The difference between the low voltage (LV) image obtained at 220 V and the higher voltage (HV) image obtained at 2000 V is evident by comparing Fig. 3(A) and (B).While in the latter the rods
show a good signal to noise ratio and are clearly separated from each other as well as the background, this is not the case for the low voltage image. The thicker rods present in the composite image clearly show a yellow core surrounded by a green shell. This appearance is a consequence of the CTAB layer being visible only in the low voltage (green) channel but not in the higher voltage channel (red). The fact that some of the rods appear entirely red is due to the thresholding used when generating the composite image. The rods in question are in fact visible in the low voltage image but with a low signal to noise and consequently have been missed when creating the composite image. The fact that the rods are visualized to be thinner in the high energy image is also clear from the cross-sections presented in Fig. 3(D). For all