• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.1
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• pp.45-49
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• 2006

A nano-stereolithography (NSL) process has been developed for the fabrication of three-dimensional (3D) micro-devices with high spatital resolution of approximately 100 nm. In the NSL process, a complicated 3D structure can be created by stacking layer-by-layer, so it does not require any sacrificial layer or any supporting structure. A laminated layer was fabricated by means of solidifying liquid-state monomers using two-photon absorption (TPA) which was induced by a femtosecond laser. When the fabrication of a 3D stacked structure was finished, unsolidified liquid resins were rinsed by ethanol to develop the fabricated structures; then, the polymerized structure was only left on the glass substrate. Through this work, several 3D microstructures such as a micro-channel, shell structures, and photonic crystals were fabricated to evaluate the possibility of the developed system.

• Computers and Concrete
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• v.24 no.3
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• pp.185-192
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• 2019

In this paper, the buckling of micro sandwich hollow circular plate is investigated with the consideration of the porous core and piezoelectric layer reinforced by functionally graded (FG)carbon nano-tube. For modeling the displacement field of sandwich hollow circular plate, the high-order shear deformation theory (HSDT) of plate and modified couple stress theory (MCST) are used. The governing differential equations of the system can be derived using the principle of minimum potential energy and Maxwell's equation that for solving these equations, the Ritz method is employed. The results of this research indicate the influence of various parameters such as porous coefficients, small length scale parameter, distribution of carbon nano-tube in piezoelectric layers and temperature on critical buckling load. The purpose of this research is to show the effect of physical parameters on the critical buckling load of micro sandwich plate and then optimize these parameters to design structures with the best efficiency. The results of this research can be used for optimization of micro-structures and manufacturing different structure in aircraft and aerospace.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.7
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• pp.777-782
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• 2011

Micro features on the surface are well-known to have significant effects on optical or mechanical properties such as the optical interference, reflectance at the surface, contact angle, interfacial friction, etc. These surface micro features are increasingly employed to enhance the functionality of the applications in various application areas such as optical components for LCD or solar panel. Diverse surface features have been proposed and some of them are showing excellent efficiency or functionality, especially in optical applications. Most applications employing the micro features need manufacturing process for mass production and the injection molding and roll-to-roll forming, which are typical processes for mass production adopting polymeric materials, may be also preferred for micro patterned plastic product. Since the functionality or efficiency of the surface structures generally depends on the shape and the size of the structure itself or the array of the structures on the surface, it would be very important to replicate the features very precisely as being designed during the molding the micro pattern applications. In this paper, a series of research activities is introduced for roll-to-roll forming of micro patterned film including filling of patterns with UV curable resin, demolding of surface structures from the roll tool, control of surface energy and cure shrinkage of resin and dispose time and intensity of the UV light for curing of UV curable resin.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.381-381
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• 2011

The influence of the water vapor on the growth of single-walled carbon nanotubes (SWCNTs) was investigated. SWCNTs were synthesized by catalytic chemical vapor deposition of acetylene over Fe-Mo/MgO catalyst with injection of water vapor. The morphologies and structures of the water-assisted SWCNTs were investigated according to the growth conditions such as water vapor concentrations, flow rate of the gas, furnace temperature, and growth time. Water-assisted SWCNTs exhibited large bundle morphological features with well-alignment of each CNT, while SWCNTs synthesized in the absence of water vapor showed entangled CNT with the random orientation. We also found that the diameter of the SWCNT bundle could be controlled by the growth condition. In our optimal growth condition, the product yield and the purity were 300 wt. % and 75%, which were 7.5 and 2.5 times higher than those of SWCNTs synthesized without water vapor, respectively. More detail discussion will be offered at the poster presentation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.8
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• pp.531-536
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• 2017

Nano/micro technology is currently applied to improve solid surface wettability, with recent research studies indicating that nanostructures can improve surface wettability in the hydrophilic direction, and liquid spreading (propagation) is generated by capillary wicking. The majority of the existing research involves qualitative analysis of the spreading phenomena, owing to the difficulty in conducting small-scale analysis (nanostructures). In this study, the droplet interfacial behavior on silicon surfaces with micro/nano/micro-nano structures is experimentally investigated. The interfacial behavior is directly visualized using synchrotron X-ray imaging (side view). The spreading phenomena occur on structured surfaces, and the liquid interface behaviors on the surfaces differ. The liquid film thickness is uniform during spreading on the microstructured surface, but not on the nano case which shows a gentle slope. These combined spreading shapes were observed on a micro-nano structured surface, and liquid propagation was enhanced when the micro- and nano-structures are combined.

• Composites Research
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• v.20 no.2
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• pp.17-20
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• 2007

Superhydrophobic polytetrafluoroethylene ($Teflon^{(R)}$, Dupont) sub-micro and nanostructures were fabricated by the dipping method, based on anodization process in oxalic acid. The polymer sticking phenomenon during the replication creates the sub-microstructures on the negative polytetrafluoroethylene nanostructure replica. This process gives a hierarchical structure with nanostructures on sub-microstructures, which looks like the same structures as lotus leaf and enables commercialization. The diameter and the height of the replicated nano pillars were 40 nm and 40 um respectively. The aspect ratio is approximately 1000. The fabricated surface has a semi-permanent superhydrophobicity, the apparent contact angle of the polytetrafluoroethylene sub-micro and nanostructures is about $160^{\circ}$, and the sliding angle is less than $1^{\circ}$.

• Journal of the Korean Society of Industry Convergence
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• v.22 no.5
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• pp.467-473
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• 2019

In this study, approached to improve durability of the multi-functional nano-pattern fabricated on the curved lens surface using nanoimprint lithography (NIL) was proposed, and the effects of the proposed methods on functionality after wear test were examined. To improve the mechanical property of ultraviolet(UV)-curable resin, UV-NIL was conducted at the elevated temperature around $60^{\circ}C$. In addition, micro/nano hierarchical structures was fabricated on the lens surface with a durable film mold. Analysis on the worn surfaces of nano-hole pattern and hierarchical structures and measurements on the static water contact angle and critical water volume for roll-off indicated that the UV curing process with elevated temperature is effective to maintain wettability by increasing hardness of resin. Also, it was found that the micro-scale pattern is effective to protect nano-pattern from damage during wear test.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.96-96
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• 2016

Nanotechnology mostly employs nano-materials and nano-structures with distinctive properties based on their size, structure, and composition. It is quite difficult to produce nano-materials and nano-structures with identical sizes, structures, and compositions in large quantities, because of spatiotemporal fluctuation of production processes. In other words, fluctuation is the bottleneck in nanotechnology. We propose three strategies to suppress such fluctuations: employing 1) difference between linear and nonlinear phenomena, 2) difference in time constants, and 3) nucleation as a bottleneck phenomenon. We are also developing nano- and micro-scale guided assembly using plasmas as a plasma nanofabrication.1-5) We manipulate nano- and micro-objects using electrostatic, electromagnetic, ion drag, neutral drag, and optical forces. The accuracy of positioning the objects depends on fluctuation of position and energy of an object in plasmas. Here we evaluate such fluctuations and discuss the mechanism behind them. We conducted in-situ evaluation of local plasma potential fluctuation using tracking analysis of fine particles (=objects) in plasmas. Experiments were carried out with a radio frequency low-pressure plasma reactor, where we set two quartz windows at the top and bottom of the reactor. Ar plasmas were generated at 200 Pa by applying 13.56MHz, 450V peak-to-peak voltage. The injected fine particles were monodisperse methyl methacrylate-polymer spheres of $10{\mu}m$ in diameter. Fine particles were injected into the reactor and were suspended around the plasma/sheath boundary near the powered electrode. We observed binary collision of fine particles with a high-speed camera. The frame rate was 1000-10000 fps. Time evolution of their distance from the center of mass was measured by tracking analysis of the two particles. Kinetic energy during the collision was obtained from the result. Potential energy formed between the two particles was deduced by assuming the potential energy plus the kinetic energy is constant. The interaction potential is fluctuated during the collision. Maximum amplitude of the fluctuation is 25eV, and the average is 8eV. The fluctuation can be caused by neutral molecule collisions, ion collisions, and fluctuation of electrostatic force. Among theses possible causes, fluctuation of electrostatic force may be main one, because the fine particle has a large negative charge of -17000e and the corresponding electrostatic force is large compared to other forces.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.8
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• pp.966-974
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• 2011

The use of ion beams in the micro/nano scale is greatly increased by technology development. Especially, focused ion beams (FIBs) have a great potential to fabricate the device in sub micro scale. Nevertheless, FIB has several limitations, surface swelling in low ion dose regime, precipitation of incident ions, and the redeposition effect due to the sputtered atoms. In this research, we demonstrate a way which can be used to fabricate mold structures on a silicon substrate using FIBs. For the purpose of the demonstration, two essential subjects are necessary. One is that focused ion beam diameter as well as shape has to be measured and verified. The other one is that the accurate rotational symmetric model of ion-solid interaction has to be mathematically developed. We apply those two, measured beam diameter and mathematical model, to fabricate optical lenses mold on silicon. The characteristics of silicon mold fabrication will be discussed as well as simulation results.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1293-1296
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• 2009

The synthesis of nano-size ($Y_{0.955}Eu_{0.1}$)($P_{0.7}V_{0.45}$)$O_4$ red phosphors were conducted by using a Liquid Phase Precursor (LPP) method. In this method, cellulose pulp was used as a template showing the micro fibre structures to obtain the nano size YPV red phosphor. Aqueous solutions of raw materials were impregnated into cellulose pulp and subsequently impregnated pulp was dried and fired at $800-1200^{\circ}C$ for 1h. The effect of luminescence properties on compositions and temperatures was evaluated with photoluminescence spectrum, X-ray diffraction and FE-SEM, and TEM. High efficiency (~110%) of phosphor of size of ~500nm fired at $1150^{\circ}C$ was obtained compared with the micro size of commercial product. High efficiency behaviors of nano size phosphors were discussed in this paper.