Table of contents

Cancer photodynamic therapy (PDT) requires the availability of photosensitizers which have a high efficiency and selectivity for the destruction of tumor cells. Chlorophyll (Chl) a is one of the favorable photosensitizers, because it has a high extinction coefficient in the red light region, where light transmission through the human tissues is very high. However, Chl a had a serious problem that it cannot be dissolved in water, so we tried to prepare water-soluble chlorophyllide a from Chl a by several enzymes, and serendipitously came across a unique formation of Chl d from Chl a when papain was used in aqueous acetone. Similar oxidation was observed in Chl b and pheophytin a, although the reactions were very slow. Our finding will provide insight into the unsolved key question as to the biosynthetic pathway of Chl d via Chl a in a recently found novel cyanobacterium Acaryochloris marina.

Magnetic properties of a novel ferromagnetic semiconductor (Zn, Cr)Te were investigated. Zn_1−xCr_xTe thin films, both without and with the additional hole doping by nitrogen, were grown by molecular beam epitaxy. In the magnetization measurement on Zn_1−xCr_xTe without carrier doping, the ferromagnetic behaviors such as a hysteresis loop in the magnetization vs. magnetic field curve were observed. Similar hysteretic behaviors in the field dependence were reproduced in the magnetic circular dichroism measurement. The ferromagnetic transition temperature T_C deduced from Arrott plot increased almost linearly with Cr composition with the maximum T_C=275 K at a Cr composition of x=0.17. The ferromagnetic behaviors observed in the undoped samples were found to be suppressed upon the p-type doping with nitrogen. These experimental findings are discussed based on the double exchange mechanism and the suppression of ferromagnetism by the hole doping is interpreted as due to the shift of the Fermi level in the Cr 3d level with the acceptor doping.

Reactions of Schiff bases with copper(II), nickel(II), iron(II) and manganese(II) sources yielded tetranuclear complexes of [Cu₄(Hhsae)₄]·2H₂O·4CH₃CN (1), [Ni₄(sae)₄(MeOH)₄] (2), [Fe₄(Hsapd)₄]·2H₂O·4MeOH (3) and [Mn₄(sap)₄(MeOH)₄]·H₂O (4), (H₃hsae=2-(4-hydroxysalicylideneamino)-1-ethanol, H₂sae=2-salicylideneamino-1-ethanol, H₃sapd=2-salicylideneaminopropane-2-methyl-1,3-propanediol, and H₂sap=3-salicylideneamino-1-propanol), respectively. Complexes 1–4 have cubane core structures, in which four metal ions are bridged by alkoxides. Magnetic susceptibility measurements revealed that 1–3 have high-spin ground states of S=2, 4 and 8, respectively, while 4 has a diamagnetic ground state.

A wet chemistry procedure which couples chemical functionalization and a dispersion–centrifugation cycle was applied to the dissolution and purification of as-prepared electric-arc produced single-walled carbon nanotubes (SWNTs). It is validated that K₂S₂O₈ treatment generates hydrophilic groups such as carboxyl and hydroxyl on the surfaces of varying carbons, whereas such treatment also causes no severe destruction on the structure of SWNTs. Amidation of the K₂S₂O₈-treated and mixed acids shortened SWNTs leads them largely soluble in tetrahydrofuran (THF) or other organic solvents. The soluble sample was fractionated via a dispersion–centrifugation cycle and highly pure and well-separated SWNTs were successfully obtained in the middle fractions. The purity of the centrifugally fractionated samples is qualitatively estimated with Raman spectroscopy, scanning electron microscope (SEM), and atomic force microscopy (AFM). Quantitative optical absorption spectroscopy and thermogravimetric analysis show that about 60% nanotubes in the starting material are transferred into liquid phase and the carbonaceous purity reaches as high as 129% of a reference sample R2, an 'impurity-free' fragment of soot directly from the arc chamber.

'Smaller' and 'faster' are the key words in the progress of current nanoscience and technology. Thus, a method of exploring the ultrafast transient dynamics of the local quantum functions in organized small structures is eagerly desired. Ultrashort optical pulse technology has allowed us to observe transient phenomena in the femtosecond range, which, however, has the drawback of a relatively low spatial resolution due to the electromagnetic wavelength used. In contrast, scanning tunneling microscopy and its related techniques, although having a time resolution limited by the circuit bandwidth (∼100 kHz), enable us to observe spatial dynamics at the atomic level in real space. Our purpose is to combine these two techniques to achieve a new technology which will advance the pursuit of future nanoscale scientific research in terms of the ultimate temporal and spatial resolutions.

We proposed a promising new design for achieving ultimate spatial and temporal resolution, by combining a short-pulse laser and STM. Using this method, time-resolved tunneling current measurement in the subpicosecond range was successfully demonstrated, this is shaken-pulse-pair-excited STM (SPPX-STM) satisfies the requirements for exploring the ultrafast dynamics of the local quantum functions occurring in organized small structures. We hope this new technology will promote the development of future research on the nanoscale.

A brief review is given on the recent development of the vortex engineering research in our group with special emphasis on the geometrical confinement of vortices into micron-size of samples. We show that the static as well as dynamical nature of vortices is strongly affected by the geometrical constraints, which can be manipulated by the recent nano-technology engineering artificially. One of the spectacular phenomena in this context is a formation of self-organized vortex structures occuring both in static and dynamic manners. The static behaviors have been studied by the scanning SQUID microscope technique and the dynamical behaviors are mostly done in transport measurements. Some technical development of these methods is also discussed. We stress that a common generic concept here is the confinement in nano-scale superconducting systems by the existing surfaces (boundaries), which plays an essential role for the phenomena. Some typical examples are shown, such as results on the vortex arrangement in micron size superconducting disks, a formation of the giant vortex state in such a particular case and the dynamical effects of vortices, especially in the case of Josephson vortices confined in an intrinsic Josephson junction in micron size single crystal Bi₂Sr₂CaCu₂O_8+δ, where the dynamical effect of the confinement provides rich linear and non-linear phenomena due to the excitation of Josephson plasma. Making use of Josephson plasma excitations, a generator operating at T (Hz) frequencies is proposed in this intrinsic Josephson junctions. These phenomena are expected to be all beneficial to potential applications.

Performance of Rh/CeO₂/SiO₂ in the partial oxidation of tar from the pyrolysis of wood biomass (architectural salvage) was investigated and compared with various materials such as steam reforming Ni catalyst, active clay, USY zeolite, MS-13X, dolomite, alumina, silica sand, fluorite and non-catalyst. Rh/CeO₂/SiO₂ and the steam reforming Ni catalyst exhibited much higher performance than any other materials in terms of hydrogen production and the amount of tar. Therefore, the performance of Rh/CeO₂/SiO₂ and steam reforming Ni catalyst was particularly compared. From the result on the dependence of reaction temperature, equivalence ratio, and biomass feeding rate, Rh/CeO₂/SiO₂ exhibited higher performance than the Ni catalyst, especially in terms of tar and coke amount. Furthermore, Rh/CeO₂/SiO₂ was also more stable than the Ni catalyst. The catalyst deactivation can be related to the amount of coke deposition. The results indicate that Rh/CeO₂/SiO₂ has high resistance to coke formation, and this is related to higher combustion activity of Rh/CeO₂/SiO₂ than the Ni catalyst. Furthermore, from the TPR profiles, Rh/CeO₂/SiO₂ had higher reducibility than the Ni catalyst. The combination of high combustion activity with high reducibility and reforming activity can be related to high performance of tar conversion in the fluidized bed reactor.

Atomic hydrogen storage by carbon nanotubes (CNTs) and highly oriented pyrolytic graphite (HOPG) has been studied using a flow catalytic reactor and an ultra-high vacuum surface science apparatus including scanning tunneling microscope (STM), respectively. Defect sites on CNTs as adsorption sites of atomic hydrogen are introduced by oxidation pretreatment using La catalyst. Pd catalysts are then deposited on CNT surfaces for dissociation of H₂ into atomic hydrogen, which spills over to the defect sites. In the best case, 1.5 wt% of hydrogen is stored in the defective CNT with Pd particles at 1 atm and 573 K. In temperature programmed desorption (TPD) experiments, H₂ starts to desorb at 700–900 K depending on the annealing temperatures of CNTs prior to hydrogen storage. On the HOPG surface, hot atomic hydrogen produced by dissociation of H₂ using tungsten wire desorbs from graphite terraces at 400–700 K, which is much lower than that on CNTs. It is possible that one can decrease the desorption temperature by changing the method of H₂ dissociation.

For the Cu films sputter-deposited at ambient temperature on a Ta buffer layer with a clean surface (the nex-Cu film) and those on a Ta buffer layer with native oxide (the ex-Cu film), the internal stress along the film surface, σ_i∥, the Young's modulus, E_f, the internal friction, Q_f⁻¹, the decrease in Q_f⁻¹ after annealing at 400 K, ΔQ_f,400 K⁻¹/Q_f⁻¹, and the root mean square of surface roughness (the RMS roughness) were studied for the Cu film thickness, t_Cu, between 5 and 1000 nm. For the nex-Cu films with t_Cu below 100 nm, E_f showed a deviatory decrease from its theoretical value, E_f,th, which was estimated from the crystallographic texture and σ_i∥, suggesting that the constituent static anelastic strain due to grain boundaries (GBs), ε_sa,GB, was, e.g. as large as about 25% of the constituent elastic strain, ε_e, at t_Cu of 10 nm. The local maximum of the RMS roughness and the local minimum of ΔQ_f,400 K⁻¹/Q_f⁻¹ were found near below 100 nm, indicating that the properties of GBs in already deposited Cu film were modified by additional deposition (the capping effect, below) and the anomalous capping effects took place near below 100 nm in t_Cu. For the ex-Cu films, E_f showed good agreement with E_f,th except that a local decrease in E_f was found for t_Cu near below 100 nm. The local maxima of ΔQ_f,400 K⁻¹/Q_f⁻¹ and the RMS roughness were found for t_Cu near below 100 nm too. It is suggested that the properties of GBs in the ex-Cu films were of those in bulk metal for t_Cu below a few tens of nanometer and then changed to those in nanocrystalline metal with increasing t_Cu. The capping effects were also observed for the ex-Cu films.

Size control of silicon nanowires (SiNWs) synthesized by laser ablation of a Si target with iron or nickel as catalysts were investigated by changing the synthesis parameters such as the content of catalyst in targets and laser power during synthesis. The diameter and length of SiNWs significantly depended on the synthesis parameters, i.e. the size of SiNWs can be controlled by the synthesis parameters. Manipulation of SiNWs was also performed during the observation of scanning electron microscope. By changing the degree of charge-up for free-standing adjacent intertwined SiNWs at an edge of Si substrate, the distance and speed of opening motion of them can be controlled. This motion is probably caused by the Coulomb repulsive interaction between them.

The photo-induced intramolecular proton (or hydrogen atom) transfer (ESIPT) and metal binding properties of Oxa-ester were studied in methanol solution. The dissociation constant between Oxa-ester and the metal ion was highly dependent with the metal ion and was determined by Hill plots or iterative least squares fitting to be 447 mM, 14.9 μM, and 290 nM for Ca²⁺, Zn²⁺, and Cu²⁺, respectively, in methanol. The fluorescence intensity of Oxa-ester greatly increased with increasing concentration of Zn²⁺, while the fluorescence intensity decreased with the addition of Ca²⁺ and Cu²⁺. Transient absorption spectroscopy revealed that Oxa-ester underwent ESIPT to give Z-NH isomer in the excited state in benzene, while Oxa did not undergo ESIPT probably due to the hydrogen bonding with solvent water.

A single crystalline Eu-doped GaN was grown by gas-source molecular beam epitaxy and photoluminescence (PL) properties were studied. The PL spectra show red-emission at 622 nm originating from intra 4f–4f transition of Eu³⁺ ion without band-edge emission of GaN. The peak shift of the red-emission with the temperature variation from 77 K to room temperature is less than 1.6 meV, and thermal quenching of the luminescence was found to be small compared with the band-to-band transition. Fourier transform infrared spectra showed an absorption peak at about 0.37 eV, which may be due to a deep defect level. The intensity of the red luminescence and the defect-related absorption peak increased with increasing Eu concentration, and a close correlation in the intensity was observed between them. These results suggest that the deep defect level plays an important role in the radiative transition of Eu³⁺ ion in GaN and the optical process for the luminescence at 622 nm was discussed with the relation to the defect.

Terahertz electromagnetic pulses can serve as a new and unique tool for various types of spectroscopy. We first characterized the temporal and spatial properties of THz pulses generated from a large-aperture photoconductive antena, and then used them for the study of the ultrafast dynamics of electrons in semiconductros. We studied the dynamics of electrons generated by femtosecond optical pulses with positive and negative excess energies in GaAs and InP by observing the waveform of the emitted THz radiation. Subpicosecond intraband relaxation was observed with positive excess energies. With negative excess energies, a picosecond transition from the Urbach state to free carrier states was observed.

Micro-Brillouin and Raman light scattering experiments were performed on (Sr_1−xBa_x)₂Nb₂O₇ single crystals to investigate the effect of Ba addition on the normal-incommensurate phase transition. From the Brillouin frequency shift results, it was observed that the onset temperature of the normal-incommensurate phase decreased with increasing Ba concentration. This was associated to the suppression of the octahedra tilting due to substitution of larger ion on the A-site. The Raman intensity of the Q soft mode measured at room temperature also showed a similar behaviour with increasing x.

Five mononuclear oxorhenium(V) complexes containing 8-quinolinolato derivatives, [ReOCl₂(2-X-5-Y-7-Z-8-Oqn)(PPh₃)] (qn=quinoline; PPh₃=triphenylphosphine; X=Me, Y=Z=H, 1; X=Z=H, Y=Cl, 2; X=H, Y=Z=Cl, 3; X=H, Y=Cl, Z=I, 4; X=H, Y=Z=Br, 5), were newly synthesized by the reaction of [ReOCl₃(PPh₃)₂] with the corresponding 8-hydroxyquinoline ligands. From X-ray crystal structural analyses, all the obtained complexes have the same geometry; the Re=O bond occupies the trans position to the O atom of the deprotonated 8-hydroxyquinoline ligand. The complexes, which retain their structures in solution, were characterized on the basis of IR, UV–vis, ³¹P NMR spectra, and cyclic voltammetry. Depending on the existence of 2-Me substituent in the ligands, some stereochemical and electrochemical differences were observed. In contrast to the case of the corresponding 2-methylquinolin-8-ylamido complex [ReOCl₂(2-Me-8-HNqn)(PPh₃)], substitution reaction of PPh₃ to OPPh₃ (=triphenylphosphine oxide) or pyridine did not take place, reflecting the high stability of the present 8-quinolinolato complexes.

Techniques for controlling atomic step position at low-temperature and selective growth of Cu nanowires along the atomic step edges have been studied. By immersing the Si(111) substrates with well-defined step/terrace surfaces in the Cu-contained water with the dissolved oxygen content of less than 1 ppb, selective growth of Cu nanowires along the step edges was successfully achieved. Total reflection X-ray fluorescence spectroscopy (TXRF) revealed that the fabricated nanowires were composed of mono-atomic Cu rows. For step position control, the characteristics of step-flow pinning effect of SiO₂ films were investigated. Fine SiO₂ line patterns drawn by anodic oxidation using AFM probes enable us to obtain the step-free Si areas predetermined by the patterns.

A super-hydrophobic surface was used to concentrate a droplet of sample solution evaporatively for the stripping analysis of heavy metal ions. The system consisted of a working electrode at the center and a Ag/AgCl reference electrode surrounding the working electrode. Except for the sensitive area, a super-hydrophobic layer was formed with polytetrafluoroethylene (PTFE) beads. A droplet of an aqueous sample solution was placed on the sensitive area and concentrated by evaporation. The super-hydrophobic layer effectively pinned the droplet at the edge of the sensitive area. Square-wave anodic stripping voltammetry was conducted for the analysis of Cd²⁺ and Pb²⁺ ions. A significant increase in peak height was observed as the volume of the droplet increased. When a 5-μl-droplet was used, the peaks were 30 times higher than those obtained in the analysis following the conventional procedure without the evaporative concentration. In addition, the peak current increased, and the background current decreased by decreasing the working electrode area.

Alloying process and shape memory properties of a Ti/Ni multilayer thin film fabricated by a dual d.c. magnetron sputter–deposition method were investigated, and compared with those of a Ti–Ni amorphous thin film fabricated by an alloy target sputter–deposition method. The multilayer thin film was made by depositing Ti and Ni layers alternately on a SiO₂/Si substrate. The Ti and Ni of the Ti/Ni multilayer thin film were crystalline after deposition. Alloying of the Ti/Ni multilayer thin film proceeded in multi steps. Amorphous phase was formed at the interfaces between the Ti and Ni layers by inter-diffusion of the Ti and Ni atoms during heating up to 640 K. Ni-rich Ti–Ni B2 phase was formed during heating up to 710 K. During further heating up to 750 K, the Ni-content of the Ti–Ni B2 phase decreased and Ti₂Ni phase was formed. The Ti/Ni multilayer thin film exhibited shape memory effect after heat-treatment at 673 K where Ti–Ni amorphous thin films were not crystallized. The heat-treated Ti/Ni multilayer thin films exhibited the shape memory effect equivalent to that of the heat-treated Ti–Ni amorphous thin films when the heat-treatment temperature was above 873 K.

X-ray intensity measurements have been performed on the structure of the layered compound Co_xNbS₂ single crystals (x≤0.5) at room temperature. The c-axis lattice parameter changes discontinuously at around x=0.2 and remains constant with further increase of the Co content. For the lower content of Co atoms (x<0.2), no diffuse maxima appeared on the (hk0) and (hk1) reciprocal lattice planes. At x=0.23, the diffuse maxima are clearly seen at 4/3, 4/3, 1 and 5/3, 5/3, 1 reciprocal lattice points. At x=0.32, sharp intensity maxima appear at 4/3, 4/3, 0 and 5/3, 5/3, 0 in addition to at 4/3, 4/3, 1 and 5/3, 5/3, 1. It is understood that √3×√3R30° ordered structure exists at the stoichiometric composition of x=1/3. At further increasing the Co content, the intensity at 4/3, 4/3, 0 and 5/3, 5/3, 0 is weakening and disappears above x=0.4. The structural model based on the space group P6₃22 (No. 182) for Co_xNbS₂ (x>0.4) is discussed with considering both the position of the Co atoms and their occupation rate.

Despite the appearance of ever first report on the synthesis of LiNiO₂ in 1954, active research to identify and evaluate its suitability as an electrode material in rechargeable lithium batteries started only in late 80's. Following this, numerous articles discussed the synthesis, electrochemical behavior and the problems associated with the compound. In this connection, the present communication reviews certain important experimental results obtained by different research groups on various aspects of LiNiO₂, in order to understand the significance of LiNiO₂ as a potential cathode material for rechargeable lithium batteries. Also selected type of methodologies adopted to synthesize the title compound have also been discussed to substantiate the dependence of electrochemical behavior of LiNiO₂ on the method of synthesis and reaction conditions. The subject has been discussed at length and may provide useful information on the properties of LiNiO₂ and may enable the fabrication of tailor made nickel-based electrode materials for 'next generation' lithium or lithium-ion batteries along with the highlights of doped and coated derivatives of LiNiO₂.

Piezoelectric laminate composite has been successfully fabricated as a smart material by a spark plasma sintering process. Fully or nearly fully dense BaTiO₃/MgO (pre-sintered)/BaTiO₃, BaTiO₃/MgO with 10 vol% BaTiO₃/BaTiO₃ laminates were sintered at 1300 °C with a holding time of 5 min under a pressure of 35 MPa. From EDS analysis, no reaction between BaTiO₃ and MgO layers was observed along the interface. Effects of cycle stress and stress intensity factor on the voltage response of the proposed laminates were investigated for confirmation of a crack detecting capability. The resultant relationship between crack length and voltage response range clearly showed that the proposed laminates have a crack sensing capacity.

This study was aimed at developing laser welding with an applied voltage potential to increase the bead root width in laser welding. Also, in order to enhance the welding speed and the butt joint gap tolerance, the influences of the experimental conditions: supplied voltage between plate and backside electrode, welding speed, plasma operate gaseous species, and the butt joint gap, on the bead root width were investigated. Although it is necessary to avoid over heating and melting the plates, it is applicable for higher speed and wider gap butt joint welding than a conventional laser welding. In the case of butt joint welding with a thickness of 2.0 and 0.8 mm steel sheets by using 5 kW CO₂ laser system, it is concluded that this method is effective for increasing of the welding speed from 5 to 8 m/min. Knowledge of optimum conditions and configurations has guided to extend this process to more challenging structural materials such as a tailored blank steel sheet.