• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.12
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• pp.1122-1127
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• 1998

Group II-AF_2$films such as $CaF_2$, $SrF_2$, and $BaF_2$ have been commonly used many practical applications such as silicon on insulatro(SOI), three-dimensional integrated circuits, buffer layers, and gate dielectrics in filed effect transistor. This paper presents electrical and structural properties of fluoride films as a gate dielectric layer. Conventional gate dielectric materials of TFTs like oxide group exhibited problems on high interface trap charge density($D_it$), and interface state incorporation with O-H bond created by mobile hydrogen and oxygen atoms. To overcome such problems in conventional gate insulators, we have investigated $CaF_2$ films on Si substrates. Fluoride films were deposited using a high vacuum evaporation method on the Si and glass substrate. $CaF_2$ films were preferentially grown in (200) plane direction at room temperature. We were able to achieve a minimum lattice mismatch of 0.74% between Si and $CaF_2$ films. Average roughness of $CaF_2$ films was decreased from 54.1 ${\AA}$ to 8.40 ${\AA}$ as temperature increased form RT and $300^{\circ}C$. Well fabricated MIM device showed breakdown electric field of 1.27 MV/cm and low leakage current of $10^{-10}$ A/$cm^2$. Interface trap charge density between $CaF_2$ film and Si substrate was as low as $1.8{\times}10^{11}cm^{-2}eV^{-1}$.

• Journal of the korean academy of Pediatric Dentistry
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• v.34 no.4
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• pp.579-589
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• 2007

The objective of this study was to compare the shear bond strengths of five adhesive systems to the enamel and dentin of primary and permanent teeth. Fifty noncarious primary and fifty permanent teeth were collected and stored in an 0.1% thymol solution at room temperature after extraction. The tested adhesives were: Adper Scotchbond Multi-purpose Plus Adhesive (SM) Adper Single bond 2 (SB), Clearfil SE Bond (SE), Adper Prompt L-Pop (PL), GBond (GB). For the shear bonding test, the labial and lingual surfaces of primary and permanent teeth were used. To obtain a flat surface, the labial and lingual surfaces of the teeth were sanded on $SiO_2$ with number 600 grit and then divided into 20 groups of 10 surfaces each. All samples were theromocycled in water $5^{\circ}C$ and $55^{\circ}C$ for 1000 cycles. The results were as follows: 1. For primary enamel, shear bond strengths of SM and SB were significantly higher than that of SE and also SM, SB, and PL were higher than GB(p<0.05). 2. For primary dentin, there were no significant differences among the shear bond strengths of any other bonding systems except difference between SE and GB. 3. For permanent enamel, SB showed significantly higher mean shear bond strength than those of any other bonding systems(p<0.05). 4. For permanent dentin, SM showed significantly higher mean shear bond strength than that of PL and GB(p<0.05). 5. Between the primary enamel and dentin, there were significant differences in SM, SB, and GB, whereas there was statistically significant difference in PL between the permanent enamel and dentin(p<0.05). 6. Between the primary and permanent teeth on enamel, there were no significant differences among all bonding systems, whereas there were statistically significant differences in SM and SB between the primary and permanent teeth on dentin(p<0.05).

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.19-19
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• 2002

Perovskite-type titanate dielectrics have attracted much attention in memory devices such as DRAMs or FeRAMs due to their high dielectric constants. However, low volatility of the Ba, Sr, Pb or Zr precursors with only thd ligands has limitations in obtaining high quality thin films by liquid source metal organic chemical vapor deposition (LS-MOCVD) processes. To improve the volatility of these precursors, many attempts have been made such as adding polyether ligands to satisfy the coordinative saturation. We report the synthesis of new precursors Ba(thd)₂(tmeea) and Sr(thd)₂(tmeea), where tmeea = tris[2-(2-methoxyethoxy)ethyl]amino, and LS-MOCVD of barium strontium titanate (BSTO) thin films using these precursors. Due to increased basicity of amines compared with ethers, it is expected that the nitrogen-donor ligand will make a strong bond to a metal than an analogous oxygen-donor ligand, consequently improving the volatility and thermal behavior of these precursors. Thin films of BSTO were grown on Pt(111)/SiO₂/Si(100) substrates by LS-MOCVD using a cocktail source consisting of the conventional Ti precursor Ti(thd)₂(O/sup i/Pr), and these new Ba and Sr precursors. As-grown films were characterized by XPS, SEM, XRD, XRF, and C-V and I-V measurements. BSTO films grown at 420℃ were stoichiometric barium strontium titanate with very smooth surface morphology and their dielectric constants were found to be as targe as 450. Dependence of the composition, microstructure and the electrical properties of the BSTO films on the growth temperature, annealing temperature, working pressure, and the composition of the cocktail source will be discussed.

• Journal of the korean academy of Pediatric Dentistry
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• v.38 no.1
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• pp.33-41
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• 2011

The objective of this study was to compare the shear bond strengths of five dentin adhesive systems cured with three different light curing sources. Seventy five noncarious permanent teeth were collected and stored in an 0.1% thymol solution at room temperature after extraction. The tested adhesives were: Adper Scotchbond Multi-purpose Plus Adhesive (SM) Adper Single bond 2 (SB), Clearfil SE Bond (SE), Adper Prompt L-Pop (PL), G-Bond (GB). And three light curing unit systems were used: Elipar Free light 2(LED), OptiLux 501 (Halogen), Flipo (PAC). For the shear bonding test, the labial and lingual surfaces of permanent teeth were used. To obtain a flat dentin surface, the labial and lingual surfaces of the teeth were sanded on SiO2 with number 600 grit and then divided into 15 groups of 10 surfaces each. All samples were theromocycled in water $5^{\circ}C$ and $55^{\circ}C$ for 1000 cycles. The results were as follows: 1. When cured with Freelight 2, the shear bond strength of SM was significantly higher than that of PL, GB (p<0.05), whereas no significant difference was found among those of any other bonding agents. 2. When cured with Optilux 501, the shear bond strength of SM was significantly higher than those of any other bonding agents (p<0.05), whereas no singnificant difference was found among those of andy other bonding agents. 3. When cured with Flipo, the shear bond strength of SM was significantly higher than those of SB, SE, GB (p<0.05), whereas no significant differences was found among those of any other bonding agents. 4. For comparison according to three different light cure unit system, except SB and GB, each three dentin bonding agents showed no significant difference. For SB, only Freelight 2 was significantly higher than the others, with no significant difference between Optilux 501 and Flip. For GB, Statistically significant difference was found only between Freelight and Flipo.

• Korean Journal of Materials Research
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• v.33 no.11
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• pp.465-474
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• 2023

The effects of La³⁺ substitution for Sr²⁺-site on the crystal structure and the dielectric properties of (Ba_0.7Sr_0.3-3x/2La_x) (Ti_0.9Zr_0.1)O₃ (BSLTZ) (0.005 ≤ x ≤ 0.02) ceramics were investigated. The structural characteristics of the BSLTZ ceramics were quantitatively evaluated using the Rietveld refinement method from X-ray diffraction (XRD) data. For the specimens sintered at 1,550 ℃ for 6 h, a single phase with a perovskite structure and homogeneous microstructure were observed for the entire range of compositions. With increasing La³⁺ substitution (x), the unit cell volume decreased because the ionic size of La³⁺ (1.36 Å) ions is smaller than that of Sr²⁺ (1.44 Å) ions. With increasing La³⁺ substitution (x), the tetragonal phase fraction increased due to the A-site cation size mismatch effect. Dielectric constant (ε_r) increased with the La³⁺ substitution (x) due to the increase in tetragonality (c/a) and the average B-site bond valence of the ABO₃ perovskite. The BSLTZ ceramics showed a higher dielectric loss due to the smaller grain size than that of (Ba_0.7Sr_0.3)(Ti_0.9Zr_0.1)O₃ ceramics. BSLTZ (x = 0.02) ceramics met the X7R specification proposed by the Electronic Industries Association (EIA).

• Journal of Welding and Joining
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• v.28 no.3
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• pp.92-98
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• 2010

Ferritic stainless steels, which have relatively small thermal expansion coefficient and excellent corrosion resistance, are increasingly being used in vehicle manufacturing, in order to increase the lifetime of exhaust manifold parts. But, there are limits on use because of the problem related to cosmetic resistance, corrosions of condensation and high temperature salt etc. So, Aluminum-coated stainless steel instead of ferritic stainless steel are utilized in these parts due to the improved properties. In this investigation, Al-8wt% Si alloy coated 409L ferritic stainless steel was used as the base metal during Gas Tungsten Arc(GTA) welding. The effects of coated layer on the microstructure and hardness were investigated. Full penetration was obtained, when the welding current was higher than 90A and the welding speed was lower than 0.52m/min. Grain size was the largest in fusion zone and decreased from near HAZ to base metal. As welding speed increased, grain size of fusion zone decreased, and there was no big change in HAZ. Hardness had a peak value in the fusion zone and decreased from the bond line to the base metal. The highest hardness in the fusion zone resulted from the fine re-precipitation of the coarse TiN and Ti(C, N) existed in the base metal during melting and solidification process and the presence of fine $Al_2O_3$ and $SiO_2$ formed by the migration of the elements, Al and Si, from the melted coating layer into the fusion zone.

• Korean Journal of Materials Research
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• v.20 no.2
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• pp.78-81
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• 2010

Surface modification of silica nanoparticles was investigated using an aerosol self assembly. Stearic acid was used as surface treating agent. A two-fluid jet nozzle was employed to generate an aerosol of the colloidal suspension, which contained 20 nm of silica nanoparticles, surface modifier, and ethyl alcohol. Powder properties such as morphology, specific surface area and pore size distribution were analyzed by SEM, BET and BJH methods, respectively. Surface properties of the silica power were analyzed by FT-IR. The OH bond of the $SiO_2$ surface was converted to a C-H bond. It was revealed that the hydrophilic surface changed to a hydrophobic one due to the aerosol self assembly. Morphology of the surface treated powder was nanostructured with lots of pores having an average diameter of around $2\;{\mu}m$. Depending on the stearic acid concentration (0.25 to 1.0 wt%), the pore size distribution of the particles and the degree of hydrophobicity ranged from 1.5 nm to 180 nm and 29.6% to 50.2%, respectively.

• Journal of the Korean Applied Science and Technology
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• v.22 no.1
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• pp.28-34
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• 2005

The structure of a carbon monoxide sorption complex of dehydrated fully $Ca^{2+}$-exchanged zeolite X, $|Ca_{46}(CO)_{27}|[Si_{100}Al_{92}O_{384}]$-FAU, has been determined in the cubic space group $Fd\;{\overline{3}}$ at $21^{\circ}C$ (a = 24.970(4) ) by single-crystal X-ray diffraction techniques. The crystal was prepared by ion exchange in a flowing stream of 0.05 M aqueous ${Ca(NO_3)_2}$ for three days, followed by dehydration at $400^{\circ}C$ and $2{\times}10^{-6}$ Torr for two days, and exposure to 100 Torr of zeolitically dry carbon monoxide gas at $21^{\circ}C$. The structure was determined in this atmosphere and was refined, using the 356 reflections for which $F_o$ > $4{\sigma}(F_o)$, to the final error indices $R_1$ = 0.059 and $wR_2$ = 0.087. In this structure, $Ca^{2+}$ ions occupy three crystallographic sites. Sixteen $Ca^{2+}$ ions fill the octahedral site I at the centers of hexagonal prisms (Ca-O = 2.415(7) ${\AA}$). The remaining 30 $Ca^{2+}$ ions are found at two nonequivalent sites II (in the supercages) with occupancies of 3 and 27 ions. Each of these $Ca^{2+}$ ions coordinates to three framework oxygens, either at 2.276(10) or 2.298(8) ${\AA}$, respectively. Twenty-seven carbon monoxide molecules have been sorbed per unit cell, three per supercage. Each coordinates to one of the latter 16 site-II $Ca^{2+}$ ions: C-Ca = 2.72(8) ${\AA}$. The imprecisely determined N-C bond length, 1.26(14) ${\AA}$, differs insignificantly from that in carbon monoxide(g), 1.13 ${\AA}$.

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.436-440
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• 2009

This study demonstrates the use of a chemical lung containing potassium superoxide to convert carbon dioxide in air to oxygen. In order to reduce its extremely high reactivity, potassium superoxide was first mixed with calcium hydroxide and then combined at various ratios with polysiloxane. Silicone polymer used here served as both a water repellent and the polymer matrix. In general, the amount of carbon dioxide captured as well as that of oxygen produced increased as the proportion of potassium superoxide in the chemical lung increased. FT-IR spectroscopy revealed that the Si-O bond in chemical lung appeared at $1,050cm^{-1}$ and absorbance of chemical lung containing higher amounts of silicone was higher than that of chemical lung containing lower amounts. These results indicate that such a chemical lung may also be a useful sorbent for other acid gases, such as sulfur oxides and nitrogen oxides.

• Polymer(Korea)
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• v.33 no.4
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• pp.319-325
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• 2009

The solution polymerization was conducted to synthesize pressure sensitive adhesive for polarizer film using acrylic monomers. 2-Ethylhexylacrylate, butylacrylate, acrylic acid were used as acrylic monomers. The ratio was 2-ethylliexylacrylate:butylacrylate:acrylic acid=25:50:3.6 by reflecting $-40^{\circ}C$ of glass transition temperature in the pressure sensitive adhesive. When 1 wt% of coupling agent was added to the polymerized pressure sensitive adhesive, the light transmissivity was significantly increased. This result is due to the enhancement of adhesive power against liquid crystal cell by Si-O bond of coupling agents. Cross-linking agent was added by 0.5, 1.0, and 1.5 wt% with respect to the synthesized polymer. Initial tackiness decreased, while cohesion increased with increasing crosslinking agent. In the analysis of contact angle, the increase of crosslinking agents yielded the enhancement of surface energy, resulting in the decrease of contact angle. From the measurement of heat resistance, the acrylic pressure sensitive adhesive showed excellent heat resistance regardless of change in temperature and contents in crosslinking agent. In the observation of a cutting plane, the increased crosslinking agent represented a smoother and cleaner section. Comprehensively, the optimum additive amount of crosslinking agent was determined to be 1.0 wt% to monomer.