A new EXAFS method for the local structure analysis of low-Z elements.

A unique analytical method is proposed for local structure analysis via extended X-ray absorption fine structure (EXAFS) spectroscopy. The measurement of electron energy distribution curves at various excitation photon energies using an electron energy analyzer is applied to determine a specific elemental Auger spectrum. To demonstrate the method, the N K-edge EXAFS spectra for a silicon nitride film were obtained via simultaneous measurement of the N KLL Auger and background spectra using dual-energy windows. The background spectrum was then used to remove the photoelectrons and secondary electron mixing in the energy distribution curves. The spectrum obtained following this subtraction procedure represents the `true' N K-edge EXAFS spectrum without the other absorptions that are observed in total electron yield N K-edge EXAFS spectra. The first nearest-neighbor distance (N-Si) derived from the extracted N K-edge EXAFS oscillation was in good agreement with the value derived from Si K-edge analysis. This result confirmed that the present method, referred to as differential electron yield (DEY)-EXAFS, is valid for deriving local surface structure information for low-Z elements.

Photoemission study on the valence band of a ß-FeSi2 thin film using synchrotron radiation.

Resonant and constant-initial state photoemission spectroscopies using synchrotron radiation were applied to investigate the valence-band electronic structure of a semi-conducting ß-type iron-disilicide (ß-FeSi(2)) thin film. The results clearly indicated that the component elements, iron (Fe) and silicon (Si), contribute differently to the valence band features; the Fe 3d orbitals mainly concentrate in the top region of the valence band while the Si 3s and 3p orbitals spread over the wide region of the valence band. The ß-FeSi(2) thin film showed a typical p-type semi-conducting nature with a work function of 4.78 eV. The ß-FeSi(2) film showed the Fe M(1)VV Auger lines around the kinetic energy of 88 eV. It would be expected from these observations that there exist strong interactions between iron and silicon atoms in the ß-FeSi(2) film resulting in orbital mixing and band formation.

Infrared absorption change in single-walled carbon nanotubes observed by combination spectroscopy of synchrotron radiation and laser.

The Drude tail due to photo-excited carriers in single-walled carbon nanotubes (SWNTs) has been observed in the mid-infrared region by using combination spectroscopy of synchrotron radiation and Ti:sapphire laser. It is found that the density of photo-excited carriers increases as the sample temperature is raised from 12 to 300 K, and their lifetime is of the order of minutes at 300 K. These facts suggest that the movement of photo-excited carriers is largely affected by some extrinsic defect, thus resulting in the long-lasting Drude reflection in SWNTs.

Two-photon spectroscopy of core excitons in barium fluoride using synchrotron radiation and laser light.

We have conducted two-photon spectroscopy of core excitons in BaF(2). Synchrotron radiation and laser light were used for 5p core-electron excitation and Auger-free luminescence was detected as the signal. Two-photon excitation enables access to f and p orbitals that cannot be reached by one-photon excitation of electrons in p orbitals. It has been found that the spin-orbit splittings of 4f and 6p states of the Ba ion in BaF(2) are 0.7 +/- 0.1 and 1.4 +/- 0.1 eV, respectively.