• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.156.1-156.1
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• 2015

Neon and argon plasma group velocities (ug) are obtained by intensified charge coupled device (ICCD) camera images at fixed gate width time of 5 ns. The propagation velocities in upstream and downstream region are in the order of 104-105 m/s. The plasma ambipolar diffusion velocities are calculated to be in the order of 101-102 m/s. Plasma jet is generated by sinusoidal power supply in varying voltages from 1 to 4 kV at repetition frequency of 40 kHz. By employing one dimensional convective wave packet model, the neon and argon electron temperatures in non-thermal atmospheric-pressure plasma jet are estimated to be 1.95 and 1.18 eV, respectively.

• Journal of Electrochemical Science and Technology
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• v.6 no.3
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• pp.75-80
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• 2015

We introduce a new synthesis method to prepare small TiO₂ nanoparticles with a narrow particle size distribution, which is achieved by electron beam (E-beam) irradiation. The effects of E-beam irradiation on the synthesis of TiO₂ nanoparticles and the electrochemical performance of TiO₂ nanoparticles as alternative anode materials for Li-ion batteries are investigated. The TiO₂ nanoparticles induced by E-beam irradiation present better cycling performance and rate capability than the TiO₂ nanoparticles synthesized by normal hydrolysis reaction. The better electrochemical performance is attributed to small particle size and narrow particle size distribution, resulting in the large surface area that provides innumerable reaction sites and short diffusion length for Li⁺ through TiO₂ nanoparticles.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.1
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• pp.9-14
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• 2004

The fluorescent lamp has been successfully modeled by employing the radial variation of particle density and considering driving circuit effects on the characteristics of discharge process. The electron energy distribution is assumed to have a Maxwellian. The electron mobility and the ambipolar diffusion coefficients are considered to vary with an electron energy rather than a simple uniform value. Energy states of mercury atom in the discharge process are regarded as six levels rather than simple 4 or 5 levels. These discharge processes have been accurately solved by numerically employing mixed the FDM and the 2nd Runge-Kutta method. This model was applied to analyzing real circuit. Simulation and experimental results were presented to verify the feasibility of the modeling. Simulation and experimental results were presented to verify the feasibility of the modeling.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.239.1-239.1
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• 2011

Dye sensitized solar cells (DSC) are promising devices for inexpensive, nontoxic, transparent, and large-scale solar energy conversion. Generally thick $TiO_2$ nanoporous films act as efficient photoanodes with their large surface area for absorbing light. However, electron transport through nanoparticle networks causes the slowdown and the loss of electron transport because of a number of interparticle boundaries inside the conduction path. We have studied DSCs with precisely dimension-controlled $TiO_2$ nanotubes array as photoanode. $TiO_2$ nanotubes array is prepared by template-directed fabrication method with atomic layer deposition. Well-ordered nanotubes array provides not only large surface area for light absorbing but also direct pathway for electrons with minimalized grain boundaries. Large enlongated anatase grains in the nanotubes could enhance the conductivity of electrons, but also suppress the recombination with holes through defect sites during diffusion into the electrode. To study the effect of grain boundaries, we fabricated two kinds of nanotubes which have different grain sizes by controlling deposition conditions. And we studied electron conduction through two kinds of nanotubes with different grain structures. The solar cell performance was studied as a function of thickness and grain structures. And overall solar-to-electric energy conversion efficiencies of up to 7% were obtained.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.445.1-445.1
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• 2014

Dye-sensitized solar cells (DSSCs) have been widely investigated as a next-generation solar cell because of their simple structure and low manufacturing cost. The $TiO_2$ film with thickness of $8{\sim}10{\mu}m$, which consists of nanoparticles, acts as both a scaffold with a high surface-to-volume ratio for the dye loading and a pathway to remove the electrons. However, charge carriers have to move across many particle boundaries by a hopping mechanism. So, one dimensional nanostructures such as nanotubes, nanorods and nanowires should improve charge carrier transportation by providing a facile direct electron pathway and lowering the diffusion resistance. However, the efficiencies of DSSCs using one dimensional nanostructures are less than the $TiO_2$ nanoparticle-based DSSCs. In this work, the patterned $TiO_2$ film with thickness of $3{\mu}m$ was deposited using photolithography process to decrease of electron pathway and increase of surface area and transmittance of $TiO_2$ films. Properties of the patterned $TiO_2$ films were investigated by various analysis method such as X-ray diffraction, field emission scanning electron microscopy (FESEM) and UV-visible spectrophotometer.

• Polymer(Korea)
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• v.26 no.1
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• pp.80-87
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• 2002

A comparative study using electron-beam(EB) and thermal curing techniques was carried out to determine the effect of cure behavior and thermal stability of epoxy resins. In this work, benzylquinoxalinium hexafluoroantimonate(BQH) was used as a latent cationic catalyst for an epoxy resin. According to the thermogravimetric analysis(TGA), the decomposed activation energy based on Coats-Redfern method was higher in the case of thermal curing technique. This could be interpreted in terms of slow thermal diffusion rate resulted from high crosslink density of the thermally cured epoxy resin. However, the increase of hydroxyl group in the epoxy resin cured by EB technique was observed in near-infrared spectroscopy(NIRS) measurements, resulting in improving the stable short aromatic chain structure, integral procedural decomposition temperature, and finally ductile properties for high impact strengths.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.9
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• pp.773-778
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• 2001

In this dissertation the results of the combined experimental and theoretical studies designed to understand and predict the spatial growth and transport coefficients for electrons in SF$_{6}$ and SF$_{6}$-Ar mixtures have described. The ionization and attachment coefficients in pure SF$_{6}$ and SF$_{6}$-Ar mixtures have been calculated over the range of 10$_{6}$ molecule and for Ar atom proposed by other authors. The transport coefficients for electrons in (0.2%)SF$_{6}$-Ar and (0.5%)SF$_{6}$-Ar mixtures were measured by time-of-flight method, and the electron energy distribution function and the parameters of the velocity and the diffusion were determined by the variation of the collision cross-sections with energy. The results obtained in this work will provide valuable information on the fundamental haviors of electrons in weakly ionized gases and the role of electron attachment in the choice of better gases and unitary gas dielectrics or electro negative components in dielectric gas mixtures. gas mixtures.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.251.2-251.2
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• 2013

Natural photosynthesis utilizes two proteins, photosystem I and photosystem II, to efficiently oxidize water and reduce NADP+ to NADPH. Artificial photosynthesis which mimics this process achieve water splitting through a two-step Z-schematic water splitting process using man-made synthetic materials for hydrogen fuel production. In this study, Z-scheme system was achieved from the hybrid materials which composed of hydrogen production part as photosystem I protein and water oxidizing part as semiconductor BiVO4. Utilizing photosystem I as the hydrogen evolving part overcomes the problems of existing hydrogen evolving p-type semiconductors such as water instability, expensive cost, few available choices and poor red light (>600 nm) absorbance. Some problems of photosystem II, oxygen evolving part of natural photosynthesis, such as demanding isolation process and D1 photo-damage can also be solved by utilizing BiVO4 as the oxygen evolving part. Preceding research has not suggested any protein-inorganic-hybrid Z-scheme composed of both materials from natural photosynthesis and artificial photosynthesis. In this study, to realize this Z-schematic electron transfer, diffusion step of electron carrier, which usually degrades natural photosynthesis efficiency, was eliminated. Instead, BiVO4 and Pt-photosystem I were all linked together by the mediator gold. Synthesized all-solid-state hybrid materials show enhanced hydrogen evolution ability directly from water when illuminated with visible light.

• Korean Journal of Metals and Materials
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• v.50 no.7
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• pp.539-544
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• 2012

Thermal shock behavior of TiN-coated SUS 304 substrate was investigated using a laser ablation method. By short surface ablation with a pulse Nd-YAG laser, considerable surface crack and spalling were observed, whereas there were few oxidation phenomena, such as grain growth of TiN crystallites, nucleation and growth of $TiO_2$ crystallites, which were observed from the coatings quenched from $700^{\circ}C$ in a chamber. The oxygen concentration of the ablated coating surface with the pulse laser also had a lower value than that of the quenched coating surface by Auger electron spectroscopy and electron probe micro analysis. These results were attributed to the fact that the properties of the pulse laser method have a very short heating time and so the diffusion time for oxidation was insufficient. Consequently, it was verified that the laser thermal shock test provides a way to evaluate the influence of the thermal shock load reduced oxidation effect.

• Bulletin of the Korean Chemical Society
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• v.19 no.5
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• pp.527-530
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• 1998

This paper presents the electrochemistry and molecular orbital (MO) picture of a series of conformationally-restricted thioxantone derivatives. A series of $C_2-substituted$ thioxanthones were examined to probe the electronic influence of the substituent on the electrooxidation and electroreduction sites (i.e., on the electron densities at the 10-and 9-positions), respectively. In the presence of "electrophoric" groups such as C=O and S, characteristic electrochemical reduction and oxidation responses are observed. The electrochemical reaction was diffusion-controlled, because the $I_p/{\upsilon}^{1/2}$ ratio was constant for the anodic and cathodic wave of thioxantone derivatives. These substituent effects are presented in terms of correlations of oxidation (or reduction) potentials with the highest occupied molecular orbital (HOMO), or lowest unoccupied molecular orbital (LUMO) energies, respectively. There is good correlation between energies of the HOMO vs. $E_{pa}^{(+)}$ and energies of the LUMO vs. $E_{pc}^{(-)}$. Frontier Molecular Orbital (FMO) is changed by the functional group of thioxanthones. FMO energy level was offered us the information about the electron transfer direction, and the coefficient of FMO was offered the information about the electron transfer position. Sulfur atom has an important effect on oxidation potential, $E_{pa}^{(+)}$ and the carbonyl carbon has an important effect on reduction potential, $E_{pc}^{(-)}$. Therefore we were appreciated that the contribution of sulfur atom for the $E_{pa}^{(+)}$ and HOMO energies is larger than the contribution of carbonyl group for the $E_{pc}^{(-)}$ and LUMO energies.