• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.199-199
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• 2016

Commercially pure titanium (cp-Ti) and Ti alloys (typically Ti-6Al-4V) display excellent corrosion resistance and biocompatibility. Although the chemical composition and topography are considered important, the mechanical properties of the material and the loading conditions in the host have, conventionally. Ti and its alloys are not bioactive. Therefore, they do not chemically bond to the bone, whereas they physically bond with bone tissue. The electrochemical deposition process provides an effective surface for biocompatibility because large surface area can be served to cell proliferation. Electrochemical deposition method is an attractive technique for the deposition of hydroxyapatite (HAp). However, the adhesions of these coatings to the Ti surface needs to be improved for clinical used. Plasma electrolyte oxidation (PEO) enables control in the chemical com position, porous structure, and thickness of the $TiO_2$ layer on Ti surface. In addition, previous studies h ave concluded that the presence of $Ca^{+2}$ and ${PO_4}^{3-}$ ion coating on porous $TiO_2$ surface induced adhesion strength between HAp and Ti surface during electrochemical deposition. Silicon (Si) in particular has been found to be essential for normal bone and cartilage growth and development. Zinc (Zn) plays very important roles in bone formation and immune system regulation, and is also the most abundant trace element in bone. The objective of this work was to study electrochemical characteristcs of Zn and Si coating on Ti-6Al-4V by PEO treatment. The coating process involves two steps: 1) formation of porous $TiO_2$ on Ti-6Al-4V at high potential. A pulsed DC power supply was employed. 2) Electrochemical tests were carried out using potentiodynamic and AC impedance methoeds. The morphology, the chemical composition, and the micro-structure an alysis of the sample were examined using FE-SEM, EDS, and XRD. The enhancements of the HAp forming ability arise from $Si/Zn-TiO_2$ surface, which has formed the reduction of the Si/Zn ions. The promising results successfully demonstrate the immense potential of $Si/Zn-TiO_2$ coatings in dental and biomaterials applications.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.29-34
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• 2019

Silicon carbide is considered to be a potentially useful material for high-temperature electronic devices, as its large energy band gap and the p-type and/or n-type conduction can be controlled by impurity doping. Particularly, electric conductivity of porous n-type SiC semiconductors fabricated from ${\beta}-SiC$ powder at $2000^{\circ}C$ in $N_2$ atmosphere was comparable to or even larger than the reported values of SiC single crystals in the temperature region of $800^{\circ}C$ to $1000^{\circ}C$, while thermal conductivity was kept as low as 1/10 to 1/30 of that for a dense SiC ceramics. In this work, for the purpose of decreasing sintering temperature, it was attempted to fabricate porous reaction-sintered bodies at low temperatures ($1400-1600^{\circ}C$) by thermal decomposition of polycarbosilane (PCS) impregnated in n-type ${\beta}-SiC$ powder. The repetition of the impregnation and sintering process ($N_2$ atmosphere, $1600^{\circ}C$, 3h) resulted in only a slight increase in the relative density but in a great improvement in the Seebeck coefficient and electrical conductivity. However the power factor which reflects the thermoelectric conversion efficiency of the present work is 1 to 2 orders of magnitude lower than that of the porous SiC semiconductors fabricated by conventional sintering at high temperature, it can be stated that thermoelectric properties of SiC semiconductors fabricated by the present reaction-sintering process could be further improved by precise control of microstructure and carrier density.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1839-1842
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• 1999

We have synthesized carbon nanotubes by thermal chemical vapor deposition of $C_2H_2$ on transition metal-coated silicon substrates. Carbon nanotubes are uniformly synthesized on a large area of the plain Si substrates, different from Previously reported porous Si substrates. It is observed that surface modification of transition metals deposited on substrates by either etching with dipping in a HF solution and/or $NH_3$ pretreatment is a crucial step for the nanotube growth prior to the reaction of $C_2H_2$ gas. We will demonstrate that the diameters of carbon naotubes can be controlled by applying the different transition metals.

• Journal of Powder Materials
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• v.15 no.3
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• pp.196-203
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• 2008

The densification behavior of Al-20Si-5.5Fe-1.2Mg-0.5Mn powders was investigated through micro-structure analysis of sintered specimens. The specimens sintered in vacuum or in high purity (99.999%) nitrogen showed porous near-surface microstructures. The densification of near-surface part was enhanced by means of ultra-high purity (99.9999%) nitrogen atmosphere. The relationship between slow densification and oxide surfaces of Al alloy powders was discussed. And the effects of Mg addition, nitrogen gas, and humidity on densification were discussed. In addition, the rapid growth of primary Si crystals above the critical temperature was reported.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1999.06a
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• pp.115-127
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• 1999

The charged clusters or particles, which contain hundreds to thousands of atoms or even more, are suggested to form in the gas phase in the thin film processes such as CVD, thermal evaporation, laser ablation, and flame deposition. All of these processes are also used in the gas phase synthesis of the nanoparticles. Ion-induced or photo-induced nucleation is the main mechanism for the formation of these nanoclusters or nanoparticles inthe gas phase. Charged clusters can make a dense film because of its self-organizing characteristics while neutral ones make a porous skeletal structure because of its Brownian coagulation. The charged cluster model can successfully explain the unusual phenomenon of simultaneous deposition and etching taking place in diamond and silicon CVD processes. It also provides a new interpretation on the selective deposition on a conducting material in the CVDd process. The epitaxial sticking of the charged clusters on the growing surface is gettign difficult as the cluster size increases, resulting in the nanostructure such as cauliflowr or granular structures.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1908-1910
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• 2001

본 논문은 마이크로머시닝 기술을 이용하여 lift-off 공정으로 패턴닝 한 후 TMAH (Tetramethylammonium Hydroxide) 용액으로 $5{\sim}100{\mu}m$ 두께의 실리콘 다이어프램을 제작하였다. Pt/Ti 박막을 HF 전해질의 mask 물질로 사용하여 HF 용액 내에서 전기화학적 방법으로 정전압을 인가, 다이어프램 영역에 다공질 실리콘을 성장시켜 관통하였다. 140$^{\circ}C$의 질소 분위기에서 $10{\sim}15{\mu}m$두께의 LDPE(Low Density Poly Ethylene) 필름을 물리적으로 다이어프램 영역에 코팅하고 $K_2CO_3$ 용액내에서 ${CO_3}^{2-}$ 이온의 barrier에 의한 전류의 감소를 전기화학적인 분석방법에 의하여 측정하였다. 일정 전압하에서 이온 농도에 기인하는 다공질 실리콘과 LDPE 표면에서 Barrier의 두께에 따른 저항의 증가를 전극으로 감지하여 농도-전류의 특성을 측정하고 이것을 기준으로 하여 미지농도의 $K_2CO_3$ 용액내의 ${CO_3}^{2-}$ 이온 농도를 측정하였다.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1581-1583
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• 2002

본 논문은 다공질 실리콘 다이어프램에 대한 화학 센서의 일종인 습도, 에탄올, 메탄올의 감지 특성을 측정하고 전기 전도도의 변화를 고찰하였다. 먼저, TMAH 용액으로 실리콘 다이어프램을 제작한 후, HF와 에탄올의 혼합 용액내에서 일정 전압을 인가하여 다공질 실리콘 다이어프램을 형성하였다. 다공질 실리콘을 면(100)에 수직한 방향으로 $50{\sim}100{\mu}m$ 두께로 균일하게 형성하여 p+-PSi-n+ 구조의 소자를 제작하였다. 다공질 실리콘 다이어프램의 절대습도에 대한 감도는 입력 주파수 5kHz에서 인가 전압이 $2{\sim}6$Vpp에서 $376.3{\sim}784.8{\Omega}$/%RH으로 변하였다. 또, 인가 전압 6Vpp에서 입력 주파수가 $2{\sim}5$kHz으로 변할 때 $393.3{\sim}784.8{\Omega}$/%RH으로 변하였다. 또한, 에탄올에 대한 감도는 $0.068{\mu}A$/%이며, 메탄올은 $0.212{\mu}A$/%으로 다공질 실리콘 다이어프램은 에탄올 보다 메탄올이 더 민감하게 반응하였다. 일반적으로 다공질 실리콘의 전기전도도는 charged surface traps과 screening effect에 의존한다.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.2026-2028
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• 2002

본 논문에서는 실리콘 기판상의 전송선로 특성을 개선하기 위하여 표면 마이크로머시닝 기술을 이용하여 $10{\mu}m$ 두께의 다공질 실리콘 산화막으로 제조된 기판 위에 에어브리지를 가진 CPW 전송선로와 phase shifter를 제작하였다. 간격이 $30{\mu}m$, 신호선이 $80{\mu}m$인 CPW 에어브리지 전송선의 삽입손실은 4 GHz에서 -0.25 dB이며, 반사손실은 -28.9 dB를 나타내었다. CPW phase shifter의 크기는 S-W-$S_g$ = 100-30-400 ${\mu}m$로 설계되었다. "ㄷ" 모양을 가진 에어브리지의 폭은 $100{\mu}m$. 길이는 400-460-400 ${\mu}m$이다. 낮은 손실을 얻기 위한 Step된 에어브리지를 가진 phase shifter 구조가 step이 없는 에어브리지를 가진 구조보다 삽입손실이 보다 더 향상되었다. 제작된 CPW phase shifter의 위상특성은 28 GHz의 넓은 주파수 범위에서 $180^{\circ}E 의 천이를 타나내었다. 이상과 같은 결과로부터 두꺼운 다공질 실리콘은 고 저항 실리콘 집적회로 공정에서 고성능 저가의 마이크로파 및 밀리미터파 회로 응용에 충분히 활용 될 수 있으리라 기대된다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.160-160
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• 2017

Commercially pure titanium (Cp-Ti) and Ti alloys (typically Ti-6Al-4V) display excellent corrosion resistance and biocompatibility. Although the chemical composition and topography are considered important, the mechanical properties of the material and the loading conditions in the host have, conventionally. Ti and its alloys are not bioactive. Therefore, they do not chemically bond to the bone, whereas they physically bond with bone tissue. The electrochemical deposition process provides an effective surface for biocompatibility because large surface area can be served to cell proliferation. Plasma electrolyte oxidation (PEO) enables control in the chemical composition, porous structure, and thickness of the TiO2 layer on Ti surface. Silicon (Si) in particular has been found to be essential for normal bone and cartilage growth and development. Zinc (Zn) plays very important roles in bone formation and immune system regulation, and is also the most abundant trace element in bone. The objective of this work was to study on electrochemical behaviors of PEO-treated Ti-6Al-4V Alloy in solution containing Zn and Si ions. The morphology, the chemical composition, and the microstructure analysis of the sample were examined using FE-SEM, EDS, and XRD. The potentiodynamic polarization and AC impedance tests for corrosion behaviors were carried out in 0.9% NaCl solution at similar body temperature using a potentiostat. The promising results successfully demonstrated the immense potential of Si/Zn-TiO2 coatings in dental and biomaterials applications.

• Korean Journal of Materials Research
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• v.27 no.9
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• pp.471-476
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• 2017

In order to improve the high temperature oxidation resistance and lifespan of mat type porous carbon insulation, SiC was coated on carbon insulation by solution coating using polycarbosilane solution, curing in an oxidizing atmosphere at $200^{\circ}C$, and pyrolysis at temperatures up to $1200^{\circ}C$. The SiOC phase formed during the pyrolysis process was converted into SiC crystals as the heat treatment temperature increased, and a SiC coating with a thickness of 10-15 nm was formed at $1600^{\circ}C$. The SiC coated specimen showed a weight reduction of 8.6 % when it was kept in an atmospheric environment of $700^{\circ}C$ for 1 hour. On the other hand, the thermal conductivity was 0.17 W/mK, and no difference between states before and after coating was observed at all.