Effect of focusing of primary electrons on their reflection from a crystal and on the associated Auger emission

The orientational dependence for different groups of secondary electrons - quasi-elastically scattered, inelastically reflected with excitation of a plasmon and with ionization of the core level M-4.5, and the Auger electrons M4.5VV - are measured in the primary electron energy range 0.6 - 1.5 keV. The data are obtained for a Nb (100) single crystal by varying the azimuthal angle of incidence of the primary beam, with complete collection of secondaries. A relationship is established between the processes of focusing and defocusing of the electrons that have penetrated into the crystal in the (110) and(133) directions, which differ substantially in the atomic packing density. Specific details of the Auger orientation effect, due to the focusing-induced variation of the flux density of the reflected electrons, are identified and explained. The contributions, both of anisotropy of ionization of the core level and of variation of the backscattering intensity, to the angular dependence of Auger emission and reflection with ionization loss are estimated. The possibilities of using such orientational dependences for an element-sensitive analysis of the local atomic structure of surfaces are assessed. (C) 1997 American Institute of Physics.