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 electro ns - quasi-elastically scattered, inelastically reflected with excitat ion 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 r ange 0.6 - 1.5 keV. The data are obtained for a Nb (100) single crysta l by varying the azimuthal angle of incidence of the primary beam, wit h complete collection of secondaries. A relationship is established be tween the processes of focusing and defocusing of the electrons that h ave penetrated into the crystal in the (110) and(133) directions, whic h differ substantially in the atomic packing density. Specific details of the Auger orientation effect, due to the focusing-induced variatio n of the flux density of the reflected electrons, are identified and e xplained. The contributions, both of anisotropy of ionization of the c ore level and of variation of the backscattering intensity, to the ang ular dependence of Auger emission and reflection with ionization loss are estimated. The possibilities of using such orientational dependenc es for an element-sensitive analysis of the local atomic structure of surfaces are assessed. (C) 1997 American Institute of Physics.