Depth dependence for extended x-ray-absorption fine-structure spectroscopy detected via electron yield in He and in vacuum

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Abstract
X-ray absorption spectra have been measured using electron detection with both vacuum and helium gas surrounding the samples. The samples consisted of thin iron films covered with various thicknesses of aluminum to determine the contribution versus depth. The height of the iron K–absorption-edge jump decreases exponentially with aluminum covering thickness, with a 1/e depth of 1600 Å. The addition of helium gas forms an ionization detector for the electrons, which have an average energy of about 2500 eV. The effects of electrode geometry and bias voltage are evaluated. When operated in a linear-response region, the signal-to-noise ratio for this method is excellent and the extended x-ray-absorption fine-structure (EXAFS) amplitudes agree with transmission measurements to better than 3%.