Michio M. Matsushita

Spintronics in organic π-electronic systems

Molecule-based spin-transportation coexisting systems that exhibit negative giant magnetoresistance and techniques for accessing these molecular systems are introduced as a basis for the construction of molecule-based spintronics.

An organic ferromagnet: α-phase crystal of 2-(2′,5′-dihydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide (α-HQNN)

The α-phase crystal of 2-(2′,5′-dihydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide (α-HQNN), which consists of one-dimensional arrays formed by intra- and inter-molecular hydrogen bonds, showed a ferromagnetic phase transition at 0.5 K.

DALI2: A NaI(Tl) detector array for measurements of

A NaI(Tl) detector array called DALI2 (Detector Array for Lo w Intensity radiation 2) has been constructed for in-beam γ-ray spectroscopy experiments with fast radioactive isotope (R I) beams. It consists typically of 186 NaI(Tl) scintillator s covering polar angles from∼15◦ to ∼160◦ with an average angular resolution of 6 ◦ in full width at half maximum. Its high granularity (good angular resolution) enables Doppler-shift correcti ons that result in, for example, 10% energy resolution and 20 % full-energy photopeak e fficiency for 1-MeVγ rays emitted from fast-moving nuclei (velocities of v/c ≃ 0.6). DALI2 has been employed successfully in numerous experiments using fast RI beams wi th velocities ofv/c = 0.3 − 0.6 provided by the RIKEN RI Beam Factory.

\gamma

Abstract The concept of “spin-polarized” donor was successfully extended to TTF-based donor radicals. A series of TTF derivatives carrying a phenyl nitronyl nitroxide group were prepared, and they turned out to afford ground state triplet cation diradicals through one-electron oxidation. Such “spin-polarized” TTF donors are expected to become building blocks for organic conducting ferromagnets.

rays from fast nuclei

A spin-polarized donor, BTBN, which is a dibromotetrathiafulvalene derivative containing a nitronyl nitroxide group in a cross-conjugated manner, was prepared. Upon hole injection from an electrode, the neutral microcrystals of BTBN exhibited nonlinear I-V characteristics that were interpreted in terms of the space-charge-limited conduction (SCLC) mechanism. Moreover, the resistance of BTBN decreased upon application of a magnetic field below 30 K and exhibited a giant negative magnetoresistance of (R(H) - R(0))/R(0) = -76% at 2 K under 5 T. These results show that the transport of carriers in the neutral unicomponent radical crystal can be controlled by the external magnetic field. These findings are important as a basis for developing molecule-based spin electronic devices.

NOVEL SPIN-POLARIZED TTF DONORS AFFORDING GROUND STATE TRIPLET CATION DIRADICALS

We studied the electrochemistry of the thin films of octathio[8]circulene (1) in an ionic liquid, N,N-diethyl-N-methyl(2-methoxyethyl) ammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI). The compound 1 exhibited simultaneous two-electron oxidation in the oxidation scan and then stepwise reductions to the original neutral state, showing significant electrochromism. This color change was well-interpreted in terms of the n-pi transition that is allowed by the vacancy in the HOMO of 1 after electrochemical oxidation.

Influence of Magnetic Field upon the Conductance of a Unicomponent Crystal of a Tetrathiafulvalene-Based Nitronyl Nitroxide

Excited states in (38,40,42) Si nuclei have been studied via in-beam γ-ray spectroscopy with multinucleon removal reactions. Intense radioactive beams of ^{40}S and (44)S provided at the new facility of the RIKEN Radioactive Isotope Beam Factory enabled γ-γ coincidence measurements. A prominent γ line observed with an energy of 742(8) keV in (42) Si confirms the 2(+) state reported in an earlier study. Among the γ lines observed in coincidence with the 2^{+} → 0+ transition, the most probable candidate for the transition from the yrast 4(+) state was identified, leading to a 4(1)+) energy of 2173(14) keV. The energy ratio of 2.93(5) between the 2(1)+ and 4(1)(+) states indicates well-developed deformation in (42) Si at N = 28 and Z = 14. Also for 38,40)Si energy ratios with values of 2.09(5) and 2.56(5) were obtained. Together with the ratio for (42)Si, the results show a rapid deformation development of Si isotopes from N = 24 to N = 28.

Electrochemical and electrochromic properties of octathio[8]circulene thin films in ionic liquids.

Photodetection based on bis-(4-dimethylaminodithiobenzil)-Ni(II) (BDN), a representative and well-studied metal dithiolene that shows strong absorption in the near-infrared region of the electromagnetic spectrum, has been investigated. By adopting a metal/insulator/semiconductor/metal (MISM) structure, the peak photocurrent response to an oscillating light chain is increased by up to 50 times, compared to devices without an insulating layer. The transient form of the MISM photoresponse, while unsuitable for steady-state photodetection, can be used to detect periodic light signals of frequencies up to 1 MHz, and is thus applicable for optical communication. Further improvements have been realized by nanostructuring carbon black into the dithiolene layer, improving charge collection, and yielding detectivity of up to 1.6 × 10(11) Jones at wavelengths beyond the scope of silicon photodiodes. Such an architecture may allow the favorable absorption properties of other such metal dithiolenes to be harnessed, where their low charge carrier mobilities and short excitation lifetimes have previously limited their applicability to this field.

Well Developed Deformation in 42Si

An “ionic(I)–ionic(II)” charge-transfer transition has been observed in a new molecular solid composed of dineopentylbiferrocene (D) and fluorotetracyanoquinodimethane (A). The material is a monova...

Utilizing photocurrent transients for dithiolene-based photodetection: stepwise improvements at communications relevant wavelengths.

Network structures made of π-conjugated molecular wires of oligothiophene 3mer, or 9mer carrying thiol groups at α,ω-positions, and gold nanoparticles with average diameter of 4 nm were prepared on interdigitated gold electrodes. Observation of the resultant assemblies by means of FE-SEM and TEM revealed that the gold nanoparticles were connected by π-molecular wires to form a network. The networks exhibited thermally activated electron transport at room temperature with activation energies of 21and 45 meV for 3mer- and 9mer-networks, respectively, and these values were almost the same as those of networks connected with non-conjugated molecules having similar lengths. However, the activation energy became very small (∼0.1 meV) at temperatures lower than 30 K and non-linear current–voltage characteristics (I ∝ V3) appeared in π-conjugated networks at 4.2 K. These results suggest that the gold nanoparticles in the networks work as Coulomb islands and the temperature-independent behavior at lower temperatures can be interpreted in terms of a co-tunneling mechanism.