Observation of acoustic and optical surface phonons in LiF(001) by inelastic He scattering

Observation of acoustic and optical surface phonons in LiF(001) by inelastic He scattering

A433 684 Surface Science 189/190 (1987) 684-688 North-Holland, Amsterdam OBSERVATION OF ACOUSTIC AND OPTICAL IN LiF(001) BY INELASTIC He SCATfERING ...

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A433 684

Surface Science 189/190 (1987) 684-688 North-Holland, Amsterdam

OBSERVATION OF ACOUSTIC AND OPTICAL IN LiF(001) BY INELASTIC He SCATfERING G. BRACCO, M. D'AVANZO, a n d F. T O M M A S I N 1

SURFACE

C. S A L V O , R. T A T A R E K

PHONONS

*, S. T E R R E N I

Dipartimento di Fisica dell'Universit& via Dodecaneso 33, 16146 Genova, Italy Received 7 April 1987; accepted for publication 19 May 1987

The vibrational spectrum of the LiF(00I) surface measured by inelastic He scattering with time-of-flight detection along the {110~ and ~100~ crystal directions is reported. The acoustic and optical modes are described in the whole surface Brillouin zone up to energies of 50 meV.

Surface Science 189/190 (1987) 689-694 North-Holland, Amsterdam

689

HIGH RESOLUTION ELECTRON ENERGY LOSS INVESTIGATION OF THE AZIMUTHAL DEPENDENCE O F T H E S i ( l l l ) ( 2 × 1) SURFACE EXCITATIONS U. D E L P E N N I N O ,

M.G. BETH,

C. M A R I A N I

Dipartimento di Fisica, Universit~ di Modena, 1-41100 Modena, Italy

C.M. BERTONI Dipartimento di Fisica, UniversittJ di Roma "'Tor Vergata", 1-00173 Roma, ltal)'

S. N A N N A R O N E Dipartimento di Fisica, Universit~ di Roma "'La Sapienza", 1-00185 Roma, Italy

I. A B B A T I , L, B R A I C O V I C H

a n d A. R I Z Z I

Dipartimento di Fisica, Politeenico di Milano, 1-20133 Milano, Italr

Received 13 April 1987; accepted for publication 15 April 1987 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.