• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.4
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• pp.164-167
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• 2010

Bulk GaN single crystal with 1.5 mm thickness was successfully grown by hydride vapor phase epitaxy (HVPE) technique. Free-standing GaN substrates of $10{\times}10,\;15{\times}15$ mm size were fabricate after lift-off of sapphire substrate and their optical properties were characterized properties for device applications. X-ray diffraction patterns showed (002) and (004) peak, and the FWHM of the X-ray rocking curve (XRC) measurement in (002) was 98 arcsec. A sharp photoluminescence spectrum at 363 nm was observed and defect spectrum at visible range was not detected. The hexagonal-shaped etch-pits are formed on the GaN surface in $200^{\circ}C\;H_3PO_4$ at 5 minutes. The defect density calculated from observed etch-pits on surface was around $5{\times}10^6/cm^2$. This indicates that the fabricated GaN substrates can be used for applications in the field of optodevice, and high power electronics.

• The korean journal of orthodontics
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• v.25 no.2 s.49
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• pp.223-233
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• 1995

The purpose of this study was to evaluate the effects of surface conditioning with $10\%$ polyacrylic acid, etching with $38\%$ phosphoric acid, and polishing with a slurry of pumice on shear bond strengths of light-cured glass ionomer cement, chemically cured glass ionomer cement, and a composite resin to enamel, and to observe the failure patterns of bracket bondings. Shear bond strengths of glass ionomer cements were compared with that of a composite resin. Metal brackets were bonded on the extracted human bicuspids after enamel surface treatments, and samples were immersed in the $37^{\circ}C$ distilled water bath, and shear bond strengths of glass ionomer cements and a composite resin were measured on the Instron machine after 24hrs passed, and the deboned samples were measured in respect of adhesive remnant index. Scanning electron micrographs were taken of enamel surfaces after various treatments. The data were evaluated and tested by ANOVA and Duncan's multiple range test, and those results were as follows. 1. Shear bond strength of light-cured glass ionomer cement showed statistically higher than that of chemically cured glass ionomer cement. 2. Shear bond strengths of light-cured and chemically cured glass ionomer cements to enamel treated with $10\%$ polyacrylic acid and $38\%$ phosphoric acid showed statistically higher than those with a slurry of pumice. 3. According to scanning electron micrographs, enamel surface conditioned with $10\%$ polyacrylic acid is slightly etched and cleaned, that etched with $38\%$ phosphoric acid is severely etched, and that polished with a slurry of pumice is irregulary scretched and not completely cleaned. 4. After debonding, light-cured glass ionomer cement to enamel treated with $10\%$ polyacrylic acid showed less residual materials on the enamel solace than composite resin to enamel etched with $38\%$ phosphoric acid. 5. There was no significant difference in the shear bond strength of light-cured glass ionomer cement to enamel treated with $10\%$ polyacrylic acid and that of composite resin to enamel etched with $38\%$ Phosphoric acid.

• Restorative Dentistry and Endodontics
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• v.22 no.1
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• pp.1-33
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• 1997

The objective of this study was to analyze the in vitro and in vivo corrosion products of low and high copper amalgams. The four different types of amalgam alloy used in this study were Fine cut, Caulk spherical, Dispersalloy, and Tytin. After each amalgam alloy and Hg were triturated according to the directions of the manufacturer by means of the mechanical amalgamator(Amalgam mixer. Shinhung Co. Korea), the triturated mass was inserted into a cylindrical metal mold which was 12mm in diameter and 10mm in height. The mass was condensed by 150Kg/cm compressive force. The specimen was removed from the mold and aged at room temperature for about seven days. The standard surface preparation was routinely carried out by emery paper polishing under running water. In vitro amalgam specimens were potentiostatically polarized ten times in a normal saline solution at $37^{\circ}C$(potentiostat : HA-301. Hukuto Denko Corp. Japan). Each specimen was subjected to anodic polarization scan within the potential range -1700mV to+400mV(SCE). After corrosion tests, anodic polarization curves and corrosion potentials were obtained. The amount of component elements dissolved from amalgams into solution was measured three times by ICP AES(Inductive Coupled Plasma Atomic Emission Spectrometry: Plasma 40. Perkim Elmer Co. U.S.A.). The four different types of amalgam were filled in occlusal and buccal class I cavities of four human 3rd molars. After about five years the restorations were carefully removed after tooth extraction to preserve the structural details including the deteriorated margins. The occlusal surface, amalgam-tooth interface and the fractured surface of in vivo amalgam corrosion products were analyzed. In vivo and in vitro amalgam specimens were examined and analyzed metallographically by SEM(Scanning Electron Microscope: JSM 840. Jeol Co. Japan) and EDAX(Energy Dispersive Micro X-ray Analyser: JSM 840. Jeol Co. Japan). 1. The following results are obtained from in vitro corrosion tests. 1) Corrosion potentials of all amalgams became more noble after ten times passing through the in vitro corrosion test compared to first time. 2) After times through the test, released Cu concentration in saline solution was almost equal but highest in Fine cut. Ag and Hg ion concentration was highest in Caulk spherical and Sn was highest in Dispersalloy. 3) Analyses of surface corrosion products in vitro reveal the following results. a)The corroded surface of Caulk spherical has Na-Sn-Cl containing clusters of $5{\mu}m$ needle-like crystals and oval shapes of Sn-Cl phase, polyhedral Sn oxide phase. b)In Fine cut, there appeared to be a large Sn containing phase, surrounded by many Cu-Sn phases of $1{\mu}m$ granular shapes. c)Dispersalloy was covered by a thick reticular layer which contained Zn-Cl phase. d)In Tytin, a very thin, corroded layer had formed with irregularly growing Sn-Cl phases that looked like a stack of plates. 2. The following results are obtained by an analysis of in vivo amalgam corrosion products. 1) Occlusal surfaces of all amalgams were covered by thick amorphous layers containing Ca-P elements which were abraded by occlusal force. 2) In tooth-amalgam interface, Ca-P containing products were examined in all amalgams but were most clearly seen in low copper amalgams. 3) Sn oxide appeared as a polyhedral shape in internal space in Caulk spherical and Fine cut. 4) Apical pyramidal shaped Sn oxide and curved plate-like Sn-Cl phases resulted in Dispersalloy. 5) In Tytin, Sn oxide and Sn hydroxide were not seen but polyhedral Ag-Hg phase crystal appeared in internal space which assumed a ${\beta}_l$ phase.

• Korean Journal of Heritage: History & Science
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• v.53 no.4
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• pp.170-187
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• 2020

Dolmens bearing the burial layout and stone coffin tombs of the late Bronze Age were excavated from Samdeok-ri, Goseong, Gyeonsangnsamdo, and grave items such as red-burnished pottery, arrowheads, and stone swords were also discovered. In the case of the red-burnished pottery that was found, it retains a pigment layer with a thickness of about 50 to 160㎛, but with most of the other items, exfoliation and peeling-off of pigment layers can be observed on the surface. The raw materials of the red-burnished pottery contained moderately sorted minerals such as quartz, feldspar, and hornblende, and partly opaque iron oxide minerals were also identified. In particular, the raw materials of the red-burnished pottery from stone coffin tomb #6 were different from those of the other pottery, containing large amounts of hornblende and feldspar. The pottery's red pigment was identified as hematite and showed similar mineral content of raw materials such as fine grained quartz, feldspar, and hornblende. The firing temperature is estimated to have been approximately 900℃, based on their mineral phase. The possibility exists that the raw materials had been collected from the Samdeok-ri area, because diorite and granite diorite with dominant feldspar and hornblende have been identified within 3km of that area. During the pottery manufacturing process, it is estimated that the pigment was painted on the entire surface of the red-burnished pottery after it had been molded and then finished using the abrasion technique. In other words, the red-burnished pottery was made by the process of vessel forming - semi drying - coloring - polishing. The surface and cross-section of the pottery appears differently depending on the concentration of the pigment and the coloring method used after vessels were formed. Most of the excavated pottery features a distinct boundary between pigment and body fabric. However, in the case of pottery in which fine-grained pigments penetrate the body fabric so that layers cannot be distinguished, there is the possibility that the fine-grained pigment layer was applied at a low concentration or immediately after vessel forming. Many cracks can be seen on the surface pigments in thickly painted pottery items, and in many cases, only a small portion of the pigment layers remain due to surface exfoliation and abrasion in the burial environment. It is reported that pottery items may be more easily damaged by abrasion if coated with pigment and polished, so it is believed that the red-burnished pottery of the Samdeok-ri site suffered from weathering in the burial environment. This damage was more extensive in the potsherds that were scattered outside the tomb.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.375-375
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• 2010

CdTe as an absorber material is widely used in thin film solar cells with the heterostructure due to its almost ideal band gap energy of 1.45 eV, high photovoltaic conversion efficiency, low cost and stable performance. The deposition methods and preparation conditions for the fabrication of CdTe are very important for the achievement of high solar cell conversion efficiency. There are some rearranged reports about the deposition methods available for the preparation of CdTe thin films such as close spaced sublimation (CSS), physical vapor deposition (PVD), vacuum evaporation, vapor transport deposition (VTD), closed space vapor transport, electrodeposition, screen printing, spray pyrolysis, metalorganic chemical vapor deposition (MOCVD), and RF sputtering. The RF sputtering method for the preparation of CdTe thin films has important advantages in that the thin films can be prepared at low growth temperatures with large-area deposition suitable for mass-production. The authors reported that the optical and electrical properties of CdTe thin film were closely connected by the thickness-uniformity of the film in the previous study [1], which means that the better optical absorbance and the higher carrier concentration could be obtained in the better condition of thickness-uniformity for CdTe thin film. The thickness-uniformity could be controlled and improved by the some process parameters such as vacuum level and RF power in the sputtering process of CdTe thin films. However, there is a limitation to improve the thickness-uniformity only in the preparation process [1]. So it is necessary to introduce the external or additional method for improving the thickness-uniformity of CdTe thin film because the cell size of thin film solar cell will be enlarged. Therefore, the authors firstly applied the chemical mechanical polishing (CMP) process to improving the thickness-uniformity of CdTe thin films with a G&P POLI-450 CMP polisher [2]. CMP process is the most important process in semiconductor manufacturing processes in order to planarize the surface of the wafer even over 300 mm and to form the copper interconnects with damascene process. Some important CMP characteristics for CdTe were obtained including removal rate (RR), WIWNU%, RMS roughness, and peak-to-valley roughness [2]. With these important results, the CMP process for CdTe thin films was performed to improve the thickness-uniformity of the sputtering-deposited CdTe thin film which had the worst two thickness-uniformities of them. Some optical properties including optical transmittance and absorbance of the CdTe thin films were measured by using a UV-Visible spectrophotometer (Varian Techtron, Cary500scan) in the range of 400 - 800 nm. After CMP process, the thickness-uniformities became better than that of the best condition in the previous sputtering process of CdTe thin films. Consequently, the optical properties were directly affected by the thickness-uniformity of CdTe thin film. The absorbance of CdTe thin films was improved although the thickness of CdTe thin film was not changed.

• Restorative Dentistry and Endodontics
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• v.25 no.1
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• pp.46-55
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• 2000

During bonding procedure of composite resin, the prepared cavity can be contaminated by saliva. In this study, marginal microleakage and shear bond strength of a composite resin to primed enamel and dentin treated with artificial saliva(Taliva$^{(R)}$) were evaluated. For the marginal microleakage test, Class V cavities were prepared in the buccal surfaces of fifty molars. The samples were randomly assigned into 5 groups with 10 samples in each group. Control group was applied with a bonding system (Scotchbond$^{TM}$ Multi-Purpose plus) according to manufacture's directions without saliva contamination. Experimental groups were divided into 4 groups and contaminated with artificial saliva for 30 seconds after priming: Experimental 1 group ; artificial saliva was dried with compressed air only, Experimental 2 group ; artificial saliva was rinsed and dried. Experimental 3 group ; cavities were etched with 35% phosphoric acid for 15 seconds after rinsing and drying artificial saliva. Experimental 4 group ; cavities were etched with 35% phosphoric acid for 15 seconds and primer was reapplied after rinsing and drying artificial saliva. All the cavities were applied a bonding agent and filled with a composite resin (Z-100$^{TM}$). Specimens were immersed in 0.5% basic fuschin dye for 24 hours and embedded in transparent acrylic resin and sectioned buccolingually with diamond wheel saw. Four sections were obtained from one specimen. Degree of marginal leakage was scored under stereomicroscope and their scores were averaged from four sections. The data were analyzed by Kruscal-Wallis test and Fisher's LSD. For the shear bond strength test, the buccal or occlusal surfaces of one hundred molar teeth were ground to expose enamel(n=50) or dentin(n=50) using diamond wheel saw and its surface was smoothed with Lapping and Polishing Machine(South Bay Technology Co., U.S.A.). Samples were divided into 5 groups. Treatment of saliva-contaminated enamel and dentin surfaces was same as the marginal microleakage test and composite resin was bonded via a gelatin capsule. All specimens were stored in distilled water for 48 hours. The shear bond strengths were measured by universal testing machine (AGS-1000 4D, Shimaduzu Co., Japan) with a crosshead speed of 5 mm/minute. Failure mode of fracture sites was examined under stereomicroscope. The data were analyzed by ANOVA and Tukey's studentized range test. The results of this study were as follows : 1. Enamel marginal microleakage showed no significant difference among groups. 2. Dentinal marginal microleakages of control, experimental 2 and 4 groups were lower than those of experimental 1 and 3 groups (p<0.05). 3. The shear bond strength to enamel was the highest value in control group (20.03${\pm}$4.47MPa) and the lowest value in experimental 1 group (13.28${\pm}$6.52MPa). There were significant differences between experimental 1 group and other groups (p<0.05). 4. The shear bond strength to dentin was higher in control group (17.87${\pm}$4.02MPa) and experimental 4 group (16.38${\pm}$3.23MPa) than in other groups, its value was low in experimental 1 group (3.95${\pm}$2.51 MPa) and experimental 2 group (6.72${\pm}$2.26MPa)(p<0.05). 5. Failure mode of fractured site on the enamel showed mostly adhesive failures in experimental 1 and 3 groups. 6. Failure mode of fractured site on the dentin did not show adhesive failures in control group, but showed mostly adhesive failure in experimental groups. As a summary of above results, if the primed tooth surface was contaminated with artificial saliva, primer should be reapplied after re-etching it.

• The korean journal of orthodontics
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• v.27 no.2
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• pp.327-334
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• 1997

The purpose of this study was to evaluate clinical applicability of light cured glass ionomer cement as a othodontic adhesive. The metal brackets and plastic brackets were bonded with light cured glass ionomer cement(Fuji Ortho $LS^{(R)}$) after polishing with a slurry of pumice, surface conditioning with 10% polyacrylic acid and chemically cured resin(Mono-$Lok2^{(R)}$) after acid etching with 38% phosphoric acid on the extracted human bicuspids. The shear bond strength was tested with a universal testing machine(HGS-100A, Shimadzu Co., Japan) after storage in normal saline at $37^{\circ}C$ or 24 hours and 48 hours. The results were as follows: 1. The shear bond strength of light cured glass ionomer cement group polished with a slurry of pumice was significantly lower than that of chemically cured resin group(P<0.01). 2. The shear bond strength of light cured glass ionomer cement group conditioned with 10% polyacrylic acid was significantly lower than that of chemically cured resin group(P<0.01). 3. The shear bond strength of light cued glass ionorner cement group conditioned with 10% polyacrylic acid was slightly higher than that of light cured glass ionomer cement group polished with a slurry of pumice, but there was no significant difference(P>0.05). 4. There was no significant difference between metal bracket group and plastic bracket group irrelevant off enamel conditioning(P>005). In summary, although the shear bond strength of light cured glass lionomer cement was lower than that of chemically cured resin, it night be clinically applicable.

• Clean Technology
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• v.4 no.2
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• pp.41-53
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• 1998

Most of flame furnace with uncontrolled atmosphere forms oxidation scales in the surface during heat treatment. In this case, shot blasting and pickling are commonly used for reduction of oxidation scales. These processes have many disadvantages, such as long process time, high operating cost and environmental problems due to polishing dust, etc. Hence, this study aimed to develop the advanced heat treating equipment which could make a controlled atmosphere using a heatresisting structure into the flame furnace. The analysis result with SEM, EPMA, and EDX revealed that the amount of scales formed is much less than that with the conventional flame furnace. A brightness of the sample treated with the advanced process is similar compared to the treatment with vacuum furnace. In the present work, it was recommended that the inside structure of the furnace and gas line system could made up of SBB410 and STS310, respectively. The operating cost with the advanced heat treatment system could be reduced annually by forty million won. As a result of this study, it may be possible to reduce the oxidation scales. The fundamental information obtained in this study will be useful not only for improving the heat treatment process(reduction of shot blast and cleaning process), but for promoting the manufacture of bright products.

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.1
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• pp.13-17
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• 2005

Children and teenagers have a higher frequency of proximal surface caries in the posterior teeth than adults. For proximal restoration, class II amalgam or stainless steel crown has been widely used in the past, however composite resin restoration is getting ore popular due to it's superior cosmetic appearance. When applying composite resin on proximal area, various types of matrix bands can be utilized according to the operator's reference or skill. Such bands have several clinical effects including suitability for proximal margin, reduction of micro-leakage, moisture-control against saliva and ease finishing and polishing. In this case report, orthodontic bands were utilized instead of matrix bands as a remedy for proximal restorations in both primary and permanent teeth and their clinical advantages are as follows. 1. Orthodontic bands showed superior marginal adaptation compared to conventional matrix bands and moisture-control against saliva was excellent. 2. While applying composite resin, deformation of restoration material was estimated to be insignificant due to he rigidity of the orthodontic bands. 3. Natural tooth contour of the orthodontic bands facilitates to reproduce proximal tooth contour of the restoration. 4. In general, pediatric dentists are accustomed to applying orthodontic bands and this may allow pediatric dentists to make proximal composite restorations more efficiently than other dental specialists.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.6
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• pp.683-689
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• 2006

Statement of problem. Interfacial toughness is important in the mechanical property of layered dental ceramics such as core-veneered all-ceramic dental materials. The interfaces between adjacent layers must be strongly bonded to prevent delamination, however the weak interface makes delamination by the growth of lateral cracks along the interface. Purpose. The purpose of this study was to determine the effect of the reaction layer on the interfacial fracture toughness of the core/veneer structure according to the five different divesting. Materials and methods. Thirty five heat-pressed Lithia-based ceramic core bars (IPS Empress 2), $20mm{\times}3mm{\times}2mm$ were made following the five different surface divesting conditions. G1 was no dissolution or sandblasting of the interaction layer. G2 and G3 were dissolved layer with 0.2% HF in an ultrasonic unit for 15min and 30 min. G4 and G5 were dissolved layer for 15min and 30min and then same sandblasting for 60s each. We veneered bilayered ceramic bars, $20mm{\times}2.8mm{\times}3.8mm$(2mm core and 1.8mm veneer), according to the manufacturer's instruction. After polishing the specimens through $1{\mu}m$ alumina, we induced five cracks for each of five groups within the veneer close to interface under an applied indenter load of 19.6N with a Vickers microhardness indenter. Results. The results from Vickers hardness were the percentage of delamination G1:55%, G2:50%, G3:35%, G4:0% and G5:0%. SEM examination showed that the mean thickness of the reaction layer were G1 $93.5{\pm}20.6{\mu}m$, G2 $69.9{\pm}14.3{\mu}m$, G3 $59.2{\pm}20.2{\mu}m$, G4 $0.61{\pm}1.44{\mu}m$ G5 $0{\pm}0{\mu}m$. The mean interfacial delamination crack lengths were G1 $131{\pm}54.5{\mu}m$, G2 $85.2{\pm}51.3{\mu}m$, and G3 $94.9{\pm}81.8{\mu}m$. One-way ANOVA showed that there was no statistically significant difference in interfacial crack length among G1, G2 and G3(p> 0.05). Conclusion. The investment reaction layer played important role at the interfacial toughness of body ceramic bonded to Lithia-based ceramic.