Range and Depth of the BSE Signal 

Because the backscatted electrons are usually produced by multiple scattering events, they travel considerable distances within the specimen during the backscattering process

As a rough approximation, BSEs can be considered to be produced from a hemispherical region whose radius is about:

  Some rough values are:

This effect limits the resolution in images produced with BSE to a value that is of the order of 2 , regardless of how small the actual diameter of the incident electron beam may be.

It also means that the intensity of the BSE signal will be influenced to some extent by subsurface inhomogenieties in specimen composition occuring within the hemispherical region of BSE generation.