Yong Min Park

Three-Dimensional Antireflective Hemispherical Lens Covered by Nanoholes for Enhancement of Light Transmission

This paper presents a hemispherical lens covered with nanoholes for enhancing light transmission. A hemispherical lens integrated with nanoholes was fabricated by an imprinting process that combines the two elastomeric components of the nanopillar-structured membrane and hemispherical cavity. The nanopillar-structured membrane and hemispherical cavity were replicated from nanoporous anodic aluminum oxide and conventional half-ball lens, respectively. The diameter, depth, and spacing of nanoholes on the hemispherical lens were 216±17, 275±17, and 320±25 nm, respectively. The intensity of white LED light transmitted through the nanohole-covered lens was 22% higher than that through a smooth pristine half-ball lens.

Surface Nano-texturing of Stainless Steel for Biocompatibility Enhancement of Implantable Medical Devices

Stainless steel (SUS) has been used in many industrial fields such as bio and medical parts. Especially, implanted medical device (IMD) has been widely researched for enhancing a human life from biological treatment using those devices. These medical devices require some essential requirements, such as biocompatible, non-toxic and human safety. For these reason, many researchers have been suggest a method of surface treatment to decrease a biological damages due to implanted in vivo. However, these proposed methods were had some disadvantages such as semi-permanent and require additional processes. To overcome these disadvantages, our research proposes a surface texturing method that is anodic oxidation based on electro-chemical reaction. Firstly, 1μm aluminum thin layer was deposited on the 4inch SUS-316L wafer. At this point, for the comparison of SUS-316L wafer with different surface roughness conditions, we have prepared polished and unpolished surface wafer. Using suggested method, porous aluminum oxide layer was formed and then we have removed oxide layer using alumina chemical etchant. Finally, we have fabricated various shapes of irregular nano/micro dimple structures with 100nm to 50μm according to surface roughness conditions.

One-step fabrication of nanostructure-covered microstructures using selective aluminum anodization based on non-uniform electric field

This paper presents a selective aluminum anodization technique for the fabrication of microstructures covered by nanoscale dome structures. It is possible to fabricate bulging microstructures, utilizing the different growth rates of anodic aluminum oxide in non-uniform electric fields, because the growth rate of anodic aluminum oxide depends on the intensity of electric field, or current density. After anodizing under a non-uniform electric field, bulging microstructures covered by nanostructures were fabricated by removing the residual aluminum layer. The non-uniform electric field induced by insulative micropatterns was estimated by computational simulations and verified experimentally. Utilizing computational simulations, the intensity profile of the electric field was calculated according to the ratio of height and width of the insulative micropatterns. To compare computational simulation results and experimental results, insulative micropatterns were fabricated using SU-8 photoresist. The results verified that the shape of the bottom topology of anodic alumina was strongly dependent on the intensity profile of the applied electric field, or current density. The one-step fabrication of nanostructure-covered microstructures can be applied to various fields, such as nano-biochip and nano-optics, owing to its simplicity and cost effectiveness.

Fabrication of Hierarchical Micro-Nano Structures and Structural Coloring Effect of Polymer Substrate

Recently, structural coloring using hierarchical micro-nano structures as a technical field to implement a color without using a chemical colourants and dye is being developed as an attentional technology. The principle of structural coloring is that by the diffraction or multi-interference of light from a material containing a periodic or quasiperiodic structure on the length scale of the wavelength of visible light. For these reason, our research have verified the structural coloring effect on the polymer substrate by fabricate a hierarchical micro-nano structures. Firstly, we have fabricate a nano and hierarchical micro-nano structured mold for verify the structural size effect. Through the replication of structures on the PMMA substrate, we have measured optical properties in the range of visible light. As a results, the surface of nano structured PMMA showed a blue color according to induced the light. Furthermore, color intensity was increased according to increase the aspect ratio and diameter. In contrast, hierarchical micro-nano patterned surface showed iridescent colors.© 2014 ASME