• Journal of Embryo Transfer
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• v.28 no.1
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• pp.63-71
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• 2013

In this study, we used flow a cytometric assay to evaluate plasma membrane integrity and mitochondrial activity in post-thawed sperm that was supplemented with ginsenoside-$Rg_1$. Varying concentrations of ginsenoside-$Rg_1$ (0, 25, 50 and $100{\mu}M/ml$) were used in the extender during cryopreservation to protect the DNA of thawed sperm, thereby increasing the viability and motility rate as evaluated using a computer-assisted sperm analysis (CASA) method. The results derived from CASA were used to compare the fresh, control, and ginsenoside-$Rg_1$ groups. Sperm motility and the number of progressively motile sperm were significantly (p<0.05) higher in the $50{\mu}M/ml$ ginsenoside-Rg1 group ($61.0{\pm}4.65%$) than in the control ($46.6{\pm}7.02%$), $25{\mu}M/ml$ ($46.2{\pm}4.76%$), and $100{\mu}M/ml$ ginsenoside-$Rg_1$ ($52.0{\pm}1.90%$) groups. However, the velocity distribution of post-thawed sperm did not differ significantly. Membrane integrity and MMP staining as revealed using flow cytometry were significantly (p<0.05) higher ($91.6{\pm}0.82%$) in the $50{\mu}M/ml$ ginsenoside-$Rg_1$ group than in the other groups. Here, we report that ginsenoside-$Rg_1$ affects the motility and viability of boar spermatozoa. Moreover, ginsenoside-$Rg_1$ can be used as a protective additive for the suppression of intracellular mitochondrial oxidative stress caused by cryopreservation.

• Journal of the Korean Vacuum Society
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• v.13 no.4
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• pp.157-163
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• 2004

Dependence of residual compressive stress of diamond-like carbon (DLC) films on relative humidity was investigated. Polymeric, graphitic and diamond-like carbon films were prepared by r.f.-PACVD using methane or benzene with the negative self bias voltage of the substrate ranging from -100 to -800 V. In-situ measurements of the residual stress were carried out in an environment chamber where the relative humidity was varied from 10％ to 90％. In dense DLC film of high residual compressive stress and hardness, we could not observe any change in the residual compressive stress with relative humidity. However, in the cases of graphitic and polymeric DLC films, abrupt change in the residual stress occurred by changing the relative humidity. The quantity of the stress change was inversely proportional to the film thickness, which means that the stress change with humidity is not due to the penetration of the water molecule into the film structure, but due to surface interaction between water molecules and film surface.

• Journal of the Korean Vacuum Society
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• v.16 no.4
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• pp.298-304
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• 2007

We have studied the effect of $N_2$ flow rate on the structural and optical properties of GaN nanorods grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy. The hexagonal shape nanorods with lateral diameters from 80 to 190 nm with increasing $N_2$ flow rate from 1.1 to 2.0 sccm are obtained. However, the ratio of length (thickness) and compact region increases with increasing $N_2$ flow rate up to 1.7 sccm and then saturate. From the photoluminescence, free exciton transition is clearly observed for GaN nanorods with low $N_2$ flow rate. And the PL peak energies are blue-shifted with decreasing diameter of the GaN nanorods due to size effect. Temperature-dependent photoluminescence spectra for the nanorods with $N_2$ flow rate of 1.7 sccm show an abnormal behavior like "S-shape" with increasing temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.327-327
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• 2011

DLC 필름은 바이오 적합성, 특히 생체 적합성이 뛰어나기 때문에 바이오 코팅분야에서 널리 이용된다. 많은 연구 결과에 의하면 세포와 장기 등이 바이오 재료 표면에 적절히 접합할 수 있도록, 재료 표면을 산소나 질소를 이용하여 플라즈마 처리로 초친수성 표면으로 개질하고 있다. 하지만, 시간이 지남에 따라서 친수성 표면은 점차 재료의 표면 처리 전의 성질인 소수성을 회복하게 된다. D실제 생체에 적용하기 위해서 이러한 시효 효과에 대한 정확한 평가가 이루어져야 한다. 따라서 산소와 질소 플라즈마 처리 후의 친수성 성질이 소수성 성질로 변해가는 거동을 조사하는게 중요하다. 13.56 MHz의 plasma assisted chemical vapor deposition (PACVD) 법을 이용하여 DLC와 Si-DLC를 500 ${\mu}m$ 두께의 P-type 실리콘(100) 기판에 증착하였다. 박막 증착 과정에 사용한 기체는 벤젠과 희석된 silane이 사용되었다(SiH4/H2=10:90). 박막 증착은 -400 V의 바이어스 전압을 인가하였으며, 이때 증착 압력은 1.33Pa으로 일정하게 유지하여, 두께 $0.55{\pm}0.01{\mu}m$로 증착하였다. X-ray Photoelectron Spectroscopy (XPS) 법을 이용하여 실리콘 함량을 측정하였으며, 증착 된 Si-DLC의 실리콘 함량은 0~4.88 at. %였다. 이후에 질소와 산소 플라즈마를 이용하여 챔버 압력을 1.33 Pa로 유지하여, -400 V의 바이어스 전압을 인가하여 10분간 표면 처리를 하였다. 표면 처리된 DLC와 Si-DLC 표면 위에서의 물방울(water droplet)의 젖음각을 20일간 측정하였다. 플라즈마 표면 처리 된 모든 시편에서 초기 젖음각은 $10{\sim}20^{\circ}$의 친수성 성질을 보였지만, 점차 젖음각이 상승하여 산소 플라즈마 처리 된 Si-DLC를 제외하고는 5일이 지나면서 거의 소수성 표면으로 회복되었다. 산소 플라즈마 처리 된 Si-DLC의 경우, 젖음 각 측정 기간(20일) 동안 $15^{\circ}$ 미만의 친수성 성질을 유지하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.78-78
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• 2011

수열합성법을 이용하여 Si(111) 기판에 ZnO 박막을 성장하였다. ZnO 박막의 성장을 위한 씨앗층은 plasma-assisted molecular beam epitaxy (PA-MBE)를 이용하였다. 씨앗층의 표면 거칠기(root-mean-square roughness)는 2.5 nm이고, 씨앗층 위에 성장된 ZnO 박막은 다양한 크기의 입자들로 이루어져 있었으며 두께는 약 $1.8{\mu}m$로 매우 일정하였다. 배향성을 알아보기 위하여 texture coefficient (TC)를 계산해 보았다. TC(100)과 TC(200)은 a-축 배향성을, TC(002)는 c-축 배향성을 나타내는데, c-축으로 더 우세한 배향성(99.5%)을 보였다. TC 비율(TCa-axis/TCc-axis)은 열처리 온도를 $700^{\circ}C$까지 올렸을 때, 점차적으로 증가하였고, 그 이상의 열처리 온도(< $900^{\circ}C$)에서는 급격히 감소하였다. 잔류응력과 Zn와 O의 bond length도 유사한 경향을 보였다. $700^{\circ}C$까지 열처리 온도가 증가함에 따라, 잔류응력은 증가하였고 bond length는 감소하였다. Near-band-edge emission (NBE)의 피크 강도는 열처리 온도가 $700^{\circ}C$까지 증가함에 따라 점차적으로 증가하였다. 열처리 온도가 $800^{\circ}C$ 이상 증가함에 따라 deep-level emission (DLE)가 적색편이(red-shift)하였다. $700^{\circ}C$로 열처리를 한 ZnO 박막이 가장 우세한 (002)방향의 배향성을 보였을 뿐만 아니라 가장 큰 발광효율 증가를 보였다.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.7
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• pp.298-304
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• 2002

Transmuted impurity atoms formed in neutron-irradiated ZnO thin films were theoretically identified first and then experimentally confirmed by photoluminescence (PL). ZnO thin films grown by plasma-assisted molecular beam epitaxy were irradiated by neutron beam at room temperature. The ZnO films consist of eight constituent (Zn and O) isotropes, of which four are transmutable by neutron-irradiation; $^{64}$ , $^{68}$ Zn, $^{70}$ Zn and $^{18}$ O were expected to transmute into $^{65}$ Cu, $^{69}$ Ga, $^{71}$ Ga, and $^{19}$ F, respectively. The concentrations of these transmuted atoms were estimated in this study by considering natural abundance, neutron fluence and neutron cross section. The neutron-irradiated ZnO thin films were characterized by PL. In the PL spectra of the ZnO thin films, the Cu-related PL peaks were seen, but the Ga- or F-associated PL peaks were absent. This observation confirmed the existence of $^{65}$ Cu in the ZnO, but it could not do the formation of the other two. In this paper, the emission mechanism of Cu impurities is described and the reason for the absence of the Ga- or F-associated PL peaks is discussed as well.

• Korean Journal of Materials Research
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• v.30 no.3
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• pp.142-148
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• 2020

Graphene has attracted the interest of many researchers due to various its advantages such as high mobility, high transparency, and strong mechanical strength. However, large-area graphene is grown at high temperatures of about 1,000 ℃ and must be transferred to various substrates for various applications. As a result, transferred graphene shows many defects such as wrinkles/ripples and cracks that happen during the transfer process. In this study, we address transfer-free, large-scale, and high-quality monolayer graphene. Monolayer graphene was grown at low temperatures on Ti (10nm)-buffered Si (001) and PET substrates via plasma-assisted thermal chemical vapor deposition (PATCVD). The graphene area is small at low mTorr range of operating pressure, while 4 × 4 ㎠ scale graphene is grown at high working pressures from 1.5 to 1.8 Torr. Four-inch wafer scale graphene growth is achieved at growth conditions of 1.8 Torr working pressure and 150 ℃ growth temperature. The monolayer graphene that is grown directly on the Ti-buffer layer reveals a transparency of 97.4 % at a wavelength of 550 nm, a carrier mobility of about 7,000 ㎠/V×s, and a sheet resistance of 98 W/□. Transfer-free, large-scale, high-quality monolayer graphene can be applied to flexible and stretchable electronic devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.95-95
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• 2013

박막 공정 기술은 반도체 및 디스플레이뿐만 아니라 대부분의 전자소자에 적용되는 매우 중요한 기술이다. 그 중, 마그네트론 스퍼터링 공정은 플라즈마를 이용하여 금속 및 세라믹 등의 벌크 물질을 박막으로 증착 가능한 가장 널리 사용되는 방법 중의 하나이다. 하지만, Fe, Co, Ni 같은 강자성체 재료는 공정이 불가능하며, 스퍼터링 타겟 효율이 40% 이하이고, 제한적인 방전압력 범위 및 전류 상승에 의한 높은 전압 인가 제한이 있다는 단점이 있다. 본 연구에서 사용된 고밀도 플라즈마 소스를 적용한 고효율 스퍼터링 시스템은 할로우 음극을 이용한 원거리에서 고밀도 플라즈마를 생성하여 전자석 코일을 통해 자석이 없는 음극으로 이온을 수송시켜 스퍼터링을 일으킨다. 따라서 강자성체 재료의 스퍼터링이 가능하며, 90% 이상의 타겟 사용 효율 구현 및 기존 마그네트론 스퍼터링 대비 고속 증착이 가능하다. 또한, $10^{-4}$ Torr 압력영역에서 방전 및 스퍼터링이 가능하다. 타겟 이온 전류를 타겟 인가 전압과 관계없이 0~4 A까지, 타겟 이온 전류와 상관없이 타겟 인가 전압을 70~1,000 V 이상까지 독립적으로 제어가능하다. 또한 TiN과 같은 질소 반응성 공정에서 반응성 가스인 질소를 40%까지 넣어도 타겟에 수송되는 이온의 양에 영향이 없다. 할로우 음극 방전 전류 40 A에서 발생된 플라즈마의 이온에너지 분포는 55 eV에서 가우시안 분포를 보였으며, 플라즈마 포텐셜인 sheath drop은 74 V 였다. OES를 통한 광학적 진단 결과, 전자석에 의한 이온빔 초점에 따라 플라즈마 이온화율을 1.8배까지 증가시킬 수 있으며, 할로우 음극 방전 전류가 60~100 A로 증가하면서 플라즈마 이온화율을 6배까지 증가 가능하다. 또한, 타겟 이온 전류와 관계없이 타겟 인가 전압을 300~800 V로 증가시킴에 따라 Ar 이온 밀도의 경우 1.4배 증가, Ti 이온 밀도의 경우 2.2배 증가시킬 수 있었으며, TiN의 경우 증착 속도도 16~44 nm/min으로 제어가 가능하다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.105-105
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• 2016

Recently, high power impulse magnetron sputtering (HIPIMS) has attracted considerable attentions due to its high potential for industrial applications. By pulsing the sputtering target with high power density and short duration pulses, a high plasma density and high ionization of the sputtered species can be obtained. HIPIMS has exhibited several merits such as increased coating density, good adhesion, microparticle-free and smooth surface, which make the HIPIMS technique desirable for synthesizing hard coatings. However, hard coatings present intrinsic defects (columnar structures, pinholes, pores, discontinuities) which can affect the corrosion behavior, especially when substrates are active alloys like steel or in a wear-corrosion process. Atomic layer deposition (ALD), a CVD derived method with a broad spectrum of applications, has shown great potential for corrosion protection of high-precision metallic parts or systems. In ALD deposition, the growth proceeds through cyclic repetition of self-limiting surface reactions, which leads to the thin films possess high quality, low defect density, uniformity, low-temperature processing and exquisite thickness control. These merits make ALD an ideal candidate for the fabrication of excellent oxide barrier layer which can block the pinhole and other defects left in the coating structure to improve the corrosion protection of hard coatings. In this work, CrN/Al2O3/CrN multilayered coatings were synthesized by a hybrid process of HIPIMS and ALD techniques, aiming to improve the CrN hard coating properties. The influence of the Al2O3 interlayer addition, the thickness and intercalation position of the Al2O3 layer in the coatings on the microstructure, surface roughness, mechanical properties and corrosion behaviors were investigated. The results indicated that the dense Al2O3 interlayer addition by ALD lead to a significant decrease of the average grain size and surface roughness and greatly improved the mechanical properties and corrosion resistance of the CrN coatings. The thickness increase of the Al2O3 layer and intercalation position change to near the coating surface resulted in improved mechanical properties and corrosion resistance. The mechanism can be explained by that the dense Al2O3 interlayer acted as an excellent barrier for dislocation motion and diffusion of the corrosive substance.

• Journal of the Korean Vacuum Society
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• v.7 no.s1
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• pp.15-19
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• 1998

Structural and optical properties of $In_xGa_{1-X}N$ as well as $In_{0.1}Ga_{0.9}N$/GaN single quantum we11 (SQW) grown on sapphire (0001) substrate with an based GaN using rf-plasma assisted MBE have been investigated. The quality of the InXGal.,N fdm was improved as the growth temperature increased. In PL measurements at low temperatures, the band edge emission peaks of $In_xGa_{1-X}N$ was shifted to red region as an indium cell and substrate temperature increased. For $In_{0.1}Ga_{0.9}N$/GaN SQW, the optical emission energy has blue shift about 15meV in PL peak, due to the confined energy level in the well region. And, the FWHM of the $In_{0.1}Ga_{0.9}N$/GaN SQW was larger than that of the bulk Ino,la.9N films. The broadening of FWHM can be explained either as non-uniformity of Indium composition or the potential fluctuation in the well region. Photoconductivity (PC) decay measurement reveals that the optical transition lifetimes of the SQW measured gradually increased with temperatures.