• Nuclear Engineering and Technology
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• v.49 no.6
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• pp.1234-1239
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• 2017

Basic research on the accelerator-driven system is conducted by combining $^{235}U$-fueled and $^{232}Th$-loaded cores in the Kyoto University Critical Assembly with the pulsed neutron generator (14 MeV neutrons) and the proton beam accelerator (100 MeV protons with a heavy metal target). The results of experimental subcriticality are presented with a wide range of subcriticality level between near critical and 10,000 pcm, as obtained by the pulsed neutron source method, the Feynman-${\alpha}$ method, and the neutron source multiplication method.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.239-239
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• 2010

Cobalt (Co) 박막은 낮은 저항과 우수한 열적 안정성에 의해 금속 배선공정에서 copper의 확산 및 산화를 방지하기 위해 사용된다. Co 박막을 증착하기 위해서는 유기화학 증착법이 많이 사용되고, 이를 위해 많은 Co 전구체들이 연구되어지고 있다. 본 연구에서는 $Co(hfac)_2$ 전구체의 플라즈마 및 반응가스에 따른 기상상태의 변화와 증착공정에서 발생되는 입자의 크기와의 상관관계를 연구하였다. 실험의 변수로 반응가스 ($H_2$, $H_2O$)와 플라즈마 파워 (0~50W)를 사용하였다. 또한 Co 전구체의 기상분해 및 반응을 분석을 위해 fourier transform infrared (FT-IR) spectroscopy를 사용하였다. 그리고 기상상태의 변화가 입자 형성에 끼치는 영향을 관찰하기 위해 저압에서 실시간으로 나노입자를 측정할 수 있는 장비인 particle beam mass spectrometer (PBMS)를 활용하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.84-84
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• 2013

본 개발은 반도체 또는 디스플레이 공정상의 불량률을 최소화 하기 위하여 시작 되었다. PBMS를 이용하여 공정상에 발생하는 오염입자들을 모니터링하고자 하였으나 기존의 시스템은 크기, 감도, 교정등의 문제들로 현장적용에 무리가 있었던 것이 사실이다. 주식회사 이엘은 PBMS의 문제들을 개선 또는 제거하여 현장에 적용 가능하도록 하였으며 전용 프로그램을 개발하여 사용자의 편의성을 증대하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.145.2-145.2
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• 2013

The band-gap opening in graphene is a key factor in developing graphene-based field effect transistors. Although graphene is a gapless semimetal, a band-gap opens when graphene is formed into a graphene nanoribbon (GNR). Moreover, the band-gap energy can be manipulated by the width of the GNR. In this study, we propose a site-specific synthesis of a width-tailored GNR directly onto an insulating substrate. Predeposition of a diamond-like carbon nanotemplate onto a SiO2/Si wafer via focused ion beam-assisted chemical vapor deposition is first utilized for growth of the GNR. These results may present a feasible route for growing a width-tailored GNR onto a specific region of an insulating substrate.

• Structural Engineering and Mechanics
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• v.89 no.3
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• pp.323-334
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• 2024

Physical and chemical factors can cause traditional timber constructions to lose structural integrity. Knowing the dynamic properties of the building components is vital to avoid damage to the buildings from dynamic effects, a subset of physical effects. In this work, spruce and scotch pine wooden beams that had been strengthened in three distinct ways with carbon fiber strengthened polymer (CFRP) were investigated for changes in their dynamic properties. For this, CFRP was used to strengthening unstrengthened wooden beams in the form of bottom confinement, U-shaped confinement, and full confinement after the dynamic parameters of the beams were determined. By using experimental modal analysis with both free-free and fixed-fixed boundary conditions, the beams'initial natural frequencies were identified.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.167-167
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• 2010

반도체는 도핑하지 않으면 대부분 n형을 나타내는 것에 반하여 GaSb는 p형을 보이는 반도체로서, 그 근원은 명확하게 규명되어 있지 않은 상태이다. GaSb의 p형 불순물인 Be은 Ga과 치환 ([$Be_{Ga}$])되므로, p형 전도의 근원으로 추정되는 잔존결함인 [$Ga_{Sb}$]와 그 복합체인 [$Ga_{Sb}-Sb_{Ga}$]와 높은 상관관계를 가질 것으로 예측된다. 본 연구에서는 Be을 도핑한 GaSb:Be 에피층을 MBE 방법으로 성장하여, PL 스펙트럼과 Hall 효과 분석을 통하여 p형 전도의 근원을 조사하였다. 도핑하지 않은 u-GaSb는 DA (deep acceptor)와 함께 A 준위를 나타낸 반면, p-GaSb:Be의 PL 스펙트럼은 Be 도핑농도가 증가함에 따라 FWHM가 줄어들면서 점차 높은 에너지 영역으로 변위하지만 농도가 가장 높은 시료에서는 PL의 FWHM가 증가하면서 에너지는 감소함이 관측되었는데, 이것은 A 피크와 Sb 관련 피크가 경쟁적으로 중첩되어 나타난 현상으로 분석된다. Hall 효과 결과는 유효 전하밀도의 증가에 따라 이동도는 감소하는 전형적인 의존성을 나타내었으며, u-GaSb의 Hall 이동도가 p-GaSb:Be의 값보다 작은 것은 u-GaSb에 잔존하는 DA에 의한 산란 때문으로 해석된다. Gaussian 형태로 분해하여 얻은 A ([$Ga_{Sb}$])와 DA ([$Ga_{Sb}-Sb_{Ga}$]) 및 Be 관련 피크로부터 특정 도핑농도 ($1.2{\times}10^{17}cm^{-3}$)의 시료를 제외한 모든 p-GaSb:Be에는 A 피크가 중첩되고 A와 Be 준위 중간에 Be과의 복합체인 중간상태(intermediate state)인 [$Be^*$]가 존재함이 관측되었는데, 특정 도핑농도에서는 [$Be_{Ga}$]이 우세하지만 더 이상 농도가 증가하면 [$Be_{Ga}$] 준위의 강도는 오히려 감소함을 관측할 수 있었다. 이것은 적정 이상의 Be을 도핑할 경우, A ([$Be_{Ga}$])와 $Be^*([Be_{Ga}-Ga_Sb}])$가 형성 ($A[Ga_{Sb}]+Be{\rightarrow}Be^*[Be_{Ga}-Ga_{Sb}]+[Be_{Ga}]$)됨을 보여 주는 중요한 결과인 것으로 분석된다. A, [Be], [$Be^*$] PL 피크 에너지는 각각 779, 787, 794 meV (오차범위 ${\pm}3\;meV$)이고, [$Be_{Ga}$]의 활성화 에너지는 ($23{\pm}3\;meV$) (20 K)임을 밝혔다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.176-177
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• 2013

Surface plasmon polaritons (SPPs) have attracted the attention of scientists and engineers involved in a wide area of research, microscopy, diagnostics and sensing. SPPs are waves that propagate along the surface of a conductor, usually metals. These are essentially light waves that are trapped on the surface because of their interaction with the free electrons of conductor. In this interaction, the free electrons respond collectively by oscillating in resonance with the light wave. The resonant interaction between the surface charge oscillation and the electromagnetic field of the light constitutes the SPPs and gives rise to its unique properties. In this papers, we studied theoretical and experimental extraordinary transmittance (T) and reflectance (R) of 2 dimensional metal hole array (2D-MHA) on GaAs in consideration of the diffraction orders. The 2d-MHAs was fabricated using ultra-violet photolithography, electron-beam evaporation and standard lift-off process with pitches ranging from 1.8 to $3.2{\mu}m$ and diameter of half of pitch, and was deposited 5-nm thick layer of titanium (Ti) as an adhesion layer and 50-nm thick layer of gold (Au) on the semiinsulating GaAs substrate. We employed both the commercial software (CST Microwave Studio: Computer Simulation Technology GmbH, Darmstadt, Germany) based on a finite integration technique (FIT) and a rigorous coupled wave analysis (RCWA) to calculate transmittance and reflectance. The transmittance was measured at a normal incident, and the reflectance was measured at variable incident angle of range between $30^{\circ}{\sim}80^{\circ}$ with a Nicolet Fourier transmission infrared (FTIR) spectrometer with a KBr beam splitter and a MCT detector. For MHAs of pitch (P), the peaks ${\lambda}$ max in the normal incidence transmittance spectra can be indentified approximately from SP dispersion relation, that is frequency-dependent SP wave vector (ksp). Shown in Fig. 1 is the transmission of P=2.2 um sample at normal incidence. We attribute the observation to be a result of FTIR system may be able to collect the transmitted light with higher diffraction order than 0th order. This is confirmed by calculations: for the MHAs, diffraction efficiency in (0, 0) diffracted orders is lower than in the (${\pm}x$, ${\pm}y$) diffracted orders. To further investigate the result, we calculated the angular dependent transmission of P=2.2 um sample (Fig. 2). The incident angle varies from 30o to 70o with a 10o increment. We also found the splitting character on reflectance measurement. The splitting effect is considered a results of SPPs assisted diffraction process by oblique incidence.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.172-172
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• 2009

In this study, we presented comparative discrimination methods to identify various line and planar defects observed in nonpolar a-GaN epilayers on r-sapphire substrates. Unlike the case of conventional c-GaN, which is dominated by perfect threading dislocations, systematic identification of undistinguishable defects using transmission electron microscopy (TEM) is necessary to suppress the propagation of defects in nonpolar GaN epilayers. Cross-sectional TEM images near the [0001] zone axis revealed that perfect mixed and pure screw type dislocations are visible, while pure edge, partial dislocations, and basal stacking faults (BSFs) are not discernible. In tilted cross-sectional TEM images along the [$1\bar{2}10$] zone axis, the dominant defects were BSFs and partial dislocations for the $g=10\bar{1}0$ and 0002 two-beam images, respectively. From plan view TEM images taken along the [$11\bar{2}0$] axis, it was found that the dominantpartial and perfect dislocations were Frank-Shockley with b=${\pm}1/6$<$20\bar{2}3$> and mixed type without an 1 component including b=${\pm}1/3$<$1\bar{2}10$> and ${\pm}1/3$<$\bar{2}110$>, respectively. Prismatic stacking faults were observed as inclined line contrast near the [0001] zone axis and were visible as band contrast in the two-beam images along the [$1\bar{2}10$] and [$11\bar{2}0$] zone axes.

• Imaging Science in Dentistry
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• v.40 no.1
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• pp.1-7
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• 2010

Purpose : The purpose of this study was to examine the significance of increased bone density according to whether bone grafts were applied using demographic data with Cone Beam Computed Tomography (CBCT) and to compare the bone densities between before and after implant prosthesis using the Hounsfield index. Materials and Methods : Thirty-six randomly selected computed tomography (CT) scans were used for the analysis. The same sites were evaluated digitally using the Hounsfield scale with V-Implant $2.0^{TM}$, and the results were compared with maxillary posterior bone graft. Statistical data analysis was carried out to determine the correlation between the recorded Hounsfield unit (HU) of the bone graft and implant prosthesis using a Mann-Whitney U test and Wilcoxon Matched-pairs test. Results : The bone grafted maxillary posterior teeth showed an increase in the mean values from-157 HU to 387 HU, whereas non-grafted maxillary posterior teeth showed an increase from 62 HU to 342 HU. After implantation, the grafted and non-grafted groups showed significantly higher bone density than before implantation. However, the grafted group showed significantly more changes than the non-grafted group. Conclusion : Bone density measurements using CBCT might provide an objective assessment of the bone quality as well as the correlation between bone density (Hounsfield scale) and bone grafts in the maxillary molar area.

• Journal of Periodontal and Implant Science
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• v.47 no.3
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• pp.165-173
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• 2017

Purpose: The aim of this study was to radiographically and clinically compare the effect of extracellular matrix (ECM) membranes on dimensional alterations following a ridge preservation procedure. Methods: One of 2 different ECM membranes was applied during a ridge preservation procedure. A widely used ECM membrane (WEM; Bio-Gide, Geistlich Biomaterials, Wolhusen, Switzerland) was applied in the treatment group and a newly developed ECM membrane (NEM; Lyso-Gide, Oscotec Inc., Seongnam, Korea) was applied in the control group. Cone-beam computed tomography (CBCT) scans and alginate impressions were obtained 1 week and 6 months after the ridge preservation procedure. Results were analyzed using the independent t-test and the nonparametric Mann-Whitney U test. Results: There were no significant differences between the ECM membranes in the changes in the dimension, width, and height of the extraction socket or the quantity of bone tissue. Conclusions: The NEM showed comparable clinical and radiographic results to the WEM following the ridge preservation procedure.