  Future hard (10 -100 keV) X-ray telescopes (SIMBOL-X, Con-X, HEXIT-SAT, XEUS)
will implement focusing optics with multilayer coatings: in view of the
production of these optics we are exploring several deposition techniques for
the reflective coatings. In order to evaluate the achievable optical
performance X-Ray Reflectivity (XRR) measurements are performed, which are
powerful tools for the in-depth characterization of multilayer properties
(roughness, thickness and density distribution). An exact extraction of the
stack parameters is however difficult because the XRR scans depend on them in a
complex way. The PPM code, developed at ERSF in the past years, is able to
derive the layer-by-layer properties of multilayer structures from
semi-automatic XRR scan fittings by means of a global minimization procedure in
the parameters space. In this work we will present the PPM modeling of some
multilayer stacks (Pt/C and Ni/C) deposited by simple e-beam evaporation.
Moreover, in order to verify the predictions of PPM, the obtained results are
compared with TEM profiles taken on the same set of samples. As we will show,
PPM results are in good agreement with the TEM findings. In addition, we show
that the accurate fitting returns a physically correct evaluation of the
variation of layers thickness through the stack, whereas the thickness trend
derived from TEM profiles can be altered by the superposition of roughness
profiles in the sample image.
