Ju Hyeon Shin

3D Amorphous Silicon on Nanopillar Copper Electrodes as Anodes for High-Rate Lithium-Ion Batteries

We present an amorphous Si anode deposited on a Cu nanopillar current collector, fabricated using a thermal roll-to-roll process followed by electroformation and LPCVD, for application in high-rate Li-ion batteries. Cu nanopillar current collectors with diameters of 250 and 500 nm were patterned periodically with 1 μm pitch and 2 μm height to optimize the diameters of the pillars for better electrochemical performance. Void spaces between Cu nanopillars allowed not only greater effective control of the strain caused by the Si expansion during lithiation than that allowed by a nonpatterned electrode but also significantly improved cycle performance even at 20 C measured after the same rate test: After 100 cycles at 0.5 C, the patterned electrodes with 250 and 500 nm diameter nanopillars showed high capacity retentions of 86% and 84%, respectively. These electrodes retained discharge capacities of 1057 and 780 mAh/g even at 20 C, respectively.

Uniformly embedded silver nanomesh as highly bendable transparent conducting electrode

Ag-nanomesh-based highly bendable conducting electrodes are developed using a combination of metal nanotransfer printing and embossing for the 6-inch wafer scale. Two Ag nanomeshes, including pitch sizes of 7.5 and 10 μm, are used to obtain highly transparent (approximately 85% transmittance at a wavelength of 550 nm) and electrically conducting properties (below 10 Ω sq(-1)). The Ag nanomeshes are also distinguished according to the fabrication process, which is called transferred or embedded Ag nanomesh on polyethylene terephthalate (PET) substrate, in order to compare their stability against bending stress. Then the enhancement of bending stability when the Ag nanomesh is embedded in the PET substrate is confirmed.

Fabrication of functional nanosized patterns with UV-curable polysilsesquioxane on photovoltaic protective glass substrates using hybrid nano-imprint lithography

UV-curable polysilsesquioxane materials were used to incorporate moth-eye structures on photovoltaic (PV) protective glass. These patterns were formed using a hybrid nanoimprint lithography technique and annealed at 100 °C to evaporate the solvent (xylene). Compared to the bare, un-patterned PV protective glass, the PV protective glass patterned on both sides had superior optical properties. Transmittance of the PV protective glass patterned on both sides increased by up to 3.13% and reflectance decreased by up to 3.42%, and the transmittance was increased for all angles of incidence. Furthermore, the JSC of devices with the PV protective glass patterned on both sides increased by up to 3.15%. Finally, a monitoring system was set up to measure electricity generated by PV modules. The efficiency of the PV module with PV protective glass patterned on both sides was enhanced by up to 12.16% compared with that of the PV module with un-patterned PV protective glass.

A tunable method for nonwetting surfaces based on nanoimprint lithography and hydrothermal growth

In nature, some living things exhibit special wettability properties such as superhydrophobicity. Many scientists have tried to mimic these properties for utilizing them in various applications. Especially, surface morphology is as important as the surface energy to create the superhydrophobicity. In this study, we used a hybrid method—a combination of sol–gel-based nanoimprint lithography and hydrothermal growth—to tune the surface morphology. Ten kinds of TiO2 structures were fabricated using this method and their wetting properties for various liquids and evaporation of water were analyzed. In particular, TiO2 nano- and hierarchical structures, which possess superhydrophobicity, were compared on the basis of these measurements. From these analyses, we confirmed that TiO2 hierarchical structures formed the most stable superhydrophobic state, which have the contact angles over 160° for water and the longest time for natural evaporation of water, compared to other ten kinds of TiO2 structures.

Fabrication of Nanosized Antireflection Patterns on Surface of Aspheric Lens Substrate by Nanoimprint Lithography

Currently, various techniques are being explored for fabricating nano- or microsized patterns on flat and curved substrates. However, there are only a few techniques that can be used to fabricate nano- to microsized patterns on the surface of aspheric lenses. In this study, nanoimprint lithography (NIL) was used to obtain nanosized antireflection structures on the surface of aspheric lenses. In order to ensure conformal contact between the imprint mould and the aspheric lens substrate, a highly flexible poly(urethane acrylate) (PUA)-based film mould was used. As a result, various nanosized patterns were uniformly fabricated on the surface of the aspheric lens with high fidelity.

Various Metallic Nano-Sized Patterns Fabricated Using an Ag Ink Printing Technique

This paper presents a new simple metal patterning technique, which is based on soft nanoimprint lithography. By using this method with a commercial Ag nano particle ink, a nano-sized metal pattern was successfully fabricated. The problem of the residual layer of patterned Ag layer was minimized by controlling the concentration of the solution and the process conditions. By using this method, we could easily fabricate various patterns without reference to any shape. Furthermore, we fabricated an Ag mesh type pattern for the application of conducting transparent glass.

Nanosized Structural Anti-Reflection Layer for Thin Film Solar Cells

A nanosized pattern layer was formed on the front surface (glass side) of the thin film solar cell using nanoimprint lithography with a Ni based moth-eye imprint mold in order to increase the total conversion efficiency of the amorphous silicon based thin film solar cell. The imprinted pattern layer had nanosized protrusions, which suppressed the reflection of light on the glass surfaces. The nanopatterns were formed using a methacryloxypropyl terminated poly(dimethylsiloxane) (MPDMS) based hard polymeric resin. The reflectance of the thin film solar cell significantly decreased because of the nanosized structural anti-reflection layer, and the total conversion efficiency of the cell increased about 3% compared to the identical solar cell without the nanosized pattern layer. Moreover, the surface exhibited a hydrophobic nature because of the surface nanopatterns and the self-assembled monolayer coating, and this hydrophobicity provided the solar cell with a self-cleaning functionality.

Enhanced light extraction efficiency in organic light emitting diodes using a tetragonal photonic crystal with hydrogen silsesquioxane

We report an organic light emitting diode (OLED) with a hydrogen silsesquioxane as a scattering material, for enhancing light extraction efficiency. A tetragonal photonic crystal was used as pattern type, and fabricated using a direct printing technique. Planarization was accomplished using TiO₂ solgel solution, having a refractive index identical to that of the indium zinc oxide transparent electrode. The current efficiency and power efficiency of the OLED increased by 17.3% and 43.4% at 10  mA/cm², respectively, without electric degradation.

Fabrication of silica nanostructures with a microwave assisted direct patterning process

Silica nanostructures were fabricated on glass substrate using a microwave assisted direct patterning (MADP) process, which is a variety of soft lithography. During the MADP process using polydimethylsiloxane (PDMS), mold and microwave heating are performed simultaneously. Blanket thin film and micro- to nano-sized structures, including moth-eye patterns of SiO2, which consisted of coalesced silica nanoparticles, were formed on glass substrates from SiO2 nano-particle dispersed solutions with varied microwave heating time. Optical properties and surface morphologies of micro-sized hemisphere, nano-sized pillar, moth-eye and 50 nm sized line/space silica patterns were measured using UV-vis and a scanning electron microscope. X-ray diffraction analysis of SiO2 thin films with and without microwave heating was also carried out.

Fabrication of flexible UV nanoimprint mold with fluorinated polymer-coated PET film

UV curing nanoimprint lithography is one of the most promising techniques for the fabrication of micro- to nano-sized patterns on various substrates with high throughput and a low production cost. The UV nanoimprint process requires a transparent template with micro- to nano-sized surface protrusions, having a low surface energy and good flexibility. Therefore, the development of low-cost, transparent, and flexible templates is essential. In this study, a flexible polyethylene terephthalate (PET) film coated with a fluorinated polymer material was used as an imprinting mold. Micro- and nano-sized surface protrusion patterns were formed on the fluorinated polymer layer by the hot embossing process from a Si master template. Then, the replicated pattern of the fluorinated polymer, coated on the flexible PET film, was used as a template for the UV nanoimprint process without any anti-stiction coating process. In this way, the micro- to nano-sized patterns of the original master Si template were replicated on various substrates, including a flat Si substrate and curved acryl substrate, with high fidelity using UV nanoimprint lithography.