Fig. 3: A 3D reconstruction of a FIB-extracted portion of Particle 33.

a(i)–d(i) Secondary electron images of the exposed surface during a slice-and-view operation in the FIB, viewing the sample edge on. The reconstruction was made from slices cut approximately 100 nm deeper than the last. These images are in the xz plane of the 3D reconstruction. Each panel shows the sandwich structure of the particle with protective platinum (brightest) on the top and bottom. Organic is dark, and inclusions have a moderate brightness and appear as an inclusion layer. α and β denote two side-by-side grains with differing secondary electron contrasts, and therefore differing compositions within the inclusion layer. γ denotes a pocket of organics within the inclusion layer. δ denotes a large euhedral inclusion, about 1.75 μm long. a(ii)–d(ii), The same slices as a(i)–d(i) viewed in the 3D reconstruction. Superimposed lines trace the approximate position of the inclusion layer, which is frequently offset from the midline. e, Orthographic projection of the reconstruction near the xz plane. f, Top-down view of the xy plane of the reconstruction with α–δ labelled as before. Random clumping of the inclusions is apparent. The dashed lines labelled a–d in f show the locations of the slices in a(ii)–d(ii). Thin green lines in e and f delineate the outline of the inclusion phases. See also Supplementary Videos 1 and 2 for raw data.