Artifacts in Transmission Electron Microscopy - Sample Preparation Topic for Transmission Electron Microscopy - page 130

2.2 Ionic Preparation-Induced Artifacts
Redeposition : Deposition of material previously milled by an ion beam, either
intrinsic or extrinsic to the sample, which redeposits on the specimen surface
during thinning. This is a form of contamination.
Techniques involved: ion milling and focused ion beam thinning (FIB).
Implantation : Accelerated ions from the beam penetrate the sample and remain
trapped there, creating a new chemical type.
Techniques involved: ion milling and focused ion beam thinning (FIB).
Vacancies : Point defects (0D) corresponding to the loss of an atom in the crystal
network. Accelerated ions can remove atoms or ions from the matrix, creat-
ing vacancies in the crystal network or creating defects (grain boundaries,
twin boundaries, etc.). Accumulation of vacancies can form cavities.
Techniques involved: ion milling and focused ion beam thinning (FIB).
Dislocation loops : Partial dislocations that border an atomic-plane defect and
close on themselves creating a dislocation loop.
Techniques involved: ion milling and focused ion beam thinning (FIB).
Cavities : Area free of matter inside a material. It is caused by the accumulation
of vacancies and corresponds to volume defects (3D) that form an intra- or
intergranular cavity.
Techniques involved: ion milling and focused ion beam thinning (FIB).
Fractures : Splitting or separation of regions of the sample. The fracture is
caused by the relaxation of stresses due to the increase of temperature during
ion thinning.
Techniques involved: sawing, mechanical polishing, dimpling, grinding, wedge
cleavage, tripod polishing, cryo-ultramicrotomy, freeze fracture and focused
ion beam thinning FIB.
Roughness : Variation of surface relief caused by selective abrasion.
Techniques involved : ion milling and focused ion beam thinning (FIB).
Selective abrasion : The ion beam can reveal phases if one of the phases abrades
more slowly than the other. Selective abrasion can create an undulating sur-
face, cause roughness by revealing dense atomic phases, or form peaks if
there are precipitates or segregation zones (grain boundary, dislocation, etc.).
These types of defects are also preferentially torn and leave cones of material
around crystal defects. These are clouds of impurities that delay the abrasion
of the zone, particularly around screw dislocations.
Techniques involved: ion milling and focused ion beam thinning (FIB).
Structural change : Partial or total change in the crystallographic organiza-
tion of a sample, caused by ionic effects. It can lead to a change in form,