2D surface phonons in high-resolution electron-energy-loss spectra of metallic oxides

Abstract

Surface phonon features in high-resolution electron-energy-loss (HREEL) spectra of the metallic tungsten bronze oxide Na 0.7WO 3 are much weaker than for insulating WO 3. Models based on the bulk dielectric function ϵ(ω) are unable to rationalise these spectra, but a simple two-layer model involving an unscreened surface dielectric layer is shown to account for both the intensities of the metallic phonons and their energies relative to those for WO 3. The sensitivity of HREELS to details of surface structure in metallic oxides is emphasised.