• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.513-519
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• 2006

We developed two kinds of the microchip for application to electrophoresis based on both glass and quartz employing the MEMS fabrications. The poly-Si layer deposited onto the bonding interface apart from channel regions can play a role as the optical slit cutting off the stray light in order to concentrate the UV ray, from which it is possible to improve the signal-to-noise (S/N) ratio of the detection on a chip. In the glass chip, the deposited poly-Si layer had an important function of the etch mask and provided the bonding surface properly enabling the anodic bonding. The glass wafer including more impurities than quartz one results in the higher surface roughness of the channel wall, which affects subsequently on the microflow behavior of the sample solutions. In order to solve this problem, we prepared here the mixed etchant consisting HF and $NH_4F$ solutions, by which the surface roughness was reduced. Both the shape and the dimension of each channel were observed, and the electroosmotic flow velocities were measured as 0.5 mm/s for quartz and 0.36 mm/s for glass channel by implementing the microchip electrophoresis. Applying the optical slit with poly-Si layer provides that the S/N ratio of the peak is increased as ca. 2 times for quartz chip and ca. 3 times for glass chip. The maximum UV absorbance is also enhanced with ca. 1.6 and 1.7 times, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.2
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• pp.79-84
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• 2014

To investigate the plating properties of a diethylene glycol-based Ag immersion plating solution containing citric acid, silver immersion plating was performed in a range from room temperature to $50^{\circ}C$ using sputtered Cu specimens. The used Cu specimens possessed surface structure with large numbers of pinholes which were created with over-acid etching. The Ag immersion plating performed at $40^{\circ}C$ exhibited that the pinholes and copper surface were completely filled with Ag just after 5 min mainly due to galvanic displacement reaction, indicating the best plating properties. Subsequently, the surface morphology of Ag-coated Cu became rougher as the plating time increased to 30 min because of the deposition of silver nanoparticles created by chemical reduction in the solution. The specimen that its overall surface was covered with silver indicated the start of oxidation at temperature higher than around $50^{\circ}C$ in air as compared with pure Cu, indicating enhanced anti-oxidation properties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.27-36
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• 2019

The demand for a low dispersion lens with a small refractive index and a high refractive index is increasing, and accordingly, there is an increasing need for a releasable protective film with high heat resistance and abrasion resistance. On the other hand, the optical industry has not yet established a clear standard for the manufacturing process and quality standards for mold-releasing protective films used in aspheric glass lens molding. Optical lens manufacturers treat this technology as proprietary information. In this study, an experiment was conducted regarding the optimization of ion etching, magnetron, and arc current at each source and filter part, and bias voltage in FCVA (filtered cathode vacuum arc)-based Ta-C thin film coatings. This study found that compared to iridium-rhenium alloy thin film sputtering products, the coating conditions were improved by approximately 50%, 20%, and 40% in terms of thickness, hardness, and adhesive strength of the film, respectively. The thin-film coating process proposed in this study is expected to contribute significantly to the development and utilization of glass lenses, which will help enhance the minimum mechanical properties and quality of the mold-release thin film layer required for glass mold surface forming technology.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.1
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• pp.6-13
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• 2012

HVOF thermal spray coating of 80%WC-CoFe powder is one of the most promising candidate for the replacement of the traditional hard chrome plating and hard ceramics coating because of the environmental problem of the very toxic $Cr^{6+}$ known as carcinogen by chrome plating and the brittleness of ceramics coatings. 80%WC-CoFe powder was coated by HVOF thermal spraying for the study of durability improvement of the high speed spindle such as air bearing spindle. The coating procedure was designed by the Taguchi program, including 4 parameters of hydrogen and oxygen flow rates, powder feed rate and spray distance. The surface properties of the 80%WC-CoFe powder coating were investigated roughness, hardness and porosity. The optimal condition for thermal spray has been ensured by the relationship between the spary parameters and the hardness of the coatings. The optimal coating process obtained by Taguchi program is the process of oxygen flow rate 34 FRM, hydrogen flow rate 57 FRM, powder feed rate 35 g/min and spray distance 8 inch. The coating cross-sectional structure was observed scanning electron microscope before chemical etching. Estimation of coating porosity was performed using metallugical image analysis. The Friction and wear behaviors of HVOF WC-CoFe coating prepared by OCP are investigated by reciprocating sliding wear test at $25^{\circ}C$ and $450^{\circ}C$. Friction coefficients (FC) of coating decreases as sliding surface temperature increases from $25^{\circ}C$ to $450^{\circ}C$.

• Korean Journal of Materials Research
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• v.16 no.4
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• pp.225-230
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• 2006

Nanoimprint lithography (NIL) is a novel method of fabricating nanometer scale patterns. It is a simple process with low cost, high throughput and resolution. NIL creates patterns by mechanical deformation of an imprint resist and physical contact process. The imprint resist is typically a monomer or polymer formulation that is cured by heat or UV light during the imprinting process. Stiction between the resist and the stamp is resulted from this physical contact process. Stiction issue is more important in the stamps including narrow pattern size and wide area. Therefore, the antistiction layer coating is very effective to prevent this problem and ensure successful NIL. In this paper, an antistiction layer was deposited and characterized by PECVD (plasma enhanced chemical vapor deposition) method for metal stamps. Deposition rates of an antistiction layer on Si and Ni substrates were in proportion to deposited time and 3.4 nm/min and 2.5 nm/min, respectively. A 50 nm thick antistiction layer showed 90% relative transmittance at 365 nm wavelength. Contact angle result showed good hydrophobicity over 105 degree. $CF_2$ and $CF_3$ peaks were founded in ATR-FTIR analysis. The thicknesses and the contact angle of a 50 nm thick antistiction film were slightly changed during chemical resistance test using acetone and sulfuric acid. To evaluate the deposited antistiction layer, a 50 nm thick film was coated on a stainless steel stamp made by wet etching process. A PMMA substrate was successfully imprinting without pattern degradations by the stainless steel stamp with an antistiction layer. The test result shows that antistiction layer coating is very effective for NIL.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.11 no.2
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• pp.133-141
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• 2017

The hybrid acoustic sensor for implantable hearing aid has the structure in which a sound pressure based acoustic sensor (ECM) and a vibration based acceleration sensor are combined. This sensor combines the low frequency sensitivity of an acoustic sensor with the high frequency sensitivity of an acceleration sensor, allowing the acquisition of a wide range of sound from low to high frequency. In this paper, an acceleration sensor for use in a hybrid acoustic sensor has been proposed. The acceleration sensor captures the vibration of the tympanic membrane generated by the acoustic signal. The size of the proposed acceleration sensor was determined to diameter of 3.2 mm considering the anatomical structure of the tympanic membrane and the standard of ECM. In order to make the hybrid acoustic sensor have high sensitivity and wide bandwidth characteristics, the aim of the resonance frequency of the acceleration sensor is to be generated at about 3.5 kHz. The membrane of the acceleration sensor derives geometric structure through mathematical model and finite element analysis. Based on the analysis results, the membrane was implemented through a chemical etching process. In order to verify the frequency characteristics of the implemented membrane, vibration measurement experiment using external force was performed. The experiment results showed mechanical resonance of the membrane occurred at 3.4 kHz. Therefore, it is considered that the proposed acceleration sensor can be utilized for a hybrid acoustic sensor.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.276-280
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• 2010

Copper(Cu) as an interconnecting metal layer can replace aluminum (Al) in IC fabrication since Cu has low electrical resistivity, showing high immunity to electromigration compared to Al. However, it is very difficult for copper to be patterned by the dry etching processes. The chemical mechanical polishing (CMP) process has been introduced and widely used as the mainstream patterning technique for Cu in the fabrication of deep submicron integrated circuits in light of its capability to reduce surface roughness. But this process leaves a large amount of residues on the wafer surface, which must be removed by the post-CMP cleaning processes. Copper corrosion is one of the critical issues for the copper metallization process. Thus, in order to understand the copper corrosion problems in post-CMP cleaning solutions and study the effects of DC biases and post-CMP cleaning solution concentrations on the Cu film, a constant voltage was supplied at various concentrations, and then the output currents were measured and recorded with time. Most of the cases, the current was steadily decreased (i.e. resistance was increased by the oxidation). In the lowest concentration case only, the current was steadily increased with the scarce fluctuations. The higher the constant supplied DC voltage values, the higher the initial output current and the saturated current values. However the time to be taken for it to be saturated was almost the same for all the DC supplied voltage values. It was indicated that the oxide formation was not dependent on the supplied voltage values and 1 V was more than enough to form the oxide. With applied voltages lower than 3 V combined with any concentration, the perforation through the oxide film rarely took place due to the insufficient driving force (voltage) and the copper oxidation ceased. However, with the voltage higher than 3 V, the copper ions were started to diffuse out through the oxide film and thus made pores to be formed on the oxide surface, causing the current to increase and a part of the exposed copper film inside the pores gets back to be oxidized and the rest of it was remained without any further oxidation, causing the current back to decrease a little bit. With increasing the applied DC bias value, the shorter time to be taken for copper ions to be diffused out through the copper oxide film. From the discussions above, it could be concluded that the oxide film was formed and grown by the copper ion diffusion first and then the reaction with any oxidant in the post-CMP cleaning solution.

• Journal of Adhesion and Interface
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• v.13 no.2
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• pp.58-63
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• 2012

CFRP chip is the byproduct from carbon fiber reinforced plastic (CFRP) processing. CFRP chip is not simply a waste mainly composed of fine carbon fiber and epoxy resin. CFRP chip keeps matrix to maximize their reinforcing effect. To obtain a uniform length of carbon fiber in CFRP chip, chip was chopped ina mortar. CFRP chip should be purified to get better interface adhesion. Epoxy resin on the carbon fiber was removed by $H_2O_2$ surface etching treatment. Optimal dispersion and fabrication conditions of CFRP chip embedded in phenolic resin were determined by thermal stability for fire retardant applications. CFRP chip-phenolic composite exhibits better mechanical and thermal properties than neat phenolic resin. Surface condition of CFRP chip-phenolic composite was evaluated by static contact angle measurement. Contact angle of CFRP chip-phenolic composite was greater than neat phenolic due to heterogeneous condition of fine carbon fibers. From the evaluation for fire retardant (ASTM D635-06) test, thermal stability of CFRP chip-phenolic composite was found to be improved with higher concentration of CFRP chip.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.3
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• pp.111-118
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• 2023

MXene, a two-dimensional transition metal carbide or nitride, has recently attracted much attention as a lightweight and flexible electromagnetic shielding material due to its high electrical conductivity, good mechanical strength and thermal stability. In particular, the Ti-based MXene, Ti₃C₂T_x and Ti₂CT_x are reported to have the best electrical conductivity and electromagnetic shielding properties in the vast MXene family. Therefore, in this study, Ti₃C₂T_x and Ti₂CT_x films were prepared by vacuum filtration using Ti₃C₂T_x and Ti₂CT_x dispersions synthesized by interlayer metal etching and centrifugation of Ti₃AlC₂ and Ti₂AlC. The electrical conductivity and electromagnetic shielding efficiency of the films were measured after heat treatment at high temperature. Then, X-ray diffraction and photoelectron spectroscopy were performed to analyze the structural changes of Ti₃C₂T_x and Ti₂CT_x films after heat treatment and their effects on electromagnetic shielding. Based on the results of this study, we propose an optimal structure for an ultra-thin, lightweight, and high performance MXene-based electromagnetic shielding film for future applications in small and wearable electronics.

• Restorative Dentistry and Endodontics
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• v.33 no.1
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• pp.9-19
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• 2008

The purpose of this study was: (1) to compare nanoleakage patterns of a conventional 3-step etch and rinse adhesive system and two experimental hydrophobic adhesive systems and (2) to investigate the change of the nanoleakage patterns after load cycling. Two kinds of hydrophobic experimental adhesives, ethanol containing adhesive (EA) and methanol containing adhesive (MA), were prepared. Thirty extracted human molars were embedded in resin blocks and occlusal thirds of the crowns were removed. The polished dentin surfaces were etched with a 35 % phosphoric acid etching gel and rinsed with water. Scotchbond Multi-Purpose (MP), EA and MA were used for bonding procedure. Z-250 composite resin was built-up on the adhesive-treated surfaces. Five teeth of each dentin adhesive group were subjected to mechanical load cycling. The teeth were sectioned into 2 mm thick slabs and then stained with 50 % ammoniacal silver nitrate. Ten specimens for each group were examined under scanning electron microscope in backscattering electron mode. All photographs were analyzed using image analysis software. Three regions of each specimen were used for evaluation of the silver uptake within the hybrid layer. The area of silver deposition was calculated and expressed in gray value. Data were statistically analyzed by two-way ANOVA and post-hoc testing of multiple comparisons was done with the Scheffe's test. Silver particles were observed in all the groups. However, silver particles were more sparsely distributed in the EA group and the MA group than in the MP group (p < .0001). There were no changes in nanoleakage patterns after load cycling.