• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.51.2-52
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• 2021

Pulsar Wind Nebula(PWN)는 radio부터 TeV band까지 넓은 파장에 걸쳐 복사를 하며 이 복사는 Spectral Energy Distribution(SED)으로 측정된다. 관측된 SED는 두 개의 주요한 bump를 보이는데 low-energy emission bump는 synchrotron radiation에 의해 만들어지고 high-energy emission bump는 inverse Compton scattering에 의해 만들어진다. 대부분 PWN들의 SED는 단일 전자 분포로 설명이 가능하지만 최근 연구 결과에 의하면 Crab nebula, G21.5-0.9 같은 일부 young pulsar wind nebula의 X-ray SED에서 단차나 기울기의 변화 등 단일 전자 분포로 설명하기 어려운 부분이 관측되기도 한다. 이런 PWN에 대하여 우리는 이중 전자 분포를 이용해서 broadband SED가 잘 설명이 되는지 확인하고 이를 통하여 PWN 입자 가속의 특성을 이해해보고자 한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.165-165
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• 2012

비정질의 Tantalum-indium-zinc oxide (TIZO) 박막 트랜지스터는 RF-sputtering 방법으로 증착되었으며 소결된 단일 타겟을 사용하였다. 증착당시 반응 가스는 알곤과 산소를 95 : 5로 섞어 반응성 스퍼터링을 진행하였으며, 1 mtorr에서 5 mtorr까지 다양한 공정압력에서 증착한 이 후 Furnace system을 통하여 $350^{\circ}C$의 온도로 1시간 동안 후열처리 공정을 진행하였다. 비정질 TIZO 박막을 활성 층으로 사용하여 제작한 박막 트랜지스터는 공정압력이 낮아짐에 따라 높은 이동도와 낮은 subthrehsold gate swing 보였다. 이러한 현상의 원인을 규명하고자 물리적, 전기적, 광학적 분석을 통하여 공정압력의 변화가 박막 트랜지스터 구동에 미치는 영향을 해석하였다. 우선 공정압력에 따른 TIZO 박막의 Ta, In, Zn, O 각각의 조성을 분석하기 위하여 Rutherford back scattering (RBS) 분석을 실시하였다. 또한 X-선 회절(X-ray diffraction)분석을 통해 열처리된 TIZO 박막은 공정압력에 따라 물리적 구조의 변화를 일으키지 않으며 모든 박막은 비정질상을 보이는 것을 확인하였다. 3.3eV의 광학적 밴드 갭은 기존에 보고되었던 비정질 산화물 반도체(InGaZnO, HfInZnO 등)와도 유사한 밴드갭을 가지고 있음을 확인하였다. 또한, spectroscopic ellipsometry (SE)분석을 통하여 전도대 이하 밴드 갭 내에 존재하는 결함상태 및 전도대에서 결함상태까지의 에너지 준위 그리고 공정압력에 따라 결함의 양과 발생되는 에너지 준위가 변화하는 현상을 관측하였다. 박막을 제조 할 때의 공정압력은 박막 내의 결함의 양 및 발생되는 에너지 준위의 변화를 야기하고 변화된 결함의 양과 발생된 에너지 준위에 따라 박막트랜지스터의 전기적 특성을 변화시킨다는 결과를 도출하였다.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.222-225
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• 2002

Microwave dielectric properties of the layered and functionally graded materials (FGMs) of $Mg_{0.93}Ca_{0.07}TiO_3$ (MCT) and $(Ca_{0.3}Li_{0.14}Sm_{0.42})TiO_3$(CLST) were investigated as a function of the volume ratio of two components. Dielectric constant was decreased with an increase of the volume ratio of MCT which had a lower dielectric constant thant CLST. For the layered FGMs specimens, the difference of thermal expansion coefficients between two components induced thermal strain to dielectric layers, which was confirmed by the plot of ${\Delta}$k (X-ray diffraction peak width0 versus k (scattering vector) using the double-peak Lorentzian function, f(x). Quality factor of the specimens was affected by the thermal strain of dielectric layer, especially MCT layer. For the specimen with the volume ratio of MCT/CLST = 2, the qulaity factor of the specimen showed a minimum value due to the maximum thermal strain fo MCT layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.11
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• pp.1037-1043
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• 2006

We report the enhancement of hole injection using ozone-treated Ag nanodots dispersed on indium tin oxide anode in $Ir(ppy)_3-doped$ phosphorescent OLED. Phosphorescent OLED fabricated on Ag nanodots dispersed ITO anode showed a lower turn on voltage and higher luminescence than those of OLEDS prepared commercial ITO anode. Synchrotron x-ray scattering examination results showed that the Ag nanodots dispersed on ITO anode is amorphous structure due to low deposition temperature. It was thought that decrease of the energy barrier height as Ag nanodots changed to $AgO_x$ nanodots by surface treatment using ozone for 10 min led to enhancement of hole injection in phosphorescent OLED. Futhermore, efficient hole injection can be explained by increase of contact region between anode material and organic material through introduction of $Ag_2O$ nanodots.

• Polymer(Korea)
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• v.28 no.6
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• pp.509-518
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• 2004

Microdomain structures and crystallization behavior of the binary blends consisting of an asymmetric block copolymer and a homopolymer were investigated using small-angle X-ray scattering (SAXS), optical micro scope (OM) and differential scanning calorimetry (DSC). Poly(methyl methacrylate)-block-polystyrene block copolymer (PMMA-b-PS) (weight fraction of PMMA =0.53) was mixed with low molecular weight poly(vinylidene fluoride) (PVDF). As the PVDF concentration was increased, the morphological change from a lamellar to a cylindrical structure occurred. The crystallization of PVDF significantly disturbed the orientation of the pre-existing microdomain structure, resulting in a poorly ordered morphology. In the blends, PVDF exhibited unique crystallization behavior due to the PMMA block which is preferentially miscible to PVDF and the space constraint imposed by the microdomains.

• Journal of Ceramic Processing Research
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• v.21 no.1
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• pp.5-13
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• 2020

(K0.5Na0.5)NbO3-based ceramic powders for lead-free piezoelectric applications are usually prepared by solid state synthesis. This generally involves wet ball milling in an organic liquid such as ethanol, which is a drawback for industrial production. In the present work, a method for the preparation of NaNbO3 nanopowders is modified to produce a simple method of preparing (K0.5Na0.5)NbO3 nanopowders by an aqueous route. K2CO3, Na2CO3 and NH4[NbO(C2O4)2].xH2O are mixed in water and dried to form a gel, which is then calcined at temperatures between 400 ~ 650 ℃ for 1 h. The uncalcined gel and calcination products are analysed using Thermogravimetric Analysis/Differential Thermal Analysis, X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy and Raman Scattering. A single phase tetragonal (K0.5Na0.5)NbO3 nanopowder with a particle size of ~ 30 nm can be produced after calcination at 650 ℃ for 1 h.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.4
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• pp.129-134
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• 2004

In this study, we investigated the effect of a nitrogen atom on the amorphization of V-Fe alloy through solid-gas reaction during mechanical alloying (MA). MA by planetary ball mill of $V_{70}Fe_{30}$ elemental powders was carried out under the nitrogen gas atmosphere. Amorphization has been observed after 160 hours of ball milling in this case. The DSC spectrum for the mechanically alloyed ($V_{70}Fe$_{30}$)_{0.89}N_{0.11}$ powders exhibits a sharp exothermic peak due to crystallization at about $600^{\circ}C$. Structural transformation from the bcc crystalline to amorphous states was also observed through X-ray and neutron diffractions. We take a full advantage of a negligibly small scattering length of the V atom in the neutron diffraction measurement. During amorphization process the octahedral unit, which is typical of a polyhedron formed in any crystal structures, was preferentially destroyed and transformed into the tetrahedral unit. Futhermore, neutron diffraction measurements revealed that a nitrogen atom is selectively situated at a center of the polyhedron formed by V atoms.

• Textile Coloration and Finishing
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• v.28 no.4
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• pp.231-238
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• 2016

We investigated the evolution of crystal formation as a function of drawing ratio in poly(1,4-diaminobutane-co-adipic acid-co-${\varepsilon}$-caprolactam-co-diethylenetriamine)(nylon 466T) copolymer formed by four monomers, i.e 1,4-diaminobutane, adipic acid, ${\varepsilon}$-caprolactam, diethylenetriamine(DETA), using synchrotron X-ray scattering measurement. In case of pristine(as spun) nylon 466T fiber, it was consisted with unoriented nylon $6{\alpha}$ and unoriented nylon $46{\alpha}$ phases. As increase the drawing ratio, unoriented nylon $6{\alpha}$ was transformed to oriented ${\gamma}$ phase, while unoriented nylon $46{\alpha}$ changed to oriented $46{\alpha}$ phase. The effect of the addition of DETA was not observed in the pristine fibers. However, DETA affected to restrict the formation of crystals at the maximum drawing condition, and as a result it had a role to increase the moisture regain.

• Polymer(Korea)
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• v.25 no.5
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• pp.691-698
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• 2001

Nanocomposites based on epoxy acid nanoclay were prepared employing organically modified mica type silicate (OMTS), diglycidyl ether of bisphenol A (DGEBA) type epoxy. curing agent (dicyandiamide; DICY), and catalyst (benzyl dimethyl amine; BDMA). Both melt mixing and solution mixing were und for the sample preparation and structural developments with curing reaction were analyzed using X-ray diffractometer (XRD) and small angle X-ray scattering (SAXS). Because of the different curing rate between extra-gallery and intra-gallery reactions of epoxy mixtures, only intercalated structure was observed for the sample prepared by melt mixing while fully exfoliated structure was observed for the sample prepared by solution mixing. Mechanical properties of exfoliated epoxy nanocomposite were investigated using a dynamic mechanical analyzer (DMA). The dynamic storage modulus of the nanocomposite in both glass and rubbery plateau regions were increased with increasing OMTS contents, but glass transition temperatures ($T_g$) remained unchanged. Thermal properties of epoxy nanocomposite were investigated using thermogravimetric (TGA) and limit oxygen index (LOI) methods. Thermal decomposition onset points and LOI values were increased with increasing OMTS contents due to barrier effects of OMTS sheets.

• Membrane and Water Treatment
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• v.8 no.1
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• pp.51-71
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• 2017

Antimicrobial polyethersulfone ultrafiltration membranes containing zerovalent iron ($Fe^0$) and magnetite ($Fe_3O_4$) nanoparticles were synthesized via phase inversion method using polyethersulfone (PES) as membrane material and nano-iron as nanoparticle materials. Zerovalent iron nanoparticles (nZVI) were prepared by the reduction of iron ions with borohydride applying an inert atmosphere by using $N_2$ gases. The magnetite nanoparticles (nMag) were prepared via co-precipitation method by adding a base to an aqueous mixture of $Fe^{3+}$ and $Fe^{2+}$ salts. The synthesized nanoparticles were characterized by scanning electron microscopy, X-ray powder diffraction, and dynamic light scattering analysis. Moreover, the properties of the synthesized membranes were characterized by scanning electron microscopy energy dispersive X-ray spectroscopy and atomic force microscopy. The PES membranes containing the nZVI or nMag were examined for antimicrobial characteristics. Moreover, amount of iron run away from the PES composite membranes during the dead-end filtration were tested. The results showed that the permeation flux of the composite membranes was higher than the pristine PES membrane. The membranes containing nano-iron showed good antibacterial activity against gram-negative bacteria (Escherichia coli). The composite membranes can be successfully used for the domestic wastewater filtration to reduce membrane biofouling.