Observation of surface optical phonons on TiO2(100)

Surface vibrations on a Ti${\mathrm{O}}_2$(100) surface have been investigated with high-resolution electron-energy-loss spectroscopy at a resolution of 10 meV. The energy-loss spectra are interpreted in terms of single- and multiple-phonon excitation of long-wavelength Fuchs-Kliewer surface optical modes. The observed frequencies are in good agreement with the predictions of dielectric response theory.