Identification of plasmon modes in two-dimensional Er silicide epitaxially grown on Si(111)

High Resolution Electron Energy Loss Spectroscopy (HREELS) is used to study the free charge carrier gas in epitaxial two-dimensional erbium silicide on Si(111). A broad loss feature is observed on the HREELS spectra that we clearly establish as a two-dimensional plasmon, and a simple procedure is proposed to extract its width and energy dispersion. In addition, we performed an analysis of the specular data in the frame of the dielectric theory using a three layer model. The plasmon is identified as one of the thin film modes with the lowest energy that corresponds in the limit of small parallel momentum transfer to charge fluctuations parallel to the surface. From this analysis, the carrier concentration in the silicide is extracted and found to be in good agreement with electronic band structure deduced from previous photoemission measurements. Further experimental results, concerning the evolution of the plasmon dispersion and damping brought about by changes in the mean island size and temperature down to 110 K are presented. (C) 1999 Elsevier Science B.V. All rights reserved.