Observation of Anisotropy of Electronic Structures by Using Anisotropy of Inelastic Scattering Accompanied by Inner-Shell Excitation

Koh Saitoh

Abstract: The present paper describes a method to analyze anisotropy of unoccupied states above the Fermi level by using inelastic scattering patterns of fast electrons accompanied by inner-shell excitation. First, we describe how inelastic scattering patterns are observed by the energy-selected diffraction technique by showing examples of the |1s>→|π*> transition of graphite, then, we introduce our method to visualize partial density of states (pDOS) of the unoccupied states. In the present method, a series of inelastic scattering patterns obtained at successive energy-losses are quantitatively decomposed by using basis patterns calculated from orbitals which are possible as unoccupied states above the Fermi level. As a result, we can obtain the energy-loss dependence of the magnitudes of the components, that is, partial EELS (pEELS) spectra, which are closely related to pDOS of materials. The present method is applied to the derivation of pEELS spectra of carbon nanotube and superconductor MgB₂, and to the decomposition of the d hole state of a high-T_c superconductor of Bi₂Sr₂CaCu₂O₈.

Key words: Electron inelastic scattering, angular-resolved EELS, energy-selected diffraction, electron orbital anisotropy, partial density of states