A first evaluation of the chemical composition was determined by
means of Energy Dispersive Spectroscopy, coupled with SEM (EDS —
EDAX PV 9900). The chemical composition of the outermost surface
layer, the identification of the element electronic state and the presence
of chemical groups of interest (e.g. hydroxyl groups) were investigated
by means of X-Ray Photoelectron Spectroscopy (XPS, PHI 5000 VERSA
PROBE, PHYSICAL ELECTRONICS).