• Transactions on Electrical and Electronic Materials
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• v.16 no.6
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• pp.346-350
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• 2015

In this study, we carried out an investigation of the etch characteristics of TiO₂ thin films and the selectivity of TiO₂ to SiO₂ in adaptive coupled C1₂/Ar plasma. The maximum etch rate of the TiO₂ thin film was 136±5 nm/min at a gas mixing ratio of C1₂/Ar (75%:25%). The X-ray photoelectron spectroscopy (XPS) analysis showed the efficient destruction of oxide bonds by the ion bombardment as well as the accumulation of low volatile reaction products on the etched surface.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.5
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• pp.477-479
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• 2006

Carbon films was grown on Si substrates using the method of electrolysis for methanol liquid. Deposition parameters for the growth of the carbon films were current density for the electrolysis, methanol liquid temperature and electrode spacing between anode and cathode. We examined electrical resistance and the surface morphology of carbon films formed under various conditions specified by deposition parameters. It was clarified that the high electrical resistance carbon films with smooth surface morphology are grown when a distance between the electrodes was relatively wider. We found that the electrical resistance in the films was independent of both current density and methanol liquid temperature for electrolysis. The temperature dependence of the electrical resistance in the low resistance carbon films was different from one obtained in graphite.

• Polymer(Korea)
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• v.28 no.3
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• pp.218-224
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• 2004

The adhesion and proliferation of mammalian cells on polymeric biomaterials depend on the surface characteristics such as wettability, chemistry, charge and roughness. In order to recognize the correlation between the adhesion and proliferation of human bone marrow derived stem cells (BMSCs) and surface property, radio frequency generated plasma treatment on low density polyethylene (LDPE) has been carried out. The modified LDPE surfaces were characterized by measuring the static water contact angle. The adhesion and proliferation of cells on LDPE films were characterized by cell counting and reverse transcription-polymerase chain reaction (RT-PCR). The water contact angle of the film surface decreased with plasma treatment time. Proto-oncogenes (c-myc, c-fos) and tumor suppressor gene (p153) showed maximum expression with contact angle of 60 ∼ 70$^{\circ}$ range of LDPE film. By cell counting, we confirmed that the rate of cell proliferation appeared the higher on the film surface of the contact angle of 60∼70$^{\circ}$ We concluded that the surface wettability is an important role for the growth and differentiation of BMSCs.

• Journal of Sensor Science and Technology
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• v.15 no.5
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• pp.371-377
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• 2006

Nano porous, transparent silica aerogels monoliths were prepared under ambient drying (1 atm, $270^{\circ}C$) condition by the combination of sol-gel process and surface modification with subsequent heat treatment. Three kinds of solvent, n-hexane, n-heptane and xylene, were selected in the point view of low surface tension and vapor pressure in order to restrain a formation of cracks during drying. Crack-free silica aerogels with over 93 % of porosity and below $0.14g/cm^3$ of density were obtained by solvent exchange and surface modification under atmosphere condition. Optimum solvent was confirmed n-heptane among these solvents through estimation of FT-IR, TGA, BET and SEM. Modified silica aerogel exhibited a higher porosity and pore size compare to unmodified aerogels. Hydrophobicity was also controled by C-H and H-OH bonding state in the gel structure and heat treatment over $400^{\circ}C$ effects to the hydrophobicity due to oxidation of C-H radicals.

• Food Science and Biotechnology
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• v.15 no.1
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• pp.5-12
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• 2006

Degradation performance of environmentally friendly plastics that can be disintegrated by combination of sunlight, microbes in soil, and heat produced in landfills was evaluated for use in industries. Two multi-degradable master batches (MCC-101 and MCC-102 were manufactured, separately mixed with polyethylene using film molding machine to produce 0.025 mm thick films, and exposed to sunlight, microbes, and heat. Low- and high-density polyethylene (LDPE and HDPE) films containing MCC-101 and MCC-102 became unfunctional by increasing severe cleavage at the surface and showed high reduction in elongation after 40 days of exposure to ultraviolet light. LDPE and HDPE films showed significant physical degradation after 100 and 120 days, respectively, of incubation at $68{\pm}2^{\circ}C$. SEM images of films cultured in mixed mold spore suspension at $30^{\circ}C$ and 85% humidity for 30 days revealed accelerated biodegradation on film surfaces by the action of microbes. LDPE films containing MCC-l01 showed absorption of carbonyls, photo-sensitive sites, at $1710\;cm${-1}$ when exposed to light for 40 days, whereas those not exposed to ultraviolet light showed no absorption at the same frequency. MCC-101-based LDPE films showed much lower $M_w$ distribution after exposure to UV than its counterpart, due to agents accelerating photo-degradation contained in MCC-101.

• Applied Chemistry for Engineering
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• v.9 no.7
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• pp.990-997
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• 1998

In this work, the $SiO_2$ films on the silicon substrate with different orientations were first prepared by the low temperature process using the ECR plasma diffusion as a function of microwave power and oxidation time. Before and after thermal treatment, the surface morphology, Si/O ratio from physicochemical properties, and the electrical properties of the oxide films were also investigated. The oxidation rate increased with microwave power, while surface morphology showed the nonuniform due to etching. The film quality, therefore, was lowered with increasing the defect by etching and the content of positive oxide ions in the oxide films from bulk by higher self-DC bias. The content of positive oxide ions in the oxide films with different Si orientations showed Si(100) < Si(111) < poly Si. The defects in $Si/SiO_2$ interface of $SiO_2$ film could be decreased by annealing, while $Q_{it}$ and $Q_f$ were independent of thermal treatment and the dependent on concentration of reactive oxide ions and self-DC bias of substrate. At microwave power of 300, and 400 W, the high quality $SiO_2$ film that had lower surface roughness and defect in $Si/SiO_2$ interface was obtained. The value of interface trap density, then, was ${\sim}9{\times}10^{10}cm^{-2}eV^{-1}$.

• Journal of the Korean Vacuum Society
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• v.7 no.s1
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• pp.134-139
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• 1998

Amorphous fluorocarbon (a-C:F) is of interest for low dielectric interlayer material, but in this work we applied this material to FED field emitter. N-doped a-C:F films were deposited by inductively coupled plasma chemical vapor deposition (ICPCVD). The Raman spectra were measured to study the film structure and inter-band optical absorption coefficients were measured using Perkin-Elmer UV-VIS-IR spectrophotometer and optical band gap was obtained using Tauc's plot. XPS spectrum and AFM image were investigated to study bond structure and surface morphology. Current-electric field(I-E) characteristic of the film was measured for the characterization of electron emission properties. The optimum doping concentration was found to be [N2]/[CF4]=9% in the gas phase. The turn-on field and the emission current density at $[N_2]/[CF_4]$=9% were found to be 7.34V/$\mu\textrm{m}$ and 16 $\mu\textrm{A}/\textrm{cm}^2$ at 12.8V/$\mu\textrm{m}$, respectively.

• Journal of the Korean institute of surface engineering
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• v.53 no.6
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• pp.312-321
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• 2020

Morphology of porous cobalt electro-deposits was systematically investigated as functions of cobalt precursors in the plating bath and applied cathodic current density with a special focus on cobalt nano-rod formation. It was proved that the concentration of cobalt precursor plays little effect on the morphology of cobalt electro-deposits at relatively low plating current density while it significantly affects the morphology with increasing plating current density. Such a dependence was discussed in terms of the kinetics of two competitive reactions of cobalt reduction and hydrogen evolution. Cobalt nano-rod structure was created at specific ranges of cobalt precursor content and applied cathodic current density, and its diameter and length varied with plating time without notable formation of side branches which is usually found during dendrite formation. Specifically, the nano-rod length was preferentially increased in relative short plating time (<15 s), resulting in higher aspect ratio of nano-rod with plating time. Whereas, both the nano-rod length and diameter were increased nearly at the same level in a prolonged plating time, making the aspect ratio unchanged. From the analysis of crystal structure, it was confirmed that the cobalt nano-rod preferentially grew in the form of single crystal on a dense poly-crystalline cobalt thin film initially formed on the substrate.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.236.1-236.1
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• 2015

The surface morphology of front transparent conductive oxide (TCO) films is very important to achieve high current density in amorphous silicon (a-Si) thin film solar cells since it can scatter the light in a better way. In this study, we present the low cost hydrothermal deposited uniform zinc oxide (ZnO) nano-flower structure with various aspect ratios for a-Si thin film solar cells. The ZnO nano-flower structures with various aspect ratios were grown on the RF magnetron sputtered AZO films. The diameters and length of the ZnO nano-flowers was controlled by varying the annealing time. The length of ZnO nano-flowers were varied from 400 nm to $2{\mu}m$ while diameter was kept higher than 200 nm to obtain different aspect ratios. The ZnO nano-flowers with higher surface area as compared to conventional ZnO nano structure are preferred for the better light scattering. The conductivity and crystallinity of ZnO nano-flowers can be enhanced by annealing in hydrogen atmosphere at 350 oC. The vertical aligned ZnO nano-flowers showed higher haze ratio as compared to the commercially available FTO films. We also observed that the scattering in the longer wavelength region was favored for the high aspect ratio of ZnO nano-flowers. Therefore, we proposed low cost and vertically aligned ZnO nano-flowers for the high performance of thin film solar cells.

• Korean Journal of Materials Research
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• v.24 no.12
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• pp.645-651
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• 2014

GaN is most commonly used to make LED elements. But, due to differences of the thermal expansion coefficient and lattice mismatch with sapphire, dislocations have occurred at about $109{\sim}1010/cm^2$. Generally, a low temperature GaN buffer layer is used between the GaN layer and the sapphire substrate in order to reduce the dislocation density and improve the characteristics of the thin film, and thus to increase the efficiency of the LED. Further, patterned sapphire substrate (PSS) are applied to improve the light extraction efficiency. In this experiment, using an AlN buffer layer on PSS in place of the GaN buffer layer that is used mainly to improve the properties of the GaN film, light extraction efficiency and overall properties of the thin film are improved at the same time. The AlN buffer layer was deposited by using a sputter and the AlN buffer layer thickness was determined to be 25 nm through XRD analysis after growing the GaN film at $1070^{\circ}C$ on the AlN buffer CPSS (C-plane Patterned Sapphire Substrate, AlN buffer 25 nm, 100 nm, 200 nm, 300 nm). The GaN film layer formed by applying a 2 step epitaxial lateral overgrowth (ELOG) process, and by changing temperatures ($1020{\sim}1070^{\circ}C$) and pressures (85~300 Torr). To confirm the surface morphology, we used SEM, AFM, and optical microscopy. To analyze the properties (dislocation density and crystallinity) of a thin film, we used HR-XRD and Cathodoluminescence.