Semiclassical model for the inelastic scattering probability of electrons traveling parallel to four dielectric layers

Weak features in the electron energy-loss spectra of Al/SiO2/Si heterostructures in cross section have been found below the bulk plasmon energy when measured in the vicinity of either interface. A four-layer model for the electric potential distribution in this metal/oxide/semiconductor heterostructure was developed. The inelastic scattering probability curves are calculated for the electron beam moving through the oxide and are compared with the corresponding experimental loss function. A small peak around 3.5-4.0 eV is found to be due to interband transitions in Si. An 8 eV peak is attributed to the relaxed surface plasmon from Al or Si depending on which side of the oxide an electron beam is moving. The lowest intensity of this feature occurs at the oxide center. These and other smaller features are attributed to interface or bulk contributions to the electron energy-loss probability.