• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.135-135
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• 2010

In Mn-Ge equilibrium phase diagram, many Mn-Ge intermetallic phases can be formed with difference structures and magnetic properties. The MnGe has the cubic structure and antiferromagnetic(AFM) with Neel temperature of 197 K. The calculation predicted that the $MnGe_2$ with $Al_2Cu$-type is hard to separate between the paramagnetic(PM) states and the AFM states because this compound displays PM and AFM configuration swith similar energy. Mn-doped Ge showed the FM with Currie temperature of 285 K for bulk samples and 116 K for thin films. In addition, the $Mn_5Ge_3$ compound has hexagonal structure and FM with Curie temperature around 296K. The $Mn_{11}Ge_8$ compound has the orthorhombic structure and Tc is low at 274 K and spin flopping transition is near to 140 K. While the bulk $Mn_3Ge_2$ exhibited tetragonal structure ($a=5.745{\AA}$;$c=13.89{\AA}$) with the FM near to 300K and AFM below 150K. However, amorphous $Mn_3Ge_2$ ($a-Mn_3Ge_2$) was reported to show spin glass behavior with spin-glass transition temperature (Tg) of 53 K. In addition, the transition of crystalline $Mn_3Ge_2$ shifts under high pressure. At the atmospheric pressure, $Mn_3Ge_2$ undergoes the magnetic phase transition from AFM to FM at 158 K. The pressure dependence of the phase transition in $Mn_3Ge_2$ has been determined up to 1 GPa. The transition was found to occur at 1 GPa and 155 K with dT/dP=-0.3K/0.1 GPa. Here report that Ferromagnetic $Mn_3Ge_2$ thin films were successfully grown on GaAs(001) and GaSb(001) substrates using molecular beam epitaxy. Our result revealed that the substrate facilitates to modify magnetic and electrical properties due to tensile/compressive strain effect. The spin-flopping transition around 145 K remained for samples grown on GaSb(001) while it completely disappeared for samples grown on GaAs(001). The antiferromagnetism below 145K changed to ferromagnetism and remained upto 327K. The saturation magnetization was found to be 1.32 and $0.23\;{\mu}B/Mn$ at 5 K for samples grown on GaAs(001) and GaSb(001), respectively.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.42.2-42.2
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• 2011

$TiO_2$ films were modified by adding a glass frit as a light scattering particle and applied to an anode electrode in dye-sensitized solar cells (DSSCs) to enhance the adhesion between $TiO_2$ and fluorine doped transparent oxide (FTO). Low melting point glass frits at contents of (3 to 7wt%) were added to the nano crystalline $TiO_2$ films. The light scattering properties, photovoltaic properties and microstructures of the photo electrodes were examined to determine the role of the low glass transition temperature ($T_g$) glass frit. Electrochemical impedance spectroscopy, Brunauer-Emmett-Teller method and scratch test were conducted to support the results. The DSSC with the $TiO_2$ film containing 3wt% low Tg glass frit showed optimal performance (5.1%, energy conversion efficiency) compared to the $TiO_2$-based one. The photocurrent density slightly decreased by adding 3wt% of the frit due to its large size and non conductivity. However, the decrease of current density followed by the decrease of electron transfer due to the large frit in $TiO_2$ electrode was compensated by the scattering effect, high surface area and reduced the electron transfer impedance at the electrolyte-dye-$TiO_2$ interface. The stability of the photo electrodes was improved by the frit, which chemically promoted the sintering of $TiO_2$ at relatively low temperature ($450^{\circ}C$).

• Applied Chemistry for Engineering
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• v.3 no.3
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• pp.499-506
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• 1992

Copolymer of Styrene and GMA(glycidyl methachylate), having reactive ratios of $r_1=0.53$, $r_2=0.44$, was synthesized in dioxane using AIBN as free radical initiator. Followed by the reaction of ethylene diamine with copolymer PGS, amine groups were introduced to the PGS(NPGS). The composition of copolymer was determined by elemental analyzer. Poly(glycidyl methacrylate) (PGMA) was obtained in benzene using AIBN as free radical initiator. The NPGS-PGMA blend of 50/50 composition was prepared by mixing these polymers in THF at $65^{\circ}C$. Glass transition temperature (Tg) of NPGS-PGMA blend was measured by DSC. The blend showed a single Tg. Accordingly, it was clear that the NPGS was compatible with PGMA. An intermolecular reaction between amine groups of NPGS and epoxy groups of PGMA imparts compatibility in the NPGS-PGMA blend. When the NPGS-PGMA blend was added to the incompatible PS-PGMA blend, PS-PGMA blend showed Tg change. Scanning Electron Micrograph(SEM) showed a fine morphology in this blend. Consequently, it was apparent that the NPGS-PGMA blend acted as a compatibilizer for the PS-PGMA blend.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.376-376
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• 2016

Poly(ethylene oxide) (PEO)/functionalized bacterial cellulose nanowhiskers (f-BCNW) (0.1 wt%) composite nanofibers were fabricated by electrospinning process and the thermomechanical properties were significantly enhanced more than the PEO and PEO/bacterial cellulose nanowhiskers (BCNW) (0.1 wt%) composite nanofibers. The functionalization of BCNW (f-BCNW) was performed by microwave plasma treatment for effects of nitrogen functionalization of chemically-driven BCNW. The N-containing functional groups of f-BCNW enhanced chemical bonding between the hydroxyl groups of the polymer chains in the PEO matrix and diameter size of PEO/f-BCNW (0.1 wt%) composite nanofibers were decreased more than PEO and PEO/BCNW (0.1 wt%) composite nanofibers on the same concentration. The strong interfacial interactions between the f-BCNW nanofillers and polymer matrix were improved the thermomechanical properties such as crystallization temperature, weight loss and glass transition temperature (Tg) compared to PEO and PEO/BCNW composites nanofibers. The results demonstrated that N2 plasma treatment of BCNW is very useful in improving thermal stability for bio-applications.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.221-224
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• 2003

Recently, the market share of the thin-film-transistor liquid-crystalline-display (TFT-LCD) is growing rapidly in display device market. The backlight unit is used as a light source of TFT-LCD module. A light-guide is one of several important components of backlight unit. The manufacturing technology and optical system design of the light guide is very sensitive to quality and cost of the TFT-LCD module. In the present study a new manufacturing method which is called as direct surface forming(DSF) has been tested under various conditions. The result of this test, V-groove pattern shows different shapes depends on the temperature of mold surface, contact time of mold and depth of V-groove.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.281-284
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• 2004

Photo-induced memory effect of an organic light-emitting diode(OLED) composed of a hydrazone-derivative(DBAH) dispersed in bis-phenol-A type polycarbonate polymer(PCA) in the presence of thio-Michler's ketone, was investigated by the measuring of the current density and luminance at the various conditions. After the light exposure, the current of the OLED was decreased approximately one order, and the luminance of the OLED also decresed. This memory effct was erasable by heating the OLED to the temperature higher than the glass transition temperature(Tg). As shown in this result, we found the memory effect was erased by heating and returned to its original state in the hole injecting layer(HIL) of the OLED. A series of these phenomena was suggested the possibility of the application to the imaging plate.

• Journal of the Korean Society of Industry Convergence
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• v.9 no.1
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• pp.45-50
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• 2006

In order to analyse the properties of the fiber-adhesive that was used as Flocking process we synthesized quaterpolymer with the variation of the types of monomer ratio by emulsion polymerization. We characterized the properties of this adhesive: Differential Scanning Calorimeter(DSC), Thermogravimetry Analysis(TGA), Raman spectroscopy. The polymer was synthesized by changing the using amount of 2-EHAM, and then we investigated the characteristics of glass transition temperature(Tg), melting temperature(Tm), thermal stability and hydroxyl group respectively. The optimum monomer composition was 36.84% EAM, 15.79% MAM, 42.1% 2-EHAM and 5.26% AAc.

• Journal of the Korean Graphic Arts Communication Society
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• v.22 no.2
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• pp.37-54
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• 2004

IPNs have interpenetrating motion and phase separation behavior of independent polymers, respectively, and also these are affected by the physical interaction of polymer components. First of all, 2- and 3-component IPNs based on PU are prepared by combination with two or three components of PU, PMMA, PS and epoxy resin. And then the entire physical properties concerning morphological and mechanical behaviors of these IPNs are measured by employing FT-IR, SEM, Rheovibron, and DSC, etc. Compared with pure component, Tg's of IPN are shifted to higher temperature in all IPN kinds, and these are considered in attribution to internal movement of glass transition temperature or partial phenomenon of interpenetration. Rheovibron measurement results in a broader distribution with peaks of tan${\delta}$ or E", and this morphologically represents a medium degree of partially mixed IPNs in confirmation of SEM photographs.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.186-188
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• 1988

Relaxation spectra of the linear dielectric constants $\varepsilon=\varepsilon'-j{\varepsilon}"$ have been measured as functions of temperature and frequency for alternating copolymers of vinylidene cyanide (VDCN/VAc, VDCN/VPr, VDCN/VBz and VDCN/St) It is found that the linear dielectric constants e show characteristics of the temperature dependence that the real part have a large peak related to the glass transition point(Tg), and of the frequency dependence that the real port increases with decreasing frequency and the imaginary part increases largely in low frequency range. These phenomena mean Debye-type relaxation due to the micro-Brownian moi ions of non-crystalline seqments.

• Advances in materials Research
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• v.9 no.4
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• pp.311-321
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• 2020

In this study, Mangifera Indica tree sawdust reinforced bisphenol-A aniline based benzoxazine composites were prepared by varying the sawdust from 20 wt% to 45 wt%. Thermogravimetric analysis of composites revealed excellent compatibility between polybenzoxazine and sawdust from the remarkable growth in char yield from 22% (neat resin) to 36% (for highly filled) and glass transition temperature from 151 to 165℃. Ultimate weight loss of the composites evaluated from the Derivatives of TG plots. Limiting oxygen index values of the composites reported considerable growth i.e.,from 28 to 32 along with the increase in filler content. Differential scanning calorimetry results showed that sawdust particles have an insignificant effect on curing temperature (219℃) for the raise in sawdust content. Structure of the sawdust, benzoxazine monomer, polybenzoxazine and composites were studied using Fourier transformation infrared spectroscopy. Overall, polybenzoxazine composites with sawdust as filler showed improved thermal properties when compared with pure polybenzoxazine.