Rotatable high-resolution ARPES system for tunable linear-polarization geometry

A rotatable high-resolution angle-resolved photoemission spectroscopy (ARPES) system has been developed to utilize tunable linear-polarization geometries on the linear undulator beamline (BL-1) at Hiroshima Synchrotron Radiation Center. By rotating the whole ARPES measurement system, the photoelectron detection plane can be continuously changed from parallel to normal against the electric field vector of linearly polarized undulator radiation. This polarization tunability enables us to identify the symmetry of the initial electronic states with respect to the mirror planes, and to selectively observe the electronic states based on the dipole selection rule in the photoemission process. Specifications of the rotatable high-resolution ARPES system are described, as well as its capabilities with some representative experimental results.

Electron energy loss near edge structure

In inner shell absorption spectroscopy, the near edge structure (NES) up to 30 eV above threshold is a prominent solid state effect. It is well known that electron energy loss spectroscopy is advantageous for the study of light elements, like carbon, nitrogen, oxygen, and fluorine. Due to the complexity of the near edge region, it is only recently that a significant amount of research have been carried out to extract information on the solid state effects.The theory to interpret the near edge structure is based on Fermi’s Golden rule. Two methods have been derived which give different and complimentary physical pictures about the inner shell excitation process. Single electron band structure techniques have been successfully applied to the interpretation of x-ray near edge structure. using the projected densities of states (DOS) of L±1 characterpermitted by the dipole selection rule. The multiple scattering method views the near edge structure (XANES) [2.3] as coming from the interference between the outgoing ejected electron wave and renections from neighboring atoms.

BBonding in minerals: the application of PAX (photoelectron and X-ray) spectroscopy to the direct determination of electronic structure

X-ray photoelectron spectroscopy can be used to measure the ionization energies of electrons in both valence band and core orbitals. As core vacancies are the initial states for X-ray emission, a knowledge of their energies for all atoms in a mineral enables all the X-ray spectra to be placed on a common energy scale. X-ray spectra are atom specific and are governed by the dipole selection rule. Thus the individual bonding roles of the different atoms are revealed by the fine structure of valence X-ray peaks (i.e. peaks which result from electron transitions between valence band orbitals and core vacancies). The juxtaposition of such spectra enables the composition of the molecular orbitals that make up the chemical bonds of a mineral to be determined.Examples of this approach to the direct determination of electronic structure are given for silica, forsterite, brucite, and pyrite. Multi-electron effects and developments involving anisotropic X-ray emission from single crystals are also discussed.