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1
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Time and Temperature Dependent Damage Characteristics of 5083 Al Alloy under Cavitation-Corrosion Condition

100%
Lee S., Han M., Jeong J., Kim M., Kim S.
Acta Physica Polonica A
|
2016
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vol. 129
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issue 4
747-752
EN
Continuous efforts to construct high-speed and lightweight ship have been made to reduce cost against growing oil prices. In this context, aluminum has received attention as an alternative material for steel, for small and medium-sized ships. In an effort to extend service life of aluminum, various researches have been attempting to improve the corrosion resistance and anti-corrosion characteristics by applying heat treatment and alloying. The material, however, has a high probability of being attacked by corrosion and erosion, caused by high ship speed in severe marine environments. Cavitation damage is dependent on several important factors, such as shape of objects, surface roughness, rotation speed, fluid pressure and velocity. Vapor pressure, density and surface tension of fluid are also taken into account. In this study, an electrochemical cavitation erosion-corrosion experiment was conducted as a function of solution temperature and applied amplitude for 5083-O aluminum alloy used commercially as a hull material for a small sized ship. The result of the experiment revealed that the damage was accelerated due to synergistic effect of corrosion and erosion as the solution temperature was elevated, and that the weight loss showed a steady increase with increasing time of cavitation.
2
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ZnO Nanorods on Nanofibrous ZnO Seed Layers by Hydrothermal Method and Their Annealing Effects

73%
Yim K., Jeon S., Kim M., Kim S., Nam G., Lee D., Kim J., Kim J., Leem J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1
214-216
EN
ZnO nanorods were grown by using the hydrothermal method on p-type Si (100) substrates with nanofibrous ZnO seed layers. Before the ZnO nanorods growth, nanofibrous ZnO seed layers were spin-coated onto the Si substrates. The structural and optical properties of ZnO nanorods were characterized by scanning electron microscopy, X-ray diffraction, and photoluminescence. The fibrous ZnO nanorods is possible due to the surface morphology of the nanofibrous ZnO seed layers. To investigate annealing effects of the ZnO nanorods, the post-annealing process was carried out at various temperatures ranging from 300 to 700C under argon conditions. The structural and optical properties of the ZnO nanorods were also affected by the post-annealing treatment.
3
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Growth and Characterization of Indium-Doped Zinc Oxide Thin Films Prepared by Sol-Gel Method

73%
Kim M., Yim K., Kim S., Nam G., Lee D., Kim J., Kim J., Leem J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1
217-220
EN
Indium-doped ZnO thin films were deposited by sol-gel spin-coating method with various In content. The effects of In content on the structural and optical properties of the indium-doped ZnO thin films were investigated by scanning electron microscopy, X-ray diffraction, and UV-visible spectroscopy. The particle-like surface morphology and the crystallinity of the indium-doped ZnO thin films were affected by change in the In content, especially at the In content of 3 at.%. The values of direct band gap were decreased with increase in the In content. The width of localized states in the optical band gap of the indium-doped ZnO thin films were changed with In content and the Urbach energy (E_{U}) was changed inversely with optical band gap of the indium-doped ZnO thin films.
4
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Optical Properties of Multi-Stacked InAs Quantum Dots Embedded in GaAs/InGaAs Strained Layer and its Annealing Behaviors

59%
Kim D., Kim G., Jeon S., Cho M., Choi H., Kim M., Lee D., Kim J., Kim J., Eom G., Leem J.
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issue 6
941-944
EN
Multi-stacked InAs QDs embedded in ten periods of GaAs/In_{0.1}Ga_{0.9}As strained layers were grown by MBE and their optical properties were investigated by using PL spectroscopy. For the QDs embedded in ten periods of GaAs/In_{0.1}Ga_{0.9}As strained layers, the PL intensity is enhanced about 4.7 times and a narrower FWHM of 26 meV is observed compared to those of the conventional multi-stacked QDs. The PL spectra of the InAs QDs show blue-shifts of about 50 meV with increasing annealing temperature up to 850°C. At annealing temperature of 600°C, the FWHM of the PL peak is reduced to 16 meV and PL intensity is enhanced compared to those of the as-grown sample, which indicates improvement of size uniformity and crystal quality of the QDs.
5
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Fabrication and Characterization of GaN/Polymer Composite p-n Junction with PEDOT Nanoparticle Interface Layer

59%
Kim M., Jin S., Choi H., Kim G., Yim K., Kim S., Nam G., Yoon H., Kim Y., Lee D., Kim J., Kim J., Leem J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 6
875-879
EN
A heavily Si-doped GaN/polymer hybrid structure with p-type poly(3,4-ethylene-dioxythiophene):beta-1,3-glucan (PEDOT nanoparticle) interface layer has been fabricated. The Si-doped GaN thin film with carrier concentration of 1 × 10^{19} cm^{-3} was grown by metal-organic chemical vapor deposition. The PEDOT nanoparticle with various sizes ranging from 60 to 120 nm was synthesized via a miniemulsion polymerization process. The electrical conductivity of the PEDOT nanoparticle is less than 1.2 S/cm. The current-voltage (I-V) characteristic of the hybrid structure shows diode-like behavior. The I-V characteristic was examined in the framework of the thermionic emission model. The ideality factor of the structure without PEDOT nanoparticle interface layer is 12.9. However, the ideality factor of the hybrid structure with PEDOT nanoparticle interface layer is obtained as 1.9. The value of ideality factor is dramatically decreased by inserting the PEDOT nanoparticle interface layer.
6
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Influence of InAs Coverage on Transition of Size Distribution and Optical Properties of InAs Quantum Dots

59%
Kim G., Jeon S., Cho M., Choi H., Kim D., Kim M., Kwon Y., Choe J., Kim J., Kim J., Leem J.
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issue 4
673-676
EN
The influence of InAs coverage on the formation of self-assembled quantum dots grown by molecular-beam epitaxy was investigated by atomic force microscopy and photoluminescence measurements. As the InAs coverage increased from 2.0 to 3.0 monolayers, the quantum dot density decreased from 1.1 × 10^{11} to 1.36 × 10^{10} cm^{-2}. This result could be attributed to the coalescence of neighboring small InAs quantum dots resulting in the formation of much larger InAs quantum dots with lower quantum dot density. Atomic force microscopy results revealed that as the InAs quantum dot coverage increased, the transition of size distribution of InAs quantum dots from single-modal to multimodal occurred. The temperature-dependent photoluminescence spectra showed that the photoluminescence spectra red shifted and the photoluminescence peak intensity decreased as the InAs coverage increased. The thermal activation energy was strongly dependent on the InAs coverage, and for InAs quantum dots with 3.0 ML thick InAs coverage, this energy was estimated to be 147 meV.
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