• Korea-Australia Rheology Journal
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• v.14 no.2
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• pp.63-70
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• 2002

Chemical mechanical planarization (CMP) is the polishing process enabled by both chemical and mechanical actions. CMP is used in the fabrication process of the integrated circuits to achieve adequate planarity necessary for stringent photolithography depth of focus requirements. And recently copper is preferred in the metallization process because of its low resistivity. We have studied the effects of chemical reaction on the polishing rate and surface planarity in copper CMP by means of numerical simulation solving Navier-Stokes equation and copper diffusion equation. We have performed pore-scale simulation and integrated the results over all the pores underneath the wafer surface to calculate the macroscopic material removal rate. The mechanical abrasion effect was not included in our study and we concentrated our focus on the transport phenomena occurring in a single pore. We have observed the effects of several parameters such as concentration of chemical additives, relative velocity of the wafer, slurry film thickness or ash)tract ratio of the pore on the copper removal rate and the surface planarity. We observed that when the chemical reaction was rate-limiting step, the results of simulation matched well with the experimental data.

• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.2925-2930
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• 2013

We present results of molecular dynamics simulations for hydroxide ion in supercritical water of densities 0.22, 0.31, 0.40, 0.48, 0.61, and 0.74 g/cc using the SPC/E water potential with Ewald summation. The limiting molar conductance of $OH^-$ ion at 673 K monotonically increases with decreasing water density. It is also found that the hydration number of water molecules in the first hydration shells around the $OH^-$ ion decreases and the potential energy per hydrated water molecule also decreases in the whole water density region with decreasing water density. Unlike the case in our previous works on LiCl, NaCl, NaBr, and CsBr [Lee at al., Chem. Phys. Lett. 1998, 293, 289-294 and J. Chem. Phys. 2000, 112, 864-869], the number of hydrated water molecules around ions and the potential energy per hydrated water molecule give the same effect to cause a monotonically increasing of the diffusion coefficient with decreasing water density in the whole water density region. The decreasing residence times are consistent with the decreasing potential energy per hydrated water molecule.

• Journal of Forest and Environmental Science
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• v.32 no.3
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• pp.253-261
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• 2016

Xanthoceras sorbifolia seed coat (XSSC) is a processing residue of the bioenergy crop. This work aimed to evaluate the applicability of using the steam explosion to modify the residue for dye biosorption from aqueous solutions by using methylene blue as a model cationic dye. Equilibrium, kinetic and thermodynamic parameters for the biosorption of methylene blue on the steam-exploded XSSC (SE-XSSC) were evaluated. The kinetic data followed the pseudo-second-order model, and the rate-limiting step was the chemical adsorption. Intraparticle diffusion was one of the rate-controlling factors. The equilibrium data agreed well with the Langmuir isotherm, and the biosorption was favorable. The steam-explosion pretreatment strongly affected the biosorption in some respects. It reduced the adsorption rate constant and the initial sorption rate of the pseudo-second-order model. It enhanced the adsorption capacity of methylene blue at higher temperatures while reduced the capacity at lower ones. It changed the biosorption from an exothermic process driven by both the enthalpy and the entropy to an endothermic one driven by entropy only. It increased the surface area and decreased the pH point of zero charge of the biomass. Compared with the native XSSC, SE-XSSC is preferable to MB biosorption from warmer dye effluents.

• Journal of the Korean Ceramic Society
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• v.37 no.1
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• pp.50-56
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• 2000

Precursor gels with the composition of xZrO2·(100-x)SiO2 systems (x=10, 20 and 30 mol%) were prepared by the sol-gel method. Kinetic parameters, such as activation energy, Avrami's exponent, n, and dimensionality crystal growth value, m, have been simultaneously calculated from the DTA data using Kissinger and Matusita equations. The crystallite size dependence of tetragonal to monoclinic transformation of ZrO2 was investigated using XRD, in relation to the fracture toughness. The crystallization of tetragonal ZrO2 occurred through 3-dimensional diffusiion controlled growth(n=m=2) and the activation energy for crystallization was calculated using Kissinger and Matusita equations, as about 310∼325±10kJ/mol. The growth of t-ZrO2, in proportion to the cube of radius, increased with increasing heating temperature and hteat-treatment time. It was suggested that the diffusion of Zr4+ ions by Ostwald ripening was rate-limiting process for thegrowth of t-ZrO2 crystallite size. The fracture toughness of xZrO2·(100-x)SiO2 systems glass ceramics increased with increasing crystallite size of t-ZrO2. The fracture toughness of 30ZrO2·70SiO2 system glass ceramics heated at 1,100℃ for 5h was 4.84 MPam1/2 at a critical crystaliite size of 40 nm.

• Bulletin of the Korean Chemical Society
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• v.17 no.2
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• pp.162-167
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• 1996

Two redox processes of methyl viologen (+2/+, +/0) in acetonitrile were investigated by using channel electrode voltammetric and in situ electrochemical ESR methods. Two separated unequal plateau currents of the first (+2/+) and second (+/0) redox processes of the viologen were observed in the channel electrode voltammograms and showed a cube-root depedndence on the electrolyte flow rate, respectively. The simple Levich analysis resulted in two different diffusion coefficients of $D_{+2}=2.2{\times}10^{-5}\;cm^2/s$ and $D_+=3.0{\times}10^{-5}cm^2/s$ from the limiting currents. In situ electrochemical ESR studies were performed for the monocation radicals generated at the potentials of the two plateau currents in the electrolyte flow range $1.3{\times}10^{-1}{\geq}v_f{\geq}2.7{\times}10^{-3}\;cm^3/s$. Backward implicitfinite difference method was employed to simulate the electrochemical kinetic problem of two sequential electron transfers ($MV^{+2}+e{\leftrightarrows}MV^+,\;MV^{+}+e{\leftrightarrows}MV^0$) coupled with reversible comproportionation ($MV^{2+}+MV^0{{\leftrightarrows}^{k_f}_{k_b}}2MV^+$). $k_f$ was found to be greater than ($10^6M^{-1}s^{-1}.

• Journal of the Korean Electrochemical Society
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• v.3 no.1
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• pp.49-56
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• 2000

In the present we.k, temperature dependence of oxygen diffusivity in the polyvinyl chloride (PVC) film $D_f$ formed on gold electrode was investigated using steady-state rotating disk electrode (RDE) technique and modulated electrohydrodynamic (EHD) impedance technique. Both the diffusion rate defined as the ratio of oxygen diffusivity in the PVC film to the film thickness $D_f/\delta_f$ and the time constant $\delta_f^2/D_f$ for oxygen diffusion through the PVC film were obtained from plot of the limiting current versus disk rotation speed and from filing the EHD impedance spectra experimentally measured to those theoretically calculated on the basis of the diffusion equation for mass transport through the non-conductive and porous film, respectively. By combining measured $D_f/\delta_f$ with $\delta_f^2/D_f$, we determined $\delta_f\;and\;D_f$ at room temperature separately. As temperature increased, it appeared that the $D_f$ value measured for the PVC film-covered gold RDE was enhanced more rapidly than that $D_s$ value in the solution measured for the PVC film-free gold RDE. This means that the pores glowing with increasing temperature act as effective diffusion paths within the film. The present in-situ steady-state and modulated EHD measurements prove to be effective for determining $\delta_f\;and\;D_f$, separately and at the same time the porosity of the PVC film at temperatures below glass temperature $T_g$ of the film.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.2
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• pp.306-316
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• 2016

In this paper, an NMOS-diode eFuse OTP (One-Time Programmable) memory cell is proposed using a parasitic junction diode formed between a PW (P-Well), a body of an isolated NMOS (N-channel MOSFET) transistor with the small channel width, and an n+ diffusion, a source node, in a DNW (Deep N-Well) instead of an NMOS transistor with the big channel width as a program select device. Blowing of the proposed cell is done through the parasitic junction formed in the NMOS transistor in the program mode. Sensing failures of '0' data are removed because of removed contact voltage drop of a diode since a NMOS transistor is used instead of the junction diode in the read mode. In addition, a problem of being blown for a non-blown eFuse from a read current through the corresponding eFuse OTP cell is solved by limiting the read current to less than $100{\mu}A$ since a voltage is transferred to BL by using an NMOS transistor with the small channel width in the read mode.

• Clean Technology
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• v.25 no.3
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• pp.198-205
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• 2019

The adsorption equilibrium, kinetic, and thermodynamic parameters of brilliant green adsorbed by coconut based granular activated carbon were determined from various initial concentrations ($300{\sim}500mg\;L^{-1}$), contact time (1 ~ 12 h), and adsorption temperature (303 ~ 323 K) through batch experiments. The equilibrium adsorption data were analyzed by Langmuir, Freundlich, Temkin, Harkins-Jura, and Elovich isotherm models. The estimated Langmuir dimensionless separation factor ($R_L=0.018{\sim}0.040$) and Freundlich constant ($n^{-1}=0.176{\sim}0.206$) show that adsorption of brilliant green by activated carbon is an effective treatment process. Adsorption heat constants ($B=12.43{\sim}17.15J\;mol^{-1}$) estimated by the Temkin equation corresponded to physical adsorption. The isothermal parameter ($A_{HJ}$) by the Harkins-Jura equation showed that the heterogeneous pore distribution increased with increasing temperature. The maximum adsorption capacity by the Elovich equation was found to be much smaller than the experimental value. The adsorption process was best described by the pseudo second order model, and intraparticle diffusion was a rate limiting step in the adsorption process. The intraparticle diffusion rate constant increased because the dye activity increased with increases in the initial concentration. Also, as the initial concentration increased, the influence of the boundary layer also increased. Negative Gibbs free energy ($-10.3{\sim}-11.4kJ\;mol^{-1}$), positive enthalpy change ($18.63kJ\;mol^{-1}$), and activation energy ($26.28kJ\;mol^{-1}$) indicate respectively that the adsorption process is spontaneous, endothermic, and physical adsorption.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.1
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• pp.43-51
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• 2011

Natural convection heat transfer phenomena on a horizontal cylinder have been studied experimentally in order to investigate the applicability of analogy experimental methodology using a copper electroplating system and to visualize the local heat transfer rates depending on the angular position and the diameter of the horizontal cylinder. In the copper electroplating system, the copper ion produced at the anode moves by convection and diffusion to the cathode and reduces at the cathode, representing the heat transfer. By using aluminum cathode with a distinguishable color, the amount of copper plated could visualize the amount of heat transferred depending on the angular position of the cylinder. The diameter of the cylinder is varied from 0.01m to 0.15m, which correspond to Rayleigh numbers in the range of $1.73{\times}10^7$ to $5.69{\times}10^{11}$. The test results are in good agreement with existing heat transfer correlations.

• Korean Chemical Engineering Research
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• v.46 no.2
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• pp.286-290
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• 2008

Small amounts of CO in reformate fuel gas effectively block platinum catalysts by strong adsorption on the platinum surface at the operation temperature of $60{\sim}80^{\circ}C$ in PEMFC. To oxidate CO, Ru/C layer (CO filter) was placed between Pt/C layer and GDL (gas diffusion layer) in this study. Ru/C filter provided good CO-tolerant PEMFC anode, but decreased the performance of unit cell about 10% at 0.6 V due to mass transfer resistance from Ru/C filter thickness and increase of charge transfer resistance. Membrane degradation is one of the most important factors limiting the life-time of PEMFCs. Membrane durability would be dependent on the electrode catalyst type. It seemed that Ru catalyst layer would shorten the life time of PEMFC as enhanced the fluoride emission rate of membrane in acceleration test.