Design of an Auger Electron Mössbauer Spectrometer (AEMS) using a modified cylindrical mirror analyzer

Abstract

We have designed and built an Auger Electron Mössbauer Spectrometer (AEMS) for the detection of resonant ⁵⁷Fe Auger electrons using a modified commercial cylindrical mirror analyzer (CMA). The CMA final aperture was modified intentionally in order to increase electron transmission at the expense of reducing its energy resolution, from an original value of 0.5 % to a value of 11 % after the modification. The Channeltron detector electronics and the pre-amplifier were also modified in order to increase the counting efficiency. The electron energy analyzer is selective in energy in the 30 eV–3000 eV range, so the spectrometer can be used to detect MNN (45 eV) and LMM (600–700 eV) Fe Auger signals, what gives it a high surface sensitivity for Fe containing samples. We have used it to acquire the Fe LMM Auger signals generated from the de-excitation process after γ-Ray resonant nuclear absorption. The spectrometer can be used to study samples nonenriched in ⁵⁷Fe, with acquisition times from 5 to 7 days, what is a big advantage. From electron trajectory Monte Carlo simulations in metallic iron, the mean-escape-depth of the detected Auger signals has been estimated in approximately 1 nm. Fe K conversion electrons and KLL Auger electrons with mean escape depths of 129 nm and 78 nm respectively also contribute to the detected signal although in a lesser proportion.

Proceedings of the Thirteenth Latin American Conference on the Applications of the Mössbauer Effect, (LACAME 2012), Medellín, Columbia, 11–16 November 2012.