Exchange Bias Induced by the Spin-Glass-Like State in a Te-Rich FeGeTe van der Waals Ferromagnet.

We have experimentally investigated the mechanism of the exchange bias in 2D van der Waals (vdW) ferromagnets by means of the anomalous Hall effect (AHE) together with the dynamical magnetization property. The temperature dependence of the AC susceptibility with its frequency response indicates a glassy transition of the magnetic property for the Te-rich FeGeTe vdW ferromagnet. We also found that the irreversible temperature dependence in the anomalous Hall voltage follows the de Almeida-Thouless line. Moreover, the freezing temperature of the spin-glass-like phase is found to correlate with the disappearance temperature of the exchange bias. These important signatures suggest that the emergence of magnetic exchange bias in the 2D van der Waals ferromagnets is induced by the presence of the spin-glass-like state in FeGeTe. The unprecedented insights gained from these findings shed light on the underlying principles governing exchange bias in vdW ferromagnets, contributing to the advancement of our understanding.

In situ transmission electron microscopy observation of the deformation and fracture processes of an epoxy/silica nanocomposite.

Herein, we report the in situ transmission electron microscopy observation of the deformation and fracture processes of an epoxy resin thin film containing silica nanoparticles under tensile strain. Under tensile strain, the dispersed silica nanoparticles in the composite arrest the progress of the crack tip and prevent crack propagation. Concomitantly, the generation and growth of nanovoids at the epoxy matrix/nanoparticle interfaces were clearly observed, particularly in the region near the crack tip. These nanovoids contribute to the dissipation of fracture energy, thereby enhancing the fracture toughness. We also analyzed the local distributions of the true strain and strain rate in the nanocomposite film during tensile testing using the digital image correlation method. In the region around the crack tip, the strain rate increased by 3 to 10 times compared to the average of the entire test specimen. However, the presence of large filler particles in the growing crack suppressed the generation of strain, potentially contributing to hindering crack growth.

Serum miR-375-3p increase in mice exposed to a high dose of ionizing radiation.

Exposure to high-doses of ionizing radiation (IR) leads to development of a strong acute radiation syndrome (ARS) in mammals. ARS manifests after a latency period and it is important to develop fast prognostic biomarkers for its early detection and assessment. Analysis of chromosomal aberrations in peripheral blood lymphocytes is the gold standard of biological dosimetry, but it fails after high doses of IR. Therefore, it is important to establish novel biomarkers of exposure that are fast and reliable also in the high dose range. Here, we investigated the applicability of miRNA levels in mouse serum. We found significantly increased levels of miR-375-3p following whole body exposure to 7 Gy of X-rays. In addition, we analyzed their levels in various organs of control mice and found them to be especially abundant in the pancreas and the intestine. Following a dose of 7 Gy, extensive cell death occurred in these tissues and this correlated negatively with the levels of miR-375-3p in the organs. We conclude that high expressing tissues of miR-375-3p may secrete this miRNA in serum following exposure to 7 Gy. Therefore, elevated miR-375-3p in serum may be a predictor of tissue damage induced by exposure to a high radiation dose.

The first transition metal phthalocyanines: sensitizing rubrene emission based on triplet-triplet annihilation.

Metallophthalocyanines (MPc-o-Cou, M = Fe, Co, Ni, and Cu) with fourth period metal ions have been successfully applied as a sensitizer coupled with rubrene (Rub) in photon upconversion based on triplet-triplet annihilation. An upconversion quantum yield (ϕPUC) of up to 4.82% was observed in the CoPc-o-Cou : Rub couple. The absorption and phosphorescence emission spectra showed that the Q bands and phosphorescence emission peaks were dramatically dependent on the number of d-electrons of the metal ions in MPc-o-Cou. These results suggested that the photon upconversion behavior of MPc-o-Cou : Rub systems could be managed by altering the metal ions in MPc-o-Cou.

Efficient Photocurrent Enhancement from Porphyrin Molecules on Plasmonic Copper Arrays: Beneficial Utilization of Copper Nanoanntenae on Plasmonic Photoelectric Conversion Systems.

We demonstrated the usefulness of Cu light-harvesting plasmonic nanoantennae for the development of inexpensive and efficient artificial organic photoelectric conversion systems. The systems consisted of the stacked structures of layers of porphyrin as a dye molecule, oxidation-suppressing layers, and plasmonic Cu arrayed electrodes. To accurately evaluate the effect of Cu nanoantenna on the porphyrin photocurrent, the production of Cu2O by the spontaneous oxidation of the electrode surfaces, which can act as a photoexcited species under visible light irradiation, was effectively suppressed by inserting the ultrathin linking layers consisting of 16-mercaptohexadecanoic acid, titanium oxide, and poly(vinyl alcohol) between the electrode surface and porphyrin molecules. The reflection spectra in an aqueous environment of the arrayed electrodes, which were prepared by thermally depositing Cu on two-dimensional colloidal crystals of silica with diameters of 160, 260, and 330 nm, showed clear reflection dips at 596, 703, and 762 nm, respectively, which are attributed to the excitation of localized surface plasmon resonance (LSPR). While the first dip lies within the wavelengths where the imaginary part of the Cu dielectric function is moderately large, the latter two dips lie within a region of a quite small imaginary part. Consequently, the LSPR excited at the red region provided a particularly large enhancement of porphyrin photocurrent at the Q-band (ca. 59-fold), compared to that on a Cu planar electrode. These results strongly suggest that the plasmonic Cu nanoantennae contribute to the substantial improvement of photoelectric conversion efficiency at the wavelengths, where the imaginary part of the dielectric function is small.

Switch of the magnetic field effect on photon upconversion based on sensitized triplet-triplet annihilation.

Magnetic field effects (MFEs) on photon upconversion based on sensitized triplet-triplet annihilation (TTA-UC) are examined in platinum(ii) octaethylporphyrin/9,10-diphenylanthracene (DPA) systems at different DPA concentrations and laser power densities. Positive MFEs on TTA-UC are observed for the first time and are most likely attributable to aggregation of DPA.

Extraordinary enhancement of porphyrin photocurrent utilizing plasmonic silver arrays.

We demonstrate up to ∼630-fold enhancement of the photocurrent from a porphyrin monolayer on a plasmonic Ag-array electrode showing plasmon absorption in the Q-band region relative to that on a planar Ag electrode. The photocurrent obtained by the Q-band excitation in the plasmonic electrodes even exceeded that obtained by the Soret-band excitation in a normal, nonplasmonic electrode.

Thermal and Chemical Stabilization of Silver Nanoplates for Plasmonic Sensor Application.

Thermal and chemical stabilities of silver nanoplates (AgPLs), which are triangle plate-shaped silver nanoparticles, were improved by coating with titanium oxide. The titanium oxide layer prepared by a dip-coating method was certainly advantageous for the improvement of thermal stability. Furthermore, the overlayering of titanium oxide by a spray pyrolysis method was quite useful for improving the chemical stability against I(-) exposure. Such a coating exhibited satisfactory refractive index sensitivities.

Effects of silver nanoparticles with different sizes on photochemical responses of polythiophene-fullerene thin films.

Effects of size and coverage density of silver nanoparticles (AgPs) on the fluorescence emission and fluorescence lifetime of poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films were investigated. AgPs of 64 nm diameter showed greater effects on the fluorescence decay process of P3HT films as compared with 7 nm AgPs. The fluorescence lifetime (FL) of P3HT decreased from 0.61 to 0.22 ns in the presence of 64 nm AgPs, while no appreciable change (0.60 ns) was seen in the case of 7 nm AgPs. The results suggest that the 64 nm AgPs showed a greater effect on the enhancement of the decay rate of excited P3HT. The photoelectric conversion of thin films consisting of P3HT and phenyl-C61-butyric acid methyl ester (PCBM) was also investigated. AgPs of 7 or 64 nm diameters were first deposited on indium-tin-oxide substrates with controlled surface coverage densities from ~1 to 40%. When the coverage densities of deposited AgPs were ~20% for both 7 and 64 nm, the enhancement of photoelectric conversion efficiency reached maximum. The degree of enhancement in the case of 64 nm AgPs was larger than in the case of 7 nm AgPs.

Split Spy0128 as a potent scaffold for protein cross-linking and immobilization.

Site-specific cross-linking techniques between proteins and additional functional groups have become increasingly important for expanding the utility of proteins in biochemistry and biotechnology. In order to explore powerful techniques for practical bioconjugation applications, we have validated a technique mediated by a unique property of Streptcoccus pyogenes pilin subunit Spy0128, an autocatalytic intramolecular isopeptide formation in Spy0128. Recently, it has been revealed that Spy0128 can be split into two fragments (split-Spy0128 (residues 18-299 of Spy0128) and isopeptag (residues 293-308 of Spy0128)) that were capable of forming an intermolecular covalent complex. We focused on this unique reconstitution property and first studied the bioconjugation of blue and green fluorescent proteins, enabling the direct monitoring of cross-linking reactions by Förster resonance energy transfer (FRET). A fluorescence lifetime study shows that spatial control of two proteins on the Spy0128 scaffold is possible when one protein is fused to the N-terminus of split-Spy0128 and another one is tethered at the N- or C-terminus of the isopeptag. Furthermore, we demonstrated site-specific protein immobilization mediated by the reconstitution of split-Spy0128 and isopeptag. In this case, a split-Spy0128 mutant with a free N-terminal Cys residue was first immobilized onto beads chemically modified with a maleimide group through a Michael addition process. Then, an isopeptagged protein was successfully immobilized onto the split-Spy0128-immobilized beads. These results suggest that Spy0128 is a potent proteinaceous scaffold available for bioconjugation both in solution and at a solid surface.

Gold nanorods embedded in titanium oxide film for sensing applications.

We succeeded in fabricating a localized surface plasmon resonance (LSPR) sensor comprising gold nanorods (AuNRs) that were immobilized in a thin film of titanium oxide. First, AuNRs were electrostatically immobilized onto a glass substrate; then, dip-coating of the thin titanium oxide film was carried out. These procedures were realized to prepare well-dispersed AuNRs onto a substrate with a uniform titanium oxide layer. The titanium-oxide-coated AuNRs could retain their rod-shape, even after annealing at 300°C for 1 h, since titanium oxide effectively prevented any heat-induced shape change of the AuNRs. The peak shifts of the plasmon bands of the immobilized AuNRs were observed with the change in the environmental refractive indices, even after titanium oxide coating. In addition, the as-prepared titanium oxide layer exhibited photocatalytic activity for methylene blue dye molecule under UV irradiation. This suggests that the titanium-oxide-coated AuNRs can conveniently be reusable even for unwanted contamination with organic compounds, due to their photocatalytic decomposition with UV light.

Electropolymerized polythiophene photoelectrodes with density-controlled gold nanoparticles.

A polythiophene thin film was fabricated on gold nanoparticle (AuNP)-deposited indium-tin-oxide (ITO) electrodes with electropolymerization, whereas AuNPs were predeposited on the ITO surface. A photocurrent via photoexcited polythiophene increased with AuNPs which was attributed to the localized surface plasmon resonance. Investigation of the AuNP-density dependence on the relative enhancement of photocurrent revealed the maximum effect at 14% of AuNP-density, while 68% of AuNP-density exhibited smaller photocurrent than the polythiophene electrode without AuNPs. We have revealed that the effects of AuNPs saturate in the fairly low density region, and that the excess AuNPs even in the range of submonolayer resulted in the decrement of photocurrents.

Photocurrent enhancement tuned with plasmonic resonance in self-assembled monolayers fabricated on regularly arrayed gold nanostructures.

We investigated the enhancement properties of the photocurrent generation from self-assembled monolayers of porphyrin fabricated on periodic structures of gold half-shells. Tuning the surface plasmon frequency of the nanostructures led to correlated wavelength dependences of the external quantum efficiencies of the photocurrents, as well as fluorescence intensities resulting from effective electronic excitation of porphyrin molecules.

A Z-scheme type photoelectrochemical cell consisting of porphyrin-containing polymer and dye-sensitized TiO2 electrodes.

A Z-scheme type photoelectrochemical cell consisting of an electrochemically polymerized photoactive electrode and a dye-sensitized TiO(2) electrode is demonstrated. Nearly 1 V of open circuit voltage (V(OC)) was achieved by the cooperation of a couple of photoactive electrodes toward uphill electron pumping.

Selective formation and structural properties of rhombic dodecahedral [70]fullerene microparticles formed by reaction with aliphatic diamines.

We have accomplished the selective formation of rhombic dodecahedral microparticles on the submicrometer to micrometer scale by the reaction of [70]fullerene (C(70)) with primary aliphatic diamines. The morphology of the resultant microparticles was analyzed by scanning electron microscopy, powder X-ray diffraction, and other spectroscopic methods, demonstrating that the resultant particles held a rhombic dodecahedral shape having a simple cubic lattice structure and that primary aliphatic amines were mostly trapped inside the particles through electronic interaction between C(70) and amines. Furthermore, we have discovered interesting structural characteristics in which the incorporated amines could be removed from the C(70) microparticles or exchanged with other primary aliphatic diamines.

Enormous enhancement in photocurrent generation using electrochemically fabricated gold nanostructures.

A self-assembled monolayer of porphyrins fabricated on the surface of an electrochemically deposited gold nanostructure exhibits enormous enhancement of photocurrent due to porphyrin excitation, especially in the near-infrared region, where localized surface plasmon resonance was responsible.

Applications of strong interactions between photons and molecules to analytical sciences.

Spectroscopic measurements and applications to analytical sciences utilizing strong interactions between photons and molecules will be described. In particular, this report demonstrates high-sensitivity analysis of chemical species in solution through laser multiphoton ionization, and selective detection and characterization of the molecules located at solid surfaces and phase boundaries by using the method of second harmonic generation. Furthermore, new spectroscopic methods and sensitivity improvements utilizing the resonance of incident light photons with surface plasmons emerging on the surfaces of gold nanoparticles and nanostructures are presented. In addition, applications of surface plasmon resonance to spatio-selective plating to microscopic sites and to the field of nanobiotechnology are described, with special focusing on controlling biomolecules.

Plasmon-enhanced photocurrent generation from self-assembled monolayers of phthalocyanine by using gold nanoparticle films.

The effect of localized electric fields on the photocurrent responses of phthalocyanine that was self-assembled on a gold nanoparticle film was investigated by comparing the conventional and the total internal reflection (TIR) experimental systems. In the case of photocurrent measurements, self-assembled monolayers (SAMs) of a thiol derivative of palladium phthalocyanine (PdPc) were prepared on the surface of gold-nanoparticle film that was fixed on the surface of indium-tin-oxide (ITO) substrate via a polyion (PdPc/AuP/polyion/ITO) or on the ITO surface (PdPc/ITO). Photocurrent action spectra from the two samples were compared by using the conventional spectrometer, and were found that PdPc/AuP/polyion/ITO gave considerably larger photocurrent signals than PdPc/ITO under the identical concentration of PdPc. In the case of the TIR experiments for the PdPc/AuP/polyion/ITO and the PdPc/AuP/Glass systems, incident-angle profiles of photocurrent and emission signals were correlated with each other, and they were different from that of the PdPc/ITO system. Accordingly, it was demonstrated that the photocurrent signals were certainly enhanced by the localized electric fields of the gold-nanoparticle film.