• Bulletin of the Korean Chemical Society
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• v.22 no.8
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• pp.872-876
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• 2001

Topological changes caused by the alkaline and enzymatic attacks of solution-grown, chain-folded lamellar crystals (SGCs) of poly[(R)-3-hydroxybutyrate] P(3HB) have been studied in order to investigate the chain-folding structure in P(3HB) crystal regions. NaOH and an extracellular PHB depolymerase purified from Alcaligenes faecalis T1 were used for alkaline and enzymatic hydrolysis, respectively. The measurements were performed on crystals attached to a substrate which is inactive to degradation mediums. Both alkaline and enzymatic attacks lead to a breakup of the lamellar crystals along the crystallographic b-axis during initial erosion. Since hydrolysis preferentially occurs in amorphous regions, this morphological result reflects relatively loosely packed chains in core parts of lamellar crystals. Additionally, it was supported by the ridge formation along the b-axis in the lamellar crystals after thermal treatment at a low temperature because of the thermally sensitive nature of the loosely packed chains in lamellar crystals. However, the alkaline hydrolysis accompanied the chain erosions or scissions in quasi-regular folded lamellar surfaces due to smaller size of alkaline ions in comparison to the enzyme, resulting in the decrease of molecular weight.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.521-524
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• 2005

ZnO 2-D nanowall structure with around 100 nm thickness, which is composed of tens of nm scale ZnO single crystals, was fabricated through the low temperature chemical solution growth method. Electro Chemical Deposition (ECD) technique was applied to attach the ZnO seed crystals on ITO coated glass substrate. The ZnO nanowall structure was grown in the 0.015 mol$\%$ of aqueous solution of zinc nitrate and hexamethenamine at 60$^{\circ}C$ for 20 - 40 h. The nanowall structure depends on the ECD condition or the applied voltage and duration time. The nanowall shows a photoluminescence around 550 - 700 nm spectrum range.

• Polymer(Korea)
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• v.29 no.1
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• pp.54-58
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• 2005

The hydrolytic behavior of microbial poly[(R)-3-hydroxybutyrate]](P(3HB)) has been studied by using two model systems, Langmuir monolayer and solution-grown single crystals (SCs), for elucidating the mechanism for both alkaline and enzymatic degradations. An initial degradation of SCs of P(3HB) leads to breakup lamellae parallel to their short axis (b-axis). Similarly, ridge formation on the lamellar surface appears along the b-axis at lower quenching temperature than melting temperature. Both results support that the lamellar crystals contain less-ordered and more thermally sensitive regions along the b-axis. Although the enzymatic hydrolysis of P(3HB) monolayers was similar to its alkaline one, the enzymatic degradation of P(3HB) monolayers occurred at higher constant surface pressure than the alkaline degradation. This behavior might be attributed to the size of enzymes which is much larger than that of alkaline ions; that is, the enzymes need larger contact area with monolayers to be activated.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1235-1239
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• 1997

Sodium niobate single crystals were grown by high temperature solution growth with Na2O/B2O3 flux. The phase transitions and domain structures of sodium niobate were observed using transmission polarizing microscope from room temperature to $650^{\circ}C$. There was imperfect extinction region within as-grown crystals and this area could be removed by heat treatment. The area existed within crystal till 3$65^{\circ}C$, in which temperature the space group of sodium niobate is changed from Pbma to Pmnm. The phase transition from Pbma to Pmnm happened abruptly with changing domain structure. At 48$0^{\circ}C$, 52$0^{\circ}C$ and 572$^{\circ}C$, the colors and walls of domains were changed. All domains disappeared and the space group of sodium niobate was changed from P4/mbm to Pm3m at 64$0^{\circ}C$. When sodium niobate changed from high temperature phase to low temperature phase, the memory effect of domain structure was not observed.

• Proceedings of the Korea Crystallographic Association Conference
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• 2001.05a
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• pp.22-22
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• 2001

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.173-174
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• 2006

• Journal of the Korean Ceramic Society
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• v.56 no.6
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• pp.589-595
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• 2019

The top-seeded solution growth (TSSG) method is an effective approach for the growth of high-quality SiC single crystals. In this method, the temperature gradient in the melt is the key factor determining the crystal growth rate and crystal quality. In this study, the effects of the aperture at the top of the hot-zone on the growth of the SiC single crystal obtained using the TSSG method were evaluated using multiphysics simulations. The temperature distribution and C concentration profile in the Si melt were taken into consideration. The simulation results showed that the adjustment of the aperture at the top of the hot-zone and the temperature gradient in the melt could be finely controlled. The surface morphology, crystal quality, and polytype stability of the grown SiC crystals were investigated using optical microscopy, high-resolution X-ray diffraction, and micro-Raman spectroscopy, respectively. The simulation and experimental results suggested that a small temperature gradient at the crystal-melt interface is suitable for growing high-quality SiC single crystals via the TSSG method.

• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3755-3760
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• 2012

Single crystals of lithium potassium phthalate (LiKP) were successfully grown from aqueous solution by solvent evaporation technique. The grown crystals were characterized by single crystal X-ray diffraction. The lithium potassium phthalate $C_{16}\;H_{12}\;K\;Li_3\;O_{11}$ belongs to triclinic system with the following unit-cell dimensions at 298(2) K;$a=7.405(5){\AA}$;$b=9.878(5){\AA}$;$c=13.396(5){\AA}$;${\alpha}=71.778(5)^{\circ}$;${\beta}=87.300(5)^{\circ}$;${\gamma}=85.405(5)^{\circ}$; having a space group P1. Mass spectrometric analysis provides the molecular weight of the compound and possible ways of fragmentations occurs in the compound. Thermal stability of the crystal was also studied by both simultaneous TGA/DTA analyses. The UV-Vis-NIR spectrum shows a good transparency in the whole of Visible and as well as in the near IR range. Third order nonlinear optical studies have also been studied by Z-scan technique. Nonlinear absorption and nonlinear refractive index were found out and the third order bulk susceptibility of compound was also estimated. The results have been discussed in detail.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.6
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• pp.516-521
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• 2019

The top seeded solution growth (TSSG) method is an alternative technique to grow high-quality SiC crystals that has been actively studied for the last two decades. However, the TSSG method has different issues that need to be resolved when compared to the commercial SiC crystal growing method, i.e., physical vapor transport (PVT). A particular issue of the TSSG method of results from the presence of liquid droplets on the grown crystal that can remain even after crystal growth; this induces residual stress on the crystal surface. Hence, the residual droplet causes several unwanted effects on the crystal such as the initiation of micro-cracks, micro-pipes, and polytype inclusions. Therefore, this study investigated the formation of the residual droplet through multiphysics simulations and lead to the development of a liquid droplet removal method. As a result, we found that although residual liquid droplets significantly apply residual stress on the grown crystal, these could be vaporized by adopting thermal annealing processes after the relevant crystal growing steps.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.115-120
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• 1997

We have developed new algorithms for solution of the three-dimensional, time-dependent Navier-Stokes equations that utilize massively parallel supercomputing implemented on the Connection Machine 5. Here, we apply these techniques to analyze he fluid flows that occur during the growth of the tow nonlinear optical crystals-potassium dihydrogen phosphate (KDP), which is producted in a novel rapid growth system under development by the Lawrence Livermore National Laboratory Laser Division, and Potassium titanyl phosphate(KTP), which is grown from a high-temperature aqueous solution.