Studies of self-organization processes in nanoporous alumina membranes by small-angle neutron scattering.

We performed studies of the self-organization processes in nanoporous alumina membranes at initial and late stages of aluminum anodization by using scanning electron microscopy (SEM) and small-angle neutron scattering (SANS). SEM observations indicated three stages in the self-organization of nanopores in alumina: (1) nucleation of random nanopores with a broad radius distribution, (2) narrowing the radius distribution and (3) slow evolution of the nanoporous structure towards ordering of nanopores into large domains. SANS studies revealed orientational correlation between ordered domains of nanopores, which is characterized by a small misorientation angle. For the samples with high aspect ratios of nanopores, the SANS patterns showed azimuthal smearing, which was attributed to the redistribution of nanopores between the domains during their growth.

Cage lifetimes of ionic liquids as studied by the magnetic field effect probe.

Magnetic field effects (MFEs) on the photoinduced hydrogen abstraction reaction of benzophenone with phenol were investigated in ionic liquids (ILs) with a short alkyl chain (N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA TFSA)) and long alkyl chains ((N,N,N-trimethyl-N-octylammonium bis(trifluoromethanesulfonyl)amide (TMOA TFSA) and N-decyl-N,N,N-trimethylammonium bis(trifluoromethanesulfonyl)amide (DTMA TFSA)) by a nanosecond laser flash photolysis technique. In each ionic liquid, escaped radical yield of a benzophenone ketyl radical rapidly increased with increasing magnetic field strength (B) of 0 T < B≤ 0.01 T. At 0.01 T < B≤ 0.4 T, the escaped radical yield almost saturated in TMPA TFSA or gradually increased in TMOA TFSA and DTMA TFSA. At much higher fields of 0.4 T < B≤ 30 T, the yield gradually decreased, resulting in 10-15% decrease at 30 T. The observed MFEs can be explained by the hyperfine coupling and Δg mechanisms together with the relaxation mechanism. On the time profiles of the transient absorption observed for the benzophenone ketyl radical, MFEs were generated in the time range of 0 < t < 0.6 µs. The cage lifetimes of TMOA TFSA and DTMA TFSA were estimated to be at least 120 ns.

Cyclotron resonance and mass enhancement by electron correlation in KFe2As2.

Cyclotron resonance (CR) measurements for the Fe-based superconductor KFe(2)As(2) are performed. One signal for CR is observed, and is attributed to the two-dimensional α Fermi surface at the Γ point. We found a large discrepancy in the effective masses of CR [(3.4±0.05)m(e) (m(e) is the free-electron mass)] and de Haas-van Alphen results, a direct evidence of mass enhancement due to electronic correlation. A comparison of the CR and de Haas-van Alphen results shows that both intra- and interband electronic correlations contribute to the mass enhancement in KFe(2)As(2).

Influence of micro-joints formed between spheres in coupled-resonator optical waveguide.

Light propagation is simulated through coupled-resonator optical waveguides (CROWs) composed of seven transparent polystyrene microspheres, including micro-joints formed between the spheres. In nanojet-induced mode (NIM) light propagation, the micro-joints increased the optical coupling between microspheres drastically, and the light confinement by individual microspheres weakened as the micro-joint diameter increases. These results suggest that we can control NIM light propagation by changing the micro-joint diameter; this amounts to a nanojet throttle valve.

Standardization of excitation efficiency in near-field scanning optical microscopy.

Near-field scanning optical microscope (NSOM or SNOM) is a form of scanning probe microscope (SPM), which is used to observe the optical properties of a sample surface with a nanometer-scale spatial resolution. Since the near-field light strongly interacts with the sample surface, or with nanometer-scale objects on the substrate's surface, NSOM is advantageous to excite only the vicinity of a sample surface. From the view point of surface chemical analysis, a discussion about the light energy concentration within a nanometer-scale region, and an estimation of its efficiency are indispensable for accurate measurements of the optical properties in a nanometer-scale region. In this paper, we describe the concept, the cautions and the general guidelines of a method to measure the excitation efficiency of aperture-type NSOM instruments.

Magnetic field effects on hydrogen abstraction of thiobenzophenone as a probe of microviscosity.

Hydrogen abstraction reactions of thiobenzophenone with thiophenol in solutions of varying viscosities (η=0.29-42.0 cP) were studied by a nanosecond laser flash photolysis under magnetic fields of 0-15.5 T. In alcoholic solutions, the escaped radical yield (Y) of thiobenzophenone ketyl radical showed appreciable magnetic field effects (MFEs). The observed MFEs can be interpreted with the Δg mechanism through the triplet radical pair. The relative escaped radical yield (R(1.7T)=Y(1.7T)/Y(0T)) decreased with increasing η at 0<η≤3.33 cP, but then the yield increased with increasing η at 3.33 cP<η≤22.2 cP. At much higher viscosity 22.2 cP<η≤42 cP, R(1.7T) values become 1.0 within experimental errors. Such quenching of MFE was explained by the spin-orbit coupling recombination of close radical pairs associated with high viscosity. The MFEs on the present reaction is extremely sensitive to the solvent viscosity in the vicinity of the radical pairs. Using this probe reaction, microviscosities of sodium dodecyl sulfate (SDS) and Brij35 micellar solutions were estimated.

Photochemical primary process of photo-Fries rearrangement reaction of 1-naphthyl acetate as studied by MFE probe.

Photo-Fries rearrangement reactions of 1-naphthyl acetate (NA) in n-hexane and in cyclohexane were studied by the magnetic field effect probe (MFE probe) under magnetic fields (B) of 0 to 7 T. Transient absorptions of the 1-naphthoxyl radical, T-T absorption of NA, and a short-lifetime intermediate (τ = 24 ns) were observed by a nanosecond laser flash photolysis technique. In n-hexane, the yield of escaped 1-naphthoxyl radicals dropped dramatically upon application of a 3 mT field, but then the yield increased with increasing B for 3 mT < B≤ 7 T. These observed MFEs can be explained by the hyperfine coupling and the Δg mechanisms through the singlet radical pair. The fact that MFEs were observed for the present photo-Fries rearrangement reaction indicates the presence of a singlet radical pair intermediate with a lifetime as long as several tens of nanoseconds.

Fraction of a millimeter propagation of exciton polaritons in photoexcited nanofibers of organic dye.

We report propagation of exciton polaritons (EPs) in photoexcited nanofibers of thiacyanine dye over a few hundred micrometers at room temperature. We determine the complex refractive index along the nanofibers by fluorescence microscopy measurements on single nanofibers and observe its anomalous behavior due to the EP effect. The longitudinal-transverse splitting energy (ΔE(L-T)) is evaluated to be ∼1 eV. The large ΔE(L-T) and waveguide function of the nanofibers allow a millimeter propagation of EPs at room temperature, which is hardly realized in other systems.

Development of magnetically aligned single-walled carbon nanotubes-gelatin composite films.

Magnetically aligned and highly dispersed single-walled carbon nanotubes (SWNTs)-gelatin composite films were fabricated on a quartz substrate of newly designed disassemblable sample cells. After an SWNTs-gelatin composite sol in each sample cell was exposed to vertical DC magnetic fields to 28 T during the sol-gel transition, a side plate with a polytetrafluoroethylene film attached to the inner surface was removed from the sample cell carefully, and the composite gel left on the other side plate made of quartz was dehydrated in a nonmagnetic circumstance. We have found that the alignment of SWNTs is retained in uniform composite films obtained after the nonmagnetic drying process. Both polarized absorption measurements and polarized Raman scattering measurements were performed in order to confirm the alignment of SWNTs in the composite films consistently. The optical anisotropy of the composite films increased somewhat superlinearly as a function of the magnetic field applied during the sol-gel transition and reached to 0.13 at 28 T. The nonmagnetic drying process would make it easy to apply higher magnetic fields to the fabrication of aligned SWNTs films as it consumes resources to keep operating high field magnets such as hybrid magnets during the drying process.

Anomalous magnetic field effects on photochemical reactions in ionic liquid under ultrahigh fields of up to 28 T.

The magnetic field effects (MFEs) on photoinduced hydrogen abstraction reactions between benzophenone and thiophenol in an ionic liquid, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) imide (TMPA TFSI), were studied by a nanosecond laser flash photolysis technique under ultrahigh fields of up to 28 T. Extremely large and anomalous stepwise MFEs were observed for the first time. The escape yield of benzophenone ketyl radical decreased with increasing magnetic field strength (B) at 0 T

Anisotropic elasticity of magnetically ordered agarose gel.

The physical properties of agarose gel prepared under strong magnetic fields were investigated. The storage modulus was measured by the reflection method with an ultrasonic pulse. The measurement results of the gel's elasticity indicate that agarose gel has anisotropic properties. The elasticity and its anisotropy depend on the concentration of the gel and the magnetic field to which it is exposed. The experimental results indicate that the anisotropic network structure of the gel is induced by the exposure to the magnetic field during gelation. The gelation mechanism under a magnetic field is discussed.