Nanodots forming dense assembly on a substrate are difficult to characterize
in terms of size, density, morphology and cristallinity. The present study
shows how valuable information can be obtained by a combination of electron
microscopy techniques. A silicon nanodots deposit has been studied by
Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy
(TEM) to estimate essentially the dot size and density, quantities
emphasized because of their high interest for application. High resolution
SEM indicates a density of 1.6 × 1012 dots/cm2 for a 5 nm to 10 nm
dot size. TEM imaging using a phase retrieval treatment of a focus series
gives a higher dot density (2 × 1012 dots/cm2) for a 5 nm dot size.
High Resolution Transmission Electron Microscopy (HRTEM) indicates that the
dots are crystalline which is confirmed by electron diffraction. According
to HRTEM and electron diffraction, the dot size is about 3 nm which is
significantly smaller than the SEM and TEM results. These differences are
not contradictory but attributed to the fact that each technique is probing
a different phenomenon. A core-shell structure for the dot is proposed which
reconcile all the results. All along the study, Fourier transforms have been
widely used under many aspects.