• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.525-531
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• 1998

A series of $LiNbO_3$ single crystals were grown by the Czochralski method from a congruent melt, a congruent melt with 0.05 mol% $Fe_2O_3$, a congruent melt with 6 wt.% $K_2O$ and a congruent melt with 6 wt.% $K_2O$ and 0.05 mol% $Fe_2O_3$ respectively. The growth of $LiNbO_3$ crystal from a congruent melt 6 wt.% $K_2O$ leads to nearly stoichiometric specimens. This is established by studying the following properties; XRD patterns, temperature dependences of the phase transition temperature, energy of the fundamental absorption edge, the shape of the absorption band of the $OH^-$vibration and linewidths of the ESR of $Fe_{Li}^{3+}$.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.843-846
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• 1992

This thesis was investigated on optical-and ion-induced characteristics in positive(a-$Se_{75}Ge_{25}$) and negative (Ag/a-$Se_{75}Ge_{25}$) resists for focused-ion-beam microlithogaphy. The a-$Se_{75}Ge_{25}$ inorganic thin film shows an increase in optical absorption after exposure to$\sim$$10^{16}$ dose(ions/$cm^{2}$) of Ga ions. The observed shift in the absorption edge toward longer wavelengths is consistent with that in films exposed to band-gap photons ($\sim$$10^{20}$ photons/$cm^{2}$). But, ion induced shift is twice as much as that in film exposed to optical radiation. This result may be related with microstructural rearrangements with in the short range of SeGe network. Due to changes in the short range order, the chemical bonding may be affected, which results in increased chemical dissolution in ion-induced film. Also, this resist exhibits good thermal stability because of its high Tg(~220$^{\circ}C$). The composition of deposited film measured by AES is consistent with that of bulk.

• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.1-4
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• 2016

We investigated the relation between the Cu-O bond length and the superconducting properties of $BaSnO_3$ (BSO)-added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films by using extended x-ray absorption fine structure (EXAFS) spectroscopy. 4 wt.% $BaSnO_3$ (BSO) added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films with varying thickness from $0.2{\mu}m$ to $1.0{\mu}m$ were fabricated by using pulsed laser deposition (PLD) method. The transition temperature ($T_c$) and the residual resistance ratio (RRR) of the GdBCO films increased with increasing thickness up to $0.8{\mu}m$, where the crystalline BSO has the highest peak intensity, and then decreased. This uncommon behaviors of $T_c$ and RRR are likely to be created by the addition of BSO, which may change the ordering of GdBCO atomic bonds. Analysis from the Cu K-edge EXAFS spectroscopy showed an interesting thickness dependence of ordering behavior of BSO-added GdBCO films. It is noticeable that the ordering of Cu-O bond and the transition temperature are found to show opposite behaviors in the thickness dependence. Based on these results, the growth of BSO seemingly have evident effect on the alteration of the local structure of GdBCO film.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.795-800
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• 2002

Yb:$YCa_4O(BO_3)_3$ (Yb:YCOB) single crystal, in which the concentration of $Yb^{3+}$ ion 20 at%, was grown by the Czocharalski method using an iridium crucible under N2 atmosphere. The optimum growth parameters to get a high quality of single crystals were found to be 1.5∼2 mm/h of pulling rate and 10∼20 rpm of rotation rate. According to the results of spectroscopic properties, absorption edge of Yb:YCOB was 236 nm. Two strong absorption line due to $Yb^{3+}$ ions were observed at 900 and 975 nm. Thermal expansion coefficients of Yb:YCOB crystal along a, b and c crystallographic axes from 320 to 650 K were 12.1${\times}10^{-6}$/K, 5.9${\times}10^{-6}$/K, 12.9${\times}10^{-6}$/K, respectively. Specific heat was 0.162 $cal/g{\cdot}K$ at 330 K.

• Journal of Microbiology and Biotechnology
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• v.26 no.12
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• pp.2116-2126
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• 2016

Bacterial biofilms are spatially structured communities that contain bacterial cells with a wide range of physiological states. The spatial distribution and speciation of copper in unsaturated Pseudomonas putida CZ1 biofilms that accumulated 147.0 mg copper per g dry weight were determined by transmission electron microscopy coupled with energy dispersive X-ray analysis, and micro-X-ray fluorescence microscopy coupled with micro-X-ray absorption near edge structure (micro-XANES) analysis. It was found that copper was mainly precipitated in a $75{\mu}m$ thick layer as copper phosphate in the middle of the biofilm, while there were two living cell layers in the air-biofilm and biofilm-medium interfaces, respectively, distinguished from the copper precipitation layer by two interfaces. The X-ray absorption fine structure analysis of biofilm revealed that species resembling $Cu_3(PO_4)_2$ predominated in biofilm, followed by Cu-Citrate- and Cu-Glutathione-like species. Further analysis by micro-XANES revealed that 94.4% of copper were $Cu_3(PO_4)_2$-like species in the layer next to the air interface, whereas the copper species of the layer next to the medium interface were composed by 75.4% $Cu_3(PO_4)_2$, 10.9% Cu-Citrate-like species, and 11.2% Cu-Glutathione-like species. Thereby, it was suggested that copper was initially acquired by cells in the biofilm-air interface as a citrate complex, and then transported out and bound by out membranes of cells, released from the copper-bound membranes, and finally precipitated with phosphate in the extracellular matrix of the biofilm. These results revealed a clear spatial pattern of copper precipitation in unsaturated biofilm, which was responsible for the high copper tolerance and accumulation of the biofilm.

• Korean Journal of Optics and Photonics
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• v.7 no.2
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• pp.129-135
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• 1996

We observed the absorptive optical bistability in the single layer amorphous $As_2S_3$ thin film which has an isolated electron pairs at roomtemperature, for the frist time, $Ar^+$ laser beam (λ=514.5 nm) was used as a light source and was focused by thin lens. The experiment was performed in cavityless system and the occurrence of optical bistability in this material could be explained by the temperature-dependent absorption coefficient of the sample. Also, this effect was explained by the reversible shift of the absorption edge in this material. The condition of optical bistability is determined by detuning value ($a_0L$) and this value was 0.12 when thikness of that sample was about 0.8 ${\mu}{\textrm}{m}$. The switching was observed clealy when light intensity is 150~180 mW and the swiching time was about $10^{-4}$ s.

• Korean Journal of Materials Research
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• v.12 no.4
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• pp.296-303
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• 2002

For potential application to quantum mechanical devices, nano-composite thin films, consisting of GaAs quantum dots dispersed in SiO$_2$ glass matrix, were fabricated and studied in terms of structural, chemical, and optical properties. In order to form crystalline GaAs quantum dots at room temperature, uniformly dispersed in $SiO_2$matrix, the composite films were made to consist of alternating layers of GaAs and $SiO_2$in the manner of a superlattice using RF magnetron sputter deposition. Among different film samples, nominal thickness of an individual GaAs layer was varied with a total GaAs volume fraction fixed. From images of High Resolution Transmission Electron Microscopy (HRTEM), the formation of GaAs quantum dots on SiO$_2$was shown to depend on GaAs nominal thickness. GaAs deposits were crystalline and GaAs compound-like chemically according to HRTEM and XPS analysis, respectively. From measurement of optical absorbance using a spectrophotometer, absorption edges were determined and compared among composite films of varying GaAs nominal thicknesses. A progressively larger shift of absorption edge was noticed toward a blue wavelength with decreasing GaAs nominal thickness, i.e. quantum dots size. Band gaps of the composite films were also determined from Tauc plots as well as from PL measurements, displaying a linear decrease with increasing GaAs nominal thickness.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.264-265
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• 2014

This Paper reports the photocatalytic activity of $g-C_3N_4/NaTaO_3$ hybrid composite photocatalysts synthesized by ball-mill method. The $g-C_3N_4$ and $NaTaO_3$ were individually prepared by Solid state reaction and microwave hydrothermal process, respectively. The $g-C_3N_4/NaTaO_3$ composite showed the enhanced photocatalytic activity for degradation of rhodamine B dye (Rh. B) under simulated solar light irradiation. The results revealed that the band-gap energy absorption edge of hybrid composite samples was shifted to a longer wavelength as compared to $NaTaO_3$ and the 50 wt% $g-C_3N_4/NaTaO_3$ hybrid composite exhibited the highest percentage (99.6 %) of degradation of Rh. B and the highest reaction rate constant ($0.013min^{-1}$) in 4 h which could be attributed to the enhanced absorption of the hybrid composite photocatalyst in the UV-Vis region. Hence, these results suggest that the $g-C_3N_4/NaTaO_3$ hybrid composite exhibits enhanced photocatalytic activity for the degradation of rhodamine B under simulated solar light irradiation in comparison to the commercial $NaTaO_3$.

• Journal of Plant Biology
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• v.4 no.2
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• pp.51-61
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• 1961

In order to detect the way of absorption and metaboism of the urea it is sprayed on the surface of the leaves of sunflower. The sunflowers used in this study are grown in different conditions such that the one in nittogen aboundant and the other in nitrogen deficient soil, respectively. The urea-N, ammonia-N, amide-N, and 80% alcohol soluble-N in the leaves were quantitatively determined. All of the nitrogenous components measured are generally tended to increased with rising the concentration of urea except only amide-N at 24 hours after sprayed, and these were highly significances. It seemed that hydrolizing of urea into ammonia and carbon dixide and the assimilation of ammonia into other organic nitrogenous constituents were rapid in the young leaves than in the mature. It is interest that the amide content, in the young leaves and nitrogen defieient one were enhanced with the increasing concentration of urea, although in the mature leaves it did not show any change in the urea treatment. It is presumed that the assimilation rate of ammonia and the urease activity were lower in the matture leaves than in the young and nitrogen deficient leaves. No significance at 5% level showed all of the nitrogenous components except total nitrogen between nitrogen abundant and deficent leaves. Urea content was a high peak at first 12 hours, ammonia at 48 hours, and amide and alcohol soluble nitrogen at 96 hours, whence decrease4d the content of these constituents gradually. The total nitrogen content is not incrased obviously by only one time of urea spray in this study. When the concentration of urea was relatively high there appeared the wilting spots on t도 edge of leaves. As a whole, it seemed that sprayed urea was rapidly absorbed and taken part in nitrogen metabolism within relatively short period.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.1
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• pp.1-10
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• 1995

Congruent $LiNbO_3$ single crystals and $LiNbO_3$ : Mg single crystals, having high resistance to optical damage, doped with MgO to the levels of 2.0, 5.0 and 7.0 mol% were grown successfully by CZ method and optical damage of each crystal was measured by compen. sation method. With doping level reaching about 5 mol%, there was an abrupt change in the features of optical absorption edge and $OH^-$ absorption band. From these data, we confirmed indirectly the threshold in MgO doping level. When the MgO doping amount reaches about 5 mol% in the melt, $Mg^{2+}$ occupies Nb site and becomes $Mg_{Nb}^{2+}$, resulting in the sharp increase of optical damage resistance. The optical damage resistance of $LiNbO_3$ : Mg was improved more than three times when MgO amount in the melt reaches 5 mol%.