Escape probability of low-energy electrons emitted in a heterogeneous solid source, and depth distribution analysis in conversion electron Mössbauer spectroscopy
The probability T( x) to escape from the surface has been calculated by Monte Carlo simulation for electrons with initial energies 1, 5 and 7.3 keV, starting in random directions from depth x beneath the plane surface of a heterogeneous, semi-infinite solid, consisting of a surface layer S with thickness d deposited on a bulk substrate B. For the structures S/ B=Be/Au and S/ B=Au/Be, with atomic numbers widely apart, the escape probability function T( x) may, depending on initial electron energy, show a characteristic cusp-like deviation from the smooth slope found in a homogeneous material, with d T/d x discontinuous at the interface. Similar results, though less marked, are found for Al/Cu and Be/Cu. The probability to escape from such a layered solid with energy loss within a specific interval and into a specific solid angle has also been calculated for 7.3 keV electrons. The structure Al/Cu has been studied in particular, being a model which through similarity in scattering properties may be used to discuss 57Fe CEMS. Using these results, the accuracy of depth distribution analysis in conversion electron Mössbauer spectroscopy (CEMS) has been investigated.