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- 저자 : J.Senthil (검색결과 30 건)
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레이저 국소증착에 의한 탄소 미세 구조물 제조 및 분광분석
한성일,김진범,Selvan, J.Senthil,정성호 한국레이저가공학회 2002 한국레이저가공학회지 Vol.5 No.2
Characteristics of micro carbon structures fabricated with laser-induced chemical vapor deposition (LCVD) are investigated. An argon ion laser (λ=514.5nm) and ethylene gas were utilized as the energy source and precursor, respectively. The laser beam was focused onto a graphite substrate to produce carbon deposit through thermal decomposition of the precursor. Average growth rate of a carbon rod increased for increasing laser power and pressure. Micro carbon rods with good surface quality were obtained at near the threshold condition. Micro carbon rods with aspect ratio of about 100 and micro tubular structures were fabricated to demonstrate the possible application of this method to the fabrication of three-dimensional microstructures. Laser Raman spectroscopic analysis of the micro carbon structures revealed that the carbon rods are consisting of amorphous carbon.
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Senthil Kumar, M,Park, J Y,Lee, Y S,Chung, S J,Hong, C-H,Suh, E-K Institute of Physics [etc.] 2007 Journal of Physics. D, Applied Physics Vol.40 No.17
<P>Surface morphology of green InGaN/GaN multi-quantum wells (MQWs) on a sapphire substrate with various high temperature grown GaN barriers has been evaluated. Keeping the InGaN well growth temperature constant at 740 °C, a series of MQWs were grown with GaN barrier temperatures varied up to 910 °C. GaN barriers grown below 800 °C lead to the generation of a high density of V-defects and inclusions embedded within V-defects as observed by atomic force microscopy. Scanning electron microscopy and cathodoluminescence (CL) studies revealed that the embedded inclusions are of two kinds: one of them appears as bright spots in CL mapping while the other appears as the surrounding region. Temperature ramping and subsequent interruption for GaN barrier growth suppresses both kinds of inclusion defects and also significantly reduces the V-defect density. An inclusion-free smooth surface is obtained for green emitting InGaN/GaN MQWs with the GaN barrier grown at 910 °C.</P>
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Y. S. Lee,M. Senthil Kumar,T. V. Cuong,J. Y. Park,J. H. Ryu,S. J. Chung,E.-K. Suh,C.-H. Hong 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1
We report an amelioration of the electrical, thermal and optical performances of green InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with AlGaN/GaN short- superlattice (SSL)-inserted structure grown using metal-organic chemical vapor deposition. Ac- cording to an atomic force microscopic study, the GaN template with the SSL-inserted structure shows a signicant reduction in pit density compared to the conventionally-grown template. The insertion of the SSL is also found to alleviate the eect of threading dislocations on the degradation of the electrical performance and promotes the stability of the K-factor and a low thermal resis- tance under a long-term acceleration test. A relatively higher optical output power is obtained for SSL-inserted InGaN/GaN green LEDs at high injection currents. We report an amelioration of the electrical, thermal and optical performances of green InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with AlGaN/GaN short- superlattice (SSL)-inserted structure grown using metal-organic chemical vapor deposition. Ac- cording to an atomic force microscopic study, the GaN template with the SSL-inserted structure shows a signicant reduction in pit density compared to the conventionally-grown template. The insertion of the SSL is also found to alleviate the eect of threading dislocations on the degradation of the electrical performance and promotes the stability of the K-factor and a low thermal resis- tance under a long-term acceleration test. A relatively higher optical output power is obtained for SSL-inserted InGaN/GaN green LEDs at high injection currents.
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Song, Y.H.,Chung, E.J.,Jung, M.K.,Masaki, T.,Senthil, K.,Lee, S.J.,Yoo, J.S.,Yoon, D.H. North-Holland 2014 Materials letters Vol.116 No.-
High quality and single-phase Lu<SUB>3</SUB>Al<SUB>5</SUB>O<SUB>12</SUB> phosphor materials are prepared with a solid state reaction method using CeO<SUB>2</SUB>@B<SUB>2</SUB>O<SUB>3</SUB> core-shell structure. This technique makes it possible to obtain pure phase and allows enhancement of Lu<SUB>3</SUB>Al<SUB>5</SUB>O<SUB>12</SUB> phosphor. The transmittance eletron microscope image and electron energy loss spectrum of the CeO<SUB>2</SUB>@B<SUB>2</SUB>O<SUB>3</SUB> core-shell structure particles show that the B<SUB>2</SUB>O<SUB>3</SUB> coating is uniform, with a thickness of around 10nm, and that the core-shell structure is consisted of Ce and B elements. The Lu<SUB>3</SUB>Al<SUB>5</SUB>O<SUB>12</SUB>: Ce<SUP>3+</SUP> phosphor using CeO<SUB>2</SUB>@B<SUB>2</SUB>O<SUB>3</SUB> core-shell structure shows a higher emission intensity than other ones. The phosphor-converted white LEDs were realized with Lu<SUB>3</SUB>Al<SUB>5</SUB>O<SUB>12</SUB>: Ce<SUP>3+</SUP> phosphor, which shows a high CRI value with a luminous efficacy of 104.58lm/W. This phosphor and the synthesis method are expected to be promising candidates for realizing the white LEDs.
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Experimental and Computational Studies on the Reentry Capsule Aerodynamics with a Flap
Senthil Kumar,J K Prasad,Kim H D 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5
Flow field around a typical reentry capsule has been investigated adopting experiments and computations. The reentry capsule has the flap which could be useful to obtain control force. All the studies have been made at a free stream Mach number of 2 and Reynolds number of 30 X 106. Experiments consisted of schlieren flow visualization and measurement of axial force only. Three dimensional computation has been made using FLUENT and adopting k-ω turbulence model. Effect of angle of attack and flap angle has been obtained. Based on present study, it is observed the flap increases the axial force.
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Interfaces Between Rubber and Metallic or Textile Tire Cords
(Wim J . van Ooij),(Shijian Luo),(Senthil K . Jayaseelan) 한국고무학회 1999 엘라스토머 및 콤포지트 Vol.34 No.4
N/A Bonding metal and textile components to rubber has always posed a problem. In this paper, an attempt had been made to modify textile and metal surfaces for bonding with rubber. The metal surfaces were modified using silane coupling agents and textile fibers were modified using plasma polymerization techniques. Some results on adhesion of metals to a range of sulfur-cured rubber compounds using a combination of organofunctional silanes are given here. The treatment was not only effective for high-sulfur compounds but also for low-sulfur compounds as used in engine mounts and even for some semi-EV compounds. Coatings of plasma-polymerized pyrrole or acetylene were deposited on aramid and polyester tire cords. Standard pull-out force adhesion measurements were used to determine adhesion of tire cords to rubber compounds. The plasma coatings were characterized by various techniques and the performance results are explained in an interpenetrating network model.
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Gnanavadivel J,Senthil Kumar N,Yogalakshmi P 대한전기학회 2017 Journal of Electrical Engineering & Technology Vol.12 No.1
This paper presents the design of closed loop controllers operating a single-phase AC-DC three-level converter for improving power quality at AC mains. Closed loop inhibits outer voltage controller and inner current controller. Simulations of three level converter with three different voltage and current controller combinations such as PI-Hysteresis, Fuzzy-Hysteresis and Fuzzy tuned PI-ysteresis are carried out in MATLAB/Simulink. Performance parameters such as input power factor and source current total harmonic distortion (THD) are considered for comparison of the three controller combinations. The fuzzy-tuned PI voltage controller with hysteresis current controller combination provides a better result, with a source-current THD of 0.93% and unity power factor without any source side filter for the three level converter. For load variations of 25% to 100%, a THD of less than 5% is obtained with a maximum value of only 1.67%. Finally, the fuzzy-tuned PI voltage with hysteresis controller combination is implemented in a Xilinx Spartan-6 XC6SLX25 FPGA board for experimental validation of power quality enhancement. A prototype 100 W, 0-24-48 V as output converter is considered for the testing of controller performance. A source-current THD of 1.351% is obtained in the experimental study with a power factor near unity. For load variations of 25% to 100%, the THD is found to be less than 5%, with a maximum value of only 2.698% in the experimental setup which matches with the simulation results.
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Effects of High-energy Ni-ion Irradiation in the InAlGaN/GaN Heterostructure
M.Senthil Kumar,Y.S. Lee,S.J. Chung,C.-H. Hong,E.-K. Suh 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
We report the effects of high-energy Ni-ion irradiation on the properties of the InAlGaN/GaN heterostructure grown on c-plane sapphire substrates by using a low-pressure metal organic chemical vapor deposition system. The heterostructure was irradiated with 100 MeV Ni ions for a fluence of 5 × 1012 cm−2 at room temperature. The X-ray rocking curve (0002) full width at half maximum (FWHM) value of the as-grown InAlGaN layer was measured to be 250 arcsec and was not affected by Ni-ion irradiation. However, the PL peak intensity of the heterostructure was completely quenched after ion irradiation, and its electrical properties turned to be highly insulating due to irradiation-induced defects. These results indicate that optical and electrical isolation is feasible in InAlGaN/GaN devices without damaging the crystalline quality by using the Ni-ion irradiation. The thermal annealing process could partly recover the optical and electrical properties of the heterostructure whereas, the junction properties of Schottky contacts fabricated on InAlGaN layer could not be restored. We report the effects of high-energy Ni-ion irradiation on the properties of the InAlGaN/GaN heterostructure grown on c-plane sapphire substrates by using a low-pressure metal organic chemical vapor deposition system. The heterostructure was irradiated with 100 MeV Ni ions for a fluence of 5 × 1012 cm−2 at room temperature. The X-ray rocking curve (0002) full width at half maximum (FWHM) value of the as-grown InAlGaN layer was measured to be 250 arcsec and was not affected by Ni-ion irradiation. However, the PL peak intensity of the heterostructure was completely quenched after ion irradiation, and its electrical properties turned to be highly insulating due to irradiation-induced defects. These results indicate that optical and electrical isolation is feasible in InAlGaN/GaN devices without damaging the crystalline quality by using the Ni-ion irradiation. The thermal annealing process could partly recover the optical and electrical properties of the heterostructure whereas, the junction properties of Schottky contacts fabricated on InAlGaN layer could not be restored.
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