• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.389-390
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• 2012

In this study, we fabricate a superhydrophobic surface made of hierarchical nanostructures that combine wax crystalline structure with moth-eye structure using vacuum cluster system and measure their hydrophobicity and durability. Since the lotus effect was found, much work has been done on studying self-cleaning surface for decades. The surface of lotus leaf consists of multi-level layers of micro scale papillose epidermal cells and epicuticular wax crystalloids [1]. This hierarchical structure has superhydrophobic property because the sufficiently rough surface allows air pockets to form easily below the liquid, the so-called Cassie state, so that the relatively small area of water/solid interface makes the energetic cost associated with corresponding water/air interfaces smaller than the energy gained [2]. Various nanostructures have been reported for fabricating the self-cleaning surface but in general, they have the problem of low durability. More than two nanostructures on a surface can be integrated together to increase hydrophobicity and durability of the surface as in the lotus leaf [3,5]. As one of the bio-inspired nanostructures, we introduce a hierarchical nanostructure fabricated with a high vacuum cluster system. A hierarchical nanostructure is a combination of moth-eye structure with an average pitch of 300 nm and height of 700 nm, and the wax crystalline structure with an average width and height of 200 nm. The moth-eye structure is fabricated with deep reactive ion etching (DRIE) process. $SiO_2$ layer is initially deposited on a glass substrate using PECVD in the cluster system. Then, Au seed layer is deposited for a few second using DC sputtering process to provide stochastic mask for etching the underlying $SiO_2$ layer with ICP-RIE so that moth-eye structure can be fabricated. Additionally, n-hexatriacontane paraffin wax ($C_{36}H_{74}$) is deposited on the moth-eye structure in a thermal evaporator and self-recrystallized at $40^{\circ}C$ for 4h [4]. All of steps are conducted utilizing vacuum cluster system to minimize the contamination. The water contact angles are measured by tensiometer. The morphology of the surface is characterized using SEM and AFM and the reflectance is measured by spectrophotometer.

• Bulletin of the Korean Chemical Society
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• v.34 no.9
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• pp.2769-2773
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• 2013

Red phosphors $Ca_{(1-1.5x)}Eu_xWO_4$ and $Ca_{(1-2x)}Eu^_xNa_xWO_4$ were synthesized with various concentrations x of $Eu^{3+}$ ions by using a solid-state reaction method. The crystal structure of the red phosphors were found to be a tetragonal scheelite structure with space group $I4_1/a$. X-ray diffraction (XRD) results show the (112) main diffraction peak centered at $2{\theta}=28.71^{\circ}$, and indicate that there is no basic structural deformation caused by the vacancies ${V_{Ca}}^{{\prime}{\prime}}$ or the $Eu^{3+}$ (and $Na^+$) ions in the host crystals. Densities of $Ca_{(1-1.5x)}Eu_xWO_4$ were measured on a (helium) gas pycnometer. Comparative results between the experimental and theoretical densities reveal that $Eu^{3+}$ (and $Na^+$) ions replace the $Ca^{2+}$ ions in the host $CaWO_4$. Also, the photoluminescence (PL) emission and photoluminescence excitation (PLE) spectra show the optical properties of trivalent $Eu^{3+}$ ions, not of divalent $Eu^{2+}$. Raman spectra exhibit that, without showing any difference before and after the doping of activators to the host material $CaWO_4$, all the gerade normal modes occur at the identical frequencies with the same shapes and weaker intensities after the substitution. However, the FT-IR spectra show that some of the ungerade normal modes have shifted positions and different shapes, caused by different masses of $Eu^{3+}$ ions (or $Na^+$ ions, or ${V_{Ca}}^{{\prime}{\prime}}$ vacancies) from $Ca^{2+}$.

• Journal of Surface Science and Engineering
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• v.50 no.3
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• pp.206-211
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• 2017

$BiNbO_4:RE^{3+}$ (RE = Dy, Eu, Sm, Tb) phosphors were prepared by solid-state reaction at $1100^{\circ}C$ and their structural, photoluminescent, and morphological properties were investigated. XRD patterns exhibited that all the synthesized phosphors exhibited a triclinic system with a dominant (210) diffraction peak, irrespective of the type of activator ions. The surface morphologies of rare-earth-ion-doped $BiNbO_4$ phosphors were found to depend strongly on the type of activator ions. The $Eu^{3+}$ and $Dy^{3+}$ doped $BiNbO_4$ phosphors revealed a strong red (613 nm) emission resulting from the $^5D_0{\rightarrow}^7F_2$ transition of $Eu^{3+}$ and a dominant yellow (575 nm) emission originating from the $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transition of $Dy^{3+}$ respectively, which were the electric dipole transitions, indicating that the activator ions occupy sites of non-inversion symmetry in the $BiNbO_4$ phosphor. The main reddish-orange emission spectra of $Sm^{3+}$-doped $BiNbO_4$ phosphors were due to the $^4G_{5/2}{\rightarrow}^6H_{7/2}$ (607 nm) magnetic dipole transition, indicating that the $Sm^{3+}$ ions were located at inversion symmetry sites in the $BiNbO_4$ host lattice. As for $Tb^{3+}$-doped phosphors, green emission was obtained under excitation at 353 nm and its CIE chromaticity coordinates were (0.274, 0.376). These results suggest that multicolor emission can be achieved by changing the type of activator ions incorporated into the $BiNbO_4$ host crystal.

• Elastomers and Composites
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• v.43 no.4
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• pp.259-263
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• 2008

An effect of low-temperature long-term thermal degradation on a degree of crystallinity of a low density polyethylene (LDPE) was investigated by using $^1H$ solid state nuclear magnetic resonance (SSNMR). Firstly, the long-term thermal treatment makes a color of LDPE from white to pale yellow which is indicative of thermal oxidation. Secondly, it makes the $^{1}H$ NMR spin-spin and spin-lattice relaxation times ($T_1$) to be long. Lastly, the degree of crystallinity of the semicrystalline aged-LDPE also decreases with thermal treatment. Above all, the $T_1$ increase is envisaged to be due to either a decrease of the amorphous regions governing overall spin-lattice relaxation mechanism in LDPEs or a dynamically restricted motion of specific molecular motions by intermolecular hydrogen bonding or crosslinking. However, since the decrease of crystallinity implies an increase of amorphous regions by the thermal treatment, the former case is contrast to our results. Accordingly, we concluded that the latter effect is responsible for the $T_1$ increase.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.2
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• pp.87-90
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• 2002

$LiCoO_{2}$ powders were synthesized at various temperatures using lithium hydroxide and cobalt hydroxide as precursors prepared by precipitation process and freeze-drying. In this study, the$LiCoO_{2}$ samples were synthesized via a solid state reaction with various LiOH concentration between 10 % and 30 % excess. And $LiCoO_{2}$powders were calcined at 600~$800^{\circ}C$ in a short time. Measurements of XRD and SEM were performed to characterize the properties of the prepared materials. The effect of amount of Li ions on the structural change in powder has been examined using the XRD analysis. For the not added excess of LiOH, CoOOH phase presented in the XRD pattern of $LiCoO_{2}$ due to loss of Li ions during firing. The morphology and particle size of the powders were examined using SEM. The obtained powders are high temperature-$LiCoO_{2}$HT-LiCoO$_{2}$) and homogeneous with the range of grain size in the order of hundreds of nanometers. The effects of variation of LiOH concentration on the structural change in powder were investigated using the Rietveld analysis. As an analysis result, c/a is constant by 4.99 on all occasions. Finally, the structure of HT-$LiCoO_{2}$ was simulated by the commercial software $Creius^{2}$(Molecular Simulations, Inc.) from the results of Rietveld analysis.

• Korean Journal of Soil Science and Fertilizer
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• v.45 no.1
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• pp.43-50
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• 2012

Two typical animal waste management practices, composting and stockpiling, were evaluated for their effect on the degradation of three veterinary antibiotics (VAs), chlortetracycline (CTC), tylosin (TYL), and monensin (MNS). The VAs were applied to horse manure plots subject to composting or stockpiling, and core samples were collected over a period of time. Selected buffer solutions were used to extract the VAs and analysis for concentration was conducted with solid phase extraction (SPE) followed by high performance liquid chromatography tandem mass spectrometry (HPLC/MS/MS) technique. The VAs demonstrated rapid dissipation within ten days followed by a gradual decrease in concentration until the end of the experimental period (141 days). All three VAs degraded more rapidly in the composting samples than in the stockpiling samples, particularly between 20 and 60 days of the observation period. Degradation of the three VAs generally followed a first-order kinetic model, and a fitted model with a calculated rate constant was determined for each treatment. TYL in composting showed the fastest degradation, with a calculated rate constant of $0.91day^{-1}$; the slowest degradation was exhibited by MNS in stockpiling, with rate constant of $0.17day^{-1}$. Calculated correlation coefficients ranged from 0.89 to 0.96, indicating a strong correlation between measured concentrations and fitted values in this study. Although concentration of TYL in composting treatment showed below detection limit during the test period, this study suggests that composting can reduce animal waste contaminants prior to field application as fertilizer.

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.600-605
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• 2010

In order to meet the requirements of faster speed and higher packing density for devices in the field of semiconductor manufacturing, the development of Cu/Low k device material is explored for use in multi-layer interconnection. SiOC(-H) thin films containing alkylgroup are considered the most promising among all the other low k candidate materials for Cu interconnection, which materials are intended to replace conventional Al wiring. Their promising character is due to their thermal and mechanical properties, which are superior to those of organic materials such as porous $SiO_2$, SiOF, polyimides, and poly (arylene ether). SiOC(-H) thin films containing alkylgroup are generally prepared by PECVD method using trimethoxysilane as precursor. Nano voids in the film originating from the sterichindrance of alkylgroup lower the dielectric constant of the film. In this study, methyltriphenylsilane containing bulky substitute was prepared and characterized by using NMR, single-crystal X-ray, GC-MS, GPC, FT-IR and TGA analyses. Solid-state NMR is utilized to investigate the insoluble samples and the chemical shift of $^{29}Si$. X-ray single crystal results confirm that methyltriphenylsilane is composed of one Si molecule, three phenyl rings and one methyl molecule. When methyltriphenylsilane decomposes, it produces radicals such as phenyl, diphenyl, phenylsilane, diphenylsilane, triphenylsilane, etc. From the analytical data, methyltriphenylsilane was found to be very efficient as a CVD or PECVD precursor.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.1
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• pp.35-43
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• 2002

In the last decade, considerable efforts have been made to make a new class of solid state high power, high speed electronic device, namely, the Photo-Conductive Power Switch(PCPS), and to characterize the high-field performance of PCPS under high power, high voltage conditions. But the problem of surface flashover phenomena persist, preventing the realization of reliable and efficient high-speed, high voltage switching devices. It is essential to have a clear understanding on the physical processes behind the surface flashover problem to develop new technologies and device architectures so as to fabricate PCPS that are capable of high-field high-voltage. Also, it is imperative to identify new materials that could satisfy the requirements for high-field, high-power devices. Since surface flashover, surface breakdown phenomena is observed for all the devices that foiled at the applied field much lower than semiconductor bulk breakdown field, surface passivation is considered one of the important practical methods to improve the high field performance of the devices. Therefore, this paper was studied the main properties and mechanism of the semiconductor surface flashover before and after passivation under high electric-field.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.6
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• pp.361-366
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• 2014

$MnO_2$-doped $0.985[Li_{0.04}(Na_{0.545}K_{0.46})_{0.96}(Nb_{0.81}Ta_{0.15}Sb_{0.04})]O_3+0.015KNbO_3(0.985LNKNTS+0.015KNbO_3)$ lead-free ceramics were fabricated by conventional solid state method to develop excellent dielectric and piezoelectric properties. The result of X-ray diffraction patterns obviously indicated that all of the specimen has pure perovskite structure without secondary phase. In addition, orthorhombic phase and coexistance region of orthorhombic-tetragonal phase (MPB) were observed with amount of $MnO_2$. The optimal values of ${\rho}$=4.70 $g/cm^3$, $d_{33}=238$ pC/N, $k_P=0.46$, $Q_m=121$, ${\varepsilon}_r=849$, and $T_C=225^{\circ}C$ were obtained at 0.01 mol% $MnO_2$ doped $0.985LNKNTS+0.015KNbO_3$ ceramics sintered at $990^{\circ}C$ for 5 h, respectively. Hence, it was indicated that the suitable amount of $MnO_2$ could improve the electrical properties of $0.985[Li_{0.04}(Na_{0.545}K_{0.46})_{0.96}(Nb_{0.81}Ta_{0.15}Sb_{0.04})]O_3+0.015KNbO_3$ ceramics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.9
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• pp.555-560
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• 2014

In this paper, in order to develop outstanding Pb-free composition ceramics, the $Fe_2O_3$-doped ($Na_{0.525}K_{0.443}Li_{0.037}$)($Nb_{0.883}Sb_{0.08}Ta_{0.037}$)$O_3$ + 0.3 wt% $Bi_2O_3$ + x wt% $Fe_2O_3$ (x= 0~1.0 wt%)(abbreviated as NKL-NST) lead-free piezoelectric ceramics have been synthesized using the ordinary solid state reaction method. The effect of $Fe_2O_3$-doping on their microstructure and electrical properties were investigated. XRD diffraction pattern studies confirm that $Fe_2O_3$ completely diffused into the NKL-NST lattice to form a new stable soild solution with $Fe^{3+}$ entering the $Nb^{5+}$, $Sb^{5+}$ and $Ta^{5+}$ of B-site. And, phase structure of all the ceramics exhibited pure perovskite phase and no secondary phase was found in the ceramics. The ceramics doped with 0.6 wt% $Fe_2O_3$ have the optimum values of piezoelectric constant($d_{33}$), planar piezoelectric coupling coefficient($k_p$) and mechanical quality factor($Q_m$) : $d_{33}$ = 233 [pC/N], $k_p$= 0.44, $Q_m$= 95. These results indicate that the ($Na_{0.525}K_{0.443}Li_{0.037}$)($Nb_{0.883}Sb_{0.08}Ta_{0.037}$)$O_3$ +0.3 wt% $Bi_2O_3$ + 0.6 wt% $Fe_2O_3$ ceramic is a promising candidate for lead-free piezoelectric ceramics.