• 한국세라믹학회지
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• 제53권2호
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• pp.227-233
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• 2016

In order to make a highly ordered three-dimensional porous structure of titania ceramics, porogen beads of PS [Polystyrene] and PMMA [poly(methylmetacrylate)] were prepared by emulsion polymerization using styrene monomer and methyl methacrylate monomer, respectively. The uniform beads of PS or PMMA latex were closely packed by centrifugation as a porogen template for the infiltration of titanium butoxide solution. The mixed compound of PS or PMMA with titanium butoxide was dried and the dry compacts were calcined at $450^{\circ}C-750^{\circ}C$ according to the firing schedule to prepare micro- and meso- structures of polycrystalline titania with monodispersed porosity. Inorganic frameworks composed of $TiO_2$ were formed and showed a three Dimensionally Ordered Microstructure [3DOM] of $TiO_2$ ceramics. The pulverized particles of the $TiO_2$ ceramic skeleton were characterized using XRD analysis. A monodispersed crystalline micro-structure with micro/meso porosity was observed by FE-SEM with EDX analysis. The 3DOM $TiO_2$ skeleton showed opalescent color tuning according to the direction of light.

• 한국세라믹학회지
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• 제55권2호
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• pp.108-115
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• 2018

The increasing demands for three-dimensional (3D) electronic and optoelectronic devices have triggered interest in epitaxial growth of 3D semiconductor materials. However, most of the epitaxially-grown nano- and micro-structures available so far are limited to certain forms of crystal arrays, and the level of control is still very low. In this review, we describe our latest progress in 3D epitaxy of oxide and nitride semiconductor crystals. This paper covers issues ranging from (i) low-temperature solution-phase synthesis of a well-regulated array of ZnO single crystals to (ii) systematic control of the axial and lateral growth rate correlated to the diameter and interspacing of nanocrystals, as well as the concentration of additional ion additives. In addition, the critical aspects in the heteroepitaxial growth of GaN and InGaN multilayers on these ZnO nanocrystal templates are discussed to address its application to a 3D light emitting diode array.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 추계학술대회 논문집
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• pp.102-133
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• 2015

Nature, such as plants, insects, and marine animals, uses micro/nano-textured surfaces in their components (e.g., leaves, wings, eyes, legs, and skins) for multiple purposes, such as water-repellency, anti-adhesiveness, and self-cleanness. Such multifunctional surface properties are attributed to three-dimensional surface structures with modulated surface wettability. Especially, hydrophobic surface structures create a composite interface with liquid by retaining air between the structures, minimizing the contact area with liquid. Such non-wetting surface property, so-called superhydrophobicity, can offer numerous application potentials, such as hydrodynamic drag reduction, anti-biofouling, anti-corrosion, anti-fogging, anti-frosting, and anti-icing. Over the last couple of decades, we have witnessed a significant advancement in the understanding of surface superhydrophobicity as well as the design, fabrication, and applications of superhydrophobic coatings/surfaces/materials. In this talk, the designs, fabrications, and applications of superhydrophobic surfaces for multifunctionalities will be presented, including hydrodynamic friction reduction, anti-biofouling, anti-corrosion, and anti-icing.

• 센서학회지
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• 제22권2호
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• pp.100-104
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• 2013

A superhydrophobic mesh is a unique structure that blocks water, while allowing gases, sound waves, and energy to pass through the holes in the mesh. This mesh is used in various devices, such as gas- and energy-permeable waterproof membranes for underwater sensors and electronic devices. However, it is difficult to fabricate micro- and nano-structures on three-dimensional surfaces, such as the cylindrical surface of a wire mesh. In this research, we successfully produced a superhydrophobic water-repellent mesh with a high contact angle (> $150^{\circ}$) for nanofibrous structures. Conducting polymer (CP) composite nanofibers were evenly coated on a stainless steel mesh surface, to create a superhydrophobic mesh with a pore size of $100{\mu}m$. The nanofiber structure could be controlled by the deposition time. As the deposition time increased, a high-density, hierarchical nanofiber structure was deposited on the mesh. The mesh surface was then coated with Teflon, to reduce the surface energy. The fabricated mesh had a static water contact angle of $163^{\circ}$, and a water-pressure resistance of 1.92 kPa.

• 한국표면공학회지
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• 제51권6호
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• pp.387-392
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• 2018

Nanopatterning is one of the essential nanotechnologies to fabricate electronic and energy nanodevices. Therefore, many research group members made a lot of efforts to develop simple and useful nanopatterning methods to obtain highly ordered nanostructures with functionality. In this study, in order to achieve pattern formation of three-dimensional (3D) hierarchical nanostructures, we introduce a simple and useful patterning method (nano-transfer printing (n-TP) process) consisting of various linewidths for diverse materials. Pt and $WO_3$ hybrid line structures were successfully stacked on a flexible polyimide substrate as a multi-layered hybrid 3D pattern of Pt/WO3/Pt with line-widths of $1{\mu}m$, $1{\mu}m$ and 250 nm, respectively. This simple approach suggests how to fabricate multiscale hybrid nanostructures composed of multiple materials. In addition, functional hybrid nanostructures can be expected to be applicable to various next-generation electronic devices, such as nonvolatile memories and energy harvesters.

• Current Optics and Photonics
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• 제5권6호
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• pp.699-710
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• 2021

In this study, we propose a biomimetic optical structure design methodology for investigating micro-optical mechanisms associated with the compound eyes of insects. With these compound eyes, insects can respond fast while maintaining a wide field of view. Also, considerable research attention has been focused on the insect compound eyes to utilize these benefits. However, their nano micro-structures are complex and challenging to demonstrate in real applications. An effectively integrated design methodology is required considering the manufacturing difficulty. We show that photorealistic ray-traced visualization is an effective method for designing the biomimetic of a micro-compound eye of an insect. We analyze the image formation mechanism and create a three-dimensional computer-aided design model. Then, a ray-trace visualization is applied to observe the optical image formation. Finally, the segmented images are stitched together to generate an image with a wide-angle; the image is assessed for quality. The high structural similarity index (SSIM) value (approximately 0.84 to 0.89) of the stitched image proves that the proposed MATLAB-based image stitching algorithm performs effectively and comparably to the commercial software. The results may be employed for the understanding, researching, and design of advanced optical systems based on biological eyes and for other industrial applications.

• 소성∙가공
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• 제19권3호
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• pp.152-159
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• 2010

Rapid mold heating has been recent issue to enable the injection molding of thin-walled parts or micro/nano structures. High-frequency induction is an efficient way to heat mold surface by electromagnetic induction in a non-contact manner, and has been recently applied to the injection molding due to its capability of rapid heating and cooling of mold surface. The present study covers a three-dimensional finite element analysis to investigate heating efficiency and structural safety of the induction heating process of an injection mold. To simulate the induction heating process, an integrated simulation method is proposed by effectively connecting an electromagnetic field analysis, a transient heat transfer analysis and a thermal stress analysis. The estimated temperature changes are compared with experimental measurements for various types of induction coil, from which heating efficiency according to the coil shape is discussed. The resulting thermal stress distributions of the mold plate for various types of induction coils are also evaluated and discussed in terms of the structural safety.

• 한국광학회:학술대회논문집
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• 한국광학회 2003년도 하계학술발표회
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• pp.64-65
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• 2003

Stereo-lithography using the two photon absorption(TPA) makes micro structures with great resolution. The technique is applied to correcting photomask, 3-D photonic crystal, 3-D optical storage, 3-D lithography and so on. In contrast to a conventional stereo-lithography with single-photon absorption which has a size problem caused by the geometrical diffraction limit, the stereo-lithography with TPA has no size limit. (omitted)

• 센서학회지
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• 제21권3호
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• pp.217-222
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• 2012

Optical coherence tomography(OCT) is a noninvasive optical imaging tool for biomedical applications. OCT can provide depth resolved two/three dimensional morphological images on biological samples. In this paper, we integrated an OCT system that was composed of an SLED(Superluminescent Light Emitting Diode, ${\lambda}_0$=1305 nm bandwith= 141 nm), a reference arm adopting a rapid scanning optical delay line(RSOD) to get high speed imaging, and a sample arm that used a micro electro mechanical systems(MEMS) scanning mirror. The sample arm contained a compact probe for imaging dental structures. The performance of the system was evaluated by imaging in-vivo human teeth with dental calculus, and the results indicated distinct appearance of dental calculus from enamel, gum or decayed teeth. The developed probe and system could successfully confirm the presence of dental calculus with a very high spatial resolution($6{\mu}m$).

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.241-241
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• 2008

Macrofore formation in silicon and other semiconductors using electrochemical etching processes has been, in the last years, a subject of great attention of both theory and practice. Its first reason of concern is new areas of macropore silicone applications arising from microelectromechanical systems processing (MEMS), membrane techniques, solar cells, sensors, photonic crystals, and new technologies like a silicon-on-nothing (SON) technology. Its formation mechanism with a rich variety of controllable microstructures and their many potential applications have been studied extensively recently. Porous silicon is formed by anodic etching of crystalline silicon in hydrofluoric acid. During the etching process holes are required to enable the dissolution of the silicon anode. For p-type silicon, holes are the majority charge carriers, therefore porous silicon can be formed under the action of a positive bias on the silicon anode. For n-type silicon, holes to dissolve silicon is supplied by illuminating n-type silicon with above-band-gap light which allows sufficient generation of holes. To make a desired three-dimensional nano- or micro-structures, pre-structuring the masked surface in KOH solution to form a periodic array of etch pits before electrochemical etching. Due to enhanced electric field, the holes are efficiently collected at the pore tips for etching. The depletion of holes in the space charge region prevents silicon dissolution at the sidewalls, enabling anisotropic etching for the trenches. This is correct theoretical explanation for n-type Si etching. However, there are a few experimental repors in p-type silicon, while a number of theoretical models have been worked out to explain experimental dependence observed. To perform ordered macrofore formaion for p-type silicon, various kinds of mask patterns to make initial KOH etch pits were used. In order to understand the roles played by the kinds of etching solution in the formation of pillar arrays, we have undertaken a systematic study of the solvent effects in mixtures of HF, N-dimethylformamide (DMF), iso-propanol, and mixtures of HF with water on the macrofore structure formation on monocrystalline p-type silicon with a resistivity varying between 10 ~ 0.01 $\Omega$ cm. The etching solution including the iso-propanol produced a best three dimensional pillar structures. The experimental results are discussed on the base of Lehmann's comprehensive model based on SCR width.