The electron microscopy analyses were performed using a JEOL 2100 FEG S/TEM microscope operating at 200 kV and equipped with a probe spherical aberration corrector. For the acquisition of HAADF images in the STEM mode, a spot size of 0.13 nm, a current density of 140 pA, a camera focal length of 8 cm, which corresponds to inner and outer diameters of the annular detector of 73 and 194 mrad, have been used. The elemental maps were also recorded in the STEM mode by EDXS using a silicon drift detector (SDD) with a sensor size of 60 mm 2 .