Jaeyeon Hwang

Replication of cicada wing’s nano-patterns by hot embossing and UV nanoimprinting

The hydrophobicity of the cicada wing originates from its naturally occurring, surface nano-structure. The nano-structure of the cicada wing consists of an array of nano-sized pillars, 100 nm in diameter and 300 nm in height. In this study, the nano-structure of the cicada wing was successfully duplicated by using hot embossing lithography and UV nanoimprint lithography (NIL). The diameter and pitch of replication were the same as those of the original cicada wing and the height was a little smaller than that of the original master. The transmittance of the hot embossed PVC film was increased by 2-6% compared with that of the bare PVC film. The hydrophobicity was measured by water contact angle measurements. The water contact angle of the replica, made of UV cured polymer, was 132 degrees +/- 2 degrees , which was slightly lower than that of the original cicada wing (138 degrees +/- 2 degrees ), but much higher than that of the UV cured polymer surface without any nano-sized pillars (86 degrees ).

Enhanced oxygen diffusion in epitaxial lanthanum–strontium–cobaltite thin film cathodes for micro solid oxide fuel cells

The chemical diffusion coefficient (Dchem) of epitaxial LSC thin films was measured by a newly designed conductivity relaxation method. Dchem of epitaxial thin films was found to be higher than that of bulk LSC by up to two orders of magnitude, and was found to be enhanced further as the film became thinner.

Microstructure refinement of pulsed laser deposited La0.6Sr0.4CoO3−δ thin-film cathodes for solid oxide fuel cell

In this study, the microstructural modification of pulsed laser deposited La0.6Sr0.4CoO3−δ (LSC64) thin-film cathodes for solid oxide fuel cells (SOFCs) to improve the lateral conduction and to reduce the surface composition degradation is investigated. A high-temperature deposited 100 nm-thick denser LSC64 layer is added over 2.4 μm-thick porous cathode to cover and bridge the cathode domains. According to the cell performance analyses using current-voltage-power measurements, the performance of the cell modified with an additional denser layer is increased compared with the cell without the denser layer in all operating temperature range. The degree of improvement of peak power density is bigger than 10% at 650–550 °C and is about 6% at 500 °C. This performance enhancement can be attributed to the electrochemical property improvement, especially oxygen surface exchange property, rather than to the conduction improvement, based on the electrochemical impedance analysis. Improved crystallinity and composition integrity of the denser LSC64 layer is considered to enhance the surface exchange property of the cathode.