ENERGY-FILTERING AND COMPOSITION-SENSITIVE IMAGING IN SURFACE AND INTERFACE STUDIES USING HREM

Energy-filtered high-resolution electron microscopy (HREM) is an important technique for quantitative structural determination. In this paper, some fundamental quantities in applying energy-selected HREM in surface and interface studies are considered. The inelastic absorption function in zero-loss energy-selected HREM profile images of the MgO(100) surface is measured. The inelastic scattering mean-free-path length of MgO at 300 kV is determined as Lambda approximate to 181 nm for [110] zone-axis diffraction condition with an objective aperture of semi-collection angle 1 Angstrom(-1). High-resolution chemical-sensitive imaging using core-shell loss electrons in transmission electron microscopy (TEM) is also demonstrated in studies on Al/Ti multilayer thin films. A spatial resolution of similar to 0.4 nm has been obtained. It has been shown that the spatial resolution of energy-selected ionization edge electron images is dominated by the signal-to-noise ratio; the signal localization, as long as it comes from inner-shell excitation, has little effect. Thus, for a general element, the use of low loss ionization edges rather than higher loss ionization edges is recommended for forming chemical images. But caution must be exercised in the subtraction of background due to the influence of multiple plasmon peaks. Composition-sensitive imaging using plasmon-loss electrons is also feasible, and a spatial resolution better than 1.0 nm has been obtained. These results are interpreted using the calculations of the dielectric response theory for interface excitation. Lattice images formed by plasmon-loss and multiple plasmon-loss electrons are also illustrated.