Soyoung Choo

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.

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 rigid stamp on a cylindrical substrate using hydrogen silsesquioxane/ZrO2 nanoparticle composite material for roll-to-roll nanoimprinting process

In this study, a hydrogen silsesquioxane (HSQ) and zirconium oxide (ZrO2, zirconia) nanoparticle composite was used for a nanopatterned roll stamp fabricated using the direct printing technique. HSQ, referred as a spin on glass (SOG) material have been used for direct printing process with polydimethylsiloxane mold. In order to enhance mechanical properties of SOG material without losing printable property, ZrO2 nanoparticles were dispersed with HSQ solution. After direct printing process of composite material, annealing process was done to convert polymeric HSQ structure into SiO2 in order to enhance mechanical properties. We evaluate the chemical, optical and mechanical properties of the HSQ/ZrO2 composite by FT-IR, a refractive index measurement, a nanoindentation test and a pencil adhesion test. At the mechanical property tests, the composite material shows a high hardness value and good adhesion properties with glass substrate. Considering the composite material properties, it is suitable for use as a master cylindrical stamp in a roll-to-roll process.

Fabrication of a roll imprint stamp using zirconia for the UV roll imprinting process

In the present work, we have developed a new method for fabricating a roll imprint stamp containing three dimensional micro- and nanosized patterns for the ultraviolet (UV) roll imprinting process, using a flexible poly-dimethylsiloxane (PDMS) mold and a UV-curable zirconium oxide (ZrO2) nanoparticle (NP) dispersion resin. By employing the UV-curing imprinting process, the micro- and nanopatterns on the PDMS mold were successfully transferred to the ZrO2 NP dispersion resin film, attached to the surface of the roll. The obtained ZrO2 roll imprint stamp has two main advantages: a high hardness after annealing at 600 °C and a good anti-sticking surface after the surface treatment carried out using a hydrophobic self-assembled monolayer (SAM). As a result, the ZrO2 roll imprint stamp effectively transferred its micro- and nanopatterns to a large area of the flexible polymer substrate, maintaining a high quality throughout the whole UV roll imprinting process.