Papers by Author: Heon Lee

Abstract: Artificial polycarbonate moth eye structured plate was used to emboss the moth eye nano-pattern into PVC films. Embossing was done at 100°C to prevent any damage on polycarbonate template. With embossing of moth eye nano-patterns, transmittance of PVC film was increased up to 6% over 400nm to 800nm wavelength region. This embossed PVC film was then used as an imprint template after depositing thin layer of SiO2 and self-assembled monolayer. Consequently, polymer based moth eye nano-patterns were formed on glass template after UV imprinting and its transmittance was increased from 90% to 92%.

Abstract: Self-Assembled Monolayer (SAM) is a single layer of ordered molecules absorbed on a surface by chemical bonding between the molecular head group and the surface. The surface properties can be controlled by the terminal functional group of the SAM layer. In order to utilize SAM layers for device applications, SAM layer needs to be patterned as a sub-micron size. Patterning of SAM layer in sub-micron size has been done by various techniques including direct-writing by dip-pen nano lithography, selective etching with UV photons, and selective deposition of SAM layer by &-contact printing. In this study, silane based SAM layer was patterned to the sub-micron size using zero residual Nano imprint Lithography, which is regarded as next generation lithography technique due to its simplicity, high throughput and high resolution pattern transferring capability. Using zero-residual layer imprinting, 300nm~2um sized SAM patterns can successfully fabricated. In order to check the surface property of patterned SAM layer, a solution containing nano Ag particles was spin-coated on the SAM patterned substrate and nano Ag particles were selectively deposited on the substrate.

Abstract: We fabricated a CdS nano structures/CdS window layer/ ITO coated glass using electrodeposition and nano imprinting technology (NIT). The CdS nano-structures were electrodeposited using Na2S2O3 and CdSO4 electrolytes as the CdS sources and nano-imprint templates. The x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS) results show the electrodeposited CdS window layer and the secondary electron microscopy (SEM) analysis showed the well aligned CdS nano-structure shape.

Abstract: Embossing lithography is one of the most promising technologies for mass production of nano-scale structures. To advance the industrialization of embossing lithography, fabrication of low cost, high mechanical strength embossing template is essential. Electroformed Ni template can be used as an embossing template if its poor anti-adhesive property is fixed by proper releasing layer treatment, especially, when it is used with sticky thermoset polymer. In this experiment, quartz master template with 200nm to 2um sized surface protrusions was fabricated and used to emboss the PMMA coated Si wafer. Then the embossed PMMA layer was coated with metal seed layer (Ni) and electroplating of Ni was followed to fabricate Ni template. To apply anti-stiction SAM layer, SiO2 and Si layer was coated on Ni template. With proper anti-stiction treatment of Ni template, sub-micron patterns were successfully transferred to sticky thermoset polymers such as epoxy resin using Ni template without any degradation of anti-adhesive property.

Abstract: The coherent phase equilibria of binary nanoparticles, in which three phases can be formed, were examined by accounting for the particle size effect engendered by the surface stress. Considering the system geometry exhibiting radial symmetry, coherent phase diagrams could be constructed for different particle sizes. The phase diagrams exhibited several characteristics of phase equilibria unique to coherent systems. It was found that a positive surface stress results in a radial compressive stress in the particle that is inversely proportional to the particle radius, thereby increasingly stabilizing the phase having a lower molar volume as the particle size decreases.

Abstract: Nano-imprinting technology, currently developing as an alternative technology for photolithography, is mostly dealing with photo resist materials for etching barrier. In other words, the materials imprinted are used as the barriers for wet etching or RIE (reactive ion etching), and then are removed after all. Thus, most materials developed for nano-imprinting technology have relatively low Tg(<100oC), in case of solids or have a low viscosity before curing in order to fill the gap of the stamp. Such materials could not be suitable for the structures that require relatively high temperature process ability, high modulus or high durability. Epoxy is one of candidates that meet such requirements for the structures. However, it has not been reported about imprinting on epoxy materials. In this paper, nano-imprinting technology was developed to fabricate the microstructures. Instead of thermoplastic imprint resin, solid phase epoxy films, which is thermoset polymer, were imprinted with SAM (self assembly monolayer) coated quartz and silicon stamps. Feature size of stamp varies from 150nm to 1 μm and height was 300nm for quartz stamp and 3μm for Si stamp.

Abstract: A faithful pattern transferring onto a non-planar substrate was demonstrated by nano-imprinting technique. Uniform pressing of a flexible template onto a substrate was important for the faithful pattern transferring. Both the UV-based and thermal imprinting techniques were used to transfer patterns of 200nm sized features to the non-planar substrates such as outer wall of rod and inner surface of cylinder and it could be used for nano-devices such as lab on a chip.

Abstract: Flexible polyvinyl alcohol (PVA) templates with nano-sized patterns were fabricated by spin coating of PVA resin on silicon master wafer. Since PVA template has enough UV transparency, mechanical strength and thermal durability, it can be used as the template for UV-based and thermal nanoimprint lithography. The replicated patterns on the PVA template were transferred faithfully to the imprinted resin by imprinting lithography. As PVA template was dissolved in water, it was not necessary to deposit a releasing layer on the PVA template surface.

Abstract: In order to build a nano-device on polymer substrate, nano-size patterning must be done. However, conventional photolithography cannot be used to fabricate nano-sized patterns on polymer film due to the flexibility of polymer film and its potential interaction with developer solution and organic solvent. In this study, 100nm sized dense line and space patterns were made on flexible PET (polyethylene-terephthalate) substrate using newly developed monomer based imprinting lithography. Compared to hot embossing lithography, thermal curing imprint lithography uses monomer based imprint resin which consists of base monomer and thermal initiator. Since it is liquid phase and polymerization temperature is much lower than glass temperature of polymer, the nano-sized patterns can be transfer at much lower temperature and pressure. Hence, patterns as small as 100nm were successfully fabricated on flexible PET film substrate by monomer based thermal curing imprinting lithography at 85°C and 5atm.

Abstract: Embossing or imprint lithography is the key-technology for the mass production of nanosized structures with low cost. Currently Si or quartz template which is produced by e-beam or DUV lithography and reactive ion etching, is used. However they are very expensive and easily damaged due to their brittleness. On the other hand, Ni template has high mechanical durability and can be fabricated with low cost by electroplating. However, one of the key obstacles of Ni template is poor antistiction property, when it is used with sticky thermoset polymer. Due to its poor antistiction property, detachment of Ni template from epoxy substrate is one of the key obstacles. In this experiment, quartz template with 150nm to 1μm sized surface protrusion was fabricated and used to emboss the PMMA coated Si wafer. Then the imprinted PMMA layer was coated with metal seed layer and electroplating of Ni was followed to fabricate Ni template with 150nm to 1μm sized patterns. In order to form antistiction layer on Ni template, SAM antistiction layer was formed on SiO2 coated Ni template. As a result, nano patterns could be successfully transferred to sticky thermoset polymer using Ni template without any degradation of antistiction property.