The monolayer of amphiphilic merocyanine dye (MD) molecules at the air-water interface was observed by the grazing incidence X-ray diffraction (GIXD) method. At the air-water interface, the MD molecules formed two-dimensional crystallites (J-aggregates), whose excitonic absorption bands were located at longer wavelength than the monomer band. The structural analysis on the MD J-aggregate was carried out, and, using the determined structure, the relationship between the molecular arrangement and the energy shift of the visible absorption band upon crystallization was clarified. For the calculation of the energy shift, simple formulas were derived on the basis of molecular exciton theory. It was revealed that not only the transition dipole moment interaction but also the electric dipole moment interaction among the molecules plays an important role in the energy shift.
Recently, we proposed time-resolved X-ray observations of picometer-scale slow Brownian motions of individual protein molecules in aqueous solutions. In this new single molecular detection system, which we call Diffracted X-ray Tracking (DXT), we observed the rotating motions of an individual nanocrystal, linked to the specific site in individual protein molecules. Therefore, DXT can monitor dynamics of the individual molecules or specific sites in individual single molecules. Now, we observed individual DNA molecules, myosin head molecules, denatured proteins, and functional protein membranes. The most important techniques for DXT are both the size and crystallization of the nanocrystals that are labeled with single molecules. Here we introduce two fabrications of the labeled nanoparticles or nanocrystals.
We have investigated spin reorientation transitions (SRT) on magnetic ultra-thin films by X-ray magnetic circular dichroism (XMCD). The driving force of SRTs is the competition of different contribution of magnetic anisotropies: surface, interface, bulk, and shape anisotropies. The surface modification can induce SRT. The SRT is closely related to the change of the orbital magnetic moments that XMCD can probe. We reports our XMCD results for Cu/Ni/Cu(001), and Ag, NO/Co/Cu(1 1 17) surfaces together with magnetization curves by the magneto-optical Kerr effect.
High-resolution angle-resolved photoemission spectroscopy (ARPES) using tunable synchrotron radiation has recently developed rapidly. New advances in high energy and angular resolution measurements enabled us to examine quantitatively fine spectral features near the Fermi level that are directly related to the low-energy excitation. We present a high-resolution ARPES study of an itinerant ferromagnet Ni. A kink structure was found in the dispersion of the minority-spin bands, while it was not clearly observed for the majority-spin band. On the basis of the self-energy analyses, the kink structure was attributed to the electron-phonon interaction. We found that the electron-phonon interaction and electron correlation contribute to the effective mass enhancement in a different way depending on the energy band, and spin-direction. The analyses is applicable to the surface derived-electronic states. In the case of Cu, the electron-phonon coupling constant was found to be equivalent at the surface and in the bulk.
The present status of infrared synchrotron radiation (IRSR) at UVSOR-II and the application to an infrared reflection-absorption spectroscopy (IRAS) in the IR and terahertz (THz) regions using IRSR are reported. At UVSOR-II, the IRSR beam line has been upgraded to make a powerful IR-THz light source. An IRAS experiment covering the wave number range below 1,000 cm−1 was started to investigate adsorbed molecules on surfaces. The Alq3/Ag system was investigated using the apparatus. The Al-N stretching mode at around 420 cm−1 was clearly observed and the peak frequency changes to 440 cm−1 after the potassium doping. This is the evidence for the charge transfer to the Alq3 molecule from the potassium ion.
A mechanism of how the Palladium-composite Perovskite catalyst for automotive emissions control keeps its activity long-lived is investigated by using XAFS and DANES (Diffraction Anomalous Near Edge Structure), a family of an anomalous X-ray diffraction techniques. The conventional catalysts are finely divided precious metal particles dispersed on a solid support. Since they suffers from heat in the car, their activity deteriorates because of the growth and agglomeration of the particles. Recently, however, the Palladium-composite Perovskite has been found to have retention of high catalyst activity during long-term use and ageing. In order to investigate the mechanism of such an ideal property in the atomic revel, X-ray diffraction and absorption techniques were employed. We find that as the catalyst is cycled between oxidative and reductive atmospheres typically encountered in exhaust gas, palladium reversibly moves into and out of the perovskite lattice. This movement appears to suppress the growth of metallic palladium particles.
We have studied the chemisorption of benzene and pyrazine on Si(001)-2×1 at room temperature using photoelectron diffraction (PED). For benzene, comparison between the experimental and simulated PED patterns with R-factor analysis leads to the conclusion that a di-σ-bonded configuration is mainly formed at the saturation coverage. For pyrazine, the PED results show that the double dimer bridging configuration is formed, in which pyrazine molecule forms a bridging between the dimer rows with the two Si-N bonds.