The samples
were ground with sandpaper with a grit size of 120, 220, 400,
600 and 1000 (Hermes), subsequently, and then polished first with
a 3 lmdiamond suspension (Struers), and finally with a 0.1 lmsilica
suspension (Buehler; Saphir 320/330 instrument, ATM). Secondary
electron (SE) scanning electron microscopy (SEM) and
energy-dispersive X-ray spectroscopy (EDX) were carried out with
an ESEM Quanta 400 FEG instrument after sputtering with gold
and palladium (80:20). SEM-BSE was carried out with a JEOL
JSM-6500F instrument.