• Proceedings of the Korean Magnestics Society Conference
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• 1998.10a
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• pp.74-75
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• 1998

• Proceedings of the Korean Vacuum Society Conference
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• 2002.02a
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• pp.46-46
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• 2002

• Polymer Science and Technology
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• v.8 no.1
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• pp.57-66
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• 1997

• Journal of the Korean Vacuum Society
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• v.10 no.1
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• pp.93-97
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• 2001

We introduce the structure and the capability of a UHV x-ray scattering system constructed for surface structural studies. The system consists of vacuum parts required for surface preparation and a vertical-horizontal diffractometer using the S2D2 geometry. To illustrate the capability of the system, we measured the 7$\times$7 reconstruction peak of a Si (111) surface. The peak count rate was 216 counts/sec and the domain size of the 7$\times$7 reconstruction was larger than 1600 $\AA$. This demonstrates that the system is capable of providing surface structural information.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.61.2-61.2
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• 2013

우리나라 최초의 거대과학 장치인 포항방사광가속기(PLS)는 지난 16년(1994~2010) 동안 국내외 이용자에게 제3세대 방사광을 제공했다. 최초 2기의 빔라인을 시작으로 꾸준하게 빔라인 증설과 성능개선을 위해 노력해 왔다. 지속해서 늘어나는 방사광 이용자 수와 더욱더 좋은 수준의 방사광 요구에 부응하기 위하여 2009년부터 3년 동안 가속장치의 성능향상사업(PLS-II)을 마쳤다. PLS-II는 PLS 대비에너지와 빔전류는 3 GeV, 400 mA로 늘리는 반면 빔의 크기는 크게 줄이고 빔안정성을 개선한 고품질 X-선 방사광 발생장치이다. 2012년부터 16기의 삽입장치 빔라인을 포함한 30기의 빔라인을 가동하여 이용자 지원을 하고 있으며 초전도케비티 설치를 포함한 목표 성능의 확보에도 많은 노력을 기울이고 있다. 현재는 6 nm-rad의 빔에 미턴스, 3-GeV전자빔, 약 0.5 ${\mu}m-rms$ 빔안정도를 가진 200 mA Top-up 운전으로 빔을 제공 하고 있으며 2014년 말에는 저장전류 400 mA급의 PLS-II 목표치로 운전할 계획이다. 본 발표에서는 포항가속기의 25년 역사를 돌아보고 가속장치의 건설에 얽힌 이야기, 중요장치 그리고 운전과 빔제공에 관한 내용, 특히 핵심 운전가치인 빔안정성을 개선하고 유지하기 위한 노력을 빔운전 측면과 진공을 포함한 엔지지어링 측면에서 언급하고자 한다. PLS 건설부터 현재 운용 중인 30기의 빔라인에서 수행된 연구 성과의 통계에 대하여 훑어보고 X-선 산란과 광전자분광을 이용한 구조, 성분 및 물성분석, 그리고 이미징 등의 분야에서 나온 탁월한 연구 결과를 살펴본다. 앞으로 건설될 신규 빔라인과 빔라인의 향후 운영 방향을 소개한다. 마지막으로 지금 포항가속기연구소에서 건설 중인 제4세대 가속기(X-선 자유전자레이저) 프로젝트의 개요 및 건설 현황과 함께 앞으로 기대되는 새로운 과학에 대하여도 소개하고자 한다.

• Journal of the Korean Vacuum Society
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• v.15 no.2
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• pp.168-172
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• 2006

GaN nucleation layers were grown by hydride vapor phase epitaxy (HVPE) and the effect of growth temperature on the structural properties of GaN nucleation layers for nanorods was investigated by synchrotron x-ray scattering and Atomic Force Microscopy (AFM). For the samples grown at different temperatures, two-component rocking profiles of (002) GaN Bragg peaks for the GaN nucleation layers were observed with one very sharp and the other broad. It was shown that the two-component rocking profile could be qualitatively explained by surface morphology, which was in good agreement with AFM result, from which we could conclude that relatively low temperature is favorable for GaN nanorods formation.

• Journal of the Korean Vacuum Society
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• v.16 no.6
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• pp.479-482
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• 2007

InN nanograins were directly grown on $0.3^{\circ}$-miscut (toward M-plane) c-plane sapphire substrates by hydride vapor phase epitaxy (HVPE) and their growth characteristics were investigated by utilizing x-ray scattering. Depending on the various growth parameters, the formation of InN was sensitively influenced. Six samples were grown by changing HCl flow rate, the substrate temperature and Ga/In source zone temperature. All the samples were grown on unintentionally $NH_3-pretreated$ sapphire substrates. By increasing the flow rate of HCl from 10 sccm to 20 sccm, the formation of GaN grains with different orientations was observed. On the other hand, when the substrate temperature was raised from $680^{\circ}C$ to $760^{\circ}C$, the increased substrate temperature dramatically suppressed the formation of InN. A similar behavior was observed for the samples grown with different source zone temperatures. By decreasing the source zone temperature from $460^{\circ}C$ to $420^{\circ}C$, a similar behavior was observed.

• Polymer(Korea)
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• v.33 no.2
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• pp.183-188
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• 2009

Structural rearrangements of uni-axially deformed polyethylenes containing 1-octene comonomer and HDPE upon heating were investigated by time-resolved small and wide angle X-ray scattering techniques. During heating, structural changes including crystal transformation and lamellar rearrangement noted were very different depending on the comonomer contents. At low comonomer content below 2 wt%, inverse martensitic transformation of crystal lattice from monoclinic to orthorhombic cell and the rearrangement of broken lamellar units into more ordered and perfect lamellar stacks were noted with the temperature increase. At high contents above 9.5 wt%, however, polyethylene copolymers showed neither the crystal transformation nor lamellar rearrangement that can be attributed to low crystallinity and high content of branch units.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.8
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• pp.708-712
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• 2002

The crystallization of amorphous $\alpha$-Fe$_2$O$_3$/$\alpha$-AI$_2$O$_3$(0001) thin films during thermal annealing in air has been studied using real-time synchrotron x-ray scattering. The well aligned (0.02$^{\circ}$/ FWHM) $\alpha$-Fe$_2$O$_3$and Fe$_3$O$_4$interfacial crystallites (50- -thick) coexist on the $\alpha$-AI$_2$O$_3$(0001) in the sputter-grown amorphous films at room temperature. The amorphous precursor is crystallized to the epitaxial $\alpha$-Fe$_2$O$_3$grains in three steps with annealing temperature; i ) the growth of the well aligned $\alpha$-Fe$_2$O$_3$interfacial crystallites, together with the transformation of the Fe$_3$O$_4$crystallites to the $\alpha$-Fe$_2$O$_3$ crystallites, ii ) the growth of the less aligned (3.08$^{\circ}$ FWHM)$\alpha$-Fe$_2$O$_3$grains on the well aligned grains (＞40$0^{\circ}C$), and iii) the nucleation of the other less aligned (1.39$^{\circ}$ FWHM) $\alpha$-Fe$_2$O$_3$grains directly on the $\alpha$-AI$_2$O$_3$substrate (＞$600^{\circ}C$). The effective thickness thinner than 230 may be very useful for enhancing the epitaxial quality of $\alpha$-Fe$_2$O$_3$/AI$_2$O$_3$(0001) thin films.

• Journal of the Korean Magnetics Society
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• v.16 no.6
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• pp.283-286
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• 2006

We have studied the role of ${\alpha}-Al_{2}O_{3}$ buffer layer as a diffusion barrier in the Ba-ferrite/$SiO_{2}$ magnetic thin films for high-density recording media. In the interface of amorphous Ba-ferrite $(1900-{\AA}-thick)/SiO_{2}$ thin film during annealing, the interfacial diffusion started to occur at ${\sim}700^{\circ}C$. As the annealing temperature increased up to $800^{\circ}C$, the interfacial diffusion abruptly proceeded resulting in the high interface roughness and the deterioration of the magnetic properties. In order to control the interfacial diffusion at the high temperature, we introduced ${\alpha}-Al_{2}O_{3}$ buffer layer ($110-{\AA}-thick$) in the interface of Ba-ferrite/$SiO_{2}$ thin film. During the annealing of Ba-ferrite/${\alpha}-Al_{2}O_{3}/SiO_{2}$ thin film even at ${\sim}800^{\circ}C$, the interface was very smooth. The magnetic properties, such as saturation magnetization and intrinsic coercivity, were also enhanced, due to the inhibition of interfacial diffusion by the ${\alpha}-Al_{2}O_{3}$ buffer layer. Our study suggests that the ${\alpha}-Al_{2}O_{3}$ buffer layer act as a useful interfacial diffusion barrier in the Ba-ferrite/$SiO_{2}$ magnetic thin films.