Total-electron-yield current measurements for near-surface extended x-ray-absorption fine structure

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Abstract
A total-electron-yield technique is described in which near-surface extended x-ray-absorption fine-structure (EXAFS) data are obtained from direct measurements of specimen current. Experiments with several model systems—amorphous germanium and crystalline germanium, nickel, and cobalt; and arsenic ion implanted into silicon—demonstrate that this technique can reproduce EXAFS χ(k) functions obtained from transmission and fluorescence measurements. Experiments also reveal that EXAFS amplitudes from total-electron-yield data can be 5–10 % smaller than those from transmission measurements for samples where the very-near-surface structure, at depths of tens to hundreds of angstroms, differs from the bulk structure. Measurements with buried layers confirm that the sampling depth for this total-electron-yield technique is determined primarily by the penetration ranges of Auger electrons emitted from the absorbing atoms. For the model systems listed above, LMM Auger electrons have ranges of hundreds of angstroms and KLL Auger electrons have ranges of thousands of angstroms. Expressions are derived for the sampling depth for total-electron-yield EXAFS experiments. The total-electron-yield technique described here is particularly useful for studying impurities within a few thousand angstroms of the surface of single crystals, where Bragg diffraction complicates the use of fluorescence measurements.