• Korean Journal of Materials Research
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• v.12 no.3
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• pp.176-181
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• 2002

Fabrication of ${\beta}-FeSi_2$ was attempted by making use of the combined process of mechanical alloying (MA) and spark plasma sintering (SPS). MA was performed under the Ar gas atmosphere using mixed powders of pure iron and silicon having the mole fraction of 1:2. SPS process was performed at 800-85$0^{\circ}C$ with the applied pressure of 50MPa and the holding time was ranging from 0 to 30min. The mechanically alloyed powder by cyclic operation of rotor for 15hrs consisted of $\varepsilon$-FeSi and Si phases. When this mechanically alloyed powder was sintered by SPS process above 85$0^{\circ}C$, $\varepsilon$-FeSi and ${\alpha}-Fe_2Si_5$ phase were formed. Bulk product sintered at 82$0^{\circ}C$ for 30min consisted of ${beta}-FeSi_2$ phase with a small fraction of $\varepsilon$-FeSi and the density of sintered specimen was 75.3% theoretical density. It was considered that the MA/SPS combined process was effective for the preparation of ${\beta}-FeSi_2$ without heat treatment process after sintering.

• 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.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.266-270
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• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine because it has excellent high temperature strength, low coefficient of thermal expansion, good resistance to oxidation and good thermal and chemical stability etc. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, SiC/SiC composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing jiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of SiC/SiC composites by hot pressing method. In the present work, monolithic Liquid Phase Sintered SiC (LPS-SiC) was fabricated by hot pressing method in Ar atmosphere at $1800^{\circ}C$ under 20MPa using $Al_2O_3,\;Y_2O_3\;and\;SiO_2$ as sintering additives in order to low sintering temperature and sintering pressure. The starting powder was high purity $\beta-SiC$ nano-powder with all average particle size of 30mm. The characterization of LPS-SiC was investigated by means of SEM and three point bending test. Base on the composition of sintering additives-, microstructure- and mechanical property correlation, tire compositions of sintering additives are discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.54-54
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• 2008

$Eu^{2+}$, $Nd^{3+}$ co-doped $BaAl_2O_4$ are known as a long afterglow phosphor. We found that $Eu^{2+}$-doped $BaAl_2O_4$ showed ptotoconductivity in the range of UV and visual light. In this study, $BaAl_2O_4$:Eu thin film has been prepared by RF sputtering method and a sensing characteristics to UV and visual light was performed. Only $Eu^{2+}$ and $Nd^{3+}$ co-doped $BaAl_2O_4$ powders and targets for deposition were prepared by a convention solid state method, and the deposition was performed in a reducing $H_2$-Ar mixture gas on Si substrates. The observation of crystalline phase and morphology of the sputtered film were performed using XRD, EDX. The photoluminescence and photocurrent to UV and visual light were measured simultaneously using 300W-Xe solar simulator as a light source. It was confirmed that the photocurrent induced by irradiation of light showed a linear relationship to the light intensity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.162-163
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• 2008

이 논문에서는 Polyimide 기판의 $O_2$ 플라즈마 처리효과에 따른 GZO 박막의 구조적, 전기적, 광학적인 특성을 고찰하였다. ICP-RIE 방법을 이용하여 Polyimide 기판의 $O_2$ 플라즈마 처리의 변수로 RF power와 처리시간을 각 100 ~ 400 W, 120 ~ 600 초까지 조절하였다. RF 스퍼터링 방법으로 $O_2$ 플라즈마 처리효과에 따른 Polyimide 기판을 4인치의 GZO(ZnO : 95 wt%, $Ga_2O_3$ 5 wt%) 타겟을 사용하여 RF power 90 W, 공정압력 5 mTorr, Ar gas 20 sccm, 기판거리 5 cm, 박막두께 500nm, 상온의 조건으로 GZO 박막을 증착 하였다. Polyimide 기판에 $O_2$ 플라즈마 처리를 하지 않고 증착한 GZO 박막의 비저황은 $1.02\times10^{-2}\Omega$-cm 이었고 RF power 100W, 처리시간 120 초로 $O_2$ 플라즈마 처리 후에 증착한 GZO 박막의 비저항이 $1.89\times10^{-3}\Omega$-cm인 최적의 값이 측정되었으며 RF power가 증가할수록 투과도는 감소하였지만 처리시간의 변화에 따라서는 투과도 변화가 거의 없었다.

• Clean Technology
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• v.2 no.2
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• pp.100-125
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• 1996

After recycle of spent materials has been optimised, there remains a proportion of waste which must be dealt with in the most environmentally friendly manner available. For materials such as municipal waste, clinical waste, toxic waste and special wastes such as tyres, incineration is often the most appropriate technology. The study of incineration must take a process system approach covering the following aspects: ${\bullet}$ Collection and blending of waste, ${\bullet}$ The two stage combustion process, ${\bullet}$ Quenching, scrubbing and polishing of the flue gases, ${\bullet}$ Dispersion of the flue gases and disposal of any solid or liquid effluent. The design of furnaces for the burning of a bed of material is being hampered by lack of an accurate mathematical model of the process and some semi-empirical correlations have to be used at present. The prediction of the incinerator gas phase flow is in a more advanced stage of development using computational fluid dynamics (CFD) analysis, although further validation data is still required. Unfortunately, it is not possible to scale down many aspects of waste incineration and tests on full scale incinerators are essencial. Thanks to a close relationship between SUWIC and Sheffield Heat&Power Ltd., an extended research programme has been carried out ar the Bernard Road Incinerator plant in Sheffield. This plant consists of two Municipal(35 MW) and two Clinical (5MW) Waste Incinerators which provide district heating for a large part of city. The heat is distributed as hot water to commercial, domestic ( >5000 dwelling) and industrial buildings through 30km of 14" pipes plus a smaller pipe distribution system. To improve the economics, a 6 MW generator is now being added to the system.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.204-209
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• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, $SiC_f/SiC$ composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of $SiC_f/SiC$ composites by hot pressing method. In the present work, Monolithic LPS-SiC was fabricated by hot pressing method in Ar atmosphere at 1760 $^{\circ}C$, 1780 $^{\circ}C$, 1800 $^{\circ}C$ and 1820 $^{\circ}C$ under 20 MPa using $Al_2O_3-Y_2O_3$ system as sintering additives in order to low sintering temperature. The starting powder was high purity ${\beta}-SiC$ nano-powder with an average particle size of 30 nm. Monolithic LPS-SiC was evaluated in terms of sintering density, micro-structure, flexural strength, elastic modulus and so on. Sintered density, flexural strength and elastic modulus of fabricated LPS-SiC increased with increasing the sintering temperature. In the micro-structure of this specimen, it was found that grain of sintered body was grown from 30 nm to 200 nm.

• Journal of the Semiconductor & Display Technology
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• v.12 no.2
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• pp.33-37
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• 2013

In this study, we have investigated the effect of the substrate temperature and hydrogen flow rate on the characteristics of IZO thin films for the organic light emitting diodes (OLED) devices. For this purpose, IZO thin films were deposited by RF magnetron sputtering at room temperature and $300^{\circ}C$ with various $H_2$ flow rate. In order to investigate the influences of the oxygen, the flow rate of hydrogen in argon mixing gas has been changed from 0.1sccm to 0.9sccm. IZO thin films deposited at room temperature show amorphous structure, whereas IZO thin films deposited at $300^{\circ}C$ show crystalline structure having an (222) preferential orientation regardless of $H_2$ flow rate. The electrical resistivity of IZO film decreased with increasing flow rate of $H_2$ under Ar+$H_2$. The change of electrical resistivity with increasing flow rate of $H_2$ was mainly interpreted in terms of the charge carrier concentration rather than the charge carrier mobility. The electrical resistivity of the amorphous-IZO films deposited at R.T. was lower than that of the crystalline-IZO thin films deposited at $300^{\circ}C$. The increase of electrical resistivity with increasing substrate temperature was interpreted in terms of the decrease of the charge carrier mobility and the charge carrier concentration. All the films showed the average transmittance over 83% in the visible range.