Selection of Preparation Techniques Based on Material Problems and TEM Analyses - Sample Preparation Topic for Transmission Electron Microscopy - page 180

As in the previous case, for materials containing a mix of soft and hard phases, it
is necessary to reach the sample's critical thickness and end up performing an ionic
or chemical thinning. FIB thinning again produces very good results.
The preparation method for obtaining thin slices must be adapted based on
the material's hardness, i.e., based on its mechanical behavior or the mechanical
behavior of the various phases.

7.4.5 Biological Materials

With the exception of hard materials such as bone, tooth, wood, and chitin, most
biological materials are very soft, since they are in liquid phase. They are hard-
ened by using the infiltration-embedding technique, so they can be prepared using
ultramicrotomy and the freezing technique for cryo-ultramicrotomy.
Table 7.1 lists the different types of materials, as well as the possible preparation
techniques, depending on their nature. Note that metals and alloys, considered to
be soft in comparison with ceramics, are often investigated for their mechanical

Table 7.1 Examples of materials of different hardnesses and indication of the possible preparation
techniques

Soft-ductile materials Intermediate materials Hard-resistant materials

Biological materials (living
cells, living organic matter)
Polymers (epoxy, phenolic,
acrylic, resins, etc.)
Liquid crystals (pure carbon
with nematic stacking)
Some reinforced polymer
composites
Organic, natural, and artificial
matter (mesophase carbon,
carbon or petroleum tars,
kerogenes)
Metals, “bulk alloys”
Thin layers
Metallic multilayer materials
on metallic or semiconductor
substrates

Semiconductors
Metal/ceramic composites:
mesophase type carbon
Composites: carbon
fiber/polymer matrix
Multiphase
metal/oxide/semiconductor
materials in thin layers
(electronic components)
Concrete: oxide-polymer
mixtures
Thin metallic layers on oxide
substrate

Simple oxides (alumina)
Ceramic materials (carbides,
complex oxides, mixtures of
carbides and oxides)
Composites (carbon/carbon
composites, ceramic/ceramic
deposits)
Thin oxide layers on an oxide
substrate
Doped alloys

Mechanical preparation
using microtomy and
ultramicrotomy, chemical,
electrochemical thinning,
FIB

Tripod polishing, or tripod
+ chemical, or tripod + ion
milling, electrochemical
thinning, FIB

Tripod polishing, tripod +
ion milling, tripod +
chemical etching, FIB