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The bulk sample and the area of interest are tilted to a steep angle, commonly 45o or 60o. Three cuts are made
to the central membrane, framing the area of interest. Inside these cuts, the membrane will be ion polished until it
is electron transparent. Typically, the membrane is left attached to the bulk at its top two corners. This provides
structural strength and stability to the membrane during subsequent thinning.
Some damage is done to the membrane by tilting and imaging its face. However, since the penetration depth is
on the order of nanometres for any given material, any damage done to the cross-section is restricted to
essentially the surface of the sample. During the course of the next few steps in the procedure, more than the
first two hundred nanometres of material is polished away, ensuring that any damage to the electron transparent
membrane as a result of imaging is not present in the final specimen.
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