• Bulletin of the Korean Chemical Society
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• v.29 no.2
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• pp.467-470
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• 2008

• Journal of computational fluids engineering
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• v.16 no.1
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• pp.22-29
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• 2011

In this study, the glass fiber drawing from a silica preform in the furnace for the optical fiber manufacturing process is numerically simulated by considering the radiative heating of cylindrically shaped preform. The one-dimensional governing equations of the mass, momentum, and energy conservation for the heated and softened preform are solved as a set of the boundary value problems along with the radiative transfer approximation between the muffle tube and the deformed preform shape, while the furnace heating is modeled by prescribing the temperature distribution of muffle tube. The temperature-dependent viscosity of silica plays an important role in formation of preform neck-down profile when the glass fiber is drawn at high speed. The calculated neck-down profile of preform and the draw tension are found to be reasonable and comparable to the actual results observed in the optical fiber industry. This paper also presents the effects of key operating parameters such as the muffle tube temperature distribution and the fiber drawing speed on the preform neck-down profile and the draw tension. Draw tension varies drastically even with the small change of furnace heating conditions such as maximum heating temperature and heating width, and the fine adjustment of furnace heating is required in order to maintain the appropriate draw tension of 100~200 g.

• Journal of the Korean Vacuum Society
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• v.11 no.4
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• pp.249-255
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• 2002

For a formation of membrane structures, single crystal silicon wafers have been anisotropically etched with solutions of KOH and KOH-IPA. The etching rate was observed to be strongly dependent upon the etchant temperature and concentration. Mask patterns for the etching experiment was aligned to incline $45^{\circ}$on the primary flat of the silicon wafer. The different etching characteristics were observed according to pattern directions and etchant concentration. When the KOH concentration was fixed to 20 wt%, the U-groove etching shape was observed for the etching temperature of above $80^{\circ}C$, and V-groove shapes observed at below $80^{\circ}C$. Hillocks, which were generated at the etched silicon surfaces, has been decreased as the increasing of the etchant temperature and concentration.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.303-303
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• 2011

Orderings and electronic structures of organic molecules on metal substrates have been studied due to possible applications in electronic devices. In molecular systems, delocalized pi-electrons play important roles in the adsorption behaviors and electronic structures. We studied the adsorption and electronic structures of Co-Porphyrin molecules on Au(111) using scanning tunneling microscopy (STM) and spectroscopy (STS) at low temperature. Molecules form closely packed two-dimensional islands on Au(111) surface with two different types, having different shape evolutions in our energy-dependent STM observations. The Kondo resonance state, occurred by spin exchange interaction between the Co center atom and conduction electrons in the metal substrate, was observed in one type, while it was absent in the other type in scanning tunneling spectroscopy measurements. Possible origins of two molecular shapes will be discussed.

• Journal of Powder Materials
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• v.14 no.2 s.61
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• pp.145-149
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• 2007

Nanocrystalline transient aluminas (${\gamma}$-alumina) were coated on core particles (${\gamma}$-alumina) by a carbonate precipitation and thermal-assisted combustion, which is environmentally friend. The ammonium aluminum carbonate hydroxide (AACH) as a precursor for coating of transient aluminas was produced from precipitation reaction of ammonium aluminum sulfate and ammonium hydrogen carbonate. The crystalline size and morphology of the synthetic, AACH, were greatly dependent on pH and temperature. AACH with a size of 5 nm was coated on the core alumina particle at pH 9. whereas rod shape and large agglomerates were coated at pH 8 and 11, respectively. The AACH was tightly bonded coated on the core particle due to formation of surface complexes by the adsorption of carbonates, hydroxyl and ammonia groups on the surface of the core alumina powder. The synthetic precursor successfully converted to amorphous- and ${\gamma}$-alumina phase at low temperature through decomposition of surface complexes and thermal-assisted phase transformation.

• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.245-250
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• 2005

ZnO was deposited on sapphire single crystal substrate by an ultrasonic pyrolysis of Zinc Acetate Dehydrate (ZAH) with carrying Ar gas. Through Thermogravimetry-Differential Scanning Calorimetry(TG-DSC), zinc acetate dihydrate was identified to be dissolved into ZnO above $380^{\circ}C$. ZnO deposited at $380-700^{\circ}C$ showed polycrystalline structures with ZnO (101) and ZnO (002) diffraction peaks like bulk ZnO in XRD, and from which c-axis strain ${\Sigma}Z=0.2\%$ and compressive biaxial stress$\sigma=-0.907\;GPa$ was obtained for the ZnO deposited $400^{\circ}C$. Scanning electron microscope revealed that microstructures of the ZnO were dependent on the deposition temperature. ZnO grown below temperature $600^{\circ}C$ were aggregate consisting of zinc acetate and ZnO particles shaped with nanoblades. On the other hand the grain of the ZnO deposited at $700^{\circ}C$ showed a distorted hexagonal shape and was composed of many ultrafine ZnO powers of 10-25 nm in size. The formation of these ulrafine nm scale ZnO powers was explained by the model of random nucleation mechanism. The optical property of the ZnO was analyzed by the photoluminescence (PL) measurement.