• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.663-663
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• 2013

We prepared Cu oxides, and Ni and Pd-TiO2@SiO2 core-shellnanostructures, and tested their CO oxidation performances by temperature-programmed mass spectrometry. We found the starting temperatures of CO oxidation are around $200^{\circ}C$ and $300^{\circ}C$ for Ni and Pd-TiO2@SiO2 nanostructures, respectively. Cu oxides are cubes with 50~200 nm with, prepared with different concentrations of NaOH and ascorbic acid. For the core-shell structures, we prepared 100 nm SiO2 spheres, first coated the surface with TiO2 precursor, and then coated with Ni and Pd. Their characteristics are further examined by scanning electron microscopy, optical microscope, FT-IR, and UV-Vis absorption spectroscopy.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.1-7
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• 2018

Tin dioxide, $SnO_2$, is applied as an anode material in Li-ion batteries and a gas sensing materials, which shows changes in resistance in the presence of gas molecules, such as $H_2$, NO, $NO_2$ etc. Considerable research has been done on the synthesis of $SnO_2$ nanostructures. Nanomaterials exhibit a high surface to volume ratio, which means it has an advantage in sensing gas molecules and improving the specific capacity of Li-ion batteries. In this study, $SnO_2$ nanostructures were grown on a Si substrate using a thermal CVD process with the vapor transport method. The carrier gas was mixed with high purity Ar gas and oxygen gas. The crystalline phase of the as-grown tin oxide nanostructures was affected by the oxygen gas flow rate. The crystallographic property of the as-grown tin oxide nanostructures were investigated by Raman spectroscopy and XRD. The morphology of the as-grown tin oxide nanostructures was confirmed by scanning electron microscopy. As a result, the $SnO_2$ nanostructures were grown directly on Si wafers with moderate thickness and a nanodot surface morphology for a carrier gas mixture ratio of Ar gas 1000 SCCM : $O_2$ gas 10 SCCM.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.199-202
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• 2003

Ultraviolet-nanoimprint lithography (UV-NIL) is a promising method for cost-effectively defining nanoscale structures at room temperature and low pressure. Since the resolution of nanostructures depends strongly upon that of nanostamps, the nanostamp fabrication technology is a key technology to UV-NIL. In this paper, a 5$\times$5$\times$0.09 in. quartz stamp whose critical dimension is 377 nm was fabricated using the etch process in which a Cr film was employed as a hard mask for transferring nanostructures onto the quartz plate. To effectively apply tile fabricated 5-in. stamp to UV-NIL on a 4-in. Si wafer, we have proposed a new UV-NIL process using a multi-dispensing method as a way to supply resist on a wafer Experiments have shown that the multi-dispensing method can enable UV-NIL rising a large-area stamp.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.389-390
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• 2012

In this study, we fabricate a superhydrophobic surface made of hierarchical nanostructures that combine wax crystalline structure with moth-eye structure using vacuum cluster system and measure their hydrophobicity and durability. Since the lotus effect was found, much work has been done on studying self-cleaning surface for decades. The surface of lotus leaf consists of multi-level layers of micro scale papillose epidermal cells and epicuticular wax crystalloids [1]. This hierarchical structure has superhydrophobic property because the sufficiently rough surface allows air pockets to form easily below the liquid, the so-called Cassie state, so that the relatively small area of water/solid interface makes the energetic cost associated with corresponding water/air interfaces smaller than the energy gained [2]. Various nanostructures have been reported for fabricating the self-cleaning surface but in general, they have the problem of low durability. More than two nanostructures on a surface can be integrated together to increase hydrophobicity and durability of the surface as in the lotus leaf [3,5]. As one of the bio-inspired nanostructures, we introduce a hierarchical nanostructure fabricated with a high vacuum cluster system. A hierarchical nanostructure is a combination of moth-eye structure with an average pitch of 300 nm and height of 700 nm, and the wax crystalline structure with an average width and height of 200 nm. The moth-eye structure is fabricated with deep reactive ion etching (DRIE) process. $SiO_2$ layer is initially deposited on a glass substrate using PECVD in the cluster system. Then, Au seed layer is deposited for a few second using DC sputtering process to provide stochastic mask for etching the underlying $SiO_2$ layer with ICP-RIE so that moth-eye structure can be fabricated. Additionally, n-hexatriacontane paraffin wax ($C_{36}H_{74}$) is deposited on the moth-eye structure in a thermal evaporator and self-recrystallized at $40^{\circ}C$ for 4h [4]. All of steps are conducted utilizing vacuum cluster system to minimize the contamination. The water contact angles are measured by tensiometer. The morphology of the surface is characterized using SEM and AFM and the reflectance is measured by spectrophotometer.

• Proceedings of the Korean Vacuum Society Conference
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• 2007.02a
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• pp.180-180
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• 2007

• Proceedings of the Materials Research Society of Korea Conference
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• 2008.05a
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• pp.4.1-4.1
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• 2008

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.415-415
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• 2012

ZnO nanostructures were synthesized by a vapor phase transport process in a single-zone furnace within a horizontal quartz tube with an inner diameter of 38 mm and a length of 485 mm. The ZnO nanostructures were grown on Au-catalyzed Si(100) substrates by using a mixture of zinc oxide and graphite powders. The growth of ZnO nanostructures was conducted at $800^{\circ}C$ for 30 min. High-purity Ar and $O_2$ gases were pushed through the quartz tube during the process at a flow rate of 100 and 10 sccm, respectively. The sequence of ON/OFF cycles of the Ar gas flow was repeated, while the $O_2$ flow is kept constant during the growth time. The Ar gas flow was ON for 1 min/cycle and that was OFF for 2 min/cycle. The structure and optical properties of the ZnO nanostructures were investigated by field-emission scanning electron microscope, X-ray diffraction, temperature-dependent photoluminescence. The preferred orientation of the ZnO nanostructures was along c-axis with hexagonal wurtzite structure.

• Journal of Powder Materials
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• v.23 no.4
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• pp.270-275
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• 2016

We report on an all-solution-processed hydrothermal method to control the morphology of ZnO nanostructures on Si substrates from three-dimensional hemispherical structures to two-dimensional thin film layers, by controlling the seed layer and the molar contents of surfactants during their primary growth. The size and the density of the seed layer, which is composed of ZnO nanodots, change with variation in the solute concentration. The ZnO nanodots act as heterogeneous nucleation sites for the main ZnO nanostructures. When the seed layer concentration is increased, the ZnO nanostructures change from a hemispherical shape to a thin film structure, formed by densely packed ZnO hemispheres. In addition, the morphology of the ZnO layer is systematically controlled by using trisodium citrate, which acts as a surfactant to enhance the lateral growth of ZnO crystals rather than a preferential one-dimensional growth along the c-direction. X-ray diffraction and energy dispersive X-ray spectroscopy results reveal that the ZnO structure is wurtzite and did not incorporate any impurities from the surfactants used in this study.

• Journal of Electrochemical Science and Technology
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• v.11 no.4
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• pp.330-335
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• 2020

Silicon surface nanostructures, which can be easily prepared by electrochemical etching, have attracted considerable attention because of its useful physical properties that facilitate application in diverse fields. In this work, electrochemical and electrochemical-scanning tunneling microscopic (EC-STM) techniques were employed to study the evolution of surface morphology during the electrochemical etching of Si(111)-H in a fluoride solution. The results exhibited that silicon oxide of the Si(111) surface was entirely stripped and then the surface became hydrogen terminated, atomically flat, and anisotropic in the fluoride solution during chemical etching. At the potential more negative than the flat band one, the surface had a tendency to be eroded very slowly, whereas the steps of the terrace were not only etched quickly but the triangular pits also deepened on anodic potentials. These results provided information on the conditions required for the preparation of porous nanostructures on the Si(111) surface, which may be applicable for sensor (or device) preparation (Nanotechnology and Functional Materials for Engineers, Elsevier 2017, pp. 67-91).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.116-117
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• 2006

I-D ZnO nanostructures were fabricated by thermal evaporation method on Si(100), GaN and $Al_2O_3$ substrates without a catalyst at the reaction temperature of $700^{\circ}C$. Only pure Zn powder was used as a source material and Ar was used as a carrier gas. The shape and growth direction of synthesized ZnO nanostructures is determined by the crystal structure and the lattice mismatch between ZnO and substrates. The ZnO nanostructure on Si substrate were inclined regardless of their substrate orientation. The origin of ZnO/Si interface is highly lattice-mismatched and the surface of the Si substrate inevitably has the $SiO_2$ layer. The ZnO nanostructure on the $Al_2O_3$ substrate was synthesized into the rod shape and grown into particular direction. For the GaN substrate, however, ZnO nanostructure with the honeycomb-like shape was vertically grown, owing to the similar lattice parameter with GaN substrate.