• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.530-530
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• 2012

Many practical applications of carbon nanotubes(CNTs) have been proposed and there have been attempts to utilize CNT films as transparent electrodes for solar cells and displays. Our group has considered the use of the CNT film as a thin film heater (TFH) and proposed it for the first time and reported the thermal behavior of the TFH made of single walled CNTs. However, due to the relatively high electrical resistance of the CNT film, using the TFH in application areas requiring high heat flux has been a difficult problem. To overcome this obstacle, we adopted a 'branch electrodes' concept to increase the film conductance dramatically. If two branch electrodes are inserted into a TFH whose original electrical resistance is R, the total resistance will be reduced to R/9. Because of the increased aspect ratio, the resistance of each segmented TFH will be reduced to R/3. Furthermore, since they are connected in parallel, the total resistance reduces to R/9. This could be extended to n branch electrodes, and the total resistance of the film will be reduced to R/(n+1)2, if the resistance of electrodes are negligibly small. We fabricated the heaters with different number of branch electrodes. The number of branch electrodes of the fabricated heaters are 0, 2, 4, 8 and their electrical resistance are 101.4, 39.5, 20.0, $15.4{\Omega}$, respectively. We applied 20V to each heater and monitored the temperature variations. We could achieve high heating temperature even with low voltage supply. This technique could be applied to relevant industrial applications which need high power film heater.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.1
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• pp.41-45
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• 2014

We have investigated the passivation property of $SiN_x$ and $SiO_2$ thin films formed using various process conditions for the application of crystalline Si solar cells. An increase in the thickness of $SiN_x$ deposited using plasma enhanced chemical vapor deposition (PECVD) led to the improvement of passivation quality. This could be associated with the passivation of Si dangling bonds by hydrogen atoms which were supplied during PECVD deposition. The $SiO_2$ thin films grown using dry oxidation process exhibited better passivation behavior than those using wet oxidation process, implying the dry oxidation process was more effective in the formation of high quality $SiO_2$ thin films. The relative effective life time gradually decreased with increasing dry oxidation temperature. Such a degradation of passivation behavior could be attributed to the increase in interface trap density caused by thermal damages.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.11a
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• pp.35-35
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• 2001

agnesium Oxide (MgO) with a NaCI structure is well known to exhibit high secondary electron emission, excellent high temperature chemical stability, high thermal conductance and electrical insulating properties. For these reason MgO films have been widely used for a buffer layer of high $T_c$ superconducting and a protective layer for AC-plasma display panels to improve discharge characteristics and panel lifetime. Up to now MgO films have been synthesized by lE-beam evaporation, Molecular Beam Epitaxy (MBE) and Metalorganic Chemical Vapor Deposition (MOCVD), however there have been some limitations such as low film density and micro-cracks in films. Therefore magnetron sputtering process were emerged as predominant method to synthesis high density MgO films. In previous works, we designed and manufactured unbalanced magnetron source with high power density for the deposition of high quality MgO films. The magnetron discharges were sustained at the pressure of O.lmtorr with power density of $110W/\textrm{cm}^2$ and the maximum deposition rate was measured at $2.8\mu\textrm{m}/min$ for Cu films. In this study, the syntheses of MgO films were carried out by unbalanced magnetron sputtering with various $O_2$ partial pressure and specially target power densities, duty cycles and frequency using pulsed DC power supply. And also we investigated the plasma states with various $O_2$ partial pressure and pulsed DC conditions by Optical Emission Spectroscopy (OES). In order to confirm the relationships between plasma states and film properties such as microstructure and secondary electron emission coefficient were analyzed by X-Ray Diffraction(XRD), Transmission Electron Microscopy(TEM) and ${\gamma}-Focused$ Ion Beam (${\gamma}-FIB$).

• Journal of the Korean Chemical Society
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• v.65 no.2
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• pp.93-105
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• 2021

Mononuclear Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Fe(III), Ru(III), and UO2(II) complexes of 2-hydroxy-4-(p-tolyldiazenyl)benzylidene)-2-(p-tolylamino)acetohydrazide (H2L) were prepared by direct method. The ligand and its complexes were isolated in solid state and characterized by analytical techniques such as elemental and thermal analyses, molar conductance, magnetic susceptibility measurements and spectroscopic techniques such as UV-Visible, IR, 1H-NMR and 13C-NMR. The spectral data indicated that the ligand acted as neutral/monobasic bidentate or monobasic/dibasic tridentate ligand bonded to the metal ions through the oxygen atom of ketonic or enolic carbonyl group, azomethine nitrogen atom and deprotonated/protonated phenolic oxygen atom forming either tetragonally distorted octahedral or octahedral. Antimicrobial activities of the ligand and its complexes were evaluated against Escherichia coli, Bacillus subtilis and Aspergillus niger by well diffusion method. The results of antifungal activity showed that the Fe(III) complex (10) exhibited higher antifungal against Aspergillus niger than the other complexes. However, the results of antibacterial activity revealed that Cu(II) complex (4) is the most active against Escherichia coli while the Cu(II) complex (5) and Fe(III) complex (10) exhibited higher antibacterial effect on Bacillus subtilis than the other complexes.

• Korean Journal of Materials Research
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• v.29 no.8
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• pp.463-468
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• 2019

The electrical and interfacial properties of $HfO_2/Al_2O_3$ and $Al_2O_3/HfO_2$ dielectrics on AlN/p-Ge interface prepared by thermal atomic layer deposition are investigated by capacitance-voltage(C-V) and current-voltage(I-V) measurements. In the C-V measurements, humps related to mid-gap states are observed when the ac frequency is below 100 kHz, revealing lower mid-gap states for the $HfO_2/Al_2O_3$ sample. Higher frequency dispersion in the inversion region is observed for the $Al_2O_3/HfO_2$ sample, indicating the presence of slow interface states A higher interface trap density calculated from the high-low frequency method is observed for the $Al_2O_3/HfO_2$ sample. The parallel conductance method, applied to the accumulation region, shows border traps at 0.3~0.32 eV for the $Al_2O_3/HfO_2$ sample, which are not observed for the $Al_2O_3/HfO_2$ sample. I-V measurements show a reduction of leakage current of about three orders of magnitude for the $HfO_2/Al_2O_3$ sample. Using the Fowler-Nordheim emission, the barrier height is calculated and found to be about 1.08 eV for the $HfO_2/Al_2O_3$ sample. Based on these results, it is suggested that $HfO_2/Al_2O_3$ is a better dielectric stack than $Al_2O_3/HfO_2$ on AlN/p-Ge interface.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.65-70
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• 2022

A vacuum system is designed for thermal insulation of a 10 ton/day class air liquefaction cold box for liquid air energy storage. The vacuum system is composed of a turbomolecular pump, a backing pump and vacuum piping for the vacuum pumps. The turbomolecular pump is in combination with the backing pump for pumping capacity. The vacuum piping is designed with system installation conditions, such as distance from the cold box, connections to vacuum pumps and installation space. The capacity of the vacuum pump combination, namely pumping speed, is determined by analysis of the vacuum system, and pump-down time to 1×10^-5 mbar is estimated. Vacuum piping conductance, system pumping speed and outgassing rate are calculated for the pump-down time with the ultimate pumping speed range of the vacuum pump combination of 1400 - 2300 l/s. Although the pump-down time gets shorter by larger capacity vacuum pumps, it mainly depends on target vacuum degree and outgassing rate in the cold box. The pump-down time is estimated as 3 - 6 hours appropriate for cold box operation for the pumping speed range. Considering the outgassing rate has uncertainty, the vacuum pump combination with pumping speed of 1900 l/s is chosen for the vacuum system, which is middle value of the pumping speed range.

• Journal of the Korean Chemical Society
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• v.55 no.3
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• pp.412-417
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• 2011

A series of homobinuclear complexes of the type [$M_2L(NO_3)_n(H_2O)_m$] where M=$UO_2$(VI), ZrO(IV), Th(IV); L=3-benzylidine-imino-5-p-sulphonamido phenyl azo-2-thiohyatoin(bispt), 3-furfurylidine-imino-5-p-sulphonamido phenyl azo-2-thiohydantoin(fispt),3-pyridyl-2'-methylene-imino-5-p-sulphonamido phenyl azo-2-thiohydantoin(pmispt) and 3-thienyl-2'-methylene-imino-5-p-sulphoanamido phenyl azo-2-thiohydantoin(tmispt); n=8 for Th(IV) and 4 for others, m=4 for bispt and 3 for others have been synthesized and characterized on the basis of elemental analysis, thermal analysis, molar conductance, magnetic moment and spectroscopic data (IR, electronic and $^1H$-NMR). In the light of this information, the ligands can be visualized as tetradentate co-ordinating through azomethine nitrogen, carbonyl oxygen to one metal centre where as azo nitrogen and thioimido nitrogen to the other metal centre yielding homo binuclear complexes of the above composition. The fungi toxicity of the ligands & their zirconyl complexes against some fungal pathogen has been studied.

• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.567-575
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• 2012

A research was conducted to develop a 2-D nonlinear Galerkin finite element analysis of reinforced concrete structures subjected to high temperature with experiments. Algorithms for calculating the closed-form element stiffness for a triangular element with a fully populated material conductance are developed. The validity of the numerical model used in the program is established by comparing the prediction from the computer program with results from full-scale fire resistance tests. Details of fire resistance experiments carried out on reinforced concrete slabs, together with results, are presented. The results obtained from experimental test indicated in that the proposed numerical model and the implemented codes are accurate and reliable. The changes in thermal parameters are discussed from the point of view of changes of structure and chemical composition due to the high temperature exposure. The proposed numerical model takes into account time-varying thermal loads, convection and radiation affected heat fluctuation, and temperature-dependent material properties. Although, this study considered standard fire scenario for reinforced concrete slabs, other time versus temperature relationship can be easily incorporated.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.10
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• pp.678-686
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• 2001

Origins for the transconductance dispersion and the gate leakage current in a GaAs metal semiconductor field effect transistor were found using capacitance deep-level transient spectroscopy (DLTS) measurements. In DLTS spectra, we observed two surface states with thermal activation energies of 0.65 $\times$ 0.07 eV and 0.88 $\times$ 0.04 eV and an electron trap EL2 with thermal activation energy of 0.84 $\times$ 0.01 eV. Transconductance was decreased in the frequency range of 5.5 Hz ~ 300 Hz. The transition frequency shifted to higher frequencies with the increase of temperature and the activation energy for the change of the transition frequency was determined to be 0.66 $\times$ 0.02 eV. From the measurements of the gate leakage current as a function of the device temperature, the forward and reverse currents are coincident with each other below gate voltages lower than 0.15 V, namely Ohmic behavior between gate and source/drain electrodes. The activation energy for the conductance of electrons on the surface of MESFET was 0.63 $\times$ 0.01 eV. Comparing activation energies obtained by different measurements, we found surface states H1 caused the transconductance dispersion and the fate leakage current.

• Journal of the Korean Chemical Society
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• v.54 no.5
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• pp.515-522
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• 2010

A relation between antimicrobial activities and the formation constants of solid complexes of Cu(II), Ni(II), Co(II), Mn(II) and Fe(III) with tridentate Schiff base ligand, 4-hydroxy-3(1-{2-(benzylideneamino)-phenylimino}-ethyl)-6-methyl-2Hpyran-2-one (HL) derived from o-phenylene diamines, dehydroacetic acid (DHA) and p-chloro benzaldehyde have been studied. The ligand and metal complexes were characterized by elemental analysis, conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, $^1H$-NMR, UV-vis and mass spectra. From the analytical data, the stiochiometry of the complexes was found to be 1:2 (metal:ligand) with octahedral geometry. The molar conductance values suggest the nonelectrolytic nature of metal complexes. The X-ray diffraction data suggests monoclinic crystal system for Ni(II) and orthorhombic crystal system for Cu(II) and Co(II) complexes. The IR spectral data suggest that the ligand behaves as tridentate ligand with ONN donor atoms sequence towards central metal ion. Thermal behavior (TG/DTA) and kinetic parameters calculated by Coats-Redfern method suggests more ordered activated state in complex formation. The protonation constants of the complexes were determined potentiometrically in THF:water (60:40) medium at $25^{\circ}C$ and ionic strength ${\mu}=0.1\;M$ ($NaClO_4$). Antibacterial activities in vitro were performed against Staphylococcus aureu and Escherichia coli. Antifungal activities were studied against Aspergillus Niger and Trichoderma. The effect of the metal ions and stabilities of complexes on antimicrobial activities are discussed.