SEM stereoscopic technique is used to determine three-dimensional-
surface of nanostructures [16]. A less than 5 nm thick layer
of platinum was coated on the sample using a sputtering evaporation
system to increase the conductivity and consequently the image
sharpness. Three high resolution SEM images were obtained at
eucentric level of 10 mm from different perspectives using an FEI
Strata DB 235 dual beam focused ion beam system with beam energy
of 10 keV. Commercial software package, MeX 5.1 (Alicona
Imaging), was used for 3D-reconstruction and analyses of the surface
[17]. Fig. 4a and c are the left and right SEM images taken with
an angle of 10 and +10 degrees, respectively, in respect to the
middle SEM image which is Fig. 4b. These SEM images were used
to make the digital elevation model (DEM) which is shown in
Fig. 4d.