Poles of structural factor and secondary emission from a semi-infinite crystal

Secondary emission from a semi-infinite crystal is considered. The contribu tion to the emission amplitude originating from structural factor singulari ties is analyzed. Poles of the structural factor determine the main contrib ution to the emission amplitude. The energy and angular distributions of th e emission depend on the crystallographic orientation of the crystal surfac e and are characterized by a set of allowed vectors of the reciprocal latti ce. It is shown that emission anisotropy related to the crystallographic di rections is due to the coherent character of the photoabsorption process, a nd diffraction scattering leads only to relative change in the emission int ensity in allowed low-index directions. The concrete calculations are perfo rmed for (100) and (111) surfaces of a diamond-like lattice. (C) 2000 MAIK "Nauka/Interperiodica".