The photoelectron diffraction technique has been applied to investigat
e the geometrical structure of an epitaxial Sb monolayer (ML) on GaAs(
110) using low photon energies. Ultra-high surface sensitivity is comb
ined with high experimental resolution (less than or equal to 200 meV)
providing additional information about chemically shifted components.
The ordered Sb monolayer was prepared by depositing 3-4 ML onto a UHV
-cleaved GaAs(110) surface and subsequent annealing up to 620 K. Photo
electron spectra of the Sb 4d and Ga 3d core level emission lines were
recorded as a function of polar angles. The Sb 4d core level emission
line clearly exhibits two chemically shifted components which are due
to the distinct bonding sites of the Sb atoms. The two corresponding
diffraction patterns with marked modulations are compared with calcula
ted ones using a multiple scattering cluster model for various adsorpt
ion geometries of Sb. These results are in good agreement to previous
LEED and total-energy-minimization studies and demonstrate the potenti
al of this technique. In addition, a clear assignment of the two chemi
cally shifted components of the Sb 4d core level to the two distinct a
dsorption sites is achieved.