Inelastic mean free path

The inelastic mean free path (IMFP) is an index of how far an electron on average travels through a solid before losing energy.

If a monochromatic primary beam of electrons is incident on a solid surface, the majority of incident electrons lose their energy because they interact strongly with matter, leading to plasmon excitation, electron-hole pair formation, and vibrational excitation. The intensity of the primary electrons, ${\displaystyle I_{0}}$, is damped as a function of the distance, d, into the solid. The intensity decay can be expressed as follows:

where ${\displaystyle \textstyle I(d)}$ is the intensity after the primary electron beam has traveled through the solid. The parameter ${\displaystyle \textstyle \lambda (E)}$, termed the inelastic mean free path (IMFP), is defined as the distance an electron beam can travel before its intensity decays to ${\displaystyle \textstyle 1/e}$ of its initial value. The inelastic mean free path of electrons can roughly be described by a universal curve, which is the same for all materials.

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