Strong dispersion of the surface optical phonon of silicon carbide in the near vicinity of the surface Brillouin zone center

The surface optical or Fuchs-Kliewer phonons of the (0 0 1) surface of 3C-SiC and the Si-terminated (0 0 0 1) surfaces of 4H- and 6H-SiC have been investigated with high resolution electron energy loss spectroscopy (HREELS). For each of the SiC polytypes the frequency of the surface optical phonon changes with surface reconstruction, indicating subtle differences in the static polarization at differently reconstructed surfaces. Due to their anisotropy, hexagonal surfaces exhibit a second, much weaker Fuchs-Kliewer mode. For all surfaces under examination, a linear dispersion of the Fuchs-Kliewer mode frequency has been found for wave vectors close to the Γ¯-point. This dispersion can be explained by dynamical dipole coupling between atomic oscillators at the surface of the highly polar silicon carbide.