Electrical control of the direction of spin accumulation

We are able to continuously change the direction of polarization of spin accumulation in a nonmagnetic metal by varying the currents injected by two ferromagnetic spin injectors. From measurements made at a distance from the injection area, we find a cosvarphi variation of the spin signal. This confirms that the angle of polarization of the nonlocal spin polarization with respect to the magnetization of the fixed spin detector is continuously varied as we change the injection currents. We give an explanation for the origin of this simple cosvarphi variation of the spin signal.     

Simple and efficient quantum key distribution with parametric down-conversion

We propose an efficient quantum key distribution protocol based on the photon-pair generation from parametric down-conversion (PDC). It uses the same experimental setup as the conventional protocol, but a refined data analysis enables detection of photon-number splitting attacks by utilizing information from a built-in decoy state. Assuming the use of practical detectors, we analyze the unconditional security of the new scheme and show that it improves the secure key generation rate by several orders of magnitude at long distances, using a high intensity PDC source.     

Generation of in-phase pulse train from optical beat signal

We propose and demonstrate generation of an in-phase optical pulse train from an optical beat signal. The proposed method is based on four-wave mixing occurring between the two continuous waves of the beat signal and on spectral filtering to shape the spectrum to be symmetric about the carrier frequency. We perform an experiment to verify the proposed method and obtain a 1.5 ps width in-phase pulse train from a 160 GHz beat signal. Furthermore, we employ a pulse compression scheme to reshape and compress the obtained pulse train, and we show that a 160 GHz repeating, 0.7 ps FWHM, nearly transform-limited, in-phase sech pulse train is successfully generated.     

Control of diameter of ZnO nanorods grown by chemical vapor deposition with laser ablation of ZnO

We made a study of controlling diameters of well-aligned ZnO nanorods grown by low-pressure thermal chemical vapor deposition combined with laser ablation of a sintered ZnO target, which was developed by us. Until now, it has been impossible to control diameters of ZnO nanorods, while the growth orientation was maintained well-aligned. In this study we developed a multi-step growth method to fabricate well-aligned nanorods whose diameters could be controlled. Metal Zn vapor and O₂ are used as precursors to grow ZnO nanorods. N₂ is used as a carrier gas for the precursors. A substrate is an n-Si (111) wafer. A sintered ZnO target is placed near the substrate and ablated by a Nd–YAG pulsed laser during ZnO nanorod growth. The growth temperature is 530 C and the pressure is 66.5 Pa. A vertical growth orientation of ZnO nanorods to the substrate is realized in the first-step growth although the diameter cannot be controlled in this step. When an O₂ flow rate is 1.5 sccm, well-aligned nanorods with 100 nm diameter are grown. Next, the second-step nanorods are grown on only the flat tip of the first-step nanorods. The diameters of the second-step nanorods can be controlled by adjusting the O₂ flow rate, and the growth direction is kept the same as that of the first-step nanorods. When the O₂ flow rate in second-step growth is smaller than 0.6 sccm, the diameter of the second-step nanorods is 30–50 nm. When the O₂ flow rate is between 0.75 and 3.0 sccm, the diameter is almost same as that of the first-step nanorods. When the O₂ flow rate is larger than 4.5 sccm, the diameter is increased with increasing O₂ flow rate. Further, the third-step ZnO nanorods with gradually increased diameters can be grown on the second-step nanorods with 1.5 sccm O₂ flow rate and without laser ablation.     

Discovery of radioactive silver (110mAg) in spiders and other fauna in the terrestrial environment after the meltdown of Fukushima Dai-ichi nuclear power plant

Six months after the explosion of TEPCO’s Fukushima Dai-ichi nuclear power plant, radioactive silver (^110mAg), was detected in concentrations of 3754 Bq/kg in Nephila clavata (the orb-web spider; Joro-gumo in Japanese) collected at Nimaibashi, Iitate village in Fukushima Prefecture, whereas ^110mAg in the soil was 43.1 Bq/kg. A survey of 35 faunal species in the terrestrial environment during the 3.5 years after the accident showed that most of Anthropoda had two orders higher ^110mAg in their tissues than soils, although silver is not an essential element for their life. However, tracing of the activity of ^110mAg detected in spider Atypus karschi collected regularly at a fixed location showed that it declined much faster than the physical half-life. These results suggest that ^110mAg was at once biologically concentrated by faunal species, especially Arthropoda, through food chain. The factors affecting the subsequent rapid decline of ^110mAg concentration in faunal species are discussed.     

Spontaneous Ga incorporation in ZnO nanowires epitaxially grown on GaN substrate

Surface‐diffusion‐induced spontaneous Ga incorporation process is demonstrated in ZnO nanowires grown on GaN substrate. Crucially, contrasting distributions of Ga atoms in axial and radial directions are experimentally observed. Ga atoms uniformly distribute along the ～10 μm long ZnO nanowire and show a rapidly gradient distribution in the radial direction, which is attributed substantially to the difference between surface and volume diffusion. The understanding on the incorporation process can potentially modulate doping and properties in semiconductor nanomaterials.

     

Chemoselective Catalytic Conjugate Addition of Alcohols over Amines

A highly chemoselective conjugate addition of alcohols in the presence of amines is described. The cooperative nature of the catalyst enabled chemoselective activation of alcohols over amines, allowing the conjugate addition to soft Lewis basic α,β‐unsaturated nitriles. Divergent transformation of the nitrile functionality highlights the utility of the present catalysis.     

Synergistic Spin Transition between Spin Crossover and Spin‐Peierls‐like Singlet Formation in the Halogen‐Bonded Molecular Hybrid System: [Fe(Iqsal)2][Ni(dmit)2]⋅CH3CN⋅H2O

To introduce halogen‐bond interactions between a cation and an anion, a novel Fe^III complex from iodine‐substituted ligands involving a paramagnetic nickel dithiolene anion was prepared and characterized. The compound exhibited the synergy between a spin‐crossover transition and a spin‐Peierls‐like singlet formation. The halogen‐bond interactions between the iodine and the sulfur atoms stabilized the paramagnetic state of π‐spins and played a crucial role in the synergistic magnetic transition between d‐ and π‐spins. In addition, the compound showed the light‐induced excited spin state trapping effect.     

Supramolecular Approaches towards Ordered Polymer Materials

Controlled organization of polymer chains into ordered structures is highly important to tune or enhance the properties of the polymeric materials. A supramolecular approach using host–guest chemistry has allowed rational design of chain assemblies with many functional properties. Nanoporous materials with ordered channel structures are particularly useful for attaining precise assemblies of polymer chains through nanoconfinement.