H. Johansen et al., SCANNING ELECTRON-MICROSCOPIC INSPECTION OF UNCOATED CAF2 SINGLE-CRYSTALS, Physica status solidi. a, Applied research, 150(2), 1995, pp. 613-624
Cleaved and mechanically polished surfaces of CaF2 single crystals in
the uncoated stale are investigated by means of secondary (SE) and bac
kscattered (BE) electron imaging in the scanning electron microscope w
ith respect to their strongly different charge-up properties. There is
a relationship between the density of preparation-induced defects and
the amount of surface charge detectable by characteristic image distu
rbances. Different electrical contacting techniques of the crystals ar
e tested to obtain imaging free of charge. For the cleavage face the r
elatively low electrical resistance of the bulk material of Q approxim
ate to 10(13) Ohm cm controls the imaging conditions rather than the e
lectron trapping by cleavage-induced surface defects. On mechanically
polished surfaces already during the first slow scan with E(p) < 5 keV
an equipotential surface is formed leading to a pronounced electron m
irror effect detectable by SE and BE. However, also in this case Imagi
ng of selected crystal areas free of disturbances succeeds if they are
located within an electrical deceleration field.