Selection of Preparation Techniques Based on Material Problems and TEM Analyses - Sample Preparation Topic for Transmission Electron Microscopy - page 183

1 = 3.1 and 3.2 Electrolytic thinning

2 = 3.3 and 3.4 Chemical thinning

3 = 3.5 Ion milling

4 = 3.6 Focused ion beam thinning (FIB)

5 = 4.1 Crushing

6 = 4.2 Wedge cleavage

7 = 4.3 Tripod polishing

8 = 4.4 and 4.5 Ultramicrotomy and cryo-ultramicrotomy

9 = 5.1 Direct replica

10 = 5.2 Indirect replica

11 = 5.3

Extractive replica

=

12 5.4 Freeze fracture

=

13 6.1 Fine particle dispersion

14 = 6.2 Frozen hydrated film

15 = 7.1 Decoration shadowing

16 = 7.2 “Negative-staining” contrast

17 = 7.3 “Positive-staining” contrast

18 = 7.4 Immunolabeling

Tables 7.2, 7.3, and 7.4 list the different suitable preparation techniques for
bulk and multilayer materials and fine particles based on the type of analysis to
be performed.

9 Selection of the Orientation of the Sample Section

Crystallographic and structural material investigation requires one or more specific
orientations of the sample, based on the original material and with regard to the
direction of observation in the microscope. For this, the sample can be tilted in the
microscope up to maximum angles of 60 ◦ (depending on the type of microscope)
or can be orientated beforehand when it is prepared. Orientation is determined with
regard to the geometry of the thin slice to be observed in the TEM. In fact, an
unavoidable aspect of transmission electron microscopy is the changeover from 3D
of the volumic sample to the 2D projection in the image (Fig. 7.2) . The changeover
results in the superimposition of information contained in a volume (the thickness
of the sample) to a plane. The direction of projection, i.e., the thickness of the
sample combined with the direction of electron propagation, is therefore singular.
Consequently, it is important to take into account the geometry of the structures
observed with regard to this direction.
Specimens can be observed in different orientations by preparing longitudinal
slices, cross-sectional slices, or in a precisely defined direction, e.g., parallel to a set
of atomic planes. Lastly, the sample can be observed in any direction, i.e., based on
a non-specific orientation or in random directions (Table 7.5) .