• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.131-131
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• 2018

최근 절삭공구산업은 자동차, 항공기, IT, 선박, 에너지 등 첨단산업의 증가로 인해 CGI, CFRP, 내열합금 등 난삭재의 수요가 증가하고 있다. 난삭재는 고내열, 고경도, 초경량 같은 특성을 지니며 우수한 기계적 물성을 갖지만 가공의 어려움이 있어 산업에 적용하는데 한계가 있다. 이러한 한계를 극복하기 위해 개발된 가공기술 중 하드 코팅은 공구코팅비용 대비 공구의 표면경도와 수명을 효율적으로 향상시킬 수 있다고 알려져 있다. 대표적인 하드코팅으로는 AlN계, TiN계 코팅이 있다. 이러한 코팅의 경우 높은 기계적 물성과 우수한 내마모성으로 인해 절삭공구의 성능을 향상시킬 수 있기 때문에, 많은 연구가 진행되고 있으며 절삭공구산업에서 각광받고 있다. 기존 선행연구 결과에 따르면 질화물 코팅의 우수한 물성은 질화물(Nitride) 생성 및 질화 공정에 의한 코팅층의 고밀도화에 의해 나타난다고 알려져 있다. 그 중에서 AlCrN coating은 우수한 내마모성 및 향상된 고온경도를 갖고 있다. AlCrN based coating에 미량의 원소를 첨가하여 기존 AlCrN coating의 기계적 특성을 더욱 향상 시킨 coating은 일반적인 고성능 코팅 대비 공구수명이 길다고 알려져 있으며, 전반적으로 우수한 특성에 의해 전 세계적으로 습식 및 건식 기계 가공 용도로 사용되고 있다. 본 연구에서는 AlCrN based coating에 미량의 원소를 첨가한 coating의 우수한 기계적 특성의 원인을 규명하기 위해 텅스텐카바이드(WC) 기판 위에 아크 이온 플레이팅 장비를 이용하여 AlCrN based coating을 증착 시킨 sample을 분석하였다. 결정구조 및 상 분석을 위해 X선 회절분석(XRD)을 실시하였으며, 미세 구조를 분석하기 위해 전계방출형 주사전자현미경(FE-SEM), 투과 전자현미경(TEM) 분석을 실시하였다. 또한 코팅층의 화학적 성분 분석을 위해 EDX분석을 실시하였으며 기계적 특성 평가를 위해 나노압입시험(Nano-indentation test)을 진행하였다.

• Current Photovoltaic Research
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• v.2 no.3
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• pp.103-109
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• 2014

Highly efficient hydrogenated nanocrystalline silicon (nc-Si:H) thin-film solar cells were prepared on flexible stainless steel substrates using plasma-enhanced chemical vapor deposition. To enhance the performance of solar cells, material properties of back reflectors, n-doped seed layers and wide bandgap nc-SiC:H window layers were optimized. The light scattering efficiency of Ag back reflectors was improved by increasing the surface roughness of the films deposited at elevated substrate temperatures. Using the n-doped seed layers with high crystallinity, the initial crystal growth of intrinsic nc-Si:H absorber layers was improved, resulting in the elimination of the defect-dense amorphous regions at the n/i interfaces. The nc-SiC:H window layers with high bandgap over 2.2 eV were deposited under high hydrogen dilution conditions. The vertical current flow of the films was enhanced by the formation of Si nanocrystallites in the amorphous SiC:H matrix. Under optimized conditions, a high conversion efficiency of 9.13% ($V_{oc}=0.52$, $J_{sc}=25.45mA/cm^2$, FF = 0.69) was achieved for the flexible nc-Si:H thin-film solar cells.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.781-785
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• 2011

In this work, a nano-sized samaria-doped ceria(SDC) was prepared by a urea-based hydrothermal method and characterized by XRD, FESEM and TEM. It was observed that the increase in synthesis time and temperature gave rise to crystallity and particles size. Moreover, the synthesised powders had a excellent ion-conductivity(0.1 S/cm at 600~$800^{\circ}C$) which is suitable for electrolyte of intermediate temperature-solid oxide fuel cell(IT-SOFC). Subsequently for use as electrolyte for anode-supported IT-SOFC, we tried to deposit the SDC powder on a porous NiO-SDC substrate by electrophoretic deposition(EPD) method. From the FESEM observation, a compact

• Journal of the Semiconductor & Display Technology
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• v.10 no.2
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• pp.115-119
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• 2011

A tip-type carbon nanotube(CNT)-based field emitter was studied to consider it as electron source for micro-focused x-ray tube. The CNT was grown directly on a metal (tungsten) substrate by using an inductively coupled plasma-chemical vapor deposition (ICP-CVD) method. Prior to CNT growth, the metal substrate was etched to have various tip angles from $10^{\circ}$ to $180^{\circ}C$ (flat-type). The morphologies and microstructures of all the grown CNTs were analyzed via field-emission SEM. Furthermore, the effects of substrate tip-angles on the emission properties of CNT-based field emitters were characterized to estimate the maximum current density, the turn-on voltage, and the spatial distribution of electron beams. Prolonged long-term stability testing of the CNT emitters was also performed. All the experiment results obtained from this study indicated why a tip-type CNT emitter, compared with a flat-type CNT emitter, would be more desirable for a micro-focused x-ray system, in terms of the emission current level, the focused beam area, and the emission stability.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.105-105
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• 2006

IT 산업 및 반도체 산업이 발전함에 따라 초소형, 고집적화 시스템의 요구에 대응하기 위해서 고해상도 및 고정밀의 패턴 구현에 관한 많은 연구가 진행되고 있다. 이러한 연구는 각종 산업제품의 PCB(Printed Circuit Board) 및 디스플레이 장치인 PDP(Plasma Display Panel), LCD(Liquid Crystal Display) 등에 적용되어 널리 응용되고 있다. 현재 널리 사용되는 인쇄 회로 기판은 마스킹 후 선택적 에칭 방식을 적용하여 금속 배선을 형성하는 방식을 적용하고 있다. 이러한 방식은 설계가 변경될 경우 마스크를 다시 제작해야 하는 번거로움이 있어 설계 변경이 용이하지 않고 더욱 길어진 생산시간의 증가로 인하여 생산성 및 집적도가 떨어지게 된다. 따라서 최근에는 이러한 한계를 극복하기 위한 방안이 여러 가지 측면에서 시도되고 있으며, 그 중에서도 Inkjet Printing 기술에 대한 관심이 증가하고 있다. 본 연구에서는 Inkjet Printing 방식을 적용하여 금속 배선을 형성하고 선폭과 두께의 오차를 줄여 배선의 Tolerance 를 개선할 수 있는 방안을 제안하였다. Inkjet Printing 방식을 이용한 기존의 금속 배선 형성은 고해상도의 DPI(Dot Per Inch)에서 잉크 액적이 뭉치는 Bulge 현상이 발생되어 원하는 형상 및 배선의 폭을 구현하는데 어려움이 있었다. Bulge 현상은 배선의 불균일성을 야기할 뿐만 아니라 근접한 배선의 간섭에도 영향을 미처 금속 배선의 기능을 할 수 없는 단점을 발생시킨다. 따라서 본 연구에서는 이러한 Bulge 현상을 줄이고 배선간의 간섭을 방지하여 원하는 배선을 용이하게 형성할 수 있는 순차적 인쇄 방식을 적용하였다. 본 연구에서는 노즐직경 35um 의 Inkjet Head 와 나노 Ag 입자 잉크를 사용하여 Glass 표면 위에 배선을 형성하고 배선의 폭과 두께를 측정하였다. 또한 순차적 인쇄 방식을 적용하여 700DPI 이상의 고해상도에서 나타날 수 있는 Bulge 현상이 감소하였음을 관찰하였으며 금속 배선의 Tolerance를 10%내외로 유지할 수 있음을 확인하였다.

• Korean Journal of Materials Research
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• v.19 no.1
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• pp.50-53
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• 2009

Multi-walled carbon nanotubes (MWNTs) were synthesized on different substrates (bare Si and $SiO_2$/Si substrate) to investigate dye-sensitized solar cell (DSSC) applications as counter electrode materials. The synthesis of MWNTs samples used identical conditions of a Fe catalyst created by thermal chemical vapor deposition at $900^{\circ}C$. It was found that the diameter of the MWNTs on the Si substrate sample is approximately $5{\sim}10nm$ larger than that of a $SiO_2$/Si substrate sample. Moreover, MWNTs on a Si substrate sample were well-crystallized in terms of their Raman spectrum. In addition, the MWNTs on Si substrate sample show an enhanced redox reaction, as observed through a smaller interface resistance and faster reaction rates in the EIS spectrum. The results show that DSSCs with a MWNT counter electrode on a bare Si substrate sample demonstrate energy conversion efficiency in excess of 1.4 %.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.3
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• pp.188-194
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• 2016

We propose an acousto-optic technique for the nondestructive evaluation of adhesion properties of a Pt/Ti thin-film interface. Since there are some problems encountered when using prevailing techniques to nondestructively evaluate the interfacial properties of micro/nano-scale thin-films, we applied an interferometer that combined the acoustic and optical methods. This technique is based on the Michelson interferometer but the resultant surface of the thin film specimen makes interference instead of the mirror when the interface is excited from the acoustic transducer at the driving frequency. The thin film shows resonance-like behavior at a certain frequency range, resulting in a low-contrast fringe pattern. Therefore, we represented quantitatively the change in fringe pattern as a frequency spectrum and discovered the possibility that the interfacial adhesion properties of a thin film can be evaluated using the newly proposed technique.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1116-1122
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• 2010

Metal interconnections of multilayer Al/Ni and TiW/seed-Ni/Ni were formed on glass, and the adhesion strength and nanoindentation response of the composite layers were evaluated. The Al/Ni multilayer was formed by an anodic bonding of glass to Al and subsequent electroless plating of Ni, while the TiW/Ni multilayer was fabricated by sputter deposition of TiW and seed-Ni onto glass and electroless plating of Ni. Because of the diffusion of aluminum into glass during the anodic bonding, anodically bonded glass/Al joint exhibited greater interfacial strength than the sputtered glass/TiW one. The Al/Ni on glass also showed excellent resistance against delamination by bending deformation compared to the TiW/seed-Ni/Ni on glass. From the nanoindentation experiment of each metal layer on glass, it was found that the aluminum layer had extremely low hardness and elastic modulus similar to the glass substrate and played a beneficial role in the delamination resistance by lessening stress intensification at the joint. The indentation data of the multilayers also supported superior joint reliability of the Al/Ni to glass compared to that of the TiW/seed-Ni/Ni to glass.

• Korean Journal of Materials Research
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• v.29 no.3
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• pp.196-203
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• 2019

We report on the fabrication and characterization of an oxide photoanode with a zinc oxide (ZnO) nanorod array embedded in cuprous oxide ($Cu_2O$) thin film, namely a $ZnO/Cu_2O$ oxide p-n heterostructure photoanode, for enhanced efficiency of visible light driven photoelectrochemical (PEC) water splitting. A vertically oriented n-type ZnO nanorod array is first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type $Cu_2O$ thin film is directly electrodeposited onto the vertically oriented ZnO nanorod array to form an oxide p-n heterostructure. The introduction of $Cu_2O$ layer produces a noticeable enhancement in the visible light absorption. From the observed PEC current density versus voltage (J-V) behavior under visible light illumination, the photoconversion efficiency of this $ZnO/Cu_2O$ p-n heterostructure photoanode is found to reach 0.39 %, which is seven times that of a pristine ZnO nanorod photoanode. In particular, a significant PEC performance is observed even at an applied bias of 0 V vs $Hg/Hg_2Cl_2$, which makes the device self-powered. The observed improvement in the PEC performance is attributed to some synergistic effect of the p-n bilayer heterostructure on the formation of a built-in potential including the light absorption and separation processes of photoinduced charge carriers, which provides a new avenue for preparing efficient photoanodes for PEC water splitting.

• Tribology and Lubricants
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• v.37 no.2
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• pp.71-76
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• 2021

As opposed to using fossil fuels, we need to use eco-friendly resources such as sunlight, raindrops and wind to produce electricity and combat environmental pollution. A triboelectric nanogenerator (TENG) is a device that converts mechanical energy into electricity by inducing repetitive contact and separation of two dissimilar materials. During the contact and separation processes, electron flow occurs owing to a change in electric potential of the contacting surface caused by contact electrification and electrostatic induction mechanisms. A solid-solid contact TENG is widely known, but it is possible to generate electricity via liquid-solid contact. Therefore, by designing a hydrophobic TENG, we can gather electricity from raindrop energy in a feasible manner. To fabricate the superhydrophobic surface of TENGs, we employ a dip coating technique to synthesize an octadecylamine (ODA)- and polydimethylsiloxane (PDMS)-based coating on polyethylene terephthalate (PET). The synthesized coating exhibits superhydrophobicity with a contact angle greater than 150° and generates a current of 2.2 ㎂/L while water droplets fall onto it continuously. Hence, we prepare a box-type TENG, with the ODA/PDMS coating deposited on the inside, and place a 1.5 mL water droplet into it. Resultantly, we confirm that the induced vibration causes continuous impacts between the ODA/PDMS coating and the water, generating approximately 100 pA for each impact.