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.

Structural analysis of anodic porous alumina used for resistive random access memory.

Anodic porous alumina with duplex layers exhibits a voltage-induced switching effect and is a promising candidate for resistive random access memory. The nanostructural analysis of porous alumina is important for understanding the switching effect. We investigated the difference between the two layers of an anodic porous alumina film using transmission electron microscopy and electron energy-loss spectroscopy. Diffraction patterns showed that both layers are amorphous, and the electron energy-loss spectroscopy indicated that the inner layer contains less oxygen than the outer layer. We speculate that the conduction paths are mostly located in the oxygen-depleted area.

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

Molecular orientation of porphyrins accompanying the formation of chain-aligned DNA films.

Porphyrin-containing DNA solid films with several binding orientations were successfully prepared by drying the aqueous solution of porphyrins and DNA in a magnetic field. By the measurement of linear dichroism absorption spectra from three identical spatial directions, the molecular orientations of porphyrins in chain-aligned DNA films were evaluated. Tetra(N-methylpyridinium-4-yl)-porphyrin was found to be bound at the surface of DNA chains like a patch. This orientation is different from the intercalative or groove binding manners observed in solutions. In contrast, tetra(4-sulfonatophenyl)-porphyrin exhibited an orientation perpendicular to the DNA axis, which may be attributed to H-aggregation of porphyrins along the direction parallel to DNA chains. Heme-protein with coiled coil backbone was also aligned along the DNA chains, orienting ferric protoporphyrin parallel to the magnetic field. The major effect for these molecular orientations would be the molecular packing of the rod-disk or the rod-rod systems.

Optical waveguide self-assembled from organic dye molecules in solution.

Fiber-shaped H-aggregates with lengths of up to 300 microm are synthesized by self-assembly of thiacyanine (TC) dye molecules in solution. Photoluminescence (PL) images and spatially resolved PL spectra of the fibers that are transferred onto a glass substrate reveal that the fibers act as single-mode optical waveguides that propagate PL in the range of 520 to 560 nm over 250 microm without any loss.

Self-assembly of concentric quantum double rings.

We demonstrate the self-assembled formation of concentric quantum double rings with high uniformity and excellent rotational symmetry using the droplet epitaxy technique. Varying the growth process conditions can control each ring's size. Photoluminescence spectra emitted from an individual quantum ring complex show peculiar quantized levels that are specified by the carriers' orbital trajectories.

Annular self-assembly of DNA molecular chains occurring in natural dry process of diluted solutions.

The molecular orientation of DNA membranes, which were prepared by subjecting diluted solution of salmon sperm DNA to a natural drying process, was examined. X-ray diffraction and polarization microscopy revealed that the dried membranes have zonal structures. Each zone shows different features in molecular orientation. In the outer zones formed at the early stage in drying, DNA molecular chains were found to be aligned along the annular curve of the peripheral edge. Both the uneven thickness and disproportional molecular weight distribution in a membrane suggested that the radial flow transported DNA molecules to the edge and that they formed the accumulated phase. Above the critical concentration for the formation of liquid crystalline, the DNA chains would be aligned onto the preformed solid--liquid interface. The membranes with the highest birefringence were obtained from DNA samples with the relatively high molecular weight of around 29 kbp. In the innermost zone, on the other hand, the DNA molecules were radially oriented. This alignment can be attributed to the hydrodynamic effect caused by the rapid translation of the edge interface, which overcomes the Brownian motion of the chain segments. A transitive balance of physical effects was revealed in the dry process, which provided quite orthogonal molecular orientations in a single droplet.

Judgment for DNA-binding modes of dye molecules by novel chain-aligned film method.

We have succeeded in preparation of novel composite films composed of chain-oriented DNA and the DNA-binding dyes aligned in specific orientation by drying the solution under a horizontal magnetic field. The dye-DNA composite films mostly showed linear dichroism, as revealed by polarized ultraviolet-visible spectroscopy (UV-VIS) and fluorescence anisotropy measurement. The intercalators such as ethidium bromide was fixed in chain-oriented DNA films in a similar binding manner as in solutions. Also, Hoechst 33258 was found to be aligned along the minor groove even in the solid films. In addition, by means of this film method, we could estimate the DNA-binding modes of newly designed original compounds. Here, we emphasize that the method using aligned dye-DNA films is very convenient for identifying the binding modes for double-stranded DNA.

Orientation of dye molecules in DNA-based films with chain alignment and judgment of their DNA-binding modes.

Novel composite films of chain-oriented DNA, which contain the DNA-binding dyes aligned in specific orientation, were successfully prepared by drying the solution under a horizontal magnetic field. Most of the dye-DNA composite films showed linear dichroism, as revealed by polarized ultraviolet-visible (UV-vis) spectroscopy. The intercalators, ethidium bromide and acridine orange, were fixed in chain-oriented DNA films in a similar binding manner as in solutions. Also, Hoechst 33258 and 4',6-diamidino-2-phenylindole were found to be aligned along the minor groove, even in the solid films. Thus, our new method of preparing dye-DNA composite films with chain orientation is useful for aligning small molecules, and it will provide views of the novel anisotropic materials expected in various application fields. We used this method to prepare composite DNA films with newly designed original compounds. Seven of nine dyes were judged to bind obviously to DNA as intercalators by polarized UV-vis spectroscopy. The DNA-binding manners were further analyzed by fluorescence anisotropy measurements. On the basis of the curves for the rotational angle dependence of the anisotropy, we were able to estimate the angles between the transition-dipole moments of dyes and the aligned chain axis of DNA. Interestingly, two original compounds were found to be in the tilted forms with regard to the plane of base pairs. We emphasize here that the method using aligned dye-DNA films is very convenient for identifying the binding modes of the compounds for double-stranded DNA.

Magnetic anisotropy of the antiferroquadrupole phase in Ce0.50La0.50B6.

Magnetic phase diagrams for antiferroquadrupole (AFQ) phase II and antiferromagnetic (AFM) phase III in Ce0.50La0.50B6 with a Gamma(8) ground state have been investigated by ultrasonic measurements. The hybrid magnet (Gama) in the National Institute for Materials Science was employed for high-field measurements up to 30 T and a 3He-4He dilution refrigerator was used for low-temperature experiments down to 20 mK. The phase boundary from paramagnetic phase I to AFQ phase II under [001] magnetic fields closes at H(I-II) approximately 29 T, while the boundary is still open under fields along the [110] and [111] directions even up to 30 T. This anisotropic character of phase II in fields is consistent with the theoretical calculation based on the O(xy)-type AFQ ordering. We also found that AFM phase III reduces considerably in fields turning from the [001] to [110] and [111] directions.

Molecular chain orientation of DNA films induced by both the magnetic field and the interfacial effect.

DNA films showing highly homogeneous orientation of molecular chains were successfully prepared by drying a semidiluted solution in a horizontal magnetic field. Most of the molecular chain elements in the obtained film were found to be one-dimensionally oriented, as shown by X-ray diffraction, polarization microscopy, and linear dichroism spectroscopy. Because a DNA chain is theoretically expected to orientate only in divergent directions perpendicular to a magnetic field, this result suggests that the DNA chains were aligned not only by a magnetic field but also by the interfacial effect that induced the chains to fit along the air-liquid interface. The descent speed of an air-liquid interface by evaporation was faster than the estimated diffusion rate of DNA, suggesting an emergence of a concentrated layer near the surface. As proved by polarization microscopy, this emergence led to the transitional formation of a nematic-like liquid crystalline phase, which resulted in a DNA film with good chain alignment and unitary orientation. This mechanism underlying chain alignment was supported by molecular weight dependency, in which higher molecular weight DNA is more likely to evince chain alignment that exhibits a higher degree of birefringence. Low molecular weight components have such high thermal motility that it would be difficult to fit them along the air-liquid interface in the early stage of drying. For chain alignment, it was preferable to use an initial concentration of DNA lower than a critical concentration for liquid crystal formation so that the possible diffusion and assembly in a diluted solution would be essential for chain alignment. The DNA film exhibited obvious linear dichroism, indicating the potential for further applications.

Phase Manipulation between c(4 x 2) and p(2 x 2) on the Si(100) surface at 4.2 K.

Phase manipulation between c(4x2) and p(2x2) on the Si(100) surface has been demonstrated at 4.2 K for the first time using a low-temperature scanning tunneling microscope. We have discovered that it is possible to change the c(4x2) surface into the p(2x2) surface, artificially, through a flip-flop motion of the buckling dimers by using a sample bias voltage control. Also, scanning at a negative bias voltage or applying a pulse voltage can restore the c(4x2) surface. The STM images as a function of bias voltage and tunneling current reveal the interesting dynamics of the buckling dimers on the long debated surface. Our results will show that energetic tunneling electrons are most likely responsible for the observed phase transition from c(4x2) to p(2x2).