• Journal of the Korean Ceramic Society
• /
• v.42 no.9 s.280
• /
• pp.599-601
• /
• 2005

The coarsening process of two different $BaTiO_3$ single crystal seeds, one with a (111) double twin and the other without it, was investigated. Due to the presence of Twin Plane Reentrant Edge (TPRE), the coarsening rate of the twinned seed crystal was significantly higher than that without a twin. For the coarsening by the 2-dimensional nucleation and lateral growth, the energy barrier for nucleation at the TPRE was analyzed to be about a half compared with that at the terrace planes.

• Journal of the Korean Ceramic Society
• /
• v.36 no.12
• /
• pp.1310-1315
• /
• 1999

• Journal of Korea Foundry Society
• /
• v.26 no.3
• /
• pp.140-145
• /
• 2006

Sr, added in the hypereutectic Al-Si alloys, is absorbed on the surfaces of primary Si as well as eutectic Si, and can change the growth mode of primary Si from non-faceted to faceted mode, as the amount of Sr increases larger than 0.04 wt.%, even though it cannot affect the grain size of primary Si, significantly. The EBSD analysis shows that the traction of ${\Sigma}3$ boundary(twin boundary) increases as the amount of Sr in the hypereutectic Al-Si alloys increase until the over-modification occurs at 1.6 wt.%Sr and proves that the change in growth mode of primary Si results from the change of TPRE growth to IIT growth.

• Korean Journal of Crystallography
• /
• v.14 no.2
• /
• pp.93-104
• /
• 2003

The crystals of group-Ⅲ nitride semiconductors with wurtzite structure exhibit a strong polarity. Especially, GaN has characteristics of different growth rate, anisotropic electrical and optical properties due to the polarity. In this work, GaN epilayer was grown and the polarities of the crystals were observed by the chemical wet etching and SP-EFM. GaN thin films were deposited on c-plane A1₂O₃ substrate under the variations of growth conditions by HVPE such as the deposition temperature of the buffer layer, the deposition time, the ratio of Group-V and Ⅲ and the deposition temperature of the film. The adquate results were obtained under the conditions of 500℃, 90 seconds, 1333 and 1080℃, respectively. It is observed that the GaN layer grown without the buffer layer has N-polarity and the GaN layer grown on the buffer layer has Ga-polarity. Fine crystal single particles were grown on c-plane A1₂O₃ and SiO₂, layer. The external shape of the crystal shows ｛10-11｝｛10-10｝(000-1) planes as expected in the PBC theory and anisotropic behavior along c-axis is obvious. As a result of etching on each plane, (000-1) and ｛10-11｝planes were etched strongly due to the N-polarity and ｛10-10｝ plane was not affected due to the non-polarity. In the case of the crystal grown on c-plane A1₂O₃, two types of crystals were grown. They were hexagonal pyramidal-shape with ｛10-11｝plane and hexagonal prism with basal plane. The latter might be grown by twin plane reentrant edge (TPRE) growth.

• Journal of Korea Foundry Society
• /
• v.8 no.4
• /
• pp.453-458
• /
• 1988

Al-Si alloy powder produced by the gas atomizer showed fine eutectic structure between ${\alpha}-dendrites$, that was grown by coupled growth, and there remained small amount of ${\alpha}$ in Al - 20 wt% Si alloy. The morphology of Si in the eutectic structure was largely influenced by the recalescence caused by solidification latent heat, and that was thought to be due to decrement of the surface energy of Si. In modified eutectic Si by rapid solidification, fine twin about $0.01\;{\mu}m$ was observed and growth direction of eutectic Si was <112>. This fact implied that the growth mechanism of eutectic Si in rapid solidification was related to TPRE mechanism. Due to rapid solidification Si was soluble in ${\alpha}-phase$ in Al - 12.6wt%Si alloy up to about 3.4wt%, and the solubility of Si in ${\alpha}-phase$ reaches the equilibrium solubility stare after 60min, holding when it was held isothermally at $253-296^{\circ}C$.

• Korean Journal of Materials Research
• /
• v.27 no.10
• /
• pp.544-551
• /
• 2017

In order to develop a new commercial Al-12%Si casting alloy with improved physical properties, we investigated the effect of adding Sr and TiB to the alloy. Al-12%Si alloys were prepared by die casting at $660^{\circ}C$. The eutectic temperature of the Sr-modified Al-12%Si alloy decreased to $9^{\circ}C$ and the mushy zone region increased. The shape of the Si phase changed from coarse acicula to fine fiber with the addition of Sr. The addition of TiB in the Al-12%Si alloy reduced the size of the primary ${\alpha}$-Al and eutectic Si phases. When Sr and TiB were added together, it worked more effectively in refinement and modification. The density of twins in the Si phase-doped Sr increased and the width of the twins was refined to 5 nm. These results are related to the impurity induced twinning(IIT) growth.

• 전자공학회논문지 IE
• /
• v.45 no.4
• /
• pp.1-6
• /
• 2008

A fast-hopping frequency synthesizer that reduces complexity and power consumption is presented for MB-OFDM UWB applications. The proposed architecture uses 3960 MHz LC VCO, 528 MHz ring oscillator, passive mixer and LC-tuned Q-enhancement BPF to generate Band Group 1 frequencies. The adjacent channel rejection ratio is less than -40 dBc for 3432 MHz and -H dBc for 4488 MHz. A fast switching SCL-tpre MUX is used to produce the required channel output signal and it takes less than 2.2 ns for band switching. The total power consumption is 47.9 mW from a 1.8 V supply.