Electron-energy-loss spectroscopy in a scanning transmission electron microscope has been used to study the interface plasmon peak (IPP) observed at the ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}\mathrm{O}}_2$ interface. A precise line-spectrum recording shows a shift of the interface plasmon peak from 7.8 to 6.8 eV from the interface to 5 nm from it. This shift is explained by considering relativistic effects, demonstrating the importance of obtaining the relativistic formulas given in the two appendixes. The agreement of the simulations with the experiment, both in position and intensity is very good and is improved further by the introduction of a 1.0-nm-thick intermediate layer of SiO. A crystalline phase of ${\mathrm{SiO}}_2$ seems to be in poorer agreement with experiment. This implies that the careful recording and simulation of the IPP can actually give some information about the nature of interfaces.

• Received 21 March 1997

DOI:https://doi.org/10.1103/PhysRevB.56.6774