The modern trend towards low electron energies in scanning electron microsc
opy (SEM), characterised by lowering the acceleration voltages in low-volta
ge SEM (LVSEM) or by utilising a retarding-field optical element in low-ene
rgy SEM (LESEM), makes the energy range where new contrasts appear accessib
le. This range is further extended by a scanning low-energy electron micros
cope (SLEEM) fitted with a cathode lens that achieves nearly constant spati
al resolution throughout the energy scale. This enables one to optimise fre
ely the electron beam energy according to the given task. At low energies,
there exist classes of image contrast that make particular specimen data vi
sible most effectively or even exclusively within certain energy intervals
or at certain energy values. Some contrasts are well understood and can pre
sently be utilised for practical surface examinations, but others have not
yet been reliably explained and therefore supplementary experiments are nee
ded.