Anomalous diffraction effect on the surface core-level photoemission from Si(001)2 × 1-Cs surface

The angular dependence of the Si 2p photoelectron intensity has been measured for a Cs-saturated Si(001)2 × 1 surface. A surface Si 2p component, which is attributed to the Si-dimer underneath the Cs overlayer, shows a large intensity variation as a function of azimuthal angle. This denies the asymmetrical Si-dimer model proposed recently [Y.-C. Chao, L.S.O. Johansson, R.I.G. Uhrberg, Phys. Rev. B 54 (1996) 5901] on the basis of photoemission intensity of the surface Si 2p component. The present result shows that the effect of photoelectron diffraction must be taken into account when discussing the origin of a surface component from a seemingly angle-integrated photoemission intensity of the surface component.