A quantitative high resolution transmission electron microscopy
(HRTEM) study of amorphous materials has been undertaken in the
study-case of amorphous germanium. The analysis consists in a
modeling of amorphous germanium, suitable to run multislice
calculations, and to simulate HRTEM images, the computed diffractograms
of which are numerically compared to experimental ones obtained
from a through-focus series taken on a dedicated high resolution
microscope equipped with a field-emission gun. The final aim
of this work is to quantify the structural information that can
be retrieved from HRTEM images of amorphous materials. As a preliminary
step, the coefficient of spherical aberration (Cs) of the microscope,
as well as the amount of defocus (δf) of each micrograph have
to be known. The aim of the first part of this paper is to determine,
as precisely as possible, these parameters. A new method is proposed,
as an alternative to usual methods based on least-squares fittings
of the zeros of the experimental diffractograms: the theoretical
diffractograms are computed, and numerically compared, through
the minimization of a profile agreement factor depending upon
the Cs and δf values, and the thickness of the amorphous film,
to the experimental ones. The critical steps of this approach
are the modeling of the scattering of the amorphous material,
and, more drastically, the estimation of the experimental thickness,
which influences significantly the values of Cs and δfs.