• Journal of the Korean institute of surface engineering
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• v.38 no.2
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• pp.65-68
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• 2005

The effect of crystal orientation and microstructure on the mechanical properties of $TaN_x$ was investigated. $TaN_x$ films were grown on $SiO_2$ substrates by ultrahigh vacuum unbalanced magnetron sputter deposition in mixed $Ar/N_2$ discharges at 20 mTorr (2.67 Pa) and at $350^{\circ}C$. Unlike the Ti-N system, in which TiN is the terminal phase, a large number of N-rich phases in the Ta-N system could lead to layers which had nano-sized lamella structure of coherent cubic and hexagonal phases, with a correct choice of nitrogen fraction in the sputtering mixture and ion irradiation energy during growth. The preferred orientations and the micro-structure of $TaN_x$ layers were controlled by varing incident ion energy $E_i\;(=30eV\~50eV)$ and nitrogen fractions $f_{N2}\;(=0.1\~0.15)$. $TaN_x$ layers were grown on (0002)-Ti underlayer as a crystallographic template in order to relieve the stress on the films. The structure of the $TaN_x$ film transformed from Bl-NaCl $\delta-TaN_x$ to lamellar structured Bl-NaCl $\delta-TaN_x$ + hexagonal $\varepsilon-TaN_x$ or Bl-NaCl $\delta-TaN_x$ + hexagonal $\gamma-TaN_x$ with increasing the ion energy at the same nitrogen fraction $f_{N2}$. The hardness of the films also increased by the structural change. At the nitrogen fraction of $0.1\~0.125$, the structure of the $TaN_x$ films was changed from $\delta-TaN_x\;+\;\varepsilon-TaN_x\;to\;\delta-TaN_x\;+\;\gamma-TaN_x$ with increasing the ion energy. However, at the nitrogen fraction of 0.15 the film structure did not change from $\delta-TaN_x\;+\;\varepsilon-TaN_x$ over the whole range of the applied ion energy. The hardness increased significantly from 21.1 GPa to 45.5 GPa with increasing the ion energy.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.8
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• pp.587-592
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• 2010

We have fabricated schottky barrier diode (SBDs) using polar (c-plane) and non polar (a-, m-plane) n-type 6H-SiC wafers. Ni/SiC ohmic contact was accomplished on the backside of the SiC wafers by thermal evaporation and annealed for 20minutes at $950^{\circ}C$ in mixture gas ($N_2$ 90% + $H_2$ balanced). The specific contact resistance was $3.6{\times}10^{-4}{\Omega}cm^2$ after annealing at $950^{\circ}C$. The XRD results of the alloyed contact layer show that formation of $NiSi_2$ layer might be responsible for the ohmic contact. The active rectifying electrode was formed by the same thermal evaporation of Ni thin film on topside of the SiC wafers and annealed for 5 minutes at $500^{\circ}C$ in mixture gas ($N_2$ 90% + $H_2$ balanced). The electrical properties of SBDs have been characterized by means of I-V and C-V curves. The forward voltage drop is about 0.95 V, 0.8 V and 0.8 V for c-, a- and m-plane SiC SBDs respectively. The ideality factor (${\eta}$) of all SBDs have been calculated from log(I)-V plot. The values of ideality factor were 1.46, 1.46 and 1.61 for c-, a- and m-plane SiC SBDs, respectively. The schottky barrier height (SBH) of all SBDs have been calculated from C-V curve. The values of SBH were 1.37 eV, 1.09 eV and 1.02 eV for c-, a- and m-plane SiC SBDs, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.425-425
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• 2009

그라핀을 금속 촉매를 이용하여 상압 혹은 저진공 CVD로 성장할 경우 대형 기판을 쉽게 얻을 수 있으므로 최근 들어 금속 촉매를 이용한 CVD 기술이 재 각광받고 있다. 최근 MIT의 Jing Kong 그룹, Purdue 대학의 Yong P. Chen 그룹, 국내에서는 성균관대학에서 이에 대한 논문을 발표한 바 있다. CVD 방법의 가장 큰 장점은 그라핀 박막의 가장 큰 문제점 중 하나인 대형 기판에 매우 유리하다는 점이다. 본 연구에서는 결함 없는 대형 그라핀기판을 얻기위해 Si/$SiO_2$/Ni 박막위에 그라핀을 LPCVD로 성장하는 실험을 진행하였다. 우선 시료는 Si위에 $SiO_2$를 Sputtering으로 증착하였고, 그 위에 250nm, 300nm두께의 Ni 박막을 e-beam evaporator로 증착하였다. $0.5-1cm^2$ 크기의 샘플을 Thermal CVD 장비를 이용하여 그라핀을 성장하는 실험을 진행하였다. 성장 압력은 95 torr, 성장온도는 $800^{\circ}C$, $850^{\circ}C$, $900^{\circ}C$에서 Hydrocarbon ($C_2H_2$)을 5min, 10min으로 성장시간을 split하였다. Hydrocarbon을 흘리기 전에 Ni grain을 성장하기 위해 성장온도에서 30~60min정도 $H_2$분위기에서 Ni 산화막의 환원 및 어닐링을 진행하였다. 그림.1은 $850^{\circ}C$, 5분간 성장한 그라핀/Ni 샘플의 광학사진이다. 그림.2는 $850^{\circ}C$에서 5min, 10min 성장한 샘플의 Raman spectrum이다. (파장은 514.532nm). 850C 10min 샘플은 G>G' peak 이지만, 5min으로 성장한 샘플의 경우 G'>G peak 임을 알 수 있고, 따라서 5min의 조건에서는 층 두께가 4층 미만의 그라핀 박막을 얻을 수 있음을 보여준다. 또한 G' peak의 위치가 두께가 감소할수록 내려감을 확인할 수 있다. 다만 D peak가 실험한 대부분의 샘플에서 보여서 아직 성장한 그라핀의 결합이 많은 것으로 보인다. 이러한 이유는 성장온도가 낮은 것이 일차 원인으로 생각되며 박막의 균일도 향상과 결함을 줄이기 위한 추가적인 개선 실험을 진행 중이다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.2
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• pp.75-79
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• 2017

Honeycomb-shaped Ag-grid transparent conductive electrodes (TCEs) were fabricated using two different processes, high density plasma etching and lift-off, and the optical and electrical properties were compared according to the fabrication method. For the fabrication of the Ag-grid TCEs by plasma etching, etch characteristics of the Ag thin film in $10CF_4/5Ar$ inductively coupled plasma (ICP) discharges were studied. The Ag etch rate increased as the power increased at relatively low ICP source power or rf chuck power conditions, and then decreased at higher powers due to either decrease in $Ar^+$ ion energy or $Ar^+$ ion-assisted removal of the reactive F radicals. The Ag-grid TCEs fabricated by the $10CF_4/5Ar$ ICP etching process showed better grid pattern transfer efficiency without any distortion or breakage in the grid pattern and higher optical transmittance values of average 83.3 % (pixel size $30{\mu}m/line$ width $5{\mu}m$) and 71 % (pixel size $26{\mu}m/line$ width $8{\mu}m$) in the visible range of spectrum, respectively. On the other hand, the Ag-grid TCEs fabricated by the lift-off process showed lower sheet resistance values of $2.163{\Omega}/{\square}$ (pixel size $26{\mu}m/line$ width $18{\mu}m$) and $4.932{\Omega}/{\square}$ (pixel size $30{\mu}m/line$ width $5{\mu}m$), respectively.

• Journal of the Korean Ceramic Society
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• v.39 no.5
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• pp.460-466
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• 2002

Titanium oxide film was deposited on the commercially pure titanium (cp-Ti) by thermal oxidation method for its medical application. The cp-Ti disks were cleaned and then heat-treated at the temperatures of 500, 550, 600, 650, and 700${\circ}C$, respectively, for 10 min in air or Ar. To test the ability of calcium phosphate formation, the specimens were immersed in the Eagle's minimum essential medium solution at 36.5${\circ}C$ for 15 days. The morphology and chemical composition of the surfaces before and after soaking were analyzed by using FE-SEM and EDS. The in-vitro formation of carbonated calcium phosphate on the thin films containing nano-sized $TiO_2$ crystals was identified.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.127-134
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• 2015

Aluminum nitride (AlN) single crystals have attracted much attention for a next-generation semiconductor application because of wide bandgap (6.2 eV), high thermal conductivity ($285W/m{\cdot}K$), high electrical resistivity (${\geq}10^{14}{\Omega}{\cdot}cm$), and high mechanical strength. The bulk AlN single crystals or thin film templates have been mainly grown by PVT (sublimation) method, flux method, solution growth method, and hydride vapor phase epitaxy (HVPE) method. Since AlN suffers difficulty in commercialization due to the defects that occur during single crystal growth, crystalline quality improvement via defects analyses is necessary. Etch pit density (EPD) analysis showed that the growth misorientations and the defects in the AlN surface exist. Transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) analyses were employed to investigate the overall crystalline quality and various kinds of defects. TEM studies show that the morphology of the AlN is clearly influenced by stacking fault, dislocation, second phase, etc. In addition EBSD analysis also showed that the zinc blende polymorph of AlN exists as a growth defects resulting in dislocation initiator.

• Korean Journal of Metals and Materials
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• v.47 no.5
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• pp.322-329
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• 2009

60 nm- and 20 nm-thick hydrogenated amorphous silicon (a-Si:H) layers were deposited on 200 nm $SiO_2/Si$ substrates using ICP-CVD (inductively coupled plasma chemical vapor deposition). A 10 nm-Ni layer was then deposited by e-beam evaporation. Finally, 10 nm-Ni/60 nm a-Si:H/200 nm-$SiO_2/Si$ and 10 nm-Ni/20 nm a-Si:H/200 nm-$SiO_2/Si$ structures were prepared. The samples were annealed by rapid thermal annealing for 40 seconds at $200{\sim}500^{\circ}C$ to produce $NiSi_x$. The resulting changes in sheet resistance, microstructure, phase, chemical composition and surface roughness were examined. The nickel silicide on a 60 nm a-Si:H substrate showed a low sheet resistance at T (temperatures) >$450^{\circ}C$. The nickel silicide on the 20 nm a-Si:H substrate showed a low sheet resistance at T > $300^{\circ}C$. HRXRD analysis revealed a phase transformation of the nickel silicide on a 60 nm a-Si:H substrate (${\delta}-Ni_2Si{\rightarrow}{\zeta}-Ni_2Si{\rightarrow}(NiSi+{\zeta}-Ni_2Si)$) at annealing temperatures of $300^{\circ}C{\rightarrow}400^{\circ}C{\rightarrow}500^{\circ}C$. The nickel silicide on the 20 nm a-Si:H substrate had a composition of ${\delta}-Ni_2Si$ with no secondary phases. Through FE-SEM and TEM analysis, the nickel silicide layer on the 60 nm a-Si:H substrate showed a 60 nm-thick silicide layer with a columnar shape, which contained both residual a-Si:H and $Ni_2Si$ layers, regardless of annealing temperatures. The nickel silicide on the 20 nm a-Si:H substrate had a uniform thickness of 40 nm with a columnar shape and no residual silicon. SPM analysis shows that the surface roughness was < 1.8 nm regardless of the a-Si:H-thickness. It was confirmed that the low temperature silicide process using a 20 nm a-Si:H substrate is more suitable for thin film transistor (TFT) active layer applications.

• Journal of Industrial Convergence
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• v.20 no.10
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• pp.33-38
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• 2022

In this paper, a simple method of forming a solution-based carbon nanotube (CNT) for use as a conductive material for electronic devices was studied. The CNT thin film coating was performed on the glass by applying the spin coating method and the argon atmospheric pressure plasma process. In order to observe changes in electrical and physical properties according to the number of coatings, samples formed in the same manner from times 1 to 5 were prepared, and surface shape, reflectance, transmittance, absorbance, and sheet resistance were measured for each sample. As the number of coatings increased, the transmittance decreased, and the reflectance and absorptivity increased in the entire measurement wavelength range. Also, as the wavelength decreases, the transmittance decreases, and the reflectance and absorption increase. In the case of electrical properties, it was confirmed that the conductivity was significantly improved when the second coating was applied. In conclusion, in order to replace CNT with a transparent electrode, it is necessary to consider the number of coatings in consideration of reflectivity and electrical conductivity together, and it can be seen that 2 times is optimal.

• Membrane Journal
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• v.33 no.4
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• pp.149-157
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• 2023

Covalent organic frameworks (COFs) have shown promise in various applications, including molecular separation, dye separation, gas separation, filtration, and desalination. Integrating COFs into membranes enhances permeability, selectivity, and stability, improving separation processes. Combining COFs with single-walled carbon nanotubes (SWCNT) creates nanocomposite membranes with high permeability and stability, ideal for dye separation. Incorporating COFs into polyamide (PA) membranes improves permeability and selectivity through a synthetic interfacial strategy. Three-dimensional COF fillers in mixed-matrix membranes (MMMs) enhance CO₂/CH₄ separation, making them suitable for biogas upgrading. All-nanoporous composite (ANC) membranes, which combine COFs and metal-organic framework (MOF) membranes, overcome permeance-selectivity trade-offs, significantly improving gas permeance. Computational simulations using hypothetical COFs (hypoCOFs) demonstrate superior CO₂ selectivity and working capacity relevant for CO₂ separation and H₂ purification. COFs integrated into thin-film composite (TFC) and polysulfonamide (PSA) membranes enhance rejection performance for organic contaminants, salt contaminants, and heavy metal ions, improving separation capabilities. TpPa-SO₃H/PAN covalent organic framework membranes (COFMs) exhibited superior desalination performance compared to traditional polyamide membranes by utilizing charged groups to enable efficient desalination through electrostatic repulsion, suggesting their potential for ionic and molecular separations. These findings highlight COFs' potential in membrane technology for enhanced separation processes by improving permeability, selectivity, and stability. In this review, COF applied for the separation process is discussed.