STRONG ELEMENT DEPENDENCE OF C 1S AND SI 2P X-RAY PHOTOELECTRON DIFFRACTION PROFILES FOR IDENTICAL C AND SI LOCAL GEOMETRIES IN BETA-SIC

We have measured photoelectron diffraction polar profiles for a beta-S iC film grown epitaxially on Si(001). Tha data reveal dominant single domain growth with a good crystallinity but the C 1s and Si 2p profile s exhibit remarkably strong differences in spite of the identical geom etries of the sites occupied by these elements in the ZnS-type lattice . Mast obvious are the large angular shifts and changes in intensity b etween expected and measured forward scattering peaks. Our results obt ained at low angular resolution (similar to 5 degrees) in the high kin etic energy range (similar to 1000 eV) provide a striking example of t he limitations of the often invoked forward scattering picture. The me asured profiles are rather well reproduced by single scattering cluste r simulations. The observed elemental dependence can be traced back to the marked change in complex scattering amplitude between C and Si al ong with the very general fact, by no means restricted to the SiC(001) case, that a large number of scatterers, in particular out-of-chain a toms with a low scattering angle, make a substantial contribution to t he photoelectron wave around forward scattering directions. The: relat ed energy and element dependent interference effects are particularly strong along the low density [001] C chains of the open ZnS-type struc ture and reflect in a drastic peak splitting due to the strong scatter ing at lateral Si atoms. In contrast, the [001] Si chains in beta-SiC lead to an essentially structureless forward scattering peak due to th e lower scattering amplitude of lateral C atoms.