• Journal of the Mineralogical Society of Korea
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• v.28 no.1
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• pp.9-16
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• 2015

A mineralogical analysis on the factors affecting the luster of pearls was carried out using gravity measurement, optical microscope observation, X-ray diffraction analysis, and scanning electron microscopy. We divided the seawater cultured pearls from Tongyeong into the following four types based on luster and shape; good luster and round (LR), lackluster and round (LLR), lackluster and baroque (LLB), and lackluster and two nucleus (LTN) pearls. Pearls with high-quality luster had slightly lower specific gravity as compared to pearls with low-quality luster, but both these types of pearls are within the specific gravity range of commercial pearls. Regarding the cross-sectional thickness of the mother-of-pearl layer, LR pearls showed a uniform thickness of about 0.3 mm in average. On the other hand, LLR pearls were characterized by relatively thinner, but uniform thickness. LTN and LLB pearls showed a tendency of significantly large variation in thickness even within a single pearl. For the surface of pearls, pearls with high-quality luster showed narrower and clearer growth lines of aragonite crystals as compared to pearls with low-quality luster. Pearls with high-quality luster were characterized by fewer aragonite crystal lattice defects as compared to pearls with low-quality luster, and the former showed parallel arrangement, thinner thickness, and less difference in thickness on the surface and inside. If a pearl has a prismatic layer, it is composed of aragonite with calcite in the prismatic and nacreous layer, and calcite content is very high in the lackluster pearl. Pearls without a prismatic layer were devoid of calcite irrespective of their quality of luster, and were composed of aragonite.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.3
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• pp.363-378
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• 2005

Statement of problem. Hydroxyapatite(HA) coated titanium surfaces have not yet showed the reliable osseointegration in various conditions. Purpose. This study was aimed to investigate microstructures, chemical composition, and surface roughness of the surface coated by the hydrothermal method and to evaluate the effect of hydrothermal coating on the cell attachment, as well as cell proliferation. Material and Methods. Commercially pure(c.p.) titanium discs were used as substrates. The HA coating on c.p. titanium discs by hydrothermal method was performed in 0.12M HCl solution mixed with HA(group I) and 0.1M NaOH solution mixed with HA(group II). GroupⅠ was heated at 180 $^{\circ}C$ for 24, 48, and 72 hours. GroupⅡ was heated at 180 $^{\circ}C$ for 12, 24, and 36 hours. And the treated surfaces were evaluated by Scanning electron microscopy(SEM), Energy dispersive X-ray spectroscopy(EDS), X-ray photoelectron spectroscopy(XPS), X-ray diffraction method(XRD), Confocal laser scanning microscopy(CLSM). And SEM of fibroblast and 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide(MTT) assay were used for cellular responses of the treated surfaces. Results. The color of surface changed in both groups after the hydrothermal process. SEM images showed that coating pattern was homogeneous in group II, while inhomogeneous in group I. H72 had rosette-like precipitates. The crystalline structure grew gradually in group II, according to extending treatment period. The long needle-like crystals were prominent in N36. Calcium(Ca) and phosphorus(P) were not detected in H24 and H48 in EDS. In all specimens of group II and H72, Ca was found. Ca and P were identified in all treated groups through the analysis of XPS, but they were amorphous. Surface roughness did not increase in both groups after hydrothermal treatment. The values of surface roughness were not significantly different between groups I and II. According to the SEM images of fibroblasts, cell attachments were oriented and spread well in both treated groups, while they were not in the control group. However, no substantial amount of difference was found between groups I and II. Conclusions. In this study during the hydrothermal process procedure, coating characteristics, including the HA precipitates, crystal growth, and crystalline phases, were more satisfactory in NaOH treated group than in HCl treated group. Still, the biological responses of the modified surface by this method were not fully understood for the two tested groups did not differ significantly. Therefore, more continuous research on the relationship between the surface features and cellular responses seems to be in need.

• Korean Journal of Materials Research
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• v.20 no.6
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• pp.289-293
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• 2010

Silicon quantum dots (Si QDs) in a superlattice for high efficiency tandem solar cells were fabricated by magnetron rf sputtering and their characteristics were investigated. SiC/$Si_{1-x}C_x$ superlattices were deposited by co-sputtering of Si and C targets and annealed at $1000^{\circ}C$ for 20 minutes in a nitrogen atmosphere. The Si QDs in Si-rich layers were verified by transmission electron microscopy (TEM) and X-ray diffraction. The size of the QDs was observed to be 3-6 nm through high resolution TEM. Some crystal Si and -SiC peaks were clearly observed in the grazing incident X-ray diffractogram. Raman spectroscopy in the annealed sample showed a sharp peak at $516\;cm^{-1}$ which is an indication of Si QDs. Based on the Raman shift the size of the QD was estimated to be 4-6 nm. The volume fraction of Si crystals was calculated to be about 33%. The change of the FT-IR absorption spectrum from a Gaussian shape to a Lorentzian shape also confirmed the phase transition from an amorphous phase before annealing to a crystalline phase after annealing. The optical absorption coefficient also decreased, but the optical band gap increased from 1.5 eV to 2.1 eV after annealing. Therefore, it is expected that the optical energy gap of the QDs can be controlled with growth and annealing conditions.

• 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 Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.249-249
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• 2009

We have grown large area BSTO($(Ba_{1-x}Sr_x)TiO_3$) thin films (x=0.4) on 2 inch diameter MgO (001) single crystal substrates using a pulse laser deposition(PLD) system. Substrate temperature and oxygen pressure in the deposition chamber, and the laser optics for ablating a target have been controlled to obtain the uniform thickness and preferred orientation of the films. Results of x-ray diffraction and rocking curve analysis revealed that the BSTO films were grown on MgO substrates with a preferred orientation (002), and the full width half maximum of the rocking curve was measured to be 0.86 degree at optimum condition. Roughness of the films have been measured to be $3.42{\AA}$ rms by using atomic force microscopy. We have successfully deposited the large area BSTO thin films of $4000{\AA}$ thickness on 50 mm diameter MgO substrates.

• Economic and Environmental Geology
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• v.45 no.5
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• pp.535-549
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• 2012

Main aspect of this study are to clarify mineral compositions on granites in Youngkwang-Naju area. These granites are is divided into four rock facies based on the geologic ages, mineralogical composition and chemical constituents, and texture : hornblende-biotite granodiorite, biotite granite, porphyritic granite and two mica granite. These granites constitude an igneous complex formed by a series of differentiation from cogenetic magma. In compressive stress field between the Ogcheon folded belt and the Youngnam massif, the foliated and undeformed granites had formed owing to heterogeneous distribution of stress. The geochemical data of study area indicate magma of these rocks would had been generated by melting in lower and middle crust. The major minerals of granitic rocks in study area are plagioclase, biotite, muscovite and hornblende. Plagioclase range in composition from oligoclase ($An_{19.3-27.7}$) to andesine ($An_{28.4-31}$), and shows normal zoning patterns, This uniformed composition indicated slow crystallization, and it is obvious that the growth of these crystal occurred before final consolidation of the magma. The Mg content of biotite are increases with increasing of $f_{O2}$ and grade of differentiation, changing from phlogopite to siderophyllite. Its $Al^{iv}$/$Al^{total}$ ratios are propertional to bulk rock alumina content. Muscovite is primary in origin with high content of $TiO_2$, and Its composition correspond to celadonitic muscovite. Hornblende indicated calc amphibole group ($(Ca+Na)_{M4}{\geq}1.43$, $Na_{M4}<0.67$). and consolidation pressure of granitic body by geobarometer of Hammerstrume and Zen show 11.3~17.2 Km.

• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.105-111
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• 1999

When the preparation method of iron silicide films possess the annealing process, the interfacial state of the films is not fine. The good quality films were obtained as the plasma was used without annealing processing. Since the injected precursors were various active species in the plasma state, the organic compound was contained in the prepared films. We confirmed the formation of Fe-Si bonds as well as the organic compound by Fe and Si vibration mode in Raman scattering spectrum at $250cm^{-1}$ and Ft-IR. Because of epitaxy growth being progressed by the high energy of plasma at the low temperature of substrate, iron silicide was epitaxially grown to ${\beta}$-phase that had lattice structure such as [220]/[202] and [115]. Band gap of the prepared films had value of 1.182~1.174 eV and optical gap energy was shown value of 3.4~3.7 eV. The Urbach tail and the sub-band-gap absorptions were appeared by organic compound in films. We knew that the prepared films by plasma were obtained a good quality films because of being grown single crystal.

• Korean Journal of Materials Research
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• v.4 no.1
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• pp.37-43
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• 1994

Y-Ra-Cu-0 oxide superconductors were fabricated by the sinter-forging method to make the critical current density improve through controlling of microstructure and crystal texture. The grain alignment of oxide superconductor was formed by the sinter-forging process and it's c-axis orientation was parallel to the press direction.The orientation factor of texture increased with sinking temperature and pressure, and also grain alignment was improved by the addition of Ag. As for the sinterforged Y-Ba-Cu-O/Ag sample, the $T_c$(on-set) was not almost varied with the sinter-forging temperature, but $T_c\;^{zero}$ decreased more or less at high sinter-forging temperatures. In addition, it was observed that added-Ag was mainly distributed along the grain boundar~es in the (123) matrix, resulting in the densification of microstructure. From these results, i t was thought that the improvement of $J_c$ over 2000A/$\textrm{cm}^2$ was attributed to the texture, densification of microstructure, and (123) grain growth due to the Ag addition.

• Korean Journal of Materials Research
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• v.4 no.1
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• pp.81-89
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• 1994

Ti film of lOnm thickness and Co film of 18nm thickness were sequentially e-heam evaporated onto Si (100) substrates. Metal deposited samples were rapidly thermal-annt.aled(KTA) in thr N1 en vironment a t $900^{\circ}C$ for 20 sec. to induce the reversal of metal bilayer, so that $CoSi_{2}$ thin films could be formed. The sheet resistance measured by the 4-point probe was 3.9 $\Omega /\square$This valur was maintained with increase in annealing time upto 150 seconds, showing high thermal stab~lity. Thc XRII spectra idrn tified the silicide film formed on the Si substrate as a $CoSi_{2}$ epitaxial layer. The SKM microgr;iphs showed smooth surface, and the cross-sectional TKM pictures revealed that the layer formed on the Si substrate were composed of two Co-Ti-Si alloy layers and 70nm thick $CoSi_{2}$ epl-layer. The AES analysis indicated that the native oxide on Si subs~rate was removed by TI ar the beginning of the RTA, and Ihcn that Co diffused to clean surface of Si substrate so that epitaxial $CoSi_{2}$ film could bt, formed. In thc rasp of KTA at $700^{\circ}C$. 20sec. followed by $900^{\circ}C$, 20sec., the thin film showed lower sheet resistance, but rough surface and interface owing to $CoSi_{2}$ crystal growth. The application scheme of this $CoSi_{2}$ epilayer to VLSI devices and the thermodynarnic/kinetic mechan~sms of the $CoSi_{2}$ epi-layer formation through the reversal of Co/Ti bdayer were discussed.

• The Journal of the Petrological Society of Korea
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• v.8 no.2
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• pp.92-105
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• 1999

The Cretaceous Chaeyaksan basaltic rocks consist mainly of basaltic tuffs intercalating three layers of basalt. Stratigraphically, the rocks are located between the upper Songnaedong Formation and the lower Geoncheonri Formation and contain plagioclase, augite, hornblende, and a few olivine phenocrysts. Geochemically, they show calc-alkaline characteristics in some immobile element content, but show the alkaline suite feature in the mobile major element composition. The basalts are widely spilitized but some of them is altered to shoshonitic rocks with more calcic plagioclase, calcite, and chlorite, and adularia veinlets are common in the rocks. It is supposed that the post-eruption alteration of the rocks is done through alkali-replacement by hydrothermal solution or vapor rather than by low grade regional metamorphism. It is considered that A1 in hornblende will be available for estimating the pressure of the pre-eruption magma in the reservoir although the plagioclase of the rocks are highly albitized. The crystallization pressure was calculated as 5.7Kb by the equation of Johnson and Rutherford(l989) incorporating of the effect of overestimate of .41T in hornblende in the case of quartz-free rocks. Application of the estimated temperature, pressure and the constituent of phenocrysts of the rocks to the experimental P-T phase diagram for basalts established by Green(1982) indicates the crystallization course and succession of growth of the phenocrysts during of rising and cooling of the magma reservoir; augite + augite and olivine + augite, olivine, and hornblende -+ augite and hornblende+ augite, hornblende, and plagioclase. Such evolution course of the magma may include crystal fractionation by the phenocrysts crystallization and contamination by country rock in lower crust.