• JSTS:Journal of Semiconductor Technology and Science
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• 제3권2호
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• pp.96-101
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• 2003

Direct evidence on the incorporation of high concentration of oxygen into undoped AlGaN layers for the AlGaN/GaN heterostuctures is provided by scanning photoemission microscopy using synchrotron radiation. In-situ annealing at $1000^{\circ}C$ resulted in a significant increase in the oxygen concentration at the AlGaN surface due to the predominant formation of Al-O bonds. The oxygen incorporation into the AlGaN layers resulting from the high reactivity of Al to oxygen can enhance the tunneling-assisted transport of electrons at the metal/AlGaN interface, leading to the reduction of the Schottky barrier height and the increase of the sheet carrier concentration near the AlGaN/GaN interface.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.171-171
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• 2011

Co and Fe doped multi-wall carbon nano-tubes (MWCNTs) synthesized by microwave plasma enhanced chemical vapor deposition (PECVD) technique are investigated with synchrotron radiations at Pohang Light Source (PAL) and European Synchrotron Radiation Facility (ESRF). Near edge x-ray absorption spectroscopy (NEXAFS) measurement at C K, Co $L_{3,2}$ and Fe $L_{3,2}$-edges, and x-ray magnetic circular dichroism (XMCD) at Co and Fe $L_{3,2}$-edges have been carried at 7B1 XAS KIST and 2A MS beamline, respectively, to understand the electronic structure and responsible magnetic interactions at room temperature. X-ray absorption spectroscopy (XAS) at C K-edge shows significant p-bonding and Co and Fe L-edges proves the presence of $Co^{2+}$ and $Fe^{2+}$ in octahedral symmetry. Co and Fe doped MWCNTs show good XMCD spectra at 300K. The effect on the magnetism is also studied through swift heavy ion (SHI) radiations and magnetism is found enhanced and change in the electronic structure in Co-CNTs is investigated.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.265-265
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• 2013

We have investigated the influences of dangling bonds generated by alpha particle irradiation on friction and adhesion properties of graphene. Single layer of graphene grown with chemical vapor deposition on copper foil was irradiated by the alpha beam with the average energy of 3.04 MeV and the irradiation dosing between $1{\times}10^{14}$ and $1{\times}10^{15}$/$cm^3$. Raman spectroscopic showed that the ${\pi}$ electron states below Fermi level arises and the $I_D$/$I_G$ increases as increasing the dosing of alpha particle irradiation. The core level X-ray photoelectron (XPS) revealed that these defects represent the creation of various carbon-related defects and dangling bond. The nanoscale tribological properties were investigated with atomic force microscopy in ultrahigh vacuum. The friction appeared to increase remarkably as increasing the amount of dosing, indicating that the dangling bonds on graphene layers enhances the energy dissipations in friction. This trend can be explained by the additional channel of energy dissipation by dangling bond or O- and H- terminated clusters created by alpha particle irradiation.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.342-342
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• 2010

We have investigated an Au intercalated monolayer graphene on Ni(111) using angle-resolved photoemission spectroscopy (ARPES), high resolution photoemission spectroscopy (HRPES), and low energy electron diffraction (LEED) at the 3A2 ARUPS beamline in Pohang Accelerator Laboratory. We find the monolayer graphene is well grown on the Ni(111) surface by the adsorption of acetylene. However, the graphene does not show the characteristic $\pi$ band near the Fermi level due to its strong interaction with the underlying substrate. When Au is adsorbed on the surface and then annealed at high temperature, we observe that Au is intercalated underneath the monolayer graphene. The process of the Au intercalation was monitored by HRPES of corresponding Au 4f and C 1s core levels as well as the electronic structure of the $\sigma$, $\pi$ states at $\Gamma$, K points. The $\sigma$, $\pi$ bands of graphene shift towards the Fermi level and the $\pi$ band is clearly observed at K point after the intercalation of full monolayer Au. The full width at half maximum (FWHM) of the C 1s peak narrows to approximately 0.42 eV after intercalation. These results imply that the interaction between the graphene and substrate is considerably weakened after the Au intercalation. We will discuss the graphene is really closer to ideal free standing graphene suggested recently.

• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1744-1749
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• 2018

This study investigated the feasibility of synthesizing GNPs using synchrotron radiation X-ray for use as a radiosensitizer in radiotherapy, and examined the morphology of the GNPs. Different concentration ratios of 4-mM gold precursor aqueous solution and 4-mM $NaHCO_3$ were mixed. This gold precursor aqueous solution was continuously irradiated with synchrotron radiation in the 4B X-ray microdiffraction beamline of Pohang Light Source (PLS)-II in Korea. The SEM, EDS, TEM, and XRD spectra of the GNPs synthesized using the synchrotron radiation were investigated. The GNPs synthesized using the synchrotron radiation were nanocrystals predominantly in the (111) direction of the face-centered cubic structure. We found that the shape of the gold nanoparticles was icosahedron at the molar concentrations of 0.25 mM:0.25 mM and 0.5 mM:0.5 mM mixed with 4 mM $HAuCl_4{\cdot}3H_2O$ and 4 mM $NaHCO_3$ solutions.

• Bulletin of the Korean Chemical Society
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• 제25권4호
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• pp.511-516
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• 2004

A Li$[Co_{0.17}Li_{0.28}Mn_{0.55}]O_2$ cathode compound was prepared by a simple combustion method. The X-ray diffraction pattern showed that this compound could be classified as ${\alpha} -NaFeO_2$ structure type with the lattice constants of a = 2.8405(9) ${\AA}$ and c = 14.228(4) ${\AA}$. According to XANES analysis, the oxidation state of Mn and Co ions in the compound were 4+ and 3+, respectively. During the first charge process, the irreversible voltage plateau at around 4.65 V was observed. The similar voltage-plateau was observed in the initial charge profile of other solid solution series between $Li_2MnO_3\;and\;LiMnO_2$ (M=Ni, Cr...). The first discharge capacity was 187 mAh/g and the second discharge capacity increased to 204 mAh/g. As the increase of cycling number, one smooth discharge profile was converted to two distinct sub-plateaus and the discharge capacity was slowly decreased. From the Co and Mn K-edge XANES spectra measured at different cyclic process, it can be concluded that irreversible transformation of phase is occurred during continuous cycling process.

• Journal of Radiation Protection and Research
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• 제43권3호
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• pp.97-106
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• 2018

Background: A cargo container scanner using a high-energy X-ray generates a fan beam X-ray to acquire a transmitted image. Because the generated X-rays by LINAC may affect the image quality and radiation protection of the system, it is necessary to acquire accurate information about the generated X-ray beam distribution. In this paper, a diode-based multi-channel spatial dose measuring device for measuring the X-ray dose distribution developed for measuring the high energy X-ray beam distribution of the container scanner is described. Materials and Methods: The developed high-energy X-ray spatial dose distribution measuring device can measure the spatial distribution of X-rays using 128 diode-based X-ray sensors. And precise measurement of the beam distribution is possible through automatic positioning in the vertical and horizontal directions. The response characteristics of the measurement system were evaluated by comparing the signal gain difference of each pixel, response linearity according to X-ray incident dose change, evaluation of resolution, and measurement of two-dimensional spatial beam distribution. Results and Discussion: As a result, it was found that the difference between the maximum value and the minimum value of the response signal according to the incident position showed a difference of about 10%, and the response signal was linearly increased. And it has been confirmed that high-resolution and two-dimensional measurements are possible. Conclusion: The developed X-ray spatial dose measuring device was evaluated as suitable for dose measurement of high energy X-ray through confirmation of linearity of response signal, spatial uniformity, high resolution measuring ability and ability to measure spatial dose. We will perform precise measurement of the X-ray beamline in the container scanning system using the X-ray spatial dose distribution measuring device developed through this research.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.456-456
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• 2013

We report the modifications in the electronic structureof ZnO thin films induced by swift heavy ion (SHI) irradiated ZnO thin films by using near edge X-ray absorption fine structure (NEXAFS) spectroscopy at O K-edge was performed at BL10D XAS-KIST beamline at Pohang Accelerator Lab (PAL). ZnO films of 250 nm thickness oriented in [200] plane deposited by RF magnetron sputtering using equal $Ar:O_2$ atmosphere and air annealed at $500^{\circ}C$ for 6 hours for stability were irradiated with 120 MeV Au and 100 MeV O beams separately with different doses ranging from $1{\times}10^{11}$ to $5{\times}10^{12}$ ions/$cm^2$. High Resolution X-ray diffraction and NEXAFS analysis indicates significant changes in the electronic structure and the SHI effect is different for Ag and O-beams. The NEXAFS measurements provide direct evidence of O 2p and Zn 3d orbital hybridization. The NEXAFS results will be presented in detail.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.396-399
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• 2003

In this paper, the purpose is to develop imaging technique of synchrotron radiation using CMOS image sensor. The detector using hybrid method to be research in this lab was used, in order to increase image signal. We made experiments with 1B2 Whitebeam/microprobe beamline in PAL (Pohang Accelerator Laboratory). Phosphor materials such as ZnS:(Ag,Li), ZnS:(Cu,Al), $Y_2O_2S:Eu$ were produced by spin coating on glass. Synchrotron radiation images were acquired and evaluated from monochromatic light from monochromoator in PAL 1B2line. From obtained object and phantom, MTF was 0.15 in ZnS:(Ag,Li) phosphor, and 0.178 in ZnS:( Cu,Al) at 151p/mm. MTFs were unsystematic because thickness of phosphor and uniformity of surface were not optimized. It's expected to improve MTF and the qualify of images as uniformity's optimized.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.361-361
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• 2010

The separated quasi-one-dimensional ($7{\times}7$) and ($5{\times}5$) phases on vicinal Si(557) surfaces were successfully realized by changing the crystallographic orientation and thermal treatment conditions. A small change in the crystallographic orientation of the Si(557) surface stabilized the quasi-one-dimensional ($5{\times}5$) phase of a (111) facet on vicinal Si(557) surfaces and made it coexist with a quasi-one-dimensional ($7{\times}7$) phase after an optimal thermal treatment, whereas only the quasi-one-dimensional ($7{\times}7$) phase was stable on the Si(557) surface. Interestingly, this causes the (111) terraces with different widths (L) to prefer only one of the $5{\times}5$ (L=12) and $7{\times}7$ (L=9) phases resulting in long-range order of both phases along the step edge direction, which was observed by scanning tunneling microscopy (STM) and was supported by first principle calculations. In contrast, the quasi-one-dimensional ($5{\times}5$ and ($7{\times}7$) phases were arranged randomly across the step edge direction. The change of surface morphology of vicinal Si(557) surfaces will be discussed with STM images and theoretical calculations by changing crystallographic cutting angles and thermal treatment conditions.