HIGH-RESOLUTION ELECTRON-ENERGY LOSS INVESTIGATION OF THE AZIMUTHAL DEPENDENCE OF THE SI(111)(2X1) SURFACE EXCITATIONS

Electron energy loss spectroscopy has been used, with low energy of the primary beam and azimuthal resolution, to study the anisotropy of the surface vibrational and electronic properties of the cleavage surface of silicon. The analysis of the loss function has been performed through the subtraction of the kinematic prefactor accounting for the finite angular acceptance of the spectrometer. The angular dependence of the phonon excitation, even at very low primary energies, is not so high as expected in previous works. The loss features associated with the transition between surface electronic bands is discussed in terms of a theoretical model of the surface dielectric function.