Energy loss extreme — near-edge and pre-edge structure

Abstract

During the past several years we have begun to understand many features of the core loss excitations including absolute crosssections, extended fine structure, (EXELFS) and near edge fine structure. (ELNES) In electronic materials near interfaces or defects, we expect the valence and conduction bands to be modified by the existence of isolated resonances, broadening of the band edges, or a completely filled gap region. These electronic changes have been observed with high resolution EELS in the low energy loss region (0-3eV) where direct inter-band transitions are likely. The present work is aimed at determining if pre-edge structure near the core loss scattering may reflect local changes in the electronic structure as well. There are two major experimental difficulties: 1) the necessary energy resolution is of order 0.1-0.3eV in order to define the shape of the core edge; and 2) the energy differential scattering cross section is small (of order 10-23cm2eV-1). At IBM I have addressed these problems by constructing a high resolution energy loss spectrometer system with parallel recording to allow signal collection in reasonable times.