Biomedical Engineering Reference
In-Depth Information
Chapter 7
Selection of Preparation Techniques Based
on Material Problems and TEM Analyses
1 Introduction
The best choice of preparation technique is the one that produces a suitable thin
slice of the material to be investigated. The technique must also be suitable for the
different TEM analyses and should contain a minimum of artifacts.
Given the very small size of the sample to be analyzed in the TEM, the initial
material will often need to be reduced using preliminary preparation techniques:
sawing, cutting, dimpling, cleavage, etc. In order to conduct certain TEM analyses
and to make observations in a precise direction, it is important to choose sample
slices selected with specific orientations: longitudinal cuts, cross-sectional cuts, or
cuts with a particular orientation. Sometimes it is necessary to combine several
thinning techniques to optimize the TEM observation conditions.
First, one must have a good knowledge of the available techniques in order to
select the one that will be most compatible with the material problem presented.
2 Classification of Preparation Techniques
Among the many preparation techniques for thin slices, a distinction is made
between direct and indirect preparation methods.
Direct methods are used to analyze thinned materials or fine particles on a
TEM support grid in order to perform structural, chemical, or spectroscopic anal-
ysis, i.e., to determine morphology, structure at different scales, crystallographic
organization, chemical composition, and the nature of the chemical bonds. Most
techniques in materials science are direct: twin-jet electrolytic thinning, full-
bath electrolytic thinning, twin-jet chemical thinning, full-bath chemical thinning,
focused ion beam (FIB) thinning, crushing, wedge cleavage, tripod polishing, ultra-
microtomy and cryo-ultramicrotomy, and frozen hydrated film. Direct contrast
enhancement techniques enable observation of the thinned materials or fine parti-
cles, but with the addition of chemical molecules or metallic particles in order to
facilitate morphological investigation. These are positive- or negative-staining and
decoration-shadowing techniques. They are not very suitable for chemical analyses.
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