• International Journal of Ocean System Engineering
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• 제2권2호
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• pp.106-115
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• 2012

In the present study, TiN and CrN films were coated by arc ion plating equipment onto aluminum alloy substrate, A2024. The film thickness was about 4.65 ${\mu}m$. TiN and CrN films were analyzed by X-ray diffraction and energy dispersive X-ray equipments. The Young's modulus and the micro-Vickers hardness of aluminum substrate were modified by the ceramic film coatings. The difference in Young's modulus between substrate and coating film would affect on the wear resistance. The critical load, Lc, was 75.8 N for TiN and 85.5 N for CrN. It indicated from the observation of optical micrographs for TiN and CrN films that lots of cracks widely propagated toward the both sides of scratch track in the early stage of MODE I. TiN film began to delaminate completely at MODE II stage. The substrate was finally glittered at MODE III stage. For CrN film, a few crack can be observed at MODE I stage. The delamination of film was not still occurred at MODE II and then was happened at MODE III. This agrees with critical load measurement which the adhesive strength was greater for CrN film than for TiN film. Consequently, it was difficult for CrN to delaminate because the adhesive strength was excellent against Al substrate. The wear process, which the film adheres and the ball transfers, could be enhanced because of the increase in loading. The wear weight of ball was less for CrN than for TiN. This means that the wear damage of ball was greater for TiN than for CrN film. It is also obvious that it was difficult to delaminate because the CrN coating film has high toughness. The coefficient of friction was less for CrN coating film than for TiN film.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.121-121
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• 1999

Gallium nitride (GaN) semiconductor is intensively under investigation for commercialization of short wavelength light emitting devices and laser diodes. One of serious obstacles to overcome is to reduce the defect density in GaN film grown by various techniques such as MOCVD, HVPE, etc. Many research groups including SAIT are trying to improve the defect density to 106-107/cm2 from the level of 108-1010/cm2. We have investigated epitaxial growth behaviour of GaN thin and thick films under hidride vapour phase epitaxy (HVPE) condition. In this report, we present the microstructural and crystallographical characteristics of the GaN films grown on sapphire (0001) substrate which were studied by both conventional and high-resolution transmission electron microscopy (TEM). Also we present some microscopic analysis results obtained from GaN films grown by ELO(dpitzsial lateral overgrowth)-HVPE and from GaN quantum well structures grown by MOCVD. Another serious problem in growing GaN thick film by HVPE is internal micro-cracks. We also comment the origin of the micro-crack.

• Journal of information and communication convergence engineering
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• 제1권2호
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• pp.70-73
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• 2003

We have studied the effects of solvents and additives in the precursor solutions on the characteristics of barium strontium titanate (BST) thin films. The solution having two solvents, ie. acetic acid for barium acetate and strontium acetate and 2-methoxyethanol for titanium isopropoxide and also having an additive of ethylene glycol shows good stability and remains homogeneous even after a month of ageing. It produces excellent BST thin film without cracks. Dielectric constant, loss tangent at 10KHz and leakage current density at 3V of the BST (70/30) thin film made from this solution are 339, 0.052 and 13.3 ${\mu}\textrm{A}$/$\texmrm{cm}^2$, respectively.

• Journal of the Korean Wood Science and Technology
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• 제32권6호
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• pp.23-35
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• 2004

The goal of study was to investigate the influence of the acrylated urethane oligomer on mechanical properties, the chemical resistance and thermal resistance of the UV curable urethane acrylate coatings for fancy veneer overlayed plywood flooring. The pencil hardness and abrasion resistance of the coated fancy veneer overlayed plywood floorings increased with increasing the acrylate functionality of the acrylated urethane oligomer. In the case of the UV cured film containing hexa-functional acrylated aliphatic urethane oligomer, high discoloration of the coated fancy veneer overlayed plywood flooring was observed near the cracks at the beginning of the chemical treatment. In this study, it was found that the degradation of the UV cured film caused by an alkaline reagent was higher than that of the UV cured film caused by an acidic treatment.

• 한국재료학회지
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• 제15권7호
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• pp.486-490
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• 2005

Thin films of tungsten oxide and nickel oxide were deposited on $Al_2O_3/Si-substrate$ by high vacuum thermal evaporation. The properties of microstructure and crystallinity were analyzed by SEM and XRD respectively. $WO_3$ films without addition of NiO showed polycrystalline structure after annealing at $500^{\circ}C$ for SO min. There were the cracks between the polycrystalline grains and the crack width was increased with the thickness of $WO_3$ films. The cracks in the $WO_3$ films could be controlled by an optimum deposition of NiO on $WO_3$ films and either less or more than the optimum addition fails to suppress the cracks. A process mechanism to suppress the crack has been discussed.

• 한국재료학회지
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• 제3권1호
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• pp.19-27
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• 1993

RF magnetrom sputtering으로 52/48 PZT target을 사용하여 PZT thin film을 증착시킨후, furnace annealing을 실시하여 Si 기판에서는 55$0^{\circ}C$에서부터 안정상인 peroskite구조가 형성되었다. Si기판위에서는 후속열처리시 계면에 상당한 산화막층이 형성되었으며 TiN 기판위에서는 후속열처리시 TiN층은 사라지고 Ti$O_2$층이 형성되었다. Si$O_2$기판에서는 후속열처리후에도 안정한 PZT film을 형성시킬 수 있었다. As-depo.시에는 PZT film의 조성비가 균일하게 유지되었으나 75$0^{\circ}C$후속열 처리시에는 상당량의 Pb가 Si기판으로 diffusion하였으며 Si도 out-diffusion하였다. 전기적 특성은 10KHz에서 C-V를 측정결과 약 1300정도의유전상수 값이 나왔으나 후속열처리시 표면에 crack이 발생하였다.

• International Journal of Fluid Machinery and Systems
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• 제2권1호
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• pp.55-60
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• 2009

The present study investigated temperature and thermal stress distributions in a film cooling system with normal injection cooling flow. 3D-numerical simulations using the FEM commercial code ANSYS were conducted to calculate distributions of temperature and thermal stresses. In the simulations, the surface boundary conditions used the surface heat transfer coefficients and adiabatic wall temperature which were converted from the Sherwood numbers and impermeable wall effectiveness obtained from previous mass transfer experiments. As a result, the temperature gradients, in contrast to the adiabatic wall temperature, were generated by conduction between the hot and cold regions in the film cooling system. The gradient magnitudes were about 10~20K in the y-axis (spanwise) direction and about 50~60K in the x-axis (streamwise) direction. The high thermal stresses resulting from this temperature distribution appeared in the side regions of holes. These locations were similar to those of thermal cracks in actual gas turbines. Thus, this thermal analysis can apply to a thermal design of film cooling holes to prevent or reduce thermal stresses.

• 한국재료학회지
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• 제22권1호
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• pp.1-7
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• 2012

Thin film electrode consisting purely of porous anodic tin oxide with well-defined nano-channeled structure was fabricated for the first time and its electrochemical properties were investigated for application to an anode in a rechargeable lithium battery. To prepare the thin film electrode, first, a bi-layer of porous anodic tin oxides with well-defined nano-channels and discrete nano-channels with lots of lateral micro-cracks was prepared by pulsed and continuous anodization processes, respectively. Subsequent to the Cu coating on the layer, well-defined nano-channeled tin oxide was mechanically separated from the specimen, leading to an electrode comprised of porous tin oxide and a Cu current collector. The porous tin oxide nearly maintained its initial nano-structured character in spite of there being a series of fabrication steps. The resulting tin oxide film electrode reacted reversibly with lithium as an anode in a rechargeable lithium battery. Moreover, the tin oxide showed far more enhanced cycling stability than that of powders obtained from anodic tin oxides, strongly indicating that this thin film electrode is mechanically more stable against cycling-induced internal stress. In spite of the enhanced cycling stability, however, the reduction in the initial irreversible capacity and additional improvement of cycling stability are still needed to allow for practical use.

• 한국전기전자재료학회논문지
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• 제19권6호
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• pp.552-557
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• 2006

Electrical, optical, surface, and structural properties of amorphous indium-zinc-oxide (a-IZO) grown by box cathode sputtering (BCS) were compared with crystalline indium-tin-oxide (c-ITO) anode films grown by conventional DC sputtering (DCS). Although x-ray diffraction plot of BCS-grown IZO film shows amorphous structure, the optical and electrical properties of a-IZO is comparable to those of c-ITO film. In particular, BCS-grown IZO films shows very smooth surface without defects such as pin hole and cracks because most of the energy of the sputtered atoms was confined in high density plasma region in box cathode gun. Furthermore polymer organic light emitting diodes (POLED) with the a-IZO anode film shows better electrical properties than that of POLED with the c-ITO anode film due to high work function and smooth surface of a-IZO. This suggested that BCS-grown a-IZO film is promising anode materials substituting conventional c-ITO anode in OLED and flexible displays.

• 한국재료학회지
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• 제34권4호
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• pp.215-222
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• 2024

Because collagen is inherently piezoelectric, research is being actively conducted to utilize it to harvest energy. In this study, a collagen solution was prepared using edible low-molecular-weight peptide collagen powder, and collagen films were fabricated using a dip coating method. The collagen films prepared by dip coating showed a smooth surface without defects such as pinholes or cracks. Dehydrothermal treatment of the collagen films was performed to induce a stable molecular structure through cross-linking. The collagen film subjected to dehydrothermal treatment at 110 ℃ for 24 h showed a thickness reduction rate of 19 %. Analysis of the collagen films showed that the crystallinity of the collagen film improved by about 7.9 % after dehydrothermal treatment. A collagen film-based piezoelectric nanogenerator showed output characteristics of approximately 13.7 V and 1.4 ㎂ in a pressure test of 120 N. The generator showed a maximum power density of about 2.91 mW/m² and an output voltage of about 8~19 V during various human body movements such as finger tapping. The collagen film-based piezoelectric generator showed improved output performance with improved crystallinity and piezoelectricity after dehydrothermal treatment.