• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.162-162
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• 2014

최근 들어 wearable computing에 대한 수요가 증가하면서 flexible device에 대한 연구가 활발히 진행되고 있다. 하지만, flexible device를 구현하기 위해서는 기판의 damage를 줄이기 위한 저온공정, device life-time 향상을 위한 passivation, 와이어 본딩 등 다양한 문제들이 해결 되어야 한다. 이러한 문제들 중, polymer 기판과 금속간의 접착력을 향상시키기 위해서 많은 연구자들은 기판의 표면에 adhesive layer를 도포하거나 금속잉크의 solvent를 변화시키는 등의 연구를 진행해왔다. 종래의 연구는 기존 device를 대체 할 수 있을 정도의 생산성과 polymer 기판에 대한 열 적인 손상 이 문제가 되었다. 종래의 문제를 해결하기 위하여 저온공정, in-line system이 가능한 준 준 대기압 플라즈마를 사용하였다. 본 연구에서는 금속잉크를 Ink-jet으로 jetting하여 와이어 본딩 하는 과정에서 전도성 ink의 선폭을 유지시키고 접착력을 향상하기 위하여 준 대기압 플라즈마 공정을 이용하여 이러한 문제점을 해결하고자 하였다. Polymer 기판 표면에 roughness를 만들기 위해 대략 수백 nm 크기를 갖는 graphene flake를 spray coating하여 마스크로 사용하고 준 대기압 플라즈마를 이용하여 표면을 식각 함으로써 roughness를 형성시켰다. 준 대기압 플라즈마를 발생시키기 위해 double discharge system에서 6 slm/1.5 slm (He/O2) gas composition을 하부 전극에 흘려보내고 60 kHz, 5 kV 파워를 인가하였다. 동시에 상부 전극에는 30 kHz, 5 kV 파워를 인가하여 110초 동안 표면 식각 공정을 진행하였다. Graphene flake mask가 coating되어 있는 유연기판을 산소 플라즈마 처리 한 후 물에 3초 동안 세척하여 표면에 남아있는 graphene flake를 제거하고 6 slm/0.3 slm (He/SF6)의 유량으로 주파수와 파워 모두 동일 조건으로 110초 동안 표면 처리를 하였다. Figure 1은 표면 개질 과정과 graphene flake를 mask로 사용하여 얻은 roughness 결과를 SEM을 이용하여 관찰한 결과이다. 이와 같이 실험한 결과 ink와 기판간의 접촉면적을 늘려주고 접촉 각을 조절하여 Wenzel model 을 형성 할 수 있는 표면 roughness를 생성하였고 표면의 화학적 결합을 C-F group으로 치환하여 표면의 물과 접촉각 이 $47^{\circ}$에서 $130^{\circ}$로 증가하는 것을 확인하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.153-153
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• 2017

The application of the coating supports the mechanical characteristics of the implant, and various materials and coatings are currently being used in the implant in a way to accelerate adhesion. Especially, plasma electrolytic oxidation (PEO) coating has been proposed continually with good surface treatment of titanium alloys. Also, the PEO process can incorporate Ca and P ions on the titanium surface through variables varied factor. PEO process for bioactive surface has carried out in electrolytes containing Ca and P ions. Natural bone is composed of mineral elements such as Mg, Si, Zn, Sr, and Mn, etc. Especially, Mg and Si of these elements play role in bone formation and growth after clinical implantation of bio-implants. In this study, corrosion charateristics of PEO-treated Ti-6Al-4V alloy in solution containing Si and Mg ions has been investigated using several experimental techniques. The PEO-treated surfaces were identified by X-ray diffraction, using a diffractometer (XRD, Philips X' pert PRO, Netherlands) with Cu $K{\alpha}$ radiation. The morphology was observed by field-emission scanning electron microscopy (FE-SEM, Hitachi 4800, Japan) and energy-dispersive X-ray spectroscopy (EDX, Oxford ISIS 310, England). The potentiodynamic polarization and AC impedance tests for electrochemical degradations were carried out in 0.9% NaCl solution at similar body temperature using a potentiostat with a scan rate of 1.67mV/s and potential range from -1500mV to + 2000mV.

• Journal of Surface Science and Engineering
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• v.30 no.4
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• pp.272-280
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• 1997

The Thermal Barrier Coation(TBC) to improve the that barrier and wear resistant propenrty in high temperature ofthe aircraftength between the accumlation of the aircraft engine and the automobile engine has usually the two layer structure. One is a creamic top layer for heat insulation and the other is a metal bond layer to facilitate the bond strength between the top ceramic layer and the substrate. But, the coated layers should be peeled off because of the accumulation of the thermal stress by the differance of the thermal expantion coefficient between metal and ceramics in a hrat cyclic environment. In this study, the intermediate layer by plasm spray process was introduced to reduce the thermal stress. The powders of plasm spray coating were the Yttria Stabilized Zirconia (YSZ), the Magnesia Stabillized Zirconia(MSZ) and NiCrAlY. the intermediate layer was sprayed with the powders of the bond cast for the purpose of test were executed. The high temperature wear resistance tends to decreasnceee wear and thermal shock test were exeucuted. The high temperature were resistance of the YSZ TBC is better that of the MSZ TBC. The wearrsistance tends to decrease accoring to incresing the temperature between $400^{\circ}C$to $600^{\circ}C$. The thermal shock life of the 3 layer TBC with YSZ top casting was the most outstanding thermal shock rsisstasnce. This means that the intermediate layer should play an importnat roll to alleviate the diffrerence of the thermal expansion coef frcients between metallic layer and cermics layer.

• Korean Journal of Materials Research
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• v.23 no.7
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• pp.353-358
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• 2013

To improve coating ability and the life of the coating, Ti based composite materials with hydroxyapatite(HA) should be developed. The raw materials of Ti-26wt%, Nb-1wt%, and Si with 10wt% HA were mixed for 24 h by a mixing machine and milled for 1 h to 6 h by planetary mechanical ball milling. Ti-26%Nb-1%Si-(10%HA) composites, composed of nontoxic elements, were fabricated successfully by spark plasma sintering(SPS) at $1000^{\circ}C$ under 70MPa. The relative density of the sintered Ti-Nb-Si-HA composites using the 24 h mixed powder, and the 6 h milled powder, was 91% and 97 %, respectively. The effects of HA contents and milling time on microstructure and mechanical properties were investigated by SEM and hardness tester, respectively. The Vickers hardness of the composites increased with increasing milling time and higher HA content. The Young's modulus of the sintered Ti-26%Nb-1%Si-10%HA composite using the 6 h-milled powder was 55.6 GPa, as obtained by compression test. Corrosion resistance of the Ti-26wt%Nb-1wt%Si composite was increased by milling and by the addition of 10wt%HA. Wear resistance was improved with increasing milling time. Biocompatibility of the Ti-Nb-Si alloys was improved by the addition of HA.

• 한국태양에너지학회:학술대회논문집
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• 2011.11a
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• pp.154-157
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• 2011

Hydrogenated silicon nitride deposited by LF-PECVD is commonly used for anti-reflection coating and passivation in silicon solar cell fabrication. The deposition of the optimized silicon nitride on the surface is elemental in crystalline silicon solar cell. In this work, the carrier lifetimes were measured while the thicknesses of $SiN_x$ were changed from 700 ${\AA}$ to 1150 ${\AA}$ with the gas flow of $SiH_4$ as 40 sccm and $NH_3$ as 120 sccm,. The carrier lifetime enhanced as the thickness of $SiN_x$ increased due to improved passivation effect. To study the characteristics of $SiN_x$ with various gas ratios, the gas flow of $NH_3$ was changed from 40 sccm to 200 sccm with intervals of 40 sccm. The thickness of $SiN_x$ was fixed as 1000 ${\AA}$ and the gas flow of $SiH_4$ as 40 sccm. The refractive index of SiNx and the carrier lifetime were measured before and after heat treating at $650^{\circ}C$ to investigate their change by the firing process in solar cell fabrication. The index of refraction of SiNx decreased as the gas ratios increased and the longest carrier lifetime was measured with the gas ratio $NH_3/SiH_4$ of 3.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.237-237
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• 2010

에너지소비와 엔진 부품의 마모문제를 해결하기 위해, soft-phase를 doping한 hard상의 coating에 대한 실험이 최근 중요한 연구 테마로서 진행 중이다. 특히 MoN-Cu coating은 미국 Argon 연구소의 Erdemer박사 등에 의해, 고온 및 상온 윤활성이 우수한 코팅층으로 보고된 이후 많은 연구가 진행되고 있다. 그러나 기존 연구는 Mo와 Cu의 원소타겟을 이용한 연구가 주력이 되었다. 높은 경도와 저온 고온에서의 낮은 나노 혼합물 코팅 종류는 일반적으로 Mo와 Cu와 같은 원소 합금을 이용한 다수 타겟을 이용한 공정에 의해 진행되어왔다. 이러한 복수의 타겟에 의해 증착 동안에는, 정확한 조성, 큰 크기의 시편들의 균일 증착을 조절하기가 쉽지 않다. 또한, 코팅층에 3번째 성분을 추가하기가 어렵다는 문제점이 있다. 본 연구에서는, 최상의 마찰계수와 표면경도를 보이는 MoN-Cu층을 형성시키기 위하여 합금으로 단일 타겟을 제조하였다. 이를 위한 최적 조성을 결정하기 위하여 Mo, Cu 단일 타겟을 이용한 Unbalanced Magnetron sputtering 법으로 다양한 Cu 함량의 MoN+Cu 합금을 제조하였으며, 이에 대한 경도 및 마찰계수 측정을 통해 최적의 Cu 함량을 결정하였다. 이러한 최적 조성의 Cu 타겟제조를 기계적 합금화와 Spark plasma sintering 기술을 이용하여 제작하였으며, 복수의 합금 타겟과 단일 합금 타겟으로 제조된 코팅층의 물성 비교를 통해 합금 타겟의 우수성 여부를 확인하고자 하였다. 증착된 두 조건의 물성을 비교 단일 타겟은 두가지 타겟으로 증착한 것보다 비슷한 조성에서 경도가 높았으며 경도가 비슷한 조성에서는 마찰계수가 낮았다. 또 입자는 10 at.% Cu 조성에 대해 단일타겟이 50nm 결정립을 갖는 반해 단일타겟은 측정이 불가능할 정도의 미세한 결정립을 가졌다. Erdemir의 연구 결과에 의하면, Cu 함량이 증가함에 따라 columnar 형태의 코팅층구조가 나노 구조로 변한다고 하였는데, 본 연구에서 복수의 원소 타겟에서는 확인이 안되었으며, 단일 합금 타겟에서 완벽한 featurless 형태의 코팅층 구조와 우수한 조도의 박막층을 얻을 수 있었다. 이렇게 제조된 다양한 코팅층에 대한 마찰계수 측정이 진행중이다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.356-356
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• 2010

Tribological behaviors of the hard film on soft substrate system were explored using the hard thin film of diamond-like carbon (DLC) coated the soft polymer of polydimethysiloxane (PDMS). A DLC film with the Young's modulus of 100 GPa was coated on PDMS substrate with Young's modulus of 10 MPa using plasma enhanced chemical vapor deposition (PECVD) technique. The deposition time was varied from 10 sec to 10 min, resulting in nanoscale roughness of wrinkle patterns with the thickness of 20 nm to 510 nm, respectively, at a bias voltage of $400\;V_b$, working pressure 10 mTorr. Nanoscale wrinkle patterns with 20-100 nm in width and 10-30 nm height were formed on DLC coating due to the residual stress in compression and difference in Young's modulus. Nanoscale roughness effect on tribological behaviors was observed by performing a tribo-experiment using the ball-on-disk type tribometer with a steel ball of 6 mm in diameter at the sliding speed of 220 rpm, normal load of 1N and 25% humidity at ambient temperature of $25^{\circ}C$. Friction force were measured with respect to thickness change of coated DLC thin film on PDMS. It was found that with increases the thickness of DLC coating on PDMS, the coefficient of friction decreased by comparison to that of the uncoated PDMS. The wear tracks before and after tribo-test were analyzed using SEM and AFM.

• Journal of Adhesion and Interface
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• v.20 no.2
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• pp.66-70
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• 2019

The surface of hydrophobic polypropylene (PP) fibers (spun-bonded fabric) was treated by an atmospheric plasma treatment method. These pre-treated hydrophilic PP fabrics were dip-coated in the aqueous poly(N-vinyl pyrrolidone) (PVP) solution. PVP layers on the surface of PP fiber were crosslinked by an irradiation of electron beam. The thickness of PVP hydrogels coated on the surface was easily controlled by changing the concentration of PVP in coating solution. The stepwise surface treatment, PVP coating, and hydrogel formation via electron beam irradiation were analyzed by the measurement of contact angle, scanning electron microscopy, and optical microscopy.

• Korean Chemical Engineering Research
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• v.59 no.2
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• pp.174-179
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• 2021

Recently, hybrid coal research is underway to upgrade low-grade coal. The hybrid coal is made by mixing low-grade coal with bioliquids such as molasses, sugar cane, and lignin. In the case of lignin used here, a large amount of lignin is included in the wastewater of the papermaking process, and thus, research on hybrid coal production using the same is attracting attention. However, since a large amount of metal ions are contained in the lignin wastewater from the papermaking process, substances that corrode the generator are generated during combustion, and the amount of fly ash is increased. To solve this problem, it is essential to remove metal ions in the lignin wastewater. In this study, metal ions were removed by ion exchange with a alumina hollow fiber membrane coated with K-Phillipsite (K-PHI) zeolite. The alumina hollow fiber membrane used as the support was prepared by the nonsolvent induced phase separation (NIPS) method, and K-PHI seeds were prepared by hydrothermal synthesis. The prepared K-PHI seed was seeded on the surface of the support and coated by secondary growth hydrothermal synthesis. The characteristic of prepared coating membrane was analyzed by Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Energy Dispersive Spectroscopy (EDX), and the concentration of metal ions before and after ion exchange was measured by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). The extraction amount of K+ is 86 mg/kg, and the extraction amount of Na+ is 54.9 mg/kg. Therefore, K-PHI zeolite membrane has the potential to remove potassium and sodium ions from the solution and can be used in acidic lignin wastewater.

• Korean Journal of Materials Research
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• v.33 no.4
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• pp.124-129
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• 2023

This study assessed the influences of fluorine introduced into DLC films on the structural and mechanical properties of the sample. In addition, the effects of the fluorine incorporation on the compressive stress in DLC films were investigated. For this purpose, fluorinated diamond-like carbon (F-DLC) films were deposited on cobalt-chromium-molybdenum substrates using radio-frequency plasma-enhanced chemical vapor. The coatings were examined by Raman scattering (RS), Attenuated total reflectance Fourier transform infrared spectroscopic analysis (ATR-FTIR), and a combination of elastic recoil detection analysis and Rutherford backscattering (ERDA-RBS). Nano-indentation tests were performed to measure hardness. Also, the residual stress of the films was calculated by the Stony equation. The ATR-FTIR analysis revealed that F was present in the amorphous matrix mainly as C-F and C-F₂ groups. Based on Raman spectroscopy results, it was determined that F made the DLC films more graphitic. Additionally, it was shown that adding F into the DLC coating resulted in weaker mechanical properties and the F-DLC coating exhibited lower stress than DLC films. These effects were attributed to the replacement of strong C = C by feebler C-F bonds in the F-DLC films. F-doping decreased the hardness of the DLC from 11.5 to 8.8 GPa. In addition, with F addition, the compressive stress of the DLC sample decreased from 1 to 0.7 GPa.