Surface sensitivity of low energy electron Mössbauer spectroscopy (LEEMS) using57Fe

Very low energy electrons (LEE) (E _e ≤15 eV) are produced with high intensity directly by Mössbauerabsorption and conversion in the case of⁵⁷Fe 1, 4, 5]. These electrons should be very surface sensitive due to their very low attenuation length compared to the 7.3 keV K-Conversion electrons of⁵⁷Fe 5, 11]. We have examined the surface sensitivity of these resonant LEE, using nonresonant⁵⁶Fe metal and⁵⁶Fe stainless steel foils coated with about 20 Å and 50 Å⁵⁷Fe, respectively. They were exposed to air after evaporation: The 20 Å samples are found to be fully oxidized 5]. Depth Selective Conversion Electron Mössbauer Spectroscopy (DCEMS), performed with a high transmission orange type magnetic spectrometer 5, 6, 13] reveals a two layer structure of the 50 Å samples. Low Energy Electron Mössbauer Spectroscopy (LEEMS) 5] is found to be significantly more surface sensitive than conventional DCEMS, but not as surface sensitive as Auger Electron Mössbauer Spectroscopy (AEMS) using LMM-Auger electrons of 500–600 eV, as expected due to the different mean free path. But because of the very low intensity of these Auger electrons this mode appears to be not very useful for practical application.