2. Characterization techniques for multi-nanolayer structures

A complete characterization of these multi-nanolayer structures (number of layers, continuity, regularity, homogeneity, thickness) is essential for quality control and to establish the relationship between structure and properties. Insofar as a "direct" characterization of the layers is sought, microscopic observation techniques seem to be the most relevant and are those discussed in this article. Nevertheless, a number of difficulties arise from the multi-nanolayer nature of films:

• when the layers are very thin and numerous, it is difficult to find a relevant, direct and reliable observation and analysis technique that reconciles global and local views, which immediately raises the question of the size of the area to be analyzed in order to be representative of the entire sample;

• microscopic observation requires...