Figure 2
From: Three-dimensional chemical mapping using non-destructive SEM and photogrammetry
SEM/BSE photogrammetry. (a) In SEM, multi-view photogrammetry (MVP) can be applied too by acquiring SEM images from different viewpoints. The geometry of acquisition of the images consists in tilting and rotating in-plane the sample stage. (b) The 2D SEM images are representative of a series of 36 images of the cutting tool acquired with an acceleration voltage of 30 kV and using the signal of backscattered electron (BSE) measured with a through-the-lens detector (TLD). (c) The graph shows the dependence of the backscattering coefficient with the atomic number, for an energy of the incoming electron. When E0 is increased from 5 to 30 keV the value of η of the lightest element (Al) falls approximately from 0.18 to 0.14 respectively, while for WC-Co the η-value remains almost constant (from 0.43 to 0.44). Therefore, compositional contrast in BSE is enhanced when a higher E0 is used. (d) Visualization of the 3D SEM model reconstructed using MVP with a collection of BSE images as described in the main text. The darker areas (dark pixel intensities) of the texture can be interpreted qualitatively with an aluminum-rich phase. The 3D model can be explored interactively from within the section S1 of the Supplementary Material.
