• Journal of Sensor Science and Technology
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• v.23 no.6
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• pp.383-387
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• 2014

Electrically conductive polypyrrole-polyvinylpyrrolidone (PPy-PVP) nanofiber mats with a core-shell structure have been successfully fabricated by a two-step process: the formation of FeCl3-containing PVP nanofiber mat by electrospinning, and the vapor-phase polymerization (VPP) of pyrrole monomer on the mat in a sealed chamber at room temperature. Surface morphology and chemical composition of the PPy-PVP mat were characterized by SEM, EDX and FTIR analyses. The as-prepared nonwoven mat was composed of PPy-PVP nanofibers with an average diameter of 300 nm. The sheet conductivity of the nanofiber mat was measured to be approximately 0.01 S/cm by a four-point probe. We have also investigated gas-sensing properties of PPy-PVP nanofiber mat upon exposure to methanol vapor. The PPy-PVP nanofiber sensors were observed to have excellent methanol-sensing performance. The nanofiber-based core-shell nanostructure could give an opportunity to fabricate a highly sensitive and fast response sensor due to its high surfaceto-volume ratio.

• Current Optics and Photonics
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• v.2 no.6
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• pp.568-575
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• 2018

Various techniques to measure the three-dimensional (3D) surface profile of a 3D micro- or nanostructure have been proposed. However, it is difficult to apply such techniques directly to industrial uses because most of them are relatively slow, unreliable, and expensive. The HiLo optical imaging technique, which was recently introduced in the field of fluorescence imaging, is a promising wide-field imaging technique capable of high-speed imaging with a simple optical configuration. It has not been used in measuring a 3D surface profile although confocal microscopy originally developed for fluorescence imaging has been adapted to the field of 3D optical measurement for a long time. In this paper, to the best of our knowledge, the HiLo optical imaging technique for measuring a 3D surface profile is proposed for the first time. Its optical configuration and algorithm for a precisely detecting surface position are designed, optimized, and implemented. Optical performance for several 3D microscale structures is evaluated, and it is confirmed that the capability of measuring a 3D surface profile with HiLo optical imaging technique is comparable to that with confocal microscopy.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.10a
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• pp.94-95
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• 2016

Calcium Silicate Hydrate (C-S-H), which takes up most of the hydration products of Portland Cement (PC), has the greatest impact on the mechanical behavior and strength development of concrete. The exact mechanism of its deformation, however, has not yet been elucidated. The present study aims to demonstrate the mechanism of nano-deformation behavior of C-S-H in tricalcium silicate paste under compressive loading, unloading and reloading by interpreting atomic pair distribution function (PDF) based on synchrotron X-ray scattering. The strain of the tricalcium silicate paste for a short-range of 0 ~ 20 Å under compressive load exhibited two stages, I) nano-packing of interlayer of C-S-H and II) micro-packing of C-S-H globules, whereas the deformation for a long-range order of 20 ~ 40 Å was similar to that of a calcium hydroxide phase measured by Bragg peak shift. Moreover, the residual strains due to the plastic deformation of C-S-H was clearly observed.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.2
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• pp.65-70
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• 2023

Nanoimprint lithography (NIL) has attracted much attention due to its process simplicity, excellent patternability, process scalability, high productivity, and low processing cost for pattern formation. However, the pattern size that can be implemented on metal materials through conventional NIL technologies is generally limited to the micro level. Here, we introduce a novel hard imprint lithography method, extreme-pressure imprint lithography (EPIL), for the direct nano-to-microscale pattern formation on the surfaces of metal substrates with various thicknesses. The EPIL process allows reliable nanoscopic patterning on diverse surfaces, such as polymers, metals, and ceramics, without the use of ultraviolet (UV) light, laser, imprint resist, or electrical pulse. Micro/nano molds fabricated by laser micromachining and conventional photolithography are utilized for the nanopatterning of Al substrates through precise plastic deformation by applying high load or pressure at room temperature. We demonstrate micro/nanoscale pattern formation on the Al substrates with various thicknesses from 20 ㎛ to 100 mm. Moreover, we also show how to obtain controllable pattern structures on the surface of metallic materials via the versatile EPIL technique. We expect that this imprint lithography-based new approach will be applied to other emerging nanofabrication methods for various device applications with complex geometries on the surface of metallic materials.

• Journal of the Korean institute of surface engineering
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• v.54 no.6
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• pp.340-347
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• 2021

Among various metal oxide semiconductors, ZnO has an excellent electrical, optical properties with a wide bandgap of 3.3 eV. It can be applied as a photocatalytic material due to its high absorption rate along with physical and chemical stability to UV light. In addition, it is important to control the morphology of ZnO because the size and shape of the ZnO make difference in physical properties. In this paper, we demonstrate synthesis of size-controlled ZnO tetrapods using an atmospheric pressure plasma system. A micro-sized Zn spherical powder was continuously introduced in the plume of the atmospheric plasma jet ignited with mixture of oxygen and nitrogen. The effect of plasma power and collection sites on ZnO nanostructure was investigated. After the plasma discharge for 10 min, the produced materials deposited inside the 60-cm-long quartz tube were obtained with respect to the distance from the plume. According to the SEM analysis, all the synthesized nanoparticles were found to be ZnO tetrapods ranging from 100 to 600-nm-diameter depending on both applied power and collection site. The photocatalytic efficiency was evaluated by color change of methylene blue solution using UV-Vis spectroscopy. The photocatalytic activity increased with the increase of (101) and (100) plane in ZnO tetrapods, which is caused by enhanced chemical effects of plasma process.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.275-275
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• 2013

Osteoblast is one of cells related with osseointegration and many research have conducted the adhesion of osteoblast onto the surface of implant. In the osseointegration, biocompatibility of the implant and cell adhesion to the surface are important factors. The researches related to cell adhesion have a direction from micro-scaled surface roughness to nano-scaled surface roughness with advancing nanotechnology. A cell reacts and sense to stimuli from extracellular matrix (ECM) and topography of the ECM [1]. Thus, for better osseointegration, we should provide an environment similar to ECM. In this study, we synthesize TiO2 nanowires using hydrothermal reaction because TiO2 provides inertness to titanium on its surface and enables it used as an implant material for the orthopedic treatment such as fixation of the bone fracture [2]. Ti substrate is immersed into NaOH aqueous solution. The solution are heated at $140{\sim}200^{\circ}C$ for various time (10~720 minutes). After heat treatment, we take out the sample and immerse it into HCl aqueous solution for 1 hour. The acid treated sample is heated again at $500^{\circ}C$ for 3 hours [3]. Then, we culture osteoblast on the TiO2 nanowires. For investigating cell adhesion onto nanostructured surface, we conduct several tests such as MTT assay, ALP (Alkaline phosphatase) activity assay, measuring calcium expression, and so on. These preliminary results of the cell culture on the nanowires are foundation for investigating cell-material interaction especially with nanostructure interaction.

• Composites Research
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• v.34 no.4
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• pp.264-268
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• 2021

In this study, we propose a method for fabricating hydrophobic coatings/films with three-dimensional (3D) hierarchical nanostructured organic/inorganic composite surfaces. An epoxy-based, large-area 3D ordered nanoporous template is first prepared through an advanced photolithography technique called Proximity-field nanoPatterning (PnP). Then, a hierarchically structured surface is generated by densely impregnating the template with silica nanoparticles with an average diameter of 22 nm through dip coating. Due to the coexisting micro- and nano-scale roughness on the surface, the fabricated composite film exhibits a higher contact angle (>137 degrees) for water droplets compared to the reference samples. Therefore, it is expected that the materials and processes developed through this study can be used in various ways in the traditional coating/film field.

• Journal of the Korean Vacuum Society
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• v.22 no.6
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• pp.277-284
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• 2013

Carbon coils could be synthesized using $C_2H_2/H_2$ as source gases and $SF_6$ as an incorporated additive gas under thermal chemical vapor deposition system. The Ni layer on the $SiO_2$ substrate was used as a catalyst for the formation of the carbon coils. The characteristics (formation densities, morphologies, and geometries) of the as-grown carbon coils on the substrate with or without the $H_2$ plasma pretreatment process were investigated. By the relatively short time (1 minute) $H_2$ plasma pretreatment on the Ni catalyst layered-substrate prior to the carbon coils synthesis reaction, the dominant formation of the carbon microcoils on the substrate could be achieved. After the relatively long time (30 minutes) $H_2$ plasma pretreatment process, on the other hand, we could obtain the noble-shaped geometrical nanostructures, namely the formation of the numerous carbon nanocoils along the growth of the carbon microcoils. This noble-shaped geometrical nanostructure seemed to play a promising role as the good catalyst support for holding the very tiny Ni catalyst grains.

• Journal of Adhesion and Interface
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• v.20 no.1
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• pp.23-28
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• 2019

In this study, the micro- and nano-particles were used and their shapes were transferred into the polydimethylsiloxane (PDMS) film to fabricate the dry adhesives and their properties were investigated. The Cu nanoparticles of the sizes of 20 nm, 40 nm and 70 nm and the polymethylmethacrylate (PMMA) beads of the size of $5{\mu}m$ were used to transfer their images and the resultant properties of the dry adhesives were compared. The effects of particle size and materials on the mechanical property, tensile adhesion strength, light transmittance, surface morphology, water contact angle were studied. The dry adhesives obtained from the transfer process of Cu nanoparticles with the size of 20 nm resulted in the enhancement of tensile adhesion strength more than 300% compared to that of the bare PDMS. The formation of nanostructure of large surface area on the surface of the PDMS film by the Cu nanoparticles may responsible for the improvement. This study suggests that the use of nanoparticles during the fabrication of PDMS dry adhesives is easy and effective and could be applied to the fabrication of the medical patch.