S.Korea

Cd1-xZnxS nanocrystals are prepared by a co-precipitation method with different atomic fractions of Zn. The texture, structural transformation and optical properties with increasing x value in Cd1-xZnxS are studied with scanning electron microscopy, electron diffraction patterning, and absorption spectra respectively. Quantum confinement in a strained CdS/Cd1-xZnxS related nanodot with various Zn content values is investigated theoretically. Binding energies on exciton bound CdS/CdxZn1-xS quantum dot are computed, with consideration of the internal electric field induced by the spontaneous and piezoelectric polarizations, and thereby the interband emission energy is calculated as a function of the dot radius. The optical band gap from the UV absorption spectrum is compared with the interband emission energy computed theoretically. Our results show that the average diameter of composite nanoparticles ranges from 3 nm to 6 nm. The X-ray diffraction pattern shows that all the peaks shift towards the higher diffracting angles with an increase in Zn content. The lattice constant gradually decreases as the Zn content increases. The strong absorption edge shifts towards the lower wavelength region and hence the band gap of the films increases as the Zn content increases. The values of the absorption edge are found to shift towards the shorter wave length region and hence the direct band gap energy varies from 2.5 eV for the CdS film and 3.5 eV for the ZnS film. Our numerical results are in good agreement with the experimental results.

关键词： quantum dots quasicrystals semiconductor

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Radiative life time of an exciton confined in a strained GaN/Ga_(1-x)Al_xN cylindrical dot:built-in electric field effects

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Chinese Physics B 2011年第7期20卷 367-372页

作者： chang woo lee A.John Peter Department of Chemical Engineering and Green Energy Center College of EngineeringKyung Hee University1 SeochunGihungYonginGyeonggi 446-701Republic of Korea Department of Physics Government Arts and Science CollegeMelur-625106India

The binding energy of an exciton in a wurtzite GaN/GaAlN strained cylindrical quantum dot is investigated theoretically. The strong built-in electric field due to the spontaneous and piezoelectric polarizations of a GaN/GaAlN quantum dot is included. Numerical calculations are performed using a variational procedure within the single band effective mass approximation. Valence-band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. The exciton oscillator strength and the exciton lifetime for radiative recombination each as a function of dot radius have been computed. The result elucidates that the strong built-in electric field influences the oscillator strength and the recombination life time of the exciton. It is observed that the ground state exciton binding energy and the interband emission energy increase when the cylindrical quantum dot height or radius is decreased, and that the exciton binding energy, the oscillator strength and the radiative lifetime each as a function of structural parameters （height and radius） sensitively depend on the strong built-in electric field. The obtained results are useful for the design of some opto-photoelectronic devices.

关键词： quantum dot donor bound excitons oscillator strength

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Photo-Induced Electron Spin Polarization in a Narrow Band Gap Semiconductor Nanostructure

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Chinese Physics Letters 2012年第11期29卷 186-190页

作者： A.John Peter chang woo lee Department of Chemical Engineering and Green Energy Center College of EngineeringKyung Hee University1 SeochunGihungYonginGyeonggi 446-701S.Korea

Photo-induced spin dependent electron transmission through a narrow gap InSb/InGa_(x)Sb_(1-x) semiconductor symmetric well is theoretically studied using transfer matrix *** transparency of electron transmission is calculated as a function of electron energy for different concentrations of *** spin-polarized photon assisted resonant tunnelling in the heterostructure due to Dresselhaus and Rashba spin-orbit coupling induced splitting of the resonant level and compressed spin-polarization are *** results show that Dresselhaus spin-orbit coupling is dominant for the photon effect and the computed polarization efficiency increases with the photon effect and the gallium concentration.

关键词： polarization resonant photon

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Biomass seaweed-derived n itrogen self-doped porous carb on anodes for sodium-ion batteries:Insights into the structure and electrochemical activity

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Journal of Energy Chemistry 2022年第1期31卷 286-295,I0008页

作者： Chenrayan Senthil Jae woo Park Nitheesha Shaji Gyu Sang Sim chang woo lee Department of Chemical Engineering(Integrated Engineering)&Center for the SMART Energy Platform College of EngineeringKyung Hee University1732 Deogyeong-daeroCihuengYonginGyeonggi 17104South Korea

Sustainable transformation and efficient utilization of biomasses and their derived materials are environ-mentally as well as economically compliant *** seaweed-derived nitrogen self-doped porous carbon with tailored surface area and pore structures are prepared through carb on izatio n and *** in fluence of carb on ization temperature on morphology,surface area,and heteroatom dopants are investigated to optimize sodium-ion storage ***-derived nitrogen selfdoped activated carbon(SAC)as anode materials for sodium-ion batteries exhibits remarkable reversible capacity of 303/192 mAh g^(-1) after 100/500 cycles at current densities of 100/200 mA g^(-1) respectively,and a good rate *** interconnected and porous conducting nature along with the heteroatom dopant role in creating defective sites and charge stabilization are favorable for ion storage and diffusion and electron transport,indicating the electrodes can offer improved electrochemical *** addition,post-mortem analysis of the cycled carbon electrodes through ex-situ tools demonstrates the sodium-ion storage mechanism.

关键词： Biomass Heteroatom self-doping Porous carbon Anode Sodium-ion batteries Post-mortem ex-situ analysis

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Advancing Li-ion storage performance with hybrid vertical carbon/Ni_(3)S_(2)-based electrodes

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Journal of Energy Chemistry 2022年第4期31卷 8-18页

作者： Neelakandan M.Santhosh Nitheesha Shaji d Petra Stražar Gregor Filipič Janez Zavašnik chang Won Ho Murugan Nanthagopal chang woo lee UrošCvelbar Department of Gaseous Electronics(F6) Jožef Stefan InstituteJamova cesta 39SI-1000 LjubljanaEUSlovenia Jožef Stefan International Postgraduate School Jamova cesta 39SI-1000 LjubljanaEUSlovenia Faculty of Mathematics and Physics University of LjubljanaJadranska cesta 19SI-1000 LjubljanaEUSlovenia Department of Chemical Engineering(Integrated Engineering) College of EngineeringKyung Hee University1732 Deogyeong-daeroGiheungYonginGyeonggi 17104South Korea Center for the SMART Energy Platform College of EngineeringKyung Hee University1732 Deogyeong-daeroGiheungYonginGyeonggi 17104South Korea

Conversion-reaction induced charge storage mechanisms of transition metal sulphides have received considerable interest in designing high-capacity electrodes for electrochemical energy storage ***,their low conductivity and structural degradation during cycling limit their applications as energy storage devices.A combination of different nickel sulphide phases tailored with carbon nanostructures is suggested to address these ***,a facile,two-step approach is demonstrated for fabricating a hybrid electrode,consisting of trinickel disulphide(Ni_(3)S_(2))formed on a metallic Ni nanoparticle supported by vertical carbon nanotubes(VCN)backbone in the form Ni_(3)S_(2)/Ni@***_(3)S_(2)/Ni@VCN electrodes were tested as anode for lithium-ion batteries,and the electrode featured outstanding lithiumstorage capabilities with a high reversible capacity(1113 m Ah g^(-1) after 100 cycles at 100 m A g^(-1)),excellent long-term cycling stability(770 m Ah g^(-1) after 500 cycles at 200 m A g^(-1)),and good rate *** resulting electrode performance is one of the best Li-ion storage capabilities in the Ni_(3)S_(2)-type anode materials described.A unique “broccoli-like”structure of polycrystalline Ni_(3)S_(2)capped on conductive VCN backbone helps the interface storage process and boosts lithium storage performance.

关键词： Ni_(3)S_(2) Vertical carbon nanostructures Hierarchical structures Binder-free electrode Lithium-ion batteries

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Ssu72 is a T-cell receptor-responsive modifier that is indispensable for regulatory T cells

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Cellular & Molecular Immunology 2021年第6期18卷 1395-1411页

作者： Jin-Kwan lee Seo-Young Koo Hye-Mi Nam Jee-Boong lee Jiwon Ko Kyung-Mo Kim Eun-Ji Park Tae Jin Kim Ho lee Heounjeong Go chang-woo lee Research Institute Curogen TechnologySuwonSouth Korea Department of Molecular Cell Biology Samsung Medical CenterSungkyunkwan University School of MedicineSuwonSouth Korea MOGAM Institute for Biomedical Research GyeonggiSouth Korea Department of Pathology Asan Medical CenterUniversity of Ulsan College of MedicineSeoulSouth Korea Asan Institute for Life Sciences Asan Medical CenterUniversity of Ulsan College of MedicineSeoulSouth Korea Department of Immunology Sungkyunkwan University School of MedicineSeoulSouth Korea Department of Cancer Biomedical Science Graduate School of Cancer Science and PolicyResearch InstituteNational Cancer CenterGyeonggiSouth Korea

The homeostatic balance between effector T cells and regulatory T cells(Tregs)is crucial for adaptive immunity;however,epigenetic programs that inhibit phosphorylation to regulate Treg development,peripheral expression,and suppressive activity are ***,we found that the Ssu72 phosphatase is activated by various T-cell receptor signaling pathways,including the T-cell receptor and IL-2R pathways,and localizes at the cell *** of Ssu72 in T cells disrupts CD4+T-cell differentiation into Tregs in the periphery via the production of high levels of the effector cytokines IL-2 and IFNγ,which induce CD4+T-cell activation and differentiation into effector cell *** also found a close correlation between downregulation of Ssu72 and severe defects in mucosal tolerance in ***,Ssu72 forms a complex with PLCγ1,which is an essential effector molecule for T-cell receptor signaling as well as Treg development and ***72 deficiency impairs PLCγ1 downstream signaling and results in failure of Foxp3 ***,our studies show that the Ssu72-mediated cytokine response coordinates the differentiation and function of Treg cells in the periphery.

关键词： Ssu72 Regulatory T cells FoxP3 T cell receptor Autoimmunity

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Random pinhole attenuator for high-power laser beams

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High Power Laser Science and Engineering 2024年第3期12卷 116-121页

作者： Seong Cheol Park Hyeok Yun Jin woo Yoon Seong Ku lee Jae Hee Sung Il woo Choi chang Hee Nam Kyung Taec Kim Department of Physics and Photon Science Gwangju Institute of Science and TechnologyGwangjuRepublic of Korea Center for Relativistic Laser Science Institute for Basic ScienceGwangjuRepublic of Korea Advanced Photonics Research Institute Gwangju Institute of Science and TechnologyGwangjuRepublic of Korea

The intensity attenuation of a high-power laser is a frequent task in the measurements of optical *** intensity can be attenuated by inserting an optical element,such as a partial reflector,polarizer or absorption *** devices are,however,not always easily applicable,especially in the case of ultra-high-power lasers,because they can alter the characteristics of a laser beam or become easily *** this study,we demonstrated that the intensity of a laser beam could be effectively attenuated using a random pinhole attenuator(RPA),a device with randomly distributed pinholes,without changing the beam *** this device,a multi-PW laser beam was successfully attenuated and the focused beam profile was measured without any alterations of its *** addition,it was confirmed that the temporal profile of a laser pulse,including the spectral phase,was ***,the RPA possesses significant potential for a wide range of applications.

关键词： high-power laser intensity attenuation laser diagnostics

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Optical properties of excitons in strained Ga_x In_1-x As/GaAs quantum dot: effect of geometrical confinement on exciton g-factor

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Chinese Optics Letters 2013年第8期11卷 80-86页

作者： N. R. Senthil Kumar A. John Peter chang woo lee Department of Physics RVS School of Engineering College Department of Physics Govt.Arts College Department of Chemical Engineering and Green Energy Center College of EngineeringKyung Hee University

Taking into account anisotropy, nonparabolicity of the conduction band, and geometrical confinement, we discuss the heavy-hole excitonic states in a strained GaxIn1-xAs/GaAs quantum dot for various Ga alloy contents. The strained quantum dot is considered as a spherical InAs dot surrounded by a GaAs barrier material. The dependence of the effective excitonic g-factor as a function of dot radius and Ga ion content is numerically measured. Interband optical energy with and without the parabolic effect is computed using structural confinement. The interband matrix element for different Ga concentrations is also calculated. The oscillator strength of interband transitions on the dot radius is studied at different Ga concentrations in the GaxIn1-xAs/GaAs quantum dot. Heavy-hole excitonic absorption spectra are recorded for various Ga alloy contents in the GaxIn1-xAs/GaAs quantum dot. Results show that oscillator strength diminishes when dot size decreases because of the dominance of the quantum size effect. Furthermore, exchange enhancement and exchange sDlitting increase as exciton confinement inereases.

关键词： GaAs effect of geometrical confinement on exciton g-factor Optical properties of excitons in strained Gax In1-x As/GaAs quantum dot

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Spontaneous Spin Polarization of Electrons by Diluted Magnetic Heterostructures

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Journal of Modern Physics 2011年第11期2卷 1272-1279页

作者： chang woo lee Amalorpavam John Peter 不详

The spin dependent electron transmission phenomenon in a diluted resonant semiconductor heterostructure is employed theoretically to investigate the output transmission current polarization at zero magnetic field. Transparency of electron transmission is calculated as a function of electron energy and the well width, within the one electron band approximation along with the spin orbit interaction. Enhanced spin-polarized resonant tunneling in the heterostructure due to Dresselhaus and Rashba spin-orbit coupling induced splitting of the resonant level is observed. We predict that a spin-polarized current spontaneously emerges in this heterostructure and we estimate theoretically that the polarization can reach 40%. This effect could be employed in the fabrication of spin filters, spin injectors and detectors based on non-magnetic semiconductors.

关键词： Spin Polarized Transport Spin Injection Spin-Orbit Coupling Resonant Tunneling

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Generalized polynomial chaos expansion by reanalysis using static condensation based on substructuring

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Applied Mathematics and Mechanics(English Edition) 2024年第5期45卷 819-836页

作者： D.lee S.chang J.lee Department of Automotive Engineering Hanyang UniversitySeoul 04763Republic of Korea School of Mechanical Engineering Chungnam National UniversityDaejeon 34134Republic of Korea Department of Mechanical Robotics and Energy EngineeringDongguk UniversitySeoul 04620Republic of Korea

This paper presents a new computational method for forward uncertainty quantification(UQ)analyses on large-scale structural systems in the presence of arbitrary and dependent random *** method consists of a generalized polynomial chaos expansion(GPCE)for statistical moment and reliability analyses associated with the stochastic output and a static reanalysis method to generate the input-output data *** the reanalysis,we employ substructuring for a structure to isolate its local regions that vary due to random *** allows for avoiding repeated computations of invariant substructures while generating the input-output data *** substructuring with static condensation further improves the computational efficiency of the reanalysis without losing ***,the GPCE with the static reanalysis method can achieve significant computational saving,thus mitigating the curse of dimensionality to some degree for UQ under high-dimensional *** numerical results obtained from a simple structure indicate that the proposed method for UQ produces accurate solutions more efficiently than the GPCE using full finite element analyses(FEAs).We also demonstrate the efficiency and scalability of the proposed method by executing UQ for a large-scale wing-box structure under ten-dimensional(all-dependent)random inputs.

关键词： forward uncertainty quantification(UQ) generalized polynomial chaos expansion(GPCE) static reanalysis method static condensation substructuring

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