• Journal of Korean Vacuum Science & Technology
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• v.2 no.2
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• pp.63-77
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• 1998

The oxidation of NiAl(110) was investigated in the temperature regime between 300K and 1300 K using LEED (low energy electron diffraction), TPD (temperature programmed desorption) and HREELS (high resolution electron energy loss spectroscopy). The adsorption of N2O and O2 up to reconstructions. Stepwise annealing of the oxygen-saturated sample from 600 K to 1300K in UHV (ultra-high vacuum,) results in firstly the onset of randomly oriented then finally fairly well-ordered. 5 ${\AA}$ Al2O3 film with quasi-hexagonal periodicity. Ordered thicker oxide films of 18-30 ${\AA}$ seem to be grown on this interfacial oxide layer by direct oxidation of sample at elevated temperature between 1150 and 1300 K because of the LEED pattern consisting of new broad hexagonal spots and the previous 5 ${\AA}$ spots. Although the periodicity of surface oxygen arrays shows no significant change from an hexagonal close-packing, the O-O distance changes from ∼3.0 ${\AA}$ film to ∼2.9 ${\AA}$ for thicker oxides. with the appearance of Auger parameter, for the 5${\AA}$ film can be described better as an interfacial oxide layer. The observation of three symmetric phonon peaks can be also a supporting evidence for this phase assignment since thicker oxide films on the Same Ni2Al3(110) show somewhat different phonon structure much closer to that of the ${\gamma}$-Al2O3. The adsorption/desorption of methanol further proves the preparation of less-defective and/or oxygen-terminated Al2O3 films showing ordered phase transitions with the change of oxide thickness between 5 ${\AA}$ to 30 ${\AA}$.

• Journal of the Korean Vacuum Society
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• v.9 no.3
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• pp.221-226
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• 2000

After manufacturing the electrochromic device (structure: ITO glass/$WO_3$/electrolyte/$V_2O_5$/ITO;glass) by using of sol-gel process and evaporation, optical properties and migration effect were investigated. The result shows that electrochromic device with heat treated (at water vapor ambient, $500^{\circ}C$, 1 hour) sol-gel coated $WO_3$ and $V_2O_5$ films had the highest transmittance variance. Electrochromic devices are based on the reversible insertion of guest atoms into structure of the host solid. But after cyclic operation, we find that the tungsten in $WO_3$ film and the indium in ITO film were migrated with each other. For the purpose of blocking migration, tungsten barrier film is inserted between ITO and $WO_3$ film. The result of cyclic voltamogram and the Auger depth profile show that the peak separation of cyclic voltamogram is reduced to below 1/10 and we could effectively block the indium and tungsten migration that is caused by flow of Li ions.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.33-33
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• 2000

일반적으로 GaN-based light emitting diodes(LEDs)는 Top layer위에 금속박막으로 contact을 형성하고 있으며 광소자 구성에 있어 빛은 이러한 금속 contact을 통과할 수 없다. 그러나 만약 이러한 contact이 투명전도막으로 구성될 수 있다면 보다 효율적인 광소자의 구성이 기대되어진다. 특히 GaN photodetector, GaN-based LEDs, GaN vertical cavity surface emitting lasers(VCSELs)등의 소자형성에 있어 투명전도막 contact은 매우 중요하며 그 응용에 앞서 기본적인 구조적, 전기적, 광학적 특성에 대한 연구가 반드시 선행되어져야 한다. 따라서 본 실험에서는 이러한 투명전도막으로써 Indium Tin Oxide(ITO)를 사용하였으며 박막형태의 contact으로 제조하여 n-GaN, p-GaN와 corning glass위에 e-beam evaporation법로써 제조하였다. 또한 각 n-, p-type과 corning glass위에 증착된 ITO박막의 구조적 특성을 분석하기 위하여 x-ray diffractometry(XRD)와 Auger electron spectroscopy(AES)등을 사용하였으며 전기적 특성을 측정하기 위하여 four point probe를 사용하였고 그들의 I-V 곡선을 측정하였다. 또한 UV spectrometry를 사용하여 그들의 광학적 특성을 측정하고자 하였다. ITO 박막의 제조에 있어 기판은 초음파 유기세정 후 HCl과 H2O2(1:1)의 혼합용액을 사용하여 GaO2를 제거하고자 하였으며 이후 초순수로 세척하여 사용하였다. 초기 진공도는 3$\times$10-5 Torr이하였으며 기판온도 50$0^{\circ}C$에서 0.6 /s의 증착속도로 약 2000 증착하였다. 이렇게 제조된 ITO 박막은 5$\times$10-5 Torr이하의 진공분위기에서 $600^{\circ}C$로 열처리를 실시하였으며 열처리 시간의 변화에 따른 그들의 전기적, 구조적, 광학적 특성을 측정하였다. 열처리 과정을 통한 ITO박막은 투과도는 420nm의 영역에서 80%이상을 나타내었으며 이때의 면저항은 약 50ohm/ 이었다. 또한 I-V 곡선 측정에 의한 contact특성의 측정결과 열처리 전의 ITO contact은 n-GaN와 n-GaN에 대해 각각 ohmic과 schottky contact의 일반적인 contact 특성을 나타내었다. 그러나 이러한 contact 특성은 열처리 시간의 변화에 따라 변화하는 것을 확인할 수 있었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.131-131
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• 2010

We compared the electrical, optical, structural, and interface properties of indium zinc oxide (IZO)-Ag-IZO and IZO-Au-IZO multilayer electrodes deposited by linear facing target sputtering system at room temperature for organic photovoltaics. The IZO-Ag-IZO and IZO-Au-IZO multilayer electrodes show a significant reduction in their sheet resistance (4.15 and 5.49 Ohm/square) and resistivity ($3.9{\times}10^{-5}$ and $5.5{\times}10^{-5}$Ohm-cm) with increasing thickness of the Ag and Au layers, respectively. In spite of its similar electrical properties, the optical transmittance of the IZO-Ag-IZO electrode is much higher than that of the IZO-Au-IZO electrode, due to the more effective antireflection effect of Ag than Au in the visible region. In addition, the Auger electron spectroscopy depth profile results for the IZO/Ag/IZO and IZO/Au/IZO multilayer electrodes showed no interfacial reaction between the IZO layer and Ag or Au layer, due to the low preparation temperature. To investigate in detail the Ag and Au structures on the bottom IZO electrode with increasing thickness, a synchrotron x-ray scattering examination was employed. Moreover, the OSC fabricated on the IZO-Ag-IZO electrode shows a higher power conversion efficiency (3.05%) than the OSC prepared on the IZO-Au-IZO electrode (2.66%), due to its high optical transmittance in the wavelength range of 400-600 nm, which is the absorption wavelength of the P3HT:PCBM active layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.229.2-229.2
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• 2013

Yttrium oxide (Y2O3)는 band gap이 5.5 eV 정도로 상대적으로 넓고, 굴절상수가 1.8, 유전율이 10~15, Silicon 과의 격자 불일치가 작은 특성을 가지고 있다. 또한 녹는점이 높아 열적으로 안정하기 때문에 전자소자 및 광학소자에 다양하게 응용되는 물질이다. Y2O3 박막은 다양한 방법으로 증착할 수 있는데, 그 방법에는 e-beam evaporation, laser ablation, sputtering, thermal oxidation, metal-organic chemical vapor deposition, and atomic layer deposition (ALD) 등이 있다. ALD는 기판 표면에 흡착된 원자들의 자기 제한적 반응에 의하여 박막이 증착되기 때문에 박막 두께조절이 용이하고 step coverage와 uniformity 측면에서 큰 장점이 있다. 이전에는 Y(thd)3 and Y(CH3Cp)3 와 같은 금속 전구체를 이용하여 ALD를 진행하여, 증착 속도가 낮고 defect이 많아 non-stoichiometric한 조성의 박막이 증착되는 문제점이 있었다. 이번 연구에서는, (iPrCp)2Y(iPr-amd)와 탈이온수를 사용하여 Y2O3 박막을 증착하였다. Y2O3 박막 증착에 사용한 Y 전구체는 상온에서 액체이고 $192^{\circ}C$ 에서 1 Torr의 높은 증기압을 갖는다. Y2O3 박막 증착을 위하여 Y 전구체는 $150^{\circ}C$ 로 가열하여 N2 gas를 이용하여 bubbling 방식으로 공정 챔버 내로 공급하였다. Y2O3 박막의 ALD window는 $250{\sim}350^{\circ}C$ 였으며, Y 전구체의 공급시간이 5초에 다다르자 더 이상 증착 두께가 증가하지 않는 자기 제한적 반응을 확인할 수 있었다. 그리고 증착된 Y2O3 박막의 특성 분석을 위해 Atomic force microscopy (AFM)과 X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) 를 진행하였다. 박막의 Surface morphology 는 매끄럽고 uniform 하였으며, 특히 고체 금속 전구체를 사용했을 때와 비교하여 수산화물이 거의 없는 박막을 얻을 수 있었다. 그리고 조성 분석을 통해 증착된 Y2O3 박막이 stoichiometric하다는 것을 알수 있었다. 또한 metal-insulator-metal (MIM) 구조 (Ru/Y2O3/Ru) 의 resistor 소자를 형성하여 저항 스위칭 특성을 확인하였다.

• Korean Journal of Materials Research
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• v.11 no.2
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• pp.71-75
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• 2001

The reaction stability of nickel with side-wall materials of SiO$_2$ and Si$_3$N$_4$ on p-type 4"(100) Si substrate were investigated. Ni on 1300 $\AA$ thick SiO$_2$ and 500 $\AA$ - thick Si$_3$N$_4$ were deposited. Then the samples were annealed at 400, 500, 750 and 100$0^{\circ}C$ for 30min, and the residual Ni layer was removed by a wet process. The interface reaction stability was probed by AES depth Profiling. No reaction was observed at the Ni/SiO$_2$ and Ni/Si$_3$N$_4$, interfaces at 400 and 50$0^{\circ}C$. At 75$0^{\circ}C$, no reaction occurred at Ni/SiO$_2$ interface, while $NiO_x$ and Si$_3$N$_4$ interdiffused at Ni/Si$_3$N$_4$ interface. At 100$0^{\circ}C$, Ni layers on SiO$_2$ and Si$_3$N$_4$ oxidized into $NiO_x$ and then $NiO_x$ interacted with side-wall materials. Once $NiO_x$ was formed, it was not removed in wet etching process and easily diffused into sidewall materials, which could lead to bridge effect of gate-source/drain.

• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.916-922
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• 1997

A superconducting phase La2CuO4+δ (Tc=44 K) has been prepared by electrochemical oxidation which allows the oxygen to intercalat into the La2O2 layers. According to the Cu K-edge X-ray absorption near edge structure spectroscopic analysis, the oxidized phase shows an overall spectra shift of about 0.5 eV to a higher energy region compared to the as sintered one with the occurrence of an additional peak corresponding to the transition to the |1s13dn+1L-14pσ1 > final state, indicating the oxidation of CuO2 layer. From the X-ray photoelectron spectroscopic studies, it is found that the binding energy of La 3d5/2 is significantly shifted from 834.3 eV (as sintered La2CuO4) to 833.6 eV (as electrochemically oxidized La2CuO4+δ), implying that the covalency of the (La-O) bond is decreased due to the oxygen intercalation. The O 1s spectra do not provide an evidence of the superoxide or peroxide, but the oxide (O2-) with the contaminated carbonate (CO32-) based on the peaks at 529 eV and 532 eV, respectively, which is clearly confirmed by the Auger spectroscopic analysis. Oxygen contents determined by iodometric titration (δ=0.07) and thermogravimetry (δ=0.09) show good coincidence each other, also giving an evidence for the "O2-" nature of excess oxygen. From the above results, it is concluded that "O2-" appeared as O 1s peak at 528.6 eV is responsible for superconductivity of La2CuO4+δ.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.109-118
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• 2018

Two-row overlap pile wall, currently under development for use in deep excavations, is a novel retaining structure designed to perform itself as a cutoff wall as well as a high-stiffness wall by constructing four overlapping piles arranged in zigzag manner at a time using a tetra-axis auger. This wall has a relatively complex cross-section, compared with other types of pile wall, which would make it difficult to determine design parameters related to cross-section. In this study, a flexural rigidity equation has been derived by analyzing both theoretically and statistically various wall cross-sections with different pile diameters and overlap lengths. The flexural rigidity equation was found to show the maximum error rate of 3%.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.129-139
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• 2018

The Discrete Element Method (DEM) has been widely used in granular material researches. Especially, if material has a large deformation, such as ground, it can be a useful method to analyze. In this study, to simulate ground formations, DEM was used. The main purpose of DEM analysis was to investigate the numerical model which can predict the TBM performance by simulating excavating procedure. The selected EPB TBM has a 7.73 m of diameter and six spokes. And two pre-defined excavation conditions with the different rotation speeds per minute (RPM) of the cutterhead was applied. In the modeled cutterhead, the open ratio of cutterhead was 21.31% and number of cutters (including disc cutter and cutter bit) was 219. From the results, reaction forces and resistant torques at the cutterhead face and cutting tools, were measured and compared. Additionally the muck discharge rate and accumulated muck discharge by the screw auger were evaluated.

• Korean Journal of Metals and Materials
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• v.49 no.4
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• pp.313-320
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• 2011

100 nm-thick hydrogenated amorphous silicon $({\alpha}-Si:H)$ films were deposited on a glass and glass/30 nm Ni substrates by inductively-coupled plasma chemical vapor deposition (ICP-CVD) at temperatures ranging from 100 to $550^{\circ}C$. The sheet resistance, microstructure, phase transformation and surface roughness of the films were characterized using a four-point probe, AFM (atomic force microscope), TEM (transmission electron microscope), AES (Auger electron spectroscopy), HR-XRD(high resolution X-ray diffraction), and micro-Raman spectroscopy. A nano-thick NiSi phase was formed at substrate temperatures >$400^{\circ}C$. AFM confirmed that the surface roughness did not change as the substrate temperature increased, but it increased abruptly to 6.6 nm above $400^{\circ}C$ on the glass/30 nm Ni substrates. HR-XRD and micro-Raman spectroscopy showed that all the Si samples were amorphous on the glass substrates, whereas crystalline silicon appeared at $550^{\circ}C$ on the glass/30 nm Ni substrates. These results show that crystalline NiSi and Si can be prepared simultaneously on Ni-inserted substrates.