Kenji Kawasaki

Reduction in Viscosity of Quasi-2D-Confined Nanoimprint Resin through the Addition of Fluorine-Containing Monomers: Shear Resonance Study

The fluidity of the resin for the nanoimprint lithography was investigated in a quasi-2D space by the shear resonance measurement, which enables us to measure the viscous property of the resin confined in a nanometer gap between mica surfaces. With this technique, we could observe that the resin fluidity was enhanced by the addition of the fluorine-containing monomer. The fluidity of the resin with the fluorine-containing monomer was maintained until the distance between mica surfaces became smaller than 15 nm, wheras the resin without the fluorine-containing monomer started losing its fluidity when the distance became 30 nm. Two reasons possibly explain the result; (i) the interaction between the resin and mica was reduced by the existence of the fluorine-containing segregated layer at the interface, and (ii) the reduction in viscosity took place by the addition of the fluorine-containing monomer that reduced the degree of chain entanglement in the resin because of its small intermolecular interaction force. The effect of the length of the perfluoroalkyl chain in the fluorine-containing monomer is also discussed.

Development of cryogenic probe system for high-sensitive NMR spectroscopy

Utilizing a cryogenic probe system is a promising approach to improve signal-to-noise-ratio (SNR) in the nuclear magnetic resonance (NMR) spectrometer. We have been developing an NMR spectrometer based on a superconducting-split-pair magnet. This unique structure of the magnet allows using solenoid-shaped antenna coil, which ensures about 2 times higher sensitivity than the conventional saddle-shaped antenna coil. The goal of the present study is to realize higher sensitivity by implementing the superconducting-split-pair magnet and solenoidal-shaped antenna coil. Our immediate objective is to establish the cryogenic probe system for the superconducting-split-pair magnet. In this paper, the basic idea and design of the system and some preliminary results are described.

Sensitivity of Cryogenic Solenoidal Probe for Split-Pair Superconducting Magnet With Cross-Bore

By using a split-pair superconducting magnet with cross-bore, one can implement a solenoidal radio frequency (RF) coil for solution nuclear magnetic resonance (NMR). We expect the solenoidal RF coil to give us higher sensitivity than an ordinary saddle-shaped RF coil. We have developed both room temperature and cryogenic NMR probes with a solenoidal RF coil for a split-pair superconducting magnet. The probes and the solenoidal RF coils were evaluated using a sensitivity test with standard 0.1% ethylbenzene. The sensitivity tests of the room temperature probes indicated that the signal-to-noise ratio (SNR) of the solenoidal RF coil was higher than that of an ordinary saddle-shaped RF coil. In the sensitivity test of the cryogenic probe, we compared a four-turn solenoidal RF coil with a two-turn one. As a result, the SNR of the one of two-turn RF coil was higher than that of the one of the four-turn one. It is believed that the reason is that the SNR depends on the quality factor of the specimen Qs and, furthermore, Qs depends on the shape of the RF coil.

Selection of Diacrylate Monomers for Sub-15 nm Ultraviolet Nanoimprinting by Resonance Shear Measurement

In UV nanoimprinting, the selection of monomers suitable for sub-15 nm patterning is difficult because the filling behavior of resin at this scale still remains scientifically unclear. We demonstrate sub-15 nm patterning by UV nanoimprinting using silica molds with 20, 15, and 7 nm diameter holes; however, the 7 nm diameter pillar patterns were not fabricated using hydroxy-containing monomers. The filling behavior into silica holes of around 10 nm depended on the chemical structure of the monomers. Resonance shear measurements revealed the following: (1) The viscosities of hydroxy-containing monomers confined between chlorodimethyl(3,3,3-trifluoropropyl)silane (FAS3-Cl)-modified surfaces began to increase at distances shorter than those of the monomers between unmodified surfaces. (2) The monomers confined between tridecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane-modified surfaces were squeezed out when the surface-surface distance decreased at less than 7 nm. The measured viscosities between the FAS3-Cl-modified silica surfaces were correlated with the insufficient filling behavior into the silica holes of around 10 nm in UV nanoimprinting. Contact angle measurements provided an additional insight that a higher wettability of the monomers onto the antisticking chemisorbed monolayers resulted in imprinted patterns with higher aspect ratios. Considering the increase in the monomer viscosity in the nanospace and the wettability of monomers onto chemisorbed monolayers, we concluded that the monomer showing low viscosity under confinement and high wettability onto the mold surface was suitable for single-digit nanometer UV nanoimprinting.