Localized valence spectroscopy of complex nanostructures

STEM valence loss spectra have an energy resolution of about 0.2 eV and a s patial resolution of about 1 nm. With developments of inhomogeneous dielect ric excitation theory, detailed spectral interpretation is now becoming pos sible in the complex geometry of typical nanostructures. A non-relativistic , numerical approach based on the boundary charge method is outlined. This method gives useful results in good agreement with experiment for 90 degree s wedges and truncated slabs. It appears that these results form a convenie nt basis for the interpretation of loss spectra from more complex shapes su ch as the T or I junctions arising when two dielectrics form an interface i n a thin film. The numerical boundary method can be extended to the relativ istic case to include retardation and radiation. Such computations of the r adiation emitted by excited nanostructures are potentially useful for optic al emission spectroscopy in the STM and NSOM as well as in the STEM.