• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.327-327
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• 2009

ZnO with a large band gap (~3.37 eV) and exciton binding energy (~60 meV), is suitable for optoelectronic applications such as ultraviolet (UV) light emitting diodes (LEDs) and detectors. However, the ZnO-based p-n homojunction is not readily available because it is difficult to fabricate reproducible p-type ZnO with high hall concentration and mobility. In order to solve this problem, there have been numerous attempts to develop p-n heterojunction LEDs with ZnO as the n-type layer. The n-ZnO/p-GaN heterostructure is a good candidate for ZnO-based heterojunction LEDs because of their similar physical properties and the reproducible availability of p-type GaN. Especially, the reduced lattice mismatch (~1.8 %) and similar crystal structure result in the advantage of acquiring high performance LED devices. In particular, a number of ZnO films show UV band-edge emission with visible deep-level emission, which is originated from point defects such as oxygen vacancy, oxygen interstitial, zinc interstitial[1]. Thus, defect-related peak positions can be controlled by variation of growth or annealing conditions. In this work, the undoped ZnO film was grown on the p-GaN:Mg film using RF magnetron sputtering method. The undoped ZnO/p-GaN:Mg heterojunctions were annealed in a horizontal tube furnace. The annealing process was performed at $800^{\circ}C$ during 30 to 90 min in air ambient to observe the variation of the defect states in the ZnO film. Photoluminescence measurements were performed in order to confirm the deep-level position of the ZnO film. As a result, the deep-level emission showed orange-red color in the as-deposited film, while the defect-related peak positions of annealed films were shifted to greenish side as increasing annealing time. Furthermore, the electrical resistivity of the ZnO film was decreased after annealing process. The I-V characteristic of the LEDs showed nonlinear and rectifying behavior. The room-temperature electroluminescence (EL) was observed under forward bias. The EL showed a weak white and strong yellowish emission colors (~575 nm) in the undoped ZnO/p-GaN:Mg heterojunctions before and after annealing process, respectively.

• Proceedings of the Zoological Society Korea Conference
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• 1998.10b
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• pp.113-113
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• 1998

In Saccharomyces cerevisiae UV irradiation and a variety of chemical DNA -damaging agents induce the transcription of specific genes, including several involved in DNA repair. One of the best characterized of DNA -damage inducible genes is PHRI, which encodes the apoenzyme for DNA photolyase. Basal-level and damage-induced expression of PHRI require an upstream activation sequence, UASPHRI. Here we report the identification of the UlvIE6 gene of S. cerevisiae as a regulator of UASPHRl activity. Surprisingly, the effect of deletion of UME6 is growth phase dependent. In wild-type cells PHRI is induced in late exponential phase, concomitant with the initiation of glycogen accumulation that precedes the diauxic shift. Deletion of UNIE6 abolishes this induction, decreases the steady-state concentration of photolyase molecules and PHRI mRNA, and increases the UV sensitivity of a rad2 mutant. The results suggest that UM E6 contributes to the regulated expression of a subset of damage-responsive genes in yeast. Furthermore, the upstream repression sequence, URSPHRI, is required for repression and damage-induced expression of PHRl. Here we show identification of YER169W and YDR096W as putative regulators acting through $URS_{PHRI}$. These open reading frames were designated as RPHI (YERl69W) and RPH2 (YDR096W) indicating regulator of PHRI. Simultaneous disruption of both genes showed a synergistic effect, producing a four-fold increase in basal level expression and a similar decrease m the induction ratio following treatment of methyl methanesulfonate(MMS). Mutation of the sequence ($AG_4$) bound by Rphlp rendered the promoter of PHRI insensitive to changes in RPHI or RPH2 status. The data suggest that RPHI and RPH2 act as damage-responsive negative regulators of PHRI. Surprisingly, the sequence bound by Rphlp in vitro is found to be $AG_4$ which is identical to the consensus binding site for the regulators Msn2p and Msn4p involved in stress-induced expression. Deletion of MSN2 and MSN4 has little effect on the induction$.$ ratio following DNA damage. However, all deletions led to a significant decrease in basal-level and induced expression of PHRI. These results imply that MSN2 and MSN4 are positive regulators of P HRI but are not required for DNA damage repression. [Supported by grant from NIH]om NIH]

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.2
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• pp.57-62
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• 2018

In this study, we investigated the impurity effect of $Ga_2O_3$ doped thin film by simple doping method using Mg acetate solution. Both undoped $Ga_2O_3$ thin films and Mg-doped $Ga_2O_3$ thin films were grown on Si substrates at 600 and $900^{\circ}C$ for 30 minutes by means of a customized MOCVD method. As a result of the surface analysis, there were no obvious morphological differences by Mg impurity implantation. The surface of the thin film grown at $900^{\circ}C$ was rougher than those grown at $600^{\circ}C$ and polycrystallization was achieved. As a result of the optical property analysis, in the case of the doped sample, the overall emission peak was red shifted and the UV radiation intensity was increased. As a result of the I-V curve, the leakage current of the $600^{\circ}C$ growth thin film decreased by the Mg impurity and the photocurrent of the growth thin film of $900^{\circ}C$ increased.

• Journal of the Korean Society of Food Science and Nutrition
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• v.44 no.7
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• pp.1090-1099
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• 2015

Among the four different parts of mulberry (Morus alba L.) tree, ethanol extract of Morus root bark showed the highest ${\alpha}$-glucosidase inhibitory activity ($IC_{50}=12.01{\mu}g/mL$). Bioassay-guided fractionation of the ethanolic extract of root bark by Diaion HP-20, silica gel, ODS-A, and Sephadex LH-20 column chromatographies led to the isolation of four compounds, including Compound (Comp.) 1 ($IC_{50}=5.22{\mu}g/mL$), Comp. 2 ($IC_{50}=1.78{\mu}g/mL$), Comp. 3 ($IC_{50}=2.94{\mu}g/mL$), and Comp. 4 ($IC_{50}=1.54{\mu}g/mL$) with strong ${\alpha}$-glucosidase inhibitory activities. Their chemical structures were elucidated as morusin (Comp. 1), kuwanon H (Comp. 2), chalcomoracin A (Comp. 3), and chalcomoracin B (Comp. 4) by UV and NMR spectral analyses. These results suggest that prenylflavonoid and mulberrofuran of Morus root bark may be useful as potential therapeutic agents for diabetes.

• Korean Chemical Engineering Research
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• v.44 no.6
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• pp.609-613
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• 2006

Ba2-xSrxSiO4:Eu2+ phosphor particles with the high photoluminescence (PL) intensity under long wavelength ultraviolet (UV) were prepared by spray pyrolysis. The photoluminescence, morphological and crystalline characteristics of $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles prepared by spray pyrolysis were investigated. $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles prepared by spray pyrolysis had various colors from bluish green to yellow by changing the ratio of barium and strontium of the host material. In case of x=0, the main emission peak of $Ba_2SiO_4:Eu^{2+}$ phosphor was 500 nm. In case of x=2, the main emission peak of $Sr_2SiO_4:Eu^{2+}$ phosphor was 554nm. $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles obtained by spray pyrolysis had spherical shape and hollow structure. On the other hand, the post-treated $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles had large size and irregular shape. The $Ba_{1.488}Sr_{0.5}SiO_4:Eu_{0.012}{^{2+}}$ phosphor particles had the maximum PL intensity after post-treatment at temperature of $1300^{\circ}C$ for 3h under reduction atmosphere.

• Korean Journal of Materials Research
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• v.12 no.7
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• pp.555-559
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• 2002

Blue-emitting $Sr_{10}$($PO$)$_{6}$ $Cl_2$:$Eu^{2+}$ and $_{(Sr,Mg) }$ 10/($PO_4$)$_{6}$ $Cl_2$:$Eu^{2+}$ phosphor particles for application of long-wavelength UV LED were prepared by ultrasonic spray pyrolysis. The luminescence characteristics under long- wave-length ultraviolet of the $Sr_{10}$ ($PO_4$)$_{6}$ $Cl_2$:$Eu^{2+}$ and (Sr,Mg)$_{10}$ ($PO_4$)$_{6}$ $Cl_2$:$^Eu{2+}$ phosphor particles prepared by the spray pyrolysis were compared with that of the commercial product. The PL intensity of the $Sr_{10}$ ($PO_4$)$_{6}$ $Cl_2$:$Eu^{2+}$ particles prepared by the spray pyrolysis was lower than that of the commercial $Sr_{10}$ ($PO_4$)$_{6}$ $Cl_2$:$Eu^{2+}$ particles because prepared $Sr_{10}$ ($PO_4$)$_{6}$ $Cl_2$:$Eu^{2+}$ phosphor particles had porous structure and hollow morphology. However, the PL intensity of the (Sr,Mg)$_{10}$($PO_4$)$_{6}$ $Cl_2$:$Eu^{2+}$ phosphor particles prepared by the spray pyrolysis was 8% higher than that of the commercial one. The high brightness of $(Sr,Mg)_{10}$ ($PO_4$)$_{6}$ $Cl_2$:Eu$^{2+}$ phosphor particles prepared by spray pyrolysis is due to the dense structure and high crystallinity of particles. The TEX>$(Sr,Mg)<_{10}$ ($PO_4$)$_{6}$ /$Cl_2$:$Eu^{ 2+}$ phosphor particles had main emission peak t 448 nm under long- wavelength ultraviolet.

• Korean Journal of Materials Research
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• v.24 no.10
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• pp.556-564
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• 2014

To synthesize a high-performance photocatalyst, N doped $TiO_2$ nanotubes deposited with Ag nanoparticles were synthesized, and surface characteristics, electrochemical behaviors, and photocatalytic activity were investigated. The $TiO_2$ nanotubular photocatalyst was fabricated by anodization; the Ag nanoparticles on the $TiO_2$ nanotubes were synthesized by a reduction reaction in $AgNO_3$ solution under UV irradiation. The XPS results of the N doped $TiO_2$ nanotubes showed that the incorporated nitrogen ions were located in interstitial sites of the $TiO_2$ crystal structure. The N doped titania nanotubes exhibited a high dye degradation rate, which is effectively attributable to the increase of visible light absorption due to interstitial nitrogen ions in the crystalline $TiO_2$ structure. Moreover, the precipitated Ag particles on the titania nanotubes led to a decrease in the rate of electron-hole recombination; the photocurrent of this electrode was higher than that of the pure titania electrode. From electrochemical and dye degradation results, the photocurrent and photocatalytic efficiency were found to have been significantly affected by N doping and the deposition of Ag particles.

• Korean Journal of Materials Research
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• v.24 no.10
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• pp.543-549
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• 2014

A zinc oxide (ZnO) hybrid structure was successfully fabricated on a glass substrate by metal organic chemical vapor deposition (MOCVD). In-situ growth of a multi-dimensional ZnO hybrid structure was achieved by adjusting the growth temperature to determine the morphologies of either film or nanorods without any catalysts such as Au, Cu, Co, or Sn. The ZnO hybrid structure was composed of one-dimensional (1D) nanorods grown continuously on the two-dimensional (2D) ZnO film. The ZnO film of 2D mode was grown at a relatively low temperature, whereas the ZnO nanorods of 1D mode were grown at a higher temperature. The change of the morphologies of these materials led to improvements of the electrical and optical properties. The ZnO hybrid structure was characterized using various analytical tools. Scanning electron microscopy (SEM) was used to determine the surface morphology of the nanorods, which had grown well on the thin film. The structural characteristics of the polycrystalline ZnO hybrid grown on amorphous glass substrate were investigated by X-ray diffraction (XRD). Hall-effect measurement and a four-point probe were used to characterize the electrical properties. The hybrid structure was shown to be very effective at improving the electrical and the optical properties, decreasing the sheet resistance and the reflectance, and increasing the transmittance via refractive index (RI) engineering. The ZnO hybrid structure grown by MOCVD is very promising for opto-electronic devices as Photoconductive UV Detectors, anti-reflection coatings (ARC), and transparent conductive oxides (TCO).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.8
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• pp.651-654
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• 2010

This paper describes the thermal and mechanical properties of doped thin film 3C-SiC and porous 3C-SiC. In this work, the in-situ doped thin film 3C-SiC was deposited by using atmospheric pressure chemical vapor deposition (APCVD) method at $120^{\circ}C$ using single-precursor hexamethyildisilane: $Si_2(CH_3)_6$ (HMDS) as Si and C precursors. 0~40 sccm $N_2$ gas was used as doping source. After growing of doped thin film 3C-SiC, porous structure was achieved by anodization process with 380 nm UV-LED. Anodization time and current density were fixed at 60 sec and 7.1 mA/$cm^2$, respectively. The thermal and mechanical properties of the $N_2$ doped porous 3C-SiC was measured by temperature coefficient of resistance (TCR) and nano-indentation, respectively. In the case of 0 sccm, the variations of TCR of thin film and porous 3C-SiC are similar, but TCR conversely changed with increase of $N_2$ flow rate. Maximum young's modulus and hardness of porous 3C-SiC films were measured to be 276 GPa and 32 Gpa at 0 sccm $N_2$, respectively.

• Journal of the Korean Chemical Society
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• v.56 no.1
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• pp.92-101
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• 2012

The degradation of one of the commercially important hydrogel based on acrylic acid and acryl amide, (acrylic acid-co-acryl amide) hydrogels, by means of ultrasound irradiation and its combination with heterogeneous ($TiO_2$) was investigated. 24 kHz of ultrasound irradiation was provided by a sonicator, while an ultraviolet source of 16 W was used for UV irradiation. The extent of sonolytic degradation increased with increasing ultrasound power (in the range 30-80 W). $TiO_2$ sonophotocatalysis led to complete (acrylic acid-co-acryl amide) hydrogels degradation with increasing catalyst loading, while, the presence of $TiO_2$ in the dark generally had little effect on degradation. Therefore, emphasis was totally on the sonolytic and sonophotocatalytic degradation of hydrogels and a synergy effect was calculated for combined degradation procedures (Ultrasound and Ultraviolet) in the presence of $TiO_2$ nanoparticles. $TiO_2$ sonophotocatalysis was always faster than the respective individual processes due to the enhanced formation of reactive radicals as well as the possible ultrasound-induced increase of the active surface area of the catalyst. A kinetics model based on viscosity data was used for estimation of degradation rate constants at different conditions and a negative order for the dependence of the reaction rate on total molar concentration of (acrylic acid-co-acryl amide) hydrogels solution within the degradation process was suggested.