Phase detection using low-loss with aberration corrected STEM
The loss-loss region of the electron energy loss spectrum (EELS) is dominated by the zero loss peak (ZLP) and peak intensities due to plasmon excitations. The width of the zero loss peak represents the energy spread of the system and its intensity is governed by the degree to which electrons were not inelastically scattered and were collected by the spectrometer (Ie less counts means more inelastic scattering, more counts mean less inelastic scattering). The plasmon peaks are generally due to excitations of collective oscillations in the valence electrons of the sample. In semiconducting materials, the valence electrons are highly localised and different phases can be readily mapped according to differences in plasmon energy, Ep. In metallic systems the valence electrons are not as localised and the 'electron gas' will be strongly influenced by the presence of nearby phases so as to equilibrate Fermi levels, making differences in plasmon energies subtle near interfaces.