While moving through the substance, the primary electron can take part
various inelastic scattering events corresponding to excitation of surface and bulk
plasmons, interband electron transitions from core to empty levels. These processes
exclude the electron from the group which forms the IL. As long as elementary acts of
inelastic scattering are considered to be statistically independent, the decay of IL
electrons current is described by exponent:  , where z – traversed length,  - mean free path of the electron with energy E between inelastic collisions.
A detailed review of and corresponding references can be found in [Ref 3] and
[Ref 5].
The electrons, which form the IL, cross the presurface layer twice
(before and after the inelastic scattering). That’s why the length at which electron can
be inealstically scattered is at least two times bigger than the thickness of this layer.
Therefore, effective analysis depth  in the IS technique is approximately twice smaller than
 .
It is noteworthy that in Auger electron spectroscopy (AES) and
X-ray photoelectron spectroscopy (XPS) the effective analysis depth is approximately
equal [Ref 3].
The contributions of inelastic scattering mechanisms into the value of
depend on energy in different ways for different substances, but in the region of E >100 eV
a general tendency of increase is observed. This increase is very
important in IS, since changing Ep, it is possible to select the kinetic energy E of IL
electrons (formula 1.1.2). This allows to adjust their mean free pass. This opens a
possibilty to select such an important parameter as effective analysis depth, not an
option in other techniques.
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