Re-entrant Photoinduced Morphological Transformation and Temperature-Dependent Kinetic Products of a Rectangular Amphiphilic Diarylethene Assembly

An amphiphilic rectangular-shaped photochromic diarylethene bearing two hydrophobic alkyl chains and two hydrophilic tri(ethylene glycol) chains was synthesized, and its photoinduced morphological transformation in water was investigated. Two unexpected phenomena were revealed in the course of the experiments: a re-entrant photoinduced macroscopic morphological transformation and temperature-dependent kinetic products of supramolecular assembly. When the pure closed-ring isomer was dispersed in water, a re-entrant photoinduced morphological transformation, that is, a photoinduced transition from the hydrated phase to the dehydrated phase and then back to the hydrated phase, was observed by optical microscopy upon irradiation with green light at 20 °C; this was interpreted by the V-shaped phase diagram of the LCST transition. The aqueous assembly of the pure closed-ring isomer was controlled by changing the temperature; specifically, rapid cooling to 15 and 5 °C gave J and H aggregates, respectively, as the kinetic products. The thermodynamic product at both temperatures was a mixture of mostly H aggregate with a small amount of J aggregate. This behavior was rationalized by the temperature-dependent potential energy surface of the supramolecular assembly.     

Kink in the dispersion of layered strontium ruthenates

We present detailed energy dispersions near the Fermi level along the high symmetry line GammaX on the monolayer and bilayer strontium ruthenates Sr2RuO4 and Sr3Ru2O7, determined by high-resolution angle-resolved photoemission spectroscopy. A kink in the dispersion is clearly shown for the both ruthenates. The energy position of the kink and the slope in the low-energy part near the Fermi level are almost identical between them, whereas the dispersion in the high-energy part varies, like the behavior of the kink for the cuprate superconductors.     

Experimental observation of soft X-rays and suprathermal ions from rare-gas cryogenic solid targets

We investigated characteristics of the soft X-ray emission in the wavelength range of 6–16 nm using various rare-gas cryogenic solid targets irradiated with a nanosecond laser pulse. Suprathermal ions having a maximum velocity of the order of 10⁷ cm/s were detected for three rare-gas targets (Ar, Kr, and Xe). The spatial distributions of the soft X-rays and the suprathermal ions were measured for Xe cryogenic solid targets and found to vary as cos² and cos⁵, respectively, where is the angle to the target normal. By integrating the observed cos² spatial distribution, the conversion efficiency of the soft X-ray emission in the wavelength range from 6 to 16 nm was evaluated to be 0.2%/pulse. PACS 52.38.ph; 52.50.Jm     

Observation of vacuum-ultraviolet Ar2* radiation gain at 126 nm produced by an ultrashort high-intensity laser pulse propagating in a hollow fiber

We observed a small-signal gain of Ar2* emission at 126 nm by use of a hollow fiber to guide the high-intensity laser propagation in high-pressure Ar. The small-signal gain coefficient was measured to be 0.05 cm(-1) at 126 nm. Kinetic analysis revealed that the electrons produced by the high-intensity laser through an optical-field-induced ionization process initiated the Ar2* production processes. The increase in the emission intensity was measured to be exp(2.5), with an increase in the fiber length.     

Angle-resolved photoemission spectroscopy study of Fe(1 1 0) single crystal: Many-body interactions between quasi-particles at the Fermi level

A high-resolution angle-resolved photoemission spectroscopy (ARPES) study of Fe(1 1 0) single crystal was conducted to elucidate many-body interactions between quasi-particles at the Fermi level at low-temperature. Two kink structures were observed in the energy-band dispersion at the binding energies of ∼40 meV and ∼270 meV for the bulk-derived band on the majority-spin Fermi surface around the Γ point. Based on analyses of the experimentally obtained real parts of the self-energy, these kink structures are derived from electron-phonon and electron-magnon interactions.     

Full-color photochromism of a fused dithienylethene trimer

A diarylethene fused trimer, 1-(5-(2-(3,5-dimethyl-2-thienyl)hexafluorocyclopententen-1-yl)-2,4-dimethyl-3-thienyl)-2-(5-(2-(2,4-dimethyl-5-phenyl-3-thienyl)hexafluorocyclopentene-1-yl)-2,4-dimethyl-3-thienyl)hexafluorocyclopentene, was synthesized. The diarylethene derivative showed full-color photochromic performance by choosing appropriate wavelength of light.     

Development of an experimental database of EUV spectra from highly charged ions of medium to high Z elements in the Large Helical Device plasmas

We are developing an experimental database of extreme ultraviolet spectra from highly charged ions using optically thin high-temperature plasmas produced in the Large Helical Device. Spectra from a variety of elements with atomic numbers ranging from 36 to 83 have been systematically recorded in the range of 1–20 nm by a grazing incidence spectrometer. For higher Z elements from tin onward, discrete or quasicontinuum spectral features from n=4 (N-shell) ions are mainly observed depending upon the plasma temperature, which leads to some new experimental identifications of spectral lines. On the other hand, major emitters are n=3 (M-shell) ions for medium Z elements from krypton to ruthenium. The calculated wavelengths for Δn≠0 transitions agree well with the measurements and the calculated wavelengths are systematically shifted to shorter wavelengths for Δn=0 transitions associated with inner-subshell excited configurations.     

Removal of oxygen atoms from a SiO2 surface by incoherent vacuum ultraviolet excimer irradiation

We have demonstrated the non-thermal removal of oxygen atoms from an oxidized silicon surface (SiO₂) on a silicon wafer by the use of a low-power (0.3 mW cm^-2) incoherent vacuum ultraviolet (VUV) light source at 126 nm. X-ray photoelectron spectroscopy (XPS) has shown that a maximum Si concentration of 80% appears at the surface after a 20-h irradiation with 9.8 eV photons, as a result of oxygen removal from the SiO₂ matrix. The surface morphology, however, indicates no damage or melting on the surface even after the irradiation. Received: 15 April 2002 / Accepted: 17 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Permanent address: Nano-Tech Photon Inc., Shimotomita 4132-1, Shintomi, Miyazaki, 889-1404, Japan RID="**" ID="**"Corresponding author. Fax: +81-985/583-899, E-mail: kubodera@opt.miyazaki-u.jp     

High-resolution angle-resolved photoemission study of Ni(1 1 1) surface state

High-resolution angle-resolved photoemission spectroscopy (ARPES) has been conducted to study the Shockley state (SS) in ferromagnetic Ni(1 1 1) located at the point of the surface Brillouin zone. We have determined the Fermi wave vector and Fermi energy of the state with excitation photon energies of hν = 6.9-27.5 eV. On the basis of ARPES spectral shape analyses, we have found significant electron-electron interaction in the SS.