Inelastic mean free path
The inelastic mean free path (IMFP) is an index of how far an electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

 can travel 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
In physics, a plasmon is a quantum of plasma oscillation. The plasmon is a quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and mechanical vibrations, respectively...

 excitation, electron-hole
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...

pair formation, and vibrational excitation. The intensity of the primary electrons, I0, is damped as a function of the distance, d, into the solid. The intensity decay can be expressed as follows:
I(d) = I0 exp(-d / λ(E))

where I(d) is the intensity after the primary electron beam has traveled through the solid. The parameter λ(E), termed the inelastic mean free path (IMFP), is defined as the distance an electron beam can travel before its intensity decays to 1/e of its initial value.
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