Selection of Preparation Techniques Based on Material Problems and TEM Analyses - Sample Preparation Topic for Transmission Electron Microscopy - page 182

the layers or with the substrate. Therefore, in the case of a ceramic, a grain boundary
or interface analysis will require several observations of these defects with differ-
ent orientations. Therefore, several preparations with different orientations will be
necessary. The same is required for the analysis of dislocations.
The electrochemical, chemical, and ionic preparation techniques are used to
investigate structural defects. Mechanical preparation techniques generate strain
hardening and are not favorable to the investigation of dislocations.
Chemical Analysis : Phase Identification and Concentration Profiles : Chemical
composition analysis of a bulk material, thin layer material, or fine particle mate-
rial requires the use of a preparation technique that does not result in chemical
changes induced by the technique. The best preparation techniques are mechani-
cal techniques such as tripod polishing for bulk and multilayer materials, wedge
cleavage for cleavable multilayer materials, and ultramicrotomy for fine particles
after embedding. The ionic preparation techniques can also be used if there is no
modification in the chemical composition of the material under the ion effect.
Chemical analysis of interfaces can be performed on samples prepared using
the tripod and ultramicrotomy techniques and ionic techniques. However, during
ion bombardment, the ionic differential sputtering rates will favor certain grain ori-
entations and result in significant thickness variations along the grain boundary.
The quantitative chemical analysis of these boundaries will then be more difficult.
Preparations using FIB or tripod polishing help to solve this problem. The FIB tech-
nique is used to obtain a thin slice with a constant thickness, but with the drawback
of surface amorphization. The advantage of the tripod polishing method is that it
does not produce surface amorphization caused by ionic methods, which are very
unfavorable in HRTEM analysis.
Chemical Bond Analysis : The electrochemical, chemical, mechanical, and ionic
preparation techniques are used to prepare samples for EELS analyses. However,
the specimen must have a thickness less than 50 nm.
Physical Property Analysis : Investigations of mechanical and electrical proper-
ties and in situ investigations under high temperature require a sample that is not too
thin along the edges and that is mechanically resistant in order to undergo stresses
during observation without breaking. The main preparation technique is ion milling.
To investigate the optical or electronic properties using EELS analyses, mechanical
and ionic techniques are possible.
Functional Analysis : The immunolabeling technique, which is specific to biol-
ogy, helps to localize functional sites or specific molecules.
8.1 Preparation Techniques
The table below provides cross-references for the numbers used in Tables 7.2, 7.3,
and 7.4 and the preparation number provided in the “Techniques”.