Auger spectra from a Si (111) surface with about 10 Aring; oxide were utilized to demonstrate that diffraction can cause Auger intensity changes of a factor of 2 even in data acquired using the cylindrical mirror analyzer. The diffraction mechanism was revealed by a comparison of spectra taken before and after small changes in crystal orientation and noting that Auger peaks from the amorphous surface oxide did not change amplitude significantly while peaks from the crystalline Si changed by large amounts. Diffraction of the ejected Auger electron was an important process because relative intensity changes among peaks within a single ionization series were large. The collected electron image resembling a Kikuchi pattern visible in the scanning mode of the Auger apparatus was used for accurately orienting the crystal.
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