This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.

=================================================================================

The SE signal current (I_S) received by SEM detector is approximately equal to the current (I_SE) of emitted SEs minus the current (I_RE) of SEs pulled back to the specimen surface by the local surface potential due to charging. Therefore, I_S is given by,

           ----------------------------- [3827a]

The process of which SEs return to the surface is called redistribution of SEs. The redistribution rate α is the ratio of the amount of SEs collected by the surface and the amount of emitted SEs, given by,

           ----------------------------- [3827b]

The incident current (I_p) of primary electrons is given by,

           ----------------------------- [3827c]

where,
          δ -- SE yield (emission coefficient) 

Substituting Equations 3827b and 3827c into Equation 3827a, therefore, the SE signal current (I_S) can be obtained and given by,

           ----------------------------- [3827d]

For certain observation conditions in SEM, I_p and δ are constant and thus, the redistribution rate α is the only factor for determining the signal current as well as the local contrast.