The sheet plasmon in epitaxially grown graphene layers on SiC(00•1) and the influence of surface roughness were investigated in detail by means of low-energy electron diffraction and electron energy loss spectroscopy. It was shown that the existence of steps or grain boundaries in this epitaxial system was a source of strong damping, while the dispersion was rather insensitive to defects. To the first order, the lifetime of the plasmons was found to be proportional to the average terrace length and to the plasmon wavelength. A possible reason for this surprisingly efficient plasmon damping might be the close coincidence of phase (and group) velocities of the plasmons (almost linear dispersion) with the Fermi velocity of the electrons. Therefore, uncorrelated defects like steps only had to act as a momentum source to effectively couple plasmons to the electron–hole continuum.

Plasmon Damping Below the Landau Regime: the Role of Defects in Epitaxial Graphene. T.Langer, J.Baringhaus, H.Pfnür, H.W.Schumacher, C.Tegenkamp: New Journal of Physics, 2010, 12[3], 033017