Chemical analyses and studies of electronic structure of solids by electron energy loss spectroscopy with an electron microscope

Abstract

Both the thickness and the composition of a specimen can be deduced from plasmon spectroscopy, which is readily recorded with an electron microscope to which has been attached an electron spectrometer of resolution 1—3 eV. This is illustrated in the study of alkali metals and sp metals such as magnesium and aluminium , which are produced by decomposing ternary or binary hydrides (for example, NaAlH 4 or MgH 2 ). But other m aterials, including silicon, are also am enable to studies of this kind. The elemental composition, electronic structure and inter-atomic distances of a sample can be derived from the core-electron (K, L, M edge) loss peaks and their fine structure. And from the near-edge energy loss structure, and in particular from the ‘white line’ intensity ratios (for example, L 2 /L 3 ), the number of d-electrons and hence the oxidation state of transition elements in com pounds of first-row transition metal series may be determined. In the region beyond the near-edge structure, extended electron energy loss fine structure (e.x.e.l.f.s.) is observed and this may be used to obtain information about the local co-ordination of different atoms in the sample. Finally, by monitoring the Doppler broadening of the scattered electrons liberated from the sample as a consequence of the ‘electron' equivalent of the Compton-process, we can probe the electronic properties of the solid in m omentum space. This reveals the nature of the bonding in simple solids; and, in particular, reveals whether an amorphous sample of carbon is more nearly graphitic or adamantine.