• Journal of The Korean Astronomical Society
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• v.56 no.1
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• pp.23-33
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• 2023

We investigate the diffusion process of Thomson-scattered line photons in both real space and frequency space through a Monte Carlo approach. The emission source is assumed to be monochromatic and point-like embedded at the center of a free electron region in the form of a sphere and a slab. In the case of a spherical region, the line profiles emergent at a location of Thomson optical depth τ_Th from the source exhibit the full width of the half maximum σ_λ ≃ τ^1.5_Th. In the slab case, we focus on the polarization behavior where the polarization direction flips from the normal direction of the slab to the parallel as the slab optical depth τ_Th increases from τ_Th ≪ 1 to τ_Th ≫ 1. We propose that the polarization flip to the parallel direction to the slab surface in optically thick slabs is attributed to the robustness of the Stokes parameter Q along the vertical axis with respect to the observer's line of sight whereas randomization dominates the remaining region as τ_Th increases. A brief discussion on the importance of our study is presented.

• Journal of Electrochemical Science and Technology
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• v.15 no.2
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• pp.276-290
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• 2024

A study of the transition from transitory state to steady state in DSSCs based on natural dyes is presented; cochineal was used as dye and Li⁺, Na⁺, and K⁺ were the ions added to the electrolyte. The photocurrent profiles were obtained as a function of time. Several DSSCs were prepared with different cations and their role and the transitory-to-steady transition was determined. A novel hybrid charge carrier source model based on the Heaviside function H(t) and the Lambert-Beer law, was developed and applied to analysis of the transient response of the output photocurrent. Additionally, the maximum effective light absorption coefficient α and the electronic extraction rate κ for each ion were determined: ${\alpha}_{Li^+,Na^+,K^+}\,=\,(0.486,\,0.00085,\,0.1126)\,cm^{-1}$, and also the electronic extraction rate ${\kappa}^{Li^+,Na^+,K^+}_{ext.}\,=\,(1410,\,19.07,\,19.69)\,cm\,s^{-1}$. The impedance model using Fick's second law was developed for carrier recombination to characterize the photocurrent.

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.751-756
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• 2016

Graphite was diffusion-bonded by hot-pressing to W-25Re alloy using a Ti interlayer. For the joining, a uniaxial pressure of 25 MPa was applied at $1600^{\circ}C$ for 2 hrs in an argon atmosphere with a heating rate of $10^{\circ}C\;min^{-1}$. The interfacial microstructure and elemental distribution of the W-25Re/Ti/Graphite joints were analyzed by scanning electron microscopy (SEM). Hot-pressed joints appeared to form a stable interlayer without any micro-cracking, pores, or defects. To investigate the high-temperature stability of the W-25Re/Ti/Graphite joint, an oxy-acetylene torch test was conducted for 30 seconds with oxygen and acetylene at a 1.3:1 ratio. Cross-sectional analysis of the joint was performed to compare the thickness of the oxide layer and its chemical composition. The thickness of W-25Re changed from 250 to $20{\mu}m$. In the elemental analysis, a high fraction of rhenium was detected at the surface oxidation layer of W-25Re, while the W-25Re matrix was found to maintain the initial weight ratio. Tungsten was first reacted with oxygen at a torch temperature over $2500^{\circ}C$ to form a tungsten oxide layer on the surface of W-25Re. Then, the remaining rhenium was subsequently reacted with oxygen to form rhenium oxide. The interfacial microstructure of the Ti-containing interlayer was stable after the torch test at a temperature over $2500^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.05a
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• pp.22-27
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• 1993

we prepared 70K new BiPbAgSrCaCuO superconductor used diffusion of dual layer which composed of SrCaCuO and BiPbAgCuO compound. This method is used permeation and diffusion on partial melting point of BiPbAgCuO compound. Samples were analyzed by means of X-ray diffraction analysis, Thermal analysis, critical temperature and scanning electron microscopy. It was found that the best results were obtained for spread volume (A:B=1:0.6) and sintring time 210hours.

• Journal of Technologic Dentistry
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• v.27 no.1
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• pp.97-104
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• 2005

The effect of Nb on interfacial bonding characteristics of Ni-Cr alloy for porcelain fused to metal crown (PFM) has been studied in order to investigate oxide layer. A specimens, which is 0.8mm in thickness, were fired at 1,000$^{\circ}C$ with four tests such as air, vacuum, air for 5 minutes and vacuum for 5 minutes in order to examine an oxide behavior of alloy surface generated by the adding of Nb to be controlled at a rate of 0, 1, 3 and 5. It observed oxide film form of the fired specimens with optical microscope and scanning electron microscope (SEM), and chemical formation of them with energy disperse X-ray spectroscopy (EDX). The other specimens, which is 2mm in thickness, were fired at 1,000$^{\circ}C$ with air and vacuum in order to analyze the diffusion behaviors of alloy-porcelain interface by X-ray dot mapping. The results of this study were as follows: 1. The observation of microstructure of specimens by SEM showed that the more Nb content is high, the more much intermediate compound of rich Nb is observed. 2. The surface morphology of oxide film is most dense in 3% Nb. The heat treatment in air constitutes denser oxide film than heat treatment under vacuum. 3. The diffusion behavior of oxide layer by X-ray dot mapping showed that Si, Al of porcelain diffuse toward metal.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.683-690
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• 1996

In this study, the diffusion barrier properties of $1000 \AA$ thick molybdenum compounds (Mo, Mo-N, $MoSi_2$, Mo-Si-N) were investigated using sheet resistance measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and Rutherford backscattering spectrometry (RBS). Each barrier material was deposited by the dc magnetron sputtering, and annealed at 300-$800^{\circ}C$ for 30min in vacuum. Mo and $MoSi_2$ barrier were failed at low temperature due to Cu diffusion through grain bound-aries and defects of Mo thin film and the reaction of Cu with Si within $MoSi_2$ respectively. A failure temperature could be raised to $650^{\circ}C$-30min in the Mo barrier system and to $700^{\circ}C$-30min in the Mo-silicide system by replacing Mo and $MoSi_2$ with Mo-N and Mo-Si-N, respectively. The crystallization temperature in the Mo-silicide film was raised by the addition of $N_2$. It is considered that not only the N, stuffing effect but also the variation of crystallization temperature affects the reaction of Cu with Si within Mo-silicide. It was found that Mo-Si-N is more effective barrier than Mo, $MoSi_2$, or Mo-N to copper penetration preventing Cu reaction with the substrate for 30min at a temperature higher than $650^{\circ}C$.

• Journal of the Korean Electrochemical Society
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• v.14 no.3
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• pp.138-144
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• 2011

The transport phenomena of electron and ion around the electrode have been analyzed, herein the computational program to simulate the electrochemical signal of cyclic voltammetry has been implemented. For the dominant mass-transfer system, the governing equation and its boundary conditions are confined to the semi-infinite diffusion model and the reversible reaction at the electrode. In order to obtain the numerical solutions of cyclic voltammetry, MATLAB was used for the explicit finite difference method. Experimental results from the cyclic voltammetry of electrochemical system(10 mM $K_3Fe(CN)_6$ and 0.1M KCl) upon the ITO glass substrate were compared with the numerical solutions. Present program explains the experimental results fairly well, where they approached the simulated ones closely with deceasing the scan rate. Furthermore, the effects of electrode area, electrochemical reaction constants and transfering coefficients in the cyclic voltammetry were discussed quantitatively.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.311-312
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• 2010

The fabricated photovoltaic cells based on PIN heterojunctions, in this study, have a structure of ITO/poly(3, 4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)/donor/donor:C60(10nm)/C60(35nm)/2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline(8nm)/Al(100nm). The thicknesses of an active layer(donor:C60), an electron transport layer(C60), and hole/exciton blocking layer(BCP) were fixed in the organic photovoltaic cells. We investigated the performance characteristics of the PIN organic photovoltaic cells with copper phthalocyanine(CuPc), tetracene and pentacene as a hole transport layer. Discussion on the photovoltaic cells with CuPc, tetracene and pentacene as a hole transport layer is focussed on the dependency of the power conversion efficiency on the deposition rate and thickness of hole transport layer. The device performance characteristics are elucidated from open-circuit-voltage(Voc), short-circuit-current(Jsc), fill factor(FF), and power conversion efficiency($\eta$). As the deposition rate of donor is reduced, the power conversion efficiency is enhanced by increased short-circuit-current(Jsc). The CuPc-based PIN photovoltaic cell has the limited dependency of power conversion efficiency on the thickness of hole transport layer because of relatively short exciton diffusion length. The photovoltaic cell using tetracene as a hole transport layer, which has relatively long diffusion length, has low efficiency. The maximum power conversion efficiencies of CuPc, tetracene, and pentacene-based photovoltaic cells with optimized deposition rate and thickness of hole transport layer have been achieved to 1.63%, 1.33% and 2.15%, respectively. The photovoltaic cell using pentacene as a hole transport layer showed the highest efficiency because of dramatically enhanced Jsc due to long diffusion length and strong thickness dependence.

• Polymer(Korea)
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• v.31 no.3
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• pp.177-183
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• 2007

In this study, nano-sized poly(vinyl acetate) (PVAc) particles containing lavender oil as a core material were prepared by using emulsification-diffusion method. Effects of experimental parameters on the characteristics and the release behavior were examined with a field emission- scanning electron microscope, an electrophoretic light scattering spectrophotometer, a visible spectrophotometer and a high performance liquid chromatography The resulting aromatic particles could be prepared in nano-sized globular shapes with the mean particle size of 224 nm by controlling the experimental conditions. From the evaluation of release properties of aromatic PVAc nanoparticles with or without PVA coating, it was found that the aromatic particles coated with PVA show more sustaining and stable release behaviors. Our research on aromatic PVAc nanoparticles could be applied for durable fragrant finishing for textiles, leather products and so on.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.214.2-214.2
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• 2013

Device performance for the 45 and 32 nm node CMOS technology requires the integration of ultralow-k materials. To lower the dielectric constant for PECVD and spin-on materials, partial replacement of the solid network with air (k=1.01) appears to be more intuitive and direct option. This can be achieved introducting of second "labile" phase during depositoin that is removed during a subsequent UV curing and annealing step. Besides, with shrinking line dimensions the resistivity of barrier films cannot meet the International Technology Roadmap for Semiconductors (ITRS) requirements. To solve this issue self-forming diffusion barriers have drawn attention for great potential technique in meeting all ITRS requirments. In this present work, we report a Cu-V alloy as a materials for the self-forming barrier process. And we investigated diffusion barrier properties of self-formed layer on low-k dielectrics with or without UV curing treatment. Cu alloy films were directly deposited onto low-k dielectrics by co-sputtering, followed by annealing at various temperatures. X-ray diffraction revealed Cu (111), Cu (200) and Cu (220) peaks for both of Cu alloys. The self-formed layers were investigated by transmission electron microscopy. In order to compare barrier properties between V-based interlayer on low-k dielectric with UV curing and interlayer on low-k dielectric without UV curing, thermal stability was measured with various heat treatment temperature. X-ray photoelectron spectroscopy analysis showed that chemical compositions of self-formed layer. The compositions of the V based self-formed barriers after annealing were strongly dominated by the O concentration in the dielectric layers.