The mechanical and electrical characteristics can be improved in 3D stacked IC technology which can accomplish the ultra-high integration by stacking more semiconductor chips within the limited package area through the Cu direct bonding method minimizing the performance degradation to the bonding surface to the inorganic compound or the oxide film etc. The surface was treated in a ultrasonic washer using a diamond abrasive to remove other component substances from the prepared cast plate substrate surface. FE-SEM was used to analyze the bonding characteristics of the bonded copper substrates, and the cross section of the bonded Cu conjugates at the sintering junction temperature of 100 ℃, 150 ℃, 200 ℃, 350 ℃ and the pressure of 2303 N/cm² and 3087 N/cm². At 2303 N/cm², the good bonding of copper substrate was confirmed at 350 ℃, and at the increased pressure of 3087 N/cm², the bonding condition of Cu was confirmed at low temperature junction temperature of 200 ℃. However, the recrystallization of Cu particles was observed due to increased pressure of 3087 N/cm² and diffusion of Cu atoms at high temperature of 350 ℃, which can lead to degradation in semiconductor manufacturing.

In order to improve the energy density and safety of Li-ion batteries, the development of a separator with high thermal stability and electrolyte wettability is an important desire. Thus, the ceramic separator to replace the polymer type is one of the most promising materials that can prevent short-circuit caused by the formation of dendrite and thermal deformation. In this study, we introduce the fabrication of various anodic aluminum oxide membranes for the application of Li-ion battery separators with the advantages of improved mechanical/thermal stability, wettability, and a high rate of Li⁺ migration through the membrane. Two different types of through-holes and branched anodic aluminum oxide membranes are well used in lithium-ion battery separators, however, branched anodic aluminum oxide membranes exhibit the most improved performance with capacity (126.0 mAh g^-1 @ 0.3C), capacity drop at the high C-rate (30.6 %), and low internal resistance (8.2 Ω).

Icing causes various serious problems, where water vapor or water droplets adhere at cold conditions. Therefore, understanding of ice adhesion on solid surface and technology to reduce de-icing force are essential for surface finishing of metallic materials used in extreme environments and aircrafts. In this study, we controlled wettability of aluminum alloy using anodic oxidation, hydrophobic coating and lubricant-impregnation. In addition, surface porosity of anodized oxide layer was controlled to realize superhydrophilicity and superhydrophobicity. Then, de-icing force on these surfaces with a wide range of wettability and mobility of water was measured. The results show that the enhanced wettability of hydrophilic surface causes strong adhesion of ice. The hydrophobic coating on the nanoporous anodic oxide layer reduces the adhesion of ice, but the volume expansion of water during the freezing diminishes the effect. The lubricant-impregnated surface shows an extremely low adhesion of ice, since the lubricant inhibits the direct contact between ice and solid surface.

In this study, the influence of silicon contents on the microstructure, mechanical and tribological properties of Ti-Al-Si-N coatings were systematically investigated for application of cutting tools. The composition of the Ti-Al-Si-N coatings were controlled by different combinations of TiAl₂ and Ti₄Si composite target powers using an arc ion plating technique in a reactive gas mixture of high purity Ar and N₂ during depositions. Ti-Al-Si-N films were nanocomposite consisting of nanosized (Ti,Al,Si)N crystallites embedded in an amorphous Si₃N₄/SiO₂ matrix. The instrumental analyses revealed that the synthesized Ti-Al-Si-N film with Si content of 5.63 at.% was a nanocomposites consisting of nano-sized crystallites (5-7 nm in dia.) and a three dimensional thin layer of amorphous Si₃N₄ phase. The hardness of the Ti-Al-Si-N coatings also exhibited the maximum hardness value of about 47 GPa at a silicon content of ~5.63 at.% due to the microstructural change to a nanocomposite as well as the solid-solution hardening. The coating has a low friction coefficient of 0.55 at room temperature against an Inconel alloy ball. These excellent mechanical and tribological properties of the Ti-Al-Si-N coatings could help to improve the performance of machining and cutting tool applications.

PEO (plasma electrolytic oxidation) was applied to modify the surface of AZ31 magnesium alloy in this study. The mixed solution of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) was used as the electrolyte, and 0 - 0.05 g/L of Ca-GP (Glycerol Phosphate Calcium salt) was added in the electrolyte as an additive. PEO treatment was conducted at a current density of 30mA/cm² for 5 minutes using a DC power supply. The surface properties were identified by SEM, XRD and surface roughness analyses, and the corrosion resistance was evaluated by potentiodynamic polarization and immersion tests. In addition, the biocompatibility was evaluated by immersion test in SBF solution. As the concentration of Ca-GP was increased, the surface morphology was denser and more uniform, and the amount of Ca and the thickness of oxide layer increased. Only Mg peak was observed in XRD analysis due to very thin oxide layer. The corrosion resistance of PEO-treated samples increased with the concentration of Ca-GP in comparision with the untreated sample. In particular, the highest corrosion resistance was identified at the group of 0.04g Ca-GP through potentiodynamic polarization and immersion tests in saline solution (0.9 wt.%NaCl). During the immersion in saline solution, pH rapidly increased at the beginning of immersion period due to rapid corrosion, and then increase rate of pH decreased. However, the pH value in the SBF temporarily increased from 7.4 to 8.5 during the day, then decreased due to the inhibition of corrosion with HA(hydroxyapatite) formation.

This study examined the influence of post weld heat treatment (PWHT) conditions on corrosion behaviors of laser-welded super duplex stainless steel tube. Due to the high cooling rate of laser welding, the phase fraction of ferrite and austenite in the weld metal became unbalanced significantly. In addition, the Cr₂N particles were precipitated adjacent to the fusion line, which can be susceptible to the localized corrosion. On the other hand, the phase fraction in the weld metal was restored at a ratio of 5:5 when exposed to temperatures above 1060 ℃ during the post weld heat treatment. Nevertheless, the high beltline speed during the PWHT, leading to the insufficient cooling rate, caused a precipitation of σ phase at the interface between ferrite/austenite in both weld metal and base metal. This resulted in the severe corrosion damages and significant decrease in critical pitting temperature (CPT), which was even lower than that measured in as-welded condition. Moreover, the fraction of σ phase in the center region of post weld heat treated steel tube was obtained to be higher than in the surface region. These results suggest that the PWHT conditions for the steel tube should be optimized to ensure the high corrosion resistance by excluding the precipitation of σ phase even in center region.

Synthesizing low-dimensional structures of oxide semiconductors is a promising approach to fabricate highly efficient gas sensors by means of possible enhancement in surface-to-volume ratios of their sensing materials. In this work, vertically aligned zinc oxide (ZnO) nanorods are successfully synthesized on a transparent glass substrate via seed-mediated hydrothermal synthesis method with the use of a ZnO nanoparticle seed layer, which is formed by thermally oxidizing a sputtered Zn metal film. Structural and optical characterization by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy reveals the successful preparation of the ZnO nanorods array of the single hexagonal wurtzite crystalline phase. From gas sensing measurements for the nitrogen dioxide (NO₂) gas, the vertically aligned ZnO nanorod array is observed to have a highly responsive sensitivity to NO₂ gas at relatively low concentrations and operating temperatures, especially showing a high maximum sensitivity to NO₂ at 250 ℃ and a low NO₂ detection limit of 5 ppm in dry air. These results along with a facile fabrication process demonstrate that the ZnO nanorods synthesized on a transparent glass substrate are very promising for low-cost and high-performance NO₂ gas sensors.

Nitriding layers developed during gaseous nitriding of AISI4115 steels for the application of steel bushing part were investigated. The compound layer thickness of about 10㎛, 0.3mm of case depth under the same conditions, and conventional nitriding, nitrocarburizing, and controlled nitriding were performed in three methods. In the controlled nitriding, K_N was controlled by measuring the hydrogen partial pressure. The nitrided samples were analyzed by micro Vickers hardness test, optical microscopy and scanning electron microscopy. The phases of compound layer were identified by X-ray diffraction and electron backscatter diffraction. The controlled nitriding specimen indicated the highest surface hardness of about 860 HV_0.1. The compound layer of the conventional nitriding and nitrocarburizing specimen was formed with about 46% porous layer and 𝜺 + 𝜸' phase, and about 13% porous layer and about 80% 𝜸' phase were formed on the controlled nitriding specimen. As a result of the Ball-on-disk wear test, the worn mass loss of ball performed on the surface of the controlled nitriding specimen was the largest. The controlled nitriding specimen had the highest surface hardness due to the lowest porous percentage of compound layer, which improved the wear resistance.

Corrosion of steel plate is common phenomenon which results in the gradual destruction caused by a wide variety of environments. Corrosion monitoring is the tracking of the degradation progress for a long period of time. Corrosion on steel plate appears as a discoloration and any irregularities on the surface. In this study, we developed a quantitative evaluation method of the rust formed on steel plate by using k-means clustering from the corroded area in a given image. The k-means clustering for automated corrosion detection was based on the GrabCut segmentation and Gaussian mixture model(GMM). Image color of the corroded surface at cut-edge area was analyzed quantitatively based on HSV(Hue, Saturation, Value) color space.

High-entropy TiAlCrSiN nano-composite coating was designed to improve mold life for high temperature liquid molding. Alloy design, powder fabrication and single alloying target fabrication for the high-entropy nano-composite coating were carried out. Using the single alloying target, an arc ion plating method was applied to prepare a TiAlCrSiN nano-composite coating had a 30 nm TiAlCrSiN layers are deposited layer by layer, and form about 4 ㎛-thickness of multi-layered coating. TiAlCrSiN nano-composite coating had a high hardness of about 39.9 GPa and a low coefficient of friction of less than about 0.47 in a dry environment. In addition, there was no change in the structure of the coating after the dissolution loss test in the molten metal at a temperature of about 1100 degrees.