HRTEM images of all the samples show aggregates of particles
with random orientations, for example, the micrograph of Fig. 4(a),
corresponding to C25 exhibits crystals of average diameter around
12.5 nm. In this image, two particles oriented along different zone
axis have been marked. Their digital diffraction patterns (DDPs)
correspond to main zone axes of Fe3O4 structure. Fig. 4(b) is an
enlarged HRTEM micrograph of a magnetite crystal oriented along
½ ¯112 zone axis.