Stereo Scan 440 - DCU

I~.." - Chapter 3 Advanced Operation 3'-9
3.4. Specimen Charging
Electrons incident upon the sample which do not escape as backscattered or
secondary electrons are absorbed by the sample. Unless these absorbed electrons
can fmd their way to ground (as in a conductive sample) they will remain in the
sample resulting in a negative charge build up exhibited as one of the following
image defects:-
. Loss of image contrast (see Figure 3.4)
. Very bright or dark areas (see Figure 3.5)
. Image or beam shift (shearing) (see Figure 3.6)
Dust and other debris on the sample surface can also charge up, and appear as a
bright area on the image surrounded by a dark region. The charged debris may
deflect secondary electron emission and sometimes the incident beam, causing
dark region and possibly image 'shearing'(see Figure 3.6). H the sample itself is
charging, beam deflection will occur during scanning, the effect being seen as a
slow image drift followed by a jump back to its original position.
FIgUIe 3.4 Loss of Contrast Due to Charging
Stereoscan 440 Operator Manual