• Transactions on Electrical and Electronic Materials
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• v.8 no.6
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• pp.250-254
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• 2007

Applying the moving photo-carrier grating(MPG) technique and time-of-flight(TOF) measurements, we studied the transport properties of stabilized amorphous selenium typical of the material used in direct conversion X-ray imaging devices. For MPG measurement, we obtained electron and hole mobility and the recombination lifetime of $\alpha-Se$ films with arsenic(As) additions. We found an apparent increase in hole drift mobility and recombination lifetime, especially when 0.3 % As was added into $\alpha-Se$ film, whereas electron mobility decreased with the addition of As due to the defect density. For TOF measurement, a laser beam with pulse duration of 5 ns and wavelength of 350 nm was illuminated on the surface of $\alpha-Se$ with a thickness of 400 ${\mu}m$. The measured hole and electron transit times were about 8.73 ${\mu}s$ and 229.17 ${\mu}s$, respectively.

• Macromolecular Research
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• v.17 no.7
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• pp.483-490
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• 2009

Stable poly(styrene-co-divinylbenzene) [P(St-co-DVB)] micro spheres with narrow size distribution were synthesized in the presence of 2,2'-azobis(2,4-dimethyl valeronitrile) (V-65) and co-initiator in an acetone/water mixture in the precipitation polymerization at $53^{\circ}C$ for 24 h. Potassium peroxodisulfate (KPS), ammonium peroxodisulfate (APS) and sodium peroxodisulfate (NaPS) were used as co-initiators. The optimum ratio of acetone to water for the formation of a narrow distribution of P(St-co-DVB) particles was 49:11 (g/g). The optimum co-initiator compositions for narrow distribution were 9:1 (g/g) for V-65 to KPS, 11:1 for V-65 to APS and 6:1 for V-65 to NaPS. The yield for these compositions was $54{\sim}57%$ and the largest particle size was obtained with the lowest zeta-potential and CV values. From the XPS measurements, the charge density was increased but the zeta potential decreased with increasing sulfur content, implying that the sulfate group provides the electrostatic stabilization on the particle surface. This suggested that the self-crosslinking between styrene and DVB, the electrostatic stabilization of initiators, and the balanced hydrophobic and hydrophilic properties of the solvents are responsible for the formation of stable P(St-co-DVB) spherical particles with narrow size distribution.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.67.1-67.1
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• 2012

Graphene has attracted much attention for future nanoelectronics due to its superior electrical properties. Owing to its extremely high carrier mobility and controllable carrier density, graphene is a promising material for practical applications, particularly as a channel layer of high-speed FET. Furthermore, the planar form of graphene is compatible with the conventional top-down CMOS fabrication processes and large-scale synthesis by chemical vapor deposition (CVD) process is also feasible. Despite these promising characteristics of graphene, much work must still be done in order to successfully develop graphene FET. One of the key issues is the process technique for gate dielectric formation because the channel mobility of graphene FET is drastically affected by the gate dielectric interface quality. Formation of high quality gate dielectric on graphene is still a challenging. Dirac voltage, the charge neutral point of the device, also strongly depends on gate dielectrics. Another performance killer in graphene FET is source/drain contact resistance, as the contact resistant between metal and graphene S/D is usually one order of magnitude higher than that between metal and silicon S/D. In this presentation, the key issues on graphene-based FET, including organic-inorganic hybrid gate dielectric formation, controlling of Dirac voltage, reduction of source/drain contact resistance, device structure optimization, graphene gate electrode for improvement of gate dielectric reliability, and CVD graphene transfer process issues are addressed.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05d
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• pp.101-106
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• 1996

For the application of the neutron flux mapping, an accurate calculation of the sensitivity is required because the sensitivity is proportional to the neutron flux density. Sensitivity is defined as the current per unit length per unit neutron flux and it mainly depends on the depression factor(f), the escape probability from the emitter($\varepsilon$1) and the charge build-up factor of the insulator layer(c). A Monte Carlo simulation was accomplished to calculate the sensitivity of rhodium emitter material and alumina(Al$_2$O$_3$) insulator with a cylindrical geometry, based on the (n,${\beta}$) interaction and on other interaction including the secondary electron generation for the more accurate estimation of the sensitivity. From the simulation results, factors fur the sensitivity were accurately calculated and compared with other theoretical and experimental values. In addition, the sensitivity linearly increases and saturates as the emitter radius increases. The accomplished method is useful in the analysis for the change of SPND sensitivity as a function of burn-up and in the optimum design of SPND.

• Journal of the Korean Solar Energy Society
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• v.31 no.5
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• pp.119-125
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• 2011

In this paper, we have studied about minimizing the Energy Storage System (ESS) capacity for mitigating the fluctuation of Wind Turbine Generation System (WTGS) by using Electric Double Layer Capacitor (EDLC) and Battery Energy Storage System (BESS). In this case, they have some different characteristics: The EDLC has the ability of generating the output power at high frequency. Thus, it is able to reduce the fluctuation of WTGS in spite of high cost. The BESS, by using Li-Ion battery, takes the advantage of high energy density, however it is limited to use at low frequency response. To verify the effectiveness of the proposed method, simulations are carried out with the actual data of 2MW WTGS in case of worst fluctuation of WTGS is happened. By comparing simulation results, this method shows the excellent performance. Therefore, it is very useful for understanding and minimizing the ESS capacity for mitigating the fluctuation of WTGS.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.296-296
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• 2013

Supercapacitor is a capacitor with extraordinarily high energy density, which basically consists of current collector, active material and electrolyte. Ruthenium oxide ($RuO_2$) is one of the most widely studied active materials due to its high specific capacitance and good electrical conductivity. In general, it is known that the coating of $RuO_2$ on nanoarchitectured current collector shows improved performance of energy storage device compared to the coating on the planar current collector. Especially, the surface structure with standing coaxial nanopillars are most desirable since it can provide direct paths for efficient charge transport along the axial paths of each nanopillars and the inter-nanopillar spacing allows easy access of electrolyte ions. However, well-known fabrication methods for metal or metal oxide nanopillars, such as the process using anodize aluminum oxide (AAO) templates, often require long and complicated nanoprocess.In this work, we developed relatively simple method fabricating indium tin oxide (ITO) nanopillars via sputtering. We also electrodeposited $RuO_2$ nanoparticles onto these ITO nanopillars and investigated its physical and electrochemical properties.

• Bulletin of the Korean Chemical Society
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• v.30 no.2
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• pp.423-428
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• 2009

The comparative study of three calix[4]heterocycles (calix[4]pyrrole, calix[4]furan, and calix[4]thiophene) has been theoretically performed by using high-level density functional theory (DFT) at the MPWB1K/6-311G$^{**}$//B3LYP/6- 311G$^{**}$ level. The effect of different hetero-atoms (nitrogen, oxygen, and sulfur) placed in the heterocycles on the conformational flexibility, thermodynamic stability order, cavity sizes, charge distributions, and binding propensities are examined. The thermodynamic stability differences between the conformers are found to be much greater in calix[4]pyrrole compared to those in calix[4]furan and calix[4]thiophene. Relatively larger NH group and higher dipole of a pyrrole ring in calix[4]pyrrole contribute to the higher energy barrier for the conformational conversions and relatively rigid potential energy surface compared to the case of calix[4]furan and calix[4]thiophene. The computational results herein provide theoretical understanding of the conformational flexibility and the thermodynamic nature which can be applied to understand the complexation behavior of the three calix[4]heterocycles.

• Journal of the Korean Vacuum Society
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• v.8 no.2
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• pp.141-147
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• 1999

The electrochromic characteristics of tungsten oxide films are largely affected by deposition conditions, such as substrate temperature and gas flow rate and also post-annealing. We have considered gas flow rate and temperature as important factors having an effect on an electrical, optical phenomenon and structural variation of $WO_3$ . The tungsten oxide films were deposited onto ITO(20$\Omega\box$, 1000$\AA$) using rf magnetron sputtering method. In particular, the films deposited at room temperature were annealed at various temperatures in air. All specimens had crystal structure except one being deposited at room temperature with nearly amorphous-like structure. The specimen deposited at $100^{\circ}C$ had a structure in which the increase in deposition temperature. The specimen deposited at $100^{\circ}C$ had a structure in which the cations$(Li^+)$ are easily movable because of void boundaries induced by regularly arrayed large grains. The specimen deposited at $300^{\circ}C$ had a dense structure with small grains but it exhibited the large mobility and charge density in $WO_3$ because of distinct grain boundaries.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.1
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• pp.41-46
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• 2009

The low dielectric SiOCH films were deposited on p-type Si(100) substrates through the dissociation of BTMSM $(((CH_3)_3Si)_2CH_2)$ precursors with oxygen gas by using PECVD method. BTMSM precursor was introduced with the flow rates from 42 to 60 sccm by 2 sccm step into reaction chamber but with the constant flow rate of 60 sccm $O_2$. SiOCH thin films were annealed at $450^{\circ}C$ for 30 minutes. The electrical property of SiOCH thin films was studied by MIS, Al/SiOCH/p-Si(100), structure. Annealed samples showed large reduction of the maximum capacitance yielding low dielectric constant owing to reductions of surface charge density. After exposure at room temperature and atmospheric pressure, dielectric constant of SiOCH films was totally increased. However, annealed SiOCH thin films were more stable than as-deposited SiOCH thin films for natural oxidation.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.3
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• pp.188-196
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• 2009

Due to its high power density, long cycle life and clean nature supercapacitors are widely used for improving the dynamic characteristics of the new and renewable energy sources and extending the battery run-time and life. In this paper improved dynamic model of the supercapacitor is developed by the electrochemical impedance spectroscopy technique. The developed model can be used to accurately estimate the dynamic behaviour of the supercapacitor and calculate the exact capacitance value at a certain state of charges. The model of the supercapacitor in the frequency domain is equivalently transformed into that in the time domain for Matlab/Simulink simulaton. The simulation data shows fine agreements with experimental results, thereby proving the validity and the accuracy of the developed model.