The morphology of the powders was observed using an EVO
50 SEM (Carl Zeiss AG, Germany). Each sample was mounted separately
onto SEM stubs using double-sided copper tape and then
coated with gold using a sputter coater (Electron Microscopy Sciences,
Hatfield, PA) for 2 min under vacuum at 0.2 mbar. The SEM
was operated at high vacuum with accelerating voltage 15 kV and
specimen working distance 8 mm.