• Korean Journal of Materials Research
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• v.24 no.1
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• pp.33-36
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• 2014

This study was aimed at synthesizing and characterizing cerium-doped titania. Cerium-doped anatase titania powders were prepared by sol-gel process, with ammonium (IV) nitrate and titanium (IV) butoxide as the raw materials. The characteristics of pure $TiO_2$ and cerium-doped $TiO_2$ were investigated by XRD, TG/DTA, FE-SEM, and UV-vis spectroscopy. The results of this study show that anatase type of $TiO_2$ was obtained in as-prepared and calcined $TiO_2$ and Ce-$TiO_2$ powder. A DTA curve was also observed as the crystallization temperature decreased with increasing cerium contents. We found that the crystallite size of the obtained anatase particles decreased from 55 nm to 25 nm and the particle size decreased with increasing cerium contents. Moreover, UV-vis spectra showed that anatase titania powders with various cerium contents effectively extend the light absorption properties to the visible region.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.8
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• pp.508-513
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• 2017

Ultraviolet (UV) photodetectors are used in various industries and fields of research, including optical communication, flame sensing, missile plume detection, astronomical studies, biological sensors, and environmental research. However, general UV detectors that employ Schottky junction diodes and p-n junctions have high fabrication cost and low quantum efficiency. In this study, we investigated the characteristics of materials used to manufacture UV photodetectors in a low-cost solution process that requires easy fabrication of flexible substrates. We fabricated p-type NiO and n-type ZnO substrates with wide band gap by the sol-gel method and compared the characteristics of substrates prepared under different spin-coating and heat-treatment conditions.

• Journal of Surface Science and Engineering
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• v.41 no.3
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• pp.114-120
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• 2008

The pyrolysized carbon xerogel and aerogels were prepared from the sol-gel polymerization of resorcinol-formaldehyde(RF) followed by the dry process under ambient pressure and supercritical carbon dioxide condition respectively. The thermal behaviour of RF polymer xerogel was investigated with TGA analyzer to correspond with the pyrolysis process. The surface properties such as particle size, morphology and the point of zero charge of the pyrolysized porous carbon aerogels were studied for the precious metal catalyst supported media. It was found that the volume of the polymer aerogel decreased because of the significant linear shrinkage and weight loss of polymer gel during the carbonization. The point of zero charge of the carbon aerogel pyrolysized at $1050^{\circ}C$ under inert gas flow was about 10.

• Korean Journal of Metals and Materials
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• v.49 no.5
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• pp.395-399
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• 2011

In this study, micro gas sensors for ammonia gas were prepared by adopting MEMS technology and using a sol-gel process. Three types of sensors were prepared via different synthesis routes starting with W sol and Ru sol mixture. This mixture was deposited on a MEMS platform and the platform was subsegueny heated to a temperature of $350^{\circ}C$. The topography and crystal structure of the sensing film were studied using FE-SEM and XRD. The response of the gas sensor to $NH_3$ gas was examined at various operating temperatures and gas concentrations. The sensor response increased almost linearly with gas concentration and the best sensing response was obtained at $333^{\circ}C$ for 5.0 ppm $NH_3$ for the specimen prepared by coating $WO_3$ powders with the Ru sol mixture.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.239-244
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• 2015

Lead zirconate titanate (PZT) thick films with thickness of $10{\sim}20{\mu}m$ were fabricated on silicon substrate by aerosol deposition method. As-deposited films on silicon were annealed at the temperatures of $700^{\circ}C$. The electrical properties of films deposited by PZT powders were characterized using impedance analyzer and Sawyer-Tower circuit. The PZT powder was prepared by both conventional solid reaction process and sol-gel process. The remanent polarization, coercive field, and dielectric constant of the $10{\mu}m$ thick film with solid reaction process were $20{\mu}C/cm^2$, 30 kV/cm and 1320, respectively. On the other hand, the PZT films by sol-gel process showed a poor dielectric constant of 635. The reason was probably due to the presence of pores produced from organic residue during annealing.

• Korean Journal of Materials Research
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• v.23 no.6
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• pp.299-303
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• 2013

In this study, a micro gas sensor for $NO_x$ was fabricated using a microelectromechanical system (MEMS) technology and sol-gel process. The membrane and micro heater of the sensor platform were fabricated by a standard MEMS and CMOS technology with minor changes. The sensing electrode and micro heater were designed to have a co-planar structure with a Pt thin film layer. The size of the gas sensor device was about $2mm{\times}2mm$. Indium oxide as a sensing material for the $NO_x$ gas was synthesized by a sol-gel process. The particle size of synthesized $In_2O_3$ was identified as about 50 nm by field emission scanning electron microscopy (FE-SEM). The maximum gas sensitivity of indium oxide, as measured in terms of the relative resistance ($R_s=R_{gas}/R_{air}$), occurred at $300^{\circ}C$ with a value of 8.0 at 1 ppm $NO_2$ gas. The response and recovery times were within 60 seconds and 2 min, respectively. The sensing properties of the $NO_2$ gas showed good linear behavior with an increase of gas concentration. This study confirms that a MEMS-based gas sensor is a potential candidate as an automobile gas sensor with many advantages: small dimension, high sensitivity, short response time and low power consumption.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.48-52
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• 2014

The Mg-enriched magnesium aluminum silicate (MAS) glass is known for its higher mechanical strength and chemical resistance. Among such glasses, cordierite ($Mg_2Al_4Si_5O_{18}$) is well known to have a low thermal expansion and low melting point. Polycrystalline engineering ceramics such as alumina can be strengthened by a surface modification with low thermal expansion materials. The present study involves the synthesis of cordierite by a sol-gel process and investigates the effect of glass penetration on the surface of alumina. The cordierite powders were prepared from $Al(OC_3H_7)_3$, $Mg(OC_2H_5)_2$ and tetraethyl orthosilicate by hydrolysis and condensation reaction. The cordierite powders were characterized by X-ray diffraction (XRD, Rigaku), scanning electron microscope (SEM, JEOL: JSM-5610), energy dispersive spectroscopy (EDS, JEOL: JSM-5610), and universal testing machine (UTM, INSTRON). The X-ray diffraction patterns showed that the synthesized particles were ${\mu}$-cordierite calcined at $1100^{\circ}C$ for 1 h. The shape of synthesized cordierite was changed from ${\mu}$-cordierite to ${\alpha}$-cordierite with increasing calcination temperature. Synthesized cordierite was used for surface modification of alumina. Cordierite powders penetrated deeply into the alumina sample along grain boundaries with increasing temperature. The results of surface modification tests showed that the strength of the prepared alumina sample increased after surface modification. The strength of a surface modified with synthesized cordierite increased the most, to about 134.6MPa.

• Proceedings of the Materials Research Society of Korea Conference
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• 2004.05a
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• pp.46-46
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• 2004

• Restorative Dentistry and Endodontics
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• v.37 no.3
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• pp.149-154
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• 2012

Objectives: To evaluate the accuracy of the Root ZX in teeth with simulated root perforation in the presence of gel or liquid type endodontic irrigants, such as saline, 5.25% sodium hypochlorite (NaOCl), 2% chlorhexidine liquid, 2% chlorhexidine gel, and RC-Prep, and also to determine the electrical conductivities of these endodontic irrigants. Materials and Methods: A root perforation was simulated on twenty freshly extracted teeth by means of a small perforation made on the proximal surface of the root at 4 mm from the anatomic apex. Root ZX was used to locate root perforation and measure the electronic working lengths. The results obtained were compared with the actual working length (AWL) and the actual location of perforations (AP), allowing tolerances of 0.5 or 1.0 mm. Measurements within these limits were considered as acceptable. Chi-square test or the Fisher's exact test was used to evaluate significance. Electrical conductivities of each irrigant were also measured with an electrical conductivity tester. Results: The accuracies of the Root ZX in perforated teeth were significantly different between liquid types (saline, NaOCl) and gel types (chlorhexidine gel, RC-Prep). The accuracies of electronic working lengths in perforated teeth were higher in gel types than in liquid types. The accuracy in locating root perforation was higher in liquid types than gel types. 5.25% NaOCl had the highest electrical conductivity, whereas 2% chlorhexidine gel and RC-Prep gel had the lowest electrical conductivities among the five irrigants. Conclusions: Different canal irrigants with different electrical conductivities may affect the accuracy of the Root ZX in perforated teeth.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.7
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• pp.1491-1496
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• 2005

We fabricated the $Pb_{0.72}La_{0.28}TiO_3$ (PLT(28)) thin film successfully by using the sol-gel method and characterized it to evaluate its potential for being utilized as the capacitor dielectrics of ULSI DRAMs. In our sol-gel process, the acetates were used as the starting materials. Through the TGA-DTA analysis, we established the excellent fabrication conditions of the sol-gel method for the PLT(28) thin film. We obtained the dense and crack-free PLT(28) thin film of $100\%$ perovskite phase by drying at $350^{\circ}C$ after each coating and final annealing at $650^{\circ}C$. Electrical properties of PLT(28) thin film were measured through formation on the $Pt/Ti/SiO_2/Si$ substrate and its dielectric constant and leakage current density were measured as 936 and $1.1{\mu}A/cm^2$, respectively.