Bong Kuk Lee

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.

Stepwise Self‐Assembly of a Protein Nanoarray from a Nanoimprinted Poly(Ethylene Glycol) Hydrogel

This work was supported by Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology Agency (JST), and New Energy and Industrial Technology Development Organization (NEDO).

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.

Nanoarrays of tethered lipid bilayer rafts on poly(vinyl alcohol) hydrogels

Lipid rafts are cholesterol- and sphingolipid-rich domains that function as platforms for signal transduction and other cellular processes. Tethered lipid bilayers have been proposed as a promising model to describe the structure and function of cell membranes. We report a nano(submicro) array of tethered lipid bilayer raft membranes (tLBRMs) comprising a biosensing platform. Poly(vinyl alcohol) (PVA) hydrogel was directly patterned onto a solid substrate, using ultraviolet-nanoimprint lithography (UV-NIL), as an inert barrier to prevent biofouling. The robust structures of the nanopatterned PVA hydrogel were stable for up to three weeks in phosphate-buffered saline solution despite significant swelling (100% in height) by hydration. The PVA hydrogel strongly restricted the adhesion of vesicles, resulting in an array of highly selective hydrogel nanowells. tLBRMs were not formed by direct vesicle fusion, although raft vesicles containing poly(ethylene glycol) lipopolymer were selectively immobilized on gold substrates patterned with PVA hydrogel. The deposition of tLBRM nano(submicro) arrays was accomplished by a mixed, self-assembled monolayer-assisted vesicle fusion method. The monolayer was composed of a mixture of 2-mercaptoethanol and poly(ethylene glycol) lipopolymer, which promoted vesicle rupture. These results suggest that the fabrication of inert nanostructures and the site-selective modification of solid surfaces to induce vesicle rupture may be essential in the construction of tLBRM nano(submicro) arrays using stepwise self-assembly.

Epitaxial nanodot arrays of transition-metal oxides fabricated by dry deposition combined with a nanoimprint-lithography-based molybdenum lift-off technique.

Information technology (IT) is continuously developing, strongly supported by silicon nanotechnology, but the precision in processing Si is approaching 10 nm, which is considered the lower limit for Si devices. Thus, progress in IT will cease unless future nanodevices have special functions. Transition-metal oxides are known to possess a variety of peculiar features due to their strongly correlated electron system, such as ferroelectricity, ferromagnetism, high-criticaltemperature (Tc) superconductivity, and colossal magnetoresistance. These features are expected to be applied in various new types of memories and sensors, such as halfmetallic ferromagnetic oxides (e.g., (La,Sr)MnO3) for application in magnetic random access memory, due to their possible large tunneling magnetoresistance effect even at room temperature. Ferroelectric random access memory and resistance random access memory are also superior devices for nonvolatile data storage. As transition-metal oxide devices mature, the necessity of nanofabrication and largearea integration for their practical use will increase. However, nanofabrication of oxide films is difficult. Currently, fabrication of oxide films with a lateral size smaller than 1mm is very difficult by photolithography. Although there are many reports on the fabrication of oxide nanostructures, whose lateral sizes are as small as or less than several hundreds of nanometers, by atomic force microscopy (AFM), focused ion beam (FIB), and electron beam (EB)-based lithography techniques, these methods are not suitable for large-area fabrication and mass production in industry. Nanoimprint lithography (NIL) is an emerging technology that enables fabrication of nanostructures as small as 10 nm. In this process, a patterned mold

Direct fabrication of integrated 3D Au nanobox arrays by sidewall deposition with controllable heights and thicknesses

This paper provides a unique strategy for controlling integrated hollow nanostructure arrays such as boxes or pillars at the nanometer scale. The key merit of this technique is that it can overcome resolution limits by sidewall deposition and deposit various materials using a sputtering method. The sputtering method can be replaced by other dry deposition techniques such as pulsed laser deposition (PLD) for complex functional materials. Furthermore, it can produce low-cost large-area fabrication and high reproducibility using the NIL (nanoimprint lithograph) process. The fabrication method consists of a sequence of bilayer spin-coating, UV-NIL, RIE (reactive ion etching), sputtering, ion milling and piranha cleaning processes. By changing the deposition time and molds, various thicknesses and shapes can be fabricated, respectively. Furthermore, the fabricated Au box nanostructure has a bending zone of the top layer and a approximately 17 nm undercut of the bottom layer as observed by SEM (scanning electron microscope). The sidewall thickness was changed from 12 to 61 nm by controlling the deposition time, and was investigated to understand the relationship with blanket thicknesses and geometric effects. The calculated sidewall thickness matched well with experimental results. Using smaller hole-patterned molds, integrated nanobox arrays, with inner squares measuring approximately 160 nm, and nanopillar arrays, with inside pores measuring approximately 65 nm, were fabricated under the same conditions.

Self-organized functional lipid vesicle array for sensitive immunoassay chip.

We report the self-assembly immobilization of functional lipid vesicles (FLVs) by electrostatic interaction onto N-inscription-nanosized geometrics. The well-organized three-dimensional physical structures of liposome were observed by AFM. Generally, two involved forces for the binding to surfaces and the repulsion between individual liposome are necessary to array lipid vesicles individually similar to the physical configuration in solution. The immobilized FLVs demonstrated clearly defined redox activity in electrochemical measurements. We observed a notable current decrease, indicating the binding of the capture antibody with the target human serum albumin (HSA) antigen. We believe these findings can be related to various vesicles applications such as drug delivery system, nanobiosensors and nano-scale membrane function studies.

Characteristic Variations of Graphene Field-Effect Transistors Induced by CF4 Gas

The influence of tetrafluoromethane (CF4) gas on the electrical characteristics of monolithic graphene field-effect transistors (FETs) is reported. Compared with the results in nitrogen ambient, FETs in CF4 ambient exhibit a positive shift in the Dirac point voltage and an increase in drain current. These changes are ascribed to the electronegative nature of the fluorine atoms in CF4 gas, which is found to induce p-type doping and excess charge carriers in graphene. The electrical response to CF4 gas exposure demonstrates the feasibility of using monolithic graphene FETs as chemical sensors.