• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.54-54
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• 2010

Zinc oxide is metal oxide semiconductor with the 3.37 eV bandgap energy. Zinc oxide is very attractive materials for many application fields. Zinc Oxide has many advantages such as high conductivity and good transmittance in visible region. Also it is cheaper than other semiconductor materials such as indium tin oxide (ITO). Therefore, ZnO is alternative material for ITO. ZnO is attracting attention for its application to transparent conductive oxide (TCO) films, surface acoustic wave (SAW), films bulk acoustic resonator (FBAR), piezoelectric materials, gas-sensing, solar cells and photocatalyst. In this study, we synthesized ZnO nanoparticles and defined their physical and chemical properties. Also we studied about the application of ZnO nanoparticles as a photocatalyst and try to find a enhancement photocatalytic activity of ZnO nanorticles.. We synthesized ZnO nanoparticles using spray-pyrolysis method and defined the physical and optical properties of ZnO nanoparticles in experiment I. When the ZnO are exposed to UV light, reduction and oxidation(REDOX) reaction will occur on the ZnO surface and generate ${O_2}^-$ and OH radicals. These powerful oxidizing agents are proven to be effective in decomposition of the harmful organic materials and convert them into $CO_2$ and $H_2O$. Therefore, we investigated that the photocatalytic activity was increased through the surface modification of synthesized ZnO nanoparticles. In experiment II, we studied on the stability of ZnO nanoparticles in water. It is well known that ZnO is unstable in water in comparison with $TiO_2$. $Zn(OH)_2$ was formed at the ZnO surface and ZnO become inactive as a photocatalyst when ZnO is present in the solution. Therefore, we prepared synthesized ZnO nanoparticles that were immersed in the water and dried in the oven. After that, we measured photocatalytic activities of prepared samples and find the cause of their photocatalytic activity changes.

• Journal of the Korean institute of surface engineering
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• v.51 no.4
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• pp.231-236
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• 2018

We report p-type electrical characteristics of the amorphous $La_2NiO_{4+{\delta}}$ thin films which were sputtered on the glass substrates using an RF sputtering system. As-deposited thin films at room temperature and $300^{\circ}C$ were amorphous in nature. Post-annealing of the thin film samples over $400^{\circ}C$ resulted in the nano-crystallization of the $La_2NiO_{4+{\delta}}$. The electrical properties of the films were much dependent on the oxygen partial pressure, temperature of the post-annealing and sputtering ambient. The as-deposited samples at room temperature show a hole concentration of $7.82{\times}10^{13}cm^{-3}$, and it could be increased as high as $3.51{\times}10^{22}cm^{-3}$ when the films were post-annealed in an oxygen atmosphere at $500^{\circ}C$. Such p-type conductivity behavior of the $La_2NiO_{4+{\delta}}$ films suggests that the amorphous and nano-crystallized $La_2NiO_{4+{\delta}}$ films have potential for the application as p-type semiconductive or conductive materials at low temperatures where material diffusion is limited.

• Macromolecular Research
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• v.16 no.3
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• pp.212-217
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• 2008

PVDF ($Kynar^{(R)}$ 761) nanofibers were made by electrospinning with an external voltage of 6-10 kV, a traveling distance of 7-15 cm and a flow rate of 0.4-1 mL/h. Although the mean diameter of the fibers has not changed significantly, the conditions affected the change in diameter distribution. This was attributed to interactions, both attraction and repulsion, between the positive charges on the polymer solutions and the electrically grounded collector. Higher voltages and traveling distance increased the level of attraction between the positive charge on the polymer solution and the electrically grounded collector, resulting in a narrow diameter distribution, In addition, a high flow rate allowed a high population of uniformly charged solutions to travel to the grounded collector, which resulted in a narrow diameter distribution. The optimum conditions for electrospinning of PVDF in DMAc/acetone (3/7 by wt) were a collector voltage of 6 kV, a syringe tip to collector of 7 cm, a flux rate of 0.4 mL/h and 10 kV, 10 cm, 1 mL/h, Since PVDF is widely used as a filtration membrane, it was electrospun on a PET support with a rotating drum as a grounded collector. Surprisingly, some straight nanofibers were separated from the randomly deposited nanofibers. The straight nanofiber area was transparent, while the randomly deposited nanofiber area was opaque. Both straight nanofibers and aligned nanotibers could be obtained by manipulating the PET drum collector. These phenomena were not observed when the support was changed to an Al sheet. This suggests that a pseudo dual collector was generated on the PET sheet. No negative charge was created because the PET sheet was not a conductive material. However, less charge was created when the sheet was not perfectly attached to the metal drum. Hence, the nanotibers jumped from one grounded site to the nearest one, yielding a straight nanofiber.

• Journal of Sensor Science and Technology
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• v.27 no.6
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• pp.397-402
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• 2018

Proper seat design is critical to the safety, comfort, and ergonomics of automotive driver's seats. To ensure effective seat design, quantitative methods should be used to evaluate the characteristics of automotive seats. This paper presents a system that is capable of simultaneously monitoring body pressure distribution and surface deformation in a textile material. In this study, a textile-based capacitive sensor was used to detect the body pressure distribution in an automotive seat. In addition, a strain gauge sensor was used to detect the degree of curvature deformation due to high-pressure points. The textile-based capacitive sensor was fabricated from the conductive fabric and a polyurethane insulator with a high signal-to-noise ratio. The strain gauge sensor was attached on the guiding film to maximize the effect of its deformation due to bending. Ten pressure sensors were placed symmetrically in the hip area and six strain gauge sensors were distributed on both sides of the seat cushion. A readout circuit monitored the absolute and relative values from the sensors in realtime, and the results were displayed as a color map. Moreover, we verified the proposed system for quantifying the body pressure and fabric deformation by studying 18 participants who performed three predefined postures. The proposed system showed desirable results and is expected to improve seat safety and comfort when applied to the design of various seat types. Moreover, the proposed system will provide analytical criteria in the design and durability testing of automotive seats.

• Composites Research
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• v.35 no.1
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• pp.47-51
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• 2022

In order to efficiently control the heat generation of electronic devices, many research has been conducted on thermally conductive composite materials. In this study, milled carbon fiber was dispersed in four solvent to investigate the relationship of carbon fiber alignment according to dispersion by solvents, and carbon fiberreinforced composite material(CFRP) was manufactured using vacuum filtration. To evaluate the arrangement of CFRP the arrangement of the prepared specimen was observed under an optical microscope, and thermal conductivity was measured by Laser Flash Analysis. The Through-plane thermal conductivity of CFRP using NMP and Ethanol was 10.79 W/mK and 10.57 W/mK respectively, which were improved by 218% and 209% compared to the In-plane thermal conductivity. The high viscosity of the solvent greatly affects the shear of the fluid, and it seemed to determine the alignment of the filler.

• Fashion & Textile Research Journal
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• v.24 no.1
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• pp.138-145
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• 2022

Today, graphene loaded textiles are being considered promising smart clothing due to their high conductivity. In this study, we reported reduced graphene oxide(r-GO) deposited pure cotton fabrics fabricated with a colloidal solution of graphene(GO), using a one-step aerosol spray pyrolysis(ASP) process and their potential application on smart textiles. The ASP process is advantageous in that it is easily implementable and can be applied for continuous processing. Moreover, this process has never been applied to deposit r-GO on pure cotton fabric. The field emission-scanning microscopy (FE-SEM) observation, Fourier transform-infrared(FT-IR) analysis, Raman spectroscopy, X-ray diffraction(XRD) analysis, and ultraviolet transmittance(UVT) were used to evaluate material properties of the r-GO colloids. The resistance was also measured to evaluate the electrical conductivity of the specimens. The results revealed that the r-GO was successfully deposed on specimens, and the specimen with the highest electrical conductivity demonstrated an electrical resistance value of 2.27 kΩ/sq. Taken together, the results revealed that the ASP method demonstrated a high potential for effective deposition of r-GO on cotton fabric specimens and is a prospect for the development of conductive cotton-based smart clothing. Therefore, this study is also meaningful in that the ASP process can be newly applied by depositing r-GO on the pure cotton fabric.

• Journal of Electrochemical Science and Technology
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• v.12 no.4
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• pp.458-464
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• 2021

Lithium ion batteries (LIBs) is a kind of rechargeable secondary battery, developed from lithium battery, lithium ions move between the positive and negative electrodes to realize the charging and discharging of external circuits. Zeolitic imidazolate frameworks (ZIFs) are porous crystalline materials in which organic imidazole esters are cross-linked to transition metals to form a framework structure. In this article, ZIF-67 is used as a sacrificial template to prepare nano porous carbon (NPC) coated cobalt nanoparticles. The final product Co/NPC composites with complete structure, regular morphology and uniform size were obtained by this method. The conductive network of cobalt and nitrogen doped carbon can shorten the lithium ion transport path and present high conductivity. In addition, amorphous carbon has more pores that can be fully in contact with the electrolyte during charging and discharging. At the same time, it also reduces the volume expansion during the cycle and slows down the rate of capacity attenuation caused by structure collapse. Co/NPC composites first discharge specific capacity up to 3115 mA h/g, under the current density of 200 mA/g, circular 200 reversible capacity as high as 751.1 mA h/g, and the excellent rate and resistance performance. The experimental results show that the Co/NPC composite material improves the electrical conductivity and electrochemical properties of the electrode. The cobalt based ZIF-67 as the precursor has opened the way for the design of highly performance electrodes for energy storage and electrochemical catalysis.

• Journal of Electrochemical Science and Technology
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• v.13 no.1
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• pp.78-89
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• 2022

ANODE-free Li-metal batteries (AFLMBs) operating with Li of cathode material have attracted enormous attention due to their exceptional energy density originating from anode-free structure in the confined cell volume. However, uncontrolled dendritic growth of lithium on a copper current collector can limit its practical application as it causes fatal issues for stable cycling such as dead Li formation, unstable solid electrolyte interphase, electrolyte exhaustion, and internal short-circuit. To overcome this limitation, here, we report a novel dual-salt electrolyte comprising of 0.2 M LiPF₆ + 3.8 M lithium bis(fluorosulfonyl)imide in a carbonate/ester co-solvent with 5 wt% fluoroethylene carbonate, 2 wt% vinylene carbonate, and 0.2 wt% LiNO₃ additives. Because the dual-salt electrolyte facilitates uniform/dense Li deposition on the current collector and can form robust/ionic conductive LiF-based SEI layer on the deposited Li, a Li/Li symmetrical cell exhibits improved cycling performance and low polarization for over 200 h operation. Furthermore, the anode-free LiFePO₄/Cu cells in the carbonate electrolyte shows significantly enhanced cycling stability compared to the counterparts consisting of different salt ratios. This study shows an importance of electrolyte design guiding uniform Li deposition and forming stable SEI layer for AFLMBs.

• The Journal of the Convergence on Culture Technology
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• v.8 no.5
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• pp.749-754
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• 2022

High adhesion and water resistance of the skin surface are required for wearable and skin-attachable electronic patches in various medical applications. In this study, we report a stretchable electronic patch that mimics the drainable structure pattern of the hexagonal channels of frog's pads and the sucker of an octopus based on carbon-based conductive polymer composite materials. The hexagonal channel structure that mimics the pads of frogs drains water and improves adhesion through crack arresting effect, and the suction structure that mimics an octopus sucker shows high adhesion on wet surfaces. In addition, the high-adhesive electronic patch has excellent adhesion to various surfaces such as silicone wafer (max. 4.06 N/cm²) and skin replica surface (max. 1.84 N/cm²) in dry and wet conditions. The high skin-adhesive electronic patch made of a polymer composite material based on a polymer matrix and carbon particles can reliably detect electrocardiogram (ECG) in dry and humid environments. The proposed electronic patch presents potential applications for wearable and skin-attachable electronic devices for detecting various biosignals.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.2
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• pp.21-32
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• 2023

CuNWs(Copper nanowires) are attracting attention as a transparent electrode material because of their excellent electrical conductivity, high mechanical flexibility, and cost-effectiveness. However, since copper nanowires are easily oxidized, there is a disadvantage that properties of the transparent electrode may be deteriorated due to this, and researches are being conducted to improve this. Accordingly, in this review, various methods and studies to prevent oxidation and improve stability of copper nanowire transparent electrodes by using coating materials such as carbon-based materials, metals, and conductive polymers are introduced. Through this, we intend to provide solutions to solve the problem of development and oxidation of copper nanowire-based technology.