Lan-Young Hong

Photocurable silsesquioxane-based formulations as versatile resins for nanoimprint lithography.

Methacrylate octafunctionalized silsesquioxane (SSQMA) was shown to be an ideal material with high performance for ultraviolet (UV)-based nanoimprint lithography (NIL). The total viscosity of SSQMA-based formulations was adjusted to between 0.8 and 50 cP by incorporating low-viscosity acrylic additives, making the formulations suitable for UV-based NIL. The cured SSQMA-based formulations showed numerous desirable characteristics, including low volumetric shrinkage (4%), high Youngs modulus (2.445-4.272 GPa), high resistance to oxygen plasma, high transparency to UV light, and high resistance to organic/aqueous media, as a functional imprint material for UV-based NIL and step-and-flash imprint lithography (SFIL). Using both techniques, the SSQMA-based formulations were easily transferred to relief structures with excellent imprint fidelity and minimal residual thickness. Formulations containing 50% SSQMA (wt %) were able to reproduce high-aspect-ratio nanostructures with aspect ratios as high as 4.5 using bilayer SFIL. Transparent rigiflex molds and hard replica molds with sub-50-nm size features were reproducibly duplicated by using UV-NIL with the SSQMA-based resin. Nanostructures with feature sizes down to 50 nm were successfully reproduced using these molds in both UV- and thermal-NIL processes. After repeating 20 imprinting cycles at relatively high temperature and pressure, no detectable collapse or contamination on the replica surface was observed. These properties of the SSQMA-based resins make them suitable as inexpensive and convenient components in all NIL processes that are based on physical contact.

Replica mold for nanoimprint lithography from a novel hybrid resin.

The use of durable replica molds with high feature resolution has been proposed as an inexpensive and convenient route for manufacturing nanostructured materials. A simple and fast duplication method, involving the use of a master mold to create durable polymer replicas as imprinting molds, has been demonstrated using both UV- and thermal nanoimprinting lithography (NIL). To obtain a high-durability replicating material, a dual UV/thermal-curable, organic-inorganic hybrid resin was synthesized using a sol-gel-based combinatorial method. The cross-linked hybrid resin exhibited high transparency to UV light and resistance to organic solvents. Molds made of this material showed good mechanical properties (Youngs modulus=1.76 GPa) and gas permeability. The low viscosity of the hybrid resin (approximately 29 cP) allowed it to be easily transferred to relief nanostructures on transparent glass substrates using UV-NIL at room temperature and low pressure (0.2 MPa) over a relatively short time (80 s). A low surface energy release agent was successfully coated onto the hybrid mold surface without destroying the imprinted nanostructures, even after O2 plasma treatment. Nanostructures with feature sizes down to 80 nm were successfully reproduced using these molds in both UV- and thermal-NIL processes. After repeating 10 imprinting cycles at relatively high temperature and pressure, no detectable collapse or contamination of the replica surface was observed. These results indicate that the hybrid molds could tolerate repeated UV- and thermal-NIL processes.

Novel Micro/Nanofluidics Fabricated by Imprint Molding of Inorganic Polymers

We have successfully fabricated the polysilazane glass derived microfluidics with high optical transparency, biocompatibility thermal stability and chemical inertness via simple fabrication process. And also a hydrophilic nanofluidic system was fabricated with newly synthesized organic-inorganic material with excellent patternability. The preliminary study for photochemical reactions with the microfluidics, the separation of biomolecules with nanofluidics, it was claimed the obvious niche between conventional devices using glass and PDMS materials, thus it holds tremendous potential in the field of micro reaction technology as well as biosensor and bioreactors

Thermostatic Pyrolysis Process of Cured Polycarbosilane Fiber

As precursor fiber of advanced SiC fiber, cured polycarbosilane (PCS) fiber is prepared, and thermostatic pyrolysis of this fiber is studied in detail. Since the weight change is the most important characteristic of the pyrolysis degree of cured PCS fiber, a precise balance is applied on-line to follow the weight change of the cured PCS fiber, which was carried out in a standing style furnace. In thermostatic pyrolysis, the degree of pyrolysis, which is characterized by the weight loss of the fiber, and the properties of the final SiC fibers were found to be strongly dependent on the process conditions such as N2 flow and the amount of fibers. From much evidence, it is the offgas evacuated in the process that plays an important role by accelerating pyrolysis and increasing pyrolysis degree.

Fabrication of SiC-based Ceramic Microstructures from Preceramic Polymers with Sacrificial Templates and Softlithography Techniques

Silicon derived polymers containing nitrogen, carbon and boron have been considered as precursors for various non-oxide ceramics such as SiC, SiCN and SiBCN (Madou, 2002, Nguyen & Wereley, 2002, Liew et al., 2003). These ceramics can be easily shaped using various forming processes and then crosslinked by exposure to heat or UV radiation to form an infusible solid. The consolidated preceramic polymers are finally pyrolyzed at high temperatures to transform into the dense ceramic phases. These materials can be used for high temperature applications in areas such as structural composites (Kim et al., 1996), electronic devices (Xia & Whitesides, 1998) and catalytic chemical reactions (Xia et al., 1999). Table 1 shows some selected important preceramic polymers that have been studied in various aspects. In particular, silicon carbide (SiC) is a typical non-oxide ceramic that has attracted the most interest on account of its unique physical and chemical properties such as high thermal conductivity, excellent thermal stability, superior stability towards oxidation compared with carbon, high mechanical strength and chemical inertness. Commercially available polysilazane (VL-20, KiON Corp. USA) and two types of polycarbosilanes, Polymethylsilane (PMS) and Allyhydridopolycarbosilane (Starfire System, USA) are readily used as preceramic polymers for SiCN and SiC ceramics, respectively.

Durable hydrophilic microchannels with controlled morphology by the direct molding method.

We present a laminated hydrophilic microchannel fabricated by a direct micromolding and facile bonding technique with a hydrophilic organic-inorganic hybrid (HP) resin, which is built into two supporting parallel polydimethylsiloxane (PDMS) substrates. This approach allows one to shape the cross-section of the hydrophilic channel into a regular rectangular or geometrically complicated mouth-throat structure. Spontaneous self-wetting flow of water occurs when water is introduced to the HP microchannel with rectangular cross-section without the aid of mechanical pumping or electric field. The capillary flow velocity can be controlled by varying the channel size. The channel surface behaves like a glass surface in terms of zeta potential for pH larger than 3, and the electro-osmotic flow (EOF) velocity can be as high as 4.7 × 10(-4) cm(2)/V·sec at pH 9.0. The capillary electrophoresis (CE) module made of the HP resin for amino acid or DNA separation is demonstrated to yield a higher resolution in a shorter retention time with repeatability and long-lasting durable performance with antifouling property, when compared with PDMS CE.

Preparation and Applications of Ceramic Composite Phases from Inorganic Polymers

Silicon-based polymers containing nitrogen, carbon and boron have been considered as precursors for various non-oxide ceramics such as silicon carbide (SiC), SiCN and SiBCN.[1] These ceramics can be easily shaped using various forming processes and then cross-linked by exposure to heat or radiation to form an infusible solid. The consolidated preceramic polymers are finally pyrolyzed at high temperature to transform into the dense ceramic phases. These materials can be used for high temperature applications in areas such as electronic devices and structural composites.[2] Table 4.1 shows some selected important preceramic polymers that have been studied in various aspects. The polymers such as polysilanes, polycarbosilanes, polysilanzane, polysiloxanes are good candidates for ceramic phases due to their high ceramic yields on account of the combination of cross-linking and pyrolysis. Commercially available polysilazane (VL-20, KiON Corp., USA) and two types of polycarbosilane (Starfire System, USA and Nippon Carbon Co., Ltd., Japan) are readily used as preceramic polymers for SiCN and SiC ceramics, respectively.

Fast cell immobilization by using non-immunological method for cell based biosensor

This paper reports a concept of a micro cell analysis system for fast cell immobilization by using a non-immunological method which is composed of a cell/drug inlet, a sheath flow inlet, a micro chamber and a outlet to biosensor/waste. Micro cell wells were located in the micro chamber. To define optimized parameters of micro cell analysis system, cell adhesion experiment using Hela at 0.5×10⁶, 1.0×10⁶ or 2.0×10⁶ cells/ml in micro wells with 10µm depth and 25µm, 50µm and 100µm size respectively was performed. Different tendencies of cell adhesion between 0.5×10⁶ cells/ml and 1.0×10⁶ cells/ml concentration were not detected. The highest concentration gave the best performance of cell immobilization, even though cell congregation appeared.