• Korean Journal of Materials Research
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• v.24 no.12
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• pp.694-699
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• 2014

We report the chemical vapor deposition growth characteristics of graphene on various catalytic metal substrates such as Ni, Fe, Ag, Au, and Pt. 50-nm-thick metal films were deposited on $SiO_2/Si$ substrates using dc magnetron sputtering. Graphene was synthesized on the metal/$SiO_2$/Si substrates with $CH_4$ gas (1 SCCM) diluted in mixed gases of 10% $H_2$ and 90 % Ar (99 SCCM) using inductively-coupled plasma chemical vapor deposition (ICP-CVD). The highest quality of graphene film was achieved on Ni and Fe substrates at $900^{\circ}C$ and 500 W of ICP power. Ni substrate seemed to be the best catalytic material among the tested materials for graphene growth because it required the lowest growth temperature ($600^{\circ}C$) as well as showing a low ICP power of 200W. Graphene films were successfully grown on Ag, Au, and Pt substrates as well. Graphene was formed on Pt substrate within 2 sec, while graphene film was achieved on Ni substrate over a period of 5 min of growth. These results can be understood as showing the direct CVD growth of graphene with a highly efficient catalytic reaction on the Pt surface.

• Korean Journal of Materials Research
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• v.23 no.1
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• pp.47-52
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• 2013

Graphene has been synthesized on 100- and 300-nm-thick Ni/$SiO_2$/Si substrates with $CH_4$ gas (1 SCCM) diluted in mixed gases of 10% $H_2$ and 90% Ar (99 SCCM) at $900^{\circ}C$ by using inductively-coupled plasma chemical vapor deposition (ICP-CVD). The film morphology of 100-nm-thick Ni changed to islands on $SiO_2$/Si substrate after heat treatment at $900^{\circ}C$ for 2 min because of grain growth, whereas 300-nm-thick Ni still maintained a film morphology. Interestingly, suspended graphene was formed among Ni islands on 100-nm-thick Ni/$SiO_2$/Si substrate for the very short growth of 1 sec. In addition, the size of the graphene domains was much larger than that of Ni grains of 300-nm-thick Ni/$SiO_2$/Si substrate. These results suggest that graphene growth is strongly governed by the direct formation of graphene on the Ni surface due to reactive carbon radicals highly activated by ICP, rather than to well-known carbon precipitation from carbon-containing Ni. The D peak intensity of the Raman spectrum of graphene on 300-nm-thick Ni/$SiO_2$/Si was negligible, suggesting that high-quality graphene was formed. The 2D to G peak intensity ratio and the full-width at half maximum of the 2D peak were approximately 2.6 and $47cm^{-1}$, respectively. The several-layer graphene showed a low sheet resistance value of $718{\Omega}/sq$ and a high light transmittance of 87% at 550 nm.

• Journal of the Korean institute of surface engineering
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• v.48 no.6
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• pp.297-302
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• 2015

Nanocrystalline diamond(NCD) coated aluminium plates were prepared and applied as heat sinks for LED modules. NCD films were deposited on 1 mm thick Al plates for times of 2 - 10 h in a microwave plasma chemical vapor deposition reactor. Deposition parameters were the microwave power of 1.2 kW, the working pressure of 90 Torr, the $CH_4/Ar$ gas ratio of 2/200 sccm. In order to enhance diamond nucleation, DC bias voltage of -90 V was applied to the substrate during deposition without external heating. NCD film was identified by X-ray diffraction and Raman spectroscopy. The Al plates with about 300 nm thick NCD film were attached to LED modules and thermal analysis was carried out using Thermal Transient Tester (T3ster) in a still air box. Thermal resistance of the module with NCD/Al plate was 3.88 K/W while that with Al plate was 5.55 K/W. The smaller the thermal resistance, the better the heat emission. From structure function analysis, the differences between junction and ambient temperatures were $12.1^{\circ}C$ for NCD/Al plate and $15.5^{\circ}C$ for Al plate. The hot spot size of infrared images was larger on NCD/Al than Al plate for a given period of LED operation. In conclusion, NCD coated Al plate exhibited better thermal spreading performance than conventional Al heat sink.

• Journal of the Korean institute of surface engineering
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• v.46 no.1
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• pp.29-35
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• 2013

The effect of DC bias on the growth of nanocrystalline diamond films on silicon substrate by microwave plasma chemical vapor deposition has been studied varying the substrate temperature (400, 500, 600, and $700^{\circ}C$), deposition time (0.5, 1, and 2h), and bias voltage (-50, -100, -150, and -200 V) at the microwave power of 1.2 kW, working pressure of 110 torr, and gas ratio of Ar/1%$CH_4$. In the case of low negative bias voltages (-50 and -100 V), the diamond particles were observed to grow to thin film slower than the case without bias. Applying the moderate DC bias is believed to induce the bombardment of energetic carbon and argon ions on the substrate to result in etching the surfaces of growing diamond particles or film. In the case of higher negative voltages (-150 and -200 V), the growth rate of diamond film increased with the increasing DC bias. Applying the higher DC bias increased the number of nucleation sites, and, subsequently, enhanced the film growth rate. Under the -150 V bias, the height (h) of diamond films exhibited an $h=k{\sqrt{t}}$ relationship with deposition time (t), where the growth rate constant (k) showed an Arrhenius relationship with the activation energy of 7.19 kcal/mol. The rate determining step is believed to be the surface diffusion of activated carbon species, but the more subtle theoretical treatment is required for the more precise interpretation.

• Korean Journal of Materials Research
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• v.31 no.9
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• pp.525-531
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• 2021

Carbon-encapsulated Ni catalysts are synthesized by an electrical explosion of wires (EEW) method and applied for CO₂ methanation. We find that the presence of carbon shell on Ni nanoparticles as catalyst can positively affect CO₂ methanation reaction. Ni@5C that is produced under 5 % CH₄ partial pressure in Ar gas has highest conversions of 68 % at 350 ℃ and 70 % at 400 ℃, which are 73 and 75 % of the thermodynamic equilibrium conversion, respectively. The catalyst of Ni@10C with thicker carbon layer shows much reduced activity. The EEW-produced Ni catalysts with low specific surface area outperform Ni catalysts with high surface area synthesized by solution-based precipitation methods. Our finding in this study shows the possibility of utilizing carbon-encapsulated metal catalysts for heterogeneous catalysis reaction including CO₂ methanation. Furthermore, EEW, which is a highly promising method for massive production of metal nanoparticles, can be applied for various catalysis system, requiring scaled-up synthesis of catalysts.

• Korean Journal of Materials Research
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• v.9 no.11
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• pp.1129-1136
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• 1999

TIN films were prepared on Si(100) substrate by ICP-CVD(inductive1y coupled plasma enhanced chemical vapor deposition) using TEMAT(tetrakis ethylmethamido titanium : Ti$[\textrm{N}\textrm{(CH)}_{3}\textrm{C}_{2}\textrm{H}_{5}]_{4}$) precursor at various deposition conditions. Phase, microstructure, and the electrical properties of TIN films were characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and electrical measurements. Polycrystalline TiN films with B1 structure were grown at temperatures over $200^{\circ}C$. Preferentially oriented along TiN(111) films were obtained at temperatures over $300^{\circ}C$ with the flow rates of 10, 5, and 5 sccm for TEMAT, $\textrm{N}_{2}$ and Ar gas. The TiN/Si(100) interface was flat and no chemical reaction between TIN and $\textrm{SiO}_2$ was found. The resistivity, carrier concentration and the carrier mobility for the TiN sample prepared at $500^{\circ}C$ are 21 $\mu\Omega$cm, 9.5$\times\textrm{10}^{18}\textrm{cm}^{-3}$ and $462.6\textrm{cm}^{2}$/Vs, respectively.

• Journal of the Korean Vacuum Society
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• v.18 no.3
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• pp.229-235
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• 2009

Millimeter-scale aligned arrays of thin-multiwalled carbon nanotube (t-MWCNT) on layered Si substrates have been synthesized by oxygen-assisted microwave plasma chemical vapor deposition (MPCVD). We have succeeded in growth of vertically aligned MWCNTs up to 2.7 mm in height for 150 min. The effect of $O_2$ and water vapour on growth rate was systematically investigated. In the case of $O_2$ gas, the growth rate was ${\sim}22{\mu}m/min$, which is outstanding growth rate comparing with those of conventional thermal CVD (TCVD). Scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and Raman spectroscopy were used to analyze the CNT morphology, composition and growth mechanism. The role of $O_2$ gas during the CNT growth was discussed on.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.429-432
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• 1996

An x-ray astronomy experiment consisting of three collimated proportional counters and an X-ray Sky Monitor (XSM) was flown aboard the Indian Satellite IRS-P3 launched on March 21, 1996 from SHAR range in India. The Satellite is in a circular orbit of 830 km altitude with an orbital inclination of $98^{\circ}$ and has three axis stabilized pointing capability. Each pointed-mode Proportional Counter (PPC) is a multilayer, multianode unit filled with P-10 gas ($90\%$ Ar + $10\%\;CH_4$) at 800 torr and having an aluminized mylar window of 25 micron thickness. The three PPCs are identical and have a field of view of $2^{\circ}{\times}2^{\circ}$ defined by silver coated aluminium honeycomb collimators. The total effective area of the three PPCs is about 1200 $cm^2$. The PPCs are sensitive in 2-20 keV band. The XSM consists of a pin-hole of 1 $cm^2$ area placed 16 cm above the anode plane of a 32 cm$\times$32 cm position sensitive proportional counter sensitive in 3-8 keV interval. The position of the x-ray events is determined by charge division technique using nichrome wires as anodes. The principal objective of this experiment is to carry out timing studies of x-ray pulsars, x-ray binaries and other rapidly varying x-ray sources. The XSM will be used to detect transient x-ray sources and monitor intensity of bright x-ray binaries. Observations of black-hole binary Cyg X-1 and few other binary sources were carried out in early May and July-August 1996 period. Details of the x-ray detector characteristics are presented and preliminary results from the observations are discussed.