Quantitative electron spectroscopy of surfaces: A standard data base for electron inelastic mean free paths in solids

TLDR

The study compiles all published measurements of electron inelastic mean free path lengths in solids for electron energies between 0 and 10 000 eV above the Fermi level. Materials are grouped by element, inorganic compound, organic compound, and adsorbed gas, and the path lengths are expressed in nanometers, monolayers, and milligrams per square metre. Findings show that electron inelastic mean free paths are very long at low energies, drop to 0.1–0.8 nm between 30–100 eV, then increase again, with the least scatter when expressed in monolayers and described by empirical relations λm = 538 E⁻² + 0.41(aE)¹ᐟ² for elements and λm = 2170 E⁻² + 0.72(aE)¹ᐟ² for inorganic compounds, while organic compounds follow λd = 49 E⁻² + 0.11 E¹ᐟ² mg m⁻², and theoretical predictions above 150 eV are less accurate.

Abstract

Abstract A compilation is presented of all published measurements of electron inelastic mean free path lengths in solids for energies in the range 0–10 000 eV above the Fermi level. For analysis, the materials are grouped under one of the headings: element, inorganic compound, organic compound and adsorbed gas, with the path lengths each time expressed in nanometers, monolayers and milligrams per square metre. The path lengths are vary high at low energies, fall to 0.1–0.8 nm for energies in the range 30–100 eV and then rise again as the energy increases further. For elements and inorganic compounds the scatter about a ‘universal curve’ is least when the path lengths are expressed in monolayers, λ m . Analysis of the inter‐element and inter‐compound effects shows that λ m is related to atom size and the most accuratae relations are λ m = 538 E −2 +0.41( aE ) 1/2 for elements and λ m =2170 E −2 +0.72( aE ) 1/2 for inorganic compounds, where a is the monolayer thickness (nm) and E is the electron energy above the Fermi level in eV. For organic compounds λ d =49 E −2 +0.11 E 1/2 mgm −2 . Published general theoretical predictions for λ, valid above 150 eV, do not show as good correlations with the experimental data as the above relations.