Kang Soo Han

Fabrication of complex nanoscale structures on various substrates

Polymer based complex nanoscale structures were fabricated and transferred to various substrates using reverse nanoimprint lithography. To facilitate the fabrication and transference of the large area of the nanostructured layer to the substrates, a water-soluble polyvinyl alcohol mold was used. After generation and transference of the nanostructured layer, the polyvinyl alcohol mold was removed by dissolving in water. A residue-free, UV-curable, glue layer was formulated and used to bond the nanostructured layer onto the substrates. As a result, nanometer scale patterned polymer layers were bonded to various substrates and three-dimensional nanostructures were also fabricated by stacking of the layers.

Fabrication of 3D nano-structures using reverse imprint lithography

In spite of the fact that the fabrication process of three-dimensional nano-structures is complicated and expensive, it can be applied to a range of devices to increase their efficiency and sensitivity. Simple and inexpensive fabrication of three-dimensional nano-structures is necessary. In this study, reverse imprint lithography (RIL) with UV-curable benzylmethacrylate, methacryloxypropyl terminated poly-dimethylsiloxane (M-PDMS) resin and ZnO-nano-particle-dispersed resin was used to fabricate three-dimensional nano-structures.UV-curable resins were placed between a silicon stamp and a PVA transfer template, followed by a UV curing process. Then, the silicon stamp was detached and a 2D pattern layer was transferred to the substrate using diluted UV-curable glue. Consequently, three-dimensional nano-structures were formed by stacking the two-dimensional nano-patterned layers. RIL was applied to a light-emitting diode (LED) to evaluate the optical effects of a nano-patterned layer. As a result, the light extraction of the patterned LED was increased by about 12% compared to an unpatterned LED.

Fabrication of sub-100 nm sized patterns on curved acryl substrate using a flexible stamp

As small as 100 nm patterns were successfully transferred onto a non-planar acryl substrate using both UV nanoimprinting and hot embossing techniques. Two different types of flexible imprint stamps, electroformed nickel foil stamp and molded water-soluble poly(vinyl alcohol) (PVA) stamp, were used. 100 nm line and space pattern of Si master was successfully transferred to nickel foil stamp and PVA stamp and their patterns were also transferred to the surface of curved acryl substrate using either UV nanoimprint lithography or hot embossing lithography.

A Fabrication Method of the Silica-Based Moth-Eye Structures and Its Application to the Organic Light-Emitting Diodes

For the application of moth-eye patterns to practical optical devices, a novel nano-patterning technique, which can fabricate transparent and robust material based nano patterns through a simple process, needs to be developed, because the moth-eye structures are usually exposed to the outer environment. In this study, silica based moth-eye structures were directly fabricated on a glass substrate by the direct hydrogen silsesquioxane (HSQ) printing and annealing technique. The transmittance of the glass substrate was enhanced by 3–4% in the visible range by the silica moth-eye structures and it was confirmed that the light output efficiency of the green organiclight emitting diode (OLED) was enhanced by 7–9% using the encapsulation glass with the silica moth-eye patterns.

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.

Fabrication of Nano-Porous Structure on Silicon Substrate Using Nanoimprint Lithography with an Anodic Aluminum Oxide Nano-Template

A polymer template, which has an array of 300 nm diameter pillar patterns, was fabricated by hot embossing method using anodic aluminum oxide (AAO) template as an embossing stamp. After depositing the thin layer of silicon oxide and coating of anti-adhesion monolayer of organic film on silicon oxide, UV nanoimprint lithography was carried out with the polymer template. As a result, nano-pore array pattern, identical to anodic aluminum oxide pattern, was fabricated on silicon substrate. Residual layer of imprinted nano-pore array pattern was removed by oxygen plasma etch and thin film of Au/Ti was deposited. After lift-off process, Au/Ti dot array was also fabricated on silicon substrate.

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.

Functional patterns for thin-film-type amorphous silicon solar cells

Three types of patterns acting as light-scattering centers were constructed on bulk glass surfaces and applied to solar cell fabrication. In order to fabricate a scattering center in the transparent conducted oxide (TCO) layer, the SiO2-based solution hydrogen silsesquioxane (HSQ; Dow Corning FOx-16) was used for direct nano-patterning. Direct nano-patterning is a simple and fast process that exploits the solvent permeability of poly(dimethylsiloxane) (PDMS). The nano- and micro-structured SiO2 layer fabricated directs diffused light into the active layer of the solar cell, enabling effective use of this layer. This increases the external quantum efficiency and conversion efficiency of the cell. Additionally, a thinner Si junction was fabricated to ensure the effect of each pattern.

Fabrication of Diverse-Scale Patterned Layer on Organic Photovoltaics

In order to increase the conversion efficiency of organic photovoltaics (OPV), diverse-scale patterns were formed on a glass substrate using the direct printing technique. The optical properties of the patterns depended on the size, shape, height, and pitch of the patterns. Randomly distributed nano- and micro-patterns caused light scattering, which increased the diffusion transmittance. The other pattern, which was a nano-sized anti-reflective pattern comprising a 300 nm sized hexagonal array, decreased the reflectance of light on the surface. The optical properties of these patterns, can be used to improve solar cell efficiency by increasing the light allowed onto the light-absorbing layer. We used a direct printing method with a poly(dimethylsiloxane) (PDMS) mold to fabricate these patterns on glass substrates. These patterns were transferred from PDMS to the surface of a glass substrate. Hydrogen silsesquioxane (HSQ) was used as a resin since its properties include volatility and allow for spin-coating; it also has a reflective index similar to that of glass. This method has low cost and a simple process compared to optic-based lithography. After these patterns were formed outside the glass substrate, a conductive polymer layer and the active layer were formed by spin-coating, and the cathode was deposited by a thermal evaporator. The electrical properties of solar cells fabricated with these patterns on their surfaces were measured with a solar simulator. The conversion efficiency of the solar cells with these surface patterns showed an increase of up to 6.8% in comparison with conventional cells.

Fabrication of Mo Nano Patterns Using Nano Transfer Printing with Poly Vinyl Alcohol Mold

)Abstract Nanofabrication is an essential process throughout industry. Technologies that produce generalnanofabrication, such as e-beam lithography, dip-pen lithography, DUV lithography, immersion lithography,and laser interference lithography, have drawbacks including complicated processes, low throughput, and highcosts, whereas nano-transfer printing (nTP) is inexpensive, simple, and can produce patterns on non-planesubstrates and multilayer structures. In general nTP, the coherency of gold-deposited stamps is strengthenedby using SAM treatment on substrates, so the gold patterns are transferred from stamps to substrates.However, it is hard to apply to transfer other metallic materials, and the existing nTP process requires acomplicated surface treatment. Therefore, it is necessary to simplify the nTP technology to obtain an easy andsimple method for fabricating metal patterns. In this paper, asnTP process with poly vinyl alcohol (PVA) moldwas proposed without any chemical treatment. At first, a PVA mold was duplicated from the master mold.Then, a Mo layer, with a thickness of 20 nm, was deposited on the PVA mold. The Mo deposited PVA moldwas put on the Si wafer substrate, and nTP process progressed. After the nTP process, the PVA mold wasremoved using DI water, and transferred Mo nano patterns were characterized by a Scanning electronmicrograph (SEM) and Energy Dispersive spectroscopy (EDS). Key wordsnano-transfer printing (nTP), poly vinyl alcohol (PVA), Mo nano pattern.