Selection of Preparation Techniques Based on Material Problems and TEM Analyses - Sample Preparation Topic for Transmission Electron Microscopy - page 173

Focused ion beam (FIB) thinning is used to prepare all materials, including com-
plex multiphase materials, while maintaining all phases and porosities, with the
exception of soft biological materials and soft polymers, which have to be thinned
using cryo-FIB.
The crushing technique can be used for any type of brittle material, but does not
save sample microstructure.
The wedge-cleavage technique is used to prepare cross sections of thin or
multilayer materials on a cleavable monocrystalline substrate.
The tripod polishing technique is used to prepare hard or brittle materials and
also to obtain thin regions over large surface areas.
The ultramicrotomy technique is used to prepare any material, from soft to rel-
atively hard, with very small dimensions. It is the main technique for biological
materials and polymers and is also used for some minerals.
The cryo-ultramicrotomy technique is used to prepare any material that is very
soft and/or has a liquid phase, over very small surface areas. This is the main
technique for biological materials and polymers.
Replica techniques are used to prepare direct or indirect surface imprints of large-
dimensional materials or isolated particles.
The freeze-fracture technique enables us to prepare, after fracturing the material,
a topographical imprint of the internal surface of a biological material.
The fine particle dispersion technique is used to prepare a suspension of any
material (bulk ground material, fine particles, or isolated material) of a thickness
enabling TEM observation.
The frozen hydrated film technique is used to prepare a thin film of ice including
isolated particles or macromolecules.
The decoration-shadowing contrast technique is used to enhance contrast using
metallic particles.
The negative-staining contrast technique is used to enhance the contrast of the
support of the organic fine particles via deposition of heavy-metal salts.
The positive-staining contrast technique is used to enhance the contrast of the
thin slice of any organic fine particle via deposition of heavy-metal salts.
The immunolabeling technique is used to localize the functional sites of specific
proteins.
4 Criteria Used to Select a Preparation Technique
The choice of a preparation technique for a thin slice depends on several criteria:
(i) Material type and properties
(ii) TEM analysis type
(iii) Specific preparation-induced artifacts
(iv) Thin slice orientation
All of the criteria involved in technique selection are shown in Fig. 7.1.