Physical and Chemical Mechanisms of Preparation Techniques - Sample Preparation Topic for Transmission Electron Microscopy - page 98

Fig. 5.13 FIB abrasion
principles

Ion Beam

Ga Ions
Pulverized
Atoms

Sample

The acceleration voltage of the ions is between 1 and 30 keV, and the current
density is on the order of between a few tens of picoamps and several hundreds of
nanoamps. The use of a high voltage and a strong current is required to quickly
abrade the sample. However, as with the ion beam thinning technique, this induces
significant artifacts that are substantially the same. These artifacts must therefore be
reduced through the use of low voltage and a weak current.
The incidence angle between the beam and the sample is adjusted by tilting the
sample. It is generally 0 ◦ with regard to the plane of the future thin slice for quick
abrasion of the material and can be varied between 0.5 ◦ and 2 ◦ for the final thinning
step and for “cleaning” the thin slice. The introduction of an angle in the final step is
necessary to compensate for the non-homogenous thickness caused by the Gaussian
distribution of intensity in the ion beam.
The use of a beam with a very small diameter and an angle of incidence near zero
limits preparation artifacts.

5 Actions Resulting in a State Change of Materials Containing
an Aqueous Phase

Materials containing an aqueous phase cannot be observed directly in the micro-
scope because of the high vacuum. These materials are also usually soft and cannot
be thinned by abrasion or fracture. One or more prior preparations must be applied in
order to modify their physical state for preparation and observation. This is generally
the case for biological organic samples.

5.1 Elimination of the Aqueous Phase

There are several methods for removing the water contained in a material. The water
phase diagram (Fig. 5.14) shows that there are two ways to change to the gaseous