• The Journal of the Korea institute of electronic communication sciences
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• v.19 no.1
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• pp.39-46
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• 2024

In this study, GTZO(Ga-Ti-Zn-O) thin films were deposited at various working pressures (1~7mTorr) by RF magnetron sputtering to examine the structural, electrical, and optical properties. All GTZO thin films exhibited c-axis preferential growth regardless of working pressure, the GTZO thin film deposited at 1mTorr showed the most excellent crystallinity having 0.38˚ of FWHM. The average transmittance in the visible light region (400~800nm) showed 80% or more regardless of the working pressure. We could observed the Burstein-Moss effect that carrier concentration decrease with the increase of working pressure and thus the energy band gap is narrowed. Figure of merits of GTZO thin film deposited at 1mTorr showed the highest value of 9.08 × 103 Ω-1·cm-1, in this case resistivity and average transmittance in the visible light region were 5.12 × 10-4 Ω·cm and 80.64%, respectively.

• Journal of Conservation Science
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• v.25 no.1
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• pp.17-24
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• 2009

The feasibility of the geopolymer as a cultural asset restoration material was studied by investigating compressive strength and chromaticity change. Metakaolin that was synthesized by calcination of the kaolin at $750^{\circ}C$ for 6 hours was used as a geopolymeric starting material. Kaolin lost its crystallinity and changed into non-crystalline phase during calcination. NaOH solution and water glass were used as an initiator for the geopolymeric reaction. As the concentration of NaOH solution and water glass increased the compressive strength increased. When alumina was substituted with metakaolin, the compressive strength decreased at a small amount of alumina, but increased at a large substitution. For the most composition of geopolymers, the change of chroma values remained within the limit of slight variation after exposure to sunlight for 8 and 100 days. However, even small amount of organic pigment addition increased chroma values of metakaoline. It was shown that geopolymer had excellent chroma value change over epoxy resins.

• Food Science and Preservation
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• v.19 no.4
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• pp.532-538
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• 2012

Seven rice varieties (Dasan, Keunseon, Goami, Baekjinju, Seolgaeng, Hangangchal and Heukseol) were used to study the physicochemical properties of dry milled (200-mesh) rice flour species. The moisture and crude protein contents of rice were 15.00-15.10% and 6.09-8.21%, respectively. The crude lipid and crude ash of rice were 0.21-1.02% and 0.37-1.62%, respectively. As for the Hunter's color value, the L value was highest in the Dasan flour (96.47); the a value was highest in the Heukseol flour (5.03); and the b value was highest in the Baekjinju flour (3.36). The water aborption index was highest in the Goami flour (1.45), and the water solubility index was highest in the Hangangchal flour (9.16%). The amylose contents of the rice flour species were highest in the Goami (26.42%) rice flour, followed by the Dasan (19.39%), Seolgaeng (19.24%), Keunseon (18.06%), Heukseol (15.52%), Baekjinju (9.16%), and Hangangchal (0.84%) rice flour. In the X-raydiffractin patterns of the diverse species, seven tice varieties showed A-type crystallinity. As for the amylogram properties, the initial pasting temperature was 58.00-$69.03^{\circ}C$. The maximum viscosity was highest in the Dasan flour. The Heukseol flour had the lowest maximum viscosity, breakdown, and setback. In terms of the thermal properties of the differential scanning calorimeter (DSC), the onset temperature was 59.03-$66.84^{\circ}C$; the peak temperature, 66-70-$72.82^{\circ}C$; and the end temperature, 74.06-$78.66^{\circ}C$. The enthalpy (${\Delta}H$) was lowest in the Heukseol flour (7.59 J/g) and highest in the Seolgaeng flour (11.36J/g).

• Polymer(Korea)
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• v.36 no.6
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• pp.712-720
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• 2012

Thermal degradation for glass fiber-reinforced polyamide 66 composite (PA 66) with respect of thermal exposure time has been investigated using optical microscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. As the thermal exposure time was prolonged, a slight increase in tensile strength for only initial stage and afterward, a proportional decrease of tensile strength was observed. These results can be explained by the increase of crystallinity, followed by the increase of crosslinking density, chain scission and the decrease in chain mobility, due to thermal oxidation with the exposure time. Fourier transform infrared spectroscopy results showed the increase of ketone peak and silica peak on the surface of thermally exposed PA 66. In addition, the thermal decomposition kinetics of PA 66 was analyzed using thermogravimetric analysis at three different heating rates. The relationship between activation energy and lifetime-prediction of PA 66 was investigated by several methodologies, such as statistical tool, UL 746B, Ozawa and Kissinger. The activation energy determined by thermogravimetric analysis had a relatively large value compared with that from the accelerated test. This may result in over-estimating the lifetime of PA 66. In this study, a master curve of exponential fitting has been developed to extrapolate the activation energy at various service temperatures.

• Journal of the Korean Applied Science and Technology
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• v.34 no.1
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• pp.50-57
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• 2017

Zinc oxide is, one of metal oxide semiconductor, harmless to human and environment-friendly. It has excellent chemical and thermal stability properties. Wurtzite-zinc oxide is a large band gap energy of 3.37 eV and high exciton binding energy of 60 meV. It can be applied to various fields, such as solar cells, degradation of the dye waste, the gas sensor. The photocatalytic activity of zinc oxide is varied according to the particle shape and change of crystallinity. Therefore, It is very important to specify the additives and the experimental variables. In this study, the zinc oxide were synthesized by using a microwave assisted hydrothermal synthesis. The precursor was used as the zinc nitrate, the pH value was controlled as 11 by NaOH. Surfactants are the ethanolamine, cetyltrimethylammonium bromide, sodium dodecyl sulfate, sorbitan monooleate was added by changing the concentration. The composite particles had the shape of a star-like, curcular cone, seed shape, flake-sphere. Physical and chemical properties of the obtained zinc oxide was characterized using x-ray diffractometer, field emission scanning electron microscopy, thermogravimetric analysis and optical properties was characterized using UV-visible spectroscopy, photoluminescence and raman spectroscopy.

• Journal of Electrochemical Science and Technology
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• v.10 no.4
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• pp.424-432
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• 2019

Planar BiVO₄ and 3 wt% Mo-doped BiVO₄ (abbreviated as Mo:BiVO₄) film were prepared by the facile spin-coating method on fluorine doped SnO₂(FTO) substrate in the same precursor solution including the Mo precursor in Mo:BiVO₄ film. After annealing at a high temperature of 450℃ for 30 min to improve crystallinity, the films exhibited the monoclinic crystalline phase and nanoporous architecture. Both films showed no remarkably discrepancy in crystalline or morphological properties. To investigate the effect of surface passivation exploring the Al₂O₃ layer, the ultra-thin Al₂O₃ layer with a thickness of approximately 2 nm was deposited on BiVO₄ film using the atomic layer deposition (ALD) method. No distinct morphological modification was observed for all prepared BiVO₄ and Mo:BiVO₄ films. Only slightly reduced nanopores were observed. Although both samples showed some reduction of light absorption in the visible wavelength after coating of Al₂O₃ layer, the Al₂O₃ coated BiVO₄ (Al₂O₃/BiVO₄) film exhibited enhanced photoelectrochemical performance in 0.5 M Na₂SO₄ solution (pH 6.5), having higher photocurrent density (0.91 mA/㎠ at 1.23 V vs. reversible hydrogen electrode (RHE), briefly abbreviated as V_RHE) than BiVO₄ film (0.12 mA/㎠ at 1.23 V_RHE). Moreover, Al₂O₃ coating on the Mo:BiVO₄ film exhibited more enhanced photocurrent density (1.5 mA/㎠ at 1.23 V_RHE) than the Mo:BiVO₄ film (0.86 mA/㎠ at 1.23 V_RHE). To examine the reasons, capacitance measurement and Mott-Schottky analysis were conducted, revealing that the significant degradation of capacitance value was observed in both BiVO₄ film and Al₂O₃/Mo:BiVO₄ film, probably due to degraded capacitance by surface passivation. Furthermore, the flat-band potential (V_FB) was negatively shifted to about 200 mV while the electronic conductivities were enhanced by Al₂O₃ coating in both samples, contributing to the advancement of PEC performance by ultra-thin Al₂O₃ layer.

• Journal of the Korean Chemical Society
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• v.43 no.2
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• pp.199-205
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• 1999

The electrochemical properties of PAN-PVDF-PEGME blend polymer electrolyte system are investigated and the physical properties are also measured with varying the content of PEGME. This PEGME partially reduces the crystallinity of PVDF. The ionic conductivities of the polymer electrolytes are about $10^{-3}S/cm$, which may be applicable to a constituent of lithium secondary battery. From the temperature dependence of ionic conductivity, it is suggested that the ionic conductivity increases with the PEGME content due to the fomation of effective ion-conducting path. The cation transference number reaches its maximum value for the electrolytes (SPE 2) with 10 wt% PEGME and then decreases for further increase of PEGME contnet. The electrochemically stable range of SPE 1 (without PEGME) is about 4.3 V, but SPE 2-4 (PAN-PVDF-PEGME system) is about 4.6 V. When these polymer electrolyte are used as electrolyte in rechargeable battery and the cell performances are tested, the discharge capacity increses with the amount of PEGME. Therefore, PEGME increases the ionic conductivity, extends the electrochemical stable range, and finally improves the discharge capacity of cell adopting the electrolyte system.

• Polymer(Korea)
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• v.27 no.3
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• pp.265-270
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• 2003

In spite of high ionic conductivity, the polymer gels have poor mechanical properties and high reactivity with lithium metal anode. To solve these problems, the dry solid systems and polymer composites have been intensively studied, due to their good mechanical, thermal, chemical, and electrochemical stability. The objectives of this experiment were to improve ionic conductivity and mechanical properties of the solid polymer electrolytes based on PEO-LiClO$_4$. To obtain higher ionic conductivity and better mechanical properties, ceramic or rubber phase was added in the PEO-LiClO$_4$(8:1) matrix. The results showed that ionic conductivity and mechanical properties were improved. The ionic conductivity of the samples was as high as 10$\^$-5/ S cm$\^$-1/. This value is similar to the best ionic conductivity ever reported in the solid drying system. To obtain better results, we used PEO with various molecular weights (600∼8000) and changed the salt contents. By using DSC, we found that the addition of salt reduced the crystallinity of PEO. The mobility of polymer dependence on salt contents was examined by FT-IR.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.12
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• pp.1219-1227
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• 2014

For development of the surface acoustic wave bandpass filter(SAW-BPF), we fabricated the high quality ZnO thin films through the step-by-step(double) deposition using two different deposition methods which are pulsed laser deposition(PLD) and RF sputtering techniques. The second growth of ZnO thin films was completed by RF sputtering method on the first ZnO thin films pre-deposited by PLD method. The characteristics of ZnO thin films were analyzed by XRD, SEM and AFM systems. The FWHM of ${\omega}$-scan analysis and the minimum RMS value of surface roughness of step-by-step grown ZnO thin films were $0.79^{\circ}$ and 1.108 nm respectively. As a result, the crystallinity and the preferred orientation of the grown ZnO thin films were kept good quality and the surface roughnesses of those were improved by post-annealing process as comparison with ZnO thin film fabricated by the conventional PLD technique only. Using these proposed ZnO thin films, we demonstrated the RF device such as SAW-BPF, built by the proposed ZnO thin films, shows that it has the bandwidth of 2.98 MHz and the insertion loss of 36.5 dB at the center frequency of 260.8 MHz, respectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.5
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• pp.986-991
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• 2016

In this study, we prepared ITO thin films on $Nb_2O_5/SiO_2$ double buffer layer using DC magnetron sputtering method and investigated electrical and optical properties with various substrate temperatures (room temperature ~ $400^{\circ}C$). The resistivity showed a decreasing tendency, because crystallinity has been improved due to the enlarged grain size with increasing substrate temperature. ITO thin film deposited at $400^{\circ}C$ showed the most excellent value of resistivity and sheet resistance as $3.03{\times}10^{-4}{\Omega}{\cdot}cm$, $86.6{\Omega}/sq.$, respectively. In results of optical properties, average transmittance was increased but chromaticity ($b^*$) was decreased in visible light region (400~800nm) with increasing substrate temperature. Average transmittance and chromaticity ($b^*$) of ITO thin film deposited at $400^{\circ}C$ exhibited significantly improved results as 85.8% and 2.13 compared to 82.8% and 4.56 of the ITO thin film without buffer layer. Finally, we found that ITO thin film introduced $Nb_2O_5/SiO_2$ double buffer layer has a remarkably improved optical property such as transmittance and chromaticity due to the index matching effect.